Path Sciences 3

Which of the following structures make up the outer most layer of the skin? 

Hypodermis

Dermis

Epidermis

Epidermis

In which of the following layers of skin may you find blood vessels?

You may select more than one answer here.

Epidermis

Hypodermis

Dermis

Hypodermis

Dermis

Langerhans cells are found within the epidermis.  What is the role of this type of cell?

Antigen presenting cell - an arm of the immune system

Pigment- producing cells.

Connective skin cells.

Antigen presenting cell - an arm of the immune system

In which layer of the skin may we find calory reserves.

Epidermis

Hypodermis

Dermis

Hypodermis

Which of the following organisms are associated with skin and soft tissue infections?

Haemophilus influenzae

Salmonella species

Staphylococcus aureus

Staphylococcus aureus

Which of the following organisms are associated with skin and soft tissue infections?

Streptococcus pneumoniae

Shigella species

Dermatophytes

Dermatophytes

Responsible for a number of skin conditions including ring worm and athletes foot.

Which of the following organisms are associated with skin and soft tissue infections?

Chlamydia trachomatis

Treponema pallidum

Clostridium difficile

Treponema pallidum

this organism causes Syphilis and secondary syphilis causes a non specific skin rash.

Do Staphylococci possess the catalase enzyme?

Yes, Staphylococci are catalase positive, this enzyme helps to break down toxic H2O2, into O2 and H2O. 

What is the role of Protein A?

Membrane damaging toxin

Assist in the bacteria gaining entry into the cell?

Bind to fibrinogen and covert to fibrin to form a clot

Bind to the Fc receptors of antibodies rendering them inactive

Bind to the Fc receptors of antibodies rendering them inactive

Protein A helps Staph aureus to evade the immune system

What is the role of hyaluronidase?

Breaks down the hyaluronic acid in connective tissue to aid the spread of the infection.

Converts fibrinogen to fibrin. 

Dissolves fibrin clots.

Converts H2O2 into H2O and O2.

Breaks down the hyaluronic acid in connective tissue to aid the spread of the infection.

Streptococci pyogenes capsule is composed of hyaluronic acid.  Why is this beneficial?

Hyaluronic acid will lyse a range of cells including erythrocytes, leukocytes and platelets.

Hyaluronic acid will attach to immunoglobulins and cause them to malfunction.

Degrades C3b and therefore evades the innate immune response.

Hyaluronic acid is found in most connective tissue, so is therefore no immunogenic.

Hyaluronic acid is found in most connective tissue, so is therefore no immunogenic.

What is the role of the M Proteins?

Lyse cells including erythrocytes, leukocytes and platelets.

Break down toxic substances that could be harmful to the bacteria.

Degrade C3b, so evade the innate immune response.

Aid in the attachment of bacteria to host cells.

Degrade C3b, so evade the innate immune response.

Which of the following toxins are produced by Streptococcus pyogenes?

TSST-1

Spe A, Spe B and Spe C

PVL Toxin

Scalded Skin Syndrome Toxin

Spe A, Spe B and Spe C

Toxin production is associated with deep infections such as necrotising fasciitis.

What is the role of Streptolysin S?

Acts as a receptor to aid in bacterial adhesion.

Breaks down connective tissue to aid the spread of the infection.

Lyses cells including erythrocytes, leukocytes and platelets.

Breaks down DNA within purulent material.

Lyses cells including erythrocytes, leukocytes and platelets.

Streptolysin S is a cell bound haemolysin

Which of the following tissue type do fungal elements invade?

Muscle tissue.

Nervous tissue.

Connective tissue.

Keratinised tissue.

Keratinised tissue.

fungi tend to invade, skin, hair and nails.

Which of the following organisms are the cause of fungal infections?

Burkholderia cepacia

Neisseria gonorrhoea

Trichophyton rubrum

Stenotrophomonas maltophilia

Trichophyton rubrum

Trichophyton rubrum can cause infections such as athletes foot.

In order to isolate clinically relevant fungi, which antifungal element is added to the media?

Fluconazole

Cycloheximide

Amphotericin

Terbinafine

Cycloheximide

only dermatophytes will grow in the presence of cycloheximide

Who long do fungal infections typically take to grow?

40 days

2 days

21 days

10 days

21 days

Which layer of the skin is the outermost layer?

A. Dermis
B. Hypodermis
C. Subcutaneous layer
D. Epidermis
E. Fascia

D. Epidermis

Which of the following is found within the dermis?

A. Only dead skin cells
B. Blood vessels and nerve fibres
C. Calorie reserves only
D. Langerhans cells only
E. Muscle fibres

B. Blood vessels and nerve fibres

Why can an infection involving the dermis increase the risk of septicaemia?

A. The dermis contains large amounts of keratin
B. The dermis prevents bacteria from entering the body
C. The dermis contains blood vessels that bacteria can gain access to
D. The dermis contains only dead cells
E. The dermis is the deepest layer of the skin

C. The dermis contains blood vessels that bacteria can gain access to

Which of the following is given as an example of an infection that can migrate into the subcutaneous layer and cause a serious problem?

A. Superficial burn
B. Graze
C. Necrotising fasciitis
D. Minor abrasion
E. Contact dermatitis

C. Necrotising fasciitis

What is one important reason why diabetic patients may develop severe infections in their lower extremities?

A. They have increased numbers of healthy nerve endings
B. They have increased blood flow to their feet
C. Their skin contains fewer lipid cells
D. Poor blood flow and neuropathy can predispose them to infection and delay detection
E. Their epidermis contains no immune cells

D. Poor blood flow and neuropathy can predispose them to infection and delay detection

How does the natural shedding of skin cells help protect against infection?

A. It increases the temperature of the skin
B. It removes bacteria attached to the cells as they are shed
C. It increases the number of blood vessels in the epidermis
D. It prevents the production of antimicrobial peptides
E. It activates the complement system continuously

B. It removes bacteria attached to the cells as they are shed

Which of the following is a protective mechanism provided by normal flora on the skin?

A. Normal flora increases skin temperature
B. Normal flora destroys all immune cells
C. Normal flora occupies receptor sites that pathogens could otherwise use
D. Normal flora prevents all wounds from occurring
E. Normal flora increases the salinity of the skin

C. Normal flora occupies receptor sites that pathogens could otherwise use

Which type of organism is more commonly associated with superficial skin infections because it can survive in the presence of oxygen?

A. Obligate anaerobe
B. Aerobic organism
C. Strict anaerobe only
D. Viral organism
E. Fungal organism

B. Aerobic organism

Why can facultatively anaerobic bacteria be particularly useful in deeper tissue infections?

A. They can only survive in environments with high oxygen levels
B. They destroy all normal flora immediately
C. They can survive with or without oxygen and may consume oxygen, allowing obligate anaerobes to survive
D. They prevent the activation of complement
E. They can only survive on the surface of the skin

C. They can survive with or without oxygen and may consume oxygen, allowing obligate anaerobes to survive

Which organism is specifically associated with colonising burn wounds and potentially preventing them from healing?

A. Clostridium tetani
B. Langerhans cells
C. Pseudomonas aeruginosa
D. Complement
E. Normal skin flora

C. Pseudomonas aeruginosa

Which group of patients is identified as being at increased risk of skin and soft tissue infections?

A. Patients with diabetes, limited mobility, or immunocompromise
B. Patients with normal circulation and intact skin
C. Patients with increased mobility only
D. Patients without any underlying conditions
E. Patients with increased skin temperature only

A. Patients with diabetes, limited mobility, or immunocompromise

Why are infections that reach the dermis or subcutaneous layer potentially more serious?

A. These layers contain no immune cells
B. They contain blood vessels and lymphatic vessels, providing pathways for infection to spread
C. These layers are made entirely of dead cells
D. They prevent bacteria from entering deeper tissues
E. They contain no nerve endings

B. They contain blood vessels and lymphatic vessels, providing pathways for infection to spread

Which skin infection is particularly contagious and commonly affects children, often around the face and lips?

A. Cellulitis
B. Impetigo
C. Folliculitis
D. Necrotising fasciitis
E. Ringworm

B. Impetigo

Why is it recommended that a person with impetigo does not share towels with other family members?

A. Towels increase the temperature of the skin
B. Towels prevent the infection from healing
C. Towels can act as fomites and facilitate transmission of the infection
D. Towels cause the bacteria to become anaerobic
E. Towels increase lymphatic drainage

C. Towels can act as fomites and facilitate transmission of the infection

Which statement best describes cellulitis?

A. It is always limited to the epidermis
B. It is a fungal infection affecting the hair follicles
C. It can involve the epidermis, dermis and potentially the subcutaneous layer
D. It only occurs following an insect bite
E. It is always caused by an obligate anaerobe

C. It can involve the epidermis, dermis and potentially the subcutaneous layer

Why may the margins of cellulitis be marked and the time recorded by a healthcare professional?

A. To determine the patient's blood group
B. To monitor how far the infection spreads over time
C. To identify whether the infection is fungal
D. To determine whether the patient has impetigo
E. To measure the patient's lymphocyte count

B. To monitor how far the infection spreads over time

Which two organisms are described as major causes of skin and soft tissue infections?

A. E. coli and Klebsiella pneumoniae
B. Pseudomonas aeruginosa and Proteus mirabilis
C. Staphylococcus aureus and Group A Streptococcus
D. Treponema pallidum and Neisseria meningitidis
E. Clostridium tetani and E. coli

C. Staphylococcus aureus and Group A Streptococcus

Which of the following is an example of a condition that can produce a skin manifestation even though the infection is not primarily a skin infection?

A. Folliculitis
B. Cellulitis
C. Impetigo
D. Secondary syphilis
E. Abscess

D. Secondary syphilis

Why is Staphylococcus aureus considered a successful skin pathogen?

A. It can only survive in completely dry environments
B. It can survive the salty environment of the skin and has multiple mechanisms for attachment
C. It cannot survive on normal skin
D. It only causes infections when the skin is completely intact
E. It is unable to produce virulence factors

B. It can survive the salty environment of the skin and has multiple mechanisms for attachment

Which of the following is an example of an infection or condition associated with Staphylococcus aureus?

A. Folliculitis
B. Meningitis only
C. Malaria
D. Tetanus only
E. Viral hepatitis

A. Folliculitis

What does it mean when Staphylococcus aureus is described as halotolerant?

A. It can survive only in freshwater
B. It requires extremely low salt concentrations
C. It can tolerate relatively high concentrations of sodium chloride
D. It cannot survive on human skin
E. It can only grow in the absence of salt

C. It can tolerate relatively high concentrations of sodium chloride

Approximately how many Staphylococcus aureus cells may be required to cause a lesion when there is no noticeable break in the skin?

A. 1–10 cells
B. 10–100 cells
C. 100–1,000 cells
D. 10,000–100,000 cells
E. Around 1 million cells

E. Around 1 million cells

Which virulence factor produced by Staphylococcus aureus can break down connective tissue and help the organism spread through tissues?

A. Catalase
B. Coagulase
C. Hyaluronidase
D. Lipopolysaccharide
E. Fibronectin

C. Hyaluronidase

Which combination of laboratory results is expected for Staphylococcus aureus?

A. Gram-negative cocci, catalase negative, coagulase negative
B. Gram-positive cocci, catalase positive, coagulase positive
C. Gram-positive rods, catalase negative, coagulase positive
D. Gram-negative rods, catalase positive, coagulase negative
E. Gram-positive cocci, catalase negative, coagulase negative

B. Gram-positive cocci, catalase positive, coagulase positive

Why can coagulase-negative staphylococci cause significant infections in immunocompromised patients with catheters or peripheral lines?

A. They are never found as part of normal flora
B. They can form biofilms on plastic surfaces and the patient's immune system may be unable to effectively control the infection
C. They are always more pathogenic than S. aureus
D. They cannot survive on catheter surfaces
E. They are Gram-negative organisms that produce endotoxin

B. They can form biofilms on plastic surfaces and the patient's immune system may be unable to effectively control the infection

A 68-year-old patient is admitted to hospital following surgery. Two days after the procedure, the patient develops increasing redness, swelling and tenderness around the surgical wound. The wound is producing pus and appears to be healing poorly. A wound swab is collected from the infected area and sent to the microbiology laboratory.

After incubation, the laboratory observes Gram-positive cocci. The organism is catalase positive and coagulase positive.

9. Based on the clinical presentation and laboratory results, which organism is most likely responsible for the patient's infection?

A. Escherichia coli
B. Streptococcus pyogenes
C. Staphylococcus aureus
D. Pseudomonas aeruginosa
E. Coagulase-negative staphylococci

C. Staphylococcus aureus

A 68-year-old patient is admitted to hospital following surgery. Two days after the procedure, the patient develops increasing redness, swelling and tenderness around the surgical wound. The wound is producing pus and appears to be healing poorly. A wound swab is collected from the infected area and sent to the microbiology laboratory.

After incubation, the laboratory observes Gram-positive cocci. The organism is catalase positive and coagulase positive.

The laboratory performs antimicrobial susceptibility testing and identifies the organism as MRSA. What does MRSA indicate?

A. The organism is resistant to many beta-lactam antibiotics
B. The organism is unable to cause skin infections
C. The organism is always resistant to every available antibiotic
D. The organism is a Gram-negative bacterium
E. The organism cannot colonise surgical wounds

A. The organism is resistant to many beta-lactam antibiotics

A 68-year-old patient is admitted to hospital following surgery. Two days after the procedure, the patient develops increasing redness, swelling and tenderness around the surgical wound. The wound is producing pus and appears to be healing poorly. A wound swab is collected from the infected area and sent to the microbiology laboratory.

After incubation, the laboratory observes Gram-positive cocci. The organism is catalase positive and coagulase positive.

The patient also has a peripheral intravenous line that was inserted without adequate skin cleansing. Why could this provide an additional opportunity for S. aureus infection?

A. The line increases the patient's normal skin flora
B. Insertion of the line can breach the protective skin barrier, allowing normal skin flora such as S. aureus to enter
C. S. aureus can only cause infection when oxygen is absent
D. The line prevents bacteria from attaching to tissues
E. S. aureus cannot survive around medical devices

B. Insertion of the line can breach the protective skin barrier, allowing normal skin flora such as S. aureus to enter

A 45-year-old patient presents with a painful, swollen area of skin on their lower leg. The area is red and warm, and the redness appears to be spreading. The healthcare professional marks the edge of the redness and records the time. The patient is advised to attend A&E so that the progression of the infection can be assessed.

Which condition is most likely being described?

A. Impetigo
B. Folliculitis
C. Cellulitis
D. Ringworm
E. Eczema

C. Cellulitis

A 32-year-old patient develops several painful, pus-filled lesions around hair follicles on their thighs after using a communal hot tub. A wound sample is collected for microbiological investigation.

Which organism is most strongly associated with this presentation?

A. Treponema pallidum
B. Pseudomonas aeruginosa
C. Neisseria meningitidis
D. Clostridium tetani
E. Escherichia coli

B. Pseudomonas aeruginosa

A 59-year-old patient with diabetes has a chronic ulcer on their foot. A wound swab grows several different organisms, including Staphylococcus aureus, E. coli and Klebsiella. The clinician notes that the wound contains a mixture of pathogenic and colonising organisms.

Why is it important to interpret the microbiology results alongside the patient's clinical presentation?

A. All organisms isolated from wounds are automatically responsible for the infection
B. S. aureus can never colonise a wound
C. Some organisms may simply be colonising the wound rather than causing the infection
D. Wound infections are always caused by a single organism
E. Gram-negative organisms cannot survive in wounds

C. Some organisms may simply be colonising the wound rather than causing the infection

A 24-year-old patient develops a painful abscess on their thigh. The abscess is drained and a sample is sent to the microbiology laboratory. Several different bacterial species are identified. The microbiologist explains that some of the organisms can survive in the presence of oxygen, while others require an environment with little or no oxygen.

Why are abscesses commonly associated with a mixture of facultatively anaerobic and obligately anaerobic organisms?

A. Facultative anaerobes produce oxygen, preventing anaerobes from growing
B. Facultative anaerobes can use oxygen, helping create conditions suitable for obligate anaerobes
C. Obligate anaerobes require high levels of oxygen
D. Both types of organisms can only grow on the surface of the skin
E. Facultative anaerobes cannot survive in deeper tissues

B. Facultative anaerobes can use oxygen, helping create conditions suitable for obligate anaerobes

Which organism is also known as Group A Streptococcus?

A. Staphylococcus aureus
B. Streptococcus pneumoniae
C. Streptococcus pyogenes
D. Streptococcus agalactiae
E. Enterococcus faecalis

C. Streptococcus pyogenes

What is the main function of hyaluronidase produced by Streptococcus pyogenes?

A. It destroys red blood cells
B. It breaks down hyaluronic acid, helping the bacteria spread through tissue
C. It prevents bacterial attachment to skin cells
D. It destroys fibronectin receptors
E. It inhibits the inflammatory response

B. It breaks down hyaluronic acid, helping the bacteria spread through tissue

Which skin infection is primarily associated with the superficial epidermis?

A. Cellulitis
B. Necrotising fasciitis
C. Erysipelas
D. Impetigo
E. Myositis

D. Impetigo

Which toxins produced by Streptococcus pyogenes are associated with necrotising fasciitis?

A. TSST-1, enterotoxin A and enterotoxin B
B. Spe A, Spe B and Spe C
C. Hyaluronidase, catalase and coagulase
D. Spe A, TSST-1 and coagulase
E. Spe B, catalase and leukocidin

B. Spe A, Spe B and Spe C

What result would be expected when Streptococcus pyogenes is grown on a blood agar plate?

A. No haemolysis
B. Alpha haemolysis with green colonies
C. Beta haemolysis with zones of clearing around colonies
D. Black colonies with a metallic sheen
E. Gamma haemolysis with yellow colonies

C. Beta haemolysis with zones of clearing around colonies

Which test helps differentiate Streptococci from Staphylococci?

A. Oxidase test
B. Indole test
C. Urease test
D. Catalase test
E. Coagulase test

D. Catalase test

What is the purpose of Lancefield grouping when investigating beta-haemolytic Streptococci?

A. To determine antibiotic resistance
B. To identify whether the organism is Gram-positive or Gram-negative
C. To identify antigens expressed on the surface of the organism and assign a group
D. To determine whether the organism is catalase positive
E. To measure the depth of the skin infection

C. To identify antigens expressed on the surface of the organism and assign a group

A patient presents with an infected skin lesion. A swab is taken directly from the lesion and cultured on blood agar. After 24–48 hours, the colonies show clear zones of haemolysis around them. Gram staining demonstrates Gram-positive cocci. The organism is catalase negative.

Which additional test would be most appropriate to help identify the organism as Group A Streptococcus?

A. Coagulase testing
B. Lancefield grouping
C. Oxidase testing
D. Indole testing
E. Urease testing

B. Lancefield grouping

A laboratory scientist suspects Pseudomonas aeruginosa is present in a wound sample. The organism grows on MacConkey agar but does not ferment lactose. What would be expected?

A. Pink colonies
B. Green colonies
C. Black colonies
D. Orange-coloured colonies with no lactose fermentation
E. No growth on the agar

D. Orange-coloured colonies with no lactose fermentation

Which enzyme test is expected to be positive for Pseudomonas aeruginosa and can help differentiate it from other Gram-negative organisms?

A. Catalase
B. Coagulase
C. Oxidase
D. Urease
E. Indole

C. Oxidase

A patient with a large burn has a wound colonised by Pseudomonas aeruginosa. The organism produces Las A and Las B. What is the main effect of these enzymes?

A. They inhibit bacterial protein synthesis
B. They degrade elastin and contribute to tissue damage
C. They ferment lactose
D. They destroy red blood cells
E. They inhibit cytochrome oxidase

B. They degrade elastin and contribute to tissue damage

Which Pseudomonas aeruginosa virulence factor is associated with tissue damage by inhibiting protein synthesis within host cells?

A. Exoenzyme S
B. Lipid A
C. Las A
D. Las B
E. Cytochrome oxidase

A. Exoenzyme S

An immunocompromised patient has a skin lesion, and the laboratory needs to investigate whether Candida is present. Which culture medium would be appropriate?

A. MacConkey agar
B. Blood agar
C. CLED agar
D. Sabouraud agar
E. Staph/Strep agar

D. Sabouraud agar

A wound swab grows Pseudomonas aeruginosa. Which description best explains its effect on a burn wound?

A. It always causes an invasive infection requiring antibiotics
B. It prevents other bacteria from colonising the wound
C. It commonly colonises the wound and can prevent it from healing
D. It causes only superficial infection of the epidermis
E. It exclusively infects healthy, intact skin

C. It commonly colonises the wound and can prevent it from healing

A deep wound swab is received in the laboratory, and anaerobic organisms are suspected. Which approach would be most appropriate?

A. Culture only on MacConkey agar in aerobic conditions
B. Culture on anaerobic agar and incubate under anaerobic conditions
C. Culture only on Sabouraud agar
D. Culture only on CLED agar in aerobic conditions
E. Culture on blood agar but leave the plate unincubated

B. Culture on anaerobic agar and incubate under anaerobic conditions

A patient with a large burn has a wound swab that grows Pseudomonas aeruginosa. The patient is otherwise clinically stable, and there are no clear signs that the organism is causing an invasive infection. However, the wound has failed to heal normally. The clinical team considers regular wound cleaning rather than immediately prescribing antibiotics.

Why might antibiotics not be required in this situation?

A. Pseudomonas aeruginosa cannot survive on wounds
B. Pseudomonas aeruginosa is always resistant to antibiotics
C. The organism may be colonising the wound and interfering with healing rather than causing an active infection
D. Antibiotics cannot be used for Gram-negative organisms
E. Pseudomonas aeruginosa only causes fungal infections

C. The organism may be colonising the wound and interfering with healing rather than causing an active infection

A wound swab from a patient with a chronic ulcer is cultured on MacConkey agar. After incubation, the organism produces colonies that remain the original orange colour of the medium rather than becoming pink. Further testing shows that the organism is Gram-negative and oxidase positive.

Which characteristic best explains the appearance on MacConkey agar?

A. The organism ferments lactose rapidly
B. The organism is unable to ferment lactose
C. The organism produces beta-haemolysis
D. The organism is Gram-positive
E. The organism requires anaerobic conditions

B. The organism is unable to ferment lactose

A 42-year-old patient is recovering from extensive burns. Several days after the injury, the wound is not healing as expected. A wound swab is taken and cultured. The laboratory observes colonies with a distinctive sheen and a characteristic smell. The organism is Gram-negative and produces a positive cytochrome oxidase test.

Which organism is most likely responsible?

A. Staphylococcus aureus
B. Streptococcus pyogenes
C. Candida albicans
D. Pseudomonas aeruginosa
E. Enterococcus faecalis

D. Pseudomonas aeruginosa

Which two groups of fungi are highlighted as important causes of skin infections?

A. Candida species and dermatophytes
B. Aspergillus species and Mucor species
C. Cryptococcus species and Candida species
D. Dermatophytes and bacteria
E. Candida species and protozoa

A. Candida species and dermatophytes

Which three genera are classified as dermatophytes?

A. Candida, Microsporum and Trichophyton
B. Epidermophyton, Microsporum and Trichophyton
C. Epidermophyton, Candida and Microsporum
D. Trichophyton, Aspergillus and Candida
E. Microsporum, Cryptococcus and Epidermophyton

B. Epidermophyton, Microsporum and Trichophyton

A laboratory receives a skin sample from a patient with suspected dermatophyte infection. The sample is cultured on Sabouraud agar and on agar containing cycloheximide. What is the purpose of the cycloheximide-containing medium?

A. To encourage bacterial growth
B. To inhibit all fungal growth
C. To inhibit non-dermatophyte fungal growth
D. To identify Gram-positive bacteria
E. To increase the speed of fungal growth

C. To inhibit non-dermatophyte fungal growth

A laboratory technician performs direct microscopy on a skin sample suspected of containing fungal elements. Which stain is described as producing a particularly clear fluorescent appearance of fungal elements?

A. Gram stain
B. Acid fuchsin
C. Calcofluor
D. Methylene blue
E. Crystal violet

C. Calcofluor

A patient has antibodies against a virus, but the laboratory finds a high level of IgG rather than IgM. What does this finding most likely indicate?

A. A current acute infection
B. A previous infection
C. Complete absence of previous exposure
D. A bacterial infection
E. A fungal infection

B. A previous infection

Why can viruses not be cultured using conventional bacterial culture media?

A. Viruses are too large to grow on agar
B. Viruses require host cells to replicate
C. Viruses cannot survive at room temperature
D. Viruses only grow under anaerobic conditions
E. Viruses require lactose for replication

B. Viruses require host cells to replicate

Which gastrointestinal pathogen has a particularly low infective dose, meaning that only a small number of organisms may be required to cause illness?

A. Salmonella
B. Campylobacter
C. Clostridium difficile
D. Escherichia coli O157
E. Giardia

D. Escherichia coli O157

Why is normal gastrointestinal flora protective against pathogenic organisms?

A. It increases the acidity of the blood
B. It occupies receptor sites that pathogens would otherwise use to attach and colonise
C. It prevents all viruses from entering the body
D. It destroys all food-borne organisms immediately
E. It prevents the stomach from producing bile

B. It occupies receptor sites that pathogens would otherwise use to attach and colonise

A patient develops diarrhoea after receiving broad-spectrum antibiotics, particularly a cephalosporin. Which organism is associated with this type of antibiotic-associated diarrhoea?

A. Campylobacter jejuni
B. Salmonella enterica
C. Clostridium difficile
D. Giardia lamblia
E. Shigella sonnei

C. Clostridium difficile

A previously healthy adult develops severe diarrhoea and abdominal pain after eating contaminated food. A stool sample is sent to the laboratory. Testing identifies Escherichia coli O157. The clinician explains that only a small number of organisms were required to cause the infection and that the patient needs monitoring for complications affecting the kidneys.

Which complication is particularly associated with E. coli O157?

A. Haemolytic uraemic syndrome
B. Antibiotic-associated diarrhoea
C. Liver cirrhosis
D. Gastric ulceration
E. Bacterial meningitis

A. Haemolytic uraemic syndrome

A previously healthy 25-year-old attends a barbecue during the summer. They eat chicken that appears cooked on the outside but was undercooked in the centre. Two days later, they develop diarrhoea, abdominal pain and a fever, followed by flu-like symptoms.

Which organism is most strongly associated with this presentation?

A. Clostridium difficile
B. Giardia
C. Campylobacter
D. Candida albicans
E. Staphylococcus aureus

C. Campylobacter

A 25-year-old man develops abdominal cramps and diarrhoea several days after eating chicken at a barbecue. Which characteristic of Campylobacter is most useful for its laboratory identification?

A. Catalase negative
B. Oxidase positive
C. Lactose fermentation
D. Coagulase production
E. Urease production

B. Oxidase positive

A patient develops diarrhoea after eating undercooked chicken. The laboratory suspects Campylobacter. Which atmospheric condition is required to culture this organism?

A. Strictly anaerobic conditions
B. Normal atmospheric oxygen levels
C. Microaerophilic conditions
D. 100% oxygen
E. Carbon dioxide-free conditions

C. Microaerophilic conditions

A stool sample is cultured for suspected Campylobacter. The laboratory observes grey colonies that appear to be spreading or "swarming" on selective agar. Which organism is most likely?

A. Shigella
B. Campylobacter
C. Giardia
D. Escherichia coli O157
E. Clostridioides difficile

B. Campylobacter

A patient with Campylobacter gastroenteritis asks why the organism is able to colonise the gastrointestinal tract. Which host structure can Campylobacter use as a receptor for attachment?

A. Keratin
B. Collagen
C. Fibronectin
D. Elastin
E. Haemoglobin

C. Fibronectin

A patient recovers from a Campylobacter infection but develops muscle weakness several weeks later. Which complication is associated with previous Campylobacter infection?

A. Guillain-Barré syndrome
B. Rheumatic fever
C. Haemolytic uraemic syndrome
D. Toxic shock syndrome
E. Infective endocarditis

A. Guillain-Barré syndrome

A 30-year-old healthy patient develops Campylobacter gastroenteritis. The symptoms are uncomfortable but are expected to resolve without specific treatment. Which statement best describes the usual management?

A. All patients require intravenous antibiotics
B. All patients require long-term antifungal therapy
C. Campylobacter infection is usually self-limiting
D. Surgery is normally required
E. Antiviral treatment is routinely required

C. Campylobacter infection is usually self-limiting

A 22-year-old patient develops flu-like symptoms followed by severe abdominal cramps and diarrhoea after eating undercooked chicken at a barbecue. A stool sample is sent to the laboratory. Gram staining shows curved, Gram-negative organisms, and an oxidase test is positive.

Which organism is the most likely cause?

A. Salmonella enterica
B. Campylobacter
C. Shigella sonnei
D. Escherichia coli O157
E. Clostridioides difficile

B. Campylobacter

A patient develops abdominal pain and diarrhoea after eating contaminated chicken. The laboratory suspects Salmonella. Which mechanism allows Salmonella to inject virulence proteins directly into host cells?

A. Production of exotoxin A
B. Type 3 secretory system
C. Release of lipopolysaccharide
D. Formation of bacterial spores
E. Production of cytochrome oxidase

B. Type 3 secretory system

A patient has suspected Salmonella gastroenteritis. The organism has survived the acidic environment of the stomach before reaching the gastrointestinal tract. Which Salmonella factor helps it tolerate this acidic environment?

A. H antigen
B. Type 3 secretory system
C. Acid tolerance response (ATR) gene
D. Fimbrial capsule
E. Prostaglandin pathway

C. Acid tolerance response (ATR) gene

A patient with Salmonella gastroenteritis develops severe diarrhoea. Laboratory investigations suggest significant inflammation and damage to the gastrointestinal tract. Which mechanism best explains the diarrhoea?

A. Increased absorption of fluid from the intestine
B. Reduced inflammation within the intestinal wall
C. Damage and inflammation reducing normal fluid and nutrient absorption
D. Complete inhibition of intestinal blood flow
E. Increased production of digestive enzymes by Salmonella

C. Damage and inflammation reducing normal fluid and nutrient absorption

A patient with Salmonella infection subsequently develops painful inflammation affecting a joint. The clinician considers a rare complication of Salmonella infection. Which complication is being considered?

A. Guillain-Barré syndrome
B. Reactive arthritis
C. Rheumatic fever
D. Haemolytic uraemic syndrome
E. Cellulitis

B. Reactive arthritis

A laboratory scientist is investigating a suspected Shigella infection. Which species is described as the most common Shigella species in the UK?

A. Shigella flexneri
B. Shigella boydii
C. Shigella dysenteriae
D. Shigella sonnei
E. Shigella enteritidis

D. Shigella sonnei

A patient has suspected Shigella infection. The organism needs to invade intestinal epithelial cells. Which type of cell does Shigella preferentially use to enter the intestinal tissue?

A. Goblet cells
B. Apical epithelial cells
C. M cells
D. Paneth cells
E. Red blood cells

C. M cells

A stool sample contains an organism suspected to be Shigella. The organism has entered a host cell inside a vesicle. What happens next that distinguishes Shigella from Salmonella?

A. Shigella remains permanently inside the vesicle
B. Shigella immediately leaves the gastrointestinal tract
C. Shigella lyses the vesicle and replicates in the cell cytoplasm
D. Shigella forms spores inside the vesicle
E. Shigella destroys the host cell without replicating

C. Shigella lyses the vesicle and replicates in the cell cytoplasm

A laboratory receives a stool sample from a patient suspected of having Shigella. The laboratory decides to use DCA (desoxycholate citrate agar). What is the main purpose of the desoxycholate in this medium?

A. To encourage the growth of normal intestinal flora
B. To inhibit non-pathogenic Gram-negative organisms
C. To identify antibiotic resistance
D. To increase bacterial motility
E. To detect hydrogen sulphide production

B. To inhibit non-pathogenic Gram-negative organisms

A laboratory technician inoculates a stool sample onto DCA. The suspected Shigella colonies do not ferment lactose. What colony appearance would be expected?

A. Bright pink colonies
B. Black colonies
C. Colourless colonies
D. Green colonies
E. Yellow colonies

C. Colourless colonies

A patient has a suspected gastrointestinal infection, but only a small number of organisms are present in the stool sample. The laboratory wants to increase the number of organisms before plating the sample onto selective agar. Which approach would be most appropriate?

A. Immediately discard the sample
B. Perform an enrichment step using selective broth
C. Place the sample in distilled water
D. Incubate the sample without nutrients
E. Perform only a Gram stain

B. Perform an enrichment step using selective broth

A 4-year-old child develops severe diarrhoea after several children at their nursery become unwell. A stool sample shows blood and mucus. The laboratory suspects Shigella. Which feature of Shigella most likely contributes to its easy transmission in this setting?

A. It requires a very high infective dose
B. It has a very low infective dose
C. It can only infect immunocompromised patients
D. It requires prolonged exposure to contaminated water
E. It cannot survive inside host cells

B. It has a very low infective dose

A patient has suspected Shigella infection. During laboratory investigation, the organism attaches to intestinal cells and is taken into a vesicle. The organism then escapes from the vesicle and begins multiplying within the cytoplasm. Which protein is responsible for mediating the lysis of the vesicle?

A. IpaA
B. IpaB
C. Lipopolysaccharide
D. ATPase
E. Hydrogen sulphide

B. IpaB

A stool sample is cultured on XLD agar. A suspected Shigella colony appears red and does not produce a black colour. Which explanation best accounts for this appearance?

A. Shigella ferments xylose and produces hydrogen sulphide
B. Shigella ferments lactose and produces acid
C. Shigella cannot ferment xylose and does not produce hydrogen sulphide
D. Shigella produces large amounts of hydrogen sulphide
E. Shigella is inhibited completely by the desoxycholate

C. Shigella cannot ferment xylose and does not produce hydrogen sulphide

A 35-year-old patient returns from travelling in a country where cholera is endemic. Shortly after returning, they develop profuse, watery diarrhoea described as resembling “rice water.” Which mechanism best explains the diarrhoea?

A. Destruction of red blood cells by Shiga toxin
B. Increased cyclic AMP causing loss of electrolytes and water into the intestine
C. Invasion of intestinal cells followed by intracellular replication
D. Inhibition of sorbitol fermentation
E. Destruction of intestinal cells by hydrogen sulphide

B. Increased cyclic AMP causing loss of electrolytes and water into the intestine