Bacterial Diseases

pyoderma

pus-filled

Where do Staphylococcal infections (Staphylococcus aureus) infections enter?

hair follicle (folliculitis), eyelash follicle (sty), deeper pus-filled infection (furuncle/boil), or multiple connected boils/more severe spread (carbuncle)

How does S. aureus evade the immune system?

prevents movement of phagocytic cells to site of infection + can kill a macrophage (white blood cell) with leukocidin; it is Coagulase (+) so blood will clot around bacteria, and their thick peptidoglycan layer resists digestion by lysozyme

Why can you get infection by S. aureus twice?

It evades immune response even in presence of antibodies

What does it mean that S. aureus may act as a superantigen?

It may cause an intense immune response due to release of cytokines from host cells (T cells)

Can Staphylococcal Infections be asymptomatic?

Yes! 50% of adults are nasal carriers

What bacteria causes Impetigo's pyoderma lesions?

Staphylocci and/or Streptococcus pyogenes

How is impetigo spread?

highly contagious, spread by direct contact with minor break in skin; can spread to surrounding areas

How is impetigo treated?

topical antibiotics

What causes Scalded Skin Syndrome (SSS)

Staphylococcus aureus which produces exfoliative exotoxins: Toxin A (encoded on a plasmid) and Toxin B (encoded on a bacterial chromosome)

Why does SSS spread all over the body?

Toxin B enters the blood stream and circulates, causing widespread skin damage

Who is most affected by SSS?

newborns and young children

What is a common result of SSS in newborns?

Pemphigus neonatorum (Impetigo)

What are the key features of SSS?

red/tender skin, blistering, skin peeling like a burn, possible fever

What causes Toxic Shock Syndrome (TSS)

Staphylococcus aureus producing Toxic Shock Syndrome Toxin (TSST-1 superantigen)

How does TSS spread?

enters bloodstream and circulates; causes widespread immune activation + massive inflammation (cytokine "storm")

What are the symptoms of TSS?

shock (low BP), organ failure, starving organs of blood

What is the classic associated cause of TSS?

leaving a tampon in for too, long; however anyone exposed can contract it

What organism is associated with Streptococcal infections? Describe it.

Streptococcus pyogenes (GAS); gram-negative cocci; grows in chains; many strains classified by carbohydrate on cell wall

What throat/systemic diseases are caused by Streptococcus pyogenes?

Strep throat – classic sore throat, fever, and tonsillar exudate.

Scarlet fever – a complication of strep throat caused by an erythrogenic toxin, which is actually encoded on a prophage (virus DNA inserted into the bacterial genome). It causes a red, sandpaper-like rash.

What skin infections are caused by Streptococcus pyogenes?

Erysipelas – painful, red, raised skin rash, often on the face or legs.

Necrotizing fasciitis – rare but deadly “flesh-eating” infection.

Streptococcal toxic shock syndrome (STSS) – systemic infection with shock, similar to Staphylococcal TSS, caused by exotoxins acting as superantigens.

What Immune-related complications are caused by Streptococcus pyogenes?

Rheumatic fever – occurs after untreated strep throat, involves an autoimmune reaction (antibodies cross-react with heart and joint tissues).

Post-streptococcal glomerulonephritis – another immune-mediated complication affecting the kidneys.

What are the virulence factors produced by Streptococci?

Hemolysins / Streptolysins - Destroy red and white blood cells. Streptolysin O is oxygen-sensitive, streptolysin S is oxygen-stable.

M protein - Helps bacteria stick to host tissues and inhibits phagocytosis by macrophages. Very important in immune evasion.

Capsule (hyaluronic acid) - Prevents phagocytosis, making it harder for immune cells to kill bacteria.

Streptokinase - Dissolves blood clots, helping bacteria spread through tissues.

Hyaluronidase - Breaks down connective tissue (hyaluronic acid), allowing the bacteria to invade deeper tissues.

Deoxyribonucleases (DNases) - Break down DNA in pus, helping bacteria spread more easily.

What organism causes Acne?

Propionibacterium acnes (anaerobic)

How does Acne occur?

Increased sebum production by sebaceous glands (often during puberty) causes bacterial overgrowth + clogged pores; bacteria produces enzymes and inflammatory molecules leading to red swollen pimples/cysts

What organism causes Pseudomonas dermatitis?

Pseudomonas aeruginosa (gram-negative rod > lipid A in its endotoxin which can trigger strong immune responses); Ubiquious > found in water, soil, and even moist environments like soap or sinks

What are the key characteristics of Psuedomonas aeruginosa?

highly resistant to antibiotics and disinfections, biofilm formation, exotoxins and endotoxin (contributes to tissue damage and immune activation)

What diseases are caused by pseudomonas aeruginosa?

Pseudomonas dermatitis - mild skin rash; often after swimming in contaminated water

Serious infections in burn patients - Pseudomonas and Serratia marcescens are common in burns because the skin barrier is lost

Opportunistic pathogen - usually infects people with compromised skin or immune systems

What is Ophthalmia neonatorum?

conjunctivitis (eye infection) in newborns

How does a newborn contract Ophthalmia neonatorum?

when the baby passes through the birth canal in the mother is infected

What organisms cause Ophthalmia neonatorum?

Neisseria gonorrhoeae - can cause severe purulent conjunctivitis; rapid onset (usually 2-5 days after birth)

Chlamydia trachomatis - causes a milder, often slower-onset conjunctivitis (5-14 days after birth); intracellular pathogen, so antibiotic must penetrate host cells

How do you treat/prevent Ophthalmia neonatorum?

Silver nitrate drops - historically used, mainly effective against gonorrhea

Tetracycline ointment - can treat both gonorrhea and chlamydia; antibiotic must reach inside cells because Chlamydia is intracellular

What is Bacterial Conjunctivitis otherwise known as? What does it cause?

pink eye; inflammation of the conjunctiva caused by bacteria (any organism); redness + discharge + irritation

What organisms cause bacterial conjunctivitis? (pink eye)

Staphylococcus

Streptococcus

Neisseria

Haemophilus influenzae

Pseudomonas spp.

*Note: many different bacteria can cause it

What is Trachoma and what bacteria causes it?

chronic infection of the conjunctiva caused by certain strains of Chlamydia trachomatis; more serious than pink eye

What can trachoma result in for the patient?

eyelid deformities; lashes may turn inwards and scratch cornea; can cause blindness if left untreated

What strain of Chlamydia tracomatis does NOT infect the baby if patient is pregnant?

Trachoma

What is a Urinary Tract Infection (UTI)?

infection of any part of the urinary tract (urethra, bladder, ureters, kidneys)

What are the two classifications of UTIs? Describe them.

Ascending UTI - infection starts in urethra or bladder and moves upwards towards the kidneys (more common)

Descending UTI - infection starts in kidneys (usually from bloodstream) and moves downward to bladder/urethra

What organisms cause UTIs?

E. coli - causes 80% of UTIs

Can also be caused by other fecal organisms:

Proteus

Klebsiella

What is a common cause of UTI's other than poor hygene?

post-catheterization infection from a hospital (nosocomial)

What is bacterial vaginosis (BV)?

imbalance of pH causes imbalance of normal vaginal flora where Gardnerella vaginalis and other anaerobes overgrow (***not to be confused with fungal [yeast] vaginitis)

What causes bacterial vaginosis (BV)?

normal flora becoming overgrown (caused by antibiotic use, diabetes, hormonal changes)

How is bacterial vaginosis diagnosed?

Clue cells > vaginal epithelial cells coated with Gardnerella bacteria, seen under a microscope

Describe the organism associated with Gonorrhea.

Neisseria gonorrhoeae; gram-negative diplococcus; humans are only natural host

What are the virulence factors of Gonorrhea?

1. Attachment pili (fimbriae) - Helps the bacterium attach to epithelial cells.

2. Endotoxin (lipid A) - Part of Gram-negative LPS → triggers inflammation.

3. Opa proteins - Interfere with T cell activation, helping bacteria evade immune response.

4. IgA protease - Cleaves IgA antibodies in mucosal surfaces → avoids immune detection.

5. Intracellular survival - Can survive inside polymorphonuclear leukocytes (neutrophils) and sometimes macrophages → allows dissemination.

How does one get infected with Gonorrhea?

transmitted sexually

What infections can gonorrhea lead to?

Local infection - urethra, cervix, pharynx or rectum

PID (Pelvic Inflammatory Disease) – in women, infection can ascend to uterus, fallopian tubes, ovaries.

Disseminated gonococcal infection (DGI) – bacteria travel in blood inside phagocytes → can affect joints, skin, or other organs.

Ophthalmia neonatorum – eye infection in newborns exposed during birth.

How can gonorrhea survive outside of body?

In pus > for hours

Formites (like sheets) > briefly

What organism is associated with Syphilis?

Treponema pallidum - spirochete bacterium (long corkscrew, gram-negative)

How is syphilis transmitted?

usually sexually; can also be transmitted through saliva or direct contact with lesions, rapidly enters bloodstream (humans only natural host)

What are the five stages of syphilis?

1. Incubation - No symptoms; organism is multiplying.

2. Primary - Chancre at site of infection (painless ulcer) ; High bacterial load → highly contagious ; Wound may heal on its own, but infection persists systemically

3. Secondary - Organism in circulation → systemic ; Skin eruptions / pustular rashes, mucous patches in mouth ; Immune response causes inflammation; person still highly contagious

4. Latent - No symptoms; Organism may replicate slowly; Can cross placenta → congenital syphilis, causing fetal neurological damage

5. Tertiary - Can occur years later; Gumma = walled-off inflammatory lesions; Any organ can be damaged (heart, CNS, bones, etc.)

What is the life cycle of Chlamydia? (6 steps)

1. The elementary body (infectious form) attaches to host cell

2. Host cell phagocytizes the elementary body, housing it in a vacuole

3. Elementary body reorganizes to form a reticulate body

4. Reticulate body divides successively, producing multiple reticulate bodies

5. Reticulate bodies begin to convert back to elementary bodies

6. Elementary bodies are released from host cell

What organism is associated with Chlamydia infections?

Chlamydia trachomatis = obligate intracellular bacterium (needs host cells to replicate) (humans only natural host); Mycoplasma genitalium and Mycoplasma hominis can also cause nongonococcal urethritis (NGU) (mycoplasmas lack a cell wall)

What diseases and complications can be caused by Chlamydia?

Nongonococcal urethritis (NGU) - inflammation of the urethra not caused by gonorrhea

Pelvic Inflammatory Disease (PID) - infection can ascend from the urethra/cervix to uterus, fallopian tubes, and ovaries

Pregnancy complications - can colonize the placenta leading to miscarriages or abortions

What bacteria is responsible for Streptococcal Pharyngitis? (upper respiratory)

Streptococcus pyogenes

What bacteria causes Diptheria?

Corynebacterium diphtheria

What does Corynebacterium diphtheria do and how does it cause illness?

It makes an exotoxin which is carried on a prophage and inhibits protein synthesis. It goes into circulation starting from an organism in the throat and can damage any organ.

What does Diptheria cause in the airway?

A pseudomembrane; can cause suffocation if untreated

What is the vaccine for Diptheria?

DTP vaccine (humans only natural host)

What organism causes Whooping cough (Pertussis)

Bordetella pertussis

What toxins does pertussis produce?

tracheal cytotoxin, pertussis toxin and endotoxin (they only infect humans)

What are the three stages of the disease whooping cough/pertussis?

1. catarrhal stage (common cold symptoms)

2. paroxysmal (violent coughing with the potential complication of cyanosis from mucus build-up)

3. convalescent stage with the chance for secondary infections

What organism usually causes pneumonia?

Streptococcus pneumonia (other organisms cause it too)

What is the major virulence factor of pneumonia?

the capsule

Is there a vaccine for pneumonia?

Yes (composed of many serotypes)

What bacteria causes Mycoplasma pneumonia (atypical/walking pneumonia)?

Mycoplasma pneumoniae, lacks a peptidoglycan layer

What is Legionnaires Disease?

caused by Legionella pneumophila a gram negative rod that survives in macrophages

How is Legionnaires disease transmitted?

an aerosol, from things like air conditioners, humidifiers, hospital waterlines, etc. (not really spread from person to person)

What bacteria causes tuberculosis?

Mycobacterium tuberculosis

How does tuberculosis survive in the body and infect the host?

can survive in macrophages and white blood cells; can survive in sputum for months; can spread through circulation and infect organs and even bones (miliary tuberculosis); can remain dormant in the body and can become reactivated later if the person is immunocompromised

Tuberculosis causes lung lesions referred to as what?

tubercles

How is tuberculosis diagnosed and treated?

skin test; cocktail of drugs (isoniazid, rifampin, pyrazinamide and ethambutol); vaccine but effetiveness is questionable

How can M. bovis infect humans?

through unpasteurized milk

How does food poisoning hurt a host?

food can have preformed toxins in it and the diseases caused by toxins are referred to as intoxications rather than infections

What are the intoxications known to cause food poisoning?

Staphylococcus, Clostridium (perfringens and botulinum), and Bacillus cereus

What does S. aureus make that affects the GI tract?

enterotoxins (specifically Enterotoxin A)

What is Enterotoxin A and what does it do?

a heat stable toxin that can enter the blood and travel back to the intestine; inflames the intestines and stimulates the vomiting center of the brain

What does Clostridium perfringens do?

makes an enterotoxin and the organism is a endospore former which can survive in food even after cooking; if conditions allow endospores can germinate

What does Bacillus cereus do?

makes two different enterotoxins. One induces vomiting and the other diarrhea. Since it makes an endospore, heating food does not destroy the endospore which can eventually germinate

What is Enteritis?

inflammation of the intestine (usually the small intestine; if the large intestine is involved it is called dysentery)

What organism causes Sallmonellosis?

Salmonella enterica (gram negative; makes an endotoxin)

Who/what carries Sallmonellosis?

contaminated water, animals, reptiles, and humans (+ meat and dairy)

What are the complications of Sallmonellosis?

entercolitis; and it can spread to other organs

Who can carry Salmonellosis?

animals, water, reptiles and human carriers (can contaminate food)

What does salmonellosis often contaminate?

meat and dairy products

What are the complications of Salmonellosis?

enterocolitis, and it can spread to other organs

What is the organism associated with Typhoid Fever?

 Salmonella typhi (makes an endotoxin)

How does typhoid fever (salmonella typhi) spread?

travels from the intestine into the lymph tissue and multiplies in the macrophages; then spreads to multiple organs (there IS an attenuated vaccine)

What does typhoid fever do? What can it lead to?

can lead to septicemia so it must be treated with antibiotics; can survive in the gallbladder so a person can become a chronic carrier

How does one catch Shigellosis (bacillary dysentery)?

humans/primates ingest it with food and found in unclean environments (produces an endotoxin) (disease uses actin to propel itself into other cells of intestinal lining)

What does shigellosis cause and why?

dehydration and electrolyte loss since there is a large volume of fluid lost with the infection

What is the bacteria most commonly associated with shigellosis?

 S. sonnei

What toxin does S. dysenteriae make?

Shiga toxin; a neurotoxin

What bacteria is associated with Cholera?

Vibrio cholerae

What does vibrio cholerae do?

makes an enterotoxin called cholera toxin which damages intestinal lining

What is the milder form of cholera?

Vibriosis (Vibrio parahaemolyticus); also makes an enterotoxin

What is the major characteristic of Cholera and how it is harmful?

"Rice water stools"; can result in severe dehydration resulting in shock

What can vibrio cholerae contaminate?

water and the shellfish living in the water

What does Enteroinvasive E. coli (EIEC) produce that helps it infect cells?

K antigen (from plasmids) → allows attachment and invasion of mucosal cells