Microbiology Solo 3 Study Questions and Kahoot

Case Study 3-1

A teenage male with a history of colitis, most likely Crohn disease, has had difficulty controlling his disease despite medical management including long-term parenteral nutrition and pain medication. He attends high school and is socially adjusted, even though his illness has caused him to be small in stature. He lives with his mother, who works for a veterinarian. He was admitted to the hospital for abdominal discomfort and erythema at the exit site and along the tunnel of his central line. Blood cultures were collected, and both the blood cultures and his catheter tip cultures grew catalase-positive, gram-positive cocci. The coagulase tube test was positive, but the slide and latex test for coagulase were negative

Refer to Case Study 3-1

What could be the reason the tube coagulase test was positive, but the slide latex coagulase test was negative?

There are two forms of coagulase produced by organisms, bound (clumping factor) and free. The slide test is testing for the presence of bound coagulase, and the tube test allows us to see if free coagulase is present. Organisms can have either a variable or a negative reaction to clumping factor and still end up being positive for tube coagulase due to producing free coagulase

Refer to Case Study 3-1

Given the patient and patient’s family history, what organism(s) is MOST likely to be the cause for the positive blood cultures and catheter tip cultures?

Staphylococcus intermedius

Staphylococcus pseudointermedius

Examine the following isolated antibiotic sensitivity profiles for Staphylococcus aureus. Identify the methicillin-resistant organism and the methicillin-sensitive organism based on the pattern of resistance and sensitivities. Explain your answer

S = susceptible

R = resistant

POS = positive

NEG = negative

Isolate 1

Antibiotic	Automated Result	Final Result
Beta-lactamase		POS
Cefoxitin screen	NEG (-)	NEG
Clindamycin	<=0.25	S
Erythromycin	<=0.25	S
Inducible Clindamycin	NEG (-)	NEG
Oxacillin	0.5	S

 

 

Isolate 2

Antibiotic	Automated Result	Final Result
Beta-lactamase		POS
Cefoxitin screen	POS (+)	POS
Clindamycin	<=0.25	S
Erythromycin	>=8	R
Inducible Clindamycin	NEG (-)	NEG
Oxacillin	>=4	R

When determining if Staphylococcus aureus strains are resistant to Methicillin, there are two antibiotics that are looked at first, Cefoxitin and Oxacillin. Isolate 1 is susceptible to Oxacillin and has a negative Cefoxitin screen so we know that this strain is Methicillin-Sensitive

When looking at Isolate 2, it is showing resistance to Oxacillin and has a positive Cefoxitin screen. Because of this we know that it is resistant to all beta-lactam antibiotics so isolate 2 is the Methicillin-Resistant strain

A clinical isolate’s test demonstrated the following results:

Catalase - Positive

Gram Stain - Gram positive cocci

Non-hemolytic on BAP

Coagulase - Negative

Novobiocin - Resistant

PYR - Negative

Glucosidase - Positive

The organism is most likely?

Staphylococcus saprophyticus

Which of the following organisms is coagulase positive?

Staphylococcus pseudintermedius

All of the following media used for the cultivation of Micrococcaceae are selective except

5% Sheep blood agar

Colistin nalidixic acid sugar

Mannitol salt agar

Phenylethyl alcohol agar

5% sheep blood agar

Case Study 3-2

A 13-year-old female arrives at an urgent care clinic with the chief complaint of a sore throat. Pharyngitis is suspected and a rapid strep A is ordered. The rapid strep A test comes back negative, so a complete throat culture is ordered and sent to the microbiology department for analysis. After 24 hours of growth, small, grayish-white colonies, with a large zone of hemolysis are seen on 5% sheep blood agar. Rapid identification tests were used to identify the pathogen. The results were

Gram stain - Gram positive cocci in chains

Catalase - Negative

PYR - Negative

Bacitracin - Resistant

CAMP test- Negative

Refer to Case Study 3-2

What organism is MOST likely the cause of this acute pharyngitis?

Group C Streptococcus, specifically Streptococcus dysgalactiae

Refer to Case Study 3-2

What rapid method could be used to identify this pathogen?

PathoDxtra Strep Latex Agglutination Kit Testing

Necrotizing fasciitis is a serious infection associated with:

Streptococcus pyogenes

Rheumatic fever is a poststreptococcal disease typically associated with

Pharyngitis associated with Group A Streptococci

Which of the following organism(s) are PYR positive? Select all that apply

Enterococcus faecalis

Staphylococcus aureus

Streptococcus pyogenes

Streptococcus gallolyticus

Streptococcus agalactiae

Enterococcus faecalis

Streptococcus pyogenes

When streaking a throat culture on 5% sheep blood agar, there is one plate incubated aerobically and one plate incubated anaerobically. What enzyme would be destroyed if plates were planted aerobically ONLY?

Streptolysin O

Optochin susceptibility is used to differentiate

Streptococcus pneumoniae from other alpha-hemolytic streptococci

A 24-hour growth on a urine culture from a 20-year old woman demonstrates grayish white beta-hemolytic colonies, which are catalase negative. What would be the next step for the microbiologist?

Perform a CAMP test and/or a Hippurate hydrolysis

Which organism is able to hydrolyze esculin and is a serious nosocomial pathogen?

Enterococcus faecalis

What bacteria cause neonatal sepsis in 1- to 5-day old infants?

Streptococcus agalactiae

Sputum specimen inoculated on 5% sheep blood agar reveals alpha-hemolytic grayish colonies that are very mucoid. What test should be set up next

Optochin

What is the antibiotic of choice for beta-hemolytic Streptococcus

Penicillin

Staphylococcus aureus contains the enzyme Beta lactamase. What does this enzyme do?

Cleaves a key ring of the penicillin molecule, rendering it ineffective

Staphylococcus aureus contains an enzyme that converts hydrogen peroxide into oxygen and water. What enzyme is this?

Catalase

Given a beta hemolytic colony and GPC on a gram stain, what would be the first test to start the identification process?

Catalase

A wound culture grows a beta hemolytic colony, GPC, catalase neg. List the next test needed to ID S. pyogenes

Bacitracin

If a black colony on a BEA plate showed GPC on a gram stain, and a PYR was negative, how would the organism be reported?

Streptococcus bovis group

What is the drug of choice for Streptococcus agalactiae?

Penicillin

What is the test used to identify Streptococcus pneumoniae

Optochin >14mm

What is the test used to identify Enterococcus species from other Group D Streptococcus?

PYR

What are the correct biochemical tests and results to identify Streptococcus viridians group?

Esculin neg, PYR neg, 6.5% NaCl negC

What is the test used to separate a Staphylococcus aureus from a Staphylococcus epidermidis?

Coagulase

Which Streptococcus species is not considered normal flora?

Streptococcus pyogenes

What does the M protein do in streptococcus pyogenes

It is anti-phagocytic and produces several enzymes and hemolysins that contribute to tissue invasion and destruction

Staphyloccus lugdunensis has what type of coagulase?

Bound coagulase only

What are the two post-Streptococcal infections?

Acute rheumatic fever; glomerulonephritis

What causes Streptococcus pyogenes beta hemolysis in anaerobic conditions?

Streptolysin O and S

Which of the following organisms is considered a typical pathogen for the lower respiratory system?

Haemophilus influenzae

What is the correct test that is used to distinguish Staphyloccus saprophyticus from other coagulase-negative Staph

Novobiocin

What two antimicrobials are used to manually perform a “D-test” for Staphylococcus aureus

Clindamycin and Erythromycin

What test is used to identify a Micrococcus species

Modified OxidaseW

What causes Streptococcus pneumoniae type III colonies to be produced?

Over production of polysaccharide capsule

A small grey beta colony isolated from a throat culture did not type with Group A antigen. What was most likely isolated?

Streptococcus dysgalactiae