Exam 2- (CH 14) Staphylococcus Textbook Review Questions

Question 1

Micrococci are
A. catalase and coagulase negative.
B. catalase positive and coagulase negative
C. resistant to bacitracin.
D. modified oxidase negative and resistant to lysosome

Answer 1

B. catalase positive and coagulase negative

Question 2

Which organism might be confused with Staphylococcus aureus because it possesses clumping factor?
A. Staphylococcus epidermidis
B. Staphylococcus saprophyticus
C. Staphylococcus lugdunensis
D. Staphylococcus haemolyticus

Answer 2

C. Staphylococcus lugdunensis

Question 3

Which of the following is true of staphylococcal enterotoxins?
A. Produced by over 90% of Staphylococcus aureus isolates
B. They are heat-stable exotoxins that cause diarrhea and vomiting.
C. Heating contaminated food at 100° C for 30 minutes will prevent symptoms.
D. The majority of clinically significant isolates fall into the serogroups of K, P, and T.

Answer 3

B. They are heat-stable exotoxins that cause diarrhea and vomiting.

Question 4

Ritter disease is caused by
A. α-hemolysin.
B. toxic shock syndrome toxin.
C. protein A.
D. exfoliative toxin.

Answer 4

D. exfoliative toxin.

Question 5

All of the following are often incriminated in staphylococcal food poisoning except
A. fried rice.
B. egg salad.
C. sandwich meat.
D. potato salad.

Answer 5

A. fried rice.

Question 6

This hemolysin created by Staphylococcus aureus is associated with Panton-Valentine leucocidin.
A. Alpha
B. Beta
C. Delta
D. Gamma

Answer 6

D. Gamma

Question 7

Which of the staphylococci are pyrrolidonlyl arylamidase (PYR) positive?
A. Staphylococcus aureus
B. Staphylococcus epidermidis
C. Staphylococcus haemolyticus
D. Staphylococcus saprophyticus

Answer 7

C. Staphylococcus haemolyticus

Question 8

A young woman presents to the emergency department with a urinary tract infection that, when cultured, grows gram-positive cocci in clusters. Which of the following tests will differentiate the most likely organism from the other staphylococci?
A. Alkaline phosphatase
B. Ornithine decarboxylase
C. Urease
D. Novobiocin resistance

Answer 8

D. Novobiocin resistance

Question 9

Rare strains called small colony variants of staphylococci are fastidious and may require
A. menadione.
B. citrate.
C. increased oxygen.
D. sphingomyelinase C.

Answer 9

A. menadione.

Question 10

Most oxacillin resistance is due to the __ gene which codes for an altered ____.
A. qnrD; transposons
B. vat; acetyltransferases
C. blaCMY; insertion sequence
D. mecA; penicillin-binding protein

Answer 10

D. mecA; penicillin-binding protein

Question 11

What types of infections are associated with S. aureus?

Answer 11

S. aureus is noted for causing skin infections such as impetigo; bullous impetigo; furuncles (boils); carbuncles; cellulitis; wound infections associated with trauma, surgery, and burns; pneumonia; organ abscesses; bacteremia; endocarditis; osteomyelitis; and septic arthritis.

Question 12

Compare the populations in which S. aureus infections occur.

Answer 12

Although S. aureus has had a lengthy association with hospitalized and nursing home patients, recovery in community populations, including pediatric populations and student athletes, has increased.

Question 13

Describe how protein A contributes to the virulence of S. aureus.

Answer 13

Protein A is able to bind the Fc portion of immunoglobulin G (IgG), thereby interfering with phagocytosis and blocking the protective action of IgG.

Question 14

What toxin causes toxic shock syndrome?

Answer 14

Toxic shock syndrome (TSS) is associated mainly with TSST-1. However, some cases of TSS have been linked to enterotoxin B or C.

Question 15

What type of toxin is associated with staphylococcal scalded skin syndrome?

Answer 15

Exfoliative toxin or epidermolytic toxin causes staphylococcal scalded skin syndrome.

Question 16

What toxins are involved in staphylococcal food poisoning?

Answer 16

Enterotoxins A to E and G to J, most commonly A and D, are associated with staphylococcal food poisonings.

Question 17

Discuss in what clinical condition coagulase-negative staphylococci would be significant and in what condition they might be considered a contaminant.

Answer 17

Although not all coagulase-negative staphylococci (CoNS) are considered clinically significant, those CoNS associated with indwelling devices and immunocompromised patients are considered potential pathogens. S. lugdunensis infections are usually more invasive. Also, because they have a distinct susceptibility category separate from the other CoNS, it is important to identify suspected S. lugdunensis to the species level, as in the case of blood isolates. Urinary tract infections caused by S. saprophyticus are also clinically significant.

Question 18

Which coagulase-negative staphylococci are considered more significant and might need to be identified to the species level?

Answer 18

The clinically significant CoNS include S. epidermidis and S. saprophyticus. In addition, infections (e.g., endocarditis, septicemia, peritonitis) caused by S. haemolyticus and S. lugdunensis have become more common. S. saprophyticus is clinically significant when isolated from urine. Other CoNS, such as S. pseudintermedius, will gain importance as they become more frequently recovered and identified using the latest techniques.

Question 19

What are the two types of coagulase produced by S. aureus, and which one can be used as a confirmatory test for coagulase in a clinical laboratory?

Answer 19

Tube-coagulase and clumping factor (slide) coagulase are two tests used to detect coagulase activity of S. aureus. The tube-coagulase can be used as a confirmatory test for coagulase, whereas the traditional slide coagulase using plasma is considered obsolete.

Question 20

How is S. aureus differentiated from other, similar isolates?

Answer 20

A positive coagulase test would differentiate S. aureus from most other staphylococci. Numerous commercial kits contain plasma-coated latex particles or antibodies directed against S. aureus molecules that also accurately identify the organism.

Question 21

What test is used to identify S. saprophyticus?

Answer 21

A disk diffusion test using a 5-µg novobiocin disk can be used. S. saprophyticus will be resistant, whereas most other CoNS will be susceptible.

Question 22

What is the significance of a S. aureus isolate being oxacillin resistant?

Answer 22

An oxacillin-resistant S. aureus isolate is considered resistant to all penicillinase-stable penicillins and most β-lactam antibiotics. Such an isolate is referred to commonly as methicillin-resistant S. aureus (MRSA).

Question 23

Describe some risk factors associated with HA-MRSA and CA-MRSA.

Answer 23

Recently hospitalized patients, especially older adults; people with weakened immune systems; those residing in nursing homes or patients having an invasive medical device such as an intravenous line or urinary catheter that can provide a pathway for MRSA to travel into the body are at high risk for hospital-associated MRSA. Those who participate in sports or live in crowded or unsanitary conditions are at risk for community-associated MRSA infections. Outbreaks of MRSA have occurred in military training camps, child care centers, and jails. Carriers of MRSA have the ability to spread the bacteria, even if they are not ill themselves.

Question 24

What are the recommendations for detecting oxacillin, clindamycin, or vancomycin resistance?

Answer 24

Oxacillin commonly had been used to predict methicillin resistance. However, cefoxitin is now recommended for determining oxacillin resistance in staphylococcal species. For the most accurate detection of methicillin resistance, molecular tests for mecA or tests that detect the mecA product, PBP2, may be used. For detection of clindamycin resistance, an induction test (D-zone test) disk diffusion testing of clindamycin and erythromycin should be used. Not all susceptibility methods are able to detect vancomycin-intermediate S. aureus (VISA) or vancomycin-resistant S. aureus (VRSA). The Clinical and Laboratory Standard Institute and Centers for Disease Control and Prevention have recommended the addition of a vancomycin agar plate, which can be used as a supplemental plate when testing MRSA isolates. Most VISA and VRSA have thus far been detected in these more resistant S. aureus strains.

Question 25

Describe methods for identification of staphylococci, and evaluate which rapid methods would be appropriate and when they would be used.

Answer 25

Clinical isolates that have been grown on traditional media can be rapidly identified by simple catalase and latex agglutination tests, as described in this chapter. For many laboratories, this will continue to be a cost-effective and efficient way to identify S. aureus and CoNS. Laboratories are incorporating molecular tests to identify staphylococci. As more molecular technologies are introduced, these methods will provide rapid methods of identification, within hours, and can identify markers of antimicrobial resistance. Mass spectrometry methods, such as matrix-assisted laser desorption– ionization time-of-flight, with databases incorporating commonly recovered species of staphylococci, will also become an asset, especially in larger institutions. Although these methods can be expensive initially, they will continue to be useful and show cost savings for targeted treatment of serious infections.

Question 26

Points to Remember

Answer 26

■ The staphylococci are catalase-positive, gram-positive cocci.
■ Staphylococcus aureus is the primary pathogen within this genus, and the isolation of S. aureus from any source should be considered clinically significant.
■ S. aureus produces many virulence factors, including protein A, enterotoxins, toxic shock syndrome toxin-1, exfoliative toxin, cytolytic toxins, and numerous exoenzymes.
■ S. aureus is associated with numerous diseases, including skin infections, scalded skin syndrome, toxic shock syndrome, food poisonings, bacteremia, osteomyelitis, and pneumonia.
■ Staphylococcus epidermidis and other coagulase-negative staphylococci (CoNS) have been linked to important hospital-associated infections, often associated with foreign body implants.
■ CoNS recovered from sterile sites and sites associated with indwelling devices should be considered potential pathogens

Question 27

Points to Remember

Answer 27

■ Hospital-associated methicillin-resistant S. aureus (HA-MRSA) and community-associated methicillin-resistant S. aureus (CA-MRSA) are important and costly health care concerns. From the 1980s onward there has been a continual increase in the incidence of HA-MRSA infections. Recently published studies from the Centers for Disease Control and Prevention and others have shown a decline in the incidence of methicillin-resistant S. aureus infections in health care settings.
■ Staphylococcus saprophyticus is an important cause of urinary tract infections, especially in younger women. The identification of S. saprophyticus from urine specimens should be done, especially if the bacteria are predominant, because even lower numbers can be significant.
■ S. aureus is frequently separated from less pathogenic species by being tube coagulase positive.
■ S. saprophyticus is resistant to novobiocin, whereas many other CoNS are sensitive.
■ Increasing antimicrobial resistance is a problem with the staphylococci, particularly S. aureus.