Term
| What is the morphology and staining of Staphylococcus bacteria? |
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Definition
| medium-sized Gram-positive cocci that occur in clusters but rarely in chains/rows of more than 3 |
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Term
| What do some strains of Staphylococcus produce to promote adhesion to cells? |
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Definition
| thin extracellular polysaccharide capsule (aka slime) |
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Term
| Are Staphylococcus motile or non-motile? |
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Definition
| Non-motile, with no flagella |
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Term
| What type of agar plate can Staphylococcus cultures be grown on? |
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Definition
| blood or chocolate, in aerobic conditions |
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Term
| What do Staphylococcus cultures look like? |
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Definition
- Soft, circular, slightly convex
- 2-5 times larger than streptococci
- whitish color that turns yellow with age
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Term
| What is the most common pathogenic Staphylococcus species and is it non-hemolytic, slightly alpha hemolytic, or beta hemolytic? |
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Definition
| Staphylococcus aureus, beta-hemolytic |
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Term
| What is the primary test to separate Staphylcocci from Streptococci? |
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Definition
- catalase test (catalase converts hydrogen peroxide to water and oxygen)
- Staphylcocci are positive and streptococci are negative
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Term
| What is the key test for confirming that a bacteria is Staphylococcus aureus? |
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Definition
| coagulase test: causes clot formation in rabbit or human plasma |
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Term
| How is Staphylcoccus aureus primarily spread? |
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Definition
| by hand to the site of infection (an open wound) |
|
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Term
| What mode of Staphylcoccus aureus infection is common in the community, and what mode is common in hospitals? |
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Definition
| Autoinfection is common in the community, and nosocomial spread is common in hospitals |
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Term
| What is the main way of stopping the spread of hospital-acquired Staphylcoccus aureus infection? |
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Definition
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Term
| What are some toxins/enzymes produced by Staphylcoccus aureus? |
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Definition
- alpha-toxin
- pyrogenic exotoxins
- staphylcoccal enterotoxins
- toxic shock syndrome toxin
- exfoliatins
- coagulase
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|
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Term
| What do Staphylococcal enterotoxins do? |
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Definition
| cause acute vomiting and other GI symptoms within 1-5 hours, but not bloody diarrhea |
|
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Term
| What does Staphylococcus aureus alpha-toxin do? |
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Definition
It is a chromosomally-encoded, low molecular weight protein that causes necrosis or death by causing mammalian cell membranes to leak
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|
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Term
| What do Staphylococcus aureus pyrogenic exotoxins do? |
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Definition
| cause toxic effects at sites remote from site of infection by direct interaction with surface receptors on T lymphocytes to cause cytokine release |
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Term
| Which specific pyrogenic exotoxin has direct toxic effects on endothelial cells? |
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Definition
| TSST-1 (toxic shock syndrome toxin) |
|
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Term
| What do Staphylococcus aureus exfoliatins do? |
|
Definition
- lead to intracellular splitting of the epidermis between the stratum spinosum and stratum granulosum by disruption of intercellular junctions
- causes epithelial desquamation at remote sites of the body => Scalded Skin Syndrome
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Term
| How many Staphylococcus aureus organisms are needed to initiate an infection? |
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Definition
- 105 - 106 at the site of infection
- 102 if a foreign body such as a suture is added
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|
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Term
| What are the clinical aspects of Staphylococcus cellulitis? |
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Definition
| It is infection of skin and soft tissues that alternates between walling off and rapid extension of infection |
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Term
| What causes typical pustular impetigo? |
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Definition
| Staphylococcus aureus alone, or together with group A streptococci (30% of cases) |
|
|
Term
| What is bullous impetigo? |
|
Definition
A highly communicable superficial skin infection that produces blisters
- often seen in infants and children
- spread by contaminated towels
|
|
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Term
| What is a major cause of wound infection? |
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Definition
|
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Term
| Where can S. aureus be isolated from in scalded skin syndrome? |
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Definition
| Not at the remote desquamation sites |
|
|
Term
| How long does it take for staphylococcal food poisoning to cause symptoms? |
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Definition
|
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Term
| How is S. aureus diagnosed in a lab? |
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Definition
- material is aspirated or swabbed from the site of infection
- do a Gram stain, which will show many PMN cells as well as intra- and extra- cellular Gram-positive cocci
- then grow organisms on blood agar plates and confirm using a gram stain and a catalase and coagulase test
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Term
| How are hospitals attempting to limit the spread of MRSA? |
|
Definition
| contact precautions or antibiotic resistance organism (ARO) precautions |
|
|
Term
| What drugs is MRSA resistant to? |
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Definition
| All penicillins and cephalosporins- considered resistant by lab regardless of susceptibility tests because slow expression of resistance causes inaccurate test results |
|
|
Term
| What is the problem with treating community acquired MRSA? |
|
Definition
| oral antibiotic choices for MRSA (the usual outpatient antibiotics) are not as good as IM or IV antibiotics |
|
|
Term
| Why is it difficult to detect MRSA? |
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Definition
| a small percentage of bacteria carry the activated Mec gene for methicillin resistance, so initially the strain may test "sensitive" because of heterogenous expression of resistance |
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Term
| What is the different between VRSA and VISA? |
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Definition
| VISA is harder to detect and has weaker resistance to vancomycin than VRSA (a high and prolonged concentration may have therapeutic effect) |
|
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Term
|
Definition
a variant of VISA composed mostly of vancomycin susceptible bacteria but containing a small percentage of bacteria with intermediate resistance
- makes up 6% of S. aureus strains in hospitals
- hVISA is often missed on routine antibiotic susceptibility tests |
|
|
Term
How is Staphylococcus aureus infection prevented in infants?
|
|
Definition
| The umbilical cord is treated with a triple antimicrobial disinfectant dye after delivery (just washing the cord is not effective) |
|
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Term
| What is the newest government mandated method to get rid of MRSA? |
|
Definition
Screen all high risk persons coming into the hospital using nares swabs plus culture, or PCR
* patients that positive are not treated with systemic antibiotics unless they develop a nosocomial infection |
|
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Term
| Who are high risk patients that should be screened for MRSA? |
|
Definition
- nursing home patients
- prisoners
- past MRSA patients
- patients going into ICU
- patients expecting prolonged stays
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|
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Term
| Where are coagulase negative staphylococci usually found? |
|
Definition
| skin, anterior nares, ear canals, and mucous membranes |
|
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Term
| How can coagulase negative staphylococci become opportunistic pathogens? |
|
Definition
- indwelling plastic and metal devices in seriously ill patients
- immunosuppressed patients
- major surgery involving large areas
|
|
|
Term
|
Definition
| produces extracellular polysaccharide slime (biofilm) that allows it to adhere to indwelling devices and protects it from phagocytosis and antibiotics |
|
|
Term
|
Definition
- 1 million nosocomial infections/yr in the US
- abscesses, prosthetic failure, osteomyelitis |
|
|
Term
| What is Staphylococcus lugdenensis? |
|
Definition
| beta-hemolytic coagulase negative pathogen that occasionally causes very serious infections and abscesses |
|
|
Term
| Which coagulase negative species is responsible for 10-20% of primary urinary tract infections in young women? |
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Definition
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Term
| How can you avoid the difficulty of determining the clinical significance of coagulase negative Staph specimens? |
|
Definition
| collect deep, invasive samples to avoid superficial contaminants (a few colonies are normal in superficially obtained wound specimens) |
|
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Term
| When is coagulase negative Staph considered clinically significant in lab? |
|
Definition
Present in multiple blood cultures.
Intracellular Gram-positive cocci are seen in Gram stain.
Culture shows moderate to heavy numbers on culture plates from wound specimens
(if only the broth culture is positive and all other cultures are negative, then result is likely insignificant) |
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Term
| What is the threshold for clinical significance of catheter infections? |
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Definition
| If 15 or more colonies of coagulase negative staph are found |
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