Nelson - Ch. 181 Staphylococcus Flashcards by CM A

MCC of pyogenic infection of the skin and soft tissues

S. aureus

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___ of staph interacts with fibrinogen to cause large clumps of organisms, interfering with phagocytosis

Clumping factor and/or coagulase

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Produced by staph; may have an important role in localization of infection by forming an abscess

Coagulase

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Staph: Reacts specifically with immunoglobulin G; located on the outermost coat of the cell wall; can absorb serum Ig preventing antibacterial antibodies from acting as opsonins and thus inhibiting phagocytosis

Protein A

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Staph: Promotes intracellular survival

Catalase

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Staph: Associated with skin infection

Lipase

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A protein that S. aureus combines with phospholipids in the leukocytic cell membrane, producing increased permeability and eventual death of the cell

Panton-Valentine leukocidin

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Strains of S. aureus that produce ___ are associated with more severe and invasive skin disease, pneumonia, and osteomyelitis

Panton-Valentine leukocidin

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Staph: Serologically distinct proteins that produce localized or generalized dermatologic manifestations by producing skin separation

Exfoliatins A and B

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Staph: Exfoliatins produce skin separation by

1) Splitting desmosome 2) Altering the intracellular matrix in the stratum granulosum

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Staph: Ingestion of ___ can result in food poisoning

Preformed enterotoxin, particularly types A or B

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Staph: By ___ years old, almost all individuals have antibodies to at least 1 enterotoxin

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Staph: A super antigen that induces production of interleukin-1 and tumor necrosis factor, resulting in hypotension, fever, and multi system involvement

TSST-1

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Staph: Associated with non-menstrual TSS

Enterotoxins A and B

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Staph: Mediates adhesion to mucosal cell proteins that promote adhesion to fibrinogen, fibronectin, collagen, and the human proteins

Teichoic acid

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Staph: Production of ___ in the bacterial cell wall mediates resistance to penicillinase resistant antibiotics

Penicillin binding proteins (PBP)

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Responsible for the methicillin resistance of MRSA isolates

Altered PBP-2A

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T/F Skin infections caused by S. aureus are considerably more prevalent among persons living in low socioeconomic circumstances

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Most significant risk factors for development of staph infection

1) Disruption of intact skin 2) VPS 3) Indwelling intravascular or intrathecal catheters

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Reason why patients with HIV have higher risk for developing staph infection

Neutrophils that are defective in their ability to kill S.aureus

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T/F Infants may acquire type-specific humoral immunity to staphylococci transplacentally

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T/F Antibody to the various S. aureus toxins appears to protect against those specific toxin-mediated diseases, but humoral immunity does not necessarily protect against focal or disseminated S. aureus infection with the same organisms.

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T/F Staph most commonly affects the skin

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T/F Infections of the upper respiratory tract (otitis media, sinusitis) caused by S. aureus are rare

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Most common cause of osteomyelitis and suppurative arthritis in children

S. aureus

T/F Meningitis caused by S. aureus is not common

T/F S. aureus is a common cause of acute endocarditis on prosthetic valves

F, native valves

T/F S. aureus is a common cause of renal and perinephric abscess

T/F S. aureus is a common cause of pyelonephritis

The principal cause of TSS

S. aureus

Food poisoning caused by staph enterotoxin manifests approx ___ hrs after toxin ingestion

2-7

Fever associated with staph food poisoning is characteristically

Absent or low

T/F Symptoms associated with staph food poisoning usually persists longer than 12-24 hrs

F, rarely

T/F In suspected staph infection, cellulitic lesions are ideally cultured using injected saline and targeting the leading edge

F, using a needle aspirate from the most inflamed area

T/F Compared to that of Staph, skin lesions caused by Group A strep spread more rapidly and can be very aggressive

Staphylococcus pneumonia is often suspected on the basis of chest roentgenograms that reveal

Pneumatoceles, pyopneumothorax, or lung abscess

Other than staph, 2 other etiologies of cavitary pneumonias include

1) K. pneumoniae 2) M. tuberculosis

In bone and joint infections, ___ is the only reliable way to differentiate S. aureus from other less-common etiologies

Culture

For most patients with serious S. aureus infections, IV treatment is recommended until

Patient has become afebrile and other signs of infection have improved

Choices as initial treatment for serious infections thought to be caused by MSSA

1) Semisynthetic penicillin 2) first-gen cephalosporin

Penicillin and ampicillin are not appropriate for MSSA because

>90% of staph are resistant to these agents

T/F Addition of a beta lactamase inhibitor to a penicillin-based drug improves its effect against MRSA

Inducible Clindamycin resistance in isolates initially reported as susceptible must be ruled out by ___ or molecular methods

D test

T/F Clindamycin is bacteriostatic and should not be used to treat endocarditis, brain abscess, or meningitis caused by S. aureus

T/F MRSA is resistant to carbapenems and unreliably susceptible to quinolones

___ or ___ may be added to a beta lactam or vancomycin for synergy in serious infections such as endocarditis, particularly when prosthetic valve material is involved

Rifampin, Gentamicin

Despite in vitro susceptibility of S. aureus to ___, these agents should not be used in serious staph infections because their use is associated with rapid development of resistance

Cipro and other quinolones

DOC: Initial empiric therapy for life threatening MRSA infections

Vancomycin (15) q6 + Nafcillin or Oxacillin

DOC: Initial empiric therapy for non life threatening infection when rates of MRSA infection in the community are substantial

Vancomycin (15) q8

DOC: Initial empiric therapy for non life threatening infection when rates of MRSA infection in the community are substantial and prevalence of clindamycin resistance is low

Clindamycin

DOC: MSSA

Nafcillin or Oxacillin

DOC: MRSA

Vanco+Genta

DOC: Community, not multi drug-resistant for life threatening infections

Vanco+Genta

___ is the most effective measure for preventing the spread of staph from 1 individual to another

Strict attention to hand washing techniques

Use of hand wash containing ___ is recommended

Chlorhexidine or alcohol

T/F Food poisoning may be prevented by excluding individuals with S.aureus infections of the skin from preparation and handling food

T/F Most strains of S. aureus associated with TSS are methicillin susceptible

Mechanism of TSST-1 and enterotoxins that cause TSS

They act as superantigens, which trigger cytokine release causing massive loss of fluid from the intravascular space and end-organ cellular injury

Toxins that cause TSS are selectively produced in a clinical environment consisting of

1) Neutral pH 2) High pCO2 3) Aerobic pO2

Approx ___% of adults have antibody to TSST-1 without a history of clinical TSS

90%

Recovery from TSS occurs within ___

7-10 days

Major criteria for toxic shock syndrome (All Required)

1) Acute fever; temp >38.8C 2) Hypotension 3) Rash

Minor criteria for TSS (any 3 or more required)

1) Mucous membrane inflammation 2) Vomiting, diarrhea 3) Liver abnormalities 4) Renal abnormalities 5) Muscle abnormalities 6) CNS abnormalities 7) Thrombocytopenia

Exclusionary criteria for TSS

1) Absence of another explanation 2) Negative blood cultures

Recommended antibiotic therapy for TSS

b-lactamase resistant antistaphylococcal antibiotic plus clindamycin

TSS is most commonly caused by

MSSA

In order to prevent TSS, changing tampons at least every ___ is recommended

8 hours

CoNS: Common cause of UTI in sexually active females

S. saprophyticus

CoNS produce ___ that surrounds the organism and may enhance adhesion to foreign surfaces, resist phagocytosis, and impart penetration of antibiotics.

Exopolysaccharide protective biofilm or slime layer

Risk factors for development of CoNS infection

1) Presence of medical device (most significant) 2) Immature or immunocompromised immunity 3) Significant exposure to antibiotics

MCC of nosocomial bacteremia

CoNS, specifically S. epidermidis

T/F CoNS are a rare cause of acute endocarditis on native valves

T/F CoNS are a common cause of acute endocarditis on native valves

F, prosthetic

MC pathogen that causes central venous catheter infection

S. epidermidis (owing partly to its high rate of cutaneous colonization)

MC pathogen associated with CSF shunt meningiits

CoNS (introduced at the time of surgery)

Most CSF shunt meningitis occur within ___ after surgery

2 months

True bacteremia should be suspected if blood cultures grow within

rapidly, within 24hr

T/F No blood culture that is positive for CoNS in a neonate or patient with intravascular catheter should be considered contaminated without a careful assessment

T/F Before initiating presumptive antimicrobial therapy in patients that grow CoNS, it is always prudent to draw 2 separate blood cultures to facilitate subsequent interpretation

T/F Most CoNS are resistant to methicillin

___ is the drug of choice for methicillin resistant CoNS

Vancomycin

The addition of ___ to vancomycin for the treatment of CoNS may increase antimicrobial efficacy

Rifampin

A trial of ___ is indicated to attempt to preserve the use of central line as long as systemic manifestations of infection are not severe

IV Vancomycin

May increase the likelihood of curing CoNS line sepsis without line removal

1) Antibiotic therapy given through an infected central venous catheter (alternating lumens if multiple) 2) Use of antibiotic locks

T/F Peritonitis caused by S. epidermidis in patients on CAPD is an infection that may be treated with IV or intraperitoneal antibiotics WITHOUT removing the dialysis catheter

Unlike most CoNS, ___ is usually methicillin susceptible

S. saprophyticus

UTI caused by S. saprophyticus can usually be treated with

1) 1st gen cephalosporin 2) CoAmox 3) TMP-SMX

Poor prognosis with CoNS infection is associated with

1) Malignancy 2) Neutropenia 3) Infected prosthetic or native heart valves