Gram Positive Bacteria – Flashcards

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causes 80% suppurative infections

 

2nd leading cause of nosocomial infections

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Staphylococcus Aureus
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staphylococcus aureus colonization (prevalence)
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community: 20-50%

 

healthcare workers: 90%

 

higher in hemodialysis patients

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predominant site(s) of staphylococcus aureus colonization
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#1: anterior nares

 

others: skin, vagina, axilla, perineum, & oropharynx

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most staphylococcus aureus infections result from:
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own strains
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common transmission of staphylococcus aureus

(epidemiology)

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from hands of healthcare provider

 

patient to patient (hospital setting)

 

not seasonal (except warm seasons' prevalence for food poisoning)

;

community: major cause of soft tissue infection

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3 Staphylococcus aureus virulence factors
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1. structural

;

2. enzymes

;

3. toxins

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staphylococcus aureus virulence factors (structural-4)
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1. capsule (inhibit chemotaxis/phagocytosis; adheres to foreign bodies)

;

2. peptidoglycan (inhibit phagocytosis; endotoxin-like)

;

3. teichoic acid (major component of cell wall; mediates attachment to mucosal surface; regulate cationic conc @ cell mem; bind Fn)

;

4. protein A (bind IgG-Fc frag; inhibit opsonization/complement activation)

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Ig bound to protein A elicits...
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cell-mediated response =; pus formation AND necrosis
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Quorum sensing - Staphylococcus aureus virulence factor
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bacteria makes genetic changes due to changes in growth density (different growth phases)

*S. Aureus is a classic example;

;

during initial part of infection, S. aureus growth density is low: bacteria doesn't need to produce toxins, it needs to produce cell surface proteins (ie. Protein A) to establish a colony

*agr locus of S. aureus regulates many of its cell surface proteins (RNA molecule rather than the usual protein gene-expression-regulator)

 

later on, once the infection is established and the organism needs more room, this feature of the bacteria allows it to produce the toxins against the host => degraded host cells serve as bacterial nutrients (tissue damage/disease)

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staphylococcus aureus virulence factors (enzymes-5)
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1. coagulase (fibrinogen --> fibrin)

 

2. catalase (detoxify h202)

 

3. hyaluronidase (hydrolyze HAs (major component of host ECM)=spreading factor)

 

4. lipases (hydrolyze lipids in sebaceous areas of host)

 

5. nucleases (digest DNA/RNA=spreading factor)

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Staphylococcus aureus virulence factor 

(toxins-4)

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1. alpha/beta/delta/gamma & leukocidins

(toxic for: leukocytes, RBCs, platelets, macrophages, & fibroblasts)

 

2. ETA & ETB = serine proteases (digest anchors holding epidermis to dermis)

 

3. TSST-1 (superantigen; systemic effects)

 

4. enterotoxins (A-E) (superantigens; stim T cells/cytokine release/inflamm med by mast cells; incr intestinal peristalsis/fluid loss/vomiting)

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superantigen mechanism (S. aureus virulence)
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activate T cell (binds TCR & MHC II on APC) => no antigen needed

*=> excessive T cell #s (up to 20% of total)

*high cytokine #s (IL-1/TNF/IL-2)

 

=> non-specific immune response (extremely dangerous)

 

 

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catalase/superoxide dismutase mechanism

(S. aureus virulence factor)

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SOD: 02+2H-->02+h202

catalase: h202-->h20+02

*s. aureus breaks down the h202 required by PMN myeloperoxidase to generate more toxic ROIs (to use against bacteria)

 

=> pts w/ chronic granulomatous disease vulnerable to s. aureus & NOT streptococcal infection because catalase-negative organisms are susceptible to the host immune system's use of h202 produced through the bacteria's metabolic processes

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staph infections caused by MRSA (in the US):

1974

1995

2004

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1974: 2%

1995: 22%

2004: 63%

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2 types of staphylococcus aureus caused disease
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1. invasive (cutaneous and non-cutaneous) 

-organism is located w/in the affected areas

 

2. toxigenic

-disease caused by bacterial toxins

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Impetigo
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Bacterial cause: (S. aureus: 80%; S. pyogenes OR mixed: 20%) invasive & cutaneous disease

 

limited to epidermis

 

acute & contagious

 

common in children (face & limb) AND during summer/tropical climates

 

progression:small macule (small discolored spot on skin) --> pustule on erythematous base --> pustule ruptures & is replaced by honey brown crusting

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folliculitis
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most common cause: S. aureus (invasive & cutaneous)

 

superficial & pyogenic infection of hair follicles

 

reduced risk: w/ good skin hygiene

 

 

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furuncle
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most common cause: S. aureus (invasive & cutaneous)

 

boil: several hair follicles & adjacent tissues are affected

 

reduced risk: w/ good skin hygiene

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hordeolum/style
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most common cause: S. aureus (invasive & cutaneous)

 

folliculitis of eyelid

 

erythematous or pustular appearance

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carbuncle
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S. aureus disease: (invasive & cutaneous)

 

coalesced furuncles (more serious disease); extended to deeper subcutaneous tissue (multiple sinus tracts)

 

common locations: nape of neck, upper back, or buttocks

 

progression: tight/erythematic skin --> effaces & releases pus

 

associated symptoms: chills & fever

 

 

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wound infections
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most commonly colonized by gram negative organisms

 

most common gram positive organism: staphylococcus aureus (invasive & cutaneous disease)

 

occurs after surgery/trauma

 

presentation: edema, erythema, pain, accumulation of purulent material

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mastitis
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s. aureus intro into ductal system through cracked nipples (invasive & cutaneous disease)

 

presentation: tenderness, fever, fatigue, possibly aggressive, may require drainage

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bacteremia
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when s. aureus (invasive & non-cutaneous disease) is the cause

 

> 50% acquired after surgery OR from contaminated IV catheter

 

usually from innocuous-appearing skin infections

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endocarditis
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when s. aureus is the cause (invasive & non-cutaneous disease)

*does NOT require any pre-existing damage to heart tissues (as would endocarditis from other causes)

 

life threatening (50% mortality)

 

incr freq of embolization of friable vegetations (=> erythematous lesions in periphery)

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staphylococcal pneumonia
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prevalence: 2% of community pneumonia (*PV leukocidins important role here); 20% nosocomial-pneumonia (15-40% fatality <= those who develop are already ill)

 

cause: aspiration of oral secretions OR hematogenous spread

 

presentation: tissue destruction, massive hemoptysis, septic shock (all due to toxins)

 

remember: streptococcus pneumoniae is the most common cause of bacterial pneumonia

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osteomyelitis
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most common cause: s. aureus (invasive & non-cutaneous disease)

 

cause: hematogenous spread OR extension from subcutaneous infection

 

children: in metaphyseal areas of long bones (from low flow areas => time for bacteria to get out of the circulation)

 

adults: vertebra (rarely in long bones)

 

presentation: sudden onset of localized pain AND high fever

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septic arthritis
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most common cause in most individuals:

s. aureus (however, N. gonorrhoeae (gram-negative coccus) is most common among the sexually active)

 

presentation: pain w/ mvmt, erythematous/swollen joints, pus in aspirated fluid

 

common location(s): knee (50% of cases), wrists, ankles, & hips

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Scalded Skin Syndrome (Ritter's disease)
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caused by: exfoliative toxins A ; B (s. aureus-toxigenic disease) break desmoglein-1 (polypeptide) in desmosome (connect adjacent skin cells)

*stratum granulosum is susceptible be/c it lacks the Dsg-3 (polypeptide) that usually compensates for ETA/ETB hydrolysis of Dsg-1 in other strata

;

presentation/progression: abrupt onset of perioral erythema (covers entire body in 2 d) --> large bullae/cutaneous blisters (like burns) --> desquamation (in 5-7 d) --> blisters (2 wks) & positive nikolsky's sign

 

*blisters do NOT contain organism

 

 

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positive nikolsky's sign
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pressure displaces the skin
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bullous impetigo
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localized SSSS

 

infection, NOT toxigenic => bacteria will be present w/in blister fluid

 

presentation: erythema does not extend beyond blister borders

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toxic shock syndrome
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cause: enterotoxin or enterotoxin-like TSST-1

*in menstruation-associated TSS cases: >90% caused by TSST-1

 

mechanism: TSST-1 strains multiply in hyper-absorbant tampons 

 

presentation: abrupt (fever, hT, whole-body-erythematous rash); multiple organs involved; entire skin desquamates (2-3 wks); markedly red tongue

 

fatality: previously high, currently 5%

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food poisoning
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most common cause of food borne illness: staphylococcus aureus (50% strains produce 8 distinct enterotoxins)

*heat stable (produced by bact in food @ RT, stable in re-heating)

 

superantigen mechanism? (not well understood)

 

presentation: severe vomiting (w/in 3-4 hrs)

*toxin w/in vomitus (bacteria absent)

 

therapy: fluid replacement NOT antibiotic (be/c this in an intoxication NOT an infection)

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antibiotic associated enterocolitis
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most common cause: Clostridium difficile 

2nd: staphylococcus aureus (produce ETA & leukotoxin E/D)

 

presentation: watery diarrhea, abdominal cramps, fever, inflammation of intestinal mucous membrane (bacteria present in stool)

 

increased risk: w/ use of broad spectrum antibiotics

 

 

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s. aureus ID

 

abscess (scrape the base)

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fewer organisms in pus

 

gram stains: gram positive cocci

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s. aureus ID

 

bacteremia 

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good: culturing blood

 

bad: staining blood (so few organisms)

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s. aureus ID

 

ssss

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good: look at nasopharyngeal sample

 

bad: looking at blister fluid (usually not here!)

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s. aureus id

 

bullous impetigo

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:) looking in blister fluid (bacteria found here!)
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s. aureus id

 

tss

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check vaginal samples, bacteria will be there

 

bacteria will NOT be in blood :(

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s aureus id

 

food poisoning

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:) bacteria in food/toxin in vomitus

 

:( bacteria NOT in feces/vomitus

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s aureus id

 

blood agar

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hemolytic and golden yellow colonies
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s aureus id

 

tellurite-glycine agar

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positive: s aureus changes color --> black

 

glycine inhibits growth of species OTHER than staph

 

differential due to tellurite reduction to tellurium

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staphylococcus epidermidis 

 

"CNS" or "CONS"

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Coagulase Negative Staphylococcus
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staphylococcus epidermidis virulence factors

 (3)

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1. NO protein A, alpha-toxin, or coagulase (s epidermidis is often drug resistant)

 

2. teichoic acid (glycerol teichoic acid & glucosyl residues)

 

3. slime (facilitate adherence to catheters; forms protective biofilm; interferes w/ PMN phagocytosis)

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What organism is this?

 

gram positive coccus

 

coagulase positive

 

catalase positive

 

grape-like clusters

 

tellurite-glycine/mannitol-salt agar positive

 

blood agar: golden-yellow colonies exhibiting hemolysis

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staphylococcus aureus
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staphylococcus epidermidis diseases (2)
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1. major cause of infections associated w/ intravascular devices (ie. prosthetic heart valves, shunts, etc.); also in prosthetic joints, large wounds, and catheter induced UTIs

 

2. high incidence in hospital setting (contaminates pt care equipment/environmental surf w/ biofilm)

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prosthetic valve endocarditis
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due to s. epidermidis (high mortality rate ~60%)

 

location of vegetations: prosthesis-tissue junction @ sewing ring (bacteria cannot grow on inert material of the prostheses)

 

complications: sepsis, embolization, congestive heart failure, cardiac rupture, etc.

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staphylococcus epidermidis identification
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gram positive coccus

 

catalase positive

 

coagulase negative

 

blood agar: white non-hemolytic colonies

 

mannitol-salt/tellurite-glycine agar negative

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staphylococcus saprophyticus virulence factor
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not known

 

can colonize periurethral skin & mucosa

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staphylococcus saprophyticus diseases
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cystitis (inflammed bladder)

pyelonephritis

*commonly present w/ dysuria and/or pyuria

 

bacterial UTI in sexually active women (7-20%)

*E. coli the most common cause

 

side note: commonly drug resistant

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identify staphylococcus saprophyticus
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NOVOBIOCIN-RESISTANT

 

gram positive coccus

 

blood agar: white colonies

 

catalase positive

 

coagulase negative

 

mannitol-salt agar test negative (cannot ferment mannitol)

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other staphylococci (2)

 

and their associated diseases

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staphylococcus haemolyticus

 

staphylococcus capitis

 

endocarditis, UTIs, wound infections, opportunistic infections

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[image]
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staphylococcus saprophyticus is noboviocin resistant
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[image]
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osteomyelitis

 

acute form most commonly caused by staphylococcus aureus

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[image]
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septic arthritis

 

most common cause, generally: staphylococcus aureus

most common cause, among sexually active: neisseria gonorrhoeae

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[image]
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catalase positive: staphylococcus species

 

catalase negative: streptococcus & enterococcus species

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[image]
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mannitol salt agar

 

growth selective for staphylococcus <= high salt

test differential for S. aureus <= mannitol fermentation indicated by color change (positive result = orange/yellow)

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[image]
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tellurite-glycine agar

 

growth selective for staphylococcus <= normal flora growth inhibited by glycine

 

test differential for S. aureus <= tellurite reduction to tellurium (indicated by color change: positive result = black)

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[image]
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coagulase test (ONLY staphylococcus aureus is coagulase+)

 

positive result: w/ incubation in plasma, S. aureus => coagulation

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