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Gram Positive Bacteria
Catalase Negative: Streptococcus & Enterococcus
58
Microbiology
Graduate
03/26/2011

Additional Microbiology Flashcards

 


 

Cards

Term
capnophilic
Definition
co2 loving
Term
streptococcus general characteristics
Definition

gram positive coccus (pairs or chains)

 

facultative anaerobes

 

capnophilic

 

fastidious (complex nutritional requirements)

Term
streptococcus species differentiation methods (3)
Definition

1. serologic properties (lancefield groupings: A-W)

 

2. hemolysis (alpha-partial; beta-complete; gamma-absent)

 

3. biochemical & physiological properties

Term
streptococcus: group A (GAS)
Definition

group A antigen in cell wall (plus other additional type-specific (M & T) antigens)

 

PYR positive

 

catalase negative

 

bacitracin susceptible

 

beta hemolytic

 

associated w/ pyogenic (pus generating) infections

Term

streptococcus pyogenes:

colonization & transmission

Definition

asymptomatic URT colonization; transient skin colonization

 

person --> person via respiratory droplets

incr risk: crowding in daycare/classrooms

 

"flesh-eating bacteria"

Term
at risk patients for streptococcus pyogenes infection
Definition

pharyngitis: 5-15 yoa; winter (RF/AGN)

pyoderma: 2-5 yoa (w/ poor hygiene); summer

 

TSS: pts w/ soft tissue infection & bacteremia

 

 

Term
streptococcus pyogenes virulence factors (5)
Definition

1. capsule (antiphagocytic)

 

2. LTA (binds epithelial cells ~60% of adhesion)

 

3. M protein (adhesion; antiphagocytic; degrades C3b)

 

4. M-like protein (bind IgG & IgM; antiphagocytic)

 

5. F protein (mediate adhering to epithelial cells & internalization)

Term
streptococcus pyogenes: M proteins (virulence factor)
Definition

most important virulence factor for GAS infection

 

>120 serotypes (some w/ epitopes similar to heart tissue proteins)

 

structure: fibrillar (anchored in cell wall --> surface --> binds plasma fibrinogen => prevent complement activation/opsonization)

 

sequence: constant proximally, variable distally

*PCR/sequencing of variable region used to serotype

 

M antibody (only for particular serotype): may overcome phagocytic resistance

Term
types of GAS infections (2)
Definition

1. suppurrative

pharyngitis, scarlet fever, pyoderma, erysipeias, cellulitis, necrotizing fasciitis, streptococcal toxic shock syndrome

2. non-suppurrative

rheumatic fever & acute glomerulonephritis

Term
pharyngitis (strep throat)
Definition

common age groups: 5-15 (20-40% of cases)

 

transmission: respiratory droplets & close contact (esp winter)

 

progression: 1-4 d incubation --> sore throat; fever; chills; malaise

 

suppurative complications: peritonsillar OR retropharyngeal abscess *rare w/ early antibiotic treatment

 

non-supp complications: RF & AGN

 

diagnosis: rapid strep test + culture

*collecting sample: rub swab over both tonsillar pillars

Term
scarlet fever (most characteristics of disease)
Definition

streptococcus pyogenes disease (erythrogenic toxin encoded by lysogenic)

cause: streptococcal pyrogenic exotoxins A, B, & C

(toxins spreads via blood --> localizes in skin => diffuse erythematous rash)

 

progression: initially, rash on upper chest & tongue is furred --> later, tongue is white/red/strawberry --> rash to extremities (esp abdomen & skin folds) --> rash disappears (5-7 d) --> desquamation

*rash rarely on perioral, palm, & sole areas; suppuration rare

 

Term
what is important about the scarlet fever rash?
Definition

it is generally not serious except that it signals a harmful S. pyogenes infection AND is evidence that a hypersensitivity reaction is occurring (requires prior toxin exposure)

 

*scarlet fever currently rare (unknown) however toxin producing GAS still prevalent

Term
most common bacterial infection causing impetigo/pyoderma
Definition

1. staphylococcus aureus (perhaps due to penicillin resistance)

 

2. streptococcus pyogenes

*skin colonization w/ GAS (minor trauma) precedes clinical infection

Term
cellulitis vs erysipelas
Definition

similarities: local signs of inflammation (warmth, erythema, & pain); fever; lymphangitis; lymphadenitis *streptococcus pyogenes

differences: 

cellulitis - infection of skin/subcut tissue <= traumatic/surgical wound/insect bite; no apparent entry site

erysipelas - a form of cellulitis; more erythema/elevation; malar area of face => butterfly rash

Term
necrotizing fasciitis (NF)
Definition

hemolytic streptococcal gangrene (streptococcus pyogenes) *GAS infection ~60% NF cases

 

affected areas: superficial and/or deep fascia

 

progression: like cellulitis --> bullaes gangrene; systemic signs (extensive necrosis, obstructed blood supply, inflam fluid along fascial lines)

 

treatment: extensive debridement & antibiotic treatment

Term
streptococcal toxic shock syndrome
Definition

*seen in bacteremic pts w/ GAS

 

cause: streptococcal toxins (superantigens)

 

presentation: like StaphTTS (fever, malaise, hT, multiple organ failure)

 

diagnostic criteria existis to differentiate bt/w staph and GAS TSS (created in 1993)

Term
name the two post infection complications of GAS disease - when do they occur?
Definition

1. acute rheumatic fever/rheumatic heart disease (RF/RHD)

 

2. acute glomerulonephritis (AGN)

 

*1-3 wks after acute illness

Term
what are ARF & RHD, describe its epidemiology, w/ which GAS disease is it associated?
Definition

*nearly ONLY after URT infection (pharyngitis- SLO not inactivated in pharynx => antibody response)

 

multisystem disease (autoimmune rxn to GAS)

all symptoms resolve EXCEPT cardiac valvular dmg (in RHD)

 

more common location: under-developed/developing countries

Term
mechanism/presentation/tx/dx of ARF/RHD
Definition

rheumatogenic GAS: encapsulated; rich in immunogenic M proteins (many epitopes are similar to human tissue proteins) 

human ex. myosin, tropomyosin, laminin, actin, keratin

*anti-M IgG cross react w/ heart proteins => pancarditis

 

ARF presentation: subcut nodules/arthralgia --> arthritis

 

tx: antibiotic phrophylaxis (to prevent subseq GAS infect) 

dx: evidence of recent GAS infection; modified Jones Criteria; anti-SLO for RF

Term
AGN: w/ which GAS disease does it associate? dx? recurrence? tx? mechanism? presentation?
Definition

pharyngitis AND skin infections (streptolysin O inactivated in skin => NO antibody response

dx: anti-DNaseB for AGN

 

recurrence unlikely, as only 4-5 M strains => AGN

therefore, do NOT use antibiotic prophylaxis (will not likely be necessary to prevent subseq infe)

 

mechanism: Ag-Ab-complement complexes on glomerular basement membrane --> glom cap filled w/ monocytes & PMN

 

presentation: acute inflamm, HT, hematuria, proteinuria, etc.

Term
how to culture for streptococcus pyogenes?
Definition
culture w/ sulfamethoxazole-trimethoprim to inhibit normal flora
Term
how to identify streptococcus pyogenes?
Definition

PYR test positive (pyogenes is the only streptococci to => positive result)

 

optochin resistant (P disk)

 

bacitracin sensitive (A disk)

Term
gram stain of all cocci
Definition
gram positive
Term
staphylococcus agalactiae: group, characteristics, epidemiology, & virulence factors
Definition

GBS

 

gram+, facultative, beta-hemolytic, long chains

 

normal flora of GIT/GUT

mothers-->babies<--other babies

women w/ genital colonization: higher risk for postpartum sepsis

 

virulence: undefined (capsule, PG, DNases, hyaluronidase, hemolysins)

 

Term

some diseases that can be caused by streptococcus agalactiae:

men and non-pregnanat women

Definition

bacteremia, pneumonia, bone/skin/soft tissue infections

 

higher risk: older; pts w/ debilitating underlying disease

Term
which group of streptococcus causes more serious infections?
Definition
GAS, not GBS
Term

diseases caused by streptococcus agalactiae:

pregnant women

Definition

UTI: during/immediately following pregnancy

 

endometritis: after delivery

 

chorioamnionitis: w/ heavy 2nd trimester colonization

 

puerperal sepsis (rare serious septicemia in pregnant mother): during/shortly after childbirth; starts w/ puerperal fever

Term
early onset neonatal disease (streptococcus agalactiae)
Definition

mortality rates now decr (5%)

 

15-30% of survivors from meningitis have lasting complications (eg. blindness, deafness)

 

 

Term
most common cause of meningitis in neonates
Definition
streptococcus agalactiae
Term
pathogenesis of S. agalactiae disease in newborns
Definition

time of acquisition => early or late onset

(happens @ time of birth OR w/ aspiration of infected amniotic fluid)

 

newborns have few alveolar macrophages, poor PMN chemotaxis/phagocytosis

 

bacterial cell wall components => sepsis (systemic hT, hypoxia)

Term
late onset neonatal disease (streptococcus agalactiae)
Definition

> 7 d after birth

 

transmission: from infected mother or nosocomial

 

characterized by: bacteremia w/ meningitis; high survival rate; neurologic sequelae

Term
identifying features of streptococcus agalactiae
Definition

large buttery, beta-hemolytic colonies on blood agar

 

gram+, catalase-, bacitracin-resistant, CAMP test+

 

sodium hippurate+ (does hydrolyze)

 

bile esculin- (does NOT hydrolyze)

Term
[image]
Definition
pharyngitis late stage
Term
[image]
Definition
pharyngitis early stage
Term
[image]
Definition
scarlet fever tongue
Term
[image]
Definition
streptococcus pneumoniae is sensitive to optochin (ONLY strep that is NOT resistant)
Term
[image]
Definition

streptococcus agalactiae is the ONLY streptococcus w/ positive CAMP test (note the enhanced zone of hemolysis)

 

CAMP factor is a phospholipase => synergistic hemolysis w/ beta-lysin from certain S. aureus

Term
[image]
Definition
erysipelas
Term
[image]
Definition

streptococcus pneumoniae capnophilic, mucoid (capsule producing) colonies on blood agar

 

alpha-hemolysis

Term
[image]
Definition
impetigo
Term
[image]
Definition
necrotizing fasciitis
Term
[image]
Definition
pneumococcal pneumonia presenting w/ lobar consolidation
Term
[image]
Definition
scarlet fever rash
Term
characteristics of viridans streptococci
Definition

gram+, catalase-, produce green pigment on blood agar, optochin resistant 

 

*streptococcus pneumoniae is the ONLY optochin sensitive viridans streptococcus

 

most prevalent: oral cavity

 

=> life-threatening diseases: subacute endocarditis, meningitis, pneumonia

Term
growth requirements of streptococcus pneumoniae
Definition

fastidious and facultative (requires blood or serum)

 

enhanced w/ CO2

Term
identification of streptococcus pneumoniae
Definition

alpha hemolysis on blood agar

 

bile salt susceptible

Term
how are most streptococcus pneumoniae infections caused?
Definition

endogenous (URT --> middle ear, sinuses, meninges, lungs, & blood)

 

infections from new strains (resp droplets/fomites) are rare

Term
six virulence factors of streptococcus pneumoniae
Definition

1. PspA (protect from host's complements)

 

2. hyaluronate lyase (surf protein acts on ECM; incr tissue perm, essential for virulence in pneumon, bacteremia, & meningitis)

 

3. neuaminidase (cleaves sialic acid from cell surf glycans; change glycosylation & expose host surf (by incr receptors)

 

4. capsule *primary VF-those w/o are harmless (inhib phago/complement activation)

 

5. proteases (degrade SIgA => enhance oral/intestinal mucosal infections)

 

6. pneumolysin (Ply) those w/o are less harmful (binds cholesterol of ciliated bronchial epithelia/phagocytes => pores => edema; hemorrhage; bacterial growth; penetration via epithel --> interstitium/blood

Term
most common cause of otitis media
Definition
streptococcus pneumoniae
Term
most common cause of community pneumonia
Definition
streptococcus pneumoniae
Term
pneumonia: presentation & cause
Definition

streptococcus pneumonia don't produce sig proteases

 

presentation: lobar consolidation (seldom destroy parenchyma); often preceded by viral illness; acute onset of high fever; rigors common; productive cough; pleural pain, dyspnea, tachypnea, tachycardia, sweats, malaise

 

sputum (rusty-from blood leaking out of capillaries) + for: PMN & lancet shaped diplococci

Term
most common cause of bacterial sinusitis
Definition

streptococcus pneumoniae

 

most sinusitis has viral origin, but acute sinusitis is usually bacterial

 

presentation: facial pain, headache, tenderness, fever, nasal discharge

Term
most common agent of bacterial meningitis of childhood and adulthood
Definition

streptococcus pneumoniae

 

predisposing conditions: pneumonia, otitis media

 

>4-20xs fatal/severe neurologic defects than meningitis by other bacteria

Term
enterococcus characteristics/identifying features
Definition

> 35 species, most common E. faecalis & faecium

 

gram+ coccus (pairs and short chains), more ovate than streptococci

 

facultative

high salt/bile/heat stress tolerant

optochin resistant

large white colonies on blood agar 

usually non-hemolytic

Term
enterococcus epidemiology
Definition

enteric

present in human/animal feces/lg intestine/GUT

 

MOST infections: endogenous

nosocomial: due to cross infection

Term
enterococcus virulence factors
Definition

not well defined

 

antibiotic resistance

Term
diseases commonly caused by enterococcus
Definition

*UTI (less common than E. coli)

presentation: dysuria & pyuria

higher risk: w/ indwelling catheter OR use of broad-spectrum antibiotics

 

*Peritonitis

presentation: typically acutely ill; febrile; abdominal swelling/tenderness after abdominal trauma/surgery

 

~Endocarditis (occasionally)

associated w/: persistent bacteremia (acute or chronically)

Term
anaerobic cocci
Definition

Peptostreptococcus

 

part of normal flora, infections due to spread of these organisms to normally sterile places

colonizations: oral cavity, GIT, GUT, & skin

 

usually susceptible to penicillin; metronidazole; imipenem; & chloramphenicol

 

dx: presence of anaerobic coccus assoc w/ infection

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