Gram Positive Bacilli Flashcards
General Characteristics of Corynebacterium
- free living saprophytes (water, soil, air), usual flora of animals and humans
- diphtheriae is the most significant pathogen, others typically only in ICPs
- falcultative, gram-positive, non spore-forming rods, have Babe-Ernst granules
C. diphtheriae Virulence factors
- exotoxin - diphtheria toxin (only produced by some strains), inversely proportional to available iron
- can use IgG to block toxin
Fragments of Corynebacterium diphtheriae
- A: active fragment is cytotoxic, inhibits protein synthesis
- B: binds to specific cell membrane receptors, mediates entry of fragment A
Infections of Corynebacterium diphtheriae
- Respiratory infection, droplets spray, aerosol, or hand-to-mouth contact, unimmunized people are susceptible
- incubation 2-5 days, fever, malaise, sore throat, inflammatory response and tissue necrosis, tough gray-white pseudomembrane
- systemic infection when toxin is absorbed in bloodstream, affects kidneys, heart and nervous system
Treatment of diphtheria
- administer antitoxin, produced in horses
- antiboitics to clear infection, penicillin or erythromycin
- vaccine available
Cutaneous diphtheria
- prevalent in the tropics
- infection occurs at site of abrasion
Culturing diphtheria
- Loeffler’s serum agar: demonstrates pleomorphism and metachromatic granules (Babe-Ernst)
- Cysteine-tellurite blood agar (CTBA): modified Tinsdale media, selective and differential, brown or grayish to black around colonies
Identification of Corynebacterium diphtheriae
- identification by fermentation reactions, urease
- toxigenicity testing: must have toxin, Elek test, PCR
C. amycolatum
most frequently recovered, common on skin, opportunistic, joint infections, endocarditis, sepsis (ICPs)
C. jeikeium
infection from catheters or prosthetic vavles, endocarditis
C. psuedodiphtheriticum
opportunistic, usually endocarditis
C. psuedotuberculosis
contact with sheep, dermonecrotic toxin
C. striatum
rare infections, normal flora
C. ulcerans
mastitis in cattle, contact with animals or unpasteurized milk
C. urealyticum
urinary pathogen, highly urease positive
Characteristics of Coryneform
- speciated if found in normally sterile site, or if it’s the prominent organism of a specimen
- may require urine samples if predominant
Most significant pathogen of Corynebacterium group
C. diphtheriae
Major virulence factor of C. diphtheriae
exotoxin
toxigenic fragments
- A: active fragment, cytotoxic, inhibits protein synthesis
- B: binds to specific cell membrane receptors, mediates the entry of fragment A
C. diphtheriae on Loeffler’s serum agar
metachromatic granules (Babes-Ernst granules)
C. diphtheriae on CTBA
brown to grayish black around colonies
confirm identification of C. diphtheriae
urease from fermentation reactions
toxigenicity testing of C. diphtheriae
Elek test
Major virulence factors of Listeria monocytogenes
- the hemolysin Listeriolysin O (hemolytic and cytotoxic)
- p60 surface protein (induces phagocytosis b/c of increased adhesion to mamalian cells)
Major identifiers of Listeria
- grows at 4C, catalase positive
- umbrella motility at 25C, tumbling motility
transmission of E. rhusiopathiae
occupational exposure (animals like sheep)