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)
identification of E. rhusiopathiae
catalase negative and TSI positive (H2S production)
identification of Arcanobacterium
catalase negative, narrow zone of beta hemolysis, produces black dot under colonies
Nocardia
aerobic, weakly acid-fast, gram-variable, morphologically resemble fungi
N. cyriaciageorgica and N. farcinica
cause confluent bronchopneumonia, no sulfur granules
N. braziliensis
causes actinomycotic mycetomas (cutaneous infection), sulfur granules present
Actinomadura
colonies can be red, resemble Nocardia but non-acid-fast
have a molar tooth appearance after 2 week incubation
Rhodococcus
salmon-pink colonies, zig-zag growth
Streptomyces
smell woodsy w/ waxy, heaped colonies
Bacillus anthracis
- agent of anthrax, nonhemolytic on SBA
- identification: nonhemolytic on SBA, medusa head or egg whites, non-motile, produces lecithinase, string of pearls morphology
Virulence factors of Bacillus anthracis
protein exotoxin (EF, LF and PA)
Infections cause by Bacillus anthracis
most are cutaneous, pulmonary infection (“woolsorter’s disease”), GI anthrax, Injectional anthrax
Bacillus cereus
motile (flagella), hemolysin positive
Rothia dentocariosa
- normal oral flora
- bacteremia, endocarditis, wound infection, eye infection
- gram-positive, non spore forming rods
- found in nature, can be in produce, dairy, processed meat
characteristics of Listeria monocytogenes
Listeriolysin O (hemolytic and cytotoxic), phospholipase C, catalase, superoxide dismutase, surface protein p60
virulence factors of Listeria monocytogenes
- adults: penetration of the intestine
- ICP/elderly: septicemia, meningitis, endocarditis
- Pregnant women: premature labor, spontaneous abortion
- newborn: meningitis
infections of L. monocytogenes
- grow at cold temperature, catalase positive
- hippurate hydrolysis negative
- umbrella motility at 25C, tumbling motility
- CAMP test block
identification of L. monocytogenes
- ampicillin or penicillin G
- TMP-SMZ (sulfa drugs) if penicillin allergy
treatment of L. monocytogenes
- gram-positive, non spore forming
- in nature worldwide, found in animals
- infection through occupational exposure (hands/fingers, self-limiting)
E. rhusiopathiae characteristics
- cell surface antigens, endothelial cell adherence
- enzymes
E. rhusiopathiae virulence factors
- catalase negative, TSI positive (H2S)
- requires CO2, SBA or CA, alpha hemolysis
E. rhusiopathiae identification
pharyngitis, cellulitis
Infections of arcanobacterium
- low virulence
- catalase negative, narrow beta hemolysis
- black dot under colony
- treat with erythromycin
arcanobacterium
- stains gram-variable
- causes bacterial vaginosis, observe clue cells, treat with clindamycin
- use human blood bilayer tween agar
Gardnerella vaginalis
- aerobic, weakly acid-fast, gram-variable
- morphologically resemble fungi
- found in the environment, affect ICPs
Nocardia
- bronchopneumonia, no sulfur granules
- high mortality rate
N. cyriaciageorgica and N. farcinica
- cutaneous infection
- sulfur granules
N. braziliensis
- wet mounts, branching filaments
- parafin bait test, substrate hydrolysis/utilization
- antimicrobial susceptibility
identification of Nocardia
treatment of Nocardia
resistant to penicillin, susceptible to sulfnoamides
red colony, molar tooth appearance, non acid-fast
actinomadura
zig-zag growth, salmon-pink colony
Rhodococcus
- waxy, heaped colonies
- smell woodsy, branching with chains and spores
Streptomyces
- found in livestock, acquired by contamination of food or a wound
- large spore-forming bacilli, nonhemolytic
Bacillus anthracis
- polypeptide capsule
- potent exotoxin (edema factor, lethal factor, protective antigen)
virulence factors of B. anthracis
- cutaneous (black eschar)
- respiratory (woolsorter’s disease)
- GI infection
- injectable infection
infections of B. anthracis
nonhemolytic, medusa head or beaten eggwhites, nonmotile, produces lecithinase, string of pearls when exposed to penicillin
identification of B. anthracis
treatment of B. anthracis
most susceptible to penicillin
Food poisoning (diarrheal syndrome, emetic form), infections of the eye, septicemia, meningitis, etc.
infections of B. cereus
- exotoxin (enterotoxin), pyogenic toxin
- spores, enzymes, beta-lactamase
virulence factors of B. cereus
aerobic, beta hemolytic, motile, spores, hemolysin positive
identification of B. cereus
treatment for B. cereus
vancomycin (eye infection), clindamycin and gentamycin combo
