Module 3 Flashcards
What are the common characteristics of Corynebacterium?
Gram pos rods
Non spore forming
Aerobic or facultative
Catalase pos
Motility neg
What is the major human pathogen in Corynebacterium?
C. diphtheriae
What are the what are the cellular characteristics of C. diphtheriae?
Gram pos rods, club like shape, volutin granules
How can volutin granules be better visualized?
Loeffler’s alkaline methylene blue or Albert’s stain
Deep blue purple colour
What are the growth requirements for C. diphtheriae?
Facultative anaerobes
CO2 not required
35°C optimum
Better growth with blood or serum enrichment
Where are most C. diphtheriae specimens isolated from?
Cutaneous or upper respiratory sources
What media is used to prevent the growth of normal flora when isolating C. diphtheriae?
Potassium tellurite agar- growth reduces tellurite, producing gun metal grey colonies, Staph may also grow
Cysteine tellurite agar- inhibitory to most other organisms
Modified tinsdale medium- differentiates dips from C. diphtheriae (black colonies with brown halo)
What special requirements does modified tinsdale medium require?
Halo formation is enhanced by reduced oxygen and stabbing the inoculum into the agar
Shouldn’t be incubated in increased CO2
May require 48hr incubation
Short shelf life, constant QC required
What is the colony morphology of C. diphtheriae?
BAP- white/grey, dull, may be granular (volutin), usually nonhemolytic
Tinsdale- grey/black with brown halos, garlic odour, may be able to differentiate bio types (intermechin, gracias, mitis)
Broth culture- brittle surface growth
What is the genus ID for Corynebacterium?
Gram pos rods
Opaque dull colonies on BAP
Growth on tellurite
Volutin granules
Cat pos
Nonmotile
What is the species ID for C. diphtheriae?
Biochem testing
Urease neg
Ferments glucose, maltose, sucrose
What is the urease reaction of C. ulcerans and psuedotuberculosis?
Positive
What is the Elek test?
Tests for toxin produced by C. diphtheriae
Gel precipitation where toxin combines with antitoxin
What is the pathogenicity of C diphtheriae?
Only infects humans
Droplet transmission
1-7 days of incubation
Pharynx is usual infection site- toxin causes necrosis, swollen cervical lymph nodes, pseudomembrane
Toxin action- myocardial degeneration, neurological systems, 20% of cases
Cutaneous infections
Most isolated from carriers
Prevention by immunization (DPT)
What is the treatment of C. diphtheriae?
Antimicrobial susceptibility testing on all isolates
No resistance
Antitoxin given ASAP
What are the characteristics of dips?
Normal flora of skin and mucous membranes
Short club shaped gram pos rods
BAP- full, opaque, grey/white, nonhemolytic
Tellurite- grey/black with no brown halos
Catalase pos
What is the species ID for dips?
Normal flora so species ID is not usually required
Endocarditis is the most common infection
Biochem testing
What is the most common isolated species from dips and what is its species ID?
C. xerosis
Nitrate pos
Urease neg
Ferments glucose, maltose, sucrose
What is another common dip isolate and it’s species ID?
C. pseudodiphtheriticum
Nitrate pos
Urease pos
No fermentation
What are the characteristics of C. jeikeium?
Nosocomial pathogen in immunosuppressed patients
Normal flora on skin
Slow growing, small grey/white glistening colonies in 48hrs
Resistant to most antimicrobials other than vancomycin
What are the characteristics of Rhodococcus equi?
Serious infections in AIDS patients
Gram pos coccoid in young cultures, filamentous as they age
BAP and choc agar- 24hr tiny but large mucoid colonies at 48hrs
Catalase pos, no fermentation
Animal pathogen, survives a long time in soil
Pulmonary infections are most common
How many species of Corynebacterium are isolated?
20
