Corynebacterium Corynebacterium sensu stricto Prior to the application of refined taxonomic techniques such as DNA-DNA homology and chemical analyses of cell walls, many organisms belonging to a broad group of so called nocardioform actinomycetes were included in the genus Corynebacterium. The term coryneform is still applied to many of them (eg Arthrobacter, Cellulomonas). Valid members of the genus are referred to as Corynebacterium sensu stricto. They are closely related to Mycobacterium, Rhodococcus and Nocardia. Corynebacterium sensu stricto now includes the human pathogen C. diphtheriae, and the animal parasites C. pseudotuberculosis, C. renale, C. ulcerans, C. kutscheri, and two environmental organisms C. flavum and C. glutamicum. Properties of the genus Gram positive, slightly curved club-shaped (coryneform) rods that tend to stain irregularly. Bacteria with this appearance are referred to as "diptheroids" in medical microbiology. Nonsporeforming; Non-acid-fast; Aerobic or facultative anaerobic; Catalase-positive; Non-motile Corynebacterium pseudotuberculosis Specimen Collection If bacteriological confirmation of a diagnosis is required, then a sample of pus is aseptically collected from the abscess, usually at post mortem. The sample should be collected from the inside surface of the capsule rather than the centre of the abscess. There are more likely to be viable organisms present in this more 'active' area of the abscess. Specimens from live animals are collected by needle aspirate. Microscopic Examination of Tissues Corynebacterium pseudotubercul- osis. Gram impression Gram-positive pleomorphic rods are frequently smear from present in large numbers in smears of pus. inside of abscess capsule. Large numbers of pleomorphic rods. Cultural Examination Corynebacterium Aerobic and facultatively anaerobic. Primary pseudotubercul- isolation enchanced by increased CO osis. 48 hr 2 concentration. Grows poorly on plain media, culture. growth enhanced by blood or serum. Colonies are relatively small and translucent after 24 hrs but enlarge in 3 to 4 days to become more opaque with papilliform concentric rings and a cream to orange colour. Colonies are rather dry and crumbly and can be pushed over the surface of the agar with a loop. Often surrounded by narrow zone of complete haemolysis. Closely resembles C. diphtheriae in general morphology and behaviour. Gram-positive, slender, clubbed bacillary forms, pleomorphic, often numerous metachromatic granules. Identification Catalase — Positive; Loeffler's inspissated serum medium — Not liquified; Gelatin liquefaction — Variable. Serological Testing Not used in diagnosis. Antibiotic Sensitivity Although usually susceptible to antimicrobials such as penicillin, sulphonamides and tetracyclines, treatment of corynebacterial infections is usually unsatisfactory. This is probably because of the suppurative and fibrotic nature of the lesions. Corynebacterium renale Specimen Collection Urine from clinically affected cows or kidney tissue collected at post mortem. Microscopic Examination of Tissues Smear of pus from kidney of cow infected with Corynebacterium The organisms are readily demonstrated in the renale X1000 pus and tissue debris that accumulates in the original renal pelvis. Large gram positive rod, often with magnification. pointed ends, pleomorphic, metachromatic granules are readily observed. Cultural Examination Aerobic, facultatively anaerobic Grows well on plain media and growth is not enhanced by blood or serum. C. renale on SBA. 48 hr cultures. Colonies cream to pale yellow in colour. After 24 hours incubation are 1.5 mm diameter, punctiform with lacelike margin. Non-haemolytic. Identification Urease activity can be Does not liquefy serum. demonstrated by growing an Strong urea splitting activity. organism in medium containing urea and phenolphthalein. The ammonia released turns the medium pink Serological Testing Not used in diagnosis. Antibiotic Susceptibility Quite sensitive to penicillin in vitro but it is not effective in curing clinical cases. Antibiotic therapy may be useful in restoring infected animals for salvage slaughter..