Propionibacteria are Gram-positive nonmotile rods, which when first isolated tend to be irregular and sometimes with short branching . They show typical coryneform appearance which has led to problems in taxonomy. During laboratory culturing their cells became more regular and smaller .
Isolation requires seven days' incubation anaerobically at 35-37В°C. However, these bacteria are not strict anaerobes and procedures used for manipulation under anaerobic conditions are not required. The colonies are buff to pink depending on the species, and generally domed..
From their first discovery in 1896 by Unna these bacteria have acquired different generic names, from Bacillus, to Corynebacterium, to Propionibacterium, as well as being referred to as anaerobic diphtheroids and anaerobic coryneforms. Up to 1946, when Douglas and Gunter3 recommended the generic name Propionibacterium, Corynebacterium was used.
Since then both names have appeared in the medical literature, though Propionibacterium is now accepted by bacterial taxonomists as correct..
Johnson and Cummins recognized three species, Propionibacterium acnes, Propionibacterium avidum and Propionibacterium granulosum, which are still recommended to date. Other species described by Prevot and Fredette5, Corynebacterium liquifaciens, Corynebacterium pyogenes, Corynebacterium parvum, Corynebacterium diphtheroides and Corynebacterium anaerobium would appear to be P. acnes according to Zierdt et al6 and Cummins and Johnson..
Selected information of tests used to identify ropionibacteria to the species level. Cell wall analysis of sugars is the most reliable method of dividing both P. acnes and P. avidum into biovars (biotypes). The presence or absence of galactose in the cell walls of P. acnes and P. avidum corresponds to biovars I and II.
However, this is a lengthy procedure requiring culturing, concentration and washing of cells, acid treatment and thin-layer chromatography..
Various investigations have shown that species may be divided into serovars, biovars and phagovars. There is no universal agreement on these typing schemes apart from the simple serotyping of P. acnes and P. avidum into, in each case, types I and II. Investigators wishing to pursue strain typing should consult the references given above.
Biotyping should at present be viewed with caution because Zierdt et al6 and the present authors have shown variation in results on repeated tests. Serotyping, relying on simple agglutination tests, has technical difficulties in that many isolates self-agglutinate, and to overcome the problem an indirect fluorescent antibody test may be used.
Bacteriophage typing offers a future means of typing P. acnes for epidemiological investigations..
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