Written by Bob R. Bogle, in cooperation with the Southern Arizona Antimicrobial Resistance Survey 11. Most Gram-positive rods encountered in clinical microbiology represent contaminating skin flora that is of limited pathogenicity. These are members of the genus Corynebacterium which, like the lactobacilli, represents a great number of individual species all lumped together into a large, somewhat cumbersome group. Unlike the lactobacilli, however, diphtheroids are usually easy to recognize.
Pairs sometimes make V -shapes.
Diphtheroids are normal skin flora, and they sometimes colonize shunts and drains and may in this way be found in ventricular drainage specimens. They are almost always contaminating skin flora, being of low inherent virulence, although Corynebacterium diphtheriae and C. jekeium are members of the group. Anaerobic diphtheroids are encountered as blood culture contaminants, but only uncommonly on other direct Gram stains. Organisms such as these should simply be reported as GPR's. Diphtheroids Bacillus spp.