Diphtheroids-Important Nosocomial Pathogens

Abstract

Introduction: Diphtheroids are defined as aerobic, nonsporulating, pleomorphic Gram-positive bacilli which are more uniformly stained than Corynebacterium diphtheriae, lack the metachromatic granules and are arranged in a palisade manner. They are usually commensals of the skin and mucous membranes. They differ from C.diphtheriae in biochemical reactions as well as in toxin production. Since, they are usually found as commensals on the skin, they are often considered as mere contaminants when isolated from clinical samples. However, there are increasing reports of these organisms being associated with various infections. Hence, we felt the need to study the common species associated with infections and know the properties of these organisms which are otherwise considered as mere laboratory contaminants. Aim: To identify the various species of diphtheroids isolated as pure growth from clinical specimens whose Gram’s smear revealed numerous inflammatory cells with Gram positive bacilli and had clinical evidence. Materials and Methods: A total of 100 isolates of Gram-positive bacilli from 16,242 clinical samples received in the Microbiology Department of Kasturba Medical College were considered for this study from Dec 2013-Dec 2014. Gram-positive bacilli which were seen in the smear along with pus cells, isolated as pure growth and reported as “Corynebacterium spp having clinical significance” were taken for this study while those which were reported as ‘Probable skin contaminants’ were excluded from this study. Species identification of Grampositive bacilli was done by biochemical reactions. Antibiotic susceptibility test was done by Kirby-Bauer disk diffusion method. Biofilm production was done by the microtitre plate method of O’Toole and Kolter and statistical analysis was done by using proportion test and Chi-square test. Results: Various species of diphtheroids were isolated from different clinical specimens. C. pseudotuberculosis, C. renale, C. ulcerans, C. striatum, C. minutissimum, Corynebacterium haemolyticum isolated from catheter tips, sputum, tracheostomy secretions and wound infections were highly resistant to many antibiotics while isolates from blood namely C. pseudotuberculosis, C. minutissimum, C. ulcerans and C. renale were nearly sensitive to most of them. It was also interesting to note that there was an increased rate of biofilm production in these isolates. Conclusion: Corynebacterium pseudotuberculosis, Corynebacterium ulcerans, Corynebacterium renale, Corynebacterium bovis, Corynebacterium striatum, Corynebacterium minutissimum, Corynebacterium pseudodiphtheriticum and Corynebacterium haemolyticum may survive in the form of biofilms in hospitals and cause multidrug resistant infections. Hence, we need to judiciously identify these organisms, find their antimicrobial susceptibility, treat them and thus prevent infections in hospitals.

Keywords

• catheter tips
• multidrug resistant
• tracheostomy secretions
• wound infections