Coryneform Bacteria in Gram Stain: Introduction, Morphology, Lab Diagnosis and Treatment
Coryneform bacteria in Gram stain
Coryneform bacteria bacilli or rods in gram stain as shown above picture.
Introduction of Coryneform bacteria
Coryneform bacteria (diphtheroids) are ubiquitous in nature (soil and water). They are found on human skin and mucous membranes as commensals. They are also found on plants, in soil, and in freshwater and saltwater.
They encompass several genera, of which Corynebacterium is the most frequently encountered in clinical infections. They are characterized as irregularly shaped, non–spore-forming, aerobic, gram-positive rods.
Infections caused by them are broadly categorized as community-acquired or nosocomial; sporadic cases of zoonoses have been reported.
Rhodococcus equi usually occurs in individuals with defective cell-mediated immunity, particularly with human immunodeficiency virus (HIV) infection, with or without a history of animal exposure.
Microbiology of Coryneform bacteria
They are readily grown on standard culture media. For lipophilic strains, growth is enhanced with the addition of Tween 80. Species identification and antimicrobial testing of them is recommended when specimens are collected from normally sterile sites, there is the presence of high colony counts with a strong leukocyte reaction, or there is the recovery of high colony counts of Corynebacterium urealyticum from urine culture. Molecular tests, such as 16s ribosomal RNA sequencing, and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry(MALDI-TOFMS) are used for species identification of coryneform bacteria, including Rhodococcus, Gordonia, and Tsukamurella.
The list of coryneform bacteria are-
- Corynebacterium pseudotuberculosis,
- Corynebacterium ulcerans
- Corynebacterium renale
- Corynebacterium bovis
- Corynebacterium striatu
- Corynebacterium minutissimum
- Corynebacterium pseudodiphtheriticum
- Corynebacterium haemolyticum
- Rhodococcus equi
- Rhodococcus species
- Gordona species
- Tsukamurella species
- Arcanobacte
- Actinomyces Species
Lab Diagnosis of Coryneform bacteria
They are considered clinically significant when patients present with symptoms consistent with infection, along with recovery of bacteria. The following steps are useful for the isolation of organisms-
- culture of specimen
- Gram stain of sample or growth organism
- Biochemical tests
- If necessary, do modified Ziehl-Neelsen ( Actinomyces, Rhodococcus).
- Molecular tests using 16s ribosomal RNA sequencing and MALDI-TOFMS
Treatment of Coryneform bacteria
They are uniformly susceptible to glycopeptides, such as vancomycin and teicoplanin, and most strains are susceptible to daptomycin and linezolid whereas Rhodococcus equi is usually susceptible to vancomycin, teicoplanin, erythromycin, fluoroquinolones, rifampin, carbapenems, aminoglycosides, and linezolid.
Prevention
Prevention of infections caused by coryneform bacteria includes-
- proper skin antisepsis before invasive procedures and
- precaution when handling animals.
Further Readings
- Bailey & Scott’s Diagnostic Microbiology. Editors: Bettey A. Forbes, Daniel F. Sahm & Alice S. Weissfeld, 12th ed 2007, Publisher Elsevier.
- Clinical Microbiology Procedure Handbook Vol. I & II, Chief in editor H.D. Isenberg, Albert Einstein College of Medicine, New York, Publisher ASM (American Society for Microbiology), Washington DC.
- Jawetz, Melnick and Adelberg’s Medical Microbiology. Editors: Geo. F. Brook, Janet S. Butel & Stephen A. Morse, 21st ed 1998, Publisher Appleton & Lance, Co Stamford Connecticut.
- Mackie and Mc Cartney Practical Medical Microbiology. Editors: J.G. Colle, A.G. Fraser, B.P. Marmion, A. Simmous, 4th ed, Publisher Churchill Living Stone, New York, Melborne, Sans Franscisco 1996.
- Manual of Clinical Microbiology. Editors: P.R. Murray, E. J. Baron, M. A. Pfaller, F. C. Tenover, and R. H. Yolken, 7th ed 2005, Publisher ASM, USA
- https://www.sciencedirect.com/topics/immunology-and microbiology/coryneform-bacterium
- Bernard K. The genus Corynebacterium and other medically relevant coryneform-like bacteria. J Clin Microbiol. 2012;50:3152–58. [PMC free article] [PubMed] [Google Scholar]
- Funke G, Bernard KA. Manual of Clinical Microbiology. Ninth Edition. Washington DC: ASM Press; 2007. Coryneform Gram-positive rods. In: Murray PR, Baron EJ, Jorgensen JH, Landry ML, Pfaller MA, Eds; pp. 485–514. [Google Scholar]
- Funke G. Topley and Wilson’s Microbiology and Microbial Infections, Bacteriology. Tenth Edition. Volume 2. ASM Press; 2010. Corynebacteria and rare coryneforms. In: Borriello SP, Murray PR, Kunke G, Eds; pp. 977–97. [Google Scholar]