Corynebacterium amycolatum

Corynebacterium amycolatum is a gram-positive, non-spore-forming, aerobic or facultatively anaerobic bacillus capable of fermentation [1] with propionic acid as the major end product of its glucose metabolism. One of its best known relatives is Corynebacterium diphtheriae, the causative agent of diphtheria. C. amycolatum is a common component of the natural flora found on human skin and mucous membranes, and therefore is an occasional contaminant in human blood cultures but can rarely cause infections such as endocarditis.[2]

Corynebacterium amycolatum
Scientific classification Edit this classification
Domain: Bacteria
Phylum: Actinomycetota
Class: Actinomycetia
Order: Mycobacteriales
Family: Corynebacteriaceae
Genus: Corynebacterium
Species:
C. amycolatum
Binomial name
Corynebacterium amycolatum
Collins et al 1988

Identification

First described in 1988, C. amycolatum is one of the diphtheroid most often isolated from clinical samples. However, it is often difficult to differentiate from other fermentative corynebacteria such as C. minutissimum and C. xerosis, both of which are known human pathogens. One method of differentiation, however, is by observing the cell wall. Unlike other members of this genus, C. amycolatum lacks mycolic acid, long fatty acids usually found in the cell wall. C. amycolatum also differs in its colony morphology; the species characteristically produces flat, whitish-gray, matte or waxy colonies on Schaedler blood agar. Its antibiotic sensitivity may also aid in its identification; the organism is generally resistant to multiple antibiotics. Because of its relatively new status as a pathogen, however, no standard laboratory tests yet identify C. amycolatum.[3]

Disease

C. amycolatum has been shown to cause pneumonia, peritonitis, empyema, infectious endocarditis, and fatal sepsis, most of which occur as nosocomial infections. As an opportunistic pathogen, the bacterium is pathogenic in immunocompromised patients, mostly infecting those with underlying heart defects or intravascular devices. Corynebacterium endocarditis usually infects the left side of the heart in males, though C. amycolatum has shown a predilection for women.[4] While cases of disease have been small in number, this underreporting could be due to misdiagnosis of C. amycolatum as C. xerosis, which is a known human pathogen.[2][5]

Treatment

For the few cases thus far, vancomycin or daptomycin has been used in tandem with rifampicin for a duration ranging from four weeks to six months.[6] Valve replacement was also required in some cases of infectious endocarditis.[7] Due to its recent pathogenic status, however, few treatments have been tested, and an optimal treatment regimen has yet to be established.

Antibiotic resistance

One of C. amycolatum's characteristic traits is its resistance to a wide range of antibiotics. Various strains tested have shown resistance to beta lactam antibiotics, lincosamides, macrolides, and quinolones. Multiple drug-resistant strains were mainly isolated from wounds of patients treated in departments of general surgery and vascular surgery. However, the bacterium was shown to be particularly sensitive to glycopeptide and lipopeptide antibiotics.[8]

References
  1. Sengupta M, Naina P, Balaji V, Anandan S (December 2015). "Corynebacterium amycolatum: An Unexpected Pathogen in the Ear". Journal of Clinical and Diagnostic Research. 9 (12): DD01–DD03. doi:10.7860/JCDR/2015/15134.7002. PMC 4717710. PMID 26816893.
  2. Knox, Karen (2002). "Nosocomial Endocarditis Caused by Corynebacterium amycolatum and Other Nondiphtheriae Corynebacteria". Emerging Infectious Diseases. Centers for Disease Control and Prevention. 8 (1): 97–9. doi:10.3201/eid0801.010151. PMC 2730276. PMID 11749760. Retrieved 30 October 2012.
  3. Sengupta M, Naina P, Balaji V, Anandan S (December 2015). "Corynebacterium amycolatum: An Unexpected Pathogen in the Ear". Journal of Clinical and Diagnostic Research. 9 (12): DD01–DD03. doi:10.7860/JCDR/2015/15134.7002. PMC 4717710. PMID 26816893.
  4. Belmares, Jaime; Stephanie Detterline; Janet B Pak; Jorge P Parada (2007). "Corynebacterium endocarditis species-specific risk factors and outcomes". BMC Infectious Diseases. 7: 4. doi:10.1186/1471-2334-7-4. PMC 1804271. PMID 17284316.
  5. Berner, R; K Pelz; C Wilhelm; A Funke; J U Leititis; M Brandis (April 1997). "Fatal sepsis caused by Corynebacterium amycolatum in premature infant". Journal of Clinical Microbiology. 35 (4): 1011–1012. doi:10.1128/JCM.35.4.1011-1012.1997. PMC 229725. PMID 9157120.
  6. Sengupta M, Naina P, Balaji V, Anandan S (December 2015). "Corynebacterium amycolatum: An Unexpected Pathogen in the Ear". Journal of Clinical and Diagnostic Research. 9 (12): DD01–DD03. doi:10.7860/JCDR/2015/15134.7002. PMC 4717710. PMID 26816893.
  7. "Endocarditis". The Lecturio Medical Concept Library. Retrieved 19 July 2021.
  8. Koneman, Elmer (2006). Koneman's Color Atlas and Textbook of Diagnostic Microbiology, 6 ed. Lippincott Williams & Wilkins. p. 798. ISBN 9780781730143.
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