We have read with interest the article by Johnson et al. (7) about the variability of the results of Gram staining encountered with some anaerobes. Gram stain is one of the cornerstones for bacterial identification, but it also serves as a useful technique for rapid detection of organisms in clinical samples (6). Propionibacterium acnes is a non-spore-forming, pleomorphic, anaerobic gram-positive rod (3) that is frequently considered to be a contaminant in clinical samples but may also be implicated as the agent of human infection (2, 4, 8). In our experience, Gram stain directly performed on clinical samples from patients with documented infection by P. acnes frequently failed to detect this organism. In order to evaluate the usefulness of Gram stain for direct detection of P. acnes, the laboratory records of the Medical Microbiology Department of the Fundación Jiménez Díaz (a 600-bed university hospital in Madrid, Spain) between January 1988 and August 1995 were reviewed for culture evidence of the presence of P. acnes. Those samples with heavy (3-streak) or moderate (2-streak) growth of P. acnes together with evidence of an inflammatory reaction (as detected on Gram smear by the presence of polymorphonuclear leukocytes) and yielding pure or predominant growth of P. acnes without any other more probable pathogen were selected. Critical review of patient charts was done to evaluate the clinical significance of the isolate. In 39 cases, meeting the above mentioned selection criteria, P. acnes was judged to have clinical significance. For controlling these results we later selected randomly other charts and assessed the Gram stain utility for other infections caused by various grampositive and gram-negative organisms. Table 1 shows the results of Gram stain for P. acnes infections and controls, indicating where the ability of the Gram stain to detect P. acnes was poor, especially when growth was only moderate, as compared with the ability of the Gram stain to reveal other grampositive and gram-negative organisms. Murray et al. (5) attribute misleading Gram stain results in clinical samples to cell wall deterioration due to the inflammatory response. Alterations in the P. acnes cell wall because of interaction with leukocytes or monocytes have been reported previously (9), and this fact, together with the pleomorphic nature of this bacteria (occasionally misinterpreted as a mixed infection [1, 8]) plus the presence of fibrinous debris in the samples, may explain the observations made in our study. In conclusion, Gram stain may not be a reliable technique for the rapid diagnosis of P. acnes infections, and when evidence of an abundant inflammatory response is noted in the Gram-stained smear, a more careful evaluation of cultures must be performed, particularly when nosocomial infection is of concern.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.