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Excerpt
The authors thank Drs. Garg and Sharma for their comments regarding our article “Propionibacterium acnes as a Cause of Visually Significant Corneal Ulcers.” We agree that recovering organisms on culture does not necessarily confirm that the isolated organism is responsible for a particular disease process. However, we do feel that commensal organisms can be pathogenic. In the absence of any alternative causes, infective or otherwise, for the corneal inflammation in our patients, and based on the facts presented in the article, we feel that P. acnes are, at least, “possibly” responsible organisms in the cases discussed.
In one of the cases, pleomorphic Gram-positive rods on Gram stain confirmed that the culture was not a contaminant but, indeed, organisms from the scraped cornea. In another, the diagnosis was made based on a corneal biopsy specimen, and, in a third, we had strong evidence that a suture that was removed from an infectious crystalline keratitis was probably linked to the same organism (P. acnes) that was in the donor corneal transport media before corneal transplantation.
Drs. Garg and Sharma contend that other agents such as Nocardia, Corynebacteria, and atypical (nontuberculous) Mycobacterium were not ruled out. However, these agents would have been recovered on the media used in our cases (with the possible exception of some nontuberculous mycobacteria, such as kansasii). In addition, our cases did not clinically appear to be herpetic and, if they were, they would not have responded to antibiotic treatment directed toward P. acnes. Also, one of the cases was specifically culture-negative for herpes simplex virus.
Furthermore, although P. acnes does show sensitivity to numerous antibiotics that are effective against Gram-positive organisms, these sensitivities are usually based on minimum bacteriostatic testing. These antibiotics may not be clinically effective because bactericidal, rather than bacteriostatic, measures may be necessary. One of the studies cited in our article 1 reviewed isolates from endophthalmitis cases. It suggested that vancomycin is much more effective in producing bactericidal concentrations against P. acnes that other antibiotics, such as cefazolin. Again, the authors thank Drs. Garg and Sharma for their comments.
