Isolation of Antibiotic-Resistant Micrococcus aloeverae from Milk Powder

Abstract

The emergence of antibiotic resistance in humans via the food chain has become an area of great concern. Antibiotic resistance gene transfer from a food-borne bacteria or probiotic agent to a human gut microbe can lead to a serious food safety issue. Such seemingly harmless bacteria or probiotics can potentially become a threat to human health if they carry mobile genes conferring antibiotic resistance. The recent trend of probiotic application in powdered infant formula and milk products and the presently known contamination of these products by certain opportunistic Enterobacteriaceae bacteria serves as the rationale for evaluating their safety. In this study, 25 milk powder samples and 25 powdered infant formula samples were analyzed for the presence of antibiotic resistant bacteria of family Enterobacteriaceae using an isolation technique. Out of the 50 samples screened, an isolate was detected in one milk powder sample. Its biochemical characteristics, Gram character, antibiotic susceptibility, and motility were analyzed. It was found to be a Gram-positive, non-motile, catalase-positive and oxidase-negative microbe. The isolate was resistant to Rifampicin and Vancomycin, but susceptible towards Streptomycin, Ciprofloxacin, Ceftriaxone and Gentamycin. Molecular characterization by 16S rDNA sequencing identified the isolate as Micrococcus aloeverae. The unique occurrence of Micrococcus aloeverae in milk powder elicits an area of food safety concern for such samples. To the best of our knowledge, this study is the first to report antibiotic resistance by Micrococcus aloeverae. Although it may be a non-pathogenic microbe, its resistance towards antibiotics cannot be ignored. The possibility of Micrococcus aloeverae serving as a potential vehicle for transfer of antibiotic resistance genes to human gut microbiota represents a prospective food safety concern.