Resistance carrying plasmid in a traumatic wound

Objective

To isolate and identify antibiotic-resistant bacteria from the exudate of a complex wound and determine if antibiotic resistance genes are chromosomal or plasmid borne.

Method

Antibiotic resistant bacteria from wound exudate of a single clinical sample were selected on agar media with ampicillin. A single colony was further screened for resistance to kanamycin by antibiotic-supplemented agar and to other antibiotics by an automated Phoenix instrument. Identifi cation of the isolate was carried out by biochemical profi ling and by 16S rDNA analysis.

Results

Approximately 51% of total bacteria in the wound exudate with identical colony morphotype were resistant to 100μg/ml of ampicillin. A single colony from this population also demonstrated resistance to 50μg/ml of kanamycin on kanamycin-supplemented agar. Further antimicrobial sensitivity testing by the Phoenix instrument indicated resistance to inhibitory concentrations of amoxicillinclavulanate, ampicillin-sulbactam, cefazolin, gentamicin, nitrofurantoin, tobramycin, and trimethoprimsulfamethoxazole. Biochemical and 16S rDNA analysis identifi ed this bacterial isolate as a member of genus Enterobacter. A plasmid preparation from this isolate successfully transferred ampicillin and kanamycin resistance to E. coli competent cells. E. coli transformants displayed two resistance phenotypes and the plasmids from these transformants displayed two different restriction type patterns, with one correlating to ampicillin and kanamycin resistance and the other only to ampicillin resistance.

Conclusion

A multiple antibiotic-resistant Enterobacter spp. from the wound fluid of a clinical sample was found to carry an antibiotic-resistant plasmid in a closely related species E. coli. The presence of antibiotic resistance plasmid in Enterobacteria that are part of the normal microbial flora of the human gut and skin could lead to the spread of resistance phenotype and emergence of antibiotic resistant pathogens. This study suggests normal human microbial fl ora could be a potential reservoir for resistance genes.

Declaration of interest

None.