New aminoglycoside acetyltransferase gene, aac(3)-Id, in a class 1 integron from a multiresistant strain of Vibrio fluvialis isolated from an infant aged 6 months

OBJECTIVES: To characterize the molecular basis of antibiotic resistance in a multidrug-resistant clinical isolate of Vibrio fluvialis H-08942. PATIENT AND METHODS: V. fluvialis H-08942 was isolated from a hospitalized infant aged 6 months suffering from cholera-like diarrhoea in India in 2002. The broth microdilution method was used to determine the MICs of a range of antibiotics for this strain. PCR, DNA sequencing, Southern hybridization, cloning and expression were used to characterize the molecular basis of antibiotic resistances. RESULTS: V. fluvialis H-08942 showed resistance to chloramphenicol, streptomycin, spectinomycin, co-trimoxazole, ampicillin, furazolidone, nalidixic acid and gentamicin. A class 1 integron that contains a novel aminoglycoside acetyltransferase gene, aac(3)-Id, and aminoglycoside adenyltransferase gene, aadA7, was characterized. The aac(3)-Id gene product was found to share 50%, 45% and 44% identity to AAC(3)-Ic, AAC(3)-Ia, and AAC(3)-Ib, respectively. Both aac(3)-Id and aadA7 genes were cloned and expressed in Escherichia coli. Phylogenetic analysis suggested that the aac(3)-Id represents a fourth evolutionary lineage in the aminoglycoside acetyltransferase genes. Southern hybridization showed that this integron is located in the chromosome. CONCLUSIONS: In this study we identified a new type of aminoglycoside acetyltransferase gene, aac(3)-Id. In addition, this is the first report of identification of antibiotic resistance genes and a class 1 integron in V. fluvialis.