Abstract:

【Objective】 To analyze the plasmid-mediated 16SrRNA methylase genes and their horizontal transferable mode of Enterobacter cloacae GZL42B which was isolated from pig farm. 【Method】 Polymerase chain reaction (PCR) and sequencing were applied to detect and identify the 16SrRNA methylase resistant gene. Conjugation experiments were used to study the horizontal transferable mode of 16SrRNA methylase in E. cloacae by using the E.coli Rif+488(rifampin-resistant) as the recipient. MICs were evaluated by using the micro-dilution method. Comparison of the neighboring sequences of rmtB between E. cloacae GZL42B and Escherichia coli GZL42B which isolated from the same rectal swab of one pig and the prevalence of 16SrRNA methylases genes in 172 E. coli were investigated by PCR and sequencing. 【Result】 The fragment of rmtB was amplified succeessfully. The restriction fragments were corresponded with the expectant, and the rmtB was confirmed by using sequencing. The accession number of the rmtB sequence submitted to GenBank was EF017943. Transconjugant was obtained successfully by using the E. coli Rif+488 as the recipient. The MICs of the parental E. cloacae GZL42B and its transconjugant to kanamycin, amikacin, tobramycin, sisomicin, netilmicin and gentamycin were ≥256 μg?mL-1. The right-hand end of transposon Tn3 and the orf1 which was part of groEL/intI1 on genomic island SG1 of Salmonella enterica serovar Typhimurium were located on the upstream and downstream of rmtB in Escherichia coli GZL42H, respectively. But they were not amplified in E. cloacae GZL42B. Tweenty-five and one of all 172 isolates (15% and 0.6%) were rmtB and armA positive, respectively. 【Conclusion】 It was the first report that the 16SrRNA methylase rmtB emergenced in E. cloacae from pig farm. High resistance to 4,6- deoxystreptamine was mediated by rmtB and can be transferred to E. coli Rif+488. The rmtB can be transferred between different species of bacteria. The genetic basis for dissemination of rmtB was different between E. coli GZL42H and E. cloacae GZL42B. And the rmtB was highly prevalent in animal E. coli.

Key words: pig, Enterobacter cloacae, 16SrRNA methylases, resistance, rmtB