A novel variant of the β-lactamase ADC-61 gene in multi-drug resistant Acinetobacter baumannii

The aim of this study was to investigate the existence of a β-lactamase gene in a group of multi-drug resistant Acinetobacter baumannii. Twenty strains of multi-drug resistant A. baumannii were isolated. Thirty-four β-lactamase genes and the ISaba1-OXA-23 linkage were analyzed in these strains by polymerase chain reaction (PCR) and verified by DNA sequencing. Three kinds of β-lactamase genes (TEM, ADC, and OXA-23) were identified, among which the sequence of strain No. 20, ADC, was different from ADC subtypes recorded by GenBank, and was identified as a new variant of β-lactamase genes (named ADC-61 and registered in GenBank: accession No. JQ753702); all the other 19 strains were ADC-30. Eighteen strains of the OXA-23 group were all positive as indicated by detection of ISaba1-OXA-23 linkage. Gene sequencing indicated that the TEM gene was TEM-1. These results suggest that the three kinds of β-lactamase genes identified in this study, TEM, ADC, and OXA-23, play a key role in drug resistance in this group of A. baumannii. To our knowledge, this is the first report of an emergent new mutation of the β-lactamase gene, ADC-61, in China or abroad.