In-vitro efficacy of polymyxin B with rifampin, colistin and doxycycline against extensively drug resistant Acinetobacter baumannii

Abstract

During the course of an antimicrobial resistance surveillance programme in Guangzhou, the People’s Republic of China, single strains of Citrobacter youngae and Pseudomonas aeruginosa were identified which were resistant to imipenem and found to carry the carbapenemase gene blaIMP. PCR screening of the citrobacter strain with specific primers for the blaIMP type genes gave a 587-bp product which when sequenced gave 100% homology with the blaIMP-4 sequence reported recently from Acinetobacter spp. The determinant in the C. youngae strain was found to be located on a 156-kb plasmid capable of transfer to Escherichia coli UB1637 by conjugation. Sequencing of the blaIMP-4 open reading frame in the C. youngae strain and adjacent sequences not only confirmed the presence of blaIMP-4 but also identified that a conserved core site found within the 59-bp element of integrons was present and the same as the one described in the only other occurrence of blaIMP-4 in Acinetobacter spp. isolated from an intensive care unit in Hong Kong. This is the second report of transferable carbapenemase genes in Enterobacteriacae outside of Japan and the first in the People’s Republic of China. Under the selective pressure of carbapenems and extended spectrum cephalosporins use we might expect this gene to spread and widespread surveillance should be instituted.