Occurrence and mechanisms of amikacin resistance and its association with β-lactamases in Pseudomonas aeruginosa: a Korean nationwide study

Objectives We investigated the occurrence and mechanism of amikacin resistance and its association with various β-lactamase genes in Pseudomonas aeruginosa isolates. Methods Of the total 250 consecutive, non-duplicated isolates of P. aeruginosa, 55 isolates showed amikacin resistance. PCR amplification of genes for aminoglycoside (AG)-modifying enzymes [aac(3)-I, aac(3)-II/VI, aac(3)-III/IV, aac(6′)-I, aac(6′)-II, ant(2″)-I, ant(4′)-II and aph(3′)-VI], 16S rRNA methylases (rmtA, rmtB, rmtC and armA) and class 1 integrons was performed. In addition, we analysed the association of AG resistance genes with various β-lactamase genes. Results and conclusions In Korea, the amikacin resistance rate in P. aeruginosa was high (22%), and it varied among provinces (3.8% to 40%). Four types of AG-modifying enzyme genes [aph(3′)-VI, ant(2″)-I, aac(6′)-I and aac(3)-II/VI] were found in 48 isolates. Thirty-six strains harboured two or more types of enzymes, of which a combination of aph(3′)-VI and ant(2″)-I was the most frequent (24/36 isolates, 66.7%). None harboured aac(3)-I, aac(3)-III/IV, aac(6′)-II, ant(4′)-II, rmtA, rmtB, rmtC or armA. Forty-two isolates co-harboured β-lactamase genes (mostly blaOXA-10). A class 1 integron was detected in all but one, and all the ant(2″)-I and 26/29 blaOXA-10 were found in it. In contrast, aph(3′)-VI was not found to be associated with the class 1 integron. Considering the possibility of co-selection and dissemination, constant monitoring of resistance evolution is necessary.