Prevalence of the oqxAB gene complex in Klebsiella pneumoniae and Escherichia coli clinical isolates

To investigate the epidemiology and genetic elements of the efflux pump gene, oqxAB, in clinical isolates of Escherichia coli and Klebsiella pneumoniae. The prevalence of the oqxAB gene in a total of 308 consecutive clinical isolates of E. coli, K. pneumoniae and other Klebsiella spp. was investigated by PCR amplification. The full-length oqxAB gene was sequenced. Conjugation experiments were carried out in oqxAB-positive E. coli strains. Of 136 E. coli strains, 71.3 and 70.6 were non-susceptible to ciprofloxacin and levofloxacin, respectively, while 66.9 and 50.7 of the 154 K. pneumoniae were non-susceptible to these two quinolones. oqxA and oqxB were present in 6.6 of E. coli and in all K. pneumoniae strains. The oqxA and oqxB sequences of E. coli and randomly selected K. pneumoniae strains showed high similarity to the original oqxAB sequence of pOLA52. One or two amino acid substitutions were detected in the OqxA or OqxB sequences from two E. coli strains and were designated oqxA2, oqxB2 and oqxB3. oqxAB was transferred in seven of nine oqxAB-positive E. coli strains, and transconjugants showed 2- to 256-fold increases in ciprofloxacin and levofloxacin MICs relative to that for the recipient. Variants of the oqxAB gene, oqxA2, oqxB2 and oqxB3, were identified in two E. coli strains. The oqxAB gene was present in all K. pneumoniae strains studied and is likely located on the chromosome, thus identifying the genome of K. pneumoniae as a possible reservoir of oqxAB.