Sequence Type ST405 Escherichia coli Isolate Producing QepA1, CTX-M-15, and RmtB from Detroit, Michigan

LETTER

Plasmid-mediated fluoroquinolone resistance determinants are increasingly identified worldwide among various isolates of Enterobacteriaceae (9). Among them, QepA belongs to the major facilitator superfamily (MFS)-type group of efflux pumps. It was initially identified in Escherichia coli clinical isolates from Belgium and Japan (8, 13). QepA (now QepA1) has subsequently been detected in E. coli isolates of human (1, 5, 10) and animal (6, 7) origins. QepA2, a two-amino-acid variant of QepA1, has been reported from an E. coli clinical isolate in France (2).

Here we report identification of QepA1 in an E. coli isolate from the United States. E. coli M3006 was isolated from the urine of a 47-year-old female patient with paraplegia, who was admitted from a nursing home to a hospital in Detroit, MI, for treatment of sacral osteomyelitis in January 2010. She had received ciprofloxacin for 10 days just prior to her presentation. The isolate was highly resistant to ceftazidime, cefotaxime, cefepime, ciprofloxacin, and amikacin, all with MICs of >32 μg/ml, and susceptible to all four carbapenems (ertapenem, imipenem, meropenem, and doripenem).

PCR analysis was performed to identify various resistance genes, including β-lactamase genes bla_TEM, bla_SHV, and bla_CTX-M; 16S rRNA methylase genes armA, rmtB, and rmtC; pentapeptide repeat protein genes qnrA, qnrB, qnrC, and qnrS; the fluoroquinolone-modifying aminoglycoside acetyltransferase gene aac(6′)-Ib-cr; and the plasmid-mediated fluoroquinolone efflux pump gene qepA (11). PCR products were sequenced on both strands. As a result, bla_CTX-M-15, bla_TEM-1, qepA1, and rmtB were detected in E. coli M3006.

A cefotaxime-resistant transconjugant and a transformant containing bla_CTX-M-15 were successfully obtained from E. coli M3006 using E. coli J53 and DH10B as recipients, respectively. Both of them were positive for bla_CTX-M-15 as well as bla_TEM-1, qepA1, and rmtB, indicating that these four genes were located on the same conjugative plasmid. The MIC of ciprofloxacin for the E. coli J53 transconjugant was 0.125 μg/ml, which represented an 8-fold increase over that of the recipient alone. The level of ciprofloxacin resistance was much higher for the parental strain, which was likely due to mutations in the quinolone resistance-determining regions of the gyrA and parC genes. As expected, this transconjugant was also resistant to cephalosporins (MICs, 256 μg/ml for cefotaxime and 16 μg/ml for cefepime) and aminoglycosides (MIC, >256 μg/ml for gentamicin and amikacin).

E. coli M3006 was then subjected to phylogenetic typing and multilocus sequence typing (MLST) (3, 12). As a result, E. coli M3006 was classified into phylogenetic group D, with its allele combination corresponding to the sequence type (ST) 405. Phylogenetic group D-ST405 strains, along with phylogenetic group B2-ST131 strains, have been implicated as vehicles driving the international spread of bla_CTX-M-15 (4).

To the best of our knowledge, this is the first identification of a QepA-type efflux pump in the United States. The location of the multidrug-resistant, conjugative plasmid carrying qepA1, bla_CTX-M-15, and rmtB on a globally disseminated E. coli clone is a troubling phenomenon, as its presence simultaneously compromises the efficacy of fluoroquinolones, cephalosporins, and aminoglycosides that are commonly used in treatment of E. coli infections.