High prevalence of cross-resistance to aminoglycosides in fluoroquinolone-resistant Escherichia coli clinical isolates.
BACKGROUND
Multidrug-resistant Escherichia coli, especially a lineage of O25b:H4-ST131, has increased and spread worldwide. The surveillance of cross-resistance of E. coli is necessary.


METHODS
Cross-resistance to fluoroquinolones (FQs) and aminoglycosides (AGs) was examined in E. coli isolated in Hokkaido Prefecture, Japan, between 2008 and 2009.


RESULTS
Gentamicin (GEN) resistance was more common in FQ-resistant isolates (30/112 strains; 26.8%) than in FQ-susceptible isolates (2/100 strains; 2%). The frequency of GEN resistance was similar in two groups of FQ-resistant strains, O25b:H4-ST131 genotype (22/87 strains; 25.3%) and a group of other FQ-resistant genotypes (8/25 strains; 32.0%). The main AG resistance gene was aac(3)-II (87.5% of GEN-resistant strains). The only amikacin-resistant strain which was FQ resistant carried the aac(6')-Ib-cr gene. CTX-M type extended-spectrum β-lactamase (ESBL) genes were also found in FQ-resistant strains at a high frequency. However, the number of strains with both ESBL and AG-modifying enzyme genes was relatively low (8 strains).


CONCLUSIONS
All FQ-resistant strains, not only O25b:H4-ST131, appeared to preferentially acquire ESBL genes and/or genes encoding AG-modifying enzymes; however, the acquisitions of these genes seemed to occur independently.
Department of Microbiology, Sapporo Medical University School of Medicine, Sapporo, Japan.
Naoyuki
N
Tsukamoto
Yasuo
Y
Ohkoshi
Torahiko
T
Okubo
Toyotaka
T
Sato
Osamu
O
Kuwahara
Nobuhiro
N
Fujii
Yutaka
Y
Tamura
Shin-Ichi
S
Yokota
D000617:Aminoglycosides / Q000494:pharmacology; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D024901:Drug Resistance, Multiple, Bacterial / Q000235:genetics*; D004926:Escherichia coli / Q000187:drug effects* / Q000302:isolation & purification; D004927:Escherichia coli Infections / Q000188:drug therapy*; D024841:Fluoroquinolones / Q000494:pharmacology; D006801:Humans; D007564:Japan; D008826:Microbial Sensitivity Tests; D015995:Prevalence
D000617:Aminoglycosides; D000900:Anti-Bacterial Agents; D024841:Fluoroquinolones