Linkage of acquired quinolone resistance (qnrS1) and metallo-beta-lactamase (blaVIM-1) genes in multiple species of Enterobacteriaceae from Bolzano, Italy.
OBJECTIVE
Twenty-four of 209 oxyimino-cephalosporin- and/or aztreonam-resistant Enterobacteriaceae collected around Bolzano had reduced susceptibility or resistance to carbapenems and gave positive metallo-beta-lactamase (MBL) tests. Their resistance mechanisms were investigated.


METHODS
Resistances were identified by Vitek 2 and MIC tests and isolates were genotyped by PFGE. Resistance genes were identified by PCR and sequencing, and plasmids were transferred by conjugation and/or transformation. Plasmid-borne genes were identified by Southern blotting, and their genetic surroundings were investigated by PCR mapping.


RESULTS
The 24 isolates with positive EDTA/imipenem synergy tests had bla(VIM-1) carried on 40-150 kb plasmids. Imipenem MICs ranged from 2 to >32 mg/L, while those of meropenem and ertapenem were lower. The isolates included a clonal cluster of 10 Klebsiella pneumoniae, two other K. pneumoniae isolates, and diverse isolates of Escherichia coli (seven), Klebsiella oxytoca (three) and Citrobacter freundii (two). Six MBL producers were aztreonam-susceptible; the 18 aztreonam-resistant isolates had co-resident extended-spectrum beta-lactamases. bla(VIM-1) occurred as the first cassette in class 1 integrons, with aacA4 as the second cassette. Quinolone resistance gene qnrS1 was detected in 21 of 24 (87.5%) bla(VIM-1)-positive isolates versus 14 of 185 (7.6%) bla(VIM)-negative isolates (P < 0.0001), with 13 of the latter belonging to a clonal cluster of E. coli. qnrS1 was located on the same plasmids as bla(VIM-1) and aacA4, but was not closely linked, as judged by PCR mapping.


CONCLUSIONS
bla(VIM-1) has become disseminated among enterobacteria in a small Italian town. The frequent association of genes conferring carbapenem, aminoglycoside and quinolone resistance on single plasmids will facilitate co-selection.
Aschbacher
Richard
R
Laboratorio Interaziendale di Microbiologia e Virologia, Via Amba Alagi 5, I-39100 Bolzano, Italy.
Doumith
Michel
M
Livermore
David M
DM
Larcher
Clara
C
Woodford
Neil
N
D024901:Drug Resistance, Multiple, Bacterial / Q000187:drug effects / Q000235:genetics*; D004755:Enterobacteriaceae / Q000187:drug effects / Q000235:genetics* / Q000302:isolation & purification; D008040:Genetic Linkage / Q000235:genetics*; D006801:Humans; D007558:Italy; D015363:Quinolones / Q000494:pharmacology / Q000627:therapeutic use; D001618:beta-Lactamases / Q000235:genetics / Q000302:isolation & purification
D015363:Quinolones; C417264:VIM-1 metallo-beta-lactamase; D001618:beta-Lactamases