Integrons, β-lactamase and qnr genes in multidrug resistant clinical isolates of Proteus mirabilis and P. vulgaris.

Thirty-three isolates of Proteus mirabilis and two P. vulgaris were examined for their antimicrobial resistance, the presence of integrons with regard to gene cassette content, and genetic determinants of β-lactam and low-level quinolone resistance. Integrons were detected in 23 (69.7%) P. mirabilis isolates; six (18.2%) of them had class 1 integrons, 11 (33.3%) possessed class 2 integrons and six (18.2%) carried integrons of both classes. One P. vulgaris strain possessed class 1 and class 2 integrons. The presence of integrons was associated with increased frequency of resistance to gentamicin, ciprofloxacin, sulfamethoxazole and co-trimoxazole. Moreover, integron presence was associated with increased resistance range in terms of both the number of antimicrobials and the number of classes of antimicrobials to which a strain was resistant. Class 1 integrons contained aadA1, aadB-aadA1, dfrA1-aadA1, bla(PSE-1) -aadA1 and aacA4-orfA-orfB-aadA1 gene cassette arrays, whereas all class 2 integrons had a dfrA1-sat2-aada1 array. β-lactamase genes not associated with integrons comprised bla(TEM-2) , bla(DHA-1) and bla(CMY-15) . Plasmid-mediated fluoroquinolone resistance was determined by qnrD and qnrS1 genes. This is the first report of P. vulgaris strains harbouring qnrD genes in Europe.