Class I integrons in Gram-negative isolates from different European hospitals and association with decreased susceptibility to multiple antibiotic compounds

Abstract

Class I integrons are associated with carriage of genes encoding resistance to antibiotics. Expression of inserted resistance genes within these structures can be poor and, as such, the clinical relevance in terms of the effect of integron carriage on susceptibility has not been investigated. Of 163 unrelated Gram-negative isolates randomly selected from the intensive care and surgical units of 14 different hospitals in nine European countries, 43.0% (70/163) of isolates were shown to be integron-positive, with inserted gene cassettes of various sizes. Integrons were detected in isolates from all hospitals with no particular geographical variations. Integron-positive isolates were statistically more likely to be resistant to aminoglycoside, quinolone and beta8-lactam compounds, including third-generation cephalosporins and monobactams, than integron-negative isolates. Integron-positive isolates were also more likely to be multi-resistant than integron-negative isolates. This association implicates integrons in multi-drug resistance either directly through carriage of specific resistance genes, or indirectly by virtue of linkage to other resistance determinants such as extended-spectrum beta-lactamase genes. As such their widespread presence is a cause for concern. There was no association between the presence of integrons and susceptibility to cefepime, amikacin and the carbapenems, to which at least 97% of isolates were fully susceptible.