Metallo-β-lactamase expression confers an advantage to Pseudomonas aeruginosa isolates compared with other β-lactam resistance mechanisms, favoring the prevalence of metallo-β-lactamase producers in a clinical environment.

The Pseudomonas aeruginosa isolate TS-832035 exhibited a high level resistance to carbapenems for the contemporary presence of two independent mechanisms: the production of a carbapenemase, coded by a blaVIM-1 determinant carried by a class 1 integron In70.2 and the lack of the OprD porin. We compared TS-832035 with a strictly related isolate, TS-103 that didn’t carry In70.2. These experiments highlighted a significant in vitro fitness cost associated with the integron. On the contrary, none of the resistance determinants other than the blaVIM-1seemed to confer a real selective advantage to its host. Comparison of these results with the in vivo behaviour, showing that the In70.2-carrying isolates largely prevailed over the In70.2-lacking ones, evidence the need to investigate accurately the causes of their large distribution, as possible soft spots could exist in the ability of their hosts to adapt to the hospital settings.