Multidrug-resistant (MDR) Aeromonas recovered from the metropolitan area of Valencia (Spain): diseases spectrum and prevalence in the environment

Aeromonas infections are rare in Europe and often related to traveller's diarrhoea. A total of 185 Aeromonas isolates from river water, fish and clinical sources, recovered during a 1-year period, were used to investigate the disease spectrum and impact of multidrug-resistant (MDR) strains. They were all identified by biochemical tests and 25 % of them were also identified by sequencing of the 16S rRNA gene. The minimum inhibitory concentrations (MICs) of 21 antimicrobials were determined for all isolates by broth microdilution/E-strips methods, and susceptibility was assessed according to the Clinical and Laboratory Standards Institute (CLSI). Strains pathogenicity was determined by using Swiss Webster mice as the animal model. Aeromonas diseases had an incidence of around 20 cases/million inhabitants in the metropolitan area of Valencia (Spain). Acute gastroenteritis in children with no history of travel abroad was the main pathology. These cases were related to A. caviae, A. veronii biovar sobria, A. hydrophila and A. dhakensis. A significant incidence of A. caviae in humans was found, while the other species were equally present in clinical and environmental origins. A. jandaei, A. bestiarum and A. media had mainly an environmental distribution. The prevalence of MDR Aeromonas was maximal in clinical samples, and resistance phenotypes were significantly related to this source. 7.2 % of environmental Aeromonas was resistant to at least five drugs; most of them were moderately virulent for mice and, in addition, belonged to clinically significant species. The present study demonstrates a diseases spectrum similar to that reported in tropical countries, and also that pathogenic and heavily MDR Aeromonas are present in environmental reservoirs. MDR Aeromonas from any source analysed were susceptible to aztreonam, netilmicin, cefotaxime, ceftazidime, cefepime and fluoroquinolones.