Multidrug resistant clones of Salmonella Infantis of broiler origin in Europe

The aim of the study was to investigate the potential spread of the previously described multidrug-resistant (MDR) Hungarian clone of Salmonella Infantis of broiler origin in Europe. Therefore, 76 strains isolated between 2004 and 2009 from raw meat and fecal samples of broiler origin in nine European countries – including Hungary – were examined by phage typing, antimicrobial resistance typing, pulsed-field gel electrophoresis (PFGE) profile and plasmid analysis. The strains could be divided into two large PFGE clusters with 92% similarity. Cluster A (n = 39) contained 15 German, seven Italian, five British, five Polish isolates, one Austrian and one Hungarian isolate. Five Hungarian isolates that were isolated prior to the appearance of the MDR clone also belonged to this cluster. Strains of this cluster comprised seven pulsotypes and 14 different phage types and were mostly susceptible to the 12 antimicrobials tested. Cluster B (n = 33) contained all but one of the recent Austrian (n = 14) and of Hungarian (n = 9), six Polish, one Italian and one German as well as the single Turkish and the Romanian strains, representing five pulsotypes. The strains of this cluster were mostly PT213, with MDR (nalidixic acid-streptomycin-sulphomamide-tetracycline), and the carriage of the same class 1 integron located on a large plasmid (> 168 kb) characteristic of the current predominant Hungarian clone. The results suggest that two large related clusters (A and B) of S. Infantis isolates can be found in various European countries, of which Austrian and Polish MDR clones of cluster B are identical with, or closely related to, the dominant Hungarian clone. The emergence of a few dominant MDR S. Infantis clones in broilers reported here, raises the possibility that further dissemination of such clones in broilers and in broiler meat may occur and represent a potential threat to public health in Europe.

► Clonality and spread of multidrug-resistant, and of sensitive strains of S. Infantis is different.
► European Salmonella Infantis multidrug resistant clones of broiler origin are closely related.
► More detailed characterization of Salmonella serovars and clonal lines in poultry and man is needed.