Emergenza di una variante monofasica di Salmonella Typhimurium : caratteri di antibiotico-resistenza in stipiti isolati dalla filiera suinicola e da casi di infezione nell’uomo

Salmonella enterica serovar Typhimurium (S. Typhimurium) is a common cause of non-typhoideal salmonellosis in humans and animals; since the end of ’90 has been emerged a monophasic serovar, defined by the antigenic formula 4,5:i:-. This study shows the occurrence of the monophasic serovar in Italy (Lombardia Region) and analyses the antimicrobial resistance of 147 S. Typhimurium and 45 monophasic strains. Multiple drug resistance (MDR) has been detected in 94,5% and 76,6% of 55 porcine and 137 human isolates, respectively; the tetra-resistance pattern AmSSuTe is the most common among both the sources (55/116 strains of MDR S. Typhimurium and 16/41 strains of MDR monophasic variant). The transfer of resistance determinants has been investigated by the plasmid conjugation for all the 157 MDR strains: only 16 isolates (10,2%) gave positive results, and the transfer has almost been partial. Data from our study and those reported by the Literature show a wide difference in the circulating phenotypes and in the polymorphism of S. Typhimurium, confirmed also by the emergence of the monophasic serovar.