Serogroups and antimicrobial susceptibility of <i>Salmonella</i> isolated from people and food items in southern provinces of Vietnam

Abstract

This article presents current relevant data on the serogroups and antimicrobial susceptibility of Salmonella strains isolated in the southern provinces of the Socialist Republic of Vietnam. There were examined 189 Salmonella strains isolated from: human feces in acute diarrhea (86 strains); and pork samples (103 strains). Serological O-group identification was performed by slide agglutination with O- and H-antisera and multiplex PCR to detect H phase-1 and phase-2. Antimicrobial susceptibility testing was performed by using the disk-diffusion method according to the EUCAST (version 2019) recommendations. Strains isolated from humans predominantly belonged to O4 group (69.8%). The percentage of other serogroups varied from 1.2% (rare group O16) to 11.6% (O9). About a half of strains (44.7%) isolated from pork samples turned out to belong to the О3,10 serogroup (vs 7.0% of strains from humans). Serogroups О7, О4 and О8 were less frequent (22.3%, 14.6% and 13.6%, respectively). Single strains belonged to serogroups О9, О13, and О18. Regardless of the isolation source, about 80% of Salmonella strains were resistant to antibiotics from different antimicrobial groups (besides carbapenems): 67.0% were resistant to tetracycline; about half were resistant to pefloxacin, ampicillin and chloramphenicol (54.0%, 47.1%, 46.6%); and up to 40% were resistant to trimethoprim/sulfamethoxazole and nalidixic acid. The proportion of strains resistant to ceftriaxone and gentamycin was markedly higher in those of human vs pork origin: 12.8% vs 1.0% and 30.2 vs 1.9%, respectively. Moreover, 62.8% and 43.7% strains of human and pork origin, respectively, showed multidrug resistance (to 3 and more antimicrobial groups). In addition, simultaneous resistance to 6 antimicrobial groups was detected much more frequently in Salmonella strains isolated from humans vs pork samples (15.1% vs 1.0%, respectively). Multidrug resistance (MDR) was observed in strains of different serovars, predominantly S. Typhimurium (36.4%). The predominant MDR (30.3%) phenotype (AMP, TE, QN, C, SXT) was revealed in serovars of S. Typhimurium, S. Bredeney, S. Corvallis, S. Give, S. London, S. Rissen, and S. Meleagridis. Thus, Salmonella strains isolated in the southern Vietnamese provinces featured resistance to fluoroquinolones and cephalosporins. Taking into account simultaneous loss of susceptibility to old antimicrobials (ampicillin, chloramphenicol, trimethoprim/sulfamethoxazole), it crucially restricts the list of effective medicines to treat complicated salmonellosis cases.