Abstract
Salmonella enterica subspecies enterica serovar Typhimurium is the most common zoonotic pathogen in Bulgaria. To allow efficient outbreak investigations and surveillance in the food chain, accurate and discriminatory methods for typing are needed. This study evaluated the use of multiple‐locus variable‐number of tandem repeats analysis (MLVA) and compared results with antimicrobial resistance (AMR) determinations for 100 S. Typhimurium strains isolated in Bulgaria during 2008–2012 (50 veterinary/food and 50 human isolates). Results showed that isolates were divided into 80 and 34 groups using MLVA and AMR, respectively. Simpson's index of diversity was determined to 0.994 ± 0.003 and 0.945 ± 0.012. The most frequently encountered MLVA profiles were 3‐11‐9‐NA‐211 (n = 5); 3‐12‐9‐NA‐211 (n = 3); 3‐12‐11‐21‐311 (n = 3); 3‐17‐10‐NA‐311 (n = 3); 2‐20‐9‐7‐212 (n = 3); and 2‐23‐NA‐NA‐111 (n = 3). No clustering of isolates related to susceptibility/resistance to antimicrobials, source of isolation, or year of isolation was observed. Some MLVA types were found in both human and veterinary/food isolates, indicating a possible route of transmission. A majority (83%) of the isolates were found to be resistant against at least one antimicrobial and 44% against ≥4 antimicrobials. Further studies are needed to verify MLVA usefulness over a longer period of time and with more isolates, including outbreak strains.
Highlights
Nontyphoid salmonellae are among the leading causes for human food- borne infections worldwide
Typhimurium isolates from human, veterinary, and food sources in Bulgaria from 2006 to 2012 to obtain background information about multiple-locus variable-number of tandem repeats analysis (MLVA) types, and the discriminatory ability of the different MLVA loci, in order to evaluate its applicability for routine surveillance and outbreak investigations
Typhimurium is one of the serotypes that are most often isolated from humans, as well as animals and food (European Food Safety Authority (EFSA) and EuropeanCentre for Disease Prevention and Control (ECDC), 2013), it is important from a public health perspective to rapidly differentiate between strains to enable efficient tracing throughout the food production chain
Summary
Nontyphoid salmonellae are among the leading causes for human food- borne infections worldwide. KEYWORDS antimicrobial resistance, laboratory surveillance, MLVA, public health, Salmonella genetic diversity, zoonoses The currently existing phenotyping methods for Salmonella, including serotyping, phage typing, and antimicrobial resistance (AMR) determination, have several disadvantages, such as being time consuming and laborious, and having insufficient discriminatory power for certain purposes (Lindstedt, 2011; Wattiau, Boland, & Bertrand, 2011).
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