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Selective Pressure and Impact on Salmonella enterica from Swine Production Environment in the U.S

Research Scholar

Julius Medardus, Veterinary Preventive Medicine (Tanzania)
Bayleyegn Z. Molla, Co-Researcher
Wondwossen A Gebreyes, Faculty Mentor


Julius Medardus received a bachelor's in veterinary medicine and a master's in veterinary preventive medicine from Sokoine University of Agriculture (SUA) in Tanzania. He teaches veterinary anatomy and cell biology courses to veterinary and education undergraduate students at SUA. He has also worked as district veterinarian and veterinary tutor before he joined the university faculty. His research interests are on antimicrobial resistance and their mechanisms of resistance in foodborne pathogens. Currently, he is a visiting scholar in the Department of Veterinary Preventive Medicine at The Ohio State University.

What is the issue or problem addressed in your research?

Salmonella is one of the major bacterial foodborne pathogens transmitted commonly through contaminated food. Various studies on antimicrobial resistance in Salmonella have shown the existence and persistence of multi-drug resistance in Salmonella in swine production systems even when there was no history of antimicrobial use.

The emergence and persistence of multi-drug resistant (MDR) Salmonella serovars in swine production environment is attributable not only to use of antimicrobial agents but also other risk factors such as selective pressure including the use of disinfectants and micronutrients in intensive swine production units. The use of biocides for disinfection of swine barns and supplementation of heavy metal micronutrients to swine feed and their role in the emergence and persistence of important foodborne pathogens such as MDR Salmonella has not been understood. 

What methodology did you use in your research?

The goal of this study is to determine the association between the use of specific classes of biocides and heavy metals nutrients such as copper and zinc with the occurrence and persistence of biocide, heavy metal tolerant Salmonella and with that of MDR Salmonella in commercial swine production units.

To address this problem, we randomly selected Salmonella isolates recovered from swine barns treated with different biocides in the course of 2 years. The selected Salmonella isolates were isolated from swine barn floors before and after disinfection, feces at early and late finishing stages and feed from three swine production systems where feed supplementation with micronutrients is common.

What are the purpose/rationale and implications of your research?

Our study will show the association between biocides and heavy metal micronutrients interventions and the occurrence and persistence of MDR-Salmonella strains in the swine production units. This implies that despite the good side of using disinfectants for disinfection purposes and importance of micronutrients supplementation in the animal feed in growth promotion and increasing feed intake it will still have bad side as they also select bacteria to be more resistant and these bacteria if will access entry to human body through food chain will be life threatening as they will not respond to many antibiotics used in treatment of human sick cases.