Submitted to: Clinical Infectious Diseases
Publication Type: Peer reviewed journal
Publication Acceptance Date: 8/22/2005
Publication Date: 1/1/2006
Citation: Zaidi, M.B., Mcdermott, P.F., Cray, P.J., Leon, V., Canche, C., Hubert, S.K., Abbott, J., Leon, M., Zhao, S., Headrick, M. 2006. Non typhoidal salmonella from human clinical cases asymptomatic carriers and raw retail meats in yucatan mexico. Clinical Infectious Diseases. 42 21-28. Interpretive Summary: Salmonella is a zoonotic pathogen which can be transferred from animals to humans, most often through consumption of contaminated food. Infection with Salmonella can cause mild to severe gastroenteritis in humans while infection in food animals is often without clinical signs of disease. We collected samples from people with and without diarrhea, and from retail pork, poultry and beef in Yucatan, Mexico over three years for culture of Salmonella. Subsequently, we also characterized the antimicrobial susceptibility patterns of those isolates and analyzed the isolates to see if those isolated from humans matched those isolated from food products. People with diarrhea and pork were more like to be positive for Salmonella than people without diarrhea and beef or poultry. Antimicrobial resistance was frequently observed, particularly to tetracycline, streptomycin and sulfamethoxazole, antimicrobials which have been used for many decades in both people and animals. Some, but not all, of the isolates from both people and meat appeared to be genetically related. Collectively, these data indicate that food is a likely source of Salmonella in Yucatan, Mexico. These data are necessary to enable a more informed debate among scientists, commodity groups, government regulators, and animal industry personnel regarding the transmission of Salmonella between contaminated food and people as well as providing information on Salmonella that is frequently isolated in countries other than the United States.
Technical Abstract: Background: We report the results of a 3-year Salmonella surveillance study of persons with diarrhea; asymptomatic children; and retail pork, poultry and beef in Yucatan, Mexico. Methods: Isolates were characterized for serotype, antimicrobial susceptibility and genetic relatedness using pulsed-field gel electrophoresis. Results: Salmonella Typhimurium was the most common serotype found in ill humans (21.8% of isolates), followed by S. Agona (21% of isolates). Salmonella Enteritidis was a minor serotype (4.2% of isolates). Asymptomatic children carried S. Agona (12.1% of isolates), S. Meleagridis (11.6% of isolates), Salmonella Anatum (8% of isolates) and S. Enteritidis (5.8% of isolates). A high percentage of retail meats contained Salmonella; it was most commonly found in pork (58.1% of samples), followed by beef (54% of samples) and poultry (39.7% of samples). Resistance to oral drugs used for the treatment of salmonellosis was observed for ampicillin (14.6% of isolates), chloramphenicol (14.0% of isolates) and trimethoprim-sulfamethoxazole (19.7% of isolates). Resistance to ceftriaxone emerged in 2002 and was limited to the serotype S. Typhimurium. Twenty-six percent of the isolates were resistant to nalidixic acid, and none were resistant to ciprofloxacin. Multidrug resistance was most common among isolates of serotypes S.Typhimurium and S. Anatum. Pulsed-field gel electrophoresis showed that strains found in retail meats were genetically identical to strains found in both asymptomatic children and ill humans. Conclusions: Our study found a high prevalence of Salmonella in retail meats and persons with enteric infection; many of these isolates were resistant to clinically important antimicrobials. A random selection of isolates from human and retail meat showed genetic relatedness, which suggests that, in Yucatan, considerable transfer of Salmonella occurs through the food chain.