Molecular epidemiological study of multi-strain Salmonella outbreaks in Monterey County, California

Salmonella infections are among the most common causes of food-borne gastroenteritis. Between 2004 and 2005, three outbreaks of human Salmonellosis (serotypes Brandenburg, Saintpaul, and Typhimurium) occurred in correctional facilities located in Salinas, CA. In total, 92 outbreak and non-outbreak associated Salmonella isolates were collected to compare local antmicrobial resistance rates, differentiate outbreak strains, and identify any correlations between particular strains and antimicrobial resistance phenotypes. Our results indicated a significantly higher antimicrobial resistance rate in Monterey County isolates compared to the reported national average, including an increasing rate of cephalosporin resistance and resistance to five or more antimicrobial subclasses over time. Pulsed-field gel electrophoretic analysis of outbreak isolates indicated several closely related strains within the Brandenburg and Typhimurium outbreaks. No correlations between genetic profiles and antimicrobial resistance was observed. Antimicrobial resistance testing of Salmonella samples should be strongly emphasized, particularly for isolates collected from persons or animals located in the agricultural areas of Monterey County.