Distributions of Salmonella Subtypes Differ between Two U.S. Produce-Growing Regions

Abstract

bSalmonella accounts for approximately 50% of produce-associated outbreaks in the United States, several of which have been traced back to contamination in the produce production environment. To quantify Salmonella diversity and aid in identification of Salmonella contamination sources, we characterized Salmonella isolates from two geographically diverse produce-growing regions in the United States. Initially, we characterized the Salmonella serotype and subtype diversity associated with 1,677 samples collected from 33 produce farms in New York State (NYS). Among these 1,677 samples, 74 were Salmonella positive, yielding 80 unique isolates (from 147 total isolates), which represented 14 serovars and 23 different pulsed-field gel electrophoresis (PFGE) types. To explore regional Salmonella diversity associated with production environments, we collected a smaller set of samples (n ‫؍‬ 65) from South Florida (SFL) production environments and compared the Salmonella diversity associated with these samples with the diversity found among NYS production environments. Among these 65 samples, 23 were Salmonella positive, yielding 32 unique isolates (from 81 total isolates), which represented 11 serovars and 17 different PFGE types. The most common serovars isolated in NYS were Salmonella enterica serovars Newport, Cerro, and Thompson, while common serovars isolated in SFL were Salmonella serovars Saphra and Newport and S. enterica subsp. diarizonae serovar 50:r:z. High PFGE type diversity (Simpson's diversity index, 0.90 ؎ 0.02) was observed among Salmonella isolates across both regions; only three PFGE types were shared between the two regions. The probability of three or fewer shared PFGE types was <0.000001; therefore, Salmonella isolates were considerably different between the two sampled regions. These findings suggest the potential for PFGEbased source tracking of Salmonella in production environments.

Distribution and Characterization of Salmonella enterica Isolates from Irrigation Ponds in the Southeastern United States

“…Recently, Newport, Cerro, and Thompson were reported as the most common serovars of isolates from produce-growing regions of New York State, while Saphra, Newport, and S. enterica subsp. diarizonae serovar 50:r:z were most common in south Florida (56). The disparities among studies could represent differences in either sampling methodologies or the discriminatory powers of the different typing methods.…”

Meta-analysis of the Effects of Sanitizing Treatments on Salmonella, Escherichia coli O157:H7, and Listeria monocytogenes Inactivation in Fresh Produce

“…Epidemiological investigations indicate that Salmonella, pathogenic Escherichia coli, and Listeria monocytogenes stand out as the most important bacterial agents linked to fresh-produce disease outbreaks (3,(5)(6)(7). Recent studies have reported the occurrence and high diversity of these microorganisms in the environment or in close areas of produce farming areas (8)(9)(10)(11)(12)(13).…”

Diversity of Salmonella Isolates from Central Florida Surface Waters

“…One of the nonhost reservoirs of Salmonella on which considerable effort has focused is surface water, which poses a potential public health risk through consumption, indirect consumption (for example, irrigation of edible horticultural crops), or direct contact. A number of studies have characterized the distribution of Salmonella isolates from different water sources (5)(6)(7)(8)(9)(10). In evaluations of surface water for Salmonella isolates, multiple serotypes are often identified from a single environmental sample, indicating the diversity of this genus in the environment.…”

“…Salmonella serotypes isolated from surface waters are often not clinically common (4)(5)(6)(7)(8)(9)(10)(11)(12) and often include serotypes of Salmonella enterica subsp. enterica, Salmonella enterica subsp.…”