Dataset Information

Incidence and tracking of Escherichia coli O157:H7 in a major produce production region in California.

ABSTRACT: Fresh vegetables have become associated with outbreaks caused by Escherichia coli O157:H7 (EcO157). Between 1995-2006, 22 produce outbreaks were documented in the United States, with nearly half traced to lettuce or spinach grown in California. Outbreaks between 2002 and 2006 induced investigations of possible sources of pre-harvest contamination on implicated farms in the Salinas and San Juan valleys of California, and a survey of the Salinas watershed. EcO157 was isolated at least once from 15 of 22 different watershed sites over a 19 month period. The incidence of EcO157 increased significantly when heavy rain caused an increased flow rate in the rivers. Approximately 1000 EcO157 isolates obtained from cultures of>100 individual samples were typed using Multi-Locus Variable-number-tandem-repeat Analysis (MLVA) to assist in identifying potential fate and transport of EcO157 in this region. A subset of these environmental isolates were typed by Pulse Field Gel Electrophoresis (PFGE) in order to make comparisons with human clinical isolates associated with outbreak and sporadic illness. Recurrence of identical and closely related EcO157 strains from specific locations in the Salinas and San Juan valleys suggests that transport of the pathogen is usually restricted. In a preliminary study, EcO157 was detected in water at multiple locations in a low-flow creek only within 135 meters of a point source. However, possible transport up to 32 km was detected during periods of higher water flow associated with flooding. During the 2006 baby spinach outbreak investigation, transport was also detected where water was unlikely to be involved. These results indicate that contamination of the environment is a dynamic process involving multiple sources and methods of transport. Intensive studies of the sources, incidence, fate and transport of EcO157 near produce production are required to determine the mechanisms of pre-harvest contamination and potential risks for human illness.

SUBMITTER: Cooley M

PROVIDER: S-EPMC2174234 | biostudies-literature | 2007 Nov

REPOSITORIES: biostudies-literature

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Incidence and tracking of Escherichia coli O157:H7 in a major produce production region in California.

Cooley Michael M Carychao Diana D Crawford-Miksza Leta L Jay Michele T MT Myers Carol C Rose Christopher C Keys Christine C Farrar Jeff J Mandrell Robert E RE

PloS one 20071114 11

Fresh vegetables have become associated with outbreaks caused by Escherichia coli O157:H7 (EcO157). Between 1995-2006, 22 produce outbreaks were documented in the United States, with nearly half traced to lettuce or spinach grown in California. Outbreaks between 2002 and 2006 induced investigations of possible sources of pre-harvest contamination on implicated farms in the Salinas and San Juan valleys of California, and a survey of the Salinas watershed. EcO157 was isolated at least once from 15 ...[more]

PMID: 18174909

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Project description:BackgroundGenetic analysis of Escherichia coli O157:H7 strains has shown divergence into two distinct lineages, lineages I and II, that appear to have distinct ecological characteristics, with lineage I strains more commonly associated with human disease. In this study, microarray-based comparative genomic hybridization (CGH) was used to identify genomic differences among 31 E. coli O157:H7 strains that belong to various phage types (PTs) and different lineage-specific polymorphism assay (LSPA) types.ResultsA total of 4,084 out of 6,057 ORFs were detected in all E. coli O157:H7 strains and 1,751 were variably present or absent. Based on this data, E. coli O157:H7 strains were divided into three distinct clusters, which consisted of 15 lineage I (LSPA type 111111), four lineage I/II (designated in this study) (LSPA type 211111) and 12 lineage II strains (LSPA 222222, 222211, 222212, and 222221), respectively. Eleven different genomic regions that were dominant in lineage I strains (present in > or =80% of lineage I and absent from > or = 92% of lineage II strains) spanned segments containing as few as two and up to 25 ORFs each. These regions were identified within E. coli Sakai S-loops # 14, 16, 69, 72, 78, 83, 85, 153 and 286, Sakai phage 10 (S-loops # 91, 92 and 93) and a genomic backbone region. All four lineage I/II strains were of PT 2 and possessed eight of these 11 lineage I-dominant loci. Several differences in virulence-associated loci were noted between lineage I and lineage II strains, including divergence within S-loop 69, which encodes Shiga toxin 2, and absence of the non-LEE encoded effector genes nleF and nleH1-2 and the perC homologue gene pchD in lineage II strains.ConclusionCGH data suggest the existence of two dominant lineages as well as LSPA type and PT-related subgroups within E. coli O157:H7. The genomic composition of these subgroups supports the phylogeny that has been inferred from other methods and further suggests that genomic divergence from an ancestral form and lateral gene transfer have contributed to their evolution. The genomic features identified in this study may contribute to apparent differences in the epidemiology and ecology of strains of different E. coli O157:H7 lineages.

Project description:Escherichia coli serotype O157:H7 is a zoonotic food- and waterborne bacterial pathogen that causes a high hospitalization rate and can cause life-threatening complications. Increasingly, E. coli O157:H7 infections appear to originate from fresh produce. Ruminants, such as cattle, are a prominent reservoir of E. coli O157:H7 in the United States. California is one of the most agriculturally productive regions in the world for fresh produce, beef, and milk. The close proximity of fresh produce and cattle presents food safety challenges on a uniquely large scale. We performed a survey of E. coli O157:H7 on 20 farms in California to observe the regional diversity and prevalence of E. coli O157:H7. Isolates were obtained from enrichment cultures of cow feces. Some farms were sampled on two dates. Genomes from isolates were sequenced to determine their relatedness and pathogenic potential. E. coli O157:H7 was isolated from approximately half of the farms. The point prevalence of E. coli O157:H7 on farms was highly variable, ranging from zero to nearly 90%. Within farms, generally one or a few lineages were found, even when the rate of isolation was high. On farms with high isolation rates, a single clonal lineage accounted for most of the isolates. Farms that were visited months after the first visit might have had the same lineages of E. coli O157:H7. Strains of E. coli O157:H7 may be persistent for months on farms.IMPORTANCE This survey of 20 cow-calf operations from different regions of California provides an in depth look at resident Escherichia coli O157:H7 populations at the molecular level. E. coli O157:H7 is found to have a highly variable prevalence, and with whole-genome sequencing, high prevalences in herds were found to be due to a single lineage shed from multiple cows. Few repeat lineages were found between farms in this area; therefore, we predict that E. coli O157:H7 has significant diversity in this area beyond what is detected in this survey. All isolates from this study were found to have pathogenic potential based on the presence of key virulence gene sequences. This represents a novel insight into pathogen diversity within a single subtype and will inform future attempts to survey regional pathogen populations.

Dataset Information

Incidence and tracking of Escherichia coli O157:H7 in a major produce production region in California.

Publications

Incidence and tracking of Escherichia coli O157:H7 in a major produce production region in California.

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