title: Development of a robust method for isolation of shiga toxin-positive Escherichia coli (STEC) from fecal, plant, soil and water samples from a leafy greens production region in California.
abstract: During a 2.5-year survey of 33 farms and ranches in a major leafy greens production region in California, 13,650 produce, soil, livestock, wildlife, and water samples were tested for Shiga toxin (stx)-producing Escherichia coli (STEC). Overall, 357 and 1,912 samples were positive for E. coli O157:H7 (2.6%) or non-O157 STEC (14.0%), respectively. Isolates differentiated by O-typing ELISA and multilocus variable number tandem repeat analysis (MLVA) resulted in 697 O157:H7 and 3,256 non-O157 STEC isolates saved for further analysis. Cattle (7.1%), feral swine (4.7%), sediment (4.4%), and water (3.3%) samples were positive for E. coli O157:H7; 7/32 birds, 2/145 coyotes, 3/88 samples from elk also were positive. Non-O157 STEC were at approximately 5-fold higher incidence compared to O157 STEC: cattle (37.9%), feral swine (21.4%), birds (2.4%), small mammals (3.5%), deer or elk (8.3%), water (14.0%), sediment (12.3%), produce (0.3%) and soil adjacent to produce (0.6%). stx1, stx2 and stx1/stx2 genes were detected in 63%, 74% and 35% of STEC isolates, respectively. Subtilase, intimin and hemolysin genes were present in 28%, 25% and 79% of non-O157 STEC, respectively; 23% were of the "Top 6″ O-types. The initial method was modified twice during the study revealing evidence of culture bias based on differences in virulence and O-antigen profiles. MLVA typing revealed a diverse collection of O157 and non-O157 STEC strains isolated from multiple locations and sources and O157 STEC strains matching outbreak strains. These results emphasize the importance of multiple approaches for isolation of non-O157 STEC, that livestock and wildlife are common sources of potentially virulent STEC, and evidence of STEC persistence and movement in a leafy greens production environment.
authors.affiliation: Produce Safety and Microbiology Research Unit, United States Department of Agriculture-Agricultural Research Service, Albany, California, United States of America. michael.cooley@ars.usda.gov
authors.forename: Michael B
authors.initials: MB
authors.lastname: Cooley
authors.forename: Michele
authors.initials: M
authors.lastname: Jay-Russell
authors.forename: Edward R
authors.initials: ER
authors.lastname: Atwill
authors.forename: Diana
authors.initials: D
authors.lastname: Carychao
authors.forename: Kimberly
authors.initials: K
authors.lastname: Nguyen
authors.forename: Beatriz
authors.initials: B
authors.lastname: Quiñones
authors.forename: Ronak
authors.initials: R
authors.lastname: Patel
authors.forename: Samarpita
authors.initials: S
authors.lastname: Walker
authors.forename: Michelle
authors.initials: M
authors.lastname: Swimley
authors.forename: Edith
authors.initials: E
authors.lastname: Pierre-Jerome
authors.forename: Andrew G
authors.initials: AG
authors.lastname: Gordus
authors.forename: Robert E
authors.initials: RE
authors.lastname: Mandrell
mesh_terms: D000818:Animals; D002140:California; D002417:Cattle; D060766:Drinking Water / Q000382:microbiology; D019453:Escherichia coli O157 / Q000145:classification / Q000235:genetics / Q000302:isolation & purification*; D029968:Escherichia coli Proteins / Q000145:classification / Q000235:genetics / Q000302:isolation & purification*; D005243:Feces / Q000382:microbiology; D005516:Food Microbiology; D058885:Multilocus Sequence Typing; D060885:Multiplex Polymerase Chain Reaction; D019081:O Antigens / Q000145:classification / Q000235:genetics / Q000302:isolation & purification*; D010802:Phylogeny; D054323:Shiga-Toxigenic Escherichia coli / Q000145:classification / Q000235:genetics / Q000302:isolation & purification*; D012988:Soil Microbiology; D013552:Swine; D014675:Vegetables / Q000382:microbiology*; D062065:Wastewater / Q000382:microbiology
chemical_list: D060766:Drinking Water; D029968:Escherichia coli Proteins; D019081:O Antigens; D062065:Wastewater