Phage types, virulence genes and PFGE profiles of Shiga toxin-producing Escherichia coli O157:H7 isolated from raw beef, soft cheese and vegetables in Lima (Peru)

• Published in: International journal of food microbiology Vol. 114; no. 2; pp. 204 - 210
• Main Authors: Mora, Azucena, León, Santana L., Blanco, Miguel, Blanco, Jesús E., López, Cecilia, Dahbi, Ghizlane, Echeita, Aurora, González, Enrique A., Blanco, Jorge
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 10.03.2007; Elsevier
• Subjects: Animals; bacterial contamination; Bacteriophage Typing; bacteriophages; Beef; Biological and medical sciences; Cattle; Cheese; Cheese - microbiology; Colony Count, Microbial; Consumer Product Safety; E. coli O157:H7; Electrophoresis, Gel, Pulsed-Field; Escherichia coli; Escherichia coli O157 - genetics; Escherichia coli O157 - metabolism; Escherichia coli O157 - pathogenicity; Escherichia coli O157:H7; Food contamination; Food Contamination - analysis; Food industries; Food Microbiology; food pathogens; Fundamental and applied biological sciences. Psychology; genes; ground beef; Humans; Immunomagnetic Separation; isolation; Lima; Meat - microbiology; Meat Products - microbiology; Milk and cheese industries. Ice creams; Peru; PFGE; Phage typing; raw meat; raw vegetables; Shiga toxins; Shiga Toxins - analysis; Shiga Toxins - biosynthesis; Shiga-like toxins; soft cheeses; STEC; Vegetables; Vegetables - microbiology; Verotoxins; virulence; Virulence - genetics; Peru; Canada; Argentina, Buenos Aire, Lima; Europe; PFGE; Vegetables; Verotoxins; Phage typing; Food contamination; E. coli O157:H7; STEC; Shiga toxins; Cheese; Beef; Peru; Escherichia coli; Virulence; Soft cheese; Meat product; Gene; Bacteria; Shiga like toxin; Enterobacteriaceae; Food; Typing; Dairy product; Contamination; Virus; Phage
• ISSN: 0168-1605; 1879-3460
• DOI: 10.1016/j.ijfoodmicro.2006.09.009

The present study was conducted in Lima Metropolitana to evaluate the prevalence of Shiga toxin-producing Escherichia coli (STEC) O157:H7 in raw beef, raw ground beef, soft cheese and fresh vegetables, sampled at different markets in the city. Between October 2000 and February 2001, 407 food samples were collected from different markets in the 42 districts of Lima Metropolitana. Samples were assayed for E. coli O157 by selective enrichment in modified Tryptic Soy Broth containing novobiocin, followed by immunomagnetic separation (IMS) and plating onto sorbitol MacConkey agar supplemented with cefixime and potassium tellurite. Fifty (12.3%) of 407 food samples resulted positive for E. coli O157 isolation (23 of 102 ground beef; 15 of 102 beef meat; eight of 102 soft cheese and four of 101 fresh vegetables). Thirty-five E. coli O157 isolates were further analysed for the presence of virulence genes. All 35 were positive by PCR for O157 rfbE, fliCh7, eae-γ1 and ehxA genes. In addition, genes encoding Shiga toxins were detected in 33 of 35 isolates, five isolates (14%) encoded stx 1, stx 2, and 28 (80%) stx2 only. The isolates were of seven different phage types (PT4, PT8, PT14, PT21, PT34, PT54, and PT87) with three phage types accounting for 80% of isolates: PT4 (15 isolates), PT14 (8 isolates), and PT21 (5 isolates). Interestingly, the majority (31 of 35; 89%) of E. coli O157:H7 isolates characterized in this study belonged mainly to the phage types previously found in STEC O157:H7 strains associated with severe human disease in Europe and Canada. Pulsed-field gel electrophoresis (PFGE) of 32 isolates revealed 14 XbaI-PFGE groups (I to XIV) of similarity > 85%, with 23 (72%) isolates grouped in five clusters. Some isolates from different districts presented a high clonal relatedness. Thus, PFGE group VIII clustered eleven strains from nine different districts. The broad range of PFGE subtypes found in this study demonstrates the natural occurrence of many genetic variants among STEC O157:H7 spread in Lima.