The Prevalence of Escherichia coli O157:H7 and Other Verotoxin- Producing E. coli in Raw, Ground Beef Samples from Wet Markets in Laguna, Philippines
Forty raw, ground beef samples were collected from wet markets in 15 towns of Laguna, Philippines. The samples were enriched using Tryptic Soy Broth (TSB) containing cefixime, cefsulodin and vancomycin and were plated out on Cefixime-Tellurite Sorbitol MacConkey Agar (CT-SMAC). Four hundred presumptive isolates were obtained and screened for typical E. coli O157:H7 characteristics. Two isolates (B2S7-6 and B4S3-6) were determined to be Escherichia coli exhibiting typical E. coli O157:H7 characteristics based on morphological and biochemical tests. Polymerase chain reaction (PCR) using the E. coli DASTM Kit (BIOTECH) likewise confirmed these isolates to be E. coli. However, none of the isolates was found to possess the O157 antigen using the O157 Latex Agglutination Kit (Oxoid®). The isolates were also tested for genes coding for shiga-like toxin 1 (slt I) and shiga-like toxin 2 (slt II) using PCR and slt I and slt II primers, respectively. Both isolates were negative for slt I but positive for slt II. The prevalence of E. coli O157:H7 in ground beef collected from wet markets in Laguna was 0%. However, the prevalence of non-sorbitol-fermenting, non-β-glucuronidase-producing E. coli in the collected samples was 5%. The prevalence of verotoxin (Shiga-like toxin)-producing non- O157 E. coli in the beef samples was 5%.
Key Words: Escherichia coli 0157:H7, verotoxin-producing E. coli, ground beef
Abbreviations: CT-SMAC – Cefixime-Tellurite Sorbitol MacConkey Agar, EHEC – enterohemorrhagic E. coli, EMBA – Eosin Methylene Blue Agar, HPLC – High Performance Liquid Chromatography, IMVIC – Indole Test, Methyl Red Test, Voges-Proskauer Test and Citrate Utilization, LDB – Lysine Decarboxylase Broth, MUG – 4- methylumbelliferyl-ß-D-glucuronide, NBG – Nutrient Broth (Pronadisa® with 1% D(-) Gluconase, PCR – polymerase chain reaction, SCA – Simmons Citrate Agar, SIM – Sulfide Indole Motility Medium, slt – Shiga-like toxin, TSA – Tryptic Soy Agar, TSAYE – Tryptic Soy Agar with Yeast Extract, TSB – Tryptic Soy Broth, TSI – Triple Sugar Iron Agar, VTECs – verotoxin-producing serotypes