Serogroup distribution and virulence characteristics of sorbitol-negativeEscherichia colifrom food and cattle stool

Abstract

Aims: To (i) study the serogroup distribution and virulence characteristics of non‐sorbitol‐fermenting Escherichia coli isolates from foods of animal origin and cattle faeces and (ii) re‐examine the true sorbitol and β‐d‐glucuronidase (GUD) reactions of sorbitol‐negative (Sor−) strains from MacConkey sorbitol agar (SMAC) to assess their phenotypic similarity with E. coli O157. Methods and Results: One hundred and thirty Sor−E. coli were isolated from 556 food samples and 177 cattle stool samples using cefixime tellurite–supplemented SMAC (CT‐SMAC) and chromogenic HiCrome MS.O157 agar respectively. Based on typing of somatic antigen, the isolates were classified into 38 serogroups. PCR results identified about 40% strains, belonging to O5, O8, O20, O28, O48, O60, O78, O82, O84, O101, O110, O123, O132, O156, O157, O‐rough and OUT as Shiga toxigenic. Majority of O5, O84, O101, O105, O123, O157, O‐rough and OUT strains were enterohaemolytic. Further, 39·2% and 63·1% of Sor− isolates from CT‐SMAC fermented sorbitol in phenol red broth and hydrolysed 4‐methylumbelliferyl‐β‐d‐glucuronide (MUG) respectively. Members of serogroups O5, O28, O32, O81, O82, O84, O101, O‐rough lacked both the sorbitol fermentation (broth test) and GUD activity and might create confusion in phenotypic identification of E. coli O157. Conclusions: Sor−E. coli isolates from raw meat, milk, shrimp and cattle stool belonged to 38 serogroups, with E. coli O157 constituting only 14·6% of the isolates. Many of these nonclinical Sor− strains were potentially pathogenic. Nearly 39% of these Sor−E. coli from CT‐SMAC fermented sorbitol in broth, indicating the need for confirmation of sorbitol reaction in broth. Significance and Impacts of the Study: Classical sorbitol utilization and GUD tests are not likely definitive tests for E. coli O157. Further improvement of differential media based on these phenotypic properties is necessary for detection of pathogenic serotypes from foods and environmental samples.

Diversity of antibiotic‐resistant Shiga toxin‐producing Escherichia coli serogroups in foodstuffs of animal origin in northern India

“…Raw beef had more non‐O157 STEC isolates compared to all other types of foodstuffs (45%) ( χ 2 , p < .1), that was expected given that bovines are the main environmental reservoir of various STEC serogroups, both O157 and non‐O157 serogroups (Karmali et al, ; Synge, ). Our findings agrees with reports obtained from India and the rest of the world indicating that foodstuffs of bovine origin were found to carry higher numbers of STEC, including non‐O157 serogroups (Bai et al, ; Hazarika et al, ; Manna et al, ; Sinha et al, ; Xia et al, ).…”

“…The diversity of E. coli serogroups in foodstuffs samples showed the prevalence of serogroup O60 (19, n = 158) as the first most prevalent serogroup, particularly in food of bovine origin (raw beef, milk, and beef kebab). Serogroup O60 was detected in food of bovine origin and cattle feces with various degrees of predominance in India (Manna et al, ; Sinha et al, ). Another two serogroups that were exclusively of bovine origin in this study were O8 (7, n = 158) and O68 (7, n = 158), these two serogroups were also commonly reported in food of bovine origin and cattle feces in India and worldwide (Blanco et al, ; Manna et al, ; Orden et al, ; Sinha et al, ).…”

Escherichia coliO157:H7: Animal Reservoir and Sources of Human Infection

“…Moreover, non-O157 E. coli may be unable to ferment sorbitol, whereas sorbitolnegative isolates obtained by selective plating may be able to process the sugar. Among 139 sorbitol-negative isolates of 38 E. coli serogroups from food and cattle feces, only 14.6% were O157; however, 39.2% of 139 fermented sorbitol in broth, and exclusion of these increased the percentage of O157 serotype to over 24% (Manna et al, 2009). Serotyping may generate false-negatives since H7 and O157 antigens may not be expressed; out of 100 meat isolates, 42 were H7-negative by latex agglutination but H7 positive by polymerase chain reaction (Narang et al, 2009).…”

&lt;i&gt;Escherichia coli&lt;/i&gt; in seafood: A brief overview

“…Manna et al [45] acknowledged the presence of non-sorbitol-fermenting E. coli in foods-shrimp, raw meat, milk, and cattle stool-those of which belonged to 38 different serogroups, with E. coli O157 constituting 14.6% from the total of isolates.…”