Shiga Toxin-Producing Escherichia coli in Plateau Pika (Ochotona curzoniae) on the Qinghai-Tibetan Plateau, China

Abstract

Shiga toxin-producing Escherichia coli (STEC) are an emerging group of zoonotic pathogens. Ruminants are the natural reservoir of STEC. In this study we determined the prevalence and characteristics of the STEC in plateau pika (Ochotona curzoniae) on the Qinghai-Tibetan Plateau, China. A total of 1116 pika samples, including 294 intestinal contents samples, 317 fecal samples, and 505 intestinal contents samples, were collected from May to August in the years 2012, 2013, and 2015, respectively. Twenty-one samples (1.88%) yielded at least one STEC isolate; in total, 22 STEC isolates were recovered. Thirteen different O serogroups and 14 serotypes were identified. One stx 1 subtype (stx 1a) and three stx 2 subtypes (stx 2a, stx 2b, and stx 2d) were present in the STEC isolates. Fifteen, fourteen, and three STEC isolates harbored the virulence genes ehxA, subA, and astA, respectively. Adherence-associated genes iha and saa were, respectively, present in 72.73 and 68.18% of the STEC isolates. Twenty antibiotics were active against all the STEC isolates; all strains were resistant to penicillin G, and some to cephalothin or streptomycin. The 22 STEC isolates were divided into 16 pulsed-field gel electrophoresis patterns and 12 sequence types. Plateau pikas may play a role in the ongoing circulation of STEC in the Qinghai-Tibetan plateau. This study provides the first report on STEC in plateau pikas and new information about STEC reservoirs in wildlife. Based on the serotypes, virulence gene profiles and multi-locus sequence typing (MLST) analysis, the majority of these pika STECs may pose a low public health risk.

Keywords: MLST; PFGE; Shiga toxin-producing Escherichia coli; antibiotic resistance; plateau pika.

FIGURE 1

Pulsed-field gel electrophoresis (PFGE) profiles of 22 non-O157 Shiga toxin-producing Escherichia coli (STEC) isolates from plateau pikas. The corresponding isolate names, PFGE patterns, sequence types (STs), serotypes, stx₁ and stx₂ subtypes, the profiles of ehxA, iha, saa, subA, and astA genes, and antibiotic resistances are listed on the right. Year of sampling is contained in the first two numbers of the isolate names: 12 means year 2012, 13 means 2013, and 15 means 2015. Abbreviations for antibiotics are: S, Streptomycin; KF, Cephalothin. ‘+’ means genes positive or antibiotic resistant; ‘-’ means genes negative or antibiotic susceptible.

FIGURE 2

Minimum spanning tree of 12 STs from this study (blue), 32 STs from the HUSEC collection (red), and 36 STs from human STEC STs of serogroups O26, O45, O103, O111, O121, O145, and O157 in the E. coli MLST database (green). Each circle represents a ST, with the pie divided proportionally to the number of isolates in that ST from different sources. The number in a circle indicates the ST number. The numbers on connecting lines represent the number of allelic differences between two STs.