Characterization of Diarrheagenic Strains of Escherichia coli Isolated From Cattle Raised in Three Regions of Mexico

Armando Navarro,Martha Díaz C.,Patricia Isidra Cauich-Sánchez,Alvaro Gutiérrez,Sylvia Paz Díaz,Alejandro Trejo,Alejandro Cravioto,Carlos Eslava

doi:10.3389/fmicb.2018.02373

Abstract

Intestinal infections represent an important public health concern worldwide. Escherichia coli is one of the main bacterial agents involved in the pathogenesis of different diseases. In 2011, an outbreak of hemorrhagic colitis (HC) and hemolytic uremic syndrome (HUS) in Germany was related to a non-O157 STEC strain of O104:H4 serotype. The difficulty in identifying the origin of the bacteria related to the outbreak showed the importance of having epidemiological information from different parts of the world. The aim of this study was to perform a retrospective analysis to determine if E. coli strains isolated from cattle from different locations in Mexico have similar characteristics to those isolated in other countries. Samples obtained in different years from 252 cows belonging to 5 herds were analyzed. A total of 1,260 colonies were selected from the 252 samples, 841 (67%) of which corresponded to E. coli and 419 (33%) to other enterobacteria. In total, 78% (656) of the E. coli strains could be serotyped, of which 393 (59.9%) belonged to 5 diarrheagenic (DEC) pathotypes. Serotyping showed STEC (40.7%) and ETEC (26.7%) strains were more common. PCR assays were used to determine the presence of STEC (eae, stx1, stx2, and ehxA) and EAEC (aatA, aggR, and aapA) genes, and phylogenetic groups. The results showed that 70 strains belonging to 23 serogroups were stx1 and stx2 positive, while 13 strains from the O9 serogroup were ehxA, aggR, and eae positive. Phylogenetic analysis showed 58 (82.9%) strains belonged to A and B1 commensal phylogroups and 12 (17.1%) to B2, D and E virulent phylogroups. An assay to evaluate cross-antigenic reactivity in the serum of cattle between K9 capsular antigen and O104 LPS by ELISA showed similar responses against both antigens (p > 0.05). The antimicrobial sensitivity assay of the strains showed resistance to AM, CEP, CXM, TE, SXT, cephalosporins and fluoroquinolones. The results show that cattle are carriers and potential transmitters of STEC and ETEC strains containing virulence genes. Epidemiological retrospective studies in different countries are of great help for identifying virulent bacterial strains with the potential to cause outbreaks that may have epidemiological impact in susceptible countries.

Highlights

Escherichia coli (E. coli) strains continue to be a frequent cause of human infection
Sampling of dairy cows was conducted in accordance with specific techniques for the production, care and use of laboratory animals, as described in the Mexican Official Norm 062-Zoo-1999 (NOM-062-Zoo-1999; NORMA Oficial Mexicana, 1999)
Rectal and blood samples were collected from 252 cows belonging to five herds of lactating cows raised in Jalisco (Jal), Sinaloa (Sin), and Sonora (Son), Mexico

Summary

Introduction

Escherichia coli (E. coli) strains continue to be a frequent cause of human infection. Animal feces are a secondary source of human infection for some DEC strains, mainly those capable of producing Shiga-like toxin These group of DEC strains have been called Shiga toxin-producing E. coli (STEC) and represent the most frequent cause of severe hemorrhagic colitis (HC) and hemolytic-uremic syndrome (HUS), since their discovery in the early 80 s (Karmali et al, 1983; Riley et al, 1983). While most of the large outbreaks of HC and HUS have been associated with specific STEC belonging to the O157:H7 serotype, STEC strains belonging to other O:H serotypes have been linked to HC and HUS (Mead et al, 1999; Brooks et al, 2005; Gould et al, 2013; Luna-Gierke et al, 2014) This latter group includes the recently isolated O104:H4 strains, which were associated with an important outbreak of HC and HUS in Germany (Frank et al, 2011). Given our interest in the frequency of DEC strains as a cause of diarrheal disease in Mexican children over the past 30 years and the capacity of our laboratory to conduct full serotyping of O and H antigens, and the determination of the virulence characteristics of putative DEC strains isolated from both humans and animals, we describe here the frequency and characteristics of E. coli strains isolated from cattle raised in three different regions of Mexico and discuss the capacity of these strains to cause human disease outbreaks

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Results