Abstract
Shiga toxin-producing Escherichia coli (STEC) O157 and non-O157 are food-borne pathogens and contaminants of foods of animal origin. This study was conducted to investigate the presence of virulence and integrase genes in STEC isolates from diarrhoeic calves in Fars Province, Iran. Five hundred and forty diarrheic neonatal calves were randomly selected for sampling. Rectal swabs were collected and cultured for isolation and identification of E. coli following standard methods. The isolates were analysed for the presence of class 1 integrons and bacterial virulence factors using polymerase chain reaction (PCR). Antimicrobial susceptibility testing was performed using the Kirby–Bauer disc diffusion method. Out of 540 diarrhoeic faecal samples, 312 (57.7%) harboured E. coli and 71 (22.7%) of them were identified as STEC: 41(69.5%) carried the stx2 gene, 21 (35.6%) carried the stx1 gene and 3 (5%) carried both. Twenty-six (44%) of the isolates showed the eae gene. Among the STEC isolates examined for susceptibility to eight antimicrobial agents, erythromycin and penicillin (96.8%) resistance were most commonly observed, followed by resistances to ampicillin (71.8%), tetracycline (62.5%) and trimethoprim/sulfamethoxazole (39%). Integrons were detected by PCR in 36% of the STEC tested isolates, 57 (89%) of which showed resistance to at least three antimicrobial agents. Our findings should raise awareness about antibiotic resistance in diarrhoeic calves in Fars Province, Iran. Class 1 integrons facilitate the emergence and dissemination of multidrug-resistance (MDR) among STEC strains recovered from food animals.
Highlights
New research provides the strongest evidence that Shiga toxin-producing Escherichia coli (STEC) non-O157:H7 and in particular serogroup O157 are linked to severe gastrointestinal diseases (Dehkordi et al 2014)
Higher prevalence of the stx2 gene (54 isolates) compared to the stx1 gene (33 isolates) in this study corroborates the findings of previous reports in Iran (Dastmalchi et al 2012; Tahamtan, Hayati & Namavari 2010). These results contrast with other reports that have shown that most STEC from diarrhoeic calves only produce stx1, whereas stx2-positive strains are the dominant types in healthy calves (Nguyen, Vo & Vu-Khac 2011). The differences in these findings suggest that stx2 may be associated with a majority of E. coli isolates from diarrhoeic calves in Iran
We report the presence of class 1 integrons in the most familiar STEC strains from diarrhoeic calves
Summary
New research provides the strongest evidence that Shiga toxin-producing Escherichia coli (STEC) non-O157:H7 and in particular serogroup O157 are linked to severe gastrointestinal diseases (Dehkordi et al 2014). The clinical manifestations of STEC infection can vary, from asymptomatic carriage to very serious illnesses such as haemolytic uremic syndrome (HUS), thrombocytopenic purpura (TTP) and haemorrhagic colitis (HC) (Thomas et al 2012). But experts suggest that gastrointestinal infections are responsible for approximately 1.5 million deaths per year, over 90% of which are in developing countries (Montenegro et al 2011). Cattle, especially young animals, are known to be the primary reservoirs of both non-O157 and O157 STEC (Moura et al 2012). The pathogenicity of STEC is associated with Shiga toxin (stx) encoded by Shiga toxinogenic (stx) genes 1, 2 (stx and stx2) and an outer membrane protein which is encoded by the chromosomal eae gene (Pradel et al 2008)
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