Antimicrobial Susceptibility of Pathogenic Escherichia coli Isolated from Pigs in Korea.

Abstract

ABSTRACT. The in vitro susceptibilities of 285 isolates of Escherichia coli from preweaned and postweaned pigs with diarrhea and edema disease were tested with the 15 commonly used antimicrobial drugs by an agar dilution minimal inhibitory concentration procedure according to National Committee for Clinical Laboratory Standards (NCCLS) guidelines. All E. coli isolates tested in this study belonged to enterotoxigenic E. coli, attaching and effacing E. coli, or Shiga toxin-producing E. coli. Field isolates had low MIC 90 for ceftiofur (1 µg/ml). No correlation in antimicrobial resistance was found in three types of E. coli. Escherichia coli strains such as enterotoxigenic E. coli (ETEC), attaching and effacing E. coli (AEEC), and Shiga toxin-producing E. coli (STEC) are associated with diarrhea and edema disease in pigs. ETEC has 2 types of virulence factors, fimbrial adhesins and enterotoxins [5,14]. The production of attaching and effacing lesions by AEEC strains is associated with a chromosomal determinant, eaeA [7]. Shiga toxin 2e (Stx2e) produced by STEC plays an important role in the pathogenesis of edema disease in postweaned pigs [6,12]. AEEC have been identified as a cause of diarrhea in pigs [7]. The characteristic intestinal lesion resulting from AEEC is the attaching and effacing (A/E) histopathology, characterized by intimate bacterial adherence to enterocytes and disruption of the underlying cytoskeleton [15].Antimicrobial resistance is one of the main concerns for health professionals dealing with bacterial disease. The current trend worldwide is to reduce antibiotic use in animal production in favor of good husbandry practices and vaccination, as means to raise healthier animals. Acknowledging the susceptibility profiles of a given bacterium can help to select appropriate treatment for the infections caused by it, which reduces failure rates, and saves time and money. Isolation of such a pathogenic E. coli may be necessary for efficient treatment since numerous non-pathogenic E. coli mainly inhabit the intestinal tracts of pigs. This is a key point since mis-isolation of the causal strain could lead to treatment failure and an increase in antimicrobial resistance, but most of antimicrobial susceptibility studies did not focus on pathogenic E. coli prior to antimicrobial susceptibility procedures. The objective of this study was to select the pathogenic E. coli among E. coli isolated from pigs with diarrhea and edema disease in Korea, and determine the antimicrobial susceptibility of these pathogenic isolates by means of new standardized procedures for the antimicrobial susceptibility test for animal pathogens issued by the National Committee for Clinical Laboratory Standards (NCCLS) [16].Between 1995 and 1998, 853 isolates of E. coli were isolated from 957 diarrheic piglets younger than 14 days; and 250 isolates of E. coli were isolated from 294 postweaned pigs with diarrhea and edema disease submitted from all over Korea to the Department of Veterinary Pathology, Seoul National University. Specime...

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