Prevalence and Characterization of Shiga Toxin Producing Escherichia coli Isolated from Animal Feed in Croatia

Abstract

A survey on prevalence and number of Shiga toxin-producing Escherichia (E.) coli (STEC) in animal feed was carried out over a period of nine years in the Republic of Croatia. A total of 1688 feed samples were collected from feed factories and poultry farms. Analysis included two standard procedures: sample enrichment and (a) immunomagnetic separation and plating on two selective media; or (b) plating on two selective media. Confirmation of STEC included morphological examination, biochemical tests, serotyping, and polymerase chain reaction. Morphological and biochemical characterization revealed 629 E. coli strains. Further serological screening method revealed 78 STEC and EPEC serotypes, while only 27 strains were confirmed as STEC with PCR. All positive samples (1.6%) originated from poultry farms and contained combination of virulence genes: eaeA, stx1, and/or stx2. Since the presence of stx (especially stx2) and eae are identified as risk factors for development of severe diseases in humans, results of this survey indicate that avian sources of STEC infections might be one of those "undefined sources" of human illnesses. Further research is necessary for evaluation of risks posed by contaminated feed, poultry, and environment.

Keywords: Escherichia coli; STEC; eae; feed; poultry; stx.

Figure 1

Incidence of E. coli and STEC (confirmed at least one strain by detection of stx genes) in analyzed feed samples in a nine-year period (December 2012–November 2021).

Figure 2

Frequency of serotypes of isolated STEC from feed in Croatia during the nine-year period (n = 27 isolates). OK Pool 1: not fully typed, isolates gave positive agglutination with OK Pool 1, but not with individual antisera (n = 7).

Figure 3

Distribution of seropathotypes (SPT) of isolated STEC from feed during the nine-year period (n = 27 strains): SPT A: n = 2; SPT B: n = 13; SPT C: n = 5; Unassigned: not fully typed (n = 7), seropathotypes are defined by Karmali et al. [27].