How to Improve Surveillance Program for Shiga Toxin-Producing E. coli (STEC): Gap Analysis and Pilot Study

Abstract

Several pathotypes of enteric E. coli have been identified. The group represented by Shiga toxin-producing E. coli (STEC) is of particular interest. Raw milk and raw milk products are significant sources of STEC infection in humans; therefore, identifying pathogens at the herd level is crucial for public health. Most national surveillance programs focus solely on raw milk and raw milk cheeses that are ready for retail sale, neglecting the possibility of evaluating the source of contamination directly at the beginning of the dairy chain. To assess the viability of the application of new molecular methodologies to STEC identification in raw milk filters and in calf feces, we analyzed 290 samples from 18 different dairy herds, including 88 bulk tank milk (BTM), 104 raw milk filters (RMF), and 98 calf feces samples. In total 3.4% of BTM, 41.4% of RMF, and 73.4% of calves' feces were positive for stx, supporting our hypothesis that BTM is not a suitable matrix to assess the presence of STEC at herd level, underestimating it. Our conclusion is that the surveillance program needs critical and extensive improvements such as RMF and calves' feces analysis implementation to be more efficient in detecting and preventing STEC infections. The epidemiology of these infections and the characteristics of the pathogen clearly show how a One Health approach will be pivotal in improving our capabilities to control the spread of these infections.

Keywords: E. coli; PCR; STEC; bovines; dairy; epidemiology; molecular biology; surveillance.

Figure 1

Geographical map of the Lombardy region with areas of sampling (red circles).

Figure 2

Comparison between the distribution of the virulence genes in raw milk filter (RMF) and feces samples. Blue bars: raw milk filters virulence factors count, orange bars: fecal samples virulence factors count.

Figure 3

Comparison between the distribution of virulence genes in pre- and post-weaning calf fecal samples. Blue bars: pre-weaning samples virulence factors count, orange bars: post-weaning samples virulence factors count.

Figure 4

Comparison between the distribution of the serotypes in raw milk filters (RMF) and fecal samples.

Figure 5

Comparison of the distributions of the serotypes in pre- and post-weaning fecal samples.