Occurrence of ESBL-Producing Escherichia coli in Livestock and Farm Workers in Mecklenburg-Western Pomerania, Germany

Abstract

In recent years, extended-spectrum β-lactamases (ESBL) producing bacteria have been found in livestock, mainly as asymptomatic colonizers. The zoonotic risk for people working in close contact to animal husbandry has still not been completely assessed. Therefore, we investigated the prevalence of ESBL-producing Escherichia spp. in livestock animals and workers to determine the potential risk for an animal-human cross-transmission.In Mecklenburg-Western Pomerania, northeast Germany, inguinal swabs of 73 individuals with livestock contact from 23 different farms were tested for ESBL-producing Escherichia spp. Two pooled fecal samples per farm of animal origin from 34 different farms (17 pig farms, 11 cattle farms, 6 poultry farms) as well as cloacal swabs of 10 randomly selected broilers or turkeys were taken at each poultry farm. For identification, selective chromogenic agar was used after an enrichment step. Phenotypically ESBL-producing isolates (n = 99) were tested for CTX-M, OXA, SHV and TEM using PCR, and isolates were further characterized using multilocus sequence typing (MLST). In total, 61 diverse isolates from different sources and/or different MLST/PCR results were acquired. Five farm workers (three from cattle farms and two from pig farms) harbored ESBL-producing E. coli. All human isolates harbored the CTX-M β-lactamase; TEM and OXA β-lactamases were additionally detected in two, resp. one, isolates. ESBL-producing Escherichia spp. were found in fecal samples at pig (15/17), cattle (6/11) and poultry farms (3/6). In total, 70.6% (24/36) of the tested farms were ESBL positive. Furthermore, 9 out of 60 cloacal swabs turned out to be ESBL positive. All isolated ESBL-producing bacteria from animal sources were E. coli, except for one E. hermanii isolate. CTX-M was the most prevalent β-lactamase at cattle and pig farms, while SHV predominated in poultry. One human isolate shared an identical MLST sequence type (ST) 3891 and CTX-M allele to the isolate found in the cattle fecal sample from the same farm, indicating a zoonotic transfer. Two other pairs of human-pig and human-cattle E. coli isolates encoded the same ESBL genes but did not share the same MLST ST, which may indicate horizontal resistance gene transfer. In summary, the study shows the high prevalence of ESBL-producing E.coli in livestock in Mecklenburg- Western Pomerania and provides the risk of transfer between livestock and farm workers.

Fig 1. Minimum spanning trees based on MLST allelic profiles portraying the clonal relationship of ESBL-producing E. coli.

Each circle represents a given allelic profile (combination of the seven MLST loci) and is named according to the MLST sequence type. The numbers on the connecting lines illustrate the number of differing alleles. If applicable, the clonal complexes (CC) are shaded in grey and named. The correlations between the MLST-based phylogeny and (1A) ESBL genotype represented by the differently colored circles and (1B) origin (animal or human) of the samples are displayed.

Fig 2. Distribution of ESBL genes in samples of human, pig, cattle and chicken origin.

The figure shows the distribution of the ESBL genes CTX-M, OXA, SHV and TEM of Escherichia spp. isolates from humans (inguinal swabs), pig and cattle (fecal samples) and broiler (boot swabs). CTX-M ESBL dominated in pigs with 32 isolates; 8 were found in cattle, 5 in humans and 1 in poultry. OXA enzymes were rare, but most frequently isolated from cattle (n = 2). SHV were also rare and dominated in poultry (n = 2). TEM were most frequently found in isolates of pig origin (n = 11).