Carriage and Fecal Counts of Cefotaxime M-Producing Escherichia coli in Pigs: a Longitudinal Study

Abstract

c Current knowledge on extended-spectrum beta-lactamases (ESBLs) in animals is based largely on cross-sectional studies and qualitative data. The aim of this longitudinal study was to elucidate carriage proportions and fecal counts of ESBL-producing Escherichia coli in pigs during the production cycle. At each of three ESBL-positive single-sited farrow-to-finisher pig farms (farms A, B, and C) included in the study, individual fecal samples were taken from 17 to 20 sows 1 week before farrowing and from 2 piglets of each sow's litter four times from birth to slaughter (as piglets, weaners, and finishers). Cefotaxime (CTX)-resistant coliforms in feces were counted on MacConkey agar containing 2 g/ml CTX and characterized for the presence of ESBLencoding genes by PCR and sequencing. CTX-M-positive pigs were detected in all age groups at farms A (bla CTX-M-9 group, compatible with bla CTX-M-14/17 ) and B (bla CTX-M-1 group, compatible with bla CTX-M-1/61 ), whereas only three weaners were positive at farm C (bla CTX-M-1 group, compatible with bla CTX-M-1/61 ). A significant decrease in carriage was detected during the production cycle, with on average 50% carriage immediately after birth, 58% just before weaning, 29% during weaning, and 12% during finishing. The observed reduction in numbers of CTX-M-positive pigs was accompanied by a significant reduction in mean fecal counts of CTX-resistant coliforms from ϳ10 7 CFU/g in piglets to ϳ10 3 CFU/g in finishers (P < 0.001). These findings provide novel information about the epidemiology of ESBLs at the farm level and have important implications for assessments of risks of meat contamination during slaughter.

Strain Diversity of CTX-M-Producing Enterobacteriaceae in Individual Pigs: Insights into the Dynamics of Shedding during the Production Cycle

“…It is also known that the dominant E. coli strains of newborn piglets may differ from those observed in the feces of their dams (27,29). Thus, our findings are in line with the current knowledge of diversity and dynamics of E. coli in pigs, supporting the notion that the population dynamics of CTX-M-producing E. coli does not differ from that of other E. coli, even though these antimicrobial-resistant strains occurred at low fecal densities (approximately 10 3 to 10 7 CFU/g) compared to the total E. coli population, especially at later production stages (11).…”

“…In a recent study, marked reductions in the prevalence of pigs shedding CTX-M-producing E. coli and in the fecal concentrations of CTX-resistant coliforms were observed during the production cycles at two Danish pig farms (11). The present study was designed to elucidate the population dynamics of CTX-M-producing Enterobacteriaceae associated with this observation.…”

“…The farm had a single-sited, farrow-tofinish production system with housing of sows, piglets, weaners, and finishers on the same farm and used continuous production through all sections. Data on antimicrobial consumption at the farm level during the study period and for the preceding 6 months were reported by Hansen et al (11). A total of 15 individual pigs and 45 samples were included in the study.…”

“…In the procedure without enrichment (direct plating), 1 g of feces was suspended in 9 ml of sterile saline, and serial 10-fold dilutions were plated on MacConkey agar supplemented with 2 mg/liter of CTX. Detailed information on the plating method and quantification results has been reported previously (11). After overnight incubation at 37°C, one and two (if available) lactose-positive colonies were randomly selected from the plates deriving from the enrichment and the direct plating procedure, respectively.…”

“…Elucidation of the dynamics of shedding of ESBL-producing Enterobacteriaceae within herds is a first step needed to develop effective control measures in livestock. We recently showed a temporal decrease in both the prevalence of pigs shedding CTX-Mproducing E. coli and the fecal counts of CTX-resistant coliforms in individual pigs during the production cycles of two unrelated Danish farms (11). The objective of the present study was to evaluate the population dynamics of CTX-M-producing Enterobacteriaceae in individual pigs from birth to slaughter at one of the two farms, which was previously shown to be contaminated with CTX-M-14-producing E. coli.…”