Extended-spectrum β-lactamase-producing enterobacteriaceae in hospitalized neonatal foals: Prevalence, risk factors for shedding and association with infection

Multidrug-resistant (MDR) Enterobacteriaceae are becoming a major worldwide concern in human and veterinary medicine, mainly due to the production of extended-spectrum β-lactamases (ESBLs). These bacteria have been investigated in adult horses, but not in neonatal foals. In this study, we investigated extended-spectrum β-lactamase Enterobacteriaceae (ESBL-E) shedding and infection in hospitalized mares and their neonatal foals. Overall, we sampled rectal swabs from 55 pairs of mares and their foals on admission, and 33 of them were re-sampled on the 3rd day of hospitalization. We also collected clinical samples, when available. We found that shedding rates and bacterial species diversity increased significantly during hospitalization, both in mares and foals. On admission to hospital, foals’ shedding was associated with umbilical infection. During hospitalization, it was associated with ampicillin treatment. Foals’ shedding was independent of their mares’ shedding. Four foals were infected with ESBL-E strains, including umbilical infections and wounds. We suggest further investigation and surveillance of ESBL-E in neonatal foals, in order to reduce resistance rates and infections. Extended-spectrum β-lactamase Enterobacteriaceae (ESBL-E) have been investigated in adult horses, but not in foals. We aimed to determine shedding and infection in neonatal foals and mares. Rectal swabs were sampled from mare and foal pairs on admission and on the 3rd day of hospitalization; enriched, plated, and bacteria were verified for ESBL production. Identification and antibiotic susceptibility profiles were determined (Vitek2). Genotyping was performed by multilocus sequence typing (MLST). Genes were identified by PCR and Sanger sequencing. Medical data were analyzed for risk factors (SPSS). On admission, 55 pairs were sampled, of which 33 pairs were re-sampled. Shedding rates on admission in foals and mares were 33% (95% CI 21-47%) and 16% (95% CI 8-29%), respectively, and during hospitalization, these increased significantly to 85% (95% CI 70-94%) and 58% (95% CI 40-73%), respectively. Foal shedding was associated with umbilical infection on admission (P = 0.016) and with ampicillin treatment during hospitalization (p = 0.011), and was independent of the mare’s shedding. The most common ESBL-E was Escherichia coli. During hospitalization, species diversity increased. Four foals were infected with ESBL-E strains, including umbilical infections and wounds. This study substantiates an alarming prevalence of shedding in neonatal foals, which should be further investigated in order to reduce resistance rates.