Case Report: The Endemic Spread of Escherichia coli Positive for Cytotoxic Necrotizing Factor Type 1 in a Canine Research Facility and Impact of Infection in Neonatal Puppies

Escherichia coli strains are the most common bacterial cause of canine neonatal mortality, with rectal and vaginal contaminants from the mother reportedly serving as an important source of infection. Between July and September 2013, a canine research facility at Michigan State University experienced a spike in neonatal mortality. Thirteen of 14 puppies from 2 litters died, with 10 being submitted for necropsy. Three puppies from one litter struggled since birth to suckle and died. Five puppies from an additional litter died after presenting due to failure to thrive, depression, and lethargy. All puppies exhibited microscopic lesions consistent with septicemia represented by interstitial necrotizing pneumonia, random hepatocellular necrosis, or intravascular bacteria. Bacterial cultures of the lung and liver yielded numerous β-hemolytic Streptococcus group G and numerous Escherichia coli, which tested positive by PCR for the cytotoxic necrotizing factor 1 (cnf1) gene. Vaginal and rectal culture swabs taken from adult breeding females between 2013 and 2020 revealed that many were asymptomatic carriers of cnf1+ E. coli. The institution of prophylactic antimicrobial treatment for pregnant females testing culture positive for cnf1+ E. coli before parturition may have prevented additional puppy losses; however, it may have also contributed to resistance observed in future samples. While increased attention to pregnant females testing positive for cnf1+ E. coli prevented subsequent neonatal mortality, the source of the pathogen was not identified. More in-depth sampling of the facility environment could identify a reservoir; however, endemic carriers cannot be ruled out. Screening protocols may be warranted in facilities experiencing persistent cnf1+ E. coli infections.