Relationship between Escherichia coli virulence factors and postpartum metritis in dairy cows.

The objectives of this study were to report the prevalence of Escherichia coli and Trueperella pyogenes in the uterus of postpartum dairy cows before the onset of postpartum metritis (PPM) and to quantify their association with subsequent occurrence of PPM, to quantify the association between the presence of genes encoding E. coli virulence factors (VF) and PPM, and to determine the accuracy of using early postpartum uterine bacteriology results (bacteria and VF) to identify cows at risk of PPM. A prospective cohort study was conducted on 3 commercial dairy farms. Uterine swabs were collected from 371 Holstein dairy cows (3 commercial herds) at 1 to 7d in milk and submitted to the laboratory for identification of E. coli, T. pyogenes, and E. coli VF. A total of 40 VF were tested using the radioactive probe hybridization method. Postpartum metritis was defined as the presence of a fetid watery red-brown uterine discharge, associated with fever (rectal temperature >39.5°C), and systemic signs of illness (dullness, reduced appetite, and milk production). Surveillance of PPM was done by trained farmers blinded to laboratory results and cows were followed until 21d in milk. Statistical analyses were conducted using 2×2 tables and mixed logistical regression models. Prevalences of E. coli, T. pyogenes, and PPM were 42, 34, and 15%, respectively. A total of 32 VF were found in E. coli isolates. Most prevalent VF were extraintestinal pathogenic genes such as fimH (89%), hlyE (87%), and iss (70%). Cows positive for intrauterine E. coli were 3.2 times more likely to have subsequent PPM compared with bacteriologically negative cows. Cows with VF hra1 in their uterus were 2.7 times more likely to have PPM than cows positive for E. coli and negative for hra1 and 5.9 times more likely than bacteriologically negative cows. Cows with VF kpsMTII in their uterus were 3.2 times more likely to have PPM than cows positive for E. coli and negative for kpsMTII and 6.2 times more likely than bacteriologically negative cows. Using E. coli, hra1, and kpsMTII as predictors for subsequent PPM, positive predictive values were 23, 31, and 42%, respectively, whereas the negative predictive values were 91, 80, and 78%, respectively. Overall, these results showed that E. coli and some VF were associated with PPM.