|Cao, Huilin - University Of Maryland|
|Pradhan, Abani - University Of Maryland|
|Wolfgang, Dave - Pennsylvania State University|
|Hovingh, Ernest - Pennsylvania State University|
|Van Kessel, Jo Ann|
Submitted to: American Society for Microbiology Branch Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 5/19/2017
Publication Date: 5/30/2017
Citation: Cao, H., Pradhan, A.K., Karns, J.S., Wolfgang, D.R., Hovingh, E., Van Kessel, J.S. 2017. Prevalence of multidrug-resistant E. coli in different age groups of dairy cattle. American Society for Microbiology Branch Meeting. May 30, 2017.
Technical Abstract: Background: The emergence and dissemination of antimicrobial resistance in bacteria has become a major public health concern. The objective of this study was to examine antimicrobial resistance in commensal E. coli from different age-groups of animals on dairy farms. Materials: A total of 444 manure composite samples were collected from 80 participating farms in Pennsylvania. From each of these farms, one sample each was collected from the pens of pre-weaned calves, post-weaned calves, dry cows, and up to three groups of lactating cows. Five E. coli isolates from each sample were screened for antimicrobial resistance with Mueller Hinton agar supplemented with National Antimicrobial Resistance Monitoring System (NARMS) breakpoint concentrations of ampicillin, cefoxitin, chloramphenicol, tetracycline, streptomycin, kanamycin, ciprofloxacin, and cefotaxime. For each sample, isolates with unique resistance patterns were further characterized using the Sensititre automated antimicrobial susceptibility system on the NARMS Gram-negative Panel. MIC was interpreted based on CLSI standards where available (otherwise, NARMS breakpoint values were used). Resistance data based on Sensititre microdilution tests were analyzed using SAS v9.4 PROC GLIMMIX to compare different age groups. Cephalosporin-resistant isolates (n=72) were screened by PCR for the presence of the plasmid-mediated blaCMY gene and group-specific blaCTX-M genes. Results: Based on the prescreening results, resistant E. coli isolates (n=2370) were prevalent in all animal categories: resistant isolates were observed in pre-weaned calf samples from 88% of the farms, post-weaned calf samples from 81% of the farms, dry cow samples from 46% of the farms, and lactating cow samples from 64% of the farms. Three hundred seventy-six isolates were selected for characterization via the mirodilution method and 285 (75.8%) isolates exhibited resistance to at least one antimicrobial on the NARMS GN Panel. Of these resistant isolates, 117 (41.0%) isolates were multi-drug resistant (MDR) (resistant to =4 antimicrobials) from 50 (62.5%) farms. The predominant phenotype among MDR isolates included resistance to chloramphenicol, streptomycin, tetracycline, and sulfisoxazole. Based on a generalized linear model with Binomial distribution analysis, the prevalence of resistance to 8 drug categories was significantly higher for isolates from pre-weaned calves than from the other animal categories (p<0.05). Isolates resistant to 8 drug classes were observed in 2 pre-weaned calf samples and 2 post weaned calf samples from 4 (5.0%) different farms. MDR E. coli were significantly more prevalent among young animal groups than adult animal groups (p<0.05). Based on PCR results, blaCMY was detected in pre-weaned calf samples on 24 (31.2%) farms, post-weaned calf samples on 10 (13.3%) farms, and lactating cow samples on 3 (4.2%) farms. The blaCTX-M genes were found in isolates from 1 (1.3%) pre-weaned, 1 (1.3%) post-weaned, and 1 (1.3%) lactating cow sample. Conclusion: The results of this study indicate that resistant E. coli are more prevalent in calves than in adult cows within the same dairy herd. Given the current prevalence of multidrug resistance among commensal E. coli on dairy farms in Pennsylvania (41.0%), continued local and regional surveillance is warranted.