Abstract
We studied the prevalence of extended-spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae in dairy calves as part of a routine health check protocol. In addition, data regarding antimicrobial use (AMU), farm hygiene, and farm management were collected in order to identify possible risks for ESBL occurrence. Ten farms participated in the study with a median of 781 milking cows (319–1701). All calves investigated were younger than two weeks with an average age of 6.8 (±3.9) days. The farms were visited and samples were collected twice at an interval of 7–11 months. Faecal samples diluted 1:10, were plated onto BrillianceTM ESBL agar in duplicates. After 24 hours at 37°C, colonies were counted and total colony forming units (cfu)/ml calculated. Bacteria species were identified biochemically. ESBL-production was phenotypically confirmed using the MICRONAUT-S β-Lactamases system. Additionally, antimicrobial susceptibility was tested using VITEK® 2 technology. Phylotyping of E. coli isolates and screening for bla genes was performed by PCR. ESBL-producing enterobacteria were detected on all farms and 96.5% of calves investigated shed ESBL-positive bacteria. Of all ESBL-producing isolates, the majority were E. coli (92.9%), followed by Enterobacter cloacae (5.1%) and Klebsiella pneumoniae subsp. pneumoniae (2.0%). The majority of E. coli isolates was clearly assigned to phylogroup C (25.0%), followed by phylogroups A (15.2%) and E (14.1%). CTX-M group 1 was most frequently detected (80.4%). E. cloacae contained blaCTX-M and blaTEM or blaSHV. K. pneumoniae harboured blaSHV only. Besides resistance to penicillins and cephalosporins, the majority of isolates was also resistant to one or more antibiotic classes, with a high proportion being resistant against fluoroqinolones. 52.5% of isolates were further characterised as threefold multidrug resistant gram-negative bacteria (3MDR-GNB) according to the German Commission for Hospital Hygiene and Infection Prevention. None of the isolates were 4MDR-GNB, i.e. none revealed carbapenem-resistance. Penicillins were the most frequently administered antibiotics to calves on most farms and were the predominant substance class at herd level on all farms. Overall, the number of calves treated prior to sampling was rather low (11.7%). Analyses of data regarding the farm management identified weaknesses in biosecurity and cleaning and disinfection. Besides beta-lactam antibiotics being the most commonly used antibiotics no other risk factors could be identified. In summary, the prevalence of ESBL-carriers in dairy calves was exceptionally high and should be motivation to develop strategies for the reduction of multidrug-resistant bacteria in farm animals.
Highlights
The objectives of this project were to study the prevalence of extended-spectrum beta-lactamases (ESBL)-producing enterobacteria in newborn calves on dairy farms, and to identify possible risk factors contributing to a high occurrence of ESBL-carriers
ESBL-producing enterobacteria were detected on all ten farms examined in the study
Of 200 faecal samples, 193 contained ESBL-producing enterobacteria which corresponded to a 96.5% prevalence of animals
Summary
Risk factors for the prevalence of ESBL-producing bacteria are believed to be feeding of waste milk that contains residues of antimicrobial substances [14, 15] and the use of 3rd and 4th generation cephalosporins. Management factors, such as an open herd policy and/or poor hygiene management, such as infrequent cleaning of feeding buckets, have been identified as risk factors [16]. The data basis is steadily expanding, there is still a lack of information on the prevalence of ESBL in German dairy cattle [13, 17, 18], especially for the unique farm structure in the eastern part of Germany, where large herds are kept on few farms [19]
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