Herd-level association between antimicrobial use and antimicrobial resistance in bovine mastitis Staphylococcus aureus isolates on Canadian dairy farms.

Surveillance of antimicrobial use and resistance is needed to manage antimicrobial resistance in bacteria. In this study, data were collected on antimicrobial use and resistance in Staphylococcus aureus (n=562), isolated from intramammary infections and (sub)clinical mastitis cases on 89 dairy farms in 4 regions of Canada [Alberta, Ontario, Québec, and the Maritime Provinces (Prince Edward Island, Nova Scotia, and New Brunswick)]. Dairy producers were asked to deposit empty drug containers into specially provided receptacles, and antimicrobial drug use rate was calculated to quantify antimicrobial use. Minimum inhibitory concentrations were determined using the Sensititer bovine mastitis plate system (TREK Diagnostic Systems Inc., Cleveland, OH), containing antimicrobials commonly used for mastitis treatment and control. Multivariable logistic regression models were built to determine herd-level risk factors of penicillin, ampicillin, pirlimycin, penicillin-novobiocin combination, tetracycline and sulfadimethoxine resistance in Staph. aureus isolates. Intramammary administration of the penicillin-novobiocin combination for dry cow therapy was associated with penicillin and ampicillin resistance [odds ratio (OR): 2.17 and 3.10, respectively]. Systemic administration of penicillin was associated with penicillin resistance (OR: 1.63). Intramammary administration of pirlimycin for lactating cow mastitis treatment was associated with pirlimycin resistance as well (OR: 2.07). Average herd parity was associated with ampicillin and tetracycline resistance (OR: 3.88 and 0.02, respectively). Average herd size was also associated with tetracycline resistance (OR: 1.02). Dairy herds in the Maritime region had higher odds of penicillin and lower odds of ampicillin resistance than dairy herds in Québec (OR: 2.18 and 0.19, respectively). Alberta dairy herds had lower odds of ampicillin and sulfadimethoxine resistance than dairy herds in Québec (OR: 0.04 and 0.08, respectively). Ontario dairy herds had lower odds of tetracycline and sulfadimethoxine resistance than dairy herds in Québec (OR: 0.05 and 0.33, respectively). Herd-level use of certain antimicrobials administered for mastitis treatment and control, such as intramammary penicillin and pirlimycin as well as systemically administered penicillin and florfenicol, was positively associated with antimicrobial resistance in bovine mastitis pathogens in the field conditions. Differences in antimicrobial resistance outcomes across 4 regions of Canada were observed.

Saini V ，McClure JT ，Scholl DT ，DeVries TJ ，Barkema HW ... -  《-》

Herd-level relationship between antimicrobial use and presence or absence of antimicrobial resistance in gram-negative bovine mastitis pathogens on Canadian dairy farms.

Concurrent data on antimicrobial use (AMU) and resistance are needed to contain antimicrobial resistance (AMR) in bacteria. The present study examined a herd-level association between AMU and AMR in Escherichia coli (n=394) and Klebsiella species (n=139) isolated from bovine intramammary infections and mastitis cases on 89 dairy farms in 4 regions of Canada [Alberta, Ontario, Québec, and Maritime Provinces (Prince Edward Island, Nova Scotia, and New Brunswick)]. Antimicrobial use data were collected using inventory of empty antimicrobial containers and antimicrobial drug use rate was calculated to quantify herd-level AMU. Minimum inhibitory concentrations (MIC) were determined using Sensititre National Antimicrobial Resistance Monitoring System (NARMS) gram-negative MIC plate (Trek Diagnostic Systems Inc., Cleveland, OH). Isolates were classified as susceptible, intermediate, or resistant. Intermediate and resistant category isolates were combined to form an AMR category, and multivariable logistic regression models were built to determine herd-level odds of AMR to tetracycline, ampicillin, cefoxitin, chloramphenicol, trimethoprim-sulfamethoxazole combination, sulfisoxazole, streptomycin and kanamycin in E. coli isolates. In the case of Klebsiella species isolates, logistic regression models were built for tetracycline and sulfisoxazole; however, no associations between AMU and AMR in Klebsiella species were observed. Ampicillin-intermediate or -resistant E. coli isolates were associated with herds that used intramammarily administered cloxacillin, penicillin-novobiocin combination, and cephapirin used for dry cow therapy [odds ratios (OR)=26, 32, and 189, respectively], and intramammary ceftiofur administered for lactating cow therapy and systemically administered penicillin (OR=162 and 2.7, respectively). Use of systemically administered penicillin on a dairy farm was associated with tetracycline and streptomycin-intermediate or -resistant E. coli isolates (OR=5.6 and 2.8, respectively). Use of cephapirin and cloxacillin administered intramammarily for dry cow therapy was associated with increasing odds of having at least 1 kanamycin-intermediate or -resistant E. coli isolate at a farm (OR=8.7 and 9.3, respectively). Use of systemically administered tetracycline and ceftiofur was associated with cefoxitin-intermediate or -resistant E. coli (OR=0.13 and 0.16, respectively); however, the odds of a dairy herd having at least 1 cefoxitin-intermediate or -resistant E. coli isolate due to systemically administered ceftiofur increased with increasing average herd parity (OR=3.1). Association between herd-level AMU and AMR in bovine mastitis coliforms was observed for certain antimicrobials. Differences in AMR between different barn types and geographical regions were not observed.

Saini V ，McClure JT ，Scholl DT ，DeVries TJ ，Barkema HW ... -  《-》

Antimicrobial use on Canadian dairy farms.

Antimicrobial use (AMU) data are critical for formulating policies for containing antimicrobial resistance. The present study determined AMU on Canadian dairy farms and characterized variation in AMU based on herd-level factors such as milk production, somatic cell count, herd size, geographic region and housing type. Drug use data were collected on 89 dairy herds in 4 regions of Canada, Alberta, Ontario, Québec, and the Maritime provinces (Prince Edward Island, New Brunswick, and Nova Scotia) for an average of 540 d per herd. Dairy producers and farm personnel were asked to deposit empty drug containers into specially provided receptacles. Antimicrobial use was measured as antimicrobial drug use rate (ADUR), with the unit being number of animal defined-daily doses (ADD)/1,000 cow-days. Antimicrobial drug use rates were determined at farm, region, and national level. Combined ADUR of all antimicrobial classes was 14.35 ADD/1,000 cow-days nationally. National level ADUR of the 6 most commonly used antimicrobial drug classes, cephalosporins, penicillins, penicillin combinations, tetracyclines, trimethoprim-sulfonamide combinations, and lincosamides were 3.05, 2.56, 2.20, 1.83, 0.87, and 0.84 ADD/1,000 cow-days, respectively. Dairy herds in Ontario were higher users of third-generation cephalosporins (ceftiofur) than in Québec. Alberta dairy herds were higher users of tetracyclines in comparison to Maritimes. Antimicrobial drug use rate was higher via systemic route as compared with intramammary and other routes of administration (topical, oral, and intrauterine). The ADUR of antimicrobials used intramammarily was higher for clinical mastitis treatment than dry cow therapy. For dry cow therapy, penicillin ADUR was greater than ADUR of first-generation cephalosporins. For clinical mastitis treatment, ADUR of intramammary penicillin combinations was greater than ADUR of cephapirin. Herd-level milk production was positively associated with overall ADUR, ADUR of systemically administered ceftiofur, cephapirin administered for dry cow therapy, and pirlimycin administered for clinical mastitis treatment. Herd size and ADUR of systemically administered ceftiofur were also positively associated. In conclusion, β-lactams were most commonly used on Canadian dairy farms. Among antimicrobials of very high importance in human medicine, the use of fluoroquinolones was rare, whereas third-generation cephalosporins and penicillin combinations containing colistin were used very frequently on Canadian dairy farms.

Saini V ，McClure JT ，Léger D ，Dufour S ，Sheldon AG ，Scholl DT ，Barkema HW ... -  《-》

Minimum inhibitory concentrations of Staphylococcus aureus recovered from clinical and subclinical cases of bovine mastitis.

Antimicrobials are often used for treatment of bovine mastitis and the possibility of selection for resistant bacteria must be considered. The objectives of this study were to determine the minimum inhibitory concentration of Staphylococcus aureus recovered from cases of clinical and subclinical bovine mastitis, and to determine the prevalence of multidrug resistance in this population. Milk samples were collected from cows on commercial dairy herds (n=13), including quarters (n=1,574) of cows with subclinical mastitis cases, and cows experiencing clinical mastitis cases (n=608). Selected Staph. aureus isolates, obtained from clinical (n=58) and subclinical (n=58) mastitis cases, were used to determine minimum inhibitory concentrations of 12 selected antimicrobials. Of Staph. aureus isolates tested, 87 (75%) did not exhibit resistance to any antimicrobial, 28 (24.1%) exhibited resistance to 1 (n=21) or 2 (n=7) classes of antimicrobials, and 1 (0.9%) exhibited multidrug resistance. All Staph. aureus (clinical and subclinical cases) were inhibited by the range of concentrations tested for ceftiofur and oxacillin. Moreover, no isolates obtained from clinical mastitis cases exhibited resistance to cephalothin, penicillin-novobiocin, or sulfadimethoxine. Of isolates, 3 exhibited resistance to enrofloxacin. Of isolates exhibiting resistance to more than 1 antimicrobial, independent of antimicrobial class, the combination of erythromycin and tetracycline, and ampicillin and penicillin accounted for the majority of resistance. Of isolates tested, 19% were resistant to tetracycline and 14% were resistant to penicillin. Survival curves of Staph. aureus relative to minimum inhibitory concentration demonstrated heterogeneity among case types for ceftiofur, cephalothin, and erythromycin. Multidrug resistance was identified in only 1 isolate obtained from a single farm.

Oliveira L ，Langoni H ，Hulland C ，Ruegg PL ... -  《-》

Antimicrobial resistance in Staphylococcus aureus, Streptococcus uberis and Streptococcus dysgalactiae from dairy cows with mastitis.

McDougall S ，Hussein H ，Petrovski K 《NEW ZEALAND VETERINARY JOURNAL》