Exposure to antimicrobials through the milk diet or systemic therapy is associated with a transient increase in antimicrobial resistance in fecal Escherichia coli of dairy calves.

The objective of this prospective cohort study was to describe the relationship between exposure to antimicrobials, through both the milk diet and systemic therapy, and to describe antimicrobial resistance of fecal Escherichia coli in dairy calves pre- and postweaning. A convenience sample of 15 Minnesota dairy farms was chosen, representing 3 equal cohorts of milk diet fed to preweaned calves: medicated milk replacer (MMR), nonmedicated milk replacer (NMR), or pasteurized nonsaleable milk (PNM). Five newborn calves were enrolled on each farm, with fecal samples collected from each calf at 1, 3, 5, and 16 wk of age. After isolation, 3 colonies of E. coli were randomly selected from each sample to determine antimicrobial susceptibility by minimum inhibitory concentration (Sensititer, Thermo Scientific, Waltham, MA) to 8 antimicrobials in 8 classes. The isolate was given an antimicrobial resistance score (ARS) according to the number of antimicrobial classes to which it was resistant. Any isolate resistant to 3 or more antimicrobials was defined as being multidrug resistant (MDR). Relationships between ARS and MDR (dependent variables) and possible explanatory variables were analyzed using mixed multivariable linear and logistic regression models, respectively, with critical P-values adjusted for multiple contrasts. Seventy percent of isolates were resistant to sulfadimethoxine. For wk 1 and 3, the mean ARS values were greatest for fecal E. coli from calves fed MMR or PNM compared with NMR, with no difference in ARS values between the MMR and PNM groups at either time point. At wk 5, the mean ARS value was greatest for fecal E. coli from calves fed MMR (3.56 ± 0.45; mean ± SE), intermediate for calves fed PNM (2.64 ± 0.45), and lowest for calves fed NMR (1.54 ± 0.45). However, by wk 16, the mean ARS values were ≤1.0 and did not differ among milk diets. Evaluation of the proportion of isolates with MDR mirrored the results of the ARS analysis (MDR more prevalent in MMR and PNM groups preweaning; no difference among milk diets at 16 wk). There was a tendency for an increase in ARS at wk 5 (1.28 ± 0.70), and the odds for MDR in fecal E. coli were estimated to be 5.2 (95% confidence interval = 0.67, 35.7) and 101.1 (95% confidence interval = 1.15, >999.9) higher at wk 3 and 5 if the calf was treated with a systemic antimicrobial within the 14-d period before sampling. These findings suggest that exposure to antimicrobials through the milk diet or systemic therapy may result in a transient increase in resistance in fecal E. coli, but once the antimicrobial pressure is removed, susceptible E. coli are able to flourish again, resulting in an overall decrease in resistance.

Methicillin-resistant Staphylococcus aureus in resident animals of a long-term care facility.

UNLABELLED: Animals provide benefits to elderly and chronically ill people by decreasing loneliness, increasing social interactions, and improving mental health. As a result, many hospitals and long-term care facilities allow family pets to visit ill or convalescing patients or support animal-assisted therapy programs. These include programs that have resident animals in long-term care facilities. Despite the benefits, there are concerns about disease transmission between pets and patients. Antibiotic-resistant bacteria, such as methicillin-resistant Staphylococcus aureus (MRSA), are a recognized problem in healthcare settings leading to refractory infections and potentially life-threatening illnesses. MRSA has been isolated from numerous animal species, yet few studies are available on the carriage of this pathogen in animals residing in long-term care facilities. Our objective was to characterize MRSA carriage among resident animals in a long-term care facility. METHODS: To document MRSA colonization, nasal swabs from 12 resident animals (one dogs and 11 cats) of a long-term care facility were collected weekly for 8 weeks. Staphylococcus isolates were characterized by antimicrobial susceptibility and MRSA isolates were further characterized by pulsed-field gel electrophoresis (PFGE). PFGE isolate patterns were compared with an existing database of MRSA isolate patterns at the Minnesota Department of Health. RESULTS: Two of 11 cats were colonized with MRSA. MRSA was recovered from five of eight weekly samples in one cat and two of eight weekly samples in the other cat. All isolates were classified as USA100 (healthcare-associated strains). DISCUSSION: Long-term care resident animals may acquire MRSA. Clonally related strains were identified over the 8-week sampling period. It is unclear if pets serve as an on-going source of infection to their human companions in long-term care facilities.