Dynamic Changes in Antimicrobial Resistance in Fecal Escherichia coli from Neonatal Dairy Calves: An Individual Follow-Up Study

Impact of zinc supplementation on phenotypic antimicrobial resistance of fecal commensal bacteria from pre-weaned dairy calves

The objective of this study was to evaluate the impact of dietary zinc supplementation in pre-weaned dairy calves on the phenotypic antimicrobial resistance (AMR) of fecal commensal bacteria. A repository of fecal specimens from a random sample of calves block-randomized into placebo (n = 39) and zinc sulfate (n = 28) groups collected over a zinc supplementation clinical trial at the onset of calf diarrhea, calf diarrheal cure, and the last day of 14 cumulative days of zinc or placebo treatment were analyzed. Antimicrobial susceptibility testing was conducted for Enterococcus spp. (n = 167) and E. coli (n = 44), with one representative isolate of each commensal bacteria tested per sample. Parametric survival interval regression models were constructed to evaluate the association between zinc treatment and phenotypic AMR, with exponentiated accelerated failure time (AFT) coefficients adapted for MIC instead of time representing the degree of change in AMR (MIC Ratio, MR). Findings from our study indicated that zinc supplementation did not significantly alter the MIC in Enterococcus spp. for 13 drugs: gentamicin, vancomycin, ciprofloxacin, erythromycin, penicillin, nitrofurantoin, linezolid, quinupristin/dalfopristin, tylosin tartrate, streptomycin, daptomycin, chloramphenicol, and tigecycline (MR = 0.96-2.94, p > 0.05). In E. coli, zinc supplementation was not associated with resistance to azithromycin (MR = 0.80, p > 0.05) and ceftriaxone (MR = 0.95, p > 0.05). However, a significant reduction in E. coli MIC values was observed for ciprofloxacin (MR = 0.17, 95% CI 0.03-0.97) and nalidixic acid (MR = 0.28, 95% CI 0.15-0.53) for zinc-treated compared to placebo-treated calves. Alongside predictions of MIC values generated from these 17 AFT models, findings from this study corroborate the influence of age and antimicrobial exposure on phenotypic AMR.

Bovine Colostrum: Human and Animal Health Benefits or Route Transmission of Antibiotic Resistance-One Health Perspective

After calving, bovine colostrum is obtained from the mammary gland of the dam in the first days and fed to newborn ruminant to prevent microbial infections. Each bovine colostrum has a unique biochemical composition with high nutraceutical value compared to milk. However, bovine colostrum is influenced by various factors, such as environmental, individual, and genetic factors, as well as processing methods. Proper colostrum management is crucial for obtaining high-quality colostrum and mitigating bacterial contamination. This is important not only for the health and survival of calves but also for the health of humans who consume colostrum and its co-products. It is essential to ensure that the consumed colostrum is free of pathogens to reap its benefits. Health-promoting products based on colostrum have gained significant interest. However, colostrum can contain pathogens that, if not eliminated, can contribute to their transmission and spread, as well as antibiotic resistance. The aim of this review was to promote the animal and human health benefits of bovine colostrum by improving its microbial quality and highlighting potential routes of dissemination of antibiotic-resistant pathogens. Implementing hygienic measures is one of the key factors in mitigating colostrum bacterial contamination and obtaining safe and high-quality colostrum. This helps reduce the exposure of pathogens to newborn calves, other animals, and humans, in a One Health analysis.

Invited Review: Antimicrobial Use and Antimicrobial Resistance in Pathogens Associated with Diarrhea and Pneumonia in Dairy Calves

Antimicrobial use (AMU) is the major driver of antimicrobial resistance (AMR) among bacteria in dairy herds. There have been numerous studies on AMU and AMR in dairy cows; however, studies on AMU and AMR in dairy calves are limited. A comprehensive overview of the current state of knowledge of AMU and AMR among pathogens in dairy calves is important for the development of scientifically supported and applicable measures to curb antimicrobial use and the increasing risk of AMR. Therefore, we performed a systematic review of research on AMU and AMR in dairy calves. A total of 75 publications were included, of which 19 studies reported AMU data for dairy calves and 68 described AMR profiles of the four most prevalent bacteria that are associated with calf diarrhea and calf pneumonia. Large variation in AMU was found among herds across different regions. There seems to be a positive association between exposure to antimicrobials and occurrence of resistance. Most AMU was accounted for by treatment of diseases, while a small proportion of AMU was prophylactic. AMU was more common in treating calf diarrhea than in treating pneumonia, and the resistance rates in bacteria associated with diarrhea were higher than those in pathogens related to pneumonia. Organic farms used significantly fewer antimicrobials to treat calf disease; however, the antimicrobial resistance rates of bacteria associated with calf diarrhea and pneumonia on both types of farms were comparable. Feeding waste or pasteurized milk was associated with a higher risk of AMR in pathogens. Altogether, this review summarizes AMU and AMR data for dairy calves and suggests areas for future research, providing evidence for the design of antimicrobial use stewardship programs in dairy calf farming.

Genomic Analysis of Antibiotic-Resistant and -Susceptible Escherichia coli Isolated from Bovine Sources in Maputo, Mozambique

This study reports a genomic analysis of Escherichia coli isolates recovered from 25 bovine fecal composite samples collected from four different production units in Maputo city and around Maputo Province, Mozambique. The genomes were analyzed to determine the presence of antibiotic resistance genes (ARGs), genetic relatedness, and virulence factors known to cause diseases in humans. Whole-genome sequencing was conducted on 28 isolates using an Illumina NextSeq 500 sequencing platform. The genomes were analyzed using BLASTN for the presence of resistance genes and virulence factors, as well as to determine their phylogenetic groups, sequence types (ST), and ST complexes (ST Cplxs). The majority of the isolates (85%) were identified as members of phylogenetic groups B1, with fewer isolates identified as members of group A, and a single isolate identified as group "E/Clade I." The ST analysis demonstrated a higher level of diversity than the phylogenetic group analysis. Sixteen different STs, five ST Cplxs, and seven singleton complexes were identified. A strain identified as a novel ST (ST9215) showed a high level of similarity with an isolate recovered from a wild animal in the Gambia. Seven different ARGs were identified, with tet(B) being the most frequently detected, followed by aph(3″)-Ib, aph(6)-Id, sul2, bla_TEM-1B, and dfrA1. Three isolates encoded β-lactam-conferring point mutations in the ampC promoter (-42C>T). In total, 51 different virulence factors were identified among the genomes. This study demonstrates that E. coli from bovine sources in Mozambique encoded multiple antibiotic resistance elements, plasmids, and virulence factors. To the best of our knowledge, this is the first genomic description of antibiotic-resistant E. coli isolated from bovine sources in Mozambique.