RESUMEN
Third-generation cephalosporins such as ceftiofur are critically important antibiotics because human pathogens with resistance to these drugs contribute to high mortality rates. These antibiotics are also frequently given to dairy cattle for treating infections, emphasizing the critical role they play in both human and veterinary medicine. To investigate the impact of intramuscular ceftiofur treatment on the concentration of resistant bacteria in the gut, we focused on cows with metritis, a common bacterial infection that frequently requires antibiotic intervention. Twelve cows with metritis (cases) were enrolled and treated with intramuscular ceftiofur for 5 d along with 12 matched healthy cows that were not given ceftiofur (controls). Fecal samples were collected weekly from cows in both the case and control groups for 4 weeks, starting before the treatment of the case group. Five fecal samples per cow were used for analysis (n = 120 samples). The abundance of Gram-negative bacteria was quantified per sample after plating on MacConkey agar, which was also used to quantify the abundance of Gram-negative bacteria with resistance to ceftiofur, ampicillin, and tetracycline. Interestingly, the case cows with metritis had a greater abundance of Gram-negative bacteria than the control cows just before treatment, but no difference in abundance was observed between groups at wk 1-4. The abundance of ceftiofur-resistant Gram-negative bacteria was also similar between the case and control cows immediately before treatment of the cases. However, a significant increase in abundance of ceftiofur-resistant Gram-negative bacteria was observed in the case cows 1-week after treatment that persisted through wk 3. Although the recovery of ampicillin- and tetracycline-resistant bacteria was similar between the 2 groups post-treatment, cases had significantly higher levels of ampicillin-resistant bacteria before treatment. Collectively, these findings demonstrate that intramuscular ceftiofur treatment can affect the abundance of cultivable Gram-negative bacteria and select for ceftiofur-resistant populations that can persist for up to 3 weeks. Judicious use practices are needed to ensure that ceftiofur and other critically important antibiotics are administered only when necessary to minimize the spread of resistance and safeguard public and animal health.
RESUMEN
The gut microbiota in cattle is essential for protein, energy, and vitamin production and hence, microbiota perturbations can affect cattle performance. This study evaluated the effect of intramammary (IMM) ceftiofur treatment and lactation stage on the functional gut microbiome and metabolome. Forty dairy cows were enrolled at dry-off. Half received IMM ceftiofur and a non-antibiotic teat sealant containing bismuth subnitrate (cases), while the other half received the teat sealant (controls). Fecal samples were collected before treatment at dry off, during the dry period (weeks 1 and 5) and the first week after calving (week 9). Shotgun metagenomic sequencing was applied to predict microbial metabolic pathways whereas untargeted metabolomics was used identify polar and nonpolar metabolites. Compared to controls, long-term changes were observed in the cows given ceftiofur, including a lower abundance of microbial pathways linked to energy production, amino acid biosynthesis, and other vital molecules. The metabolome of treated cows had elevated levels of stachyose, phosphatidylethanolamine diacylglycerol (PE-DAG), and inosine a week after the IMM ceftiofur application, indicating alterations in microbial fermentation, lipid metabolism, energy, and cellular signaling. Differences were also observed by sampling, with cows in late lactation having more diverse metabolic pathways and a unique metabolome containing higher levels of histamine and histamine-producing bacteria. These data illustrate how IMM ceftiofur treatment can alter the functionality of the hindgut metabolome and microbiome. Understanding how antibiotics and lactation stages, which are each characterized by unique diets and physiology, impact the function of resident microbes is critical to define normal gut function in dairy cattle.
RESUMEN
BACKGROUND: Intramammary (IMM) ceftiofur treatment is commonly used in dairy farms to prevent mastitis, though its impact on the cattle gut microbiome and selection of antibiotic-resistant bacteria has not been elucidated. Herein, we enrolled 40 dairy (Holstein) cows at the end of the lactation phase for dry-cow therapy: 20 were treated with IMM ceftiofur (Spectramast®DC) and a non-antibiotic internal teat sealant (bismuth subnitrate) and 20 (controls) received only bismuth subnitrate. Fecal grab samples were collected before and after treatment (weeks 1, 2, 3, 5, 7, and 9) for bacterial quantification and metagenomic next-generation sequencing. RESULTS: Overall, 90% and 24% of the 278 samples had Gram-negative bacteria with resistance to ampicillin and ceftiofur, respectively. Most of the cows treated with ceftiofur did not have an increase in the number of resistant bacteria; however, a subset (25%) shed higher levels of ceftiofur-resistant bacteria for up to 2 weeks post-treatment. At week 5, the antibiotic-treated cows had lower microbiota abundance and richness, whereas a greater abundance of genes encoding extended-spectrum ß-lactamases (ESBLs), CfxA, ACI-1, and CMY, was observed at weeks 1, 5 and 9. Moreover, the contig and network analyses detected associations between ß-lactam resistance genes and phages, mobile genetic elements, and specific genera. Commensal bacterial populations belonging to Bacteroidetes most commonly possessed ESBL genes followed by members of Enterobacteriaceae. CONCLUSION: This study highlights variable, persistent effects of IMM ceftiofur treatment on the gut microbiome and resistome in dairy cattle. Antibiotic-treated cattle had an increased abundance of specific taxa and genes encoding ESBL production that persisted for 9 weeks. Fecal shedding of ESBL-producing Enterobacteriaceae, which was classified as a serious public health threat, varied across animals. Together, these findings highlight the need for additional studies aimed at identifying factors associated with shedding levels and the dissemination and persistence of antibiotic resistance determinants on dairy farms across geographic locations.