Thirty-two farms (n = 535 cows) located in the state of Guanajuato, Mexico, were sampled. Pathogens from bovine subclinical mastitis (SCM) and clinical mastitis (CLM) were identified by 16S rDNA and the sensitivity to both antibiotics and bacteriocins of Bacillus thuringiensis was tested. Forty-six milk samples were selected for their positive California Mastitis Test (CMT) (≥3) and any abnormality in the udder or milk. The frequency of SCM and CLM was 39.1% and 9.3%, respectively. Averages for test day milk yield (MY), lactation number (LN), herd size (HS), and number of days in milk (DM) were 20.6 kg, 2.8 lactations, 16.7 animals, and 164.1 days, respectively. MY was dependent on dairy herd (DH), LN, HS, and DM (P < 0.01), and correlations between udder quarters from the CMT were around 0.49 (P < 0.01). Coagulase-negative staphylococci were mainly identified, as well as Staphylococcus aureus, Streptococcus uberis, Brevibacterium stationis, B. conglomeratum, and Staphylococcus agnetis. Bacterial isolates were resistant to penicillin, clindamycin, ampicillin, and cefotaxime. Bacteriocins synthesized by Bacillus thuringiensis inhibited the growth of multiantibiotic resistance bacteria such as S. agnetis, S. equorum, Streptococcus uberis, Brevibacterium stationis, and Brachybacterium conglomeratum, but they were not active against S. sciuri, a microorganism that showed an 84% resistance to antibiotics tested in this study.

No abstract

Staphylococcus aureus is an opportunistic pathogen that may cause severe infections in livestock, and represents the major cause of mastitis in dairy cows. Currently, instead of using antibiotics, new strategies are sought to reduce this clinical health problem. The aim of this study was to determine the efficacy of phage therapy to kill S. aureus strains obtained from farms located at the State of Guanajuato, México. Thirty-six S. aureus strains from cow milk with subclinical mastitis were isolated and identified, and the susceptibility to antibiotics and four phages also isolated in this work was tested. It was found that more of 90% of S. aureus isolates were not susceptible to six or more antibiotics, and 100% were resistant to penicillin, dicloxacillin, cefotaxime, ampicillin and cephalothin, and 81 and 77%, to tetracycline and cefuroxime, respectively. Fortunately, 100% of S. aureus isolates were susceptible to phages used in this work, which was detected as clear zones using specific phage. It was shown for the first time, that phages used in this study are active against pathogenic S. aureus and might be incorporated into the therapy as an important tool for the control of staphylococcal bovine mastitis, specially to antibiotic-resistant S. aureus strains isolated in farm located at the state of Guanajuato, México; and its use might be extended to other regions inside or outside the country.

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Hepatic lipidosis and ketosis are frequent metabolic disorders in dairy cows during the transition period. The 2-methyl-2-phenoxy propionic acid (MFPA) is an activator of energy metabolism. The objective of this study was to evaluate the effect of administration of MFPA 10 days prepartum to day 36 postpartum on serum lipid profile, ovarian reactivity, and milk yield. Fifty seven multiparous Holstein cows were divided into four groups. The groups 1 (n = 14) and 2 (n = 14) had body condition score (BCS) above 4; BCS of the groups 3 (n = 15) and 4 (n = 14) was between 3.25 and 3.75 at calving. The solution containing 10 mg/kg MFPA was injected intramuscularly (IM) to cows of groups 1 and 3, 10-7 days prepartum and 6 h postpartum. The groups 2 and 4 received 50 ml of 0.9% NaCl as placebo in the same way. Blood samples for serum lipid profile were collected from all cows 10 days before calving without treatment, 2 days after the first administration of MFPA and postpartum at days 2, 10, and 21 after the second administration of MFPA. At days 21, 24, 27, 30, 33, and 36 postpartum, blood samples were obtained for plasma progesterone determination. Milk yield was registered daily during 60 days postpartum. Prepartum free fatty acids (FFA) were mildly increased without difference among all the groups (P > 0.05). b-hydroxybutyrate (BHB) was increased only at day 10 after calving in cows of group 1 treated with MFPA (P < 0.05) due to higher number of postpartum diseases. In cows from groups 3 and 4 (BCS normal), BHB was mildly increased, not indicating subclinical ketosis. The serum concentrations of triacylgycerols, cholesterol, albumin, activities of aspartate aminotransferase and creatine kinase were within the limits of reference values, indicating adequate liver integrity and function. Cows of normal BCS treated with MFPA presented better milk production but without significant difference among four groups (P > 0.05). Ovarian reactivity was present at day 21 in all groups of cows without difference (P > 0.05). The administration of MFPA had no effect on serum lipid profile and ovarian activity in this study.

Mastitis caused by microbial infections in dairy goats reduces milk yield, modifies milk composition, and potentially contributes to morbidity in herds and consumers of dairy products. Microorganisms associated with mastitis in dairy goats are commonly controlled with antibiotics, but it is known that continued use of these chemical agents promotes antibiotic resistance among bacterial populations. Recently, it has been shown that bacteriocins of Bacillus thuringiensis inhibit growth of food-borne pathogens and also bacteria associated with bovine mastitis. However, there is no report on their ability to inhibit microorganisms linked to mastitis in dairy goats. In this study, using 16S rDNA and ITS regions of rDNA, we identified nine bacterial isolates and an encapsulated yeast associated with mastitis in dairy goats. Enterococcus durans, Brevibacillus sp., and Staphylococcus epidermidis 2 were resistant to, respectively, 75, ~67, ~42, and ~42 % of the antibiotics screened. In addition, 60 % of the bacterial isolates were resistant to penicillin, ampicillin, vancomycin, and dicloxacillin. Importantly, 60 % of the isolates were inhibited by the bacteriocins, but S. epidermidis 1, Enterobacter sp., Escherichia vulneris, and Cryptococcus neoformans were not susceptible to these antimicrobial peptides. Using Brevibacillus sp. and Staphylococcus chromogenes as indicator bacteria, we show that peptides of ~10 kDa that correspond to the molecular mass of bacteriocins used in this study are responsible for the inhibitory activity. Our results demonstrate that multiple antibiotic-resistant bacteria associated with subclinical mastitis in dairy goats from Guanajuato, Mexico, are susceptible to bacteriocins produced by B. thuringiensis.

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Concentrations of calcidiol, calcitriol, and minerals in blood serum and colostrum of 14 primiparous and 16 multiparous Holstein dairy cows during short-period prepartum and postpartum were determined and compared. Blood samples were collected between days 5 and 2 prepartum and 6 h, 12 h, 7 and 21 days postpartum. Nearly 66% of primiparous and 71% of multiparous cows had subclinical postpartum hypocalcemia. Prepartum serum calcium (Ca) and inorganic phosphorus (P) were higher in primiparous cows; Ca decreased in both groups at 6 and 12 h and returned to baseline values 7 days postpartum. Calcidiol and calcitriol concentrations were equal on day 5 prepartum in both groups. In multiparous cows, calcidiol and calcitriol concentration increased at 6 h postpartum and remained elevated at 12 h postpartum; there were no changes in primiparous cows for these analytes. The total secretion of Ca in the colostrum from the first milking was similar in both groups and positively correlated with serum Ca at 6 and 12 h after calving. It is concluded that postpartum increases in the calcidiol and calcitriol concentration were a normal response to the decrease of serum calcium concentration only in multiparous cows. The total Ca secretion in the colostrum of the first milking postpartum does not reflect the grade of hypocalcemia.