Abstract
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.
Highlights
In Mexico, the national milk production has an average annual growth rate of ∼1.3%, representing an increase of 9,784 to 10,677 million liters per year during the period from 2003 to 2010 [1]
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
We found that 72.7% of isolates had a resistance pattern to three or more antimicrobial agents mainly to penicillin, clindamycin, and cefotaxime
Summary
In Mexico, the national milk production has an average annual growth rate of ∼1.3%, representing an increase of 9,784 to 10,677 million liters per year during the period from 2003 to 2010 [1]. In the last few years, family dairy herds or small-scale dairy enterprises contribute to the national milk production with values ranging from 35 to 40% [3]. Milk is mainly sold locally in different sale channels directly to consumers, or through intermediaries or the rural or commercial industry. Intermediaries collect milk either to supply fluid milk in urban areas or to manufacture traditional cheese that is in remarkable demand in cities or suburban areas [4, 5]. According to the Food and Agriculture Organization [6], small herds are a majority in the developing world.
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