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The high prevalence of antimicrobial resistance (AMR) among mastitis-causing pathogens underscores the urgent need for new types of antimicrobial agents. However, the slow discovery and development of antibiotics are failing to keep pace with the rapidly increasing AMR. Consequently, bacteriocins have emerged as a promising alternative antimicrobial agent, drawing heightened attention due to their natural and safe properties. Thus, this study evaluated the potential of bacteriocin-based formulation against multi-drug-resistant (MDR) Gram-positive and negative pathogens causing clinical mastitis among dairy cattle. The bioactivity of bacteriocin-producing LABs was tested against Gram-positive strains using a colony overlay assay, and the effectiveness of the bacteriocin nisin was assessed against Gramnegative pathogens in combination with membrane-permeabilizing agents chelator (EDTA), organic acids (citric and lactic acid), and surfactants (Triton-X and Tween 80). The combined inhibitory action of nisin and membrane permeabilizing agents was estimated by calculating the growth reduction after exposure of the test organisms to the membrane permeabilizing agents and bacteriocin. All bacteriocin-producing LAB strains demonstrated robust bioactivity when tested against 24 locally isolated Gram-positive mastitis-causing bacterial species. While combining 100 µM of the bacteriocin nisin with 40 mM EDTA significantly inhibited the growth of representative Gram-negative mastitis-causing strains, with complete inhibition observed at 500 µM nisin concentration. Pre-exposure to citric acid or lactic acid and at least 100 mM EDTA resulted in over double the growth reduction of K. pneumoniae AG-ES-14. Similar results were observed with the surfactants Triton-X and Tween 80 were sequentially used with bacteriocin treatment for this pathogen. Almost 100% growth reduction was achieved when nisin treatment was preceded by treatment at higher concentrations of EDTA (800 mM) and, combined with either surfactant or organic acid, led to almost complete growth reduction. The results of this study present promising opportunities for developing a powerful biocontrol agent to combat mastitis infections caused by MDR pathogens. [ABSTRACT FROM AUTHOR]

Mastitis is a prevalent disease in dairy cattle. One of its important etiological agents is the species belonging to the Enterobacteriaceae family. Thus, this study aims to characterize the virulence and multi-drug resistance (MDR) profiles of Enterobacteriaceae strains previously isolated from dairy cattle with clinical mastitis in Region 4-A, Philippines. Results showed that 60% of Klebsiella pneumoniae and 100% of the Proteeae tribe (Proteus spp., Providencia spp., and Morganella spp.) exhibited hemolytic activity. Hemolysin-coding gene, viz. hpmA, was suspected to contribute to the hemolytic activity of all Proteus spp. Biofilm formation was observed in several isolates and mrkD, ireA, ucaA, atfA, and ureG genes were expected to be accountable for this virulence trait. All Enterobacteriaceae strains were classified as MDR pathogens. All isolates exhibited resistance to erythromycin, penicillin, clindamycin, and lincomycin. Resistance to streptomycin and tetracycline was also exhibited by a significant number of isolates and the resistance genes (rrs and tetK) responsible for this resistance were most frequently detected. Only one isolate of M. morganii harbored integron-related gene intI2. The characterization of these strains has significant health and economic implications. Severe virulence and drug resistance of these strains pose a challenge in the management and treatment of intramammary infections in dairy farms. Being reservoirs of antimicrobial resistance-associated genes, these strains pose a threat to the food chain. [ABSTRACT FROM AUTHOR]

Bovine mastitis is a common bacterial infection that causes inflammation of the mammary gland in dairy cattle. Staphylococcus is one of the most predominant and significant pathogens known to cause mastitis. Thus, this study was designed to isolate and assess the prevalence of Staphylococcus strains in dairy cattle with clinical mastitis in Region IV-A, Philippines. Baird Parker agar (BPA) supplemented with 5% egg yolk tellurite emulsion was used as selective media to differentiate coagulase-positive S. aureus and coagulase-negative staphylococcus (CNS). The isolated pathogens were phenotypically and genetically characterized for further identification. Surprisingly, out of 85 isolates, only 56.5% belong to the genus Staphylococcus and 43.5% were non-staphylococcus strains despite the use of a staphylococcus-specific selective medium. The overall most prevalent species among the isolates were S. chromogenes with an isolation rate of 21.2%. The antimicrobial resistance profiles of the isolated bacterial pathogens were also done. Several staphylococcal isolates exhibited resistance to multiple antibiotics. S. aureus showed hyper-resistance to three out of seven antibiotics -- specifically streptomycin, clindamycin, and lincomycin. Surprisingly, most of the non-staphylococcal isolates exhibited hyper-resistance to multiple antibiotics. Proteus mirabilis, P. penneri, and Providencia stuartii showed almost 100% resistance and hyper-resistance to all antimicrobials tested except amoxicillin. These findings suggest that the detection of diverse species of mastitis-causing microorganisms is an important concern for the dairy sector, as different pathogens might represent different hazards and require distinct treatments, particularly on the type of antibiotics used to treat the infection. The erroneous choice of antimicrobial could unnecessarily expose the udder microbial flora to antimicrobials, thereby inadvertently promoting the emergence of multidrug-resistant pathogens that poses a serious threat to both animal and human health. Extreme antibiotic resistance detected in strains present in mastitic dairy cattle also raises a substantial public health concern, particularly when it comes to the consumption of food and food products, such as milk. [ABSTRACT FROM AUTHOR]