Abstract
The objectives of this study were the selection of lactic acid bacteria (LAB) isolated from raw milk and studying their technological properties and antibacterial activities against bacteria as the cause of cattle mastitis. Biochemical and molecular identification using 16S–23S rRNA gene spacer analysis and 16S rRNA gene sequencing highlighted the presence of three species: Lactiplantibacillus plantarum, Lactococcus lactis, and Levilactobacillus brevis. The enzymatic characterization followed by the determination of technofunctional properties showed that LAB strains did not exhibit any hemolytic effect and were able to produce protease and lipase enzymes. Isolates showed very high antagonistic activity against Gram-positive and Gram-negative bacteria by producing H2O2, bacteriocin(s), and organic acid(s). APIZYM micromethod demonstrated that all selected strains are capable of producing valine arylamidase, cystine arylamidase, N-acetyl-β-glucosaminidase, and ᾳ-mannosidase. The antibiotic susceptibility assay showed that all selected strains were sensible to the majority of tested antibiotics. Based on these results, it can be concluded that the technological properties of the selected LAB allow considering their industrial use in order to formulate bioactive functional foods or drug(s).
Highlights
Since ancient times, the discovery of antimicrobial drugs has made remarkable progress which plays an important role in the treatment of various types of microbial infections and the reduction of fatalities associated with infections caused by microbes
Lactic acid bacteria (LAB) classified as “generally recognized as safe” (GRAS) microorganisms are one of the most important groups of bacteria in the food industry [8]. ey can prevent the development of pathogenic bacteria [9,10,11] and are able to produce antimicrobial compounds such as lactic acid, acetic acid, diacetyl, acetoin, hydrogen peroxide, and bacteriocins [10, 12,13,14,15,16]. erefore, they are suitable for technological and industrial processes. ey are used as transformation agents for the fermentation of milk and other food products and have several technological roles, and participate in the formation of flavors and rheological qualities of cheeses and fermented milk [8, 17]
Escherichia coli and Staphylococcus aureus were isolated from cows suffering from clinical mastitis as previously described by Klibi et al [29] and were used to evaluate the antibacterial power of isolated LAB strains. e identification of both strains was carried out using molecular methods after DNA extraction. e species-specific PCR nuc and uidA genes were used for the identification of S. aureus and E. coli isolates, respectively [24, 25]
Summary
The discovery of antimicrobial drugs has made remarkable progress which plays an important role in the treatment of various types of microbial infections and the reduction of fatalities associated with infections caused by microbes Despite this progress, multidrug-resistant pathogenic microorganisms have emerged due to misuse or overuse of commercially available antimicrobial drugs in humans [1, 2]. Bovine mastitis is one of the most prevalent production diseases affecting the dairy industry worldwide [3] It can be caused by several associated factors with the host, the environment, the season, the farm management, and the specific agent pathogens, in particular, Staphylococcus and Escherichia coli [4,5,6]. The first part was devoted to the morphological and molecular identification of isolated LAB strains. en, the enzymatic characterizations followed by the determination of the technological properties of each isolate were realized
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