Biotyping of cultivable lactic acid bacteria isolated from donkey milk

Abstract

Significance and Impact of the Study: There is increased interest in using donkey's milk as a source of human nutrition. The large amounts of antimicrobial components and defence factors present in donkey's milk provide protection from microbial infections and distinguish donkey's milk from the milks of other mammals. However, the microbiota in donkey's milk has so far been poorly characterized, specifically with regard to the lactic acid bacteria (LAB). This study has identified cultivable, acidifying and thermoduric LAB that could be used to develop starter cultures. This is the first study to investigate the culturable LAB microbiota present in donkey's milk. AbstractThe diversity of lactic acid bacteria (LAB) species in donkey's milk was analysed by culture-dependent microbial techniques. Dominant strains were isolated on agar media generally used for enumerating LAB. To enrich the number of acidifying LAB present, the milk samples were incubated at 37°C for 24 h (cultured milk samples, CM). One of the CM samples was heattreated at 63°C for 10 min before incubation at 37°C (heat-treated and cultured milk sample, TCM) to select thermophilic LAB. The microflora in these CM and TCM samples was then compared to that of the raw milk samples (RM). Among the 129 LAB isolates, 10 different species (four Enterococcus, five Streptococcus and one Pediococcus) were identified by molecular methods. Although the 10 LAB species were present in the RM samples, only three and two isolates were found in CM and TCM samples, respectively. Despite the selection protocol being set up to favour the isolation of all LAB isolates present in donkey milk, relatively few species and biotypes were isolated. No LAB isolates belonging to the most technologically important dairy starter species were detected. The possible factors related to the limited LAB diversity in donkey's milk have been discussed below.

A survey on the milk chemical and microbiological quality in dairy donkey farms located in NorthWestern Italy

“…Regarding the LAB count, the overall mean number was 1.6*10 4 cfu/mL (Table 4). This LAB value is consistent with counts recently reported by Carminati et al (2014) in DM. The LAB count increase in DM during cold storage was not significant, as assessed by Student T test comparison of data at day 0 and day 5 (data not shown), for any of the surveyed farms, thus indicating a possible effect of lysozyme antimicrobial activity against LAB.…”

Effect of recycled manure solids as bedding on bulk tank milk and implications for cheese microbiological quality

“…After incubation, the colonies were counted, expressed as colony forming units per milliliter of milk. Second, heat treatment of raw milk was performed at 63°C for 10 min to enumerate thermoresistant Enterococcus and Streptococcus (Carminati et al, 2014). Heated milk and a 10-fold dilution in peptone water (1% of Bacto Peptone, BD Biosciences) were plated in duplicate on M17 Agar (Oxoid, Nepean, ON, Canada) at 37 and 42°C (for S. thermophilus).…”

Characterization of bacterial communities of donkey milk by high-throughput sequencing

“…Studies regarding the microbiota of DM have focused on the hygienic quality of DM (Pilla et al, 2010;Zhang et al, 2008;Šarić et al, 2012). Only more recently have some authors characterized the lactic bacteria for their probiotic activity and potential technological aspects (Carminati et al, 2014;Soto del Rio et al, 2016). It is generally accepted that LAB are the dominant population in milk from several species, independent of the methodology used for study.…”

“…It contains high levels of lactose and essential amino acids (Guo et al, 2007) as well as low concentrations of β-lactoglobulin and casein-the most common allergens in cow milk (Vincenzetti et al, 2008). One of the main characteristics of DM is its high concentration of lysozyme: from 1300 to 4000 mg/l, compared to 0.09 mg/l in cow milk and 40-200 mg/l in human milk (Carminati et al, 2014;Chiavari et al, 2005;Vincenzetti et al, 2008). This enzyme has bactericidal properties; it hydrolyses the murein of bacterial cell walls, causing lysis of sensitive bacteria (Chiavari et al, 2005).…”