Selective <i>Lactococcus</i> Enumeration in Raw Milk

Abstract

The Lactococcus diversity in cow and goat raw milk was investigated. To do so, a protocol had to be established for the specific enumeration of lactococci. Eight agar media and one control medium were analysed to compare their proficiency in evaluating the Lactococcus population in raw milk: M17 Nal, Elliker, modified Elliker, PCA + milk, modified KCA, modified Chalmers, Turner, FSDA. The M17 medium was used as reference. Eighteen pure strains were tested on these media for their selectivity towards lactococci: six Lactococcus species or subspecies, three Leuconostoc, three Enterococcus, two Lactobacillus, one Streptococcus thermophilus, one Pseudomonas fluorescens, one Escherichia coli and one Staphylococcus aureus. All these bacteria were chosen for their regular presence in raw milk. The KCA medium proved to be the most selective towards lactococci, on condition that 1) we discriminated the colonies using the catalase test and 2) we subtracted the Enterococcus population counted on BEA. However, it was not possible to separate the Streptococcus from the Lactococcus colonies on KCA. The "Lactococcus-like" population including these two genera was estimated at a mean level of 3.18 log(cfu)/mL and 4.14 log(cfu)/mL in cow and goat raw milk respectively. This is consistent with the data already published.

Sensory, microbiological and physico-chemical characterization of Klila, a traditional cheese made in the south-west of Algeria

“…REP-PCR was performed with primers Rep1R-Dt and Rep2-D according to the methodology followed by Gemelas et al (2013). The final identification relied on the 16S DNA sequencing.…”

Identification, typing and functional characterization of dominant lactic acid bacteria strains from Iranian traditional yoghurt

“…This result suggests the need to improve hygiene conditions in the traditional manufacturing of yoghurt. Though M17 and MRS are the recommended media for counting lactic cocci and bacilli, respectively, they have been repeatedly reported poorly selective for different LAB groups [13,49,52]. The majority LAB species in the yoghurts and single milk sample were identified, typed and characterized.…”

“…Acetaldehyde was the major compound in all fermented milk samples, having a relative concentration (6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17) and L. helveticus (18)(19). M molecular weight marker between 43 and 93 % of the total volatiles.…”

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“…Indeed, the media used are specifically selected to search for a genus we expect to encounter. It has been well known for a long time that petri dishes give a crude image of the population being looked for (Gemelas et al, 2013;Verdier-Metz et al, 2012). The sequencing of these specific bands could be of further interest to identify in detail the populations concerned, and in doing so we could evaluate the effectiveness of the methodology followed here.…”