TITLE:
Selective Lactococcus Enumeration in Raw Milk
AUTHORS:
Laetitia Gemelas, Véronique Rigobello, Maï Huong Ly-Chatain, Yann Demarigny
KEYWORDS:
Lactococcus; Culture Media; Raw Milk; LAB; Modified KCA
JOURNAL NAME:
Food and Nutrition Sciences,
Vol.4 No.9B,
September
3,
2013
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.