Bacteriostatic effect of biologically acidified milk on some Salmonella strains
Midulla, M.; Lo Russo, G.; Sabatino, G.
Bollettino della Societa Italiana di Biologia Sperimentale 52(20): 1751-1757
1976
ISSN/ISBN: 0037-8771 PMID: 829026 Document Number: 104798
The following 4 types of cows' milk were deliberately contaminated with 10 or 100 colonies of Salmonella wien, S. enteritidis or S. panama/ml and incubated for 5 h at 22 or 37 deg C: (i) partially skimmed and (ii) whole milk acidified to pH 4.6 with Streptococcus lactis Guntheri; (iii) liquid whole milk; and (iv) semi-skim milk. Milks (i), (ii) and (iv) were reconstituted from powder. The acidified milks had an inhibitory effect on the salmonellae which was independent of the bacterial species, bacterial concn. and incubation temp. The inhibitory effect tended to diminish with prolonged incubation, however, and after 5 h salmonella counts had increased 5-60X. Inhibition was more marked in milk (i) than in (ii). It is thought that the inhibition may be due to thermolabile streptococcal nisin and/or L(+) lactic acid. The higher content of lactic acid in milk (i) than in (ii), 2.5 vs. 1.7%, could explain its greater inhibitory effect. It is suggested that addition of Str. lactis to dried milk for infants could reduce the risk of gastrointestinal infections; it might also help to re-establish the natural intestinal flora which may be disturbed by artificial feeding, infection or antibiotics.