The effect of the presence of penicillinase producing micrococci on the growth of cheese and yogurt starters in milk contaminated with penicillin

Abstract

SummaryCoagulase-negative micrococci isolated from the cow's udder, when cultivated together with cheese and yogurt starters in milk containing 0·3 I.U./ml of penicillin, contributed sufficient penicillinase to permit normal rates of acid production by the starters. Subcultures of such ‘mixed’ cultures also grew at normal rates in milk contaminated with penicillin at the same level.The possibility of using such micrococci to protect the starter organisms in both the preparation of bulk starters and during manufacture of cheese and yogurt is discussed.

Factors affecting the multiplication and survival of coagulase positive staphylococci in Cheddar cheese

“…Cheese made from 'low grade' milk, with a high total bacterial count, permitted less growth of the staphylococci than did high grade milk, probably because of the action of inhibitory organisms (Takahashi & Johns, 1959). Staphylococci died out rapidly at about pH 5-0 in cheese (Mattick et al 1959) and in starter (Reiter, Vazquez & Newland, 1961). Mattick et al (1959) also showed that a difference of 0-2 pH units in the range of pH 5-1-5-3 significantly affected the rate of reduction in numbers, the least rapid decrease being in the cheese of higher pH.…”

Section B. Cheese and butter starters

“…Earlier at-tempts to show incorporation of U CO 2 into Str. lactis had failed (220) but CO 2 had been shown by several workers (221)(222)(223)(224) to be required for initiation of growth and CO 2 produced by the HMP could well be utilized in biosynthetic processes. Summing up the modern conception of homo-and hetero-fermentation it appears that the lactic acid bacteria are better classified into three categories, as proposed by Buyze, Hamer & Haar (225):…”