No abstract

Summary: The classification of 1,466 bacteria, isolated on Yeastrel‐milk agar incubated at 30° from 68 rinses of steam sterilized dairy equipment taken at five farms, showed that micrococci were dominant, with corynebacteria and aerobic sporeforming rods frequent, representatives of these three groups constituting 73% of the isolates. The microflora was characterized by the dominance of organisms which were relatively inactive in milk. Typical milk souring organisms such as lactic streptococci and coli‐aerogenes organisms were rarely isolated, but anaerogenic Gram‐negative rods resembling Achromobacter, Pseudomonas and Flavobacterium were not uncommon on milking machine clusters and on a cooling unit. The glass recorder jars contained a relatively high proportion of sporeformers.

A series of 170 rinses and 14 milk residue deposits from poorly clean& dairy equipment on 136 farms, giving colony counts a t 30" of > 106/ft' for rinses or /g wet w t for residues, were claasitied into 8 groups according to the composition and milk spoilage activity of their microflora. Five of the groups were dominated by active milk spoilage types of bacteria and three by inactive organisms. Micrococci, coryneform bacteria and aerobic sporeforming rods dominated the microflora of 1/3 of the 184 samples. Gram negative rods, including coli-aerogenes orgenismS, were dominant in another 1/3, e combination of micrococci, coryneform bacteria and Gram negative rods constituted the microflora of 19% and streptococci were dominant in 10%. Active milk spoilage types of bacteria were predominant in 106 (58%) of the rinses and deposits, but inactive types forming no reaction in litmus milk in 72 h at 22" were dominant in 78 (42%).

The classification of the predominant types of bacteria found in 87 farm milk supplies, examined within 8–10 hr of production, was done by plating on Yeastrel‐milk agar, incubating for 72 hr at 30° and picking 24 colonies at random from each countable plate for detailed study. Although the results indicate some general trends, such as the predominance of micrococci in milk of low count (< 2 times 104 colonies/ml), the co‐dominance of streptococci, corynebacteria and micrococci in milk with colony counts between 2 times 104 and 2 times 105/ml, and the dominance of nonpigmented Gram‐negative rods and streptococci in the high count milks (2 times 105–5 times 106 colonies/ml), several milk samples, irrespective of colony count level, had a characteristic individual microflora dominated by either corynebacteria, aerobic sporeformers, coli‐aerogenes organisms, fluorescent pseudomonads or flavobacteria.

The examination of a series of 713 milk bottles cleansed by hand washing at producer-retailer farm dairies showed that though nearly 60% attained satisfactory bacteriological standards, about 30% gave high colony counts (> 600/bottle), while coli-esrogenes organisms were found i n 17% and milk spoilage organisms in 26% of them. The microflora of efficiently cleansed bottles, with colony counts of <200/bottle. waa dominated by micrococci and aerobic sporeforming rods. Only 3.7% of the 269 cultures from these bottles gave acid reactions i n litmus milk in 72 h at 22". Inefficiently cleansed bottles, with colony counts of >600/bottle, had quite a different type of microflora which was usually dominated by Gram negative rods (achrornobecteria, noduorescent pseudomonads and flavobacteria). A much higher proportion (19%) of the 393 cultures from these bottles gave acid reactions in litmus milk. P PI b E P, U 8 3. * After incubating at 30" for 72 h. t After hcUb8thg at 22" for 72h.