No abstract

A study of the psychrotrophic bacterial content, determined a t 3-5", of soil, grass and hay showed that these habitats were prolific sources of many different types of psychrotrophs, which sometimes exceeded lO'/g. Untreated farm water supplies had a much lower content, few samples giving colony counts >104/ml. Gram positive or Gram variable, nonsporeforming rods, resembling coryneform bacteria, constituted e relatively high proportion of the psyohrotrophic microflora of soil, Gram negative rods only forming about t of the isolates. In contrast, Pseudomonaa and Acinetobacter spp. and yellow or orange pigmented Gram negative rods were the predominant psychrotrophs in untreated water. Pseudomonao and a taxonomically heterogeneous group of yellow pigmented, Uram negative rods, a few of which resembled Plavobacterium and some Enoinia herbiwla, together with Acinetobacter accounted for nearly 90% of the isolates from grass, but < 60 % of those from hay, which had a more complex psychrotrophio microflora than had grms.[4201

Farm water supplies giving 37" positives in MacConkey's broth within 24 hr. had a much higher incidence of presumptive Bact. coli type I than those which gave 37' positives during the second day of incubation only; presumptive Bact. coli reactions were obtained with SiiO,& of the 7,522 tubes positive in 24 hr. compared with 23% for the 7,593 tubes showing positive reactions during the second day at 37".

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.

Violet red bile agar (VRB) incubated at 30" for 20-24 hr was as good an indicator of coli-aerogenes bacteria in milk as MacConkey's broth. A high proportion (82%) of the large, deep red colonies considered to be formed by coli-aerogenes bacteria were confirmed as such. A British brand of dehydrated VRB agar was as suitable as an American brand of this medinm for determining the coli-aerogenes content of milk. All the strains of typical coli-aerogenes bacteria tested formed red colonies. In a small proportion of cases the diameter was less than 0.5 mm. The only other milk bacteria which formed colonies resembling those of coli-aerogenes organisms were some acid forming strains of Gram-negative rods. Coli-aerogenes bacteria, determined on VRB agar at 30", generally constituted only a small proportion of the microflora of fresh raw milk and of farm dairy equipment.