Coli‐aerogenes Bacteria Isolated From Grass

SUMMARY: The numbers of coli‐aerogenes bacteria on ungrazed herbage and on intensively grazed pasture were determined by inoculation into MacConkey's broth incubated at 30°, 37° and 44°. From the cultures producing acid and gas at 30° organisms were isolated on eosin methylene blue agar and classified according to the recommendations of the Coliform Sub‐Committee. These micro‐organisms were abundant in grass from both habitats, and sometimes exceeded 10 7 /g. The numbers were much lower at 37°, 80% of the samples of ungrazed herbage and 37% of those from grazed pasture containing less than 10 3 /g. Bacterium coli , intermediate and aerogenes‐cloacae types were found with frequencies of 4, 19 and 77% respectively on ungrazed harbage, compared with 9, 17 and 73% on grazed pasture. Aerogenes‐cloacae types were dominant among the 37° positive cultures. A high proportion (53%) of the 249 classifiable cultures did not produce acid and gas in MacConkey's broth within 2 days at 37°. Anaerogenic and paracolon types at 30° were infrequent (5%) of ungrazed herbage, but constituted 18% of the classifiable cultures from grazed pasture. Unclassifiable cultures, mainly paracolons giving —–+ IMViC reactions and liquefying gelatin rapidly, were infrequent. There was no appreciable difference in the incidence of different types of coli‐aerogenes bacteria on flowering heads of grass examined during summer to that for the herbage samples examined throughout the year. Only 6 of the cultures picked from eosin methylene blue agar plates developed the golden‐yellow pigment on nutrient agar characteristic of the so‐called Bacterium herbicola , though lactose‐negative strains producing golden‐yellow or lemon‐yellow pigments were common in the epiphytic microflora of the herbage.