Isolation and Identification of Psychrophilic Species of Bacillus from Milk

Abstract

Forty isolates from 97 raw milk samples (heated to 80 C for 10 min and stored at 4 to 7 C for 3 to 4 weeks) were sporeforming, aerobic, gram-positive or gramvariable, rod-shaped bacteria. Fifteen isolates that were identified had characteristics similar to species of Bacillus, except that they had lower growth temperature ranges, were gram-variable, and were somewhat different in sugar fermentations. Four isolates grew well within 2 weeks at 0 C, but they grew faster at 20 to 25 C. These psychrophilic sporeforming bacteria, the importance of which is discussed, are considered to be variant strains of mesophilic bacilli adapted to low temperatures. Most psychrophilic bacteria isolated from natural sources are heat-sensitive, gram-negative, nonsporeforming rods (3, 5, 10, 19, 22). However, Larkin and Stokes (11) and Sinclair and Stokes (15) isolated psychrophilic species of Bacillus and Clostridium from soil, mud, and water, and Marshall and Ohye (12) isolated a gram-negative psychrophilic Bacillus from sub

Occurrence and Thermoresistance of Spores of Psychrophilic and Psychrotrophic Aerobic Sporeformers in Soil and Foods

“…Comparable results were found by Shehata & Collins (1972) for 8 psychrotrophic Bacillus spp. from milk, for which the D,,.,-value in skim milk ranged from 4.4-6.6 min (our D,,.,-values ranged from 1-1 1 min).…”

Incidence of thermoduric psychrotrophs in milk produced in the west of Scotland

“…Other authors have also reported that milk is not a favourable sporulation medium for many spore-forming bacteria (Grinsted & Clegg 1955 ;Donovan 1959). However, the levels of Bacillus contamination found in this survey are of the same order as those reported by a number of workers (Grosskopf & Harper 1969;Shehata & Collins 1971;Coghill & Juffs 1979) although levels of contamination as high as 83% have been reported (Chung & Cannon 1971).…”

“…The first report of psychrotrophic sporeforming bacteria in milk was that of Grosskopf & Harper (1969). Since then many workers have isolated thermoduric psychrotrophs from milk, commonly of the genus Bacillus (Chung & Cannon 1971;Shehata & Collins 1971;Credit et al 1972;Mikolajcik & Simon 1978;Coghill & Jufs 1979) and more rarely of the genus Closrridiurn (Bhadsavle et al 1972). A few authors have also reported the occurrence of thermoduric psychrotrophs which d o not produce endospores (Credit et al 1972;Washam et al 1977).…”

Evaluation of the incubated plate count test for pasteurized milk

“…Bacillus species were also frequently isolated. The spores of these species can survive pasteurization and psychrotrophic species have also been identified in both raw and pasteurized milk (Grosskopf and Harper, 1969;Chung and Cannon, 1971;Shehata and Collins, 1971;Coghill and Juffs, 1979). B cereus was isolated on six occasions from plate count agar and on 22 occasions from B cereus selective agar (Oxoid).…”