The Nature, Significance and Control of Psychrophilic Bacteria in Dairy Products1

Olson, Joseph; Parker, R. B.; Mueller, W.S.

doi:10.4315/0022-2747-18.8.200

Cited by 15 publications

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“…It was amply demonstrated, however, that incubation of plates a t 10" or higher does not give a true representation of the psychrotrophic bacterial content of milk, because thermoduric bacteria can form colonies at this temperature, and the psychrotrophic count cannot then be used as an index of postpasteurization contamination of freshly processed milk (e.g. Olsen, Willoughby, Atherton, Doan & Watrous, 1953Boyd, Smith & Trout, 1954;Olson, Parker & Mueller, 1955;Thome5 & Ljunggren, 1957; Thomas, Reinbold & Nelson, 1963). Baumann & Reinbold (1963~) cite 11 investigations demonstrating the importance of a true psychrotrophic count as an indication of postpasteurization contamination of milk.…”

Section: Development Of Standard Methodsmentioning

confidence: 99%

“…After publication of the APHA (1953) recommended procedure of incubation a t 5" for 7 days, several investigators considered that this low temperature was too selective for dairy purposes, as refrigerated milk is frequently exposed to temperatures > 5", and that 45°F (7.3") was a fair average temperature for milk during distribution (Ford & Babel, 1959;Johns, 1960). Dahlberg, Adams & Held (1953) used incubation at 6-7" (44°F) for 10 days for enumeration of psychrotrophs during their survey of sanitary milk control in the U.S.A.; while Olson, Nielson, , Olson, Willoughby, Thomas & Morris (1953), Hempler (1955) and Olson, Parker & Mueller (1955) employed incubation at 7" for 10 days. During much earlier work, Robinton, Borman & Mickle (1941) and Jezeski & Macy (1946) had used incubation at 8" for 4 days and 7 days, respectively.…”

Section: (C) Incubation At 7"mentioning

confidence: 99%

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Methods of Assessing the Psychrotrophic Bacterial Content of Milk

Thomas¹

1969

Journal of Applied Bacteriology

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Introduction . Development of standard methods . (a) Incubationat 10" . (b) Incubation a t 5" .(c) Incubation a t 7" . Standard reference method . . Technique of examination . (a) Age of raw milk on examination . (b) Age of pasteurized milk on examination . (c) Effect of sublethal heat treatment .(d) Diluent and preparation of dilutions . (e) Temperature of agar medium a t pouring .(f) Temperature variation in refrigerator incubators . (a) Violet red-bile agar . (b) Crystal violet agar (c) Penicillin agar . (d) Other selective media . (e) Oxidase positive colony count Selective media for Gram negative bacteria . Indicator agar media . Preliminary incubation of plates . Surface plating methods . Total colony count of refrigerated milk The Moseley method . Screening and quick methods . (a) Frost little plate method. . -. (b) Microcolonies in the drop plate method . (c) Microcolonies on membrane filters . Conclusions . Acknowledgments . References . PAQE 270 271 272 272 272 273 274 2 74 275 2 76 276 277 277 277 278 278 280 281 281 283 2 84 285 286 288 289 2 89 290 290 290 291 291 SUMMARY. The vaiious methods used for the determination of the psychrotrophic bacterial content of refrigerated milk are reviewed and assessed. A standard reference method, involving incubation of poured plates at 7" for 10 days, is recommended for the determination of psychrotrophic colony counts for investigational purposes. Many ingenious techniques, based on media selective for Gram negative bacteria, with incubation a t higher temperatures and shorter times are described and appraised. A simple procedure which would provide a more rapid assessment of the number of active milk spoilage types of psychrotrophs is needed for routine purposes, and i t is suggested that the enumeration of microcolonies by the drop plate or membrane filter methods with incubation at 7" for 72 h would provide a suitable technique for this purpose.Incubation of plates at 25" for 5 days is recommended as a standard reference method for determining the total colony count of bacteria in refrigerated milk, but for routine purposes where large numbers of milk samples are being examined incubation at 28-30" for 3 4 days would provide a sound enough estimate.

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Section: Development Of Standard Methodsmentioning

confidence: 99%

Section: (C) Incubation At 7"mentioning

confidence: 99%

Methods of Assessing the Psychrotrophic Bacterial Content of Milk

Thomas¹

1969

Journal of Applied Bacteriology

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“…The part played by pseudomonads in the spoilage of fish has been discussed by various workers (Shewan, Hobbs, and Hodgkiss, 1960;Adams, Farber, and Lerke, 1964), and the predominance of pseudomonads during the spoilage of eggs (Florian and Trussell, 1957), dairy products (Schultze and Olson, 1960;Olson, Parker, and Mueller, 1955;Witter, 1961), poultry (Ayres, Ogilvy, and Stewart, 1950), and beef (Ayres, 1960;Halleck, Ball, and Stier, 1958) is well documented. That water may be an important source of contaminating pseudomonads, especially in the dairy industry, has been emphasized by Olson et al (1955) and Witter (1961).…”

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Characterization of Certain Gram-Negative Bacteria from Surface Waters1

Hoadley¹,

McCoy²

1965

Applied Microbiology

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HOADLEY, A. W. (University of Wisconsin, Madison), AND ELIZABETH MCCOY. Characterization of certain gram-negative bacteria from surface waters. Appl. Microbiol. 13:575-578. 1965.-Cultures of gram-negative bacteria with oxidative glucose metabolism were isolated from surface waters by a highly selective technique, and were classified into 11 types. The predominant type, making up about 50% of the isolated cultures, was cytochrome oxidase-positive, produced fluorescent pigment, and failed to grow at 37 C. A similar type, which differed in being cytochrome oxidase-negative, constituited about 10% of the isolates. Both types of bacteria probably were composed of more than one species. A third type, composed of purple-pigmented pseudomonads, made up approximately 30% of the isolated cultures, and probably represented the predominant species. Other bacterial types isolated constituted less than 10% of the cultures examined.

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Control of Bacteria in Nondomestic Water Supplies

Chambers¹,

Clarke²

1966

Advances in Applied Microbiology

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The Nature, Significance and Control of Psychrophilic Bacteria in Dairy Products1

Cited by 15 publications

References 0 publications

Methods of Assessing the Psychrotrophic Bacterial Content of Milk

Methods of Assessing the Psychrotrophic Bacterial Content of Milk

Characterization of Certain Gram-Negative Bacteria from Surface Waters1

Control of Bacteria in Nondomestic Water Supplies

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