Several lactic acid bacteria (LAB) of the Lactococcus, Lactobacillus,
Leuconostoc and Pediococcus genera were screened for inhibition of
food-borne pathogens and spoilage microorganisms in raw milk and
dairy products. Listeria monocytogenes was killed by Lactococcus
lactis subsp. lactis and Pediococcus pentosaceus due to their
production of bacteriocin-type inhibitors. Staphylococcus aureus
was not able to grow in raw milk at temperatures below 5°C even
without LAB being present. Gram negative Salmonella enteritidis.
Salmonella typhimurium and Escherichia coli, along with spoilage
bacteria of the genus Pseudomonas were dramatically inhibited by a
Lactobacillus species, designated AS-1, in raw and pasteurized milk
as well as in cottage cheese. However, other LAB were not able to
inhibit these organisms. Lactobacillus AS-1, did not produce
hydrogen peroxide but carbon dioxide was produced. The AS-1
strain was a gram positive coccobacillus, catalase and oxidase negative and produced DL-lactic acid. It deaminated arginine and
grew over a temperature range of 5°C to 45°C. It was also able to
ferment glucose, galactose, fructose and lactose in addition to 17
other carbohydrates. High numbers (107 CFU/ml) of AS-1 were
required to obtain complete inhibition of gram negative bacteria. A
selective medium (ASLM) for Listeria monocytogenes was developed
to follow the fate of this particular pathogen in association with LAB
in raw milk; other selective media were not able to inhibit the growth
of background flora of raw milk. ASLM was superior to four other
media in allowing only the growth of the target pathogen. For the
Lactococcus genus, a selective and differential agar medium (Alsan)
was formulated to selectively allow growth of Lactococcus spp. and
to differentiate between Lactococcus lactis subsp. lactis and the
biovariety diacetylactis, based on citrate utilization. / Graduation date: 1993
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/27112 |
| Date | 27 August 1992 |
| Creators | Al-Zoreky, Nageb |
| Contributors | Sandine, William E. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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