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...
Microgard, a commercially-available pasteurized
fermented milk, was found inhibitory to gram negative
bacteria such as Pseudomonas putida, some well-known foodborne
pathogens (e.g. Salmonella, Yersinia and Aeromonas)
and some fungi as revealed by an agar incorporation assay
method. Gram positive bacteria, however, were not
inhibited. Rather, some bacteria in this group...
Cheddar cheese making from ultrafiltered (UF) concentrated milk
potentially increases yield, saves raw materials, cuts transportation costs,
minimizes waste pollution, and stream-lines production. However, the resulting
UF-cheese has been found to differ from conventionally made cheese (CM-cheese)
in its casein matrix and ripening process.
UF and CM Cheddar cheeses were...
The fecal flora of healthy bottle or breast-fed infants was
examined for the presence of Bifidobacterium. Identification was
based on the presence of fructose-6-phosphate phosphoketolase,
which is found only in these bacteria. No bifidobacteria were
recovered from bottle-fed infants. However, bifidobacteria were
readily isolated from 15 day to 3 month...
The purposeful induction of malolactic fermentation (MLF) in wines such as Pinot Noir
and Chardonnay is an established commercial wine making practice in Oregon. This induction
is not always successful, especially with white wines, such as Chardonnay. A study was
initiated to examine the compatibility of yeasts commonly used in...
Strains of Lactococcus lactis ssp. lactis and Lactococcus lactis ssp. cremoris with potential use in the food industry which had been previously isolated from nature using 16S rRNA probes were characterized for unique identifying traits and for attributes important for potential use in cheese manufacture. Strains of Lc. cremoris which...
Dairy leuconostocs are frequently used as aroma-producing bacteria in mesophilic cultures used as starters for milk fermentations. Sixty Leuconostoc strains from different culture collections were studied taxonomically for species identification. Based on morphological, physiological and biochemical tests, twenty of these strains were typed as Leuconostoc mesenteroides ssp. cremoris (Leu. cremoris)....
The present investigation was undertaken to characterize a
number of strains of Lactobacillus bulgaricus and Streptococcus
thermophilus intended for use by a commercial starter supply
company. Thorough characterization of each culture was required in
order to combine compatible strains so that their usefulness in
Mozzarella cheese manufacture would be maximized....
The work presented in this thesis is concerned with the
effect of several antibiotics and quaternary ammonium
sanitizers upon growth of lactic acid bacteria. Section I
reports the purification of beta-lactamase from Lactococcus
cremoris PR-108, by ion exchange chromatography, using the
chromogenic substrate pyridine-2-azo-p-dimethylaniline
(PADAC) as the enzymatic indicator. Section...
Internally-pH-controlled, phosphate containing and non-phosphate
containing Italian bulk starter media were compared to
reconstituted nonfat dry milk and commercial bulk starter media
for their ability to support the growth and activities of
commercially frozen thermophilic lactic acid cultures. Cultures
grown in internally-pH-controlled media demonstrated superior
acid-production capability. The cheese made...
Lactobacilli are microorganisms with many applications in the
fermented food and dairy industries. In addition to the actual
fermentation of food products, lactobacilli are involved in the
metabolic breakdown of lactose in dairy products, enabling a large
population of lactose-intolerant humans to ingest milk. Lactobacilli
are also used as health...
Three commercial sausage starter cultures were grown in
an internal-pH-controlled medium (PHASE 4) and in a soluble
phosphate-buffered medium. The cultures were tested by
comparing viable counts before and after freezing at -40 C
or freeze-drying and subsequent storage for 3 months in the
frozen or dried state. Strains varied...
Mutants of Streptococcus lactis 7962 with various combinations of plasmid molecular masses were screened for nisin production. Nisin was produced by both wild type and mutants that contained a 17.5 Md plasmid, which was usually obscured by the chromosomal fragments. No nisin was produced by plasmid-free mutants. Sucrose fermentation and...
The ability of Propionibacterium shermanii to produce
growth metabolites which were inhibitory to food spoilage
indicator organisms was investigated. Asperqillus niqer,
a Pseudomonas species and Kluyveromyces fraqilis were the
spoilage indicators chosen to represent molds, gram
negative psychrotrophic bacteria and yeasts, respectively.
Supplementation of milk or whey based media was...
A method for rapid isolation of plasmid DNA from group N
streptococci was developed. Chief advantages of the method were
simplicity, the utilization of microliter quantities of reagents,
and the obtainment of preparations highly enriched for covalently
closed circular plasmid DNA. The method was also applied to over
15 Leuconostoc...
Commercial vats of Chardonnay and Pinot Noir were
inoculated during yeast fermentation with starter cultures
containing 10⁷ - 10⁹ cfu/ml of the malolactic bacteria
Leuconostoc oenos Erla and Ey2d in lots ranging from 55 to
4,000 gallons. Chardonnay inoculated with Ey2d completed
MLF in an average of 56 days at...
A study of malolactic bacteria of the Leuconostoc
genus, especially L. oenos, and their bacteriophages was
conducted. A search for the presence of infectious
bacteriophages in grapes, musts, and juices employed in
malo-lactic fermentation (MLF) was conducted; no
evidence, either physical or biological, was found for
the existence of these...
Several bulk starter media, consisting of two experimental blends and four commercial preparations, were examined for each medium's ability to grow, preserve, and/or recover lactic streptococcal starter cultures. Nonfat milk was used as a control. Results showed that cultures which had the greatest survival rate in frozen storage had been...
Gram positive cocci isolated from Oregon wines
were characterized and their relative malate fermentation
abilities compared. They were heterofermentative,
catalase negative, and facultatively anaerobic. Glucose,
fructose, cellobiose, maltose, ribose, trehalose, salicin
and esculin were fermented by all strains. Arabinose was
fermented weakly but lactose, raffinose, sucrose, xylose,
rhamnose, mannose and...
Fast acid-producing streptomycin-resistant mutants for several
strains of lactic streptococci currently used in commercial Cheddar
cheese manufacture were isolated. Their isolation involved use of a
recently developed differential plating medium that allows identification
of fast acid-producing colonies. Both parents and mutants were characterized
with regard to growth, acid production, proteolytic...
Lactic streptococcal agglutinins are known to promote settling of starter bacteria in milk, resulting in spongy, mealy, shattered curd and sludge formation defects in cottage cheese. These agglutinins are natural antibodies secreted by lactating cows in mature milk in response to infections (mastitis) and in colostrum milk as protective antibodies...
A survey was conducted of six North American cheese plants to
determine levels of bacteriophages present. Fifty-nine lactic streptococcal
host bacterial strains were utilized in the survey. Phage levels
were generally lower in plants employing modern manufacturing techniques
than in plants employing traditional manufacturing techniques; this
difference was attributed to...
Two multiple strain lactic streptococcal starter concentrates
were examined to determine whether or not elimination of one of the
three component strains, by addition of its specific phage, resulted
in disproportionate inhibition of acid production (strain dominance).
Both starters showed dominance when tested three to four weeks after
freezing and...
Seven commercially prepared brands of lactic streptococcal
phage inhibitory media were obtained from their manufacturers.
Comparisons between the different media were made with respect
to buffering capacity, ability to support lactic streptococcal growth,
ability to suppress bacteriophage replication, and ability to support
Leuconostoc growth. Nonfat milk was used during experiments...
The concentrations of iodophor necessary to reduce the activity
of several metabolic enzyme systems 50 percent was used as the
basic approach in attempts to elucidate the mechanism of germicidal
action of iodine. For comparisons, a chlorine-releasing germicide
(Trichlorocide) and a quaternary ammonium compound were also
tested. It was found...
Rapid acid production by lactic streptococci used in the manufacture of fermented dairy products is essential to the economy of the
industry and to the public health of consumers.
There remains to
developed, however, an adequate laboratory procedure to detect and
distinguish between slow and fast strains of these bacteria....
Pseudomonas aeruginosa cells were selected for their ability
to grow in the presence of 750 ppm alkyldimethylethylbenzyl
ammonium chloride (QAC). These cells were found to retain their
resistance to the germicide throughout tri-weekly transfers for 7
months in tryptone glucose yeast extract (TGY) broth containing no
QAC. Comparisons of the...
Factors influencing diacetyl production by the aroma bacteria
Leuconostoc citrovorum and Streptococcus diacetilactis were investigated.
When grown in association with lactic streptococci, L. citrovorum
strain 91404 decreased in cell numbers from 10⁸ to 10⁶ over
two weeks of daily subculturing in sterile non-fat milk incubated at
21°C. The ability to...
The enzymes and pathways involved in the catabolism of
glucose by several strains of Streptococcus diacetilactis, Streptococcus
cremoris, and Streptococcus lactis, commonly called the
lactic streptococci, were studied. The presence of aldolase,
triosephosphate isomerase and alcohol dehydrogenase in these
organisms provided evidence for the operation of the Embden-Meyerhof-Parnas (EMP) pathway...
This study was undertaken to determine the role Leuconostoc
citrovorum may play in carbon dioxide production in milk. The
ability of L. citrovorum strains to produce gas was studied by two
methods. A qualitative method used visual measurement of gas where
an agar plug was forced up the neck of...
This study was carried out to compare the effects of a quaternary
ammonium compound (QAC) upon strains of Pseudomonas aeruginosa
which were either sensitive or resistant to the germicide. The cationic
QAC used was alkyldimethylbenzylammonium chloride. The resistant
types were isolated from the sensitive population by selection
of mutants which...
This study involved an investigation of lactic streptococci which
had irreversibly lost ability to produce the high levels of acid in milk
necessary during the manufacture of certain fermented dairy products.
The slow acid producing mutants studied were obtained from
a normal acid producing strain by natural selection following induction...
Comparisons were made of the abilities of Streptococcus lactis,
Streptococcus cremoris and Streptococcus diacetilactis bacteriophages
to endure various laboratory isolation and storage treatments.
Neutralization of Cottage cheese whey containing phages offered no
survival advantage over unneutralized samples, refrigeration of
neutral and acid whey samples increased the survival of only the...
To determine whether some bacteria are more susceptible
than others to quaternary ammonium compounds, the following bacteria
were grown on agar slants containing various concentrations of
alkyl dimethyl ethyl benzyl ammonium chloride (ADEBAC), and alkyl
dimethyl benzyl ammonium chloride (ADBAC): Aerobacter aerogenes
12658, Alcaligenes metalcaligenes, Brevibacterium linens, Chromobacterium
lividum, Escherichia...
The public health and economic significance of rapid acid production
by lactic streptococci in controlled dairy fermentations is well
known. However, the fast acid-producing characteristic of these organisms
is not stable, and cultures of fast organisms have been shown
to contain slow cells. These studies were carried out to characterize...
The dairy industry relies primarily on consistent acid production
by the lactic streptococci for the manufacture of certain cheeses
and fermented dairy products. Variation in these cultures due to
genetic exchange has not been thoroughly investigated. This study
was undertaken to determine if genetic homology exists within the lactic
group,...
Bacillus cereus excretes large amounts of penicillinase
into growth media during incubation, hence the
widely-used penicillin selection technique for isolating
biochemical mutants of bacteria is not applicable to this
species. Genetic transfer in B. cereus has not been
reported; this is partly due to the lack of an effective
isolation...