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T M Cogan

Publications and source records attributed to T M Cogan.

At least 19 recordsLinked to original sources
PubMed2003

Applicability of a bacteriocin-producing Enterococcus faecium as a co-culture in Cheddar cheese manufacture.

Two strains, Enterococcus faecium RZS C5 and E. faecium DPC 1146, produce listericidal bacteriocins, so-called enterocins. E. faecium RZS C5 was studied during batch fermentation in both a complex medium (MRS) and in milk to understand the influence of environmental factors, characteristic for milk and cheese, on both growth and bacteriocin production. Fermentation conditions were chosen in view of the applicability of in situ enterocin production during Cheddar cheese production. Enterocin production by E. faecium RZS C5 in MRS started in the early logarithmic growth phase, and enterocin activity decreased during the stationary phase. The effect of pH on enterocin production and decrease of activity was as intense as the effect on bacterial growth. Higher enterocin production took place at pH 5.5 compared with pH 6.5. The use of lactose instead of glucose increased the production of enterocin, and at higher lactose concentration, production increased more and loss of activity decreased. The production in skimmed milk compared to MRS was lower and was detected mainly in the stationary phase. When casein hydrolysate was added to the milk, enterocin production was higher and started earlier, indicating the importance of an additional nitrogen source for growth of E. faecium in milk. For co-cultures of E. faecium RZS C5 with the starters used during Cheddar cheese manufacture, no enterocin activity was detected during the milk fermentation. Furthermore, the applicability of E. faecium RZS C5 and E. faecium DPC 1146 strains was tested in Cheddar cheese manufacture on pilot scale. Enterocin production took place from the beginning of the cheese manufacturing and was stable during the whole ripening phase of the cheese. This indicates that both an early and late contamination of the milk or cheese can be combated with a stable, in situ enterocin production. The use of such a co-culture is an additional safety provision beyond good manufacturing practices.

Bacteriocins↗
PubMed2002

Source of enterococci in a farmhouse raw-milk cheese.

Enterococci are widely distributed in raw-milk cheeses and are generally thought to positively affect flavor development. Their natural habitats are the human and animal intestinal tracts, but they are also found in soil, on plants, and in the intestines of insects and birds. The source of enterococci in raw-milk cheese is unknown. In the present study, an epidemiological approach with pulsed-field gel electrophoresis (PFGE) was used to type 646 Enterococcus strains which were isolated from a Cheddar-type cheese, the milk it was made from, the feces of cows and humans associated with the cheese-making unit, and the environment, including the milking equipment, the water used on the farm, and the cows' teats. Nine different PFGE patterns, three of Enterococcus casseliflavus, five of Enterococcus faecalis, and one of Enterococcus durans, were found. The same three clones, one of E. faecalis and two of E. casseliflavus, dominated almost all of the milk, cheese, and human fecal samples. The two E. casseliflavus clones were also found in the bulk tank and the milking machine even after chlorination, suggesting that a niche where enterococci could grow was present and that contamination with enterococci begins with the milking equipment. It is likely but unproven that the enterococci present in the human feces are due to consumption of the cheese. Cow feces were not considered the source of enterococci in the cheese, as Enterococcus faecium and Streptococcus bovis, which largely dominated the cows' intestinal tracts, were not found in either the milk or the cheese.

Animals↗
PubMed2001

Enterococcal diversity in the environment of an Irish Cheddar-type cheesemaking factory.

Enterococci are natural residents of human and animal intestinal tracts and grow to high levels in a variety of artisanal cheeses. The aim of this study was to determine the diversity of enterococci in a farmhouse raw-milk cheese production unit. Putative enterococci were isolated from the faeces of all the cows and all the people associated with the cheesemaking, from the milk and cheese during manufacture and ripening and from the environment in three separate trials. Almost 1400 isolates were screened using a genus-specific primer. The results indicated that all the human, milk, curd and cheese isolates but only 33.7%, 6.7% and 4.4% of the bovine isolates from the three trials, respectively, were members of the genus Enterococcus. RAPD-PCR was used to type the enterococcal isolates. In general, only E. faecium was found in the bovine faeces while E. casseliflavus dominated the human faeces, milk and cheese followed by lower numbers of E. faecalis. Environmental sampling of the water in the milking parlour and rinses of the cows' teats, the bulk-milk storage tank and the milking machine corroborated these results as E. casseliflavus and E. faecalis were the only Enterococcus species found in these samples. The putative vancomycin-resistant enterococci (VRE), isolated in Trial 1, were shown to be Pediococcus spp. by genotypic and phenotypic analysis.

Animals↗
PubMed2001

Purification and characterisation of acetolactate decarboxylase from Leuconostoc lactis NCW1.

A two-step strategy involving DEAE-cellulose and POROS PI anion exchange chromatography has been developed for rapid purification of acetolactate decarboxylase (ALD) from Leuconostoc lactis NCW1. This results in 5333-fold purification with a yield of 30%. Purified ALD is a dimer of 49-kDa subunits, has a pH optimum of 6.0, a pI of 4.2 and its activity is independent of metals or branched chain amino acids. At the optimum pH, the K(m) for 2-acetolactate (ALA) was found to be 1.3 mM and the turnover number was 4000 min(-1). N-terminal sequence comparison with other ALDs showed little sequence conservation in this region. Purified ALD does not catalyse direct production of diacetyl from ALA, unlike the crude extract.

Anion Exchange Resins↗
PubMed2001

Spatial and temporal distribution of non-starter lactic acid bacteria in Cheddar cheese.

AIMS: The aim of this work was to investigate the spatial and temporal distribution of species and strains of non-starter lactic acid bacteria (NSLAB) within Cheddar cheese. METHODS AND RESULTS: Randomly amplified polymorphic DNA was used to identify and track the principle species and strain groups of NSLAB present. The same strains dominated each location examined within a cheese at any particular time point. Temporal change in species and strains of NSLAB during ripening was observed. A mixture of Lactobacillus paracasei, Lact. plantarum, Lact. rhamnosus and unidentified strains was found up to 6 weeks of maturation, thereafter only Lact. paracasei strains were isolated. CONCLUSION: Little variation in the spatial distribution of NSLAB strains occurs within Cheddar cheese; however, temporal changes in the species and strains were observed during ripening. SIGNIFICANCE AND IMPACT OF THE STUDY: The complex changes in the composition of the NSLAB community of Cheddar cheese may be the source of the variation in flavour that is seen in commercial practice.

Cheese↗
PubMed2001

Corynebacterium mooreparkense sp. nov. and Corynebacterium casei sp. nov., isolated from the surface of a smear-ripened cheese.

Ten isolates each of two different bacterial species isolated from the surface of a smear-ripened cheese were found to exhibit many characteristics of the genus Corynebacterium. The isolates were Gram-positive, catalase-positive, non-spore-forming rods that did not undergo a rod/coccus transformation when grown on complex media. Chemotaxonomic investigation revealed that the strains belonged unambiguously to the genus Corynebacterium. Their cell walls contained arabinose, galactose and short-chain mycolic acids (C22 to C36) and their peptidoglycan contained meso-diaminopimelic acid. The G+C content of the DNA was 51-60 mol%. MK-9 (H2) was the principal menaquinone. The 16S rDNA sequences of four isolates of each bacterium were determined and aligned with those of other members of the coryneform group. Phylogenetic analysis showed that the strains represented two new sublines within the genus Corynebacterium; Corynebacterium variabile and Corynebacterium ammoniagenes were their nearest known phylogenetic neighbours. Corynebacterium variabile and Corynebacterium ammoniagenes showed the highest levels of sequence homology with the isolates; however, DNA-DNA hydridization studies indicated that the Corynebacterium strains isolated from the cheese smear did not belong to either Corynebacterium variabile or Corynebacterium ammoniagenes (26 and 46% chromosomal similarity, respectively). On the basis of the phylogenetic and phenotypic distinctiveness of the unknown isolates, it is proposed that the bacteria be classified as two new Corynebacterium species, for which the names Corynebacterium mooreparkense sp. nov. and Corynebacterium casei sp. nov. are proposed. Type strains have been deposited in culture collections as Corynebacterium mooreparkense LMG S-19265T (= NCIMB 30131T) and Corynebacterium casei LMG S-19264T (= NCIMB 30130T).

Biomass↗
PubMed2001

Microbacterium gubbeenense sp. nov., from the surface of a smear-ripened cheese.

Phenotypic and phylogenetic studies were performed on 11 strains of a Microbacterium-like organism isolated from the surface of a smear-ripened cheese. The isolates were Gram-positive, catalase-positive, facultatively anaerobic, oxidase-negative, non-spore-forming, non-motile, small, slender rods and grew in 12% (w/v) NaCl. Chemotaxonomic investigation revealed that all the isolates belonged unambiguously to the genus Microbacterium. They contained type B1 peptidoglycans with L-lysine as the diamino acid and glycolyl acyl types; rhamnose and galactose were the cell wall sugars. The G+C content ranged from 69 to 72 mol%. The major menaquinones were MK-11 and MK-12 and the major fatty acids were anteiso C15:0 and C17:0 and iso C16:0. Phylogenetic analysis of the 16S rRNA sequences of four isolates showed that they represented a new subline in the genus Microbacterium, with Microbacterium barkeri as their nearest phylogenetic neighbour. M. barkeri showed the highest sequence similarity to the isolates; however, DNA-DNA hybridization showed that the isolates had only 38% chromosomal similarity to M. barkeri. Based on the phylogenetic and phenotypic distinctiveness of the isolates, it is proposed that they be classified as a new Microbacterium species, for which the name Microbacterium gubbeenense sp. nov. is suggested. The type strain has been deposited as LMG S-19263T (= NCIMB 30129T). The GenBank accession number for the 16S rDNA sequence of the type strain is AF263563.

Actinomycetales↗
PubMed2000

A rapid PCR based method to distinguish between Lactococcus and Enterococcus.

Phenotypic characterisation of Lactococcus and Enterococcus species remains unreliable as strains of both genera have been isolated which do not conform to the traditional criteria for separation of these genera. A bank of 131 isolates was phenotypically characterised by three methods: (a) traditional broth tests, (b) API Rapid ID 32 Strep and (c) BBL Crystal ID kits. Differences in genus designation between commercial kits were evident for 12 strains (9%), while 7 strains (5%) remained unidentified by either kit. Published 16S rRNA sequences were aligned and used to design genus-specific primers which, when used in separate PCR reactions, were capable of distinguishing all type strains of Lactococcus and Enterococcus. These primers did not react with known species of Streptococcus, Pediococcus, Lactobacillus, Leuconostoc or Tetragenococcus. Isolates which could not be identified by phenotype were assigned to either genus on the basis of the gene primers.

DNA Primers↗
PubMed2000

Inability of dairy propionibacteria to grow in milk from low inocula.

Growth of propionibacteria in complex media was independent of the initial number of cells; in contrast, growth of propionibacteria in milk and whey did not occur if the initial level of cells was < 10(6) cfu/ml. Addition of vitamins, minerals or complex nitrogen sources to the milk or whey, or incubation under anaerobic conditions had no effect on the lack of growth. Addition of freeze-dried whey, prepared from skim milk reconstituted from powder, to a complex medium prevented growth from low inocula in the complex medium, demonstrating the presence of an inhibitor or inhibitors in the whey. The inhibitor(s) was heat stable, had a low molecular mass and retained its activity for at least 4 weeks at 20 degrees C. Pregrowth of some lactic acid bacteria, used as starter cultures in Swiss-type cheese manufacture, in milk for 2 weeks at 20 degrees C removed the inhibition, which explains how propionibacteria develop in Swiss-type cheese from low numbers even though they are inhibited in milk.

Animals↗
PubMed1999

Heat resistance of Lactobacillus spp. isolated from Cheddar cheese.

Mesophilic Lactobacillus spp. are the dominant organisms in mature Cheddar cheese. The heat resistance of broth grown cultures of Lactobacillus plantarum DPC1919 at temperatures between 50 and 57.5 degrees C, Lact. plantarum DPC2102 at temperatures between 48 and 56 degrees C and Lact. paracasei DPC2103 at temperatures between 50 and 67.5 degrees C was determined. The z-values for Lact. plantarum DPC1919, Lact. Plantarum DPC2102 and Lact. paracasei DPC2103 were 6.7 degrees C, 6.2 degrees C and 5.3 degrees C, respectively. Lactobacillus paracasei DPC2103 showed evidence of injury and recovery, especially at higher temperatures. Milk grown cultures of strains DPC2102 and DPC2103 showed greater heat resistance than broth grown cultures, tailing of the death curves and a nonlinear z-curve. Of the three strains, Lact. paracasei DPC2103 had the potential to survive pasteurization temperatures, whether grown in milk or broth.

Animals↗
PubMed1999

Phenotypic and genotypic characterization of non-starter lactic acid bacteria in mature cheddar cheese.

Non-starter lactic acid bacteria were isolated from 14 premium-quality and 3 sensorially defective mature Irish Cheddar cheeses, obtained from six manufacturers. From countable plates of Lactobacillus-selective agar, 20 single isolated colonies were randomly picked per cheese. All 331 viable isolates were biochemically characterized as mesophilic (i.e., group II) Lactobacillus spp. Phenotypically, the isolates comprised 96.4% L. paracasei, 2.1% L. plantarum, 0.3% L. curvatus, 0.3% L. brevis, and 0.9% unidentified species. Randomly amplified polymorphic DNA (RAPD) analysis was used to rapidly identify the dominant strain groups in nine cheeses from three of the factories, and through clustering by the unweighted pair group method with arithmetic averages, an average of seven strains were found per cheese. In general, strains isolated from cheese produced at the same factory clustered together. The majority of isolates associated with premium-quality cheese grouped together and apart from clusters of strains from defective-quality cheese. No correlation was found between the isomer of lactate produced and RAPD profiles, although isolates which did not ferment ribose clustered together. The phenotypic and genotypic methods employed were validated with a selection of 31 type and reference strains of mesophilic Lactobacillus spp. commonly found in Cheddar cheese. RAPD analysis was found to be a useful and rapid method for identifying isolates to the species level. The low homology exhibited between RAPD banding profiles for cheese isolates and collection strains demonstrated the heterogeneity of the L. paracasei complex.

Bacterial Typing Techniques↗
PubMed1992

Detection of propionic acid bacteria in cheese.

Mesophilic lactic starters and thermophilic lactobacilli but not Streptococcus salivarius subsp. thermophilus grew on the sodium lactate agar (SLA) used for estimating the numbers of propionic acid bacteria (PAB) in cheese. The addition of cloxacillin (4 micrograms/ml) to SLA inhibited the starter bacteria but had no effect on the PAB. It was possible to count low numbers of PAB in the presence of high numbers of starter bacteria. A correlation coefficient of 0.9 was obtained between the level of propionic acid and the counts of PAB in cheese (n = 40). A disadvantage of the medium is that other bacteria found in cheese (mesophilic lactobacilli, enterococci, Clostridium tyrobutyricum) also grow on it; however, these bacteria are easily distinguishable from PAB on the basis of size, colour and absence of catalase.

Animals↗
PubMed1992

Intracellular pH and the role of D-lactate dehydrogenase in the production of metabolic end products by Leuconostoc lactis.

The kinetics of lactate dehydrogenase from Leuconostoc lactis NCW1 were studied. The pH optimum for the enzyme depended on the concentration of pyruvate used in the assay and the enzyme displayed an ordered mechanism with respect to substrate binding. The Km for pyruvate and NADH and the Vmax of the enzyme decreased 20-, 30- and 6-fold respectively as the pH decreased from 8.0 to 5.0. No activators were found and none of the intermediates of the phosphoketolase pathway tested inhibited the enzyme. ATP, ADP, GTP and NAD+ were inhibitory. The intracellular volume (Vol(in)) and intracellular pH (pH(in)) decreased as the extracellular pH (pH(ex)) decreased. Co-metabolism of citrate and glucose affected the Vol(in) but did not affect the pH(in), which decreased by 0.6 units per unit change in pH(ex); at pH 7.0, the pH(in) and pH(ex) were equal. The results suggest that pH(in) may play a role in determining the production of diacetyl and acetoin at low pH by Leuconostoc.

Adenosine Diphosphate↗
PubMed1992

Incidence of pathogenic bacteria in raw milk in Ireland.

Raw milk from 70 farms was sampled over 13 months for salmonellas, listerias, Escherichia coli, Staphylococcus aureus and mastitic streptococci; total bacterial counts (TBC), coliforms and somatic cells were also counted. TBC < or = 30,000/ml were obtained in 63% of samples. High count milks were found mainly during the winter months: 13% of samples had > 10(4) mastitis pathogens/ml of milk. The mean somatic cell count varied from 4.0 x 10(5) to 8.0 x 10(5)/ml throughout the year with highest counts during the late lactation period. Coliforms were present in all samples, but 65-71% of samples had < 100 coliforms/ml. Up to 60% of supplies had < or = 10 E. coli/ml. One of the 589 samples tested (0.1%) was positive for salmonellas. Yersinia enterocolitica and Y. enterocolitica-like organisms were isolated from 39% of samples with up to 68% of samples positive at some sampling periods. A total of 222 strains of yersinias were isolated; Y. enterocolitica (59%) was the most common strain followed by Y. fredriksenii (35%), Y. kristensenii (1.0%), Y. intermedia (4.5%) and Y. aldovae (0.5%). Listerias were isolated from 8.3% of samples tested; 4.9% were Listeria monocytogenes and 3.4% were L. innocua. There was a significant rise in the isolation rate between December and April from a base line of 0-5% during the spring and summer to 35-37% during the winter months while the cows were indoors. Of 66 silage samples tested from the farms involved in the survey 9% of samples were positive for listerias; 3% of these were L. monocytogenes and 6% were L. innocua.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Glycolysis and related reactions during cheese manufacture and ripening.

Fermentation of lactose to lactic acid by lactic acid bacteria is an essential primary reaction in the manufacture of all cheese varieties. The reduced pH of cheese curd, which reaches 4.5 to 5.2, depending on the variety, affects at least the following characteristics of curd and cheese: syneresis (and hence cheese composition), retention of calcium (which affects cheese texture), retention and activity of coagulant (which influences the extent and type of proteolysis during ripening), the growth of contaminating bacteria. Most (98%) of the lactose in milk is removed in the whey during cheesemaking, either as lactose or lactic acid. The residual lactose in cheese curd is metabolized during the early stages of ripening. During ripening lactic acid is also altered, mainly through the action of nonstarter bacteria. The principal changes are (1) conversion of L-lactate to D-lactate such that a racemic mixture exists in most cheeses at the end of ripening; (2) in Swiss-type cheeses, L-lactate is metabolized to propionate, acetate, and CO2, which are responsible for eye formation and contribute to typical flavor; (3) in surface mold, and probably in surface bacterially ripened cheese, lactate is metabolized to CO2 and H2O, which contributes to the increase in pH characteristic of such cheeses and that is responsible for textural changes, (4) in Cheddar and Dutch-type cheeses, some lactate may be oxidized to acetate by Pediococci. Cheese contains a low level of citrate, metabolism of which by Streptococcus diacetylactis leads to the production of diacetyl, which contributes to the flavor and is responsible for the limited eye formation characteristic of such cheeses.

Animals↗
PubMed1987

Partition of lactic streptococcal bacteriophage during the ultrafiltration concentration of milk and whey.

Milk and whey inoculated with lactic streptococcal bacteriophages 316, or 322, or both were concentrated by UF using a DDS Mini-Lab 20. The plate and frame unit was fitted with Type GR61PP polysulfone membrane with a 20,000 molecular weight cutoff. The unit was operated at an inlet pressure of .40 MPa and an outlet pressure of .23 MPa with an initial flux of 2.0 to 3.0 L/h. Samples of retentate, permeate, and membrane were analyzed for the presence of bacteriophages. Under the conditions established in this study, phage particles did not pass through the membrane but instead became trapped in the polarization concentration layer or in the membrane. Phages were recovered from the membrane by extraction in sterile buffered water with the Stomacher. The UF concentration of milk containing the host species of Streptococcus cremoris resulted in phage propagation and lysis of the host but did not result in the passage of phages through the membrane. The UF processing of milk or whey should produce a phage-free permeate.

Animals↗
PubMed1976

Citric acid metabolism in hetero- and homofermentative lactic acid bacteria.

The effect of citrate on production of diacetyl and acetoin by four strains each of heterofermentative and homofermentative lactic acid bacteria capable of utilizing citrate was studied. Acetoin was quantitatively the more important compound. The heterofermentative bacteria produced no acetoin or diacetyl in the absence of citrate, and two strains produced traces of acetoin in its presence. Citrate stimulated the growth rate of the heterofermentative lactobacilli. Acidification of all heterofermentative cultures with citric acid resulted in acetoin production. Destruction of accumulated acetoin appeared to coincide with the disappearance of citrate. All homofermentative bacteria produced more acetoin and diacetyl in the presence of citrate than in its absence. Citrate utilization was begun immediately by the streptococci but was delayed until at least the middle of the exponential phase in the case of the lactobacilli.

Acetoin↗