Showing papers in "Journal of Applied Microbiology in 1996"
TL;DR: Evaluation of predictive models by comparison to published microbial growth rate data may be inappropriate because of limitations in that data, and two complementary measures are proposed as simple indices of the performance of models in predictive food microbiology.
Abstract: Two complementary measures are proposed as simple indices of the performance of models in predictive food microbiology. The indices assess the level of confidence one can have in the predictions of the model and whether the model displays any bias which could lead to 'fail-dangerous' predictions. The use of the indices is demonstrated using data collated from independent and published literature. This analysis supports previous reports that evaluation of predictive models by comparison to published microbial growth rate data may be inappropriate because of limitations in that data. The indices may fail to reveal some forms of systematic deviation between observed and predicted behaviour. It is concluded, however, that the indices provide an objective and readily interpreted summary of model performance and may serve as a first step towards the development of an objective and useful definition of the term 'validated model' in predictive food microbiology.
979 citations
TL;DR: Experiments with 16 species of intestinal bacteria belonging to six different genera showed that environmental factors such as low pH and high carbohydrate availability markedly reduced dissimilatory aromatic amino acid metabolism in some organisms, but stimulated this process in others.
Abstract: Concentrations of phenolic compounds in human gut contents were more than fourfold higher in the distal colon (6.2 mmol kg-1) compared to the proximal bowel (1.4 mmol kg-1). Tryptophan metabolites were never found in more than trace amounts in large intestinal contents and phenol substituted fatty acids were the major products of aromatic amino acid fermentation that accumulated in the proximal colon, whereas phenol and p-cresol were more important in the distal gut, accounting for 70% of all products of dissimilatory aromatic amino acid metabolism. In vitro incubations of colonic material showed that phenol was produced most rapidly (1.0 mumol g-1 h-1), whereas indole was formed comparatively slowly (0.06 mumol g-1 h-1). Most probable number (MPN) estimations demonstrated that large populations of phenol and indole producing bacteria occur in the large intestine (range log10 9.8-11.5 (g dry wt faeces)-1, mean 10.6, N = 7). With respect to phenolic compounds, phenylacetate and phenylpropionate producers predominated, while indoleacetate-forming bacteria were the major tryptophan-utilizing organisms. Quantitation of products of dissimilatory aromatic amino acid metabolism in MPN tubes showed that phenol and phenylpropionate mainly accumulated at low sample dilutions, whereas phenylacetate, p-cresol, indoleacetate and indolepropionate were formed in greatest amounts at high sample dilutions. The significance of pH and carbohydrate availability with respect to aromatic amino acid metabolism was shown in batch culture fermentation studies, where net production of phenolic compounds by mixed populations of intestinal bacteria was reduced by approximately 33% during growth at pH 5.5 compared to pH 6.8, and by 60% in the presence of a fermentable carbohydrate. Experiments with 16 species of intestinal bacteria belonging to six different genera showed that environmental factors such as low pH and high carbohydrate availability markedly reduced dissimilatory aromatic amino acid metabolism in some organisms, but stimulated this process in others. A three-stage continuous culture model of the colon was used to investigate the effect of system retention time (27.1 or 66.7 h) on aromatic amino acid fermentation. Qualitative and quantitative increases in phenol production occurred from vessel 1 to vessel 3 in this model. Concentrations of phenolic compounds in vessel 3 were three times greater at R = 66.7 h compared to R = 27.1 h. Phenol and p-cresol were not detected in vessel 1, though formation of these metabolites increased from vessel 2 to vessel 3, in a pattern similar to that observed in the distal colon.
380 citations
TL;DR: Two types of Indian crude oil were tested for their biodegradability by Acinetobacter calcoaceticus and Alcaligenes odorans and the two strains grew very well on n-alkane up to C33 as well as on pristane (branched-chain alkane) but could not grow on cycloalkanes.
Abstract: Two types of Indian crude oil (Bombay High and Gujarat) were tested for their biodegradability by Acinetobacter calcoaceticus and Alcaligenes odorans. Acinetobacter calcoaceticus S30 and Alc. odorans P20 degraded Bombay High crude oil by 50% and 45%, while only 29% and 37% of Gujarat crude oil (heavy crude oil) was degraded by these isolates, respectively. Acinetobacter calcoaceticus and Alc. odorans in combination deraded 58% and 40% of Bombay High and Gujarat crude oils, respectively, which were significantly higher than that of by individual cultures. Acinetobacter calcoaceticus S30 degraded more of the alkanes fraction than the aromatics fraction of both crude oils. GC fingerprinting of alkane fraction showed major degradation of heptadecane (C17), octadecane (C18), nonadecane (C19), eicosane (C20), docosane (C22), tricosane (C23) and tetracosane (C24) of crude oil, while the Alc. odorans P20 degraded alkanes and aromatics equally. The asphaltenic component increased in both types of crude oil after biodegradation. The two strains grew very well on n-alkane up to C33 as well as on pristane (branched-chain alkane) but could not grow on cycloalkanes. Acinetobacter calcoaceticus S30 could not grow on pure polycyclic aromatic hydrocarbon (PAH) compounds except naphthalene but Alc. odorans P20 could grow on anthracene, phenanthrene, dibenzothiophene, fluorene, fluoranthene, pyrene and chrysene.
287 citations
TL;DR: There was a wide range of electrophoretic types present in the primary production environment, relatively few of which have been linked to cases of human listeriosis, however, these types do arise on farms and occasional contamination of food raw material by potentially virulent strains may be sufficient to allow adaptable strains to become established in the processing environment and thus be responsible for more widespread contamination of the food available to the consumer.
Abstract: Listeria monocytogenes was isolated in low numbers from a variety of environmental samples associated with the primary production of food, including vegetation, faeces and meat. The organism was rarely detected on growing grass and vegetables prior to processing. The excretion of L. monocytogenes by farm animals was linked to their diet, with animals fed entirely on hay or manufactured diets not excreting detectable levels of Listeria (i.e. absence in 25 g). However, animals fed on silage, which is frequently contaminated with L. monocytogenes, commonly excreted the organism. Transport of live animals over long distances (> 100 km) significantly increased the level of excretion of Listeria, but the contamination of carcasses of sheep and cattle was not high. Pigs and poultry faeces were free of Listeria prior to slaughter and pig carcasses were not found to have Listeria present. Frozen and chilled chicken did show detectable levels reflecting the greater potential for contamination during poultry processing. Samples of minced beef were tested and 21 of 23 samples were positive for L. monocytogenes, demonstrating that processing significantly increases the level of contamination compared to whole carcasses. Multilocus enzyme electrophoresis of a representative selection of the isolates showed that there was a wide range of electrophoretic types present in the primary production environment, relatively few of which have been linked to cases of human listeriosis. However, these types do arise on farms and occasional contamination of food raw material by potentially virulent strains may be sufficient to allow adaptable strains to become established in the processing environment and thus be responsible for more widespread contamination of the food available to the consumer.
282 citations
194 citations
TL;DR: In this paper, the combined effects of pressure, temperature, pH, initial spore concentration and the presence of nisin on the survival of spores of Bacillus coagulans were investigated.
Abstract: We investigated the combined effects of pressure, temperature, pH, initial spore concentration and the presence of nisin on the survival of spores of Bacillus coagulans. Spores were more sensitive to pressure both at lower pH and at higher treatment temperatures. An additional 1.5-log10 reduction in cfu ml-1 was observed when pH was lowered from 7.0 to 4.0 during pressurization at 400 Mpa and 45°C. A 4-log10 cfu ml-1 reduction was observed when the temperature was increased from 25°C to 70°C during pressurization at 400 Mpa. The spores were sensitive to nisin at concentrations as low as 0.2 IU ml-1. At least a 6-log10 reduction was generally achieved with pressurization at 400 Mpa in pH 4.0 buffer at 70°C for 30 min when plated in nutrient agar containing 0.8 IU ml-1 nisin.
172 citations
TL;DR: The spectrum and activity of xylan- and arabinogalactan-hydrolysing glycosidases of these new isolates, together with additional bacterial strains originally obtained from enrichments with aromatic compounds were determined.
Abstract: Termites play a major role in the recycling of photosynthetically fixed carbon. With the aid of their symbiotic intestinal flora, they are able to degrade extensively wood constituents such as cellulose and hemicellulose. Nevertheless, the microbial species involved in the degradation of hemicelluloses are poorly defined. The purpose of this paper was to examine the microflora involved in hemicellulose degradation. Different aerobic and facultatively anaerobic bacteria and yeasts were isolated using xylan, arabinogalactan and carboxymethylcellulose as substrates. Gram-positive isolates belonged to the genera Bacillus, Paenibacillus, Streptomyces or the actinobacteria group, while the Gram-negative strains were assigned to the genera Pseudomonas, Acinetobacter, Ochrobactrum, and to genera belonging to the family Enterobacteriaceae. The spectrum and activity of xylan- and arabinogalactan-hydrolysing glycosidases of these new isolates, together with additional bacterial strains originally obtained from enrichments with aromatic compounds were determined.
170 citations
TL;DR: Isolates of Pseudomonas that produced iron chelators, siderophores, inhibited growth of S. putrefaciens in a fish-extract-agar diffusion assay but no, or only weak, antagonistic activity was seen when the medium was supplemented with iron.
Abstract: The interaction between fish spoilage bacteria, Pseudomonas sp. and Shewanella putrefaciens, was investigated using fish extract and fish tissue as model systems. Isolates of Pseudomonas that produced iron chelators, siderophores, inhibited growth of S. putrefaciens in a fish-extract-agar diffusion assay but no, or only weak, antagonistic activity was seen when the medium was supplemented with iron. Sterile-filtered supernatant fluid from a siderophore-producing Pseudomonas grown in fish extract was inhibitory to S. putrefaciens if the number of Pseudomonas was above 108 cfu ml−1. In contrast, supernatant fluids from siderophore-negative Pseudomonas isolates did not inhibit growth of S. putrefaciens. The inhibitory effect was, except for one strain of Pseudomonas, not seen in supernatant fluids from iron-enriched cultures of Pseudomonas sp. Finally, siderophore-producing Pseudomonas sp. lowered the maximum cell level of S. putrefaciens 1–2 log units from 109 to 1010 cfu g−1 when the strains were grown on fish muscle blocks at 0°C but the growth rate of S. putrefaciens was not affected.
164 citations
TL;DR: The time-kill curve study showed that anacardic acid and totarol were bactericidal against MRSA, and synergistic bactericidal activities for these combinations were demonstrated.
Abstract: The inhibitory and bactericidal activities of anacardic acid and totarol, alone and in combination with methicillin, were investigated against methicillin-resistant Staphylococcus aureus (MRSA). The growth of two MRSA strains was inhibited by 6 x 25 microg ml-1 of anacardic acid and 0 x 78 microg ml-1 of totarol. The time-kill curve study showed that these two compounds were bactericidal against MRSA. Anacardic acid killed MRSA cells more rapidly than totarol, and no viable cells were detected after being exposed to 6 x 25 microg ml-1 of anacardic acid for 6 h. Anacardic acid showed bactericidal activity against MRSA at any stage of growth, and also even when cell division was inhibited by chloramphenicol. In the combination studies, the minimal inhibitory concentration (MIC) of methicillin was lowered from 800 to 1 x 56 microg ml-1 for MRSA ATCC 33591, and from 800 to 6 x 25 microg ml-1 for MRSA ATCC 33592, by combining with 1/2 x MIC of anacardic acid. The time-kill curves demonstrated synergistic bactericidal activities for these combinations.
158 citations
TL;DR: Five psychrotrophic strains of lactic acid bacteria were shown to inhibit Aeromonas hydrophila, Listeria monocytogenes, Salmonella typhimurium and Staphylococcus aureus on MRS agar, in salads and in juice prepared from vegetable salads.
Abstract: Five psychrotrophic strains of lactic acid bacteria (Lactobacillus casei, Lact. plantarum and Pediococcus spp.) were isolated from 22 samples of commercial salads. These strains were shown to inhibit Aeromonas hydrophila, Listeria monocytogenes, Salmonella typhimurium and Staphylococcus aureus on MRS agar, in salads and in juice prepared from vegetable salads. Lactobacillus casei IMPCLC34 was most effective in reducing total mesophilic bacteria and the coliform group; Aer. hydrophila, Salm. typhimurium and Staph. aureus disappeared after 6 d of storage, while the counts for L. monocytogenes remained constant. The potential application of antimicrobial-producing lactic acid bacteria as biopreservatives of ready-to-use vegetables is suggested.
148 citations
TL;DR: A commonly used agar diffusion bioassay technique for quantification of nisin in food samples was modified to increase its sensitivity, accuracy and precision.
Abstract: Nisin, a bacteriocin produced by Lactococcus lactis subsp. lactis, is used in some types of food preservation due to its inhibitory action on Gram-positive bacteria and their spores. A commonly used agar diffusion bioassay technique for quantification of nisin in food samples was modified to increase its sensitivity, accuracy and precision. Several variables were evaluated. Results showed Micrococcus luteus as the most sensitive organism tested, a lower agar concentration (0 x 75% compared 1 x 5%) increased the sensitivity of the assay (21% improvement over standard method), and incorporation of 1% Na2HPO4 buffer into the bioassay agar made it possible to prevent false inhibitory zones from developing due to the low pH of the test solutions. This resulted in a 57% improvement in accuracy and a 12% improvement in precision compared to the standard method.
TL;DR: The results indicate that most campylobacteria can be identified accurately and objectively with phenotypic tests when probabilistic methods of data assessment are employed.
Abstract: A probabilistic identification matrix for campylobacteria, comprising 67 phenotypic characters and 37 taxa, is described. The accuracy and integrity of the matrix was evaluated using established computer-assisted methods. Certain taxa (for example, Campylobacter concisus and Camp. gracilis) demonstrated significant phenotypic diversity ; previous data corroborated these findings. Differentiation between a few pairs of taxa proved difficult, although discriminatory characteristics were noted in each of these cases. The results indicate that most campylobacteria can be identified accurately and objectively with phenotypic tests when probabilistic methods of data assessment are employed.
TL;DR: It is concluded that L. monocytogenes in the broiler production is primarily localized to the abattoirs and may be reduced by improving the hygiene.
Abstract: Listeria monocytogenes was isolated from 11/236 (4 x 7%) caecal samples from parent flocks, providing broilers to the abattoirs investigated. Caecal samples from 2078 broilers representing 90 randomly selected broiler flocks were negative for L. monocytogenes. A total of 3080 samples from seven abattoirs including poultry processing line samples, and final products were also examined for L. monocytogenes. Listeria monocytogenes was isolated in 0 x 3% to 18 x 7% of the samples collected in the different abattoirs. Epidemiological typing of 247 L. monocytogenes isolates, including serotyping, phage typing, pulsed-field gel electrophoresis and ribotyping revealed 62 different clones. Based upon typability and discriminatory power, DNA typing methods used were found equally suitable as epidemiological markers. Serotyping and phage typing were not found useful as epidemiological markers for poultry isolates of L. monocytogenes since only 120/247 (48 x 6%) isolates were typable by phage typing and 230/247 (93 x 1%) L. monocytogenes belonged to serotype 01 while 6/247 (2 x 4%) belonged to 04. The discovery of a few dominating clones in each abattoir might indicate an endemic occurrence of L. monocytogenes. It is concluded that L. monocytogenes in the broiler production is primarily localized to the abattoirs. The incidence of L. monocytogenes may be reduced by improving the hygiene.
TL;DR: Mortality and/or histopathological data showed a protective effect against the pathogenic bacteria in yeast-treated mice, and protection against Salm.
Abstract: Saccharomyces boulardii was shown to be capable of inhibiting multiplication of enteropathogenic bacteria in vitro and is currently used for its anti-diarrhoea properties. We studied the capacity of this yeast to antagonize Salmonella typhimurium and Shigella flexneri in the intestinal tract of conventional or gnotobiotic NMRI mice. Conventional animals were given daily 10 mg doses of S. boulardii, whereas germ-free animals were given a single 10 mg dose. Both groups were challenged orally 5 d later with the pathogenic bacteria (10(8) or 10(2) viable cells, respectively). Control groups were treated with saline instead of S. boulardii. Mortality and/or histopathological data showed a protective effect against the pathogenic bacteria in yeast-treated mice. Saccharomyces boulardii colonized the digestive tract of gnotobiotic mice and the number of viable cells ranged around 10(10) g-1 of faeces. In experimental and control gnotobiotic animals, Salm. typhimurium and Sh. flexneri became rapidly established at a level of about 10(10) viable cells g-1 of faeces and remained at high levels until the animals died or were sacrificed. The protection against Salm. typhimurium and Sh. flexneri obtained in conventional and/or gnotobiotic mice previously associated with S. boulardii is not due to the reduction of the bacterial populations in the intestines.
TL;DR: It was found that at all temperatures tested, survivor curves deviated from log-linearity which prevented their description using traditional first order kinetics, so the survivor curves were better described using a vitalistic approach and the log-logistic transformation proposed by Cole et al. (1993).
Abstract: In this work, the death of Clostridium botulinum 213B was measured at temperatures between 101°C and 121°C. It was found that at all temperatures tested, survivor curves deviated from log-linearity which prevented their description using traditional first order kinetics. The survivor curves were better described using a vitalistic approach and the log-logistic transformation proposed by Cole et al. (1993). A single equation was derived to describe all survivor curves over the temperature range tested and a comparison of predicted and measured data showed good correlation. The implications of the use of the vitalistic approach to the validity of the ‘minimum botulinum cook’ is discussed.
TL;DR: A set of 120 isolates of Lactobacillus, Lactococcus and Leuconostoc, mainly isolated from natural starter-free fermentation processes, has been screened for technologically important traits, including lactose hydrolysis, extracellular polysaccharide production, fermentation of carbohydrates, antimicrobial agent susceptibility and bacteriocin production.
Abstract: A set of 120 isolates of Lactobacillus (75), Lactococcus (25) and Leuconostoc (20), mainly isolated from natural starter-free fermentation processes, has been screened for some technologically important traits, including lactose hydrolysis, extracellular polysaccharide production, fermentation of carbohydrates, antimicrobial agent susceptibility and bacteriocin production. Some of the strains exhibited important features for particular fermentations. Furthermore, the sensitivity resistance phenotype to antimicrobials showed genus-specific patterns.
TL;DR: The structure of six Irish kefir samples was studied in the electron microscope, and the microbial composition and fermentation kinetics during growth in 10% reconstituted skim milk at 21°C showed no gross differences in structure between samples.
Abstract: The structure of six Irish kefir samples was studied in the electron microscope, and the microbial composition and fermentation kinetics during growth in 10% reconstituted skim milk at 21°C. The microbial composition of the six samples was similar; at the end of the fermentation the counts of lactococci, leuconostocs, lactobacilli, acetic acid bacteria and yeasts were 109, 108, 5 × 106, 105 and 106 ml−1 respectively; the levels of acetic acid bacteria and lactobacilli showed some intersample differences. Lactate was the major metabolite followed in order by ethanol, acetate and acetoin. The final concentrations of L-lactate produced (66–90 mmol kg−1) were 10-fold higher than those of D-lactate. Acetate and ethanol concentrations varied from 4 to 14 and 2 to 40 mmol kg−‘1 respectively. The rates of citrate utilization and concentration of acetoin produced during growth differed between samples. Scanning electron microscopy showed not only variation between the interior and exterior of the sample but also large variation between different sections of the interiors and exteriors of the same sample. Long and short, and straight and curved rods and yeasts were seen in all samples, the curved rods observed in the interior, but lactococci were seen on the surface of only one sample. There were no gross differences in structure between samples.
TL;DR: Modification of a chemostat system to incorporate removable and replaceable hydroxyapatite (the major mineral in human dental enamel) disks on which biofilms could develop has considerable potential in studying the effects of a variety of factors on biofilm development, as well as in comparing the efficacy of antimicrobial systems againstBiofilms.
Abstract: Previously, we developed a chemostat system to study the behaviour and properties of a community of up to 10 species of oral bacteria. The present study describes modification of this system to incorporate removable and replaceable hydroxyapatite (the major mineral in human dental enamel) disks on which biofilms could develop. Hydroxyapatite disks were immersed in the chemostat for known time periods, and the bacterial content of biofilms determined by viable counting. Initial deposition rates were rapid, with all 10 species detected after 1 h, and the numbers of bacteria in biofilms continued to increase for 21 d. The species composition of biofilms reflected that of the surrounding fluid phase, and showed only limited signs of the type of 'species succession' which is observed in developing dental plaque in vivo, although anaerobic species increased in proportion in older biofilms. Four-day biofilms showed the least variability and were chosen as the 'standard biofilm' for more detailed study. Variability in the bacterial composition of 4-d biofilms was comparable both within a single chemostat run and between independent chemostat runs. Glucose pulsing in the absence of pH control resulted in the selection of cariogenic species; the disruption of the biofilm community was less marked than that of the equivalent planktonic culture. The model system has considerable potential in studying the effects of a variety of factors on biofilm development, as well as in comparing the efficacy of antimicrobial systems against biofilms.
TL;DR: Lactobacilli were selected for study because of their strong ability to adhere to IEC and poor aggregation with salmonellae and were found to have some ability to reduce the attachment of Salm.
Abstract: Single strains of Lactobacillus acidophilus and Lact. fermentum, isolated from chicken intestine, were used to study in vitro interactions with Salmonella enteritidis, Salm. pullorum or Salm. typhimurium in an ileal epithelial cell (IEC) radioactive assay. Exclusion, competition and displacement phenomena were investigated by respectively incubating (a) lactobacilli and IEC together, prior to addition of salmonellae, (b) lactobacilli, IEC and salmonellae together, and (c) salmonellae and IEC, followed by the lactobacilli. Lactobacilli were selected for study because of their strong ability to adhere to IEC and poor aggregation with salmonellae. The results demonstrated that Lact. acidophilus significantly reduced (P < 0.05) the attachment of Salm. pullorum to IEC in the tests for exclusion and competition, but not in the displacement tests. Lactobacillus fermentum was found to have some ability to reduce the attachment of Salm. typhimurium to IEC under the conditions of exclusion (P < 0.08), competition (P < 0.09), but not displacement. However, both Lact. acidophilus and Lact. fermentum were unable to reduce the adherence of Salm. enteritidis to IEC under any of the conditions.
TL;DR: The bactericidal activity of the bacteriocin was more potent when sensitive strains were in the logarithmic growth phase, inducing cell lysis, as observed by decreases in optical density and release of intracellular marker enzymes.
Abstract: A total of 203 lactic acid bacteria isolated from raw goat's milk and artisanal cheese were tested for antibacterial activity. Only two strains of Lactococcus lactis, one strain of Enterococcus faecalis and one strain of Lactobacillus curvatus were shown to produce a bacteriocin-like substance. Lactobacillus curvatus IFPL105 produced a heat-stable bacteriocin, which was hydrolysed by α-chymotrypsin, proteinase K and pancreatin and exhibited a broad spectrum of inhibitory activity. The bactericidal activity of the bacteriocin was more potent when sensitive strains were in the logarithmic growth phase, inducing cell lysis, as observed by decreases in optical density and release of intracellular marker enzymes. Curing experiments resulted in variants that lacked both bacteriocin activity and immunity to the bacteriocin. Plasmid profile analysis of the parental strain and the bacteriocin-negative variants indicated that a plasmid of about 46 kbp may be involved in bacteriocin production and immunity to this antibacterial compound.
TL;DR: Larvicidal activity, against the silkworm and/or the mosquito, was exhibited by 18 isolates belonging to H serovars kurstaki, kenyae, canadensis and aizawai, and an unidentified H serogroup.
Abstract: Mulberry leaves were examined for the occurrence of Bacillus thuringiensis. This organism was recovered from both abaxial and adaxial surfaces : a total of 186 B. thuringiensis colonies were isolated from 24 (96.0%) out of 25 mulberry trees, and from 112 (11.2%) out of 1004 leaves from 25 trees. The frequency of B. thuringiensis colonies was 3.2% among 5900 colonies belonging to the Bacillus cereus/B. thuringiensis group. Single colonies were associated with 75.9% of the B. thuringiensis-positive leaves and 2-16 colonies were occasionally found on a single phylloplane. Flagellar (H) serotypying of the isolates revealed that, among the 19 H serotypes (serovars) detected, the H serotype 13 (serovar pakistani) was the predominant, followed by the H serotypes 3abc (kurstaki), 6ac (oyamensis), 16 (indiana), 24 (neoleonensis), 4ac (kenyae), 7 (aizawai) and 10 (darmstadiensis). Larvicidal activity, against the silkworm (Bombyx mori) and/or the mosquito (Aedes aegypti), was exhibited by 18 isolates (9.7%) belonging to H serovars kurstaki, kenyae, canadensis and aizawai, and an unidentified H serogroup.
TL;DR: When this PCR system was used for the detection of Salmonella cells artificially contaminated in food samples, results obtained were satisfactory and a detection limit of N x 10(0) cells per assay could be obtained.
Abstract: A 16S DNA targeted polymerase chain reaction (PCR) method specific for the detection of Salmonella isolates with various serotypes was developed The primers used for such a PCR method were 16SF1 and 16SIII 16SF1 is the reverse and complementary strand of 16SI which has been shown to be able to hybridize with Salmonella and Citrobacter spp 16III on the other hand, is able to hybridize with Klebsiella and Serratia spp in addition to Salmonella Although 16SF1 and 16SIII were not specific to Salmonella only, when they were used as PCR primers, only the Salmonella isolates could be specifically detected The interference from Citrobacter, Klebsiella and Serratia spp could be prevented None of the other non-Salmonella isolates including strains of the family of Enterobacteriaceae closely related to Salmonella would generate the false-positive reaction When this PCR system was used for the detection of Salmonella cells artificially contaminated in food samples, results obtained were satisfactory A detection limit of N× 100 cells per assay could be obtained
TL;DR: Multiple regression equations were obtained which described the contribution of some physiochemical and other structural properties of the compounds to their biological activity and showed that in food with a high protein or lipid content antilisterial activity was much lower than predicted, making the models unacceptable in such circumstances.
Abstract: The inhibition of a cocktail of 18 strains of Listeria monocytogenes by 24 mono-, di- and tri-substituted benzoic and cinnamic acids and 16 benzaldehydes was evaluated using the concentration (C) required to give a 50% growth inhibition under anaerobic conditions at 35 degree C and pH 6.2 as a measure of biological activity (BAV). Using the method of least squares, multiple regression equations were obtained which described the contribution of some physiochemical and other structural properties of the compounds to their biological activity. The equation that best described the activity of benzoic and cinnamic acids was [formula: see text] where K is a lipophilicity parameter determined by RP-HPLC and the effect of ionization is represented by pKa. Benzaldehydes behaved differently, their activity being best described by the equation. [formula: see text] where the activity is controlled by a steric parameter, the van der Waals volume (Vw), and an electronic-steric parameter for ortho substituents. Absence of a lipophilicity parameter indicates that partitioning into the cell membrane might not be required for antimicrobial activity. The models were tested in several food systems which showed that in food with a high protein or lipid content antilisterial activity was much lower than predicted, making the models unacceptable in such circumstances.
TL;DR: The B. cereus group strains were recognizable by fatty acid components not present in any of the other paperboard strains, 11-methyldodecanoic acid and trans-9-hexadecenoic acid, each contributing 7% or more to the total cellular fatty acids.
Abstract: Liquid packaging boards and blanks were examined for microbial contaminants. A total of 218 strains were identified and representatives of the most frequent species were characterized for their potential for food spoilage. Contaminants found were aerobic spore-forming bacteria, mostly Bacillus megaterium, B. licheniformis, B. cereus group, B. pumilus, Paenibacillus macerans, P. polymyxa, P. pabuli and B. flexus. Production of amylolytic, proteolytic, lipolytic and phospholipolytic enzymes was common. Approximately 50% of the B. cereus group strains were positive in the diarrhoeal enterotoxin immunoassay test or in the enterotoxin reversed passive latex agglutination test. Strains capable of growth at 6 degrees C were found among B. cereus group, P. pabuli, P. validus, B. megaterium and P. polymyxa. All b. licheniformis strains grew at 55 degrees C. The spores of B. licheniformis were most resistant to hydrogen peroxide. The B. cereus group strains were recognizable by fatty acid components not present in any of the other paperboard strains, 11-methyldodecanoic acid (13:0 iso) and trans-9-hexadecenoic acid (16:1 omega 7 trans), each contributing 7% or more to the total cellular fatty acids.
TL;DR: The HPLC method developed proved to be a precise tool to monitor the organic acid content of milk and can be used to follow the fermentation ability of starter cultures, providing information about the type of fermentation.
Abstract: The major function of lactic starter cultures in cheese making is to produce lactic and other organic acids from the carbohydrates present in milk. The activity of six starter cultures consisting of two Lactococcus lactis ssp. lactis, two Lactococcus lactis ssp. lactis biovar. diacetylactis and two Leuconostoc strains, was tested by monitoring the evolution of the organic acid composition of milk by a modified HPLC method. In addition, their performance as cheese starters was also tested. The HPLC method developed proved to be a precise tool to monitor the organic acid content. Thus, it can be used to follow the fermentation ability of starter cultures, providing information about the type of fermentation. The use of any of the six starters assayed is suggested for manufacturing Afuega'l Pitu cheese.
TL;DR: A pair of PCR primers specific for Salm.
Abstract: A rapid and sensitive method for detection of Salmonella typhi would help in preventing the spread of outbreaks and in clinical diagnosis. In order to develop unique PCR primers to detect Salm. typhi, ribosomal RNA genes from Salm. typhi (Rawlings) were cloned in pUC18. The resulting clone was confirmed by sequencing. The cloned DNA fragment contained the 5S, part of the 23S rRNA genes and the 5S-23S spacer region (EMBL/GenBank accession No. U04734).
It was expected that the 5S-23S spacer region is divergent unlike the highly conserved 23S+5S genes. This was confirmed by comparison with the rRNA gene sequences in the EMBL/GenBank database. A pair of PCR primers specific for Salm. typhi was obtained, based on this spacer region sequence. The specificity of this pair of primers was tested with 54 Salm. typhi strains (of 27 different phage types). All these Salm. typhi strains showed the positive 300 bp PCR product with this pair of primers. Six other Salmonella species as well as six other non-Salmonella bacteria were tested and none showed the 300 bp PCR product. The sensitivity of the detection level was 0·1 pg of pure Salm. typhi genomic DNA, or approximately 40 Salm. typhi cells in a spiked food sample. This pair of primers therefore has the potential for development into a diagnostic tool for the rapid diagnosis of typhoid fever.
TL;DR: The aqueous extract of thyme possesses a therapeutic potential which merits validation by clinical studies, and had a significant inhibitory effect on H. pylori, reducing both its growth and potent urease activity.
Abstract: Extracts of several plants were tested for inhibitory activity against Helicobacter pylori. Among these plants thyme (aqueous extract) and cinnamon (alcoholic extract) were the most effective. Since aqueous extract of thyme is easier to produce and consume, it was further investigated. Compared with several antibacterials, the thyme extract had a significant inhibitory effect on H. pylori, reducing both its growth and potent urease activity. From the results of this study, the aqueous extract of thyme possesses a therapeutic potential which merits validation by clinical studies.