Showing papers in "Letters in Applied Microbiology in 1992"
TL;DR: The described procedures provide almost complete 16S rDNA sequence data within a couple of days and facilitate systematic studies.
Abstract: The 16S rRNA gene from various bacterial cultures was amplified by the polymerase chain reaction without DNA purification, and sequenced directly by using a laser fluorescent DNA sequencer and Tth polymerase with a cycle sequencing protocol. The described procedures provide almost complete 16S rDNA sequence data within a couple of days and facilitate systematic studies.
375 citations
TL;DR: The results explain the possible mechanisms by which bacteriocins of LAB enter through the walls and outer membranes to destabilize the cytoplasmic membranes and kill cells of sensitive Gram‐positive and resistant, but injured, Gram‐negative and Gram‐ positive bacteria.
Abstract: Gram-negative and some Gram-positive bacteria that are resistant to bacteriocins of lactic acid bacteria (LAB) were subjected to sublethal stresses and treated with nisin and pediocin AcH. Both bacteriocins reduced the viability of cells surviving sublethal stresses. The results explain the possible mechanisms by which bacteriocins of LAB enter through the walls (or outer membranes) to destabilize the cytoplasmic (or inner) membranes and kill cells of sensitive Gram-positive and resistant, but injured, Gram-negative and Gram-positive bacteria.
212 citations
TL;DR: P pH adaptation not only occurs in enteric bacteria but also in this Gram‐positive organism, and Alterations in the cytoplasmic membrane could be responsible.
Abstract: Growth of Listeria monocytogenes at pH 5·0 did not increase growth of the organism at pH 7·0 after exposure to low pH (3·0, 3·5), compared with cells initially grown at pH 7·0. However, growth at pH 5·0 significantly increased the survival of cells at low pH as determined by plate counts compared with cells grown at neutral pH. Thus, pH adaptation not only occurs in enteric bacteria but also in this Gram-positive organism. Alterations in the cytoplasmic membrane could be responsible.
155 citations
TL;DR: A method was developed to obtain reproducible DNA fingerprints from Campylobacter by PCR‐based amplification, without the need to isolate total DNA, which resulted in different levels of discrimination between the strains.
Abstract: A method was developed to obtain reproducible DNA fingerprints from Campylobacter by PCR-based amplification, without the need to isolate total DNA. Randomly amplified polymorphic DNA (RAPD) profiles were generated with three randomly designed 10-mers, using each separately as an amplification primer. A range of C. jejuni serotypes could be typed by RAPD analysis. Depending on the primer, the analysis of RAPD profiles resulted in different levels of discrimination between the strains. Clear correlations were observed between results of RAPD analysis and serotyping. Two of the primers tested generated RAPD profiles which allowed discrimination of strains within given Penner and Lior serotypes.
149 citations
TL;DR: N‐terminal analysis of purified pediocin AcH produced a partial sequence of23 amino acids that matched perfectly with a segment of 23 amino acids in a 62 amino acid molecule generated from the 186 nucleotide sequence open reading frame in a Hind III fragment in pSMB74 encoding pap‐gene.
Abstract: N-terminal analysis of purified pediocin AcH produced a partial sequence of 23 amino acids This sequence matched perfectly with a segment of 23 amino acids in a 62 amino acid molecule generated from the 186 nucleotide sequence open reading frame in a Hind III fragment in pSMB74 encoding pap-gene (pediocin AcH production) It is suggested that the molecule is translated as inactive prepediocin AcH of 62 amino acids Then through enzymatic modifications the leader segment of 18 amino acids is removed from the NH2-terminal The remaining segment of 44 amino acids is active pediocin AcH of 4628 Mr
122 citations
TL;DR: In this article, the effect of acid shock on the heat resistance of Listeria monocytogenes was investigated and it was shown that acidification with HCl prior to final heating can enhance heat resistance.
Abstract: The effect of acid shock on the heat resistance of Listeria monocytogenes was investigated. After growth for 24 h at 30°C in tryptic soy broth containing 0.6% yeast extract, cell culture suspensions of L. monocytogenes were acidified with HCl or acetic acid over various time periods before being heated in whole milk to a temperature of 58°C. When cells were acid-shocked immediately with HCl for 1, 2 or 4 h, those acid-shocked for 1 h demonstrated the largest increase in thermotolerance as compared to control cells, when heated at 58°C in whole milk. In fact, cells acid-shocked for longer than 1 h with HCl demonstrated in some instances a decreased recovery as compared to control cells. Other types of acid-shock treatments included lowering the pH gradually either over a 4 h or a 24 h period. However, regardless of the type of acid-shock treatment, cells acid-shocked with HCl (but not acetic acid) prior to heating had significantly greater heat resistance as compared to control (non-acid-shocked) cells. It appears that acidification with HCl prior to final heating can enhance the heat resistance of L. monocytogenes.
119 citations
TL;DR: In an aquatic environment pathogenic bacteria which are capable of growth in warm-blooded hosts may be stressed by starvtion or by exposure to sub-optimal temperature, salinity or toxic chemicals, and enter a viable but non-growing state.
Abstract: In an aquatic environment pathogenic bacteria which are capable of growth in warm-blooded hosts may be stressed by starvtion or by exposure to sub-optimal temperature, salinity or toxic chemicals. Microbial cells may enter a viable but non-growing state, as a result of such sub-lethal stresses and as a strategy for survival, in a dormant form until environmental conditions change. The isolation of micro-organisms by growth on selective media has been universally applied for the detection of viable micro-organisms in water. The reliability of culture methods is of particular importance in testing for the presence of pathogenic micro-organisms and microbial indicators of faecal polution and in monitoring the release and survival of genetically modified micro-organisms in water
119 citations
TL;DR: Findings are important in the assessment of heat‐treatments required to ensure the safety with respect to non‐proteolytic Clostridium botulinum of processed (pasteurized) refrigerated foods for extended storage such as sous‐vide foods.
Abstract: Heating spores of non-proteolytic strains of Clostridium botulinum at 85°C, followed by enumeration of survivors on a highly nutrient medium indicated a 5 decimal kill in less than 2 min. The inclusion of lysozyme or egg yolk emulsion in the recovery medium substantially increased apparent spore heat-resistance, with as little as 0.1 μg lysozyme/ml sufficient to give an increase in the number of survivors. After heating at 85°C for 2 min between 0.1% and 1% of the spores of 11 strains (5 type B, 4 type E, 2 type F) formed colonies on medium containing 10 μg lysozyme/ml. Enumeration of survivors on a medium containing lysozyme showed that heating at 85°C for 5 min resulted in an estimated 2.6 decimal kill of spores of strain 17B (type B). These findings are important in the assessment of heat-treatments required to ensure the safety with respect to non-proteolytic Clostridium botulinum of processed (pasteurized) refrigerated foods for extended storage such as sous-vide foods.
108 citations
TL;DR: Glycerol was the least toxic of the three solutes studied, and L. monocytogenes appeared to tolerate glycerol and NaCl best when growing at 30 and 15°C, respectively, while for sucrose, temperature did not appear to influence growth of the organism.
Abstract: The ability of five strains of Listeria monocytogenes to initiate growth at five different temperatures in brain heart infusion (BHI) broth adjusted to various water activity (aw) values with either sodium chloride (NaCl), sucrose or glycerol was investigated. Glycerol was the least toxic of the three solutes studied, with three of five strains of L. monocytogenes capable of growing in BHI broth adjusted with glycerol to an aw value of 0.90 at 30 C, compared to aw minima of 0.93 and 0.92 in broth adjusted with sucrose and sodium chloride, respectively. The minimum aw value required for growth generally increased as the incubation temperature decreased. Listeria monocytogenes appeared to tolerate glycerol and NaCl best when growing at 30 and 15°C, respectively, while for sucrose, temperature did not appear to influence growth of the organism. Listeria monocytogenes is one of the few food-borne pathogens that can grow at an aw value below 0.93.
103 citations
TL;DR: Yeasts were isolated from spontaneous fermentations of olives in brines and Pichia membranae‐faciens and related species dominated the yeast flora and Killer activity was observed in approximately half of the isolates, and the wider spectra were displayed by strains of PichIA anomala.
Abstract: Yeasts were isolated from spontaneous fermentations of olives in brines. Ascomycetous species dominated the yeast flora (>90%) and among them Pichia membranae-faciens and related species. Some components of the olives were tested as substrates for growth. Killer activity was observed in approximately half of the isolates, and the wider spectra were displayed by strains of Pichia anomala.
86 citations
TL;DR: Survival characteristics were similar for two strains of Escherichia coli O157: H7 and a typical indicator strain of E. coli in a portable ground water source.
Abstract: Survival characteristics were similar for two strains of Escherichia coli O157: H7 and a typical indicator strain of E. coli in a portable ground water source. Die-off was more rapid at 20°C than at 5°C. There was no significant difference among the rates of survival for the strains examined.
TL;DR: Extracts of 54 plant species were tested for ability to inhibit bacteria and fungi, especially Candida albicans, Trichophyton rubrum and Streptococcus mutans, and Lindera benzoin, a common temperate zone shrub, showed evidence of selective toxicity.
Abstract: Extracts of 54 plant species were tested for ability to inhibit bacteria and fungi, especially Candida albicans, Trichophyton rubrum and Streptococcus mutans. The latter three species cause common dermal, mucosal, or oral infections in humans that are difficult to control effectively. Fifteen plant extracts produced detectable antimicrobial activity. The most active included Celastrus scandens root bark, Juglans nigra fruit husks, Kalmia latifolia leaves, Pelargonium xhortorum leaves, and Rhus glabra root bark. Five plant species inhibited Strep. mutans, four inhibited T. rubrum, and two inhibited C. albicans. Lindera benzoin, a common temperate zone shrub, showed evidence of selective toxicity. Extract of L. benzoin bark strongly inhibited C. albicans and T. rubrum, but did not affect any of the other microorganisms tested.
TL;DR: The medium, membrane‐Lactose Glucuronide Agar (m‐LGA), employs a chromogenic substrate for the detection of β‐glucuronidase activity and sodium pyruvate to enhance recovery of chlorine‐stressed coliforms.
Abstract: A medium for the single membrane enumeration of Escherichia coli and coliforms from potable water was developed by the modification of the standard UK membrane filtration medium. The medium, membrane-Lactose Glucuronide Agar (m- LGA), employs a chromogenic substrate for the detection of β-glucuronidase activity and sodium pyruvate to enhance recovery of chlorine-stressed coliforms. Escherichia coli identification was significantly improved on m-LGA with 98.6% of presumptive isolates confirming. Recovery of coliforms from drinking water samples was also significantly improved
TL;DR: The polymerase chain reaction (PCR) has been used to detect Listeria monocytogenes in whole milk at a level of 0.1 cfu per 30 ml, extending the relevance of PCR within food and environmental microbiology.
Abstract: The polymerase chain reaction (PCR) has been used to detect Listeria monocytogenes in whole milk at a level of 0.1 cfu per 30 ml. This high degree of sensitivity has been achieved following enzymatic digestion, polysulphonone membrane filtration and amplification of a nucleotide sequence within the promoter region of hlyA. Key elements of the procedure are the absence of enrichment culture and a complete solubilization of the membrane filter, ensuring total nucleic acid recovery. The simplicity of the protocol coupled with high sample volumes and exquisite sensitivity extends the relevance of PCR within food and environmental microbiology.
TL;DR: A spore‐forming bacterium isolated from the soil of Japan was assigned to Bacillus thuringiensis serovar japonensis (flagellar antigen 23) and exhibited high larvicidal activity against coleopterous scarabaeid beetles, the cupreous chafer, and the Japanese beetle.
Abstract: A spore-forming bacterium isolated from the soil of Japan was assigned to Bacillus thuringiensis serovar japonensis (flagellar antigen 23). Parasporal inclusions of this isolate were spherical to ovoid in shape and exhibited high larvicidal activity against coleopterous scarabaeid beetles, the cupreous chafer. Anomala cuprea, the soybean beetle, Anomala rufocuprea, and the Japanese beetle. Popillia japonica. No toxicity was shown by this isolate against larvae of Lepidoptera, Diptera, and Orthoptera, and adults of a chrysomelid coleopteran.
TL;DR: An extremely halophilic archaeobacterium, strain ORE, was isolated from traditionally fermented Thai fish sauce, which has a concentration of 4·4–5·1 M NaCl, and produced salt‐stable extracellular proteases which are likely to be important in the fermentation process.
Abstract: An extremely halophilic archaeobacterium (halobacterium), strain ORE, was isolated from traditionally fermented Thai fish sauce (nam pla) which has a concentration of 4.4−5.1 M NaCl. Polar liquid analysis and DBA hybridization revealed that it was a representative of the species Halobacterium salinarium. In common with many other strains of Halobacterium salinarium this organism produces salt-stable extracellular proteases which are likely to be important in the fermentation process
TL;DR: A modified direct detection system was developed to identify the antimicrobial peptide, pediocin AcH in SDS‐PAGE by a zone of inhibition of bacterial growth surrounding the stained protein band.
Abstract: A modified direct detection system was developed to identify the antimicrobial peptide, pediocin AcH in SDS-PAGE. The gel containing pediocin AcH was stained for 30 min, destained for 1.5 h, and then overlaid with indicator bacteria. The pediocin AcH band was identified by a zone of inhibition of bacterial growth surrounding the stained protein band.
TL;DR: The advantages of the protocol used in the present study are that the cells can be washed with water instead of complex buffer, and the DNA used can be prepared by the alkaline method of Birnboim & Doly without purification by ultracentrifugation.
Abstract: Conditions were optimized for electrotransformation of Xanthomonas campestris pv. campestris by the replicative form (RF) DNA of filamentous phase phi Lf. Early logarithmic cells were washed exhaustively with deionized water and subjected to a pulse at a field strength of 12.5 kV/cm with a 25 microF capacitor and a 400 omega resistor. An efficiency of 5.1 x 10(7) pfu per microgram RF DNA was obtained. Under the same conditions, the broad host range plasmid pLAFR1 (21.6 kb) transformed X. campestris strains at efficiencies around 10(5) pfu per microgram DNA prepared from XcP20H. The advantages of the protocol used in the present study are that the cells can be washed with water instead of complex buffer, and the DNA used can be prepared by the alkaline method of Birnboim & Doly without purification by ultracentrifugation.
TL;DR: There are significant differences between lactic acid bacteria in their resistance to hopderived constituents of beer and resistance to such compounds is a stable character, both phenotypically and genetically, associated only with lactic acids capable of spoiling beer.
Abstract: There are significant differences between lactic acid bacteria (Lactobacillus spp., Pediococcus spp., Leuconostoc spp., Lactococcus spp.) in their resistance to hopderived constituents of beer. Resistance to such compounds is a stable character, both phenotypically and genetically, associated only with lactic acid bacteria capable of spoiling beer. Such bacteria can be induced to grow in beer if they are first grown in the presence of a sub-inhibitory concentration of isohumulone.
TL;DR: Nisin used at a level of 5 mg/1 resulted in a significant increase in refrigerated shelf life of pasteurized liquid whole egg from between 6–11 d to 17–20 d and protected the liquid egg from growth of Bacillus cereus.
Abstract: Nisin used at a level of 5 mg/1 resulted in a significant increase in refrigerated shelf life of pasteurized liquid whole egg from between 6-11 d to 17-20 d. In the first of two trials, nisin also protected the liquid egg from growth of Bacillus cereus. Bacillus cereus was not presented in the egg in the second trial. Effective residual levels of nisin were detected in the liquid egg post-pasteurization.
TL;DR: Salmonella detection was enhanced by reducing the number and types of competing bacteria present and concentrating the number of Salmonella in the final assay.
Abstract: A rapid method for detection of Salmonella in milk powder is described. The technique involves immunomagnetic separation of Salmonella from pre-enrichment broths using new commercially-available materials, and detection using conductance measurements. Salmonella detection was enhanced by reducing the number and types of competing bacteria present and concentrating the number of Salmonella in the final assay. After a 6 h pre-incubation period Salmonella enteritidis, from an initial inoculum size of 20 cells/ml, were detected in 7.5 h by conductance.
TL;DR: Fifty‐one strains of staphylococci isolated from French dry sausages were mainly identified with StAPHylococcus carnosus, S. xylosus and S. saprophyticus, and the API Staphylitis identification system proved to be reliable for these species.
Abstract: Fifty-one strains of staphylococci isolated from French dry sausages were mainly identified with Staphylococcus carnosus, S. xylosus, S. warneri and S. saprophyticus. The API Staphylococcus identification system proved to be reliable for S. xylosus and S. carnosus. The identification of S. warneri and S. saprophyticus was performed by DNA-DNA hybridization. These species are better identified by taking into account not only the API Staphylococcus system but also the following characters: novobiocin and lysozyme susceptibilities, production of D-lactate. hydrolysis of tri-olein.
TL;DR: An impedimetric evaluation of disinfectant efficacy has shown that biofilms of Staphylococcus aureus, Escherichia coli, Salmonella enteritidis and Listeria mono-cytogenes attached to polyvinyl chloride (PVC), Teflon, Plexiglass, wood, rubber and stainless steel are more resistant than the same bacteria in suspension as discussed by the authors.
Abstract: An impedimetric evaluation of disinfectant efficacy has shown that biofilms of Staphylococcus aureus, Escherichia coli, Salmonella enteritidis and Listeria mono-cytogenes attached to polyvinyl chloride (PVC), Teflon, Plexiglass, wood, rubber and stainless steel are more resistant than the same bacteria in suspension. Based on the activity against the test-organisms after 1, 3 and 5 min with exposures to 0.5, 1 and 2% of each disinfectant, the resistance towards disinfection was related to the type of hard-surface to which biofilms were attached.
TL;DR: The results demonstrate a means to introduce cloned genes into these organisms and were stable in each organism in the absence of antibiotic selection.
Abstract: Electroporation methods for introduction of plasmid DNA into the ruminal bacteria Butyrivibrio fibrisolvens and Streptococcus bovis were developed. Electroporation of the strictly anaerobic B. fibrisolvens was carried out in an anaerobic glovebox with a buffer of 10% (v/v) glycerol and 1 mM MgCl2 in distilled water. Streptococcus bovis electroporation could be carried out aerobically with a buffer of 10% (v/v) glycerol in distilled water. The Escherichia coli/Bacillus subtilis shuttle vector pBS42 could be transformed into B. fibrisolvens strain H17c, selecting for chloramphenicol resistance. The Streptococcus sanguis/E. coli shuttle vector pVA838 could replicate and express erythromycin resistance in Strep. bovis. Both vectors were stable in each organism in the absence of antibiotic selection. While the efficiency was low (<102/μg DNA), the results demonstrate a means to introduce cloned genes into these organisms.
TL;DR: It seems that the low incidence of listeriosis from these products is related to the low concentration and virulence of L. monocytogenes present.
Abstract: Listeria monocytogenes was isolated and enumerated in Italian fresh ground beef, fresh pork meat and industrial sausages. All the samples contained less than 2000 L. monocytogenes/g of meat. The main serotype isolated was 1/2c (56.9%). Other serotypes isolated included 1/2a, 1/2b, 3c, 4b and 4c. A prevalence of less virulent serotypes over more virulent was thus noted. It seems that the low incidence of listeriosis from these products is related to the low concentration and virulence of L. monocytogenes present.
TL;DR: In this paper, a special heat sealer and anaerocult-A sachets were used to remove oxygen from anaerobic jars and the environment inside the bags remained oxygen-free for at least 3 years.
Abstract: Nylon-aluminium-polyethylene laminated, sealable bags provided a more economical and flexible method of transportation, incubation and storage than anaerobic jars. The bags were used with a special heat sealer and ‘Anaerocult-A’ sachets to remove oxygen. The environment inside the bags remained oxygen-free for at least 3 years.
TL;DR: Utilization of organophosphonates as the sole source of phosphorus, carbon or nitrogen by a soil isolate of Penicillium citrinum was studied and it was found that the mould did not metabolize any of the phosphonates tested, when they served as the only carbon ornitrogen source.
Abstract: Utilization of organophosphonates as the sole source of phosphorus, carbon or nitrogen by a soil isolate of Penicillium citrinum was studied. Penicillium citrinum was found to utilize 2-aminoethylphosphonic and 2-oxoalkylphosphonic acids as the sole phosphorus source whereas 1-hydroxyalkylphosphonates as well as 1-aminoalkylphosphonates and their dipeptides did not support the growth of the fungus. The mould did not metabolize any of the phosphonates tested, when they served as the sole carbon or nitrogen source.
Penicillium citrinum is perhaps the first mould strain isolated from soil, shown to be capable of organophosphonate degradation.
TL;DR: In this article, a nozzle was used to generate totally enclosed thin liquid films, known as "liquid bells", from suspensions of Escherichia coli in water and humic acid solutions.
Abstract: A nozzle was used to generate freely supported totally enclosed thin liquid films, known as ‘liquid bells’, from suspensions of Escherichia coli in water and humic acid solutions. Disinfection was achieved by continuously recirculating the liquids to the nozzle and irradiating the bells generated with ultraviolet light. The absorptivities at 254 nm of the liquids treated ranged from 0.18 to 4.0 and after 30 min treatment E. coli viability, expressed in terms of surviving fractions, was reduced to 1.88 times 10-5 and 1.84 times 10-4 respectively.
TL;DR: The results indicate that the germination system in spores of non‐proteolytic Cl. botulinum was destroyed by heating, that lysozyme could replace this germinationSystem, and that treatments that increased the permeability of the spore coat could increase the proportion of heated spores that germinated on medium containing lyso enzyme.
Abstract: Heat treatment of spores of non-proteolytic Clostridium botulinum at 85°C for 120 min followed by enumeration of survivors on a medium containing lysozyme resulted in a 4.1 and 4.8 decimal reduction in numbers of spores of strains 17B (type B) and Beluga (type E), respectively. Only a small proportion of heated spores formed colonies on medium containing lysozyme; this proportion could be increased by treatments designed to increase the permeability of heated spores. The results indicate that the germination system in spores of non-proteolytic Cl. botulinum was destroyed by heating, that lysozyme could replace this germination system, and that treatments that increased the permeability of the spore coat could increase the proportion of heated spores that germinated on medium containing lysozyme. These results are important in relation to the assessment of heat-treatments required to reduce the risk of survival and growth of non-proteolytic Clostridium botulinum in processed (pasteurized) refrigerated foods for extended storage.
TL;DR: The lysostaphin structural gene was cloned in Bacillus subtilis DSM402 and in Lactobacillus casei 102S and produced lysis of growing and heat inactivated staphylococci.
Abstract: The lysostaphin structural gene was cloned in Bacillus subtilis DSM402 and in Lactobacillus casei 102S. The gene was expressed in both organisms and active lysostaphin was released into the medium. Lysostaphin produced by these organisms induced lysis of growing and heat inactivated staphylococci. Expression in a protective starter organism is a prerequisite to produce lysostaphin in situ in fermenting foods and hence, to reduce the hygienical risk of staphylococcal food poisoning.