Showing papers in "Letters in Applied Microbiology in 1998"
TL;DR: Gram‐positive bacteria were more sensitive to inhibition by plant essential oils than the Gram‐negative bacteria, and Staphylococcus aureus was extremely sensitive to the oil of nutmeg.
Abstract: The antimicrobial properties of 21 plant essential oils and two essences were investigated against five important food-borne pathogens, Campylobacter jejuni, Salmonella enteritidis, Escherichia coli, Staphylococcus aureus and Listeria monocytogenes. The oils of bay, cinnamon, clove and thyme were the most inhibitory, each having a bacteriostatic concentration of 0.075% or less against all five pathogens. In general, Gram-positive bacteria were more sensitive to inhibition by plant essential oils than the Gram-negative bacteria. Campylobacter jejuni was the most resistant of the bacteria investigated to plant essential oils, with only the oils of bay and thyme having a bacteriocidal concentration of less than 1%. At 35 degrees C, L. monocytogenes was extremely sensitive to the oil of nutmeg. A concentration of less than 0.01% was bacteriostatic and 0.05% was bacteriocidal, but when the temperature was reduced to 4 degrees, the bacteriostatic concentration was increased to 0.5% and the bacteriocidal concentration to greater than 1%.
1,058 citations
TL;DR: Tea tree oil stimulates autolysis in exponential and stationary phase cells of Escherichia coli and it was revealed that a subpopulation of stationaryphase cells demonstrated increased tolerance to TTO‐bactericidal effects.
Abstract: Tea tree oil (TTO) stimulates autolysis in exponential and stationary phase cells of Escherichia coli. Electron micrographs of cells grown in the presence of TTO showed the loss of electron dense material, coagulation of cell cytoplasm and formation of extracellular blebs. Stationary phase cells demonstrated less TTO-stimulated autolysis and also had greater tolerance to TTO-induced cell death, compared to exponentially grown cells. It was also revealed that a subpopulation of stationary phase cells demonstrated increased tolerance to TTO-bactericidal effects.
244 citations
TL;DR: Concentrations of tea tree oil which inhibit or decrease growth of Escherichia coli also inhibit glucose‐dependent respiration and stimulate the leakage of intracellular K+.
Abstract: Concentrations of tea tree oil (TTO) which inhibit or decrease growth of Escherichia coli also inhibit glucose-dependent respiration and stimulate the leakage of intracellular K+ Stationary phase cells are more tolerant to these TTO effects than exponential phase cells
229 citations
TL;DR: It is proposed that sorbic acid acts as a membrane‐active substance rather than as a weak‐acid preservative, and shows similar inhibition to other six‐carbon acids, alcohols and aldehydes.
Abstract: Weak-acid preservatives are widely used to maintain microbial stability in foods and beverages. Classical weak-acid theory proposes that undissociated acid molecules pass through the plasma membrane, dissociate in the neutral pH of the cytoplasm, release protons and inhibit growth through acidification of the cytoplasm. Inhibitory concentrations of sorbic acid are shown to liberate fewer protons than other weak-acid preservatives. Sorbic acid shows similar inhibition to other six-carbon acids, alcohols and aldehydes, the latter being unable to act as weak acids. A survey of 22 yeasts showed high correlation between sorbate resistance and ethanol tolerance. Inhibition by short-chain acids or alcohols showed strong correlation with lipophilicity. It is proposed that sorbic acid acts as a membrane-active substance rather than as a weak-acid preservative.
211 citations
TL;DR: The results of the current study indicate the need for further investigations to understand the antimicrobial effects of basil oils in the presence of other food ingredients and preservation parameters.
Abstract: Essential oils extracted by hydrodistillation from five different varieties of Ocimum basilicum L. plants (Anise, Bush, Cinnamon, Dark Opal and a commercial sample of dried basil) were examined for antimicrobial activity against a wide range of foodborne Gram-positive and -negative bacteria, yeasts and moulds by an agar well diffusion method. All five essential oils of basil showed antimicrobial activity against most of the organisms tested with the exception of Flavimonas oryzihabitans and Pseudomonas species. The inhibitory effect of Anise oil, in comparison with mixtures of the predominant components of pure linalool and methyl chavicol, against the acid-tolerant organisms, Lactobacillus curvatus and Saccharomyces cerevisiae, was examined in broth by an indirect impedance method. Synergistic effects between Anise oil, low pH (pH 4.2) and salt (5% NaCl) were determined. The antimicrobial effect of Anise oil was also assessed in a tomato juice medium by direct viable count, showing that the growth of Lact. curvatus and S. cerevisiae was completely inhibited by 0.1% and 1% Anise oil, respectively. The results of the current study indicate the need for further investigations to understand the antimicrobial effects of basil oils in the presence of other food ingredients and preservation parameters.
172 citations
TL;DR: Results indicate that the most effective harvesting method is to adjust pH to 11 after 2 weeks of incubation, and an optimal growth stage for the recovery of the green alga Botryococcus braunii growing in batch cultures is found.
Abstract: Flocculating activity was determined to evaluate the effective harvesting method and an optimal growth stage for the recovery of the green alga Botryococcus braunii growing in batch cultures. Flocculating activity was highest at 2 weeks of incubation, regardless of harvesting methods. The degree of flocculation was different with harvesting methods and growth stages. A high pH value (pH 11) was more effective for flocculation than treatment with aluminium sulphate or a microbial flocculant, Pestan, until the third week of incubation. The lipid content of the algae on a dry weight basis was unaffected by harvesting methods. These results indicate that the most effective harvesting method is to adjust pH to 11 after 2 weeks of incubation.
167 citations
TL;DR: Lactobacillus strains from the caecum showed better tolerance to acid than those from the ileum and could survive at pH 1.0 for up to 2 h of incubation; growth was moderate at pH 2.0 and good at pH 3.0.
Abstract: Twelve Lactobacillus strains isolated from chicken intestine were used to investigate acid and bile tolerance in vitro. Ten out of the 12 strains were slightly affected by 0.3% bile salts, showing a delay of growth (d) of 0.6-37.2 min compared with growth in control cultures. Two strains were not affected by the bile salts. Of the 12 strains, seven could be arbitrarily classified as resistant (d < 15 min) and five as tolerant (15 min < d < or = 40 min). Lactobacillus strains from the caecum showed better tolerance to acid than those from the ileum. Generally, the survival of the ileal strains was very low at pH 1.0 and 2.0, and moderate at pH 3.0. In contrast, caecal Lactobacillus strains could survive at pH 1.0 for up to 2 h of incubation; growth was moderate at pH 2.0 and good at pH 3.0 and 4.0.
166 citations
TL;DR: A PCR‐based test was developed to differentiate Escherichia coli from other Gram‐negative bacteria and was found to be highly specific for E. coli.
Abstract: A PCR-based test was developed to differentiate Escherichia coli from other Gram-negative bacteria. The assay employed primers derived from the nucleotide sequences flanking the gene encoding the universal stress protein (uspA) and was found to be highly specific for E. coli. An 884 base pair (bp) specific product was amplified from all of the E. coli tested (n = 45), whereas no amplification was associated with non-E. coli Gram-negative bacteria (n = 11).
159 citations
TL;DR: This appears to be the first example of cross-species induction and enhancement of antimicrobial activity in marine bacteria and has important implications for the design of antibiotic screening assays and for an understanding of microbial competition in the environment.
Abstract: Antibiotic producing marine bacteria isolated from surfaces of the marine alga Fucus vesiculosus and the nudibranch Archidoris pseudoargus were exposed to live cells of Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli and heat-killed cells of Staph. aureus. Twelve out of the 16 marine strains tested showed enhanced antimicrobial activity towards Staph. aureus, E. coli and Ps. aeruginosa following this exposure. Three out of seven strains tested showed enhanced antimicrobial activity when exposed to Ps. aeruginosa and three out of seven strains showed enhanced antimicrobial activity when exposed to E. coli. These results suggest that production of antimicrobial compounds by marine bacteria can be induced by the presence of terrestrial bacteria. This appears to be the first example of cross-species induction and enhancement of antimicrobial activity in marine bacteria and has important implications for the design of antibiotic screening assays and for an understanding of microbial competition in the environment.
143 citations
TL;DR: It is shown that pulsed light emissions can significantly reduce populations of E. coli 0157:H7 and L. monocytogenes on exposed surfaces with exposure times which are 4–6 orders of magnitude lower than those required using continuous u.v. light sources.
Abstract: The effects of high intensity light emissions, produced by a novel pulsed power energization technique (PPET), on the survival of bacterial populations of verocytotoxigenic Escherichia coli (serotype 0157:H7) and Listeria monocytogenes (serotype 4b) were investigated. Using this PPET approach, many megawatts (MW) of peak electrical power were dissipated in the light source in an extremely short energization time (about 1 μs). The light source was subjected to electric field levels greater than could be achieved under conventional continuous operation, which led to a greater production of the shorter bacteriocidal wavelengths of light. In the exposure experiments, pre-determined bacterial populations were spread onto the surface of Trypone Soya Yeast Extract Agar and were then treated to a series of light pulses (spectral range of 200–530 nm) with an exposure time ranging from 1 to 512 μs. While results showed that as few as 64 light pulses of 1 μs duration were required to reduce E. coli 0157:H7 populations by 99·9% and Listeria populations by 99%, the greater the number of light pulses the larger the reduction in cell numbers (P < 0·01). Cell populations of E. coli 0157:H7 and Listeria were reduced by as much as 6 and 7 log10 orders at the upper exposure level of 512 μs, respectively. Survival data revealed that E. coli 0157:H7 was less resistant to the lethal effects of radiation (P < 0·01). These studies have shown that pulsed light emissions can significantly reduce populations of E. coli 0157:H7 and L. monocytogenes on exposed surfaces with exposure times which are 4–6 orders of magnitude lower than those required using continuous u.v. light sources.
129 citations
TL;DR: Comparisons between proteolytic activities derived from this new strain (S.K 1–02) and commercial proteases indicated that S.K1–02 could be a useful biotechnological tool in valorization of keratin‐containing wastes, or in the depilation process in the leather industry.
Abstract: A Streptomyces sp. producing a high keratinolytic activity when cultured on feather meal medium was isolated from a naturally degraded feather. Maximal keratin degradation using supernatant fluid obtained from batch culture of this organism was observed at 70 degrees C and pH 10. Keratinolytic activity was only partially inhibited by EDTA or PMSF, suggesting that the overall keratinolytic activity was supported by different proteases. Comparisons between proteolytic activities derived from this new strain (S.K1-02) and commercial proteases indicated that S.K1-02 could be a useful biotechnological tool in valorization of keratin-containing wastes, or in the depilation process in the leather industry.
TL;DR: Oxygen, H2O2 and chiefly CO2 plasmas are clearly shown to be much more efficient in destroying Bacillus subtilis spores than pure argon plasma.
Abstract: The destruction of Bacillus spores in oxygen-based plasmas sustained in the millitorr pressure range has been studied as functions of various biological and plasma parameters, namely Bacillus species, surface concentration of spores, treatment temperature, and gas composition. In an oxygen plasma, Bacillus stearothermophilus appears less plasma-resistant than the other spores tested. Oxygen, H2O2 and chiefly CO2 plasmas are clearly shown to be much more efficient in destroying Bacillus subtilis spores than pure argon plasma. The bacterial surface concentration on the spore carriers and the treatment temperature also lead to significant variations in the destruction efficiency of spores when using CO2 plasma.
TL;DR: Methylobacterium sp.
Abstract: Methylobacterium sp. ZP24, isolated from a local pond, is able to grow in a medium containing 12 g l-1 lactose as a sole source of carbon, giving 5.25 g l-1 biomass yield and poly-3-hydroxybutyrate (PHB) up to 59% of its dry weight in 40 h. The isolate was also able to utilize cheese whey and produce 1.1 g l-1 PHB. Addition of ammonium sulphate increased the production of PHB from whey 2.5-fold. The potential of Methylobacterium sp. ZP24 in PHB production from cheese whey is discussed.
TL;DR: The small subunits ribosomal RNA (rRNA) spacer region from both eukaryotes and eubacteria could be readily amplified with DNA from different soils generating different amplification patterns.
Abstract: A rapid DNA extraction method utilizing a bead-beating machine is described. High molecular weight DNA could be extracted from up to 24 samples in less than 2 h. The DNA was suitable for direct use in the polymerase chain reaction (PCR). Both prokaryotic and eukaryotic cells were successfully lysed by the method, established using primers specific for these groups. The small subunits ribosomal RNA (rRNA) spacer region from both eukaryotes and eubacteria could be readily amplified with DNA from different soils generating different amplification patterns.
TL;DR: Although a great diversity of wild strains was observed, a sequential substitution of S. cerevisiae strains during the different phases of fermentation was detected, the most frequent strains were encountered in both years, and the dynamic populations were not influenced by climatic conditions.
Abstract: An ecological study of Saccharomyces cerevisiae strains in spontaneous alcoholic fermentation has been conducted in the same winery for two consecutive years (1994 and 1995). Yeast cells were identified and characterized using mitochondrial DNA restriction analysis. Although a great diversity of wild strains was observed, a sequential substitution of S. cerevisiae strains during the different phases of fermentation was detected. Furthermore, the most frequent strains were encountered in both years, and the dynamic populations were not influenced by climatic conditions. Finally, the RsaI restriction enzyme produced a species-specific pattern which allowed the identification of all the isolates as S. cerevisiae.
TL;DR: The rapidity and reliability of the PCR procedure established suggests that the method may be profitably applied in winery laboratories for quality control.
Abstract: Rapid identification and detection of Oenococcus oeni was achieved by species-specific PCR. Two primers flanking a 1025 bp region of the O. oeni gene encoding the malolactic enzyme were designed. The expected DNA amplificate was obtained only when purified DNA from O. oeni was used. The identity of PCR product was confirmed by nested PCR and restriction analysis. Within 8 h, 10 3 cfu ml -1 of oenococci were detected in fermenting grape must containing 10 7 yeast cells, whereas the detection limit in wine was 10 4 cfu ml -1 . The rapidity and reliability of the PCR procedure established suggests that the method may be profitably applied in winery laboratories for quality control.
TL;DR: The speed of assay, ease of use and high specificity and sensitivity of the BAX™ system for the detection of food‐borne Salmonella make it an attractive method for routine food microbiology laboratories.
Abstract: The BAX system for screening Salmonella is one of the first commercial PCR-based systems for the detection of food-borne pathogens. It is able to give a confirmed result within 28 h. There was 98.6% and 95.8% agreement between the BAX system and conventional cultural analysis for the detection of Salmonella in artificially inoculated and uninoculated food samples, respectively. In both cases, the BAX system generated more positive detections than cultural analysis. The speed of assay, case of use and high specificity and sensitivity of the BAX system for the detection of food-borne Salmonella make it an attractive method for routine food microbiology laboratories.
TL;DR: Four micro‐organism‐drug combinations were evaluated for β‐lactamase activity but its absence suggested that cell wall impermeability was responsible for cephalosporin resistance among bifidobacteria.
Abstract: Sixteen Bifidobacterium isolates from the human gastrointestinal tract were assayed for susceptibility to 44 antibiotics by soft agar overlay disc diffusion on TPY agar. Five isolates (3/7 B. bifidum and 2/3 B. breve) exhibited atypical antibiotic susceptibility profiles. Poor growth in the agar overlay accounted for susceptibility of B. bifidum but not B. breve isolates. All other isolates were resistant to cefoxitin (30 micrograms), aztreonam (30 micrograms), vancomycin (30 micrograms), amikacin (30 micrograms), gentamicin (10 micrograms), kanamycin (30 micrograms), streptomycin (10 micrograms), fusidic acid (10 micrograms), trimethoprim (5 micrograms), norfloxacin (10 micrograms), nalidixic acid (30 micrograms), metronidazole (5 micrograms), polymyxin B (300 micrograms) and colistin sulphate (10 micrograms), and they were susceptible to the six penicillins studied, cephalothin (30 micrograms), cefuroxime (30 micrograms), cefaclor (30 micrograms), ceftizoxime (30 micrograms), cefotaxime (30 micrograms), bacitracin (10 micrograms), chloramphenicol (30 micrograms), erythromycin (15 micrograms), clindamycin (2 micrograms), rifampicin (5 micrograms) and nitrofurantoin (300 micrograms). In addition, they varied in their susceptibility to cephradine (30 micrograms), cephazolin (30 micrograms), cefoperazone (75 micrograms), ceftriaxone (30 micrograms), ofloxacin (5 micrograms) and furazolidone (15 micrograms). They were resistant, or only marginally moderately susceptible, to ceftazidime (30 micrograms), netilmicin (10 micrograms), sulphamethoxazole (100 micrograms), cotrimoxazole (25 micrograms) and ciprofloxacin (5 micrograms), and susceptible or marginally moderately susceptible to tetracycline (30 micrograms). All B. bifidum isolates were susceptible to cefixime (5 micrograms). Four microorganism-drug combinations were evaluated for beta-lactamase activity but its absence suggested that cell wall impermeability was responsible for cephalosporin resistance among bifidobacteria. The antibiotic susceptibility of B. animalis 25527T was similar to that of the human isolates.
TL;DR: Gentamicin was the most active antimicrobial agent, and coagulase‐negative species were most common, and the most frequently isolated species was Staph.
Abstract: Samples were collected from 148 adult cats, processed for isolation of Staphylococcus species and tested for susceptibility to penicillin G, gentamicin, oxacillin, amoxycillin, ampicillin, cephalexin and rifampin. Methicillin resistance was also determined. Ninety-eight isolates were obtained (66% of samples). Coagulase-negative species were most common, and the most frequently isolated species (37 samples) was Staph. felis. Other coagulase-negative species, such as Staph. simulans, Staph. epidermidis and Staph. saprophyticus were also isolated. Coagulase-positive species were obtained from 40 cats; the most frequent was Staph. intermedius (26 samples), followed by Staph. aureus (14 samples). Resistance to antibiotics was frequently observed, with 58.2% of the isolates showing resistance to at least one drug. Resistance to Penicillin G was observed in 49 of the 98 isolates (50%), 22 samples were resistant to oxacillin (22.4%) and 12 to rifampin (12.2%). Resistance to amoxycillin and ampicillin was very similar to that observed to Penicillin G. Gentamicin was the most active antimicrobial agent. Three MRSA (methicillin-resistant Staphylococcus aureus) were isolated, which represents 21.4% of the isolates of that species. Nineteen MRS (methicillin resistant staphylococci) were also observed, distributed among Staph. intermedius (eight), Staph. simulans (six) and Staph. felis (five) isolates. The role of these micro-organisms on the skin of cats is discussed.
TL;DR: The results demonstrate that E. coli O157:H7 strains are susceptible to the antimicrobial effects of bLF and its peptides.
Abstract: The antimicrobial activities of bovine lactoferrin (bLF), its pepsin hydrolysate (bLFH) and the active peptide lactoferricin B (LFcinB) against four clinical isolates of enterohaemorrhagic Escherichia coli O157:H7 were studied. The MICs against these isolates were 3 mg ml-1 for bLF, 0.1-0.2 mg ml-1 for bLFH and 8-10 micrograms ml-1 for LFcinB in 1% Bactopeptone broth. LFcinB killed these bacteria within 3 h at concentrations above 10 micrograms ml-1. Transmission electron microscopy findings suggested that LFcinB acts on the bacterial surface and affects cytoplasmic contents. LFcinB was shown to influence the levels of verotoxins in the culture supernatant fluid of an E. coli O157:H7 strain. These results demonstrate that E. coli O157:H7 strains are susceptible to the antimicrobial effects of bLF and its peptides.
TL;DR: The efficacy of high‐temperature, short‐time (HTST) pasteurization when low numbers of Mycobacterium paratuberculosis are present in milk was investigated and IS900‐based PCR confirmed that these acid‐fast survivors were Myco.
Abstract: The efficacy of high-temperature, short-time (HTST) pasteurization (72 degrees C/15 s) when low numbers (< or = 10(3) cfu ml-1) of Mycobacterium paratuberculosis are present in milk was investigated. Raw cows' milk spiked with Myco. paratuberculosis (10(3) cfu ml-1, 10(2) cfu ml-1, 10 cfu ml-1, and 10 cfu 50 ml-1) was subjected to HTST pasteurization using laboratory pasteurizing units. Ten bovine strains of Myco. paratuberculosis were tested in triplicate. Culture in BACTEC Middlebrook 12B radiometric medium detected acid-fast survivors in 14.8% and 10% of HTST-pasteurized milk samples at the 10(3) and 10(2) cfu ml-1 inoculum levels, respectively, whereas conventional culture on Herrold's egg yolk medium containing mycobactin J detected acid-fast survivors in only 3.7% and 6.7% of the same milk samples. IS900-based PCR confirmed that these acid-fast survivors were Myco. paratuberculosis. No viable Myco. paratuberculosis were isolated from HTST-pasteurized milk initially containing either 10 cfu ml-1 or 10 cfu 50 ml-1.
TL;DR: This is the first demonstration of tuberculosis in non‐mummified archaeological tissue other than bone; the presence of mycobacterial mycolic acids in the sample supports this conclusion.
Abstract: Mycobacterium tuberculosis complex DNA was isolated and identified in calcified pleura from remains 1400 years old, with the polymerase chain reaction. This is the first demonstration of tuberculosis in non-mummified archaeological tissue other than bone; the presence of mycobacterial mycolic acids in the sample supports this conclusion. The study of ancient DNA from microbial pathogens is of interest as it enables verification of traditional diagnoses, may answer long-standing questions in the history of disease, and provides ancient DNA sequences that can be compared with those of modern isolates.
TL;DR: A large proportion of the bacterial flora on fresh chicken is resistant to a variety of antibiotics, and that resultant food‐related infections will be more difficult to treat.
Abstract: Animal feed is increasingly being supplemented with antibiotics to decrease the risk of epidemics in animal husbandry. This practice could lead to the selection for antibiotic resistant micro-organisms. The aim of this study was to determine the level of antibiotic resistant bacteria present on retail and abattoir chicken. Staphylococci, Enterobacteriaceae, Salmonella and isolates from total aerobic plate count were tested for resistance to vancomycin, streptomycin, methicillin, tetracycline and gentamicin using the disc diffusion susceptibility test; resistance to penicillin was determined using oxacillin. Results from the antibiotic code profile indicated that many of the bacterial strains were displaying multiple antibiotic resistance (MAR). A larger proportion of resistance to most antibiotics, except for vancomycin, was displayed by the abattoir samples, therefore suggesting that the incidence of MAR pathogenic bacteria was also higher in the abattoir samples. This resistance spectrum of abattoir samples is a result of farmers adding low doses of antibiotics to livestock feed to improve feeding efficiency so that the animals need less food to reach marketable weight. The lower incidence of MAR pathogenic bacteria in the retail samples is a result of resistance genes being lost due to lack of selective pressure, or to the fact that the resistant flora are being replaced by more sensitive flora during processing. The use of subtherapeutic levels of antibiotics for prophylaxis and as growth promoters remains a concern as the laws of evolution dictate that microbes will eventually develop resistance to practically any antibiotic. Selective pressure exerted by widespread antimicrobial use is therefore the driving force in the development of antibiotic resistance. This study indicated that a large proportion of the bacterial flora on fresh chicken is resistant to a variety of antibiotics, and that resultant food-related infections will be more difficult to treat.
TL;DR: It was concluded that the spores of Clostridium sporogenes could not be inactivated by pressure alone, and could indicate that for the effective inactivation of bacterial spores, high pressure technology may have to be used in combination with other preservation methods.
Abstract: Spores of Clostridium sporogenes were found to be resistant to ultra high pressure, with treatments of 600 MPa for 30 min at 20 degrees C causing no significant inactivation. Combination treatments including heat and pressure applied simultaneously (e.g. 400 MPa at 60 degrees C for 30 min) or sequentially (e.g. 80 degrees C for 10 min followed by 400 MPa for 30 min) proved more effective at inactivating spores. Pressure cycling (e.g. 60 MPa followed by 400 MPa at 60 degrees C) also reduced spore numbers. Overall, these pressure treatments resulted in less than a 3 log reduction, and it was concluded that the spores could not be inactivated by pressure alone. This could indicate that for the effective inactivation of bacterial spores, high pressure technology may have to be used in combination with other preservation methods.
TL;DR: The results suggest that quillaja sap onins from various sources differ in their biological activity, although all three saponins had the same content of vanillin‐sulphuric acid reactive moieties.
Abstract: Escherichia coli K-12 was exposed to Quillaja saponaria saponins from various commercial firms (Sigma, Roth and Nor-feed) and to an extract of Yucca schidigera plant powder (DK Sarsaponin 30) at different concentrations (0.05-1.0% w/v). A concentration-dependent response was observed. Quillaja saponaria saponins from Sigma increased growth up to 0.1% (w/v) level, whereas Nor-feed and Roth saponins produced maximum growth at a much higher level (0.5 and 0.75%, w/v, respectively). These results suggest that quillaja saponins from various sources differ in their biological activity, although all three saponins had the same content of vanillin-sulphuric acid reactive moieties. The lyophilized water extract from the DK Sarsaponin powder showed maximum growth at 0.1% (w/v) level. The levels at which maximum growth was observed did not change on subjecting the quillaja or yucca saponins to heat treatment in an autoclave (121 degrees C for 30 min). All the saponins and the plant extract increased growth of Escherichia coli up to a certain concentration and thereafter decreased growth. In spite of the decreased growth at higher levels of saponins, it was higher compared to the control (without saponin) up to levels of 1% (w/v) for all saponins except Quillaja saponins from Sigma, for which the growth was lower at levels of 0.25% (w/v) and higher. Saponins have the potential to modulate microbial growth in natural and artificial fermenters.
TL;DR: It can be confirmed that this serotype of Escherichia coli O157 : H7 has no unusual heat resistance and that the heating environment markedly affects resistance.
Abstract: Escherichia coli O157:H7 has been reported as being not particularly heat resistant. However, several factors which might increase its heat resistance have been investigated in this study using five strains. Increase in growth temperature to 40 degrees C, as found in the cow gut, heat-shock at sub-lethal temperatures of 42, 45, 48 and 50 degrees C, and variable heating rate (1 degree C min-1 to 23 degrees C min-1) had no dramatic effect on heat resistance. Growth phase had a marked impact on heat resistance; late stationary phase cells were more heat-resistant than were log phase cells. The difference in heat resistance between the two phases of growth became more pronounced when cells were resuspended in fresh nutrient broth; heat resistance of late stationary phase cells increased dramatically whereas no such effect was observed with log phase cells. The addition of polyphosphates to the heating medium did not increase heat resistance. A reduction in water activity of the heating medium from 0.995 to levels between 0.980 and 0.960 also resulted in a marked increase in heat resistance. This effect was more pronounced under conditions of extremely low water activity created by resuspending late stationary phase cells in sunflower oil. Survivors were detected even after a heat treatment at 60 degrees C for 1 h or 70 degrees C for 5 min. It can be confirmed that this serotype has no unusual heat resistance and that the heating environment markedly affects resistance.
TL;DR: A collection of 381 Listeria monocytogenes strains was examined for strain variations in nisin and pediocin sensitivity at three different concentrations on Tryptic Soya Agar, and it is assumed that there is accordance between the pediOCin and bavaricin sensitivity of the remaining strains.
Abstract: A collection of 381 Listeria monocytogenes strains was examined for strain variations in nisin and pediocin sensitivity at three different concentrations on Tryptic Soya Agar. Two of the strains were able to grow on agar plates containing 500 IU nisin ml−1. These strains were characterized as having an enhanced nisin tolerance. Twenty strains had normal growth on agar plates containing 1600 AU pediocin ml−1 and higher. These strains were characterized as pediocin-resistant. Another 34 strains, characterized as having enhanced tolerance, exhibited inhibited growth at 1600 AU pediocin ml−1. Bavaricin sensitivity, examined for 22 strains of L. monocytogenes, correlated with the pediocin sensitivity of the strains. It is therefore assumed that there is accordance between the pediocin and bavaricin sensitivity of the remaining strains. Cross-resistance between nisin and pediocin/bavaricin was not found.
TL;DR: Different strains previously identified as identical, using typing methods with lower resolution, could be distinguished, showing that AFLP fingerprinting is well suited for bacterial epidemiology and identification.
Abstract: H.J.M. AARTS, L.A.J.T. VAN LITH AND J. KEIJER. 1998. High resolution AFLP fingerprinting, in which subsets of genomic restriction fragments are amplified by means of PCR, was used for the identification of different Salmonella serotypes to investigate whether this technique is applicable in epidemiological studies. Seventy-eight different Salmonella strains comprising 62 serotypes were genetically identified by AFLP. Primer combination M00 (MseI primer without additional 3? nucleotides) and E11 (EcoRI primer with two additional 3? nucleotides) resulted in reproducible profiles containing approximately 50 bands. All serotypes were characterized by a unique profile. In addition, AFLP fingerprinting enabled phage type identification. Different strains previously identified as identical, using typing methods with lower resolution, could be distinguished, showing that AFLP fingerprinting is well suited for bacterial epidemiology and identification.
TL;DR: Forty strains of lactobacilli isolated from probiotic supplements or functional foods, and two clinical isolates, have been identified by API 50 CHL and tested for susceptibility to vancomycin.
Abstract: Forty strains of lactobacilli isolated from probiotic supplements or functional foods, and two clinical isolates, have been identified by API 50 CHL and tested for susceptibility to vancomycin. All the Lactobacillus acidophilus (16) and Lact. delbreuckii (two) strains were sensitive to vancomycin, while all the other strains (mainly Lact. rhamnosus, 15) were resistant. Susceptibility to other antibiotics was not species-specific. Differential susceptibility to vancomycin may be helpful in speciation of lactobacilli.
TL;DR: It was concluded that the class IIa bacteriocin‐resistant phenotype of L. monocytogenes B73 is unlikely to become stable in natural populations based on evidence, and the extrapolation of these results to the species as a whole should not be made.
Abstract: G.A. DYKES AND J.W. HASTINGS. 1998. In order to assess the potential for the spread of class IIa bacteriocin resistance in natural populations of Listeria monocytogenes, the fitness costs associated with resistance to leucocins A , B and E and sakacin A in L. monoc)itogenes B73 in the absence of bacteriocin were examined. The resistant phenotype had a lower growth rate (and thus relative fitness) than the sensitive phenotype in monoculture experiments. Furthermore, resistant phenotypes were unable to invade populations of the sensitive strain, even at frequencies of 10-' or higher, when grown in co-culture. These results held true for resistant strains that had been exposed to bacteriocin for 25 successive growth cycles. It was concluded that the class IIa bacteriocin-resistant phenotype of L. monojj , togenes B73 is unlikely to become stable in natural populations based on this evidence. Due to the possibility of variations in the frequencies of spontaneous mutation and fitness among Listeria strains, however, the extrapolation of these results to the species as a whole should not be made.