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ABSTRACT: BACKGROUND: Staphylococcus aureus is the pathogen most often and prevalently involved in skin and soft tissue infections. In recent decades outbreaks of methicillin-resistant S. aureus (MRSA) have created major problems for skin therapy, and burn and wound care units. Topical antimicrobials are most important component of wound infection therapy. Alternative therapies are being sought for treatment of MRSA and one area of interest is the use of essential oils. With the increasing interest in the use and application of natural products, we screened the potential application of terpeneless cold pressed Valencia orange oil (CPV) for topical therapy against MRSA using an in vitro dressing model and skin keratinocyte cell culture model. METHODS: The inhibitory effect of CPV was determined by disc diffusion vapor assay for MRSA and vancomycin intermediate-resistant S. aureus (VISA) strains. Antistaphylococcal effect of CPV in an in vitro dressing model was tested on S. aureus inoculated tryptic soya agar plate. Bactericidal effect of CPV on MRSA and VISA infected keratinocyte cells was examined by enumeration of extra- and intra-cellular bacterial cells at different treatment time points. Cytotoxic effects on human skin cells was tested by adding CPV to the keratinocyte (HEK001) cells grown in serum free KSFM media, and observed by phase-contrast microscope. RESULTS: CPV vapour effectively inhibited the MRSA and VISA strains in both disc diffusion vapour assay and in vitro dressing model. Compared to untreated control addition of 0.1% CPV to MRSA infected keratinocyte decreased the viable MRSA cells by 2 log CFU/mL in 1 h and in VISA strain 3 log10 CFU/mL reduction was observed in 1 h. After 3 h viable S. aureus cells were not detected in the 0.2% CPV treatment. Bactericidal concentration of CPV did not show any cytotoxic effect on the human skin keratinocyte cells in vitro. CONCLUSIONS: At lower concentration addition of CPV to keratinocytes infected with MRSA and VISA rapidly killed the bacterial cells without causing any toxic effect to the keratinocytes. Therefore, the results of this study warrant further in vivo study to evaluate the potential of CPV as a topical antistaphylococcal agent.
BMC Complementary and Alternative Medicine 08/2012; 12(1):125. · 2.24 Impact Factor
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ABSTRACT: Listeria monocytogenes is a Gram-positive foodborne pathogen responsible for a severe disease occurring in immuno-compromised populations. Foodborne illness caused by L. monocytogenes is a serious public health concern because of the high associated mortality. Study of the closely related, but nonpathogenic Listeria innocua has accounted for a better understanding of the behavior of L. monocytogenes in environments beyond the laboratory. Traditionally, the ecological co-habitation, genomic synteny, and physiological similarity of the two species have supported use of L. innocua for predicting the behavior of L. monocytogenes in farm and food processing environments. However, a careful review of the current literature indicates that in a given situation it may not be prudent to use L. innocua as a surrogate for L. monocytogenes without prior confirmation of their similar phenotypes, as an increasing number of studies have arisen demonstrating differences in L. monocytogenes and L. innocua stress response, and furthermore, there are differences among the L. monocytogenes subgroups. Future research should take into consideration that multiple surrogates might be required to accurately model even a single condition depending on the L. monocytogenes subgroup of interest.
Critical reviews in food science and nutrition 08/2012; 52(8):712-25. · 3.73 Impact Factor
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ABSTRACT: In this study bioactive caseinomacropeptide was conjugated with prebiotic galactooligosaccharides (hCMP:GOS) by Maillard reaction to synthesize value added prebiotic compounds to Lactobacillus strains. Growth study showed the ability of hCMP:GOS to serve as a sole carbon source for Lactobacillus strains. A significant amount of acetate and lactate was detected in cell free culture supernatant by HPLC. It demonstrated the ability of Lactobacillus strains to ferment the hCMP:GOS as a carbon source. In addition, hCMP:GOS grown Lactobacillus cells exhibited enhanced bile tolerance and retained 90% viability. Overall results of this study indicate that the hCMP conjugated GOS can be potential multipurpose prebiotic substrates to enhance the growth and bile tolerance in Lactobacillus strains and serve as a fermentable substrate to produce beneficial metabolites in the host.
Journal of Agricultural and Food Chemistry 06/2012; · 2.82 Impact Factor
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ABSTRACT: The objectives of this study were to evaluate the antistaphylococcal effect and elucidate the mechanism of action of orange essential oil against antibiotic-resistant Staphylococcus aureus strains.
The inhibitory effect of commercial orange essential oil (EO) against six Staph. aureus strains was tested using disc diffusion and agar dilution methods. The mechanism of EO action on MRSA was analysed by transcriptional profiling. Morphological changes of EO-treated Staph. aureus were examined using transmission electron microscopy. Results showed that 0·1% of terpeneless cold-pressed Valencia orange oil (CPV) induced the cell wall stress stimulon consistent with the inhibition of cell wall synthesis. Transmission electron microscopic observation revealed cell lysis and suggested a cell wall lysis-related mechanism of CPV.
CPV inhibits the growth of Staph. aureus, causes gene expression changes consistent with the inhibition of cell wall synthesis, and triggers cell lysis.
Multiple antibiotics resistance is becoming a serious problem in the management of Staph. aureus infections. In this study, the altered expression of cell wall-associated genes and subsequent cell lysis in MRSA caused by CPV suggest that it may be a potential antimicrobial agent to control antibiotic-resistant Staph. aureus.
Journal of Applied Microbiology 02/2012; 112(5):1020-33. · 2.34 Impact Factor
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ABSTRACT: Staphylococcus aureus (S. aureus) is an important foodborne and environmental pathogen that can produce toxins in foods and cause infections in soft tissues. S. aureus that have developed resistance to the conventional antimicrobials are commonly called Methicillin-Resistant Staphylococcus aureus (MRSA) and Vancomycin-Resistant S. aureus (VRSA). Their prevalence is believed to be due to the widespread use of antibiotics. Therefore, natural antimicrobials are in urgent demand as alternatives to conventional antibiotics to treat S. aureus infections. In this review, natural antimicrobials from plant, animal and microbiological origins are discussed, including their mode of action and mechanisms of bacterial resistance, major components, chemical structure, effectiveness, synergistic effects and future prospects.
Current pharmaceutical biotechnology 04/2011; 12(8):1240-54. · 3.40 Impact Factor
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ABSTRACT: There has been increased interest in the study of molecular survival mechanisms expressed by foodborne pathogens present on food surfaces. Determining genomic responses of these pathogens to antimicrobials is of particular interest since this helps to understand antimicrobial effects at the molecular level. Assessment of bacterial gene expression by transcriptomic analysis in response to these antimicrobials would aid prediction of the phenotypic behavior of the bacteria in the presence of antimicrobials. However, before transcriptional profiling approaches can be implemented routinely, it is important to develop an optimal method to consistently recover pathogens from the food surface and ensure optimal quality RNA so that the corresponding gene expression analysis represents the current response of the organism. Another consideration is to confirm that there is no interference from the "background" food or meat matrix that could mask the bacterial response.
Our study involved developing a food model system using chicken breast meat inoculated with mid-log Salmonella cells. First, we tested the optimum number of Salmonella cells required on the poultry meat in order to extract high quality RNA. This was analyzed by inoculating 10-fold dilutions of Salmonella on the chicken samples followed by RNA extraction. Secondly, we tested the effect of two different bacterial cell recovery solutions namely 0.1% peptone water and RNAprotect (Qiagen Inc.) on the RNA yield and purity. In addition, we compared the efficiency of sonication and bead beater methods to break the cells for RNA extraction. To check chicken nucleic acid interference on downstream Salmonella microarray experiments both chicken and Salmonella cDNA labeled with different fluorescent dyes were mixed together and hybridized on a single Salmonella array. Results of this experiment did not show any cross-hybridization signal from the chicken nucleic acids. In addition, we demonstrated the application of this method in a meat model transcriptional profiling experiment by studying the transcriptomic response of Salmonella inoculated on chicken meat and exposed to d-limonene. We successfully applied our method in this experiment to recover the bacterial cells from the meat matrix and to extract the RNA. We obtained high yield and pure RNA. Subsequently, the RNA was used for downstream transcriptional profiling studies using microarrays and over 600 differentially regulated genes were identified.
Our result showed that 8 log cfu/g of Salmonella is ideal to obtain optimal RNA amount and purity. Our results demonstrated that RNAprotect yielded higher RNA amounts (approximately 10 to 30 fold) when compared to 0.1% peptone water. The differences between the RNAprotect and 0.1% peptone samples were significant at a p-value of 0.03 for the bead beater method and 0.0005 for the sonication method, respectively. The microarray experiment demonstrated that the chicken samples do not interfere with the hybridization of Salmonella cDNA on the array slide. Hence, the background chicken RNA will not interfere with the microarray analysis when poultry meat models are used. Finally, we successfully demonstrated the application of the poultry meat model proposed in this study by conducting transcriptional profiling analysis of Salmonella inoculated on the poultry. Results of this study proved that this method has the potential to be employed in other meat model studies.
BMC Research Notes 03/2011; 4:60.
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Miranda Johnson,
Mrittika Sengupta,
Joanne Purves,
Emma Tarrant,
Peter H Williams,
Alan Cockayne, Arunachalam Muthaiyan,
Robert Stephenson,
Nagender Ledala,
Brian J Wilkinson,
Radheshyam K Jayaswal,
Julie A Morrissey
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ABSTRACT: Our previous studies showed that both Sae and Fur are required for the induction of eap and emp expression in low iron. In this study, we show that expression of sae is also iron-regulated, as sae expression is activated by Fur in low iron. We also demonstrate that both Fur and Sae are required for full induction of the oxidative stress response and expression of non-covalently bound surface proteins in low-iron growth conditions. In addition, Sae is required for the induced expression of the important virulence factors isdA and isdB in low iron. Our studies also indicate that Fur is required for the induced expression of the global regulators Agr and Rot in low iron and a number of extracellular virulence factors such as the haemolysins which are also Sae- and Agr-regulated. Hence, we show that Fur is central to a complex regulatory network that is required for the induced expression of a number of important S. aureus virulence determinants in low iron.
International journal of medical microbiology: IJMM 01/2011; 301(1):44-52. · 2.80 Impact Factor
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ABSTRACT: Listeria monocytogenes is an opportunistic human pathogen that causes listeriosis, a disease that mainly affects the immunocompromised, the elderly, infants, and pregnant women. Listeriosis has become increasingly common in the last 25 years since the first foodborne outbreak was noted. Treatment for listeriosis currently consists primarily of supportive therapy in conjunction with the use of intravenous antibiotics. Antibiotics have been commercially available for over 60 years for treatment of a myriad of clinical diseases. Bacteria resistant to antibiotics have been developing over this same period. This review seeks to elucidate the extent of antibiotic resistance in L. monocytogenes, the possible transmission mechanisms, and contributing factors to distribution of antibiotic resistance among Listeria species, and possible control strategies.
Foodborne Pathogens and Disease 12/2010; 8(5):569-78. · 2.26 Impact Factor
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ABSTRACT: Alkali stress is an important means of inactivating undesirable pathogens in a wide range of situations. Unfortunately, Listeria monocytogenes can launch an alkaline tolerance response, significantly increasing persistence of the pathogen in such environments. This study compared transcriptome patterns of alkali and non-alkali-stressed L. monocytogenes 10403S cells, to elucidate the mechanisms by which Listeria adapts and/or grows during short- or long-term alkali stress. Transcription profiles associated with alkali shock (AS) were obtained by DNA microarray analysis of midexponential cells suspended in pH 9 media for 15, 30, or 60 min. Transcription profiles associated with alkali adaptation (AA) were obtained similarly from cells grown to midexponential phase at pH 9. Comparison of AS and AA transcription profiles with control cell profiles identified a high number of differentially regulated open-reading frames in all tested conditions. Rapid (15 min) changes in expression included upregulation of genes encoding for multiple metabolic pathways (including those associated with Na+/H+ antiporters), ATP-binding cassette transporters of functional compatible solutes, motility, and virulence-associated genes as well as the σ(B) controlled stress resistance network. Slower (30 min and more) responses to AS and adaptation during growth in alkaline conditions (AA) involved a different pattern of changes in mRNA concentrations, and genes involved in proton export.
Foodborne Pathogens and Disease 10/2010; 7(10):1147-57. · 2.26 Impact Factor
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ABSTRACT: The existence of two separate genetic lineages of Escherichia coli O157:H7 has previously been reported, and research indicates that lineage I could be more pathogenic toward human hosts than lineage II. We have previously shown that lineage I as a group expresses higher levels of Shiga toxin 2 (Stx2) than lineage II. To help evaluate why lineage II strains do not express appreciable levels of this toxin, whole-genome microarrays were performed using Agilent custom microarrays. Gene expression of the two representative bovine lineage II strains (FRIK966 and FRIK2000) were compared with gene expression of E. coli O157:H7 EDL933 (lineage I clinical type strain). Missing or differentially expressed genes and pathways were identified. Quantitative reverse transcription-polymerase chain reaction was performed to validate the microarray data. Draft genomes of FRIK966 and FRIK2000 were sequenced using Roche Applied Science/454 GS-FLX technology shotgun and paired-end approaches followed by de novo assembly. These assemblies were compared with the lineage I genome sequences from E. coli O157:H7 EDL933. The bacteriophage 933W, which encodes the Stx2 genes, showed a notable repression in gene expression. Polymerase chain reaction primers, based upon EDL933 genomic information, were also designed against all of the potentially missing genes of this bacteriophage. Most of the structural genes associated with the bacteriophage were found to be absent from the genome of the two bovine strains. These analyses, combined with evaluation of the genomic information, suggest that transposon (IS629) rearrangements may be associated with disruption of the bacteriophage genome in the FRIK strains. The results support the hypothesis that lineage II strains may be less of a risk as human foodborne pathogens. The microarray and genome data have been made available to the scientific community to allow continuing analysis of these cattle-isolated lineage II genomes and their gene expression.
Foodborne Pathogens and Disease 02/2010; 7(7):763-73. · 2.26 Impact Factor
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ABSTRACT: Iron is required by almost all bacteria, but concentrations above physiological levels are toxic. In bacteria, intracellular iron is regulated mostly by the ferric uptake regulator, Fur, or a similar functional protein. Iron limitation results in the regulation of a number of genes, especially those involved in iron uptake. A subset of these genes is the Fur regulon under the control of Fur. In the present study, we have identified Fur- and iron-regulated genes in Listeria monocytogenes by DNA microarray analysis using a fur mutant and its isogenic parent. To identify genes regulated exclusively in response to iron limitation, the whole-genome transcriptional responses to the iron limitation of a fur mutant and its isogenic parent were compared. Fur-regulated genes were identified by comparing the transcriptional profile of the parent with the transcriptional profile of the isogenic fur mutant. Our studies have identified genes regulated exclusively in response to iron and those that are negatively regulated by Fur. We have identified at least 14 genes that were negatively regulated directly by Fur. Under iron-limited conditions, these genes were upregulated, while the expression of fur was found to be downregulated. To further investigate the regulation of fur in response to iron, an ectopic fur promoter-lacZ transcriptional fusion strain was constructed, and its isogenic fur and perR mutant derivatives were generated in L. monocytogenes 10403S. Analysis of the iron limitation of the perR mutant indicated that the regulation of genes under the negative control of Fur was significantly inhibited. Our results indicate that Fur and PerR proteins negatively regulate fur and that under iron-limited conditions, PerR is required for the negative regulation of genes controlled by Fur.
Applied and environmental microbiology 11/2009; 76(2):406-16. · 3.69 Impact Factor
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ABSTRACT: In recent years bioethanol has encompassed worldwide interest as a non-conventional bioenergy source. This fact has driven several bioethanol industries to produce more ethanol on a large scale via cost effective methods. However in the process of scaling up ethanol production bacterial contamination is becoming one of the more challenging problems facing the bioethanol industry. There are several traditional microbiological methods available to detect and subsequently limit these bacterial contaminants. These methods are time consuming, laborious and can be less sensitive. Consequently, it is necessary to find novel sensitive and economic detection methods to eradicate the contaminants long before they disrupt ethanol production. Molecular methods that can detect the contaminants even at very low numbers at any given stage would help in the design of more cost effective eradication strategies and better targeted antimicrobial treatments. Application of rapid molecular detection approaches have the potential to provide much more sensitive and rapid means to not only detect but quantitate microbial contaminants long before they become problematic to overall bioethanol formation.
Bioresource technology 11/2009; 101(13):5033-42. · 4.25 Impact Factor
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Ramakrishna Nannapaneni, Arunachalam Muthaiyan,
Philip G Crandall,
Michael G Johnson,
Corliss A O'Bryan,
Vesela I Chalova,
Todd R Callaway,
Jeff A Carroll,
John D Arthington,
David J Nisbet,
Steven C Ricke
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ABSTRACT: Due to increasing concerns about the development of antimicrobial resistance amongst pathogenic bacteria, alternative strategies have been sought that do not use antibiotics to reduce pathogenic bacteria from foods and patients. A natural compound that has potent antimicrobial properties is citrus peel, which contains a variety of essential oils that inhibit the growth of or kill pathogenic bacteria. In the present study, seven citrus-based natural antimicrobials were evaluated for their ability to inhibit the growth of the pathogen Escherichia coli O157:H7. Zones of inhibition of E. coli O157:H7 by the citrus-derived fraction (10 microL/6 mm disk) were determined by a disk-diffusion assay on Sorbitol-MacConkey agar. Inhibition zones were observed after 48 h lawn growth of E. coli O157:H7 cells at 37 degrees C. Two citrus-based fractions, orange CP VAL terpeneless FAB 968611 and Limonene 1x Dist FAB 955430, inhibited E. coli O157:H7 with inhibition zones of approx. 11-24 mm dia. The remaining other five citrus-derived extracts (orange oil FL VAL 1121 ARR 974760, Orange 5x Conc VAL 4121 ARR 968374, orange terpenes ESS 1120 ARR 986259, orange terpenes CP 1100 ARR 986255, and orange terpenes OEO HP 1100 ARR 986257) were noninhibitory to E. coli O157:H7, yielding no clear inhibition zones. These studies show that citrus-derived natural compounds differ in their inhibitory activity against E. coli O157:H7 and some have potential applications as inhibitory agents against E. coli O157:H7 in various pathogen reduction strategies.
Foodborne Pathogens and Disease 11/2008; 5(5):695-9. · 2.26 Impact Factor
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ABSTRACT: Fusidic acid interferes with the release of elongation factor G (EF-G) after the translocation step of protein synthesis. The objective of this study was to characterize the fusidic acid stimulon of a fusidic acid-susceptible strain of Staphylococcus aureus (SH1000).
S. aureus microarrays and real-time PCR determined transcriptome alterations occurring in SH1000 grown with fusidic acid. The Staphylococcus aureus microarray meta-database (SAMMD) compared and contrasted the SH1000 fusidic stimulon with 89 other S. aureus transcriptional datasets. Fusidic acid gradient analyses with mutant-parent strain pairs were used to identify genes required for intrinsic fusidic acid susceptibility identified during transcriptional analysis.
Many genes altered by fusidic acid challenge are associated with protein synthesis. SAMMD analysis determined that the fusidic acid stimulon has the greatest overlap with the S. aureus cold shock and stringent responses. Six out of nine peptidoglycan hydrolase genes making up the two component YycFG regulon were also up-regulated by fusidic acid, as were a carboxylesterase gene (est) and two putative drug efflux pump genes (emr-qac1 and macA). Genes down-regulated by fusidic acid induction encoded a putative secreted acid phosphatase and a number of protease genes. Roles for the agr operon, the peptidoglycan hydrolase gene isaA and two proteases (htrA1 and htrA2) in the expression of fusidic acid susceptibility were revealed.
The SH1000 fusidic acid stimulon includes genes involved with two stress responses, YycFG-regulated cell wall metabolism, drug efflux, and protein synthesis and turnover.
Journal of Antimicrobial Chemotherapy 10/2008; 62(6):1207-14. · 5.07 Impact Factor
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ABSTRACT: Daptomycin is a lipopeptide antibiotic that has recently been approved for treatment of gram-positive bacterial infections. The mode of action of daptomycin is not yet entirely clear. To further understand the mechanism transcriptomic analysis of changes in gene expression in daptomycin-treated Staphylococcus aureus was carried out. The expression profile indicated that cell wall stress stimulon member genes (B. J. Wilkinson, A. Muthaiyan, and R. K. Jayaswal, Curr. Med. Chem. Anti-Infect. Agents 4:259-276, 2005) were significantly induced by daptomycin and by the cell wall-active antibiotics vancomycin and oxacillin. Comparison of the daptomycin response of a two-component cell wall stress stimulon regulator VraSR mutant, S. aureus KVR, to its parent N315 showed diminished expression of the cell wall stress stimulon in the mutant. Daptomycin has been proposed to cause membrane depolarization, and the transcriptional responses to carbonyl cyanide m-chlorophenylhydrazone (CCCP) and nisin were determined. Transcriptional profiles of the responses to these antimicrobial agents showed significantly different patterns compared to those of the cell wall-active antibiotics, including little or no induction of the cell wall stress stimulon. However, there were a significant number of genes induced by both CCCP and daptomycin that were not induced by oxacillin or vancomycin, so the daptomycin transcriptome probably reflected a membrane depolarizing activity of this antimicrobial also. The results indicate that inhibition of peptidoglycan biosynthesis, either directly or indirectly, and membrane depolarization are parts of the mode of action of daptomycin.
Antimicrobial Agents and Chemotherapy 04/2008; 52(3):980-90. · 4.84 Impact Factor
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ABSTRACT: Information regarding the Alkali-Tolerance Response (AlTR) in Listeria monocytogenes is very limited. Treatment of alkali-adapted cells with the protein synthesis inhibitor chloramphenicol has revealed that the AlTR is at least partially protein-dependent. In order to gain a more comprehensive perspective on the physiology and regulation of the AlTR, we compared differential gene expression and protein content of cells adapted at pH 9.5 and un-adapted cells (pH 7.0) using complementary DNA (cDNA) microarray and two-dimensional (2D) gel electrophoresis, (combined with mass spectrometry) respectively.
In this study, L. monocytogenes was shown to exhibit a significant AlTR following a 1-h exposure to mild alkali (pH 9.5), which is capable of protecting cells from subsequent lethal alkali stress (pH 12.0). Adaptive intracellular gene expression involved genes that are associated with virulence, the general stress response, cell division, and changes in cell wall structure and included many genes with unknown functions. The observed variability between results of cDNA arrays and 2D gel electrophoresis may be accounted for by posttranslational modifications. Interestingly, several alkali induced genes/proteins can provide a cross protective overlap to other types of stresses.
Alkali pH provides therefore L. monocytogenes with nonspecific multiple-stress resistance that may be vital for survival in the human gastrointestinal tract as well as within food processing systems where alkali conditions prevail. This study showed strong evidence that the AlTR in L. monocytogenes functions as to minimize excess alkalisation and energy expenditures while mobilizing available carbon sources.
BMC Microbiology 02/2008; 8:102. · 3.04 Impact Factor
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ABSTRACT: Abstract
Background
Information regarding the Alkali-Tolerance Response (AlTR) in Listeria monocytogenes is very limited. Treatment of alkali-adapted cells with the protein synthesis inhibitor chloramphenicol has revealed that the AlTR is at least partially protein-dependent. In order to gain a more comprehensive perspective on the physiology and regulation of the AlTR, we compared differential gene expression and protein content of cells adapted at pH 9.5 and un-adapted cells (pH 7.0) using complementary DNA (cDNA) microarray and two-dimensional (2D) gel electrophoresis, (combined with mass spectrometry) respectively.
Results
In this study, L. monocytogenes was shown to exhibit a significant AlTR following a 1-h exposure to mild alkali (pH 9.5), which is capable of protecting cells from subsequent lethal alkali stress (pH 12.0). Adaptive intracellular gene expression involved genes that are associated with virulence, the general stress response, cell division, and changes in cell wall structure and included many genes with unknown functions. The observed variability between results of cDNA arrays and 2D gel electrophoresis may be accounted for by posttranslational modifications. Interestingly, several alkali induced genes/proteins can provide a cross protective overlap to other types of stresses.
Conclusion
Alkali pH provides therefore L. monocytogenes with nonspecific multiple-stress resistance that may be vital for survival in the human gastrointestinal tract as well as within food processing systems where alkali conditions prevail. This study showed strong evidence that the AlTR in L. monocytogenes functions as to minimize excess alkalisation and energy expenditures while mobilizing available carbon sources.
BMC Microbiology. 01/2008;
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ABSTRACT: Growth of Staphylococcus aureus with the nonsteroidal anti-inflammatory salicylate reduces susceptibility of the organism to multiple antimicrobials. Transcriptome analysis revealed that growth of S. aureus with salicylate leads to the induction of genes involved with gluconate and formate metabolism and represses genes required for gluconeogenesis and glycolysis. In addition, salicylate induction upregulates two antibiotic target genes and downregulates a multidrug efflux pump gene repressor (mgrA) and sarR, which represses a gene (sarA) important for intrinsic antimicrobial resistance. We hypothesize that these salicylate-induced alterations jointly represent a unique mechanism that allows S. aureus to resist antimicrobial stress and toxicity.
Journal of Bacteriology 02/2007; 189(1):220-7. · 3.83 Impact Factor
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ABSTRACT: By the early nineteen seventies the mechanism of inhibition of peptidoglycan biosynthesis by various cell wallactive antibiotics was well established, and the Gram-positive bacterium Staphylococcus aureus had often been used in the studies. From the early days of penicillin it was known that cell wall-active antibiotics are typically bactericidal causing cell death and lysis, a phenomenon that has recently been described as programmed cell death. Uncovering the details of the molecular and cellular events occurring subsequent to inhibition of peptidoglycan biosynthesis, a legitimate aspect of knowledge of the mode of action of these agents, has had to await the advent of the omics era-genomics, proteomics and transcriptomics-over the past several years. Genome-wide transcriptional profiling using DNA microarrays of the response of S. aureus to challenge by cell wall active antibiotics has revealed a cell wall stress stimulon of genes upregulated in their expression by these agents. Several of the genes encode proteins involved in cell wall metabolism and their induction can be regarded as a response of the organism to preserve and repair the compromised cell wall. Expression of a significant number of cell wall stress stimulon member genes is controlled by a two-component regulatory system. Cell wall stress stimulons regulated by two-component systems have also been described in Bacillus subtilis and Listeria monocytogenes, and are probably common to all Gram-positive bacteria. Unfortunately S. aureus has not remained susceptible to cell wall-active antibiotics and methicillin-resistant strains are common, and vancomycinintermediate and-resistant strains have arisen. Interestingly, some member genes of the cell wall stress stimulon have been previously encountered in the context of methicillin-resistance or vancomycin-intermediate resistance. There is a threat of pan-resistant S. aureus strains and new antimicrobial agents are needed. Cell wall biosynthesis remains a viable target for new drugs, and recognition of the transcriptomic signature of the cell wall stress stimulon can be used to indicate a cell wall mode of action. Individual cell wall stress member genes may form the basis of a screen for cell wall-active agents. Finally, agents targeting cell wall stress stimulon member gene expression or proteins might enhance the activity of cell wall-active agents that induce the cell wall stress stimulon.
Current Medicinal Chemistry - Anti-Infective Agents 06/2005; 4(3):259-276.
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ABSTRACT: The cell wall composition and autolytic properties of passage-selected glycopeptide-intermediate Staphylococcus aureus (GISA) isolates and their parent strains were studied in order to investigate the mechanism of decreased vancomycin susceptibility. GISA had relatively modest changes in peptidoglycan composition involving peptidoglycan interpeptide bridges and somewhat decreased cross-linking compared to that of parent strains. The cell wall phosphorus content of GISA strains was lower than that of susceptible parent strains, indicating somewhat lower wall teichoic acid levels in the GISA strains. Similar to whole cells, isolated crude cell walls retaining autolytic activity of GISA had drastically reduced autolytic activity compared to that of parent strains, and this arose early in the development of the GISA phenotype. This was due to an alteration in the autolytic enzymes of GISA as revealed by normal susceptibility of GISA-purified cell walls to parental strain autolysin extract and lower activity and altered peptidoglycan hydrolase activity profiles in GISA autolysin extracts compared to those of parent strains. Northern blot analysis indicated that expression of atl, the major autolysin gene, was significantly downregulated in a GISA strain compared to that of its parent strain. In contrast to whole cells, which showed decreased lysostaphin susceptibility, purified cell walls of GISA showed increased susceptibility to lysostaphin. We suggest that in our GISA strains, decreased autolytic activity is involved in the tolerance of vancomycin and the activities of endogenous autolysins are important in conferring sensitivity to lysostaphin on whole cells.
Antimicrobial Agents and Chemotherapy 11/2004; 48(10):3749-57. · 4.84 Impact Factor
