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604900.9981Probiotic Properties and Antioxidant Activity In Vitro of Lactic Acid Bacteria. The properties of probiotics such as lactic acid bacteria (LAB) have been widely studied over the last decades. In the present study, four different LAB species, namely Lactobacillus gasseri ATCC 33323, Lacticaseibacillus rhamnosus GG ATCC 53103, Levilactobacillus brevis ATCC 8287, and Lactiplantibacillus plantarum ATCC 14917, were investigated in order to determine their ability to survive in the human gut. They were evaluated based on their tolerance to acids, resistance to simulated gastrointestinal conditions, antibiotic resistance, and the identification of genes encoding bacteriocin production. All four tested strains demonstrated high resistance to simulated gastric juice after 3 h, and the viable counts revealed declines in cell concentrations of less than 1 log cycle. L. plantarum showed the highest level of survival in the human gut, with counts of 7.09 log CFU/mL. For the species L. rhamnosus and L. brevis, the values were 6.97 and 6.52, respectively. L. gasseri, after 12 h, showed a 3.96 log cycle drop in viable counts. None of the evaluated strains inhibited resistance to ampicillin, gentamicin, kanamycin, streptomycin, erythromycin, clindamycin, tetracycline, or chloramphenicol. With regard to bacteriocin genes, the Pediocin PA gene was identified in Lactiplantibacillus plantarum ATCC 14917, Lacticaseibacillus rhamnosus GG ATCC 53103, and Lactobacillus gasseri ATCC 33323. The PlnEF gene was detected in Lactiplantibacillus plantarum ATCC 14917 and Lacticaseibacillus rhamnosus GG ATCC 53103. The Brevicin 174A and PlnA genes were not detected in any bacteria. Moreover, the potential antioxidant activity of LAB's metabolites was evaluated. At the same time, the possible antioxidant activity of metabolites of LAB was first tested using the free radical DDPH(•) (a, a-Diphenyl-β-Picrylhydrazyl) and then evaluated with regard to their radical scavenging activity and inhibition against peroxyl radical induced DNA scission. All strains showed antioxidant activity; however, the best antioxidant activity was achieved by L. brevis (94.47%) and L. gasseri (91.29%) at 210 min. This study provides a comprehensive approach to the action of these LAB and their use in the food industry.202337317238
635710.9977Cloning and expression of the pediocin operon in Streptococcus thermophilus and other lactic fermentation bacteria. Production of pediocin in Pediococcus acidilactici is associated with pMBR1.0, which encodes prepediocin, a pediocin immunity protein, and two proteins involved in secretion and precursor processing. These four genes are organized as an operon under control of a single promoter. We have constructed shuttle vectors that contain all four structural genes, the chromosomal promoter ST(P2201) from Streptococcus thermophilus, and repA from the 2-kbp S. thermophilus plasmid pER8. The recombinant plasmid, pPC318, expressed and secreted active pediocin in Escherichia coli. Streptococcus thermophilus, Lactococcus lactis subsp. lactis, and Enterococcus faecalis were electrotransformed with pPC418, a modified vector fitted with an erythromycin resistance tracking gene. Pediocin was produced and secreted in each of the lactic acid bacteria, and production was stable for up to ten passages. The expression of pediocin in dairy fermentation microbes has important implications for bacteriocins as food preservatives in dairy products.199910489440
605120.9976Antibiotic susceptibility of different lactic acid bacteria strains. Five lactic acid bacteria (LAB) strains belonging to species Lactobacillus acidophilus, Lactobacillus helveticus, Lactobacillus delbrueckii subsp. bulgaricus, Lactobacillus delbrueckii subsp. lactis and Streptococcus thermophilus were tested for their susceptibility to 27 antibiotics. The minimum inhibitory concentrations of each antimicrobial were determined using a microdilution test. Among the strains a high susceptibility was detected for most of the cell-wall synthesis inhibitors (penicillins, cefoxitin and vancomycin) and resistance toward inhibitors of DNA synthesis (trimethoprim/sulfonamides and fluoroquinolones). Generally, the Lactobacillus strains were inhibited by antibiotics such as chloramphenicol, erythromycin and tetracycline at breakpoint levels lower or equal to the levels defined by the European Food Safety Authority. Despite the very similar profile of S. thermophilus LC201 to lactobacilli, the detection of resistance toward erythromycin necessitates the performance of additional tests in order to prove the absence of transferable resistance genes.201122146692
606030.9976Safety Evaluation and Colonisation Abilities of Four Lactic Acid Bacteria as Future Probiotics. The study evaluated the safety and colonisation properties of four lactic acid bacteria (LAB), by determining their cell hydrophobicity and aggregation abilities. In addition, the presence of virulence and resistance genes was assayed in these probiotic candidates. Lactobacillus reuteri ZJ625, Lactobacillus reuteri VB4, Lactobacillus salivarius ZJ614 and Streptococcus salivarius NBRC13956 were tested for cell surface hydrophobicity abilities against xylene, chloroform and ethyl acetate. The isolates were also tested for auto-aggregation and co-aggregation abilities; the optical densities of cell growth were measured after 1, 2, 3 and 4 h of experimental set-up. DNA was extracted from all the four isolates and amplified using PCR with specific primers to detect virulence genes of adhesion collagen protein (ace) and aggregation substances (agg and asa); also, resistance genes of Vancomycin vanA, Vancomycin vanC1 and Vancomycin vanC2/3 were assayed in the four isolates. The isolates showed high hydrophobicity to all solvents: xylene (78-84%), chloroform (68-75%) and ethyl acetate (52-60%). High auto- and co-aggregations ranging from 60 to 70% and from 45 to 56% respectively were observed in the isolates after 4 h of incubation at 37 °C. Some of the tested isolates showed the presence of virulence and resistance genes; however, this does not indicate that these genes are unsafe because their transmission and expression abilities are unknown. Therefore, in this study, the isolates studied are considered safe for use as future probiotics, as revealed from results presented, which generally represents the scanned safety evaluations of the isolates as promising probiotics.201929881953
605040.9974Vancomycin resistance factor of Lactobacillus rhamnosus GG in relation to enterococcal vancomycin resistance (van) genes. Lactobacillus rhamnosus GG (ATCC 53103) is a probiotic strain used in fermented dairy products in many countries and is also used as a food supplement in the form of freeze-dried powder. The relationship of the vancomycin resistance factor in L. rhamnosus GG and the vancomycin resistance (van) genes of Enterococcus faecalis and E. faecium were studied using polymerase chain reaction (PCR), Southern hybridization and conjugation methods. Our results show that the vancomycin resistance determinant in L. rhamnosus GG is not closely related to enterococcal van genes, since no PCR product was amplified in L. rhamnosus GG with any of the three sets of vanA primers used, and enterococcal vanA, vanB, vnH, vanX, vanZ, vanY, vanS and vanR genes did not hybridize with DNA of L. rhamnosus GG. This strain does not contain plasmids and transfer of chromosomal vancomycin resistance determinant from L. rhamnosus GG to enterococcal species was not detected. Our results are in accordance with previous findings of intrinsically vancomycin-resistant lactic acid bacteria.19989706787
49950.9974Characterization of the genomically encoded fosfomycin resistance enzyme from Mycobacterium abscessus. Mycobacterium abscessus belongs to a group of rapidly growing mycobacteria (RGM) and accounts for approximately 65-80% of lung disease caused by RGM. It is highly pathogenic and is considered the prominent Mycobacterium involved in pulmonary infection in patients with cystic fibrosis and chronic pulmonary disease (CPD). FosM is a putative 134 amino acid fosfomycin resistance enzyme from M. abscessus subsp. bolletii that shares approximately 30-55% sequence identity with other vicinal oxygen chelate (VOC) fosfomycin resistance enzymes and represents the first of its type found in any Mycobacterium species. Genes encoding VOC fosfomycin resistance enzymes have been found in both Gram-positive and Gram-negative pathogens. Given that FosA enzymes from Gram-negative bacteria have evolved optimum activity towards glutathione (GSH) and FosB enzymes from Gram-positive bacteria have evolved optimum activity towards bacillithiol (BSH), it was originally suggested that FosM might represent a fourth class of enzyme that has evolved to utilize mycothiol (MSH). However, a sequence similarity network (SSN) analysis identifies FosM as a member of the FosX subfamily, indicating that it may utilize water as a substrate. Here we have synthesized MSH and characterized FosM with respect to divalent metal ion activation and nucleophile selectivity. Our results indicate that FosM is a Mn(2+)-dependent FosX-type hydrase with no selectivity toward MSH or other thiols as analyzed by NMR and mass spectroscopy.201932952996
603660.9973Comprehensive Phenotypic Characterization and Genomic Analysis Unveil the Probiotic Potential of Bacillus velezensis K12. Bacillus spp. have emerged as pivotal sources of probiotic preparations, garnering considerable attention in recent years owing to their vigorous bacteriostatic activity and antimicrobial resistance. This study aimed to investigate these probiotic characteristics in depth and verify the safety of Bacillus velezensis K12, a strain isolated from broiler intestine. The K12 strain was identified as Bacillus velezensis based on its morphology and 16S rDNA sequence homology analysis. Subsequently, B. velezensis K12 was evaluated for acid resistance, bile salt resistance, gastrointestinal tolerance, drug sensitivity, and antimicrobial activity. Additionally, whole-genome sequencing technology was employed to dissect its genomic components further, aiming to explore its potential applications as a probiotic strain. B. velezensis K12 was sensitive to six antibiotics and had acid tolerance. Furthermore, it showed potent antimicrobial activity against a wide range of pathogenic bacteria, including Escherichia coli (E. coli), Staphylococcus aureus, Salmonella, Clostridium perfringens, Bacillus cereus, and Vibrio parahaemolyticus. The complete genome sequencing of B. velezensis K12 revealed a genomic length of 3,973,105 base pairs containing 4123 coding genes, among which 3973 genes were functionally annotated. The genomic analysis identified genes associated with acid and bile tolerance, adhesion, antioxidants, and secondary metabolite production, whereas no functional genes related to enterotoxins or transferable antibiotic resistance were detected, thereby confirming the probiotic properties of B. velezensis K12. B. velezensis K12 exhibits broad-spectrum bacteriostatic activity and in vitro safety, positioning it as a potential candidate strain for developing probiotic Bacillus preparations.202540150327
603370.9973Antibacterial Activity of Lactobacillus Strains Isolated from Mongolian Yogurt against Gardnerella vaginalis. Worldwide interest in the use of functional foods containing probiotic bacteria such as Lactobacillus and Bifidobacterium for health promotion and disease prevention has increased significantly. Probiotics have demonstrated beneficial properties including strengthening the body's natural defense system, inhibiting the growth of pathogenic bacteria, and regulating mental activity, but their effects on the human vagina have not been fully elucidated. The primary purpose of our study was to isolate Lactobacillus strains from old yogurt, a traditional dairy product, and investigate their probiotic potential with respect to the human vaginal system. Four Lactobacillus plantarum (L. plantarum) strains, named ZX1, ZX2, ZX27, and ZX69, were isolated from the yogurt samples. Simultaneously, we used a commercial Lactobacillus strain (Lactobacillus delbrueckii DM8909) as a control strain. We tested the antimicrobial activity of Lactobacillus isolates against Escherichia coli and Gardnerella vaginalis by agar spot and well diffusion tests. Then, we tested the antibiotic susceptibility of the 5 strains by using the minimal inhibitory concentration method. We attempted to detect possible bacteriocin genes by PCR sequencing technique. Using a chemically defined medium simulating genital tract secretions, we found that the selected Lactobacillus strains could alter the expression of known virulence genes in Gardnerella vaginalis. Bacteriocins derived from these isolated strains had potent antibacterial activity against G. vaginalis and E. coli, with the most effective activity observed in the case of ZX27. In addition, all strains including the L. delbrueckii DM8909 were positive for the presence of the plantaricin cluster of genes described in L. plantarum C11. The tested stains possessed the pln gene indicating that one of the antibacterial agents was plantaricin. We assume that the production of antimicrobial substances such as bacteriocins induce G. vaginalis to upregulate antimicrobial resistance genes. The new isolated strains have bacteriocin-related genes and can change the antimicrobial resistance gene transcription of G. vaginalis.202032382546
635880.9973Use of the alr gene as a food-grade selection marker in lactic acid bacteria. Both Lactococcus lactis and Lactobacillus plantarum contain a single alr gene, encoding an alanine racemase (EC 5.1.1.1), which catalyzes the interconversion of D-alanine and L-alanine. The alr genes of these lactic acid bacteria were investigated for their application as food-grade selection markers in a heterologous complementation approach. Since isogenic mutants of both species carrying an alr deletion (Deltaalr) showed auxotrophy for D-alanine, plasmids carrying a heterologous alr were constructed and could be selected, since they complemented D-alanine auxotrophy in the L. plantarum Deltaalr and L. lactis Deltaalr strains. Selection was found to be highly stringent, and plasmids were stably maintained over 200 generations of culturing. Moreover, the plasmids carrying the heterologous alr genes could be stably maintained in wild-type strains of L. plantarum and L. lactis by selection for resistance to D-cycloserine, a competitive inhibitor of Alr (600 and 200 micro g/ml, respectively). In addition, a plasmid carrying the L. plantarum alr gene under control of the regulated nisA promoter was constructed to demonstrate that D-cycloserine resistance of L. lactis is linearly correlated to the alr expression level. Finally, the L. lactis alr gene controlled by the nisA promoter, together with the nisin-regulatory genes nisRK, were integrated into the chromosome of L. plantarum Deltaalr. The resulting strain could grow in the absence of D-alanine only when expression of the alr gene was induced with nisin.200212406763
66290.9973Gene expression and physiological role of Pseudomonas aeruginosa methionine sulfoxide reductases during oxidative stress. Pseudomonas aeruginosa PAO1 has two differentially expressed methionine sulfoxide reductase genes: msrA (PA5018) and msrB (PA2827). The msrA gene is expressed constitutively at a high level throughout all growth phases, whereas msrB expression is highly induced by oxidative stress, such as sodium hypochlorite (NaOCl) treatment. Inactivation of either msrA or msrB or both genes (msrA msrB mutant) rendered the mutants less resistant than the parental PAO1 strain to oxidants such as NaOCl and H2O2. Unexpectedly, msr mutants have disparate resistance patterns when exposed to paraquat, a superoxide generator. The msrA mutant had a higher paraquat resistance level than the msrB mutant, which had a lower paraquat resistance level than the PAO1 strain. The expression levels of msrA showed an inverse correlation with the paraquat resistance level, and this atypical paraquat resistance pattern was not observed with msrB. Virulence testing using a Drosophila melanogaster model revealed that the msrA, msrB, and, to a greater extent, msrA msrB double mutants had an attenuated virulence phenotype. The data indicate that msrA and msrB are essential genes for oxidative stress protection and bacterial virulence. The pattern of expression and mutant phenotypes of P. aeruginosa msrA and msrB differ from previously characterized msr genes from other bacteria. Thus, as highly conserved genes, the msrA and msrB have diverse expression patterns and physiological roles that depend on the environmental niche where the bacteria thrive.201323687271
6061100.9973Isolation and characterisation of an enterocin P-producing Enterococcus lactis strain from a fresh shrimp (Penaeus vannamei). Screening for lactic acid bacteria (LAB) from fresh shrimp samples (Penaeus vannamei) collected from retail seafood markets in the Tunisian's coast, resulted in the isolation of an Enterococcus strain termed Q1. This strain was selected for its antagonistic activity against pathogenic bacteria such as Listeria monocytogenes, Pseudomonas aeruginosa, Lactococcus garvieae and against fungi (Aspergillus niger and Fusarium equiseti). The Q1 strain was characterised using standard morphological and biochemical tests, growth assays at different temperatures, pH and salinity. 16S rRNA, rpoA and pheS gene sequencing, as well as the 16S-23S rRNA intergenic spacer analyses, were combined to identify strain Q1 as a strain of Enterococcus lactis. The bacteriocin produced by E. lactis Q1 is thermostable, active in the pH range from 4.0 to 9.0 and has a bactericidal mode of action. The enterocin P structural gene was detected by specific PCR in strain E. lactis Q1, which is in good agreement with SDS-PAGE data of the purified bacteriocin. A lack of significant antibiotic resistance genes and virulence determinants was confirmed by specific PCRs. This work provides the first description of an enterocin P producer E. lactis strain isolated from a fresh shrimp. Based on its safety properties (absence of haemolytic activity, virulence factors and antibiotic resistance genes), this strain has the potential to be used as a natural additive or adjunct protective culture in food biopreservation and/or probiotic culture.201728265787
404110.9972Plasmid-borne cadmium resistance genes in Listeria monocytogenes are similar to cadA and cadC of Staphylococcus aureus and are induced by cadmium. pLm74 is the smallest known plasmid in Listeria monocytogenes. It confers resistance to the toxic divalent cation cadmium. It contains a 3.1-kb EcoRI fragment which hybridizes with the cadAC genes of plasmid pI258 of Staphylococcus aureus. When introduced into cadmium-sensitive L. monocytogenes or Bacillus subtilis strains, this fragment conferred cadmium resistance. The DNA sequence of the 3.1-kb EcoRI fragment contains two open reading frames, cadA and cadC. The deduced amino acid sequences are similar to those of the cad operon of plasmid pI258 of S. aureus, known to prevent accumulation of Cd2+ in the bacteria by an ATPase efflux mechanism. The cadmium resistance determinant of L. monocytogenes does not confer zinc resistance, in contrast to the cadAC determinant of S. aureus, suggesting that the two resistance mechanisms are slightly different. Slot blot DNA-RNA hybridization analysis showed cadmium-inducible synthesis of L. monocytogenes cadAC RNA.19948188605
5225120.9972Two genes involved in clindamycin resistance of Bacillus licheniformis and Bacillus paralicheniformis identified by comparative genomic analysis. We evaluated the minimum inhibitory concentrations of clindamycin and erythromycin toward 98 Bacillus licheniformis strains isolated from several types of fermented soybean foods manufactured in several districts of Korea. First, based on recent taxonomic standards for bacteria, the 98 strains were separated into 74 B. licheniformis strains and 24 B. paralicheniformis strains. Both species exhibited profiles of erythromycin resistance as an acquired characteristic. B. licheniformis strains exhibited acquired clindamycin resistance, while B. paralicheniformis strains showed unimodal clindamycin resistance, indicating an intrinsic characteristic. Comparative genomic analysis of five strains showing three different patterns of clindamycin and erythromycin resistance identified 23S rRNA (adenine 2058-N6)-dimethyltransferase gene ermC and spermidine acetyltransferase gene speG as candidates potentially involved in clindamycin resistance. Functional analysis of these genes using B. subtilis as a host showed that ermC contributes to cross-resistance to clindamycin and erythromycin, and speG confers resistance to clindamycin. ermC is located in the chromosomes of strains showing clindamycin and erythromycin resistance and no transposable element was identified in its flanking regions. The acquisition of ermC might be attributable to a homologous recombination. speG was identified in not only the five genome-analyzed strains but also eight strains randomly selected from the 98 test strains, and deletions in the structural gene or putative promoter region caused clindamycin sensitivity, which supports the finding that the clindamycin resistance of Bacillus species is an intrinsic property.202032271828
398130.9972The chloramphenicol-inducible catB gene in Agrobacterium tumefaciens is regulated by translation attenuation. Agrobacterium tumefaciens strains C58, A136, and BG53 are chloramphenicol resistant, and each contains the catB gene originally identified by Tennigkeit and Matzuran (Gene 99:113-116, 1991). The chloramphenicol acetyltransferase activity in all of the strains is chloramphenicol inducible. Examination of the catB gene in strain BG53 indicates that it is regulated by an attenuation mechanism similar to translation attenuation that regulates inducible catA genes resident in gram-positive bacteria and the inducible cmlA gene that confers chloramphenicol resistance in Pseudomonas spp.200212107148
6079140.9972Genomic and metabonomic methods reveal the probiotic functions of swine-derived Ligilactobacillus salivarius. BACKGROUND: As substitutes for antibiotics, probiotic bacteria protect against digestive infections caused by pathogenic bacteria. Ligilactobacillus salivarius is a species of native lactobacillus found in both humans and animals. Herein, a swine-derived Ligilactobacillus salivarius was isolated and shown to colonize the ileal mucous membrane, thereby promoting nutritional digestion, absorption, and immunity. To evaluate its probiotic role, the entire genome was sequenced, the genetic information was annotated, and the metabolic information was analyzed. RESULTS: The phylogenetic relationship indicated that the bacteria was closer to L. salivarius MT573555.1 and MT585431.1. Functional genes included transporters, membrane proteins, enzymes, heavy metal resistance proteins, and putative proteins; metabolism-related genes were the most abundant. The six types of metabolic pathways secreted by L. salivarius were mainly composed of secretory transmembrane proteins and peptides. The secretory proteins of L. salivarius were digestive enzymes, functional proteins that regulate apoptosis, antibodies, and hormones. Non-targeted metabolomic analysis of L. salivarius metabolites suggested that ceramide, pyrrolidone- 5- carboxylic acid, N2-acetyl-L-ornithine, 2-ethyl-2-hydroxybutyric acid, N-lactoyl-phenylalanine, and 12 others were involved in antioxidation, repair of the cellular membrane, anticonvulsant, hypnosis, and appetite inhibition. Metabolites of clavaminic acid, antibiotic X14889C, and five other types of bacteriocins were identified, namely phenyllactic acid, janthitrem G, 13-demethyl tacrolimus, medinoside E, and tertonasin. The adherence and antioxidation of L. salivarius were also predicted. No virulence genes were found. CONCLUSION: The main probiotic properties of L. salivarius were identified using genomic, metabonomic, and biochemical assays, which are beneficial for porcine feeding. Our results provided deeper insights into the probiotic effects of L. salivarius.202337648978
5389150.9972Identification and characterization of potential probiotic lactic acid bacteria isolated from pig feces at various production stages. Lactic acid bacteria (LAB) were isolated, identified, and characterized from pig feces at various growth stages and feed rations in order to be used as probiotic feed additives. Lactic acid bacteria numbers ranged from 7.10 ± 1.50 to 9.40 log CFUs/g for growing and lactating pigs, respectively. Isolates (n = 230) were identified by (GTG)5-polymerase chain reaction and partial sequence analysis of 16S rRNA. Major LAB populations were Limosilactobacillus reuteri (49.2%), Pediococcus pentosaceus (20%), Lactobacillus amylovorus (11.4%), and L. johnsonii (8.7%). In-vitro assays were performed, including surface characterization and tolerance to acid and bile salts. Several lactobacilli exhibited hydrophobic and aggregative characteristics and were able to withstand gastrointestinal tract conditions. In addition, lactobacilli showed starch- and phytate-degrading ability, as well as antagonistic activity against Gram-negative pathogens and the production of bacteriocin-like inhibitory substances. When resistance or susceptibility to antibiotics was evaluated, high phenotypic resistance to ampicillin, gentamicin, kanamycin, streptomycin, and tetracycline and susceptibility towards clindamycin and chloramphenicol was observed in the assayed LAB. Genotypic characterization showed that 5 out of 15 resistance genes were identified in lactobacilli; their presence did not correlate with phenotypic traits. Genes erm(B), strA, strB, and aadE conferring resistance to erythromycin and streptomycin were reported among all lactobacilli, whereas tet(M) gene was harbored by L. reuteri and L. amylovorus strains. Based on these results, 6 probiotic LAB strains (L. reuteri F207R/G9R/B66R, L. amylovorus G636T/S244T, and L. johnsonii S92R) can be selected to explore their potential as direct feed additives to promote swine health and replace antibiotics.202337020571
158160.9971Homology- and cross-resistance of Lactobacillus plantarum to acid and osmotic stress and the influence of induction conditions on its proliferation by RNA-Seq. In this study, homology- and cross-resistance of Lactobacillus plantarum L1 and Lactobacillus plantarum L2 to acid and osmotic stress were investigated. Meanwhile, its proliferation mechanism was demonstrated by transcriptomic analysis using RNA sequencing. We found that the homologous-resistance and cross-resistance of L. plantarum L1 and L. plantarum L2 increased after acid and osmotic induction treatment by lactic acid and sodium lactate solution in advance, and the survival rate of live bacteria was improved. In addition, the count of viable bacteria of L. plantarum L2 significantly increased cultivated at a pH 5.0 with a 15% sodium lactate sublethal treatment, compared with the control group. Further study revealed that genes related to membrane transport, amino acid metabolism, nucleotide metabolism, and cell growth were significantly upregulated. These findings will contribute to promote high-density cell culture of starter cultures production in the fermented food industry.202133945164
3743170.9971Expression of glycopeptide-resistance gene in response to vancomycin and teicoplanin in the cardiac vegetations of rabbits infected with VanB-type Enterococcus faecalis. VanB-type resistance in enterococci corresponds to resistance to vancomycin but not to resistance to the related glycopeptide teicoplanin, because the vanB gene cluster is activated by the VanR(B)-VanS(B) 2-component regulatory system in response to vancomycin but not to teicoplanin. Mutations in the vanS(B) gene allow for constitutive or teicoplanin-inducible expression of the resistance genes. To analyze in vivo expression of the van genes in rabbits with experimental endocarditis, a VanB-type Enterococcus faecalis with a transcriptional fusion between the P(YB) promoter of resistance genes and the gfpmut1 gene for the green-fluorescent protein in the chromosome was constructed. Rounded heaps containing fluorescent bacteria were detected in vegetation slides from rabbits treated with vancomycin but not in those from control rabbits, revealing induction of a tightly regulated vanB gene cluster. Teicoplanin-resistant mutants were detected as fluorescent bacteria in rabbits treated with teicoplanin. Thus, the reporter system monitored expression of a glycopeptide-resistance gene in vivo at a single-cell level.200414702158
407180.9971Molecular cloning and characterization of two lincomycin-resistance genes, lmrA and lmrB, from Streptomyces lincolnensis 78-11. Two different lincomycin-resistance determinants (lmrA and lmrB) from Streptomyces lincolnensis 78-11 were cloned in Streptomyces lividans 66 TK23. The gene lmrA was localized on a 2.16 kb fragment, the determined nucleotide sequence of which encoded a single open reading frame 1446 bp long. Analysis of the deduced amino acid sequence suggested the presence of 12 membrane-spanning domains and showed significant similarities to the methylenomycin-resistance protein (Mmr) from Streptomyces coelicolor, the QacA protein from Staphylococcus aureus, and several tetracycline-resistance proteins from both Gram-positive and Gram-negative bacteria, as well as to some sugar-transport proteins from Escherichia coli. The lmrB gene was actively expressed from a 2.7 kb fragment. An open reading frame of 837 bp could be localized which encoded a protein that was significantly similar to 23S rRNA adenine(2058)-N-methyltransferases conferring macrolide-lincosamide-streptogramin resistance. LmrB also had putative rRNA methyltransferase activity since lincomycin resistance of ribosomes was induced in lmrB-containing strains. Surprisingly, both enzymes, LmrA and LmrB, had a substrate specificity restricted to lincomycin and did not cause resistance to other lincosamides such as celesticetin and clindamycin, or to macrolides.19921328813
6238190.9971A novel glutamate-dependent acid resistance among strains belonging to the Proteeae tribe of Enterobacteriaceae. Morganella, Providencia and Proteus strains were capable of surviving pH 2.0 for 1 h if glutamate was present. These strains did not have glutamic acid decarboxylase activity and the gadAB genes were not detected in any of these bacteria. When exposed to pH 2.0 acid shocks, the survival rate of these bacteria was significantly increased with glutamate concentrations as low as 0.3 mM in the acid media. Escherichia coli cells incubated at pH 3.4 consumed four times more glutamate and produced at least 7-fold more gamma-amino butyric acid than Morganella, Providencia and Proteus strains. These results indicate that strains belonging to the Proteeae tribe might have novel glutamate dependent acid-resistance mechanisms.200415321677