Gram-negative Bacterial Species Research Articles

Plasmid-mediated resistance of some Gram-negative bacterial species to brands of cefuroxime and ceftriaxone

Twenty two different strains of Gram-negative bacteria, namely Pseudomonas aeruginosa, Proteus mirabilis, Klebsiella pneumoniae, Escherichia coli andHaemophilus influenzae were tested for susceptibility to 10 different brands of ceftriaxone and cefuroxime. Some of the highly resistant strains were processed for antibiotic resistance curing and extraction of plasmid DNA. Of the 10 brands of ceftriaxone and cefuroxime, 2 brands of ceftriaxone were more effective on the Gram-negative bacteria than the remaining ceftriaxone and cefuroxime brands. The highly resistant strains were resistant not only to these 2 brands but also to tetracycline, amoxicillin, cotrimoxazole, nitrofurantoin, gentamicin, nalidixic acid and ofloxacin, used in antibiogram and as also evident in high minimum inhibitory concentrations recorded for the strains against the brands of ceftriaxone and cefuroxime. Some of the resistant strains were found to lose their resistance to curing following treatment with different concentrations of a mutagen, acridine orange. Of the 8 multiple drug resistant (MDR) strains of the bacteria selected for plasmid DNA, 5 strains and a sensitive strain of H. influenzae had single plasmid DNA copy ranging in size between 24 - 28 kb. The high level multiple drug resistance of the bacterial strains tested was due not only to variation in the brands of ceftriaxone and cefuroxime but more especially to R-plasmid mediation. Key words: Plasmid mediated resistance, bacterial spp., cefuroxime and ceftriaxone.

Microbial evaluation and public health implications of urine as alternative therapy in clinical pediatric cases: health implication of urine therapy

BACKGROUND: Cultural means of pediatric treatment during ill health is a mainstay in Africa, and though urine has been known to contain enteric pathogens, urine therapy is still culturally applicable in some health conditions and also advocated as alternative therapy. The study therefore, is to evaluate the microbial contents and safety of urine. METHODS: Urinary bacteria from cows and healthy children aged 5-11 years were identified by conventional phenotypic methods and antimicrobial susceptibility testing was performed using modified agar disc and well-diffusion methods. RESULTS: A total of 116 bacterial isolates (n = 77 children; n = 39 cows) were identified as Bacillus (10.4%; 5.1%)), Staphylococcus (2.6%; 2.6%), Citrobacter (3.9%; 12.8%), Escherichia coli (36.4%; 23.1%), Klebsiella (7.8%; 12.8%), Proteus (18.2%; 23.1%), Pseudomonas (9.1%; 2.6%), Salmonella (3.9%; 5.1%) and Shigella (7.8%; 12.8%) spp. Antibiotic resistance rates of the Gram-positive bacteria were high (50.0-100%), except in Bacillus strains against chloramphenicol, gentamicin and tetracycline (14.3%), while higher resistance rates were recorded among the Gram-negative bacteria except in Citrobacter (0.0%) and Proteus (8.5%) spp. against gentamicin and tetracycline respectively. The Gram-negative bacteria from ito malu (cow urine) were more resistant bacteria except in Citrobacter (20.0%) and Shigella spp. (0.0%) against tetracycline and Proteus spp. (11.1%), (22.2%) against amoxicillin and tetracycline respectively. Multiple antibiotic resistance (MAR) rates recorded in children urinal bacterial species were 37.5-100% (Gram-positive) and 12.5-100% (Gramnegative), while MAR among the cow urinal bacteria was 12.5-75.0% (Gram-positive) and 25.0-100% (Gram-negative). Similar higher resistance rates were also recorded among the Gram-negative bacterial species from urine specimens against the paediatric antibiotic suspensions. CONCLUSION: The study reported presence of multiple antibiotic-resistant indicator bacteria in human urine and ito malu used as alternative remedy in pediatric health conditions like febrile convulsion

Resistance to polymyxins: Mechanisms, frequency and treatment options

Polymyxins act by binding to lipid A moiety of the bacterial lipopolysaccharide and subsequently disintegrating the bacterial membranes. The most important mechanism of resistance includes modifications of the bacterial outer membrane structure, including lipopolysaccharide. Lipopolysaccharide modification is mostly mediated by PmrA/PmrB and PhoP/PhoQ two-component regulatory systems. These mechanisms exist with some differences in many gram-negative bacterial species. Resistance to polymyxins is generally less than 10%. In specific regions, such as the Mediterranean basin, Korea and Singapore, they tend to be higher. Heteroresistance to polymyxins is associated with exposure to polymyxins and especially suboptimal therapeutic dosage. Polymyxin combination regimens, tigecycline and fosfomycin may be useful options for the treatment of polymyxin-resistant gram-negative infections.

The cyclotide cycloviolacin O2 from Viola odorata has potent bactericidal activity against Gram-negative bacteria

To determine the antibacterial activity of small cyclic plant proteins, i.e. cyclotides, and the importance of the surface exposed charged residues for activity. Prototypic cyclotides, including the Möbius kalata B1 and the bracelet cycloviolacin O2 (cyO2), were isolated using reversed-phase HPLC. Initial activity screenings were conducted using radial diffusion assays (RDAs) and MIC assays with Salmonella enterica serovar Typhimurium LT2, Escherichia coli and Staphylococcus aureus as test strains. For the most active peptide, cyO2, time-kill kinetics was determined in sodium phosphate buffer (containing 0.03% trypticase soy broth) against several Gram-negative and Gram-positive bacterial species. Charged residues in cyO2 were chemically modified and activity was determined in time-kill assays. CyO2 was the most active cyclotide and efficiently inhibited the growth of S. enterica serovar Typhimurium LT2 and E. coli in RDAs and MIC assays, while the other peptides were less active. In time-kill assays, cyO2 also had bactericidal activity against the Gram-negative species Klebsiella pneumoniae and Pseudomonas aeruginosa. In contrast, none of the cyclotides had high activity against S. aureus. Chemical masking of the charged Glu and Lys residues in cyO2 caused a near total loss of activity against Salmonella, while masking Arg caused a less pronounced activity reduction. CyO2 is a cyclotide with potent activity against Gram-negative bacteria. The charged residues in cyO2 are all required for optimum antibacterial activity. In combination with its previously demonstrated cytotoxic activity against cancer cells and the general stability of cyclotides, cyO2 provides a promising scaffold for future drug design.

Comparative in vitro activity of cefditoren and other antimicrobials against Enterobacteriaceae causing community-acquired uncomplicated urinary tract infections in women: a Spanish nationwide multicenter study

Cefditoren is a third-generation orally administered cephalosporin with a broad spectrum of activity against Gram-positive and Gram-negative bacterial species. After an oral 400-mg single dose, the mean concentrations in urine are 186.5 mg/L at 2 to 4 h and 12.7 mg/L at 8 to 12 h, and it is a potential drug to be used in the treatment of urinary tract infection (UTI). We performed a multicenter nationwide study in Spain in order to determine the in vitro activity of cefditoren and other comparative agents against Enterobacteriaceae causing community-acquired uncomplicated UTI in women. From June 2008 to March 2009, 89 institutions participated in the study. A total of 2152 Enterobacteriaceae were collected and sent to a coordinating laboratory where identification and antimicrobial susceptibility testing was performed against 20 antimicrobials using an automated microdilution method (MicroScan; Siemens, Sacramento, CA). Cefditoren MICs were determined by the broth microdilution method (Clinical and Laboratory Standards Institute guidelines) using the same inoculum. Microorganisms isolated were Escherichia coli (81.8%), Klebsiella pneumoniae (7.9%), Proteus mirabilis (5.2%), and others (5.1%). A total of 51 isolates (2.4%) were extended-spectrum β-lactamase (ESBL) producers, 3 (0.1%) produced plasmidic AmpC enzymes, and 64 (2.9%) produced chromosomal AmpC. The MIC 50/MIC 90 (mg/L) of cefditoren against all isolates was 0.12/0.5. Cefditoren inhibited 96.5% of isolates at 1 mg/L and was uniformly active against all isolates with the exception of strains producing ESBLs or AmpC enzymes. The MIC 50/MIC 90 of other antimicrobials were ampicillin (AMP) >16/>16, amoxicillin/clavulanic acid (A/C) ≤8/4/16/8, cefuroxime (FUR) ≤4/8, cefotaxime ≤1/≤1, ciprofloxacin (CIP) ≤0.12/>2, trimethoprim/sulfamethoxazole (SxT) ≤2/38/>4/76, and fosfomycin (FOS) ≤16/≤16. The respective percentages of resistance were 61%, 17.2%, 5.5%, 2.3%, 20.2%, 27.4%, and 4.8%. The activity of cefditoren against Enterobacteriaceae producing community-acquired uncomplicated UTI in women was superior to that of AMP, A/C, FUR, CIP, and SxT and similar to that of FOS.

Genetically Engineered Virulent Phage Banks in the Detection and Control of Emergent Pathogenic Bacteria

Natural outbreaks of multidrug-resistant microorganisms can cause widespread devastation, and several can be used or engineered as agents of bioterrorism. From a biosecurity standpoint, the capacity to detect and then efficiently control, within hours, the spread and the potential pathological effects of an emergent outbreak, for which there may be no effective antibiotics or vaccines, become key challenges that must be met. We turned to phage engineering as a potentially highly flexible and effective means to both detect and eradicate threats originating from emergent (uncharacterized) bacterial strains. To this end, we developed technologies allowing us to (1) concurrently modify multiple regions within the coding sequence of a gene while conserving intact the remainder of the gene, (2) reversibly interrupt the lytic cycle of an obligate virulent phage (T4) within its host, (3) carry out efficient insertion, by homologous recombination, of any number of engineered genes into the deactivated genomes of a T4 wild-type phage population, and (4) reactivate the lytic cycle, leading to the production of engineered infective virulent recombinant progeny. This allows the production of very large, genetically engineered lytic phage banks containing, in an E. coli host, a very wide spectrum of variants for any chosen phage-associated function, including phage host-range. Screening of such a bank should allow the rapid isolation of recombinant T4 particles capable of detecting (ie, diagnosing), infecting, and destroying hosts belonging to gram-negative bacterial species far removed from the original E. coli host.

Tigecycline – how powerful is it in the fight against antibiotic-resistant bacteria?

Tigecycline is a semisynthetic analogue of earlier tetracyclines and represents the first member of a novel class of antimicrobials - glycylcyclines - recently approved for clinical use. It is active against a broad range of gram-negative and gram-positive bacterial species including clinically important multidrug-resistant nosocomial and community-acquired bacterial pathogens. The exact molecular basis of tigecycline action is not clear at present, although similarly to the tetracyclines, it has been shown to inhibit the translation elongation step by binding to the ribosome 30S subunit and preventing aminoacylated tRNAs to accommodate in the ribosomal A site. Importantly, tigecycline overcomes the action of ribosomal protection proteins and is not a substrate for tetracycline efflux pumps of most bacteria - well-known and prevalent cellular mechanisms of microbial tetracycline resistance. The present review summarizes current knowledge on the molecular mechanism of the tigecycline action, antibacterial activity against various bacteria, clinical application, development of resistance to glycylcyclines.

Conformation Change in a Self-recognizing Autotransporter Modulates Bacterial Cell-Cell Interaction

Bacteria mostly live as multicellular communities, although they are unicellular organisms, yet the mechanisms that tie individual bacteria together are often poorly understood. The adhesin involved in diffuse adherence (AIDA-I) is an adhesin of diarrheagenic Escherichia coli strains. AIDA-I also mediates bacterial auto-aggregation and biofilm formation and thus could be important for the organization of communities of pathogens. Using purified protein and whole bacteria, we provide direct evidence that AIDA-I promotes auto-aggregation by interacting with itself. Using various biophysical and biochemical techniques, we observed a conformational change in the protein during AIDA-AIDA interactions, strengthening the notion that this is a highly specific interaction. The self-association of AIDA-I is of high affinity but can be modulated by sodium chloride. We observe that a bile salt, sodium deoxycholate, also prevents AIDA-I oligomerization and bacterial auto-aggregation. Thus, we propose that AIDA-I, and most likely other similar autotransporters such as antigen 43 (Ag43) and TibA, organize bacterial communities of pathogens through a self-recognition mechanism that is sensitive to the environment. This could permit bacteria to switch between multicellular and unicellular lifestyles to complete their infection.

In vitro activity of XF-73, a novel antibacterial agent, against antibiotic-sensitive and -resistant Gram-positive and Gram-negative bacterial species

The antibacterial activity of XF-73, a dicationic porphyrin drug, was investigated against a range of Gram-positive and Gram-negative bacteria with known antibiotic resistance profiles, including resistance to cell wall synthesis, protein synthesis, and DNA and RNA synthesis inhibitors as well as cell membrane-active antibiotics. Antibiotic-sensitive strains for each of the bacterial species tested were also included for comparison purposes. XF-73 was active [minimum inhibitory concentration (MIC) 0.25–4mg/L] against all of the Gram-positive bacteria tested, irrespective of the antibiotic resistance profile of the isolates, suggesting that the mechanism of action of XF-73 is unique compared with the major antibiotic classes. Gram-negative activity was lower (MIC 1mg/L to >64mg/L). Minimum bactericidal concentration data confirmed that the activity of XF-73 was bactericidal. Time–kill kinetics against healthcare-associated and community-associated meticillin-resistant Staphylococcus aureus isolates demonstrated that XF-73 was rapidly bactericidal, with >5log10 kill obtained after 15min at 2× MIC, the earliest time point sampled. The post-antibiotic effect (PAE) for XF-73 under conditions where the PAE for vancomycin was <0.4h was found to be >5.4h. XF-73 represents a novel broad-spectrum Gram-positive antibacterial drug with potentially beneficial characteristics for the treatment and prevention of Gram-positive bacterial infections.

Synthesis, characterization, and biological activity studies on (E)-N′-[2-hydroxy-1,2-di(pyridin-2-yl)ethylidine]aroyl hydrazides and their copper(II) complexes

The reaction of copper(II) salts with (E)-N-(2-hydroxy-1,2-di(pyridin-2-yl)ethylidene)aroyl hydrazide (H2L1, H2L2, H3L3) or (E)-N-(2-hydroxy-1,2-di(pyridin-2-yl)ethylidene) isonicotinohydrazide (H2L4) afforded the complexes [(L)Cu(H2O)3], [(H2L)Cu(OAc)(H2O)], [(HL)Cu(OAc)] n , [(H2L)Cu(H2O)](ClO4)2 and [(H2L)Cu(OAc)(H2O)], where n = 1 or 2 and L is the dinegative ion of the ligands. The ligands and their complexes are characterized by elemental analyses, spectral (IR, NMR, electronic, and ESR) and magnetic studies. The FT-IR indicates that the ligands are neutral or anionic polydentate. The number of the coordinating centers depends on the nature of the metal used and the reaction conditions. The room temperature magnetic moment values, electronic spectra and ESR data indicate square planar, trigonal bipyramidal, square pyramidal, and distorted octahedral ligand fields around copper(II). Thermal decomposition of the complexes was monitored by TG and DTG under N2 and the thermal decomposition mechanisms are given. The compounds were screened for their antimicrobial activities on some Gram-positive and Gram-negative bacterial species. The free ligands are inactive against all studied bacteria. The complexes have variable activity with the most active [(H2L)Cu(H2O)](ClO4)2, where H2L is H2L1 or H2L2. The minimum inhibition concentrations for these two complexes were determined. These biological activity results are related to the structures of the compounds.

Substrate-mediated Stabilization of a Tetrameric Drug Target Reveals Achilles Heel in Anthrax

Bacillus anthracis is a gram-positive spore-forming bacterium that causes anthrax. With the increased threat of anthrax in biowarfare, there is an urgent need to characterize new antimicrobial targets from B. anthracis. One such target is dihydrodipicolinate synthase (DHDPS), which catalyzes the committed step in the pathway yielding meso-diaminopimelate and lysine. In this study, we employed CD spectroscopy to demonstrate that the thermostability of DHDPS from B. anthracis (Ba-DHDPS) is significantly enhanced in the presence of the substrate, pyruvate. Analytical ultracentrifugation studies show that the tetramer-dimer dissociation constant of the enzyme is 3-fold tighter in the presence of pyruvate compared with the apo form. To examine the significance of this substrate-mediated stabilization phenomenon, a dimeric mutant of Ba-DHDPS (L170E/G191E) was generated and shown to have markedly reduced activity compared with the wild-type tetramer. This demonstrates that the substrate, pyruvate, stabilizes the active form of the enzyme. We next determined the high resolution (2.15 A) crystal structure of Ba-DHDPS in complex with pyruvate (3HIJ) and compared this to the apo structure (1XL9). Structural analyses show that there is a significant (91 A(2)) increase in buried surface area at the tetramerization interface of the pyruvate-bound structure. This study describes a new mechanism for stabilization of the active oligomeric form of an antibiotic target from B. anthracis and reveals an "Achilles heel" that can be exploited in structure-based drug design.

Characteristic of Two Bacteriocin-Producing Enterococcus Strains

ABSTRACTTwo newly isolated strains from yellow cheese identified as Enterococcus was screened for bacteriocin activity. It was found that the tested strains displayed a broad spectrum activity, even against Gram-negative bacterial species. The agents were proven to be of protein nature by treatment with proteinase K. High temperature treatment revealed strong thermostable properties of the molecule.

S. oneidensis Moves Electrons across Membranes to Minerals

Shewanella oneidensis and other anaerobic gram-negative bacterial species depend on several protein types to connect them to external and insoluble minerals containing iron or manganese. Those proteins act as wiring and deliver electrons to those minerals, which serve as extracellular respiratory electron acceptors, while the cells generate metabolic energy, according to biochemists Robert S. Hartshorne and David Richardson of the University of East Anglia, in Norwich, United Kingdom, and their collaborators.

Antimicrobial potentials of indigenous Lactobacillus strains on gram-negative indicator bacterial species from Clarias gariepinus (Burchell.) microbial inhibition of fish-borne pathogens

This study tries to evaluate the ability of L. fermentum LbFF4 isolated from Nigerian fermented food (fufu) and L. plantarum LbOG1 from a beverage (ogi), to inhibit some fish bacterial pathogens (Citrobacter, Enterobacter, Escherichia coli, Klebsiella, Proteus, Pseudomonas and Salmonella species) under in vitro conditions. Overall phenotypic antibiotic resistance of 124 Gram-negative bacterial isolates obtained from the gut contents of cat fish, Clarias gariepinus, using agar disc-diffusion method, indicated very high resistance to amoxicillin (88.8%), augmentin (85.1%), cotrimoxazole (80.6%), tetracycline (72.3%), gentamicin (61.9%) and nalidixic acid (57.5%). Multiple antibiotic resistance (MAR) of 37.5 - 87.5% were also recorded.None of the forty four Lactobacillus strains (L. brevis, L. delbruekii, L. fermentum, L. plantarum and L. reuterii) isolated from the gut contents of C. gariepinus was inhibitory in vitro towards the Gram-negative bacterial species. However, L.fermentum LbFF4 and L. plantarum LbOG1 exhibited in vitro antibacterial activitiesagainst 41.1 and 47.6% of the Gram-negative bacterial species respectively. The susceptibility patterns of the indicator pathogens using the probiotic candidates were significant. The potential probiotic candidates were able to survive relatively low pH (3.5 - 5.5) and the fish bile. This study therefore, signifies that lactobacilli-based probiotic candidates from Nigerian fermented foods and beverages can serve as adjunct, inhibitory food-supplements in the control of bacterial fish-borne pathogens of C. gariepinus. Key words: Antibiotic resistance, antimicrobials, aquaculture, Clarias gariepinus, Lactobacillus, probiotics.

Synthesis, characterization, and biological activity studies of copper(II)–metal(II) binuclear complexes of dipyridylglyoxal bis(2-hydroxybenzoyl hydrazone)

A new series of copper(II) mononuclear and copper(II)–metal(II) binuclear complexes [(H2L)Cu] ⋅ H2O, [CuLM] ⋅ nH2O, and [Cu(H2L)M(OAc)2] ⋅ nH2O, n = 1–2, M = Co(II), Ni(II), Cu(II), or Zn(II), and L is the anion of dipyridylglyoxal bis(2-hydroxybenzoyl hydrazone), H4L, were synthesized and characterized. Elemental analyses, molar conductivities, and FT-IR spectra support the formulation of these complexes. IR data suggest that H4L is dibasic tetradentate in [(H2L)Cu] ⋅ H2O and [Cu(H2L)M(OAc)2] ⋅ nH2O but tetrabasic hexadentate in [CuLM] ⋅ nH2O (n = 1–2). Thermal studies indicate that waters are of crystallization and the complexes are thermally stable to 347–402°C depending upon the nature of the complex. Magnetic moment values indicate magnetic exchange interaction between Cu(II) and M(II) centers in binuclear complexes. The electronic spectral data show that d–d transitions of CuN2O2 in the mononuclear complex are blue shifted in binuclear complexes in the sequences: Cu–Cu > Cu–Ni > Cu–Co > Cu–Zn, suggesting that the binuclear complexes [CuLM] ⋅ nH2O are more planar than the mononuclear complex. The structures of complexes were optimized through molecular mechanics applying MM +force field coupled with molecular dynamics simulation. [(H2L)Cu] ⋅ nH2O, [CuLM] ⋅ nH2O, and the free ligand were screened for antimicrobial activities on some Gram-positive and Gram-negative bacterial species. The free ligand is inactive against all studied bacteria. The screening data showed that [CuLCu] ⋅ H2O > [(H2L)Cu] ⋅ H2O > [CuLZn] ⋅ H2O > [CuLNi] ⋅ 2H2O ≈ [CuLCo] ⋅ H2O in order of biological activity. The data are discussed in terms of their compositions and structures.

Autoaggregation Response of Fusobacterium nucleatum

Fusobacterium nucleatum is a gram-negative oral bacterial species associated with periodontal disease progression. This species is perhaps best known for its ability to adhere to a vast array of other bacteria and eukaryotic cells. Numerous studies of F. nucleatum have examined various coaggregation partners and inhibitors, but it is largely unknown whether these interactions induce a particular genetic response. We tested coaggregation between F. nucleatum ATCC strain 25586 and various species of Streptococcus in the presence of a semidefined growth medium containing saliva. We found that this condition could support efficient coaggregation but, surprisingly, also stimulated a similar degree of autoaggregation. We further characterized the autoaggregation response, since few reports have examined this in F. nucleatum. After screening several common coaggregation inhibitors, we identified l-lysine as a competitive inhibitor of autoaggregation. We performed a microarray analysis of the planktonic versus autoaggregated cells and found nearly 100 genes that were affected after only about 60 min of aggregation. We tested a subset of these genes via real-time reverse transcription-PCR and confirmed the validity of the microarray results. Some of these genes were also found to be inducible in cell pellets created by centrifugation. Based upon these data, it appears that autoaggregation activates a genetic program that may be utilized for growth in a high cell density environment, such as the oral biofilm.

Antioxidant and antimicrobial properties of Teucrium arduini L. ( Lamiaceae) flower and leaf infusions ( Teucrium arduini L. antioxidant capacity)

Antioxidant and antimicrobial activities, as well as total phenol (TP, Folin–Ciocalteu method) and phenolic acid (UPLC–MS/MS) contents of leaf and flower infusions of Teucrium arduini L. from six different mountainous localities in Croatia (Učka, Vošac, Sveti Jure, Snježnica, Vaganac, Šušanj) were analysed in this study. Antioxidant capacity was evaluated using the ferric reducing/antioxidant power (FRAP) assay, as well as 2,2-diphenyl-1-picrylhydrazyl (DPPH), and 2,2′-azinobis (3-ethylbenzthiazoline-6-sulphonic acid) (ABTS) radical scavenging assays. The antioxidant potency composite index (ACI), giving equal weight to all three methods used to quantify antioxidant capacity, was the highest for the sample from Vošac (96.7) among flower infusions, while maximum ACI (100) was determined for the infusion from Učka among leaf infusions. Strong positive correlation was found between the total phenols and ACI for leaf ( r = 0.953) and flower ( r = 0.977) infusions. Our results point to significantly ( p < 0.05) different TP content between leaf and flower infusions, as well as across localities. Leaf infusions of T. arduini from Šušanj exhibited marked antibacterial activity against Staphylococcus aureus, while none of the tested infusions exhibited antimicrobial activity against gram-negative bacterial species, or the tested fungal species.

Synthesis, Characterization, and Biological Activity of Substituted Thiazole-5-carboxaldehydes and Their Ylidenenitriles Derivatives

The Vilsmeier–Haack reaction of 2-amino -4-(4-substituted phenyl)-thiazoles 1, in the presence of micellar media, gives formylated derivatives 2, which upon hydrolysis afforded thiazole-5-carboxaldehydes 3. Microwave-assisted Knoevenagel condensation of 3 with active methylene compounds, in the presence of piperidine as catalyst, gives excellent yields of ylidenenitrile compounds 4. The structures of the newly synthesized compounds were established on the basis of elemental analysis, IR, 1H NMR, and 13C NMR spectral analysis. All newly synthesized compounds were screened for antibacterial activity using two Gram-positive and one Gram-negative bacterial species and their antifungal activity was screened using two fungal species.

One-Pot, Multicomponent Condensation Reaction in Neutral Conditions: Synthesis, Characterization, and Biological Studies of Fused Thiazolo[2,3-b]quinazolinone Derivatives

A new series of 12-(2-chloro-6-quinoline-3-yl)-3,3,8-substituted-2,3,4,12-tetrahydro-benzo[4,5]thiazolo[2,3-b]quinazolin-1-ones 4 was synthesized in one pot by condensing various 2-chloro-3-formylquinolines 1, 2-amino-6-substituted-benzothiazoles 2, and 1,3-cyclohexanedione 3 in ethanol. All the compounds were characterized by IR, 1H NMR, 13C NMR spectra and elemental analysis. All the synthesized compounds were screened for their antibacterial activity against Grampositive bacterial species Bacillus cereus and Bacillus substilus, Gram-negative bacterial species Escherichia coli, and their fungicidal activity against Aspergillus niger, Fuserium oxisporum, and Rhizopus species.

Quorum Sensing Regulation of the Two hcp Alleles in Vibrio cholerae O1 Strains

BackgroundThe type VI secretion system (T6SS) has emerged as a protein secretion system important to several Gram-negative bacterial species. One of the common components of the system is Hcp, initially described as a hemolysin co-regulated protein in a serotype O17 strain of Vibrio cholerae. Homologs to V. cholerae hcp genes have been found in all characterized type VI secretion systems and they are present also in the serotype O1 strains of V. cholerae that are the cause of cholera diseases but seemed to have non-functional T6SS.Methodology/Principal FindingsThe serotype O1 V. cholerae strain A1552 was shown to express detectable levels of Hcp as determined by immunoblot analyses using polyclonal anti-Hcp antiserum. We found that the expression of Hcp was growth phase dependent. The levels of Hcp in quorum sensing deficient mutants of V. cholerae were compared with the levels in wild type V. cholerae O1 strain A1552. The expression of Hcp was positively and negatively regulated by the quorum sensing regulators HapR and LuxO, respectively. In addition, we observed that expression of Hcp was dependent on the cAMP-CRP global transcriptional regulatory complex and required the RpoN sigma factor.Conclusion/SignificanceOur results show that serotype O1 strains of V. cholerae do express Hcp which is regarded as one of the important T6SS components and is one of the secreted substrates in non-O1 non-O139 V. cholerae isolates. We found that expression of Hcp was strictly regulated by the quorum sensing system in the V. cholerae O1 strain. In addition, the expression of Hcp required the alternative sigma factor RpoN and the cAMP-CRP global regulatory complex. Interestingly, the environmental isolates of V. cholerae O1 strains that showed higher levels of the HapR quorum sensing regulator in comparison with our laboratory standard serotype O1 strain A1552 where also expressing higher levels of Hcp.