Diverse Antimicrobial Compounds Research Articles

A vast repertoire of secondary metabolites potentially influences community dynamics and biogeochemical processes in cold seeps.

In deep-sea cold seeps, microbial communities thrive on the geological seepage of hydrocarbons and inorganic compounds, differing from photosynthetically driven ecosystems. However, their biosynthetic capabilities remain largely unexplored. Here, we analyzed 81 metagenomes, 33 metatranscriptomes, and 7 metabolomes derived from nine different cold seep areas to investigate their secondary metabolites. Cold seep microbiomes encode diverse and abundant biosynthetic gene clusters (BGCs). Most BGCs are affiliated with understudied bacteria and archaea, including key mediators of methane and sulfur cycling. The BGCs encode diverse antimicrobial compounds that potentially shape community dynamics and various metabolites predicted to influence biogeochemical cycling. BGCs from key players are widely distributed and highly expressed, with their abundance and expression levels varying with sediment depth. Sediment metabolomics reveals unique natural products, highlighting uncharted chemical potential and confirming BGC activity in these sediments. Overall, these results demonstrate that cold seep sediments serve as a reservoir of hidden natural products and sheds light on microbial adaptation in chemosynthetically driven ecosystems.

Evaluation of Antifungal Activity of Endophytic Bacillus spp. and Identification of Secondary Metabolites Produced Against the Phytopathogenic Fungi.

Endophytic bacteria serve as a rich source of diverse antimicrobial compounds. Recently, there has been a growing interest in utilizing endophytic Bacillus spp. as biological agents against phytogenic fungi, owing to their potential to produce a wide range of antimicrobial substances. The objective of this research was to investigate the protective abilities of 15 endophytic Bacillus spp. isolated from previous study from wheat plant, against the phytopathogenic fungi, Fusarium graminearum and Macrophomina phaseolina. A dual culture plate assay was conducted as a preliminary analysis, revealing that 7 out of 15 endophytic Bacillus spp. demonstrated inhibition against one or both of the phytopathogenic fungi used in this study. All seven endophytes were further assessed for the presence of diffusible antifungal metabolites. The cultures were grown in potato dextrose broth for 120h, and the cell-free supernatant was extracted and analyzed using the cup plate method. The methanolic extract yielded similar results to the dual culture plate analysis, except for WL2-15. Additionally, deformities in the mycelial structure were examined under the light microscope upon exposure to methanolic extract. Furthermore, the analysis and identification of metabolites were carried out via gas chromatography-mass spectrometry of methanolic extract from selected seven endophytic Bacillus spp. The chromatogram revealed the presence of some major peaks such as tridecanoic acid, methyl ester, hydroperoxide, 1-methylbutyl, 9-octadecenamide, (z)-, hexane-1,3,4-triol, 3,5-dimethyl- tetradecanoic acid. To the best of our knowledge, this is the first report of these biocontrol agents in endophytic Bacillus spp. Interestingly, volatile organic compound production was also seen in all the isolates against the phytopathogenic fungi.

Streptomyces tagetis sp. nov., a chromomycin producing bacteria isolated from the roots of Tagetes patula.

A novel halotolerant actinobacterium, designated as RG38T, capable of producing black extracellular melanin pigment on SP2 agar, was isolated from the roots of Tagetes patula. Comparative analysis of the 16S rRNA gene sequence revealed the highest similarity to Streptomyces collinus NBRC 12759T (99.3%). Phylogenetic analysis showed that strain RG38T clustered within the genus Streptomyces forming a monophyletic cluster with its close relatives. The average nucleotide identity (ANI), digital DNA-DNA hybridization (dDDH), and amino-acid identity (AAI) values between strain RG38T and related species within the genus Streptomyces were below the standard threshold for prokaryotic species delineation. The DNA G + C content of the strain RG38T was determined to be 73.3%. The genome size measured 7,150,598 bp comprising 17 contigs and encompassed 6,053 protein coding genes. AntiSMASH analysis of the whole genome revealed 35 putative biosynthetic gene clusters (BGCs) responsible for various secondary metabolites. Among these clusters, two gene clusters exhibited 100% similarity to the chromomycin A3, albaflavenone, and anthracimycin, respectively. These compounds were reported to possess significant anticancer and antibacterial activities. LC-MS-based analysis, coupled with further isolation studies, confirmed the production of chromomycins A2 (1), A3 (2), and their derivatives, along with their antibiotic activities. These findings underscore the potential of this novel strain as a novel resource for the discovery of diverse antimicrobial compounds. This study is the first to report an antimicrobial compound producing Streptomyces species isolated from medicinal plant T. patula. Based on a polyphasic study, the strain RG38T isolated from an unexplored habitat with a high potential for new natural products represents a novel species within the genus Streptomyces. Accordingly, we propose the name Streptomyces tagetis sp. nov. for this novel species, with the type strain is RG38T (=KCTC 49624T = TBRC 15113T).

Streptomyces as a promising biological control agents for plant pathogens.

Plant diseases caused by pathogenic microorganisms in agriculture present a considerable obstacle, resulting in approximately 30-40% crop damage. The use of conventional techniques to manage these microorganisms, i.e., applying chemical pesticides and antimicrobials, has been discovered to have adverse effects on human health and the environment. Furthermore, these methods have contributed to the emergence of resistance among phytopathogens. Consequently, it has become imperative to investigate natural alternatives to address this issue. The Streptomyces genus of gram-positive bacteria is a potentially viable natural alternative that has been extensively researched due to its capacity to generate diverse antimicrobial compounds, such as metabolites and organic compounds. Scientists globally use diverse approaches and methodologies to extract new bioactive compounds from these bacteria. The efficacy of bioactive compounds in mitigating various phytopathogens that pose a significant threat to crops and plants has been demonstrated. Hence, the Streptomyces genus exhibits potential as a biological control agent for combating plant pathogens. This review article aims to provide further insight into the Streptomyces genus as a source of antimicrobial compounds that can potentially be a biological control against plant pathogens. The investigation of various bioactive compounds synthesized by this genus can enhance our comprehension of their prospective utilization in agriculture.

Biosensor-guided detection of outer membrane-specific antimicrobial activity against Pseudomonas aeruginosa from fungal cultures and medicinal plant extracts.

Pseudomonas aeruginosa responds to sub-lethal antimicrobial exposure by inducing the expression of lipopolysaccharide (LPS) surface modifications that mask antibiotic binding sites and contribute to repair and resistance of the outer membrane (OM). We exploit these membrane damage-responsive operons in a biosensor approach used to discover new antimicrobials that specifically target the OM. Chromosomal transcriptional luxCDABE reporters from the pmr (polymyxin resistance; aminoarabinose LPS modification) and speD2E2 (spermidine synthesis) operons are induced by validated outer membrane-acting agents including cationic antimicrobial peptides, cation chelators, ascorbic acid, detergents, and cell wall synthesis inhibitors cycloserine and bacitracin. To identify novel sources of OM-disrupting antimicrobials, we used these OM damage-responsive biosensors to screen a panel of fungal culture supernatants for novel antimicrobial and biosensor activity. Biosensor activity was used to determine the optimal time point of antimicrobial production from fungal supernatants and to guide the purification of active fractions after size-exclusion chromatography. Water and ethanol extracts of Chinese medicinal plants also proved to be a source of biosensor activity. The pathogen box is a 400-member drug library of potential antimicrobials, but none of these compounds induced our OM damage biosensors. This novel, sensitive, cell-based screening assay has potential for future discovery of lead compounds that specifically target the outer membrane, which is a significant barrier to antibiotic entry into Gram-negative bacteria.IMPORTANCENew approaches are needed to discover novel antimicrobials, particularly antibiotics that target the Gram-negative outer membrane. By exploiting bacterial sensing and responses to outer membrane (OM) damage, we used a biosensor approach consisting of polymyxin resistance gene transcriptional reporters to screen natural products and a small drug library for biosensor activity that indicates damage to the OM. The diverse antimicrobial compounds that cause induction of the polymyxin resistance genes, which correlates with outer membrane damage, suggest that these LPS and surface modifications also function in short-term repair to sublethal exposure and are required against broad membrane stress conditions.

Exploring the Promise of Endophytic Fungi: A Review of Novel Antimicrobial Compounds.

Over the last few decades, many of the existing drugs used to treat infectious diseases have become increasingly ineffective due to the global emergence of antimicrobial resistance (AMR). As such, there is a constant demand to find new, effective compounds that could help to alleviate some of this pressure. Endophytic fungi have captured the attention of many researchers in this field, as they have displayed a vast ability to produce novel bioactive compounds, many of which possess wide-ranging antimicrobial activities. However, while highly promising, research in this area is still in its infancy. Endophytes inhabit the healthy tissues of plants asymptomatically, resulting in a mutualistic symbiosis in which the endophytes produce a plethora of bioactive compounds that support the fitness of the host plant. These compounds display great chemical diversity, representing structural groups, such as aliphatic compounds, alkaloids, peptides, phenolics, polyketides and terpenoids. In this review, the significant antimicrobial potential of endophytic fungi is detailed, highlighting their ability to produce novel and diverse antimicrobial compounds active against human, plant and marine pathogens. In doing so, it also highlights the significant contributions that endophytic fungi can make in our battle against AMR, thus providing the motivation to increase efforts in the search for new and effective antimicrobial drugs.

Differential Virulence Contributions of the Efflux Transporter MexAB-OprM in Pseudomonas syringae Infecting a Variety of Host Plants.

Efflux transporters such as MexAB-OprM contribute to bacterial resistance to diverse antimicrobial compounds. Here, we show that MexB contributes to epiphytic and late-stage apoplastic growth of Pseudomonas syringae strain B728a, as well as lesion formation in common bean (Phaseolus vulgaris). Although a ∆mexB mutant formed fewer lesions after topical application to common bean, these lesions contain the same number of cells (105 to 107 cells) as those caused by the wild-type strain. The internalized population size of both the wild-type and the ∆mexB mutant within small samples of surface-sterilized asymptomatic portions of leaves varied from undetectably low to as high as 105 cells/cm2. Localized bacterial populations within individual lesions consistently exceeded 105 cells/cm2. Strain B728a was capable of moderate to extensive apoplastic growth in diverse host plants, including lima bean (P. lunatus), fava bean (Vicia faba), pepper (Capsicum annuum), Nicotiana benthamiana, sunflower (Helianthus annuus), and tomato (Solanum lycopersicum), but MexB was not required for growth in a subset of these plant species. A model is proposed that MexB provides resistance to as-yet-unidentified antimicrobials that differ between plant species. [Formula: see text] Copyright © 2022 The Author(s). This is an open access article distributed under the CC BY 4.0 International license.

Antibacterial activity and chemical composition of essential oil from Lavandula tenuisecta Coss.ex Ball. an endemic species from Morocco

IntroductionAntimicrobial resistance (AMR) presents a public health problem. Some antibiotics became ineffective and bacteria are becoming even more pathogenic. Medicinal and aromatic plants (MAP) have received greater attention as alternatives to antibiotics since they contain diverse antimicrobial compounds. This study aimed to evaluate the antibacterial activity of a medicinal plant endemic to Morocco, Lavandula tenuisecta Coss.ex Ball (L. tenuisecta). MethodsTo carry out this work, the chemical composition of the essential oil was determined using gas chromatography (GC) with the detection feature of Mass Spectrometry (MS) and Flame Ionization Detector (FID). Subsequently, the antibacterial power was studied against resistant strains that are isolated from different clinical specimens. The antibacterial screening was carried out using the disc method and then quantitative evaluation was conducted by the microdilution method. ResultsThe essential oil (EO) extraction yield represents 0.02% of the dry plant. The analysis of EO shows 38 components representing 88.6% of the EO. The major constituents were camphor (26.9 %), fenchone (22.7 %) and 1,8-cineole (18.1%). The EO was effective against almost all studied bacteria, with minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) values ranging from 6.25 to 50 μg/mL. ConclusionThis study showed that the EO from L. tenuisecta was active against all studied strains except Salmonella spp. This antibacterial activity may be related to the synergy between chemical compounds of the EO.

Studies on Antibacterial Activity and Diversity of Cultivable Actinobacteria Isolated from Mangrove Soil in Futian and Maoweihai of China.

Mangrove is a rich and underexploited ecosystem with great microbial diversity for discovery of novel and chemically diverse antimicrobial compounds. The goal of the study was to explore the pharmaceutical actinobacterial resources from mangrove soil and gain insight into the diversity and novelty of cultivable actinobacteria. Consequently, 10 mangrove soil samples were collected from Futian and Maoweihai of China, and the culture-dependent method was employed to obtain actinobacteria. A total of 539 cultivable actinobacteria were isolated and distributed in 39 genera affiliated to 18 families of 8 orders by comparison analysis of partial 16S rRNA gene sequences. The dominant genus was Streptomyces (16.0 %), followed by Microbacterium (14.5 %), Agromyces (14.3 %), and Rhodococcus (11.9 %). Other 35 rare actinobacterial genera accounted for minor proportions. Notably, 11 strains showed relatively low 16S rRNA gene sequence similarities (< 98.65 %) with validly described species. Based on genotypic analyses and phenotypic characteristics, 115 out of the 539 actinobacterial strains were chosen as representative strains to test their antibacterial activities against “ESKAPE” bacteria by agar well diffusion method and antibacterial mechanism by the double fluorescent protein reporter system. Fifty-four strains in 23 genera, including 2 potential new species, displayed antagonistic activity in antibacterial assay. Meanwhile, 5 strains in 3 genera exhibited inhibitory activity on protein biosynthesis due to ribosome stalling. These results demonstrate that cultivable actinobacteria from mangrove soil are potentially rich sources for discovery of new antibacterial metabolites and new actinobacterial taxa.

NgrA-dependent natural products are required for interspecies competition and virulence in the insect pathogenic bacterium Xenorhabdus szentirmaii.

Xenorhabdus species are symbionts of entomopathogenic nematodes and pathogens of susceptible insects. Nematodes enter insect hosts and perforate the midgut to invade the haemocoel where Xenorhabdus bacteria are released transitioning to their pathogenic stage. During nematode invasion microbes from the insect gut translocate into the haemocoel. Different species of nematodes carrying specific strains of Xenorhabdus can also invade the same insect. Xenorhabdus species thereby compete for nutrients and space with both related strains and non-related gut microbes. While Xenorhabdus species produce diverse antimicrobial compounds in complex media, their functions in insect hosts are not well understood. We show that Xenorhabdus szentirmaii produced ngrA-dependent antibiotics that were active against both gut-derived microbes and Xenorhabdus nematophila whereas antibiotics of X. nematophila were not active against X. szentirmaii. X. nematophila growth was inhibited in co-cultures with wild-type X. szentirmaii in medium that mimics insect haemolymph. An antibiotic-deficient strain of X. szentirmaii was created by inactivating the ngrA gene that encodes the enzyme that attaches the 4' phosphopantetheinyl moiety to non-ribosomal peptide synthetases involved in antibiotic biosynthesis. X. nematophila growth was not inhibited in co-cultures with the ngrA strain. The growth of X. nematophila was suppressed in Manduca sexta co-injected with wild-type X. szentirmaii and X. nematophila. In contrast, growth of X. nematophila was not suppressed in M. sexta co-injected with the ngrA strain. Two unique compounds were detected by MALDI-TOF MS analysis in haemolymph infected with the wild-type but not with the ngrA strain. Finally, killing of M. sexta was delayed in insects infected with the ngrA strain. These findings indicate that in the insect host X. szentirmaii produces ngrA-dependent products involved in both interspecies competition and virulence.

Treatment Strategies for Infected Wounds.

The treatment of skin wounds is a key research domain owing to the important functional and aesthetic role of this tissue. When the skin is impaired, bacteria can soon infiltrate into underlying tissues which can lead to life-threatening infections. Consequently, effective treatments are necessary to deal with such pathological conditions. Recently, wound dressings loaded with antimicrobial agents have emerged as viable options to reduce wound bacterial colonization and infection, in order to improve the healing process. In this paper, we present an overview of the most prominent antibiotic-embedded wound dressings, as well as the limitations of their use. A promising, but still an underrated group of potential antibacterial agents that can be integrated into wound dressings are natural products, especially essential oils. Some of the most commonly used essential oils against multidrug-resistant microorganisms, such as tea tree, St. John’s Wort, lavender and oregano, together with their incorporation into wound dressings are presented. In addition, another natural product that exhibits encouraging antibacterial activity is honey. We highlight recent results of several studies carried out by researchers from different regions of the world on wound dressings impregnated with honey, with a special emphasis on Manuka honey. Finally, we highlight recent advances in using nanoparticles as platforms to increase the effect of pharmaceutical formulations aimed at wound healing. Silver, gold, and zinc nanoparticles alone or functionalized with diverse antimicrobial compounds have been integrated into wound dressings and demonstrated therapeutic effects on wounds.

Stimulation of Fengycin-Type Antifungal Lipopeptides in Bacillus amyloliquefaciens in the Presence of the Maize Fungal Pathogen Rhizomucor variabilis.

Most isolates belonging to the Bacillus amyloliquefaciens subsp. plantarum clade retain the potential to produce a vast array of structurally diverse antimicrobial compounds that largely contribute to their efficacy as biocontrol agents against numerous plant fungal pathogens. In that context, the role of cyclic lipopeptides (CLPs) has been well-documented but still little is known about the impact of interactions with other soil-inhabiting microbes on the expression of these molecules. In this work, we wanted to investigate the antagonistic activity developed by this bacterium against Rhizomucor variabilis, a pathogen isolated from diseased maize cobs in Democratic Republic of Congo. Our data show that fengycins are the major compounds involved in the inhibitory activity but also that production of this type of CLP is significantly upregulated when co-cultured with the fungus compared to pure cultures. B. amyloliquefaciens is thus able to perceive fungal molecules that are emitted and, as a response, up-regulates the biosynthesis of some specific components of its antimicrobial arsenal.

Computational Study of the Interaction between Antimicrobial Compounds and Efflux Systems of Gram-Negative Bacteria

Nowadays, multidrug resistance in Gram-negative bacteria is a major issue for public health. The efflux pumps of the resistance nodulation division (RND) family contribute largely to this phenomenon. A well-known example is represented by the AcrAB-TolC efflux system of E. coli, in which the inner membrane translocase AcrB is the main responsible for the uptake and extrusion of different substrates. Due to the limited availability of crystallographic structures of AcrB-substrate complexes, computational methods represent an alternative approach to elucidate the nature of interactions between diverse antimicrobial compounds and the efflux protein. Here, two antibiotics known for their different affinity for the efflux pump in P. aeruginosa, namely meropenem and imipenem (respectively, strongly and poorly affected by MexB, the homologous of AcrB in P. aeruginosa), were chosen for this study. A similar behaviour for the two antibiotics has not been yet reported in the literature for the AcrB of E. coli.In this study we first performed a preliminary docking investigation using ensemble of conformations extracted from molecular dynamics simulations of both ligands and AcrB structures. The top poses of ligands were selected as initial conformations for molecular dynamics simulations. Results from MD simulations evidence a larger propensity of meropenem than imipenem to bind to the putative affinity sites of AcrB, in analogy to what observed for MexB. Moreover, a detailed analysis of the molecular interactions of the two compounds with AcrB allowed identifying the key residues involved in the extrusion/retention processes. Our results provide information that could help in designing new antibiotics less likely to be extruded by RND efflux pumps, as well as inhibitors more effective in blocking the whole efflux process.

The Redox Cofactor F 420 Protects Mycobacteria from Diverse Antimicrobial Compounds and Mediates a Reductive Detoxification System

A defining feature of mycobacterial redox metabolism is the use of an unusual deazaflavin cofactor, F420 This cofactor enhances the persistence of environmental and pathogenic mycobacteria, including after antimicrobial treatment, although the molecular basis for this remains to be understood. In this work, we explored our hypothesis that F420 enhances persistence by serving as a cofactor in antimicrobial-detoxifying enzymes. To test this, we performed a series of phenotypic, biochemical, and analytical chemistry studies in relation to the model soil bacterium Mycobacterium smegmatis Mutant strains unable to synthesize or reduce F420 were found to be more susceptible to a wide range of antibiotic and xenobiotic compounds. Compounds from three classes of antimicrobial compounds traditionally resisted by mycobacteria inhibited the growth of F420 mutant strains at subnanomolar concentrations, namely, furanocoumarins (e.g., methoxsalen), arylmethanes (e.g., malachite green), and quinone analogues (e.g., menadione). We demonstrated that promiscuous F420H2-dependent reductases directly reduce these compounds by a mechanism consistent with hydride transfer. Moreover, M. smegmatis strains unable to make F420H2 lost the capacity to reduce and detoxify representatives of the furanocoumarin and arylmethane compound classes in whole-cell assays. In contrast, mutant strains were only slightly more susceptible to clinical antimycobacterials, and this appeared to be due to indirect effects of F420 loss of function (e.g., redox imbalance) rather than loss of a detoxification system. Together, these data show that F420 enhances antimicrobial resistance in mycobacteria and suggest that one function of the F420H2-dependent reductases is to broaden the range of natural products that mycobacteria and possibly other environmental actinobacteria can reductively detoxify.IMPORTANCE This study reveals that a unique microbial cofactor, F420, is critical for antimicrobial resistance in the environmental actinobacterium Mycobacterium smegmatis We show that a superfamily of redox enzymes, the F420H2-dependent reductases, can reduce diverse antimicrobials in vitro and in vivoM. smegmatis strains unable to make or reduce F420 become sensitive to inhibition by these antimicrobial compounds. This suggests that mycobacteria have harnessed the unique properties of F420 to reduce structurally diverse antimicrobials as part of the antibiotic arms race. The F420H2-dependent reductases that facilitate this process represent a new class of antimicrobial-detoxifying enzymes with potential applications in bioremediation and biocatalysis.

Optimization of media for antimicrobial compounds production by Bacillus subtilis

Bacillus subtilis is one of the most important producers of diverse antimicrobial compounds. This bacterium grows and produces antibiotics on different substrates. The increase of the antibiotics yield can be achieved by changing the conditions of cultivation and the composition of the culture media. In this study, response surface methodology was used for optimization of glycerol, sodium nitrite, and phosphate content in media for production of antibiotics effective against Staphylococcus aureus. As biosynthesis strain Bacillus subtilis ATCC 6633 was used. The developed model predicts that the maximum inhibition zone radius (38.08 mm) against Staphylococcus aureus and minimal amount of residual nutrients (glycerol 1.75 g l−1, nitrogen 0.21 g l−1, phosphorus 0.18 g l−1) are achieved, when the initial content of glycerol, sodium nitrite, and phosphate are 49.99 g l−1, 1.00 g l−1, and 5.00 g l−1, respectively.

Bacteriocin production and safety evaluation of non-starter Enterococcus faecium IM1 and Enterococcus hirae IM1 strains isolated from homemade Egyptian dairy products

This study presents the characterization of some strains of lactic acid bacteria (LAB) from traditional Egyptian dairy products. Isolated LAB (623 isolates) were studied for their antimicrobial activity against taxonomically related microorganisms. Selected LAB were identified by PCR method as Enterococcus faecium IM1 and Enterococcus hirae IM1. Partially purified enterocins showed antimicrobial activity against Lactobacillus bulgaricus 340, Lb. brevis F104 and F145, Lb. sakei, Brochothrix thermosphacta DSMZ20171T and DSMZ20599, Carnobacterium maltaromaticum CIP103135T, C. piscicola S4312, E. faecalis JH2-2 and JH2-2rr04, E. faecium CTC492/t1362 and P13, Listeria grayi CLIP12518, L. innocua 1, CIP80.11T, F and P, L. ivanovii ATCC and CIP78.42T, L. monocytogenes CIP78.35, DSM12464, EGDe, RF124, RF125, RF131, RF132, RF133, RF142, RF151 and RF152, and Vagococcus penaei CIP 109914T but have no effect against Bacillus subtilis 168T, Moellerella wisconsensis MIP2451, Morganella psychrotolerans MIP2488, Pseudomonas fluorescens 10, Salmonella enterica, Sal. montevideo, Sal. typhimurium and Serratia liquefaciens CIP103238T. The inhibitory activity was not due to hydrogen peroxide for E. hirae IM1, but strain E. faecium IM1 may excrete diverse antimicrobial compounds such as hydrogen peroxide and bacteriocins. Antimicrobial activity of E. faecium IM1 was initially detected during exponential phase of growth, and the maximal level (1,300 AU/mL) was observed at 12 h and remained stable till the end of incubation time (48 h). Maximum of activity of E. hirae IM1 was observed during the logarithmic phase (6 h) and then decreased after 12 h. Bacteriocins produced by E. faecium IM1 and E. hirae IM1 were stable between pH 5 and pH 8 and stable also until 100 °C/20 min. Tested strains were free from virulence determinant genes as well as hemolytic and gelatinase activities. E. faecium IM1 was sensitive to penicillin, kanamycin, vancomycin, gentamicin and tetracycline but resistant to ampicillin. Otherwise, E. hirae IM1 was sensitive to penicillin, kanamycin, vancomycin and tetracycline but resistant to ampicillin and gentamicin. The isolated cultures with antimicrobial activities may be used as safe and useful starter cultures or co-cultures.

The sensitivity of Bacillus subtilis to diverse antimicrobial compounds is influenced by Abh

Abh is a transition state regulator of Bacillus subtilis that controls biofilm formation and the production of several diverse antimicrobial compounds. Using a high-throughput non-biased technique, we show for the first time that Abh influences the sensitivity of B. subtilis to diverse antimicrobial compounds. Following up on these findings with a combination of classical genetics and antibiotic susceptibility assays, we demonstrate that Abh influences cellular processes such as the remodelling of the cell wall. We present data demonstrating that the extracytoplasmic function sigma factor σ(X) controls resistance to β-lactam antibiotics by activating abh transcription. Downstream from Abh, activation of slrR expression by Abh is responsible for controlling the sensitivity of B. subtilis to such antibiotics due to the role that SlrR plays in regulating autolysin biosynthesis. The abh mutant additionally exhibits increased resistance to aminoglycoside antimicrobials. We confirm that aminoglycoside killing of B. subtilis is likely to be caused by oxidative damage but rule out the possibility that the increased resistance of the abh mutant to aminoglycosides is due to a general increase in resistance to oxidative stress.

Novel Mechanism in Salmonella Virulence, Drug Susceptibility

Researchers have discovered a novel mechanism in Salmonella that affects its virulence and its susceptibility to antibiotics by changing its production of proteins in order to respond to inhospitable conditions.Although the mechanism had not been recognized before, the scientists were intrigued to find evidence of a similar mechanism conserved throughout the course of evolution. The findings were published July 30 in Molecular Cell with the senior study author being Ferric C. Fang, MD, Professor of Microbiology, Laboratory Medicine, and Medicine at the University of Washington.While screening mutant Salmonella that were resistant to S-nitrosoglutathione, a form of nitric oxide that normally stops the bacteria from dividing, the researchers found mutations in 2 uncharacterized genes, poxA (yjeA or STM4344) and yjeK (STM4333), putatively involved in tRNA and lysine biosynthesis, respectively. “In a number of phylogenetically distant bacterial species, the poxA and yjeK genes are linked to each other and to a third gene, efp, encoding the bacterial elongation factor P (EF-P) involved in protein synthesis,” Fang and co-authors note.“Here, we report that these genes operate in a common pathway critical for virulence and resistance to several classes of antibiotics,” the report states. “Two-dimensional gel analysis revealed that the poxA and yjeK mutant strains display nearly identical phenotypes and changes in protein expression profiles, including several proteins involved in metabolism and factors encoded by the Salmonella pathogenicity island, SPI-1. Furthermore we demonstrate by biochemical means that PoxA is the enzyme responsible for the previously observed posttranslational modification of EF-P.”“Our data demonstrate that YjeK, PoxA, and EF-P affect the expression of factors that play an essential role in Salmonella virulence and intrinsic resistance to diverse antimicrobial compounds.” See: Molecular Cell 2010;39:209–221. (Figure 1). Researchers have discovered a novel mechanism in Salmonella that affects its virulence and its susceptibility to antibiotics by changing its production of proteins in order to respond to inhospitable conditions. Although the mechanism had not been recognized before, the scientists were intrigued to find evidence of a similar mechanism conserved throughout the course of evolution. The findings were published July 30 in Molecular Cell with the senior study author being Ferric C. Fang, MD, Professor of Microbiology, Laboratory Medicine, and Medicine at the University of Washington. While screening mutant Salmonella that were resistant to S-nitrosoglutathione, a form of nitric oxide that normally stops the bacteria from dividing, the researchers found mutations in 2 uncharacterized genes, poxA (yjeA or STM4344) and yjeK (STM4333), putatively involved in tRNA and lysine biosynthesis, respectively. “In a number of phylogenetically distant bacterial species, the poxA and yjeK genes are linked to each other and to a third gene, efp, encoding the bacterial elongation factor P (EF-P) involved in protein synthesis,” Fang and co-authors note. “Here, we report that these genes operate in a common pathway critical for virulence and resistance to several classes of antibiotics,” the report states. “Two-dimensional gel analysis revealed that the poxA and yjeK mutant strains display nearly identical phenotypes and changes in protein expression profiles, including several proteins involved in metabolism and factors encoded by the Salmonella pathogenicity island, SPI-1. Furthermore we demonstrate by biochemical means that PoxA is the enzyme responsible for the previously observed posttranslational modification of EF-P.” “Our data demonstrate that YjeK, PoxA, and EF-P affect the expression of factors that play an essential role in Salmonella virulence and intrinsic resistance to diverse antimicrobial compounds.” See: Molecular Cell 2010;39:209–221. (Figure 1).

Active use of the metapleural glands by ants in controlling fungal infection

Insect societies face constant challenges from disease agents. Ants deploy diverse antimicrobial compounds against pathogens and the key sources are metapleural glands (MGs). Are MG products passively secreted and used indiscriminately or are they selectively used when ants are challenged by pathogens? In 26 species from five subfamilies, ants use foreleg movements to precisely groom the MG opening. In the absence of experimental infection, MG grooming rates are low and workers groom themselves after contacting the MGs. The derived leaf-cutter ants (Atta and Acromyrmex) also groom their fungal gardens, substrata (leaves), queens and nest-mates after MG grooming. Atta respond to a challenge by fungal conidia by increasing the rate of MG grooming, but do not do so when an inert powder is applied. This increase occurs in the first hour after a potential infection, after which it returns to baseline levels. Ants with open MGs produce more infrabuccal pellets (IP) than ants with sealed MGs and conidia within pellets from the former are less likely to germinate. Thus, ants selectively groom their MGs when disease agents are present, suggesting that they also selectively use their MG secretions, which has important implications for understanding the evolution of hygienic behaviour in social groups.