Prevalence of Brucella melitensis and Brucella abortus aminoglycoside-resistant isolates: a systematic review and meta-analysis.

INTRODUCTION: Aminoglycosides are vital antibiotics for treating Brucella infections, because they interfere with bacterial protein production and are often combined with other antibiotics. They are cost-effective, have fewer side effects, and can penetrate biofilms. The prevalence of brucellosis has increased in recent years, increasing the need for effective treatments. In addition, the emergence of multidrug-resistant Brucella strains has highlighted the need for an updated and comprehensive understanding of aminoglycoside resistance. This systematic review aimed to provide a comprehensive overview of the global prevalence of aminoglycoside resistance in B. melitensis and B. abortus. METHODS: A systematic search of online databases was conducted and eligible studies met certain criteria and were published in English. Quality assessment was performed using the JBI Checklist. A random-effects model was fitted to the data, and meta-regression, subgroup, and outlier/influential analyses were performed. The analysis was performed using R and the metafor package. RESULTS: The results of this systematic review and meta-analysis suggested that the average prevalence rates of streptomycin, gentamicin, and amikacin resistance were 0.027 (95% confidence interval [CI], 0.015-0.049), 0.023 (95% CI, 0.017-0.032), and 0.008 (95% CI, 0.002-0.039), respectively. The prevalence of streptomycin resistance was higher in the unidentified Brucella group than in the B. abortus and B. melitensis groups (0.234, 0.046, and 0.017, respectively; p < 0.02). The prevalence of gentamicin resistance increased over time (r = 0.064; 95% CI, 0.018 to 0.111; p = 0.007). The prevalence of resistance did not correlate with the quality score for any antibiotic. Funnel plots showed a potential asymmetry for streptomycin and gentamicin. These results suggest a low prevalence of antibiotic resistance in the studied populations. CONCLUSION: The prevalence of aminoglycoside resistance in B. melitensis and B. abortus was low. However, gentamicin resistance has increased in recent years. This review provides a comprehensive and updated understanding of aminoglycoside resistance in B. melitensis and B. abortus.

Gut Lactobacillus contribute to the progression of breast cancer by affecting the anti-tumor activities of immune cells in the TME of tumor-bearing mice.

Studies have proven that gut microbiota dysbiosis may influence the carcinogenesis and outcomes of multiple cancers. However, it is still unclear whether gut microbiota dysbiosis affect the progression of breast cancer, especially triple-negative breast cancer. In the present study, by using gut microbiota dysbiosis murine model established by treatment of mice with streptomycin, we found Lactobacillus and the metabolite-lactic acid are the pivotal factors for 4T1 tumor progression. In fact, streptomycin-treated mice exhibited slower tumor growth, in parallel with less abundance of Lactobacillus in the gut. Supplementation with Lactobacillus resulted in a rapid tumor growth, following a decrease in the expression of mRNAs for anti-tumor-related factors but an increase in the M2 polarization. The elevated percentages of IFN-γ-producing CD4+T cells and CD8+T cells in the tumor microenvironment of streptomycin-treated tumor-bearing mice may be vanished by supplementation of Lactobacillus. It seems likely that lactobacillus-mediated pro-tumor effect is related to the production of lactic acid. A decrease in the levels of lactic acid in the cecal feces and tumor tissues were observed in streptomycin-treated tumor bearing mice. However, supplementation of Lactobacillus can restore streptomycin-reduced concentration of lactic acid in the tumor tissues, suggesting that gut Lactobacillus are the source of lactic acid. Bioinformatics analysis result suggests high concentration of lactic acid in tumor sites may be related to the diminished anti-tumor immunity in the TME. This study reveals a correlation between gut Lactobacillus and tumor progression in a murine 4T1 tumor model, providing experimental evidence for clinical treatment of breast cancer.

Protective efficacy of fish oil nanoemulsion against non-typhoidal Salmonella mediated mucosal inflammation and loss of barrier function.

Non-typhoidal Salmonella serotypes are well adapted to utilize the inflammation for colonization in the mammalian gut mucosa and cause loss of the integrity of the epithelial barrier in the mammalian intestine. The present study assessed the protective efficacy of fish oil-in-water nanoemulsion, compared to the conventional emulsion, towards the intestinal epithelial barrier against invasive infection of Salmonella enterica serovar Typhimurium strain SL1344 in an in vivo streptomycin-treated mouse model. Non-typhoidal Salmonella enterica serovar Typhimurium strain SL1344 expresses its invasiveness by creating extreme inflammatory assault in the mammalian host lumen via its repertoire of secretory or membrane-bound proteins. Prophylactic treatment of ω-3 polyunsaturated fatty acid-rich fish oil nanoemulsion not only reduced the inflammatory markers by 4-5 fold against the established infection but also retained the gut barrier efficiency as shown by FITC-dextran permeability assay. Though the conventional emulsion also showed similar trends, the efficacy was significantly better with nanoemulsion treatment but neither the nanoemulsion nor conventional emulsion caused any significant change in the microbial colonization of the murine gut mucosa. Mechanistic assessment of the nanoemulsion against inflammation and invasion across the Caco-2 cell monolayer revealed that nanoemulsion treatment protected the expression of Zona occludens-1 along the tight junction, almost by 3-fold as compared to the infected cell monolayer. Such protection was evinced by the trans-epithelial electrical resistance value and the FITC-dextran permeability analysis as well. Fish oil nanoemulsion treatment has also shown significant reduction in pro-inflammatory cytokine expression by the Salmonella strain SL1344 infected Caco-2 cell monolayer. Conventional emulsion also showed distinct protection, but the nanoemulsion offered better protection at the same dosage of fish oil, probably due to its better bioavailability. The results proved that fish oil-loaded nanoemulsion can be efficacious towards maintaining the barrier function and protecting against systemic bacteremia during invasive intestinal infection.

Transport Dynamics of MtrD: An RND Multidrug Efflux Pump from Neisseria gonorrhoeae.

The MtrCDE system confers multidrug resistance to Neisseria gonorrhoeae, the causative agent of gonorrhea. Using free and directed molecular dynamics (MD) simulations, we analyzed the interactions between MtrD and azithromycin, a transport substrate of MtrD, and a last-resort clinical treatment for multidrug-resistant gonorrhea. We then simulated the interactions between MtrD and streptomycin, an apparent nonsubstrate of MtrD. Using known conformations of MtrD homologues, we simulated a potential dynamic transport cycle of MtrD using targeted MD techniques (TMD), and we noted that forces were not applied to ligands of interest. In these TMD simulations, we observed the transport of azithromycin and the rejection of streptomycin. In an unbiased, long-time scale simulation of AZY-bound MtrD, we observed the spontaneous diffusion of azithromycin through the periplasmic cleft. Our simulations show how the peristaltic motions of the periplasmic cleft facilitate the transport of substrates by MtrD. Our data also suggest that multiple transport pathways for macrolides may exist within the periplasmic cleft of MtrD.

Genetically engineered rpsL merodiploidy impacts secondary metabolism and antibiotic resistance in Streptomyces.

Certain point mutations within gene for ribosomal protein S12, rpsL, are known to dramatically change physiological traits of bacteria, most prominently antibiotic resistance and production of various metabolites. The rpsL mutants are usually searched among spontaneous mutants resistant to aminoglycoside antibiotics, such as streptomycin or paromomycin. The shortcomings of traditional selection are as follows: random rpsL mutants may carry undesired genome alterations; many rpsL mutations cannot be isolated because they are either not associated with increased antibiotic resistance or non-viable in the absence of intact rpsLWT gene. Introduction of mutant rpsL alleles in the rpsLWT background can be used to circumvent these obstacles. Here we take the latter approach and report the generation and properties of a set of stable rpsL merodiploids for Streptomyces albus J1074. We identified several rpsL alleles that enhance endogenous and heterologous antibiotic production by this strain and show that rpsLWTrpsLK88E merodiploid displays increased streptomycin resistance. We further tested several promising rpsL alleles in two more strains, Streptomyces cyanogenus S136 and Streptomyces ghanaensis ATCC14672. In S136, plasmid-borne rpsLK88E+P91S and rpsLK88R led to elevated landomycin production; no changes were detected for ATCC14672 merodiploids. Our data outline the prospects for and limitations to rpsL merodiploids as a tool for rapid enhancement of secondary metabolism in Streptomyces.

Single molecule force spectroscopy of a streptomycin-binding RNA aptamer: An out-of-equilibrium molecular dynamics study.

Here, we investigate the unfolding behavior of a streptomycin-binding ribonucleic acid (RNA) aptamer under application of force in shear geometry. Using Langevin out-of-equilibrium simulations to emulate the single-molecule force spectroscopy (SMFS) experiment, we were able to understand the hierarchical unfolding process that occurs in the RNA molecule under application of stretching force and the influence of streptomycin modifying this unfolding. Subsequently, the application of the Jarzynski equality to the force profiles obtained in the pulling simulations shows that the free energies for individual systems and the difference of unfolding free energy upon streptomycin binding to the RNA free aptamer are in fair agreement with the experimental values, obtained through SMFS by Nick et al. [J. Phys. Chem. B 120, 6479 (2016)].

Binding energies of the drugs capreomycin and streptomycin in complex with tuberculosis bacterial ribosome subunits.

Despite advances, tuberculosis remains a significant infectious disease, whose mortality presents alarming numbers. Although it can be cured, the number of cases of antimicrobial resistant strains is increasing, requiring the use of less efficient second-line drugs. Capreomycin and streptomycin are part of this group, being antibiotics whose mechanism of action is the inhibition of protein synthesis when interacting with the tuberculosis bacterial ribosome. Their binding mechanisms are distinct: capreomycin is able to bind to both ribosomal (30S and 50S) subunits, whereas streptomycin binds only to the smaller one (30S). In this context, the biochemical characterization of these binding sites for a proper understanding of their complex interactions is of crucial importance to increase their efficacy. Through crystallographic data and computer simulations, in this work we calculated the interaction binding energies of capreomycin and streptomycin in complex with the tuberculosis bacterial ribosome subunits, by using density functional theory (DFT) within the molecular fractionation with conjugated caps (MFCC) approach. For capreomycin in the 30S (50S) subunit, we investigated the binding energies of 44 (30) residues presented within a pocket radius of 14 Å (30 Å). Regarding streptomycin, 60 nucleotide (25 amino acid) residues distributed up to 12.5 Å (15 Å) away from the drug in the 30S subunit (S12 protein) were taken into account. We also identify the contributions of hydrogen bonds and hydrophobic interactions in the drug-receptor complex, and the regions of the drugs that most contributed to the anchorages of them in their binding sites, as well as identify residues that are most associated with mutations.

An electrochemical aptasensor for streptomycin based on covalent attachment of the aptamer onto a mesoporous silica thin film-coated gold electrode.

An electrochemical method is described for the determination of streptomycin (STR). It is making use of a gold electrode coated with a thin mesoporous silica film (MSF). In addition, silver nanoparticles were coated on the MSF to increase the surface area, to bind a large amount of aptamer (Apt), and to improve the electrical conductivity. In the presence of STR, it will bind to the Apt and hinder the diffusion of the redox probe hexacyanoferrate through the nanochannels of the mesoporous film. The aptasensor, best operated at a working potential of 0.22 V (vs. Ag/AgCl) has a linear response in the 1 fg.mL-1 to 6.2 ng.mL-1 STR concentration range. The detection limit is 0.33 fg.mL-1. The assay was successfully validated by analyzing spiked samples of milk and blood serum. Graphical abstract Voltammetric assay of streptomycin (STR) by using a Fe(CN)63-/4- probe. The aptamer was immobilized on a gold electrode modified with a mesoporous silica thin film (MSF) that was functionalized with (3-aminopropyl) triethoxysilane (APTES) and silver nanoparticles (AgNP). Incubation with STR leads to a decrease of the current.

Antibacterial evaluation of silver nanoparticles synthesized from lychee peel: individual versus antibiotic conjugated effects.

This paper describes the extracellular synthesis of silver nanoparticles from waste part of lychee fruit (peel) and their conjugation with selected antibiotics (amoxicillin, cefixim, and streptomycin). FTIR studies revealed the reduction of metallic silver and stabilization of silver nanoparticles and their conjugates due to the presence of CO (carboxyl), OH (hydroxyl) and CH (alkanes) groups. The size of conjugated nanoparticles varied ranging from 3 to 10 nm as shown by XRD. TEM image revealed the spherical shape of biosynthesized silver nanoparticles. Conjugates of amoxicillin and cefixim showed highest antibacterial activity (147.43 and 107.95%, respectively) against Gram-negative bacteria i.e. Alcaligenes faecalis in comparison with their control counterparts. The highest reduction in MIC was noted against Gram-positive strains i.e. Enterococcus faecium (75%) and Microbacterium oxydans (75%) for amoxicillin conjugates. Anova two factor followed by two-tailed t test showed non-significant results both in case of cell leakage and protein estimation between nanoparticles and conjugates of amoxicillin, cefixime and streptomycin. In case of MDA release, non-significant difference among the test samples against the selected strains. Our study found green-synthesized silver nanoparticles as effective antibacterial bullet against both Gram positive and Gram negative bacteria, but they showed a more promising effect on conjugation with selected antibiotics against Gram negative type.

Polymer-augmented liposomes enhancing antibiotic delivery against intracellular infections.

Pulmonary intracellular infections, such as tuberculosis, anthrax, and tularemia, have remained a significant challenge to conventional antibiotic therapy. Ineffective antibiotic treatment of these infections can lead not only to undesired side effects, but also to the emergence of antibiotic resistance. Aminoglycosides (e.g., streptomycin) have long been part of the therapeutic regiment for many pulmonary intracellular infections. Their bioavailability for intracellular bacterial pools, however, is limited by poor membrane permeability and rapid elimination. To address this challenge, polymer-augmented liposomes (PALs) were developed to provide improved cytosolic delivery of streptomycin to alveolar macrophages, an important host cell for intracellular pathogens. A multifunctional diblock copolymer was engineered to functionalize PALs with carbohydrate-mediated targeting, pH-responsive drug release, and endosomal release activity with a single functional polymer that replaces the pegylated lipid component to simplify the liposome formulation. The pH-sensing functionality enabled PALs to provide enhanced release of streptomycin under endosomal pH conditions (70% release in 6 hours) with limited release at physiological pH 7.4 (16%). The membrane-destabilizing activity connected to endosomal release was characterized in a hemolysis assay and PALs displayed a sharp pH profile across the endosomal pH development target range. The direct connection of this membrane-destabilizing pH profile to model drug release was demonstrated in an established pyranine/p-xylene bispyridinium dibromide (DPX) fluorescence dequenching assay. PALs displayed similar sharp pH-responsive release, whereas PEGylated control liposomes did not, and similar profiles were then shown for streptomycin release. The mannose-targeting capability of the PALs was also demonstrated with 2.5 times higher internalization compared to non-targeted PEGylated liposomes. Finally, the streptomycin-loaded PALs were shown to have a significantly improved intracellular antibacterial activity in a Francisella-macrophage co-culture model, compared with free streptomycin or streptomycin delivered by control PEGylated liposomes (13× and 16×, respectively). This study suggests the potential of PALs as a useful platform to deliver antibiotics for the treatment of intracellular macrophage infections.

Structural mechanism of AadA, a dual-specificity aminoglycoside adenylyltransferase from Salmonella enterica.

Streptomycin and spectinomycin are antibiotics that bind to the bacterial ribosome and perturb protein synthesis. The clinically most prevalent bacterial resistance mechanism is their chemical modification by aminoglycoside-modifying enzymes such as aminoglycoside nucleotidyltransferases (ANTs). AadA from Salmonella enterica is an aminoglycoside (3″)(9) adenylyltransferase that O-adenylates position 3″ of streptomycin and position 9 of spectinomycin. We previously reported the apo-AadA structure with a closed active site. To clarify how AadA binds ATP and its two chemically distinct drug substrates, we here report crystal structures of WT AadA complexed with ATP, magnesium, and streptomycin and of an active-site mutant, E87Q, complexed with ATP and streptomycin or the closely related dihydrostreptomycin. These structures revealed that ATP binding induces a conformational change that positions the two domains for drug binding at the interdomain cleft and disclosed the interactions between both domains and the three rings of streptomycin. Spectinomycin docking followed by molecular dynamics simulations suggested that, despite the limited structural similarities with streptomycin, spectinomycin makes similar interactions around the modification site and, in agreement with mutational data, forms critical interactions with fewer residues. Using structure-guided sequence analyses of ANT(3″)(9) enzymes acting on both substrates and ANT(9) enzymes active only on spectinomycin, we identified sequence determinants for activity on each substrate. We experimentally confirmed that Trp-173 and Asp-178 are essential only for streptomycin resistance. Activity assays indicated that Glu-87 is the catalytic base in AadA and that the nonadenylating E87Q mutant can hydrolyze ATP in the presence of streptomycin.

Regulation of antibiotic production in Actinobacteria: new perspectives from the post-genomic era.

Covering: 2000 to 2018 The antimicrobial activity of many of their natural products has brought prominence to the Streptomycetaceae, a family of Gram-positive bacteria that inhabit both soil and aquatic sediments. In the natural environment, antimicrobial compounds are likely to limit the growth of competitors, thereby offering a selective advantage to the producer, in particular when nutrients become limited and the developmental programme leading to spores commences. The study of the control of this secondary metabolism continues to offer insights into its integration with a complex lifecycle that takes multiple cues from the environment and primary metabolism. Such information can then be harnessed to devise laboratory screening conditions to discover compounds with new or improved clinical value. Here we provide an update of the review we published in NPR in 2011. Besides providing the essential background, we focus on recent developments in our understanding of the underlying regulatory networks, ecological triggers of natural product biosynthesis, contributions from comparative genomics and approaches to awaken the biosynthesis of otherwise silent or cryptic natural products. In addition, we highlight recent discoveries on the control of antibiotic production in other Actinobacteria, which have gained considerable attention since the start of the genomics revolution. New technologies that have the potential to produce a step change in our understanding of the regulation of secondary metabolism are also described.

Drug Partitioning in Micellar Media and Its Implications in Rational Drug Design: Insights with Streptomycin.

Oral bioavailability of a drug molecule requires its effective delivery to the target site. In general, majority of synthetically developed molecular entities have high hydrophobic nature as well as low bioavailability, therefore the need for suitable delivery vehicles arises. Self-assembled structures such as micelles, niosomes, and liposomes have been used as effective delivery vehicles and studied extensively. However, the information available in literature is mostly qualitative in nature. We have quantitatively investigated the partitioning of antibiotic drug streptomycin into cationic, nonionic, and a mixture of cationic and nonionic surfactant micelles and its interaction with the transport protein serum albumin upon subsequent delivery. A combination of calorimetry and spectroscopy has been used to obtain the thermodynamic signatures associated with partitioning and interaction with the protein and the resulting conformational changes in the latter. The results have been correlated with other class of drugs of different nature to understand the role of molecular features in the partitioning process. These studies are oriented toward understanding the physical chemistry of partitioning of a variety of drug molecules into suitable delivery vehicles and hence establishing structure-property-energetics relationships. Such studies provide general guidelines toward a broader goal of rational drug design.

The complete genome sequence of the actinobacterium Streptomyces glaucescens GLA.O (DSM 40922) carrying gene clusters for the biosynthesis of tetracenomycin C, 5`-hydroxy streptomycin, and acarbose.

The secondary metabolite acarbose is used worldwide in the clinical treatment of diabetes mellitus type 2 patients. Acarbose is a - glucosidase inhibitor and supports patients to control their blood glucose as well as their serum insulin levels. The secondary metabolite is produced by strains of the class Actinobacteria, in particular from Actinoplanes sp. SE50/110, which is a progenitor of today`s production strains. Moreover, secondary metabolite clusters could also be identified in Streptomyces coelicoflavus ZG0656 as well as Streptomyces glaucescens GLA.O. In this study, the genome S. glaucescens GLA.O with focus on the acarbose biosynthesis cluster (gac-cluster) was analyzed. First, the tetracenomycin C and the 5`-hydroxy streptomycin gene clusters could be described completely. Then the gac gene region in S. glaucescens GLA.O is compared to the other known biosynthesis gene cluster. In comparison to Actinoplanes sp. SE50/110 the gac-cluster showed structural variances, like the missing homolog of the glycosyltransferase AcbD in the whole genome of S. glaucescens GLA.O. Due to the lack of the glycosyltransferase, it was of particular interest whether additional acarviose metabolites other than acarbose could be formed. For detection of acarviose metabolites biosynthesis the supernatant of S. glaucescens GLA.O grown in starch supplemented complex media was harvested at 72 and 96 hours. Although a homolog of the known glycosyltransferase is absent, the LC-MS-supported analysis revealed that a spectrum of acarviose metabolites was formed.

Enhancement of butanol production by sequential introduction of mutations conferring butanol tolerance and streptomycin resistance.

Ribosome engineering, originally applied to Streptomyces lividans, has been widely utilized for strain improvement, especially for the activation of bacterial secondary metabolism. This study assessed ribosome engineering technology to modulate primary metabolism, taking butanol production as a representative example. The introduction into Clostridium saccharoperbutylacetonicum of mutations conferring resistance to butanol (ButR) and of the str mutation (SmR; a mutation in the rpsL gene encoding ribosomal protein S12), conferring high-level resistance to streptomycin, increased butanol production 1.6-fold, to 16.5 g butanol/L. Real-time qPCR analysis demonstrated that the genes involved in butanol metabolism by C. saccharoperbutylacetonicum were activated at the transcriptional level in the drug-resistant mutants, providing a mechanism for the higher yields of butanol by the mutants. Moreover, the activity of enzymes butyraldehyde dehydrogenase (AdhE) and butanol dehydrogenases (BdhAB), the key enzymes involved in butanol synthesis, was both markedly increased in the ButR SmR mutant, reflecting the significant up-regulation of adhE and bdhA at transcriptional level in this mutant strain. These results demonstrate the efficacy of ribosome engineering for the production of not only secondary metabolites but of industrially important primary metabolites. The possible ways to overcome the reduced growth rate and/or fitness cost caused by the mutation were also discussed.

A new subclass of intrinsic aminoglycoside nucleotidyltransferases, ANT(3")-II, is horizontally transferred among Acinetobacter spp. by homologous recombination.

The emergence and spread of antibiotic resistance among Acinetobacter spp. have been investigated extensively. Most studies focused on the multiple antibiotic resistance genes located on plasmids or genomic resistance islands. On the other hand, the mechanisms controlling intrinsic resistance are still not well understood. In this study, we identified the novel subclass of aminoglycoside nucleotidyltransferase ANT(3")-II in Acinetobacter spp., which comprised numerous variants distributed among three main clades. All members of this subclass can inactivate streptomycin and spectinomycin. The three ant(3")-II genes, encoding for the three ANT(3")-II clades, are widely distributed in the genus Acinetobacter and always located in the same conserved genomic region. According to their prevalence, these genes are intrinsic in Acinetobacter baumannii, Acinetobacter pittii, and Acinetobacter gyllenbergii. We also demonstrated that the ant(3")-II genes are located in a homologous recombination hotspot and were recurrently transferred among Acinetobacter species. In conclusion, our findings demonstrated a novel mechanism of natural resistance in Acinetobacter spp., identified a novel subclass of aminoglycoside nucleotidyltransferase and provided new insight into the evolutionary history of intrinsic resistance genes.

Streptomycin favors biofilm formation by altering cell surface properties.

Studies have shown that external stress induces biofilm formation, but the underlying details are not clearly understood. This study investigates the changes in cell surface properties leading to increase in biofilm formation by Staphylococcus aureus and Pseudomonas aeruginosa in the presence of streptomycin. Bacterial attachment in the presence and absence of streptomycin was quantified by fluorescence spectroscopy. In addition, cell surface charge and contact angle were measured and the free energy barrier for attachment was modeled using extended Derjaguin-Landau-Verwey-Overbeek (xDLVO) theory. Peptides from bacterial cell surface were shaved by protease treatment and identified with ultra-performance liquid chromatography (UPLC)-QTOF and a homology search program SPIDER. Biofilm formation increased significantly in the presence of streptomycin (10 mg/L) in the culture. Bacterial cell surface charge reduced, and hydrophobicity increased leading to a net decrease in the free energy barrier for attachment. Extracellular matrix-binding protein was positively regulated in S. aureus under stress, indicating stronger interaction between bacterial cells and solid surface. In addition, several other proteins including biofilm regulatory proteins, multidrug efflux pumps, transporters, signaling proteins, and virulence factors were differentially expressed on bacterial cell surface, which is indicative of a strong stress response by bacteria to streptomycin treatment.

Streptomycin affinity depends on 13 amino acids forming a loop in homology modelled ribosomal S12 protein (rpsL gene) of Lysinibacillus sphaericus DSLS5 associated with marine sponge (Tedania anhelans).

Streptomycin, an antibiotic used against microbial infections, inhibits the protein synthesis by binding to ribosomal protein S12, encoded by rpsL12 gene, and associated mutations cause streptomycin resistance. A streptomycin resistant, Lysinibacillus sphaericus DSLS5 (MIC >300 µg/mL for streptomycin), was isolated from a marine sponge (Tedania anhelans). The characterisation of rpsL12 gene showed a region having similarity to long terminal repeat sequences of murine lukemia virus which added 13 amino acids for loop formation in RpsL12; in addition, a K56R mutation which corresponds to K43R mutation present in streptomycin-resistant Escherichia coli is also present. The RpsL12 protein was modelled and compared with that of Lysinibacillus boronitolerans, Escherichia coli and Mycobacterium tuberculosis. The modelled proteins docked with streptomycin indicate compound had less affinity. The effect of loop on streptomycin resistance was analysed by constructing three different models of RpsL12 by, (i) removing both loop and mutation, (ii) removing the loop alone while retaining the mutation and (iii) without mutation having loop. The results showed that the presence of loop causes streptomycin resistance (decreases the affinity), and it further enhanced in the presence of mutation at 56th codon. Further study will help in understanding the evolution of streptomycin resistance in organisms.

Streptomycin potency is dependent on MscL channel expression.

The antibiotic streptomycin is widely used in the treatment of microbial infections. The primary mechanism of action is inhibition of translation by binding to the ribosome, but how it enters the bacterial cell is unclear. Early in the study of this antibiotic, a mysterious streptomycin-induced potassium efflux preceding any decrease in viability was observed; it was speculated that this changed the electrochemical gradient such that streptomycin better accessed the cytoplasm. Here we use a high-throughput screen to search for compounds targeting the mechanosensitive channel of large conductance (MscL) and find dihydrostreptomycin among the 'hits'. Furthermore, we find that MscL is not only necessary for the previously described streptomycin-induced potassium efflux, but also directly increases MscL activity in electrophysiological studies. The data suggest that gating MscL is a novel mode of action of dihydrostreptomycin, and that MscL's large pore may provide a mechanism for cell entry.