Mode of action of gentamicin

Reverse stable isotope labelling with Raman spectroscopy for microbial proteomics

Global proteome changes in microbes affect the survival and overall production of commercially relevant metabolites through different bioprocesses. The existing methods to monitor proteome level changes are destructive in nature. Stable isotope probing (SIP) coupled with Raman spectroscopy is a relatively new approach for proteome analysis. However, applying this approach for monitoring changes in a large culture volume is not cost-effective. In this study, for the first time we are presenting a novel method of combining reverse SIP using 13 C-glucose and Deuterium to monitor the proteome changes through Raman spectroscopy. The findings of the study revealed visible changes (blue shifts) in proteome related peaks that can be used for monitoring proteome dynamics, that is, synthesis of nascent amino acids and its turnover with time in a non-destructive, cost-effective, and label-free manner.

Surface enhanced fluorescence and nanoscopic cell wall deformation in adhering Staphylococcus aureus upon exposure to cell wall active and non-active antibiotics

In infections, bacteria often adhere to surfaces and become deformed by the forces with which they adhere. Nanoscopic cell wall deformation defines bacterial responses to environmental conditions and is likely influenced by antibiotics. Here, staphylococcal cell wall deformation upon exposure to cell wall active and non-active antibiotics or their combinations is compared for two green-fluorescent (GFP) isogenic Staphylococcus aureus strains adhering to a gold surface, of which one lacks peptidoglycan cross-linking. Exposure to cell wall active antibiotics caused greater cell wall deformation than a buffer control in the GFP parent and in the Δpbp4GFP isogenic mutant, as measured by surface-enhanced-fluorescence. Cell wall non-active antibiotics only yielded greater deformation than a buffer control in the parent strain, while combinations of cell wall active and non-active antibiotics did not cause greater cell wall deformation. 3D-analysis of the impact of adhesion forces and Young's moduli of the cell wall, both measured using atomic force microscopy, led to the conclusion that increased deformation was mainly due to cell wall weakening and not due to the effects of antibiotics on adhesion forces. Interactions between bacteria and antibiotics are mostly studied using planktonic bacteria, while during infection, bacteria are in an adhering state that deforms their cell wall and therewith influences their adaptive responses. We anticipate that the demonstration of cell wall weakening in adhering bacteria under the influence of antibiotics and the role of peptidoglycan herein will aid in the development of new antibiotics. Surface-enhanced-fluorescence may accordingly develop into a new, highly-sensitive method for diagnosing antibiotic-resistant bacteria.

A Tick Antivirulence Protein Potentiates Antibiotics against Staphylococcus aureus

New strategies are needed to combat antibiotic resistance, especially against pathogens such as methicillin-resistant Staphylococcus aureus A tick antifreeze glycoprotein, IAFGP, possesses potent antibiofilm properties against a variety of clinical pathogens, including S. aureus Synergy between IAFGP, or a peptide (P1) representative of a repeat region of the protein, with different antibiotics was assessed in vitro Antibiotics that synergized with either IAFPG or P1 were further evaluated in vivo using vertebrate and invertebrate infection models. IAFGP readily enhanced the efficacy of antibiotics against S. aureus Synergy with daptomycin, an antibiotic used to treat methicillin-resistant S. aureus, was observed in vitro and in vivo using iafgp-transgenic mice and flies. Furthermore, synergy with ciprofloxacin or gentamicin, antibiotics not generally used to treat S. aureus, was also perceived. The combined effect of the antibiotic and IAFGP was associated with improved permeation of the antibiotic into the cell. Our results highlight that synergy of IAFGP with antibiotics traditionally used to treat this pathogen, and enhancement of the potency of antibiotics not commonly used against this microbe, can provide novel alternative therapeutic strategies to combat bacterial infections.

Phosphate concentration and the putative sensor kinase protein CckA modulate cell lysis and release of the Rhodobacter capsulatus gene transfer agent

The gene transfer agent of Rhodobacter capsulatus (RcGTA) is a bacteriophage-like genetic element with the sole known function of horizontal gene transfer. Homologues of RcGTA genes are present in many members of the alphaproteobacteria and may serve an important role in microbial evolution. Transcription of RcGTA genes is induced as cultures enter the stationary phase; however, little is known about cis-active sequences. In this work, we identify the promoter of the first gene in the RcGTA structural gene cluster. Additionally, gene transduction frequency depends on the growth medium, and the reason for this is not known. We report that millimolar concentrations of phosphate posttranslationally inhibit the lysis-dependent release of RcGTA from cells in both a complex medium and a defined medium. Furthermore, we found that cell lysis requires the genes rcc00555 and rcc00556, which were expressed and studied in Escherichia coli to determine their predicted functions as an endolysin and holin, respectively. Production of RcGTA is regulated by host systems, including a putative histidine kinase, CckA, and we found that CckA is required for maximal expression of rcc00555 and for maturation of RcGTA to yield gene transduction-functional particles.

Gentamicins

Gentamicin is a new broad-spectrum antibiotic, basic and water-soluble, produced and developed by Schering Corporation-Bloomfield, New Jersey (1967 and 1968). It is produced by Micromonospora purpurea, a member of a genus of microorganisms from which no other antibiotics have been derived. Paper chromatographic techniques showed the components of gentamicin complex designated as C', C'a, and C2. Gentamicins are bactericidal antibiotics, active in vivo in low concentrations against a wide spectrum of both Gram-positive and Gram-negative organisms. Among the responsive Gram-positive groups of microorganisms are Staphylococcus aureus including many resistant penicillinase producing strains and group A betahemolytic Streptococci. Among the clinically more important species of Gram-positive organisms responsive to gentamicin are both indole-positive and indole-negative Proteus, Pseudomonas, Escherichia coli, Aerobacter, Klebsiella, Salmonella, and Shigella. The production of gentamicins was improved by adding cobalt to the growth medium.

Gentamicin as a bactericidal antibiotic in tissue culture

The effects of gentamicin on cellular physiology were studied in a total of 9 mammalian cell lines, using the following parameters: cell morphology and viability (cytotoxicity), proliferation, culture medium acidification, lactic acid production, lactate dehydrogenase release, virus susceptibility, and effects on karyotype. With regard to cytotoxicity no gross differences could be found in the sensitivity of the diploid and aneuploid cells investigated, as judged by morphological criteria. However, cells exposed to the antibiotic in the lag-log phase of growth showed damage at lower concentrations (1000 mug/ml) than cells treated in the stationary phase (2000 mug/ml). As regards the influence of gentamicin on cell growth and metabolsim, dose-response relationship were found proving that the antibiotic causes a depression of proliferation, a striking increase in lactate production, an elevated LDH release, and changes in pH behaviour. All these parameters were unaffected by concentrations up to 125 mug/ml. No gross changes in chromosome morphology and number could be detected in huploid cell line after 10 passages with 50 mug/ml gentamicin in lieu of the usual penicillin plus streptomycin combination. The minimal bactericidal concentrations (MBC) were determined in cell-free media and in tissue cultures against 4 species of bacteria. The MBC of gentamicin was generally lower as compared with the penicillin plus streptomycin combination. In some instances MBC was higher in the presence than in the absence of ti-sue culture cells. Comparison of the bactericidal efficiency against 31 strains of 7 species of bacteria of gentamicin (50 mug/ml) and penicillin plus streptomycin (100 units plus 100 mug/ml) in cell cultures proved that gentamicin is superior for control of bacterial growth in tissue culture.