An Electron Microscopic Study of Antagonism between Cephalexin and Erythromycin in Staphylococcus aureus

This study concerns investigations at the cellular level of antagonism between cephalexin (CEX) and erythromycin (EM) with the aid of electron microscopes and a liquid scintillation counter. Exposure of Staphylococcus aureus 209-P to CEX and EM in combination was found to result in a marked antagonism between the two antibiotics in their effects on the growth of the organism. Observations under a scanning electron microscope revealed lysed cells in the presence of CEX alone but almost no lysis in the presence of a combination of CEX and EM. Observations under a transmission electron microscope, on the other hand, disclosed that nearly all of the cells exposed to 20 μg/ml of CEX were transformed into protoplasts with their morphological changes being most marked after 4 hr of exposure. When 1 μg/ml of EM was allowed to act alone, this exposure resulted in thickening of the cell walls. The combined use of CEX and EM, however, resulted in neither thickening of the cell walls as in the presence of EM alone nor in the formation of protoplasts as in the presence of CEX alone but merely produced the swelling of separating walls. Cellular uptake of ¹⁴C-L -lysine and N-acetylglucosamine-1-¹⁴C into the cell wall fraction and the protein fraction was affected by CEX and EM, respectively, when used alone or in combination.     

In Vitro Antimicrobial Activity and Human Pharmacology of Cephalexin, a New Orally Absorbed Cephalosporin C Antibiotic

Concentrations of cephalexin (an orally absorbed derivative of cephalosporin C) in serum and urine were determined in normal volunteers and patients. The in vitro antibacterial activity was also studied. All strains of group A β-hemolytic streptococci and Diplococcus pneumoniae were inhibited by 3.1 μg/ml. Of the Staphylococcus aureus strains, 88% were inhibited by 6.3 μg/ml, and 12.5 μg/ml was inhibitory for all S. aureus, 80% of Escherichia coli, 72% of Klebsiella-Aerobacter, and 56% of Proteus mirabilis strains. About 90 to 96% of E. coli, Klebsiella Aerobacter, and P. mirabilis strains were inhibited by 25 μg of cephalexin per ml. Pseudomonas and indole-positive Proteus strains proved to be quite resistant to cephalexin. Cephalexin was well absorbed after oral administration. A peak serum concentration of cephalexin of at least 5 μg/ml was achieved in each volunteer with 250 and 500-mg doses. A mean peak serum concentration of 7.7 μg/ml was achieved with 250-mg doses; 12.3μg/ml was achieved with 500-mg doses of antibiotic. Food did not interfere with absorption. Probenecid enhanced both the peak serum concentration and the duration of antibiotic activity in the serum. Over 90% of the administered dose was excreted in the urine within 6 hr. The mean peak serum concentration of cephalexin after an oral dose of 500 mg was adequate to inhibit all group A streptococci, D. pneumoniae, and S. aureus, 85% of E. coli, and about 40 to 75% of Klebsiella-Aerobacter and P. mirabilis strains. Levels of cephalexin in urine were adequate to inhibit over 90% of E. coli, and P. mirabilis and 80 to 96% of Klebsiella-Aerobacter strains.     

Drug Resistance of Staphylococci

According to an epidemiological survey of drug resistance in Staphylococcus aureus, it was found that there are three types of cross-resistance to macrolide antibiotics (EM, erythromycin: OM, oleandomycin: LM, leucomycin: SP, spiramycin), i.e., resistance to EM, OM, LM, and SP, to EM and OM, and inducible resistance to “EM, OM”. In the inducible strains of S. aureus, EM and OM are active inducers, and the optimal concentrations of the inducers are 0.1 μg/ml and 1.0 μg/ml, respectively. The induction of high resistance (800 μg/ml or more) to both EM and OM occurred within 10 min exposure to 0.1 μg/ml of EM, and the resistance of induced cells was lost after overnight growth in the absence of inducer. After 1 to 3 hr exposure to 1.0 μg/ml of OM, the inducible strains acquired high resistance (100 μg/ml or more) to EM and to a lesser extent, resistance to OM, and the acquired resistance was lost when grown in antibiotic free media. When a known concentration of EM was mixed with the induced cells or with a crude extract from induced cells which had acquired high resistance to EM and OM, the antibiotic activity of EM was still retained in the mixture, indicating that the induced mixture or the extract from the induced cells was incapable of antibiotic (EM) inactivation under the test conditions.     

A New Antimicrobial Fatty Acid from the Calcareous Sponge Paragrantia cf. waguensis

A new acetylenic fatty acid, 1 , has been isolated from the title sponge. The structure of the molecule was elucidated to contain an enyne and a thiophene by spectroscopic methods. Compound 1 showed a weak cytotoxic effect against NBT‐T2 rat bladder epithelial cells (IC₅₀>20 μg/ml), and antimicrobial activity with minimal‐inhibitory concentrations (MIC) of 64 and 128 μg/ml against Staphylococcus aureus and Escherichia coli, respectively.     

Ciprofloxacin-Induced Antibacterial Activity is Reversed by Vitamin E and Vitamin C

In the present study, we investigated the possible involvement of oxidative stress in ciprofloxacin-induced cytotoxicity against several reference bacteria including Pseudomonas aeruginosa ATCC 27853, Escherichia coli ATCC 25922, Staphylococcus aureus ATCC 29213, and clinical isolate of methicillin-resistant Staphylococcus aureus (MRSA). Oxidative stress was assessed by measurement of hydrogen peroxide generation using a FACScan flow cytometer. The antibacterial activity of ciprofloxacin was assessed using the disk diffusion method and by measuring the minimum inhibitory concentration (MIC). Ciprofloxacin induced a dose-dependent antibacterial activity against all bacteria where the highest tested concentration was 100 ug/ml. Results revealed that E. coli cells were highly sensitive to ciprofloxacin (MIC = 0.21 μg/mL ± 0.087), P. aeruginosa and S. aureus cells were intermediately sensitive (MIC = 5.40 μg/mL ± 0.14; MIC = 3.42 μg/mL ± 0.377, respectively), and MRSA cells were highly resistant (MIC = 16.76 μg/mL ± 2.1). Pretreatment of E. coli cells with either vitamin E or vitamin C has significantly protected cells against ciprofloxacin-induced cytotoxicity. These results indicate the possible antagonistic properties for vitamins C or E when they are used concurrently with ciprofloxacin.     

Inactivation and injury of Escherichia coli O157:H7 and Staphylococcus aureus by pulsed electric fields

Two pathogenic microorganisms Escherichia coli O157:H7 and Staphylococcus aureus, suspended in peptone solution (0.1% w/v) were treated with 12, 14, 16 and 20 kV/cm electric field strengths with different pulse numbers up to 60 pulses. Pulsed electric field (PEF) treatment at 20 kV/cm with 60 pulses provided nearly 2 log reduction in viable cell counts of E. coli O157:H7 and S. aureus. S. aureus cells were slightly more resistant than E.coli O157:H7 cells. The results related to the effect of initial cell concentration of E. coli O157:H7 on the PEF inactivation showed that more inactivation was obtained by decreasing initial cell concentration. Any possible injury by PEF was also investigated after applying 20 kV/cm electric field to the microorganisms. As a result, it was determined that there was 35.92 to 43.36% injury in E. coli O157:H7 cells, and 17.26 to 30.86% injury in S. aureus cells depending on pulse number. The inactivation results were also described by a kinetic model.     

In Vitro Antibacterial Activity of 4-Phenyl-1-(2-phenyl-allyl)pyridinium bromide: A Novel Class of Pyridinium Based Antibacterial Compounds

The continuing increase in the incidence of multi drug resistant pathogenic bacteria and shortage of new antimicrobial agents are the prime driver in efforts to identify the novel antimicrobial classes. In vitro antibacterial activity of 4-phenyl-1-(2-phenylallyl) pyridinium bromide was tested against Gram positive Staphylococcus aureus, Streptococcus species, Bacillus subtilis, and Gram negative Klebsiella aerogenes and Escherichia coli using disk diffusion method. Among them S. aureus showed strong antibacterial activity (21.99 ± 0.03 mm) while E. coli showed very little activity (8.97 ± 0.06 mm) towards the compound. The MIC of 4-phenyl-1-(2-phenyl-allyl)-pyridinium bromide for 90% S. aureus was ≤20 μg/ml and was compared with phenoxymethylpenicillin, cloxacillin, erythromycin and vancomycin. When 4-phenyl-1-(2-phenyl-allyl)pyridinium bromide showed MIC at ≤20 μg/ml, all others showed MIC at ≤100 μg/ml. Strong antibacterial activity of 4-phenyl-1-(2-phenyl-allyl)pyridinium bromide against S. aureus indicates that there is a possibility to use it as an effective antibacterial agent.     

Effects of 50 Hz rotating magnetic field on the viability of Escherichia coli and Staphylococcus aureus

This study presents results of research on the influence of rotating magnetic field (RMF) of the induction of 30?mT and the frequency of 50?Hz on the growth dynamics and cell metabolic activity of E. coli and S. aureus, depending on the exposure time. The studies showed that the RMF caused an increase in the growth and cell metabolic activity of all the analyzed bacterial strains, especially in the time interval t?=?30 to 150?min. However, it was also found that the optical density and cell metabolic activity after exposition to RMF were significantly higher in S. aureus cultures. In turn, the study of growth dynamics, revealed a rapid and a significant decrease in these values from t?=?90?min) in the case of E. coli samples. The obtained results prove that RMF (B?=?30?mT, f?=?50?Hz) has a stimulatory effect on the growth and metabolic activity of E. coli and S. aureus. Furthermore, taking into account the time of exposure, stronger influence of RMF on the viability was observed in S. aureus cultures, which may indicate that this effect depends on the shape of the exposed cells.     

High pressure homogenization inactivation of Escherichia coli and Staphylococcus aureus in phosphate buffered saline,milk and apple juice

High pressure homogenization (HPH) offers new opportunities for food pasteurization/sterilization. Escherichia coli and Staphylococcus aureus suspended in phosphate buffered saline (PBS) buffer, milk and apple juice at initial concentration of ~10⁶ log₁₀ CFU per ml were subjected to HPH treatments up to 200 MPa with inlet temperatures at 4–40°C. After HPH at 200 MPa with the inlet temperature at 40°C, the count of E. coli suspended in PBS, milk and apple juice reduced by 3·42, 3·67 and 3·19 log₁₀ CFU per ml respectively while the count of S. aureus decreased by 2·21, 1·02 and 2·33 log₁₀ CFU per ml respectively suggesting that S. aureus was more resistant. The inactivation data were well fitted by the polynomial equation. Milk could provide a protective effect for S. aureus against HPH. After HPH at 200 MPa with the inlet temperature at 20°C, the cell structure of E. coli was destroyed, while no obvious damages were found for S. aureus.     

A Novel GFP-Fused Eukaryotic Membrane Protein Expression System in Lactococcus lactis and Its Application to Overexpression of an Elongase

Ultraviolet (UV) irradiation has high potential to inactivate a wide range of biologic agents and is one of several nonadditive technologies being studied. The photoinactivation property of pulsed UV laser radiation (at wavelengths of 355 and 266 nm), used as an effective physical means to inactivate two typical microorganisms, prokaryotic (Escherichia coli K12) and eukaryotic (Saccharomyces cerevisiae), with respect to dose and exposure times, was examined. An E. coli population of 1.6 × 10⁴ colony-forming units (CFU)/ml was inactivated with a dose of 16.7 J/cm² energy at 355-nm wavelength. However, E. coli cells at higher concentrations were inactivated by only 98% using the same dose. Interestingly, an E. coli population of 2 × 10⁷ CFU/ml was completely inactivated using only 0.42 J/cm² at 266-nm wavelength (P ≤ 0.05). With respect to S. cerevisiae, the results were similar to those of E. coli irradiation considering that S. cerevisiae is 100 times larger than E. coli. A dose of 16.7 J/cm² completely inactivated an S. cerevisiae population of 6 × 10³ CFU/ml at 355-nm wavelength. Exposure to 266-nm wavelength, with energy doses of 1.67, 0.835, and 0.167 J/cm², successfully inactivated S. cerevisiae populations of 3 × 10⁶, 1.4 × 10⁵, and 1.5 × 10⁴ CFU/ml, respectively (P ≤ 0.05). In conclusion, compared with 355-nm wavelength, a pulsed UV laser at 266-nm wavelength inactivated a high titer of bacterial and yeast indicator standards suspended in phosphate-buffered saline-A.     

Chemical Composition and Antimicrobial Activity of Essential Oils from Chromolaena laevigata during Flowering and Fruiting Stages

The chemical compositions and antimicrobial activities of essential oils from the leaves, stems, capitula, and cypselas of Chromolaena laevigata were evaluated at two different phenological stages, flowering and fruiting. Thirty‐eight compounds were identified in the crude oils by GC/MS. The sesquiterpene laevigatin was the major constituent of the leaf, capitulum, and cypsela oils, while the sesquiterpene spathulenol was the main component in the stem oils. The antimicrobial activities of the oils were evaluated against Candida albicans, Staphylococcus aureus, Pseudomonas aeruginosa, and Escherichia coli. Stem oil obtained from Chromolaena laevigata during the fruiting stage generally showed the highest activity with minimum inhibitory concentration (MIC) values of 62.5 μg/ml against Candida albicans and S. aureus, and 500 μg/ml against P. aeruginosa and E. coli. Pure laevigatin exhibited MIC values of 500 and 125 μg/ml against C. albicans and S. aureus, respectively, indicating that this constituent could be responsible, at least in part, for the antimicrobial activities detected in the crude oils. More studies concerning the biological activities of isolated derivatives are required to improve our knowledge of the antimicrobial potential of volatile compounds present in native plants.     

Effect of the Live and Heat-Killed Cells of Staphylococcus aureus on the Resistance of Mice to the Infection with Nocardia asteroides

When living cells of Staphylococcus aureus were introduced into mice by various routes within a few hours before or after infection with Nocardia asteroides, a marked increase in mortality and enhanced severity of lesions were observed. This effect was presumably caused by a heat-labile substance(s) liberated from the cells of S. aureus. No increase in resistance occurred when S. aureus was given 2 to 7 days before the nocardial infection, contrary to the effect of E. coli as reported previously. An increased resistance was noted when heat-killed cells of E. coli were administered two to four days before concurrent infection with N. asteroides and S. aureus.     

Synergistic antibacterial activity of carvacrol loaded chitosan nanoparticles with Topoisomerase inhibitors and genotoxicity evaluation

The increasing prevalence of antibiotic resistant bacteria is a significant healthcare crisis with substantial socioeconomic impact on global community. The development of new antibiotics is both costly and time-consuming prompting the exploration of alternative solutions such as nanotechnology which represents opportunities for targeted drug delivery and reduced MIC. However, concerns have arisen regarding genotoxic effects of nanoparticles on human health necessitating an evaluation of nanoparticle induced DNA damage.This study aimed to investigate the antibacterial potential of already prepared, characterized chitosan nanoparticles loaded with carvacrol and their potential synergism with Topoisomerase II inhibitors against S. aureus, E. coli and S. typhi using agar well diffusion, microdilution and checkerboard method. Genotoxicity was assessed through comet assay.Results showed that both alone and drug combinations of varying concentrations exhibited greater zones of inhibition at higher concentrations. Carvacrol nanoparticles combined with ciprofloxacin and doxorubicin significantly reduced MIC compared to the drugs used alone. The MIC₅₀ values for ciprofloxacin were 35.8 µg/ml, 48.74 µg/ml, 35.57 µg/ml while doxorubicin showed MIC₅₀ values of 20.79 µg/ml, 34.35 µg/ml, 25.32 µg/ml against S. aureus, E. coli and S. typhi respectively. The FICI of ciprofloxacin and doxorubicin with carvacrol nanoparticles found ≤ 0.5 Such as 0.44, 0.44,0.48 for ciprofloxacin and 0.45, 0.45, 0.46 for doxorubicin against S. aureus, E. coli and S. typhi respectively revealed the synergistic effect. The analysis of comet assay output images showed alteration of DNA at high concentrations.Our results suggested that carvacrol nanoparticles in combination with Topoisomerase inhibitors may prevent and control the emergence of resistant bacteria with reduced dose.     

The Status and the Role of Glutathione under Disturbed Ionic Balance and pH Homeostasis in Escherichia coli

The study of glutathione status in aerobically grown Escherichia coli cultures showed that the total intracellular glutathione (GSH_in + GSSG_in) level falls by 63% in response to a rapid downshift in the extracellular pH from 6.5 to 5.5. The incubation of E. coli cells in the presence of 50 mM acetate or 10 g/ml gramicidin S decreased the total intracellular glutathione level by 50 and 25%, respectively. The fall in the total intracellular glutathione level was accompanied by a significant decrease in the (GSH_in : GSSG_in) ratio. The most profound effect on the extracellular glutathione level was exerted by gramicidin S, which augmented the total glutathione level by 1.8 times and the (GSH_out : GSSG_out) ratio by 2.1 times. The gramicidin S treatment and acetate stress inhibited the growth of mutant E. coli cells defective in glutathione synthesis 5 and 2 times more severely than the growth of the parent cells. The pH downshift and the exposure of E. coli cells to gramicidin S and 50 mM acetate enhanced the expression of the sodA gene coding for superoxide dismutase SodA.     

Study on the Composition and Physiological Activity of the Essential Oils and Extracts of Cinnamomum camphora Fruit

Supercritical carbon dioxide (SC-CO₂), hydrodistillation (HDO), ethanol extraction (EE), and petroleum ether extraction (PE) were used to extract the essential oil and extracts of Cinnamomum camphora fruit in this study. Gas chromatography-mass spectrometry was used to identify the volatile components of essential oils and extracts, and 63 compounds were identified. 2,2-Diphenyl-1-picrylhydrazyl (DPPH) and 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical scavenging assay and Ferric reducing ability of plasma (FRAP) assays and the inhibition experiment of bacteria and fungi (Staphylococcus aureus (S. aureus), Hay bacillus (H. bacillus), Escherichia coli (E. coli), Aspergillus niger (A. niger), Candida albicans (C. albicans)) showed these essential oils and extracts indicated antioxidant and antibacterial activities. S. aureus was the most sensitive to the essential oil (MIC=0.08 mg/ml). Combined with the Brine Shrimp Lethality Test (BSLT) experiment, HDO (LD₅₀=68.21 μg/ml) was considered to have the most potential natural preservative. Subsequently, the inhibitory mechanism of HDO on bacteria and fungi was explored through extracellular conductivity and SEM, and the possibility of HDO to preserve the freshness of bananas was verified through banana shelf-life experiments. The results suggested these essential oils and extracts of Cinnamomum camphora fruit indicated effectively inhibit the growth of microorganisms on the surface of bananas, extend the shelf-life, and have the potential to become a natural antiseptic ingredient.     

Construction and synthesis of lactoferricin derivatives with enhanced antibacterial activity

A series of peptides derived from sequences from human, bovine, murine and caprine lactoferrin has been prepared and investigated for antibacterial effect. Among the four species investigated peptides based on the bovine sequence displayed significant activity. The bovine sequence, bovine lactoferricin, showed a MIC value of 30 μg/mL on E. coli and S. aureus, whereas the three other lactoferricins possessed MIC values above 200 μg/mL. Based on these findings, novel peptides with enhanced antibacterial activities, were prepared with sequences designed by molecular modelling and structure‐activity studies. Copyright © 1999 European Peptide Society and John Wiley & Sons, Ltd.     

Molecular cloning and expression of ranalexin, a bioactive antimicrobial peptide from Rana catesbeiana in Escherichia coli and assessments of its biological activities

The coding sequence, which corresponds to the mature antimicrobial peptide ranalexin from the frog Rana catesbeiana, was chemically synthesized with preferred codons for expression in Escherichia coli. It was cloned into the vector pET32c (+) to express a thioredoxin-ranalexin fusion protein which was produced in soluble form in E. coli BL21 (DE3) induced under optimized conditions. After two purification steps through affinity chromatography, about 1 mg of the recombinant ranalexin was obtained from 1 L of culture. Mass spectrometrical analysis of the purified recombinant ranalexin demonstrated its identity with ranalexin. The purified recombinant ranalexin is biologically active. It showed antibacterial activities similar to those of the native peptide against Staphylococcus aureus, Streptococcus pyogenes, E. coli, and multidrug-resistant strains of S. aureus with minimum inhibitory concentration values between 8 and 128 μg/ml. The recombinant ranalexin is also cytotoxic in HeLa and COS7 human cancer cells (IC₅₀?=?13–15 μg/ml).     

Design,Synthesis, Docking Study of Pyrazolohydrazinopyrimidin-4-one Derivatives and Their Application as Antimicrobials

New series of pyrazoles 4a – c and pyrazolopyrimidines 5a – f had been constructed. The newly synthesized compounds were assessed for their antimicrobial activity towards E. coli and P. aeruginosa (gram –ve bacteria), B. subtilis and S. aureus (gram +ve bacteria) and A. flavus and C. albicans (representative of fungi). The pyrazolylpyrimidine-2,4-dione derivative 5b is the most active candidate against B. subtilis (MIC=60 μg/mL) and P. aeruginosa (MIC=45 μg/mL). Regarding antifungal potential, compound 5f was the most effective against A. flavus (MIC=33 μg/mL). Similarly, compound 5c displayed strong antifungal activity towards C. Albicans (MIC=36 μg/mL) in reference to amphotericin B (MIC=60 μg/mL). Finally, the novel compounds had been docked inside dihydropteroate synthase (DHPS) to suggest the binding mode of these compounds.     

Screening and identification of novel isolate Streptomyces sp., NLKPB45 from Nellore costal region for its biomedical applications

Actinobacteria, which are the prolific producers of antibiotics and significant suppliers to the pharmaceutical industry, can produce a wide variety of bioactive metabolites. An actinomycete strain designated NLKPB45 was isolated from mangrove soils samples of Nellore coastal regions Andhra Pradesh and assessed for antibiotic production and activity against pathogenic bacteria. From a total of 9 mangrove soil samples, 143 acinomycetes were isolated. Among the isolated them 6 actinomycetes strains showed potential antibacterial activity against at two tested pathogens gram positive and gram negative bacteria E. coli and S. aureus. The potent strain NLKPB45 was identified by 16S gene isolation and sequencing to the Streptomyces genus. The ethyl acetate extracts also as shown excellent antimicrobial activity against Salmonella sp., staphylococcus aureus, E. coli, and B. subtilus were detected in both the supernatant extract samples from fermentations of culture NLKPB45. The anticancer activity of extracts in the HeLa with IC₅₀ value of 37.1924 μg/ml, MCF-7 IC₅₀ value of 40.9177 μg/ml and HT 29 IC₅₀ value of 43.3758 μg/ml.