Strains Of Gram Research Articles

Bioactivity of herbal tea of Hungarian thyme based on the composition of volatiles and polyphenolics

Hungarian thyme (Thymus pannonicus All., Lamiaceae) is an aromatic herb used as traditional remedy, a refreshing beverage and a food aromatizer. Herbal teas, i.e., infusions, of Hungarian thyme from eight localities in Serbia were analyzed regarding their polyphenolic and volatile composition, and tested for their antioxidant and antimicrobial activity. The total polyphenolics content, determined by the Folin-Ciocalteu method, ranged from 1122.25 to 1979.93mg gallic acid/L. HPLC analysis revealed rosmarinic acid (367.42–1199.47mg/L) and luteolin glucuronides as the main polyphenolics. The volatile fractions of the infusions, analyzed by static headspace extraction coupled with GC and GC–MS analyses, contained citral, 3-octanone, 1-octen-3-ol, linalool and 1,8-cineole as the dominant constituents. The antioxidant activity of the infusions was examined through the ferric reducing antioxidant power (FRAP) (68.09–124.58mmol Fe2+/L) and the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical tests (SC50 1.32–2.96μL/mL). The antimicrobial activity was tested by the broth microdilution method against standard strains of Gram(+) Staphylococcus aureus, Staphylococcus epidermidis, Bacillus subtilis and Enterococcus faecalis and Gram(−) bacteria Escherichia coli, Klebsiella pneumoniae and Pseudomonas aeruginosa, and one strain of yeast Candida albicans. The infusions inhibited microbial growth in the tested concentration range (31.25–500.00μL/mL) and the strongest activity was exhibited against the strain of C. albicans (MIC 31.25–62.50μL/mL). The antioxidant and antimicrobial properties of the infusions were, to some extent, in correlation with the composition and content of the polyphenolic compounds, whereas the volatiles noticeably influenced the exhibited antimicrobial activity.

Evolution of Antimicrobial, Antioxidant Potentials and Phytochemical Studies of Three Solvent Extracts of Five Species from <i>Acacia</i> Used in Sudanese Ethnomedicine

The ethanol, chloroform and acetone extracts of five species from Acacia (Acacia albidia stems, Acacia mellifera aerial parts, Acacia nubica aerial parts, Acacia seyal var. seyal stems and Acacia tortilis aerial parts) were investigated for their antimicrobial activity against two standard bacterial strains of Gram +ve bacteria (Staphylococcus aureus (ATCC 25923)), Gram -ve bacteria (Pseudomonas aeruginosa (ATCC 27853)) and standard fungi Candida albicans (ATCC 90028) using the agar-plate well diffusion method. The chloroform extract was inactive compared to ethanol and acetone extracts. But ethanol extracts showed the maximum antimicrobial activity against the test organism. Amongst the plant species screened, ethanol extract of Acacia seyal stems showed maximum inhibitory activity (38 mm) and (37 mm) against Staphylococcus aureus and Candida albicans, respectively. The ethanol, chloroform and acetone extracts of Acacia mellifera (aerial parts) did not show any activity against the test organisms. Cholorophorm and acetone extracts via DPPH, the radical scavenging activities were found to be 91 ± 0.03, 88 ± 0.01 and 85 ± 0.04, respectively. The results of phytochemical screening showed that all extracts of studied plant contain flavonoids, saponins, terpenoids, steroids, alkaloids, phenols and tannins.

Antimicrobial activity of petroleum ether and methanolic extracts from fruits of Seseli devenyense Simonk. and the herb of Peucedanum luxurians Tamam.

Abstract Plants of the Apiaceae family usually contain coumarins. These are used worldwide in traditional medicine, as well as in modern therapeutics. The aim of our study was to determine the antimicrobial activity of four extracts (methanolic and petroleum ether extracts) obtained from two Apiaceae species: Seseli devenyense (fruits) and Peucedanum luxurians (herb). The activity of the investigated extracts was tested against 7 strains of Gram+ bacteria, and 7 strains of Gram-, as well as three of yeast. The results of this show that the best activity of such extracts (specifically, by way of petroleum ether) was seen as being against Staphylococcus aureus strains.

Antimicrobial activity of the extracts from some Phyllanthus species cultivated in vitro

In subtropical regions the extracts from Phyllanthus species are used in the treatment of bacterial, fungal and parasitic diseases (e.g. P. niruri, P. amarus). Literature data showed that antimicrobial activity of Phyllanthus species results from synergistic effects of occurring secondary metabolites. The MIC and MBC values were determined to show antibacterial activity of extracts from shoot cultures of P. glaucus, P. multiflorus and P. juglandifolius and shoot culture and non-transformed root culture of P. amarus. The dry extracts dissolved in either DMSO or methanol were examined against strains of Gram (+) bacteria – Streptococcus G, S. aureus, S. epidermidis, B. subtilis, C. sporogenes, E. hirae, strains of Gram (-) bacteria – M. catarrhalis, K. pneumoniae, E. coli, P. vulgaris, P. aeruginosa, H. pylori as well as a yeast C. albicans. As controls, the alkaloid securinine, present as a dominant compound of the alkaloid fraction in the shoot culture of P. glaucus, and flavan-3-ol – catechin present in all tested species, were used. Using DMSO to dissolve dry extracts higher MIC values were observed than when dissolved in methanol. The obtained results showed the differences in bacterial susceptibility depending on the Phyllanthus species. For the methanol extracts antimicrobial activity expressed as MIC was in a range from 0.01 mg/mL to 5.0 mg/mL, while the MBC value was determined from 0.01 mg/mL to 10.0 mg/mL. Securinine and catechin were active in a range from 0.03 to 0.25 mg/mL showing the highest activity against Streptococcus G and P. aeruginosa (securinine) and H. pylori (catechin). All extracts and standards were inactive against E. hirae while the most susceptible strain was M. catarrhalis (MBC 0.01 mg/l). Acknowledgement: This Project was supported by the Ministry of Science and Higher Education of the Republic of Poland, from the quality-promoting subsidy, under the Leading National Research Centre (KNOW) programme for the years 2012 – 2017.

The antibacterial activity of <i>Clausena anisata</i> hook, a South African medicinal plant

Background: Clausena anisata Hook also known as Iperepesi in Xhosa language is a medicinal plant used traditionally for the treatment of various ailments and some opportunistic infections associated with tuberculosis (TB). Patients in South Africa based on the phytotherapeutic information on this species in the Eastern Cape, use this medicinal plant. Hence, the antibacterial activity of various solvent extracts of the leaves and barks were respectively, evaluated using selected bacterial strains.Method: The leaves and stem bark were tested against 10 selected strains of Gram - positive and Gram - negative bacteria through the agar dilution method. Acetone, dichloromethane and water extracts were used for the extraction. MIC was determined at different concentrations (0.1mg/ml, 0.5mg/ml, 1mg/ml and 5mg/ml) and the results obtained were compared to that of standard antibiotics.Result: The acetone extract of the leaves were more active against both Gram-positive and Gram –negative bacteria with MIC ranging from 0.1 mg/ml - 0.5 mg / ml. The dichloromethane extract of the bark showed appreciable activities against Staphylococcus aureus (ATCC 6538) (MIC: 0.1mg /ml) Escherichia coli and, Streptococcus pyogenes with an MIC of 5mg/ml respectively. On the other hand, the aqueous extract of the leaves showed no activity against the tested organisms with the exception of the aqueous bark extract which inhibited Staphylococcus aureus (MIC: 0.5mg/ml) and Pseudomonas aeruginosa (MIC: 5mg/ml).Conclusion: This study confirmed the antibacterial activities of acetone extract of the leaves of Clausena anisata. The capability of this extract to inhibit both Gram positive and negative bacteria is an indication that the extract is a potential broad spectrum antibacterial. The result of this study further justified its indigenous use for the treatment of bacteria commonly associated with TB especially among the people of Nkonkobe Municipality.Key words: Clausena anisata; tuberculosis; antibacterial activity; herbal medicineAbbreviations: DCM = dichlormethane; ACT =acetone; MIC =minimum inhibitory concentration; na: not investigated beyond 5mg/ml; Cipro:Ciprofloxacin; Amox: Amoxicillin

THE ANTIBACTERIAL ACTIVITY OF CLAUSENA ANISATA HOOK, A SOUTH AFRICAN MEDICINAL PLANT

Background: Clausena anisata Hook also known as Iperepesi in Xhosa language is a medicinal plant used traditionally for the treatment of various ailments and some opportunistic infections associated with tuberculosis (TB). Patients in South Africa based on the phytotherapeutic information on this species in the Eastern Cape, use this medicinal plant. Hence, the antibacterial activity of various solvent extracts of the leaves and barks were respectively, evaluated using selected bacterial strains. 
 Method: The leaves and stem bark were tested against 10 selected strains of Gram - positive and Gram - negative bacteria through the agar dilution method. Acetone, dichloromethane and water extracts were used for the extraction. MIC was determined at different concentrations (0.1mg/ml, 0.5mg/ml, 1mg/ml and 5mg/ml) and the results obtained were compared to that of standard antibiotics. 
 Result: The acetone extract of the leaves were more active against both Gram-positive and Gram –negative bacteria with MIC ranging from 0.1 mg/ml - 0.5 mg / ml. The dichloromethane extract of the bark showed appreciable activities against Staphylococcus aureus (ATCC 6538) (MIC: 0.1mg /ml) Escherichia coli and, Streptococcus pyogenes with an MIC of 5mg/ml respectively. On the other hand, the aqueous extract of the leaves showed no activity against the tested organisms with the exception of the aqueous bark extract which inhibited Staphylococcus aureus (MIC: 0.5mg/ml) and Pseudomonas aeruginosa (MIC: 5mg/ml).
 Conclusion: This study confirmed the antibacterial activities of acetone extract of the leaves of Clausena anisata. The capability of this extract to inhibit both Gram positive and negative bacteria is an indication that the extract is a potential broad spectrum antibacterial. The result of this study further justified its indigenous use for the treatment of bacteria commonly associated with TB especially among the people of Nkonkobe Municipality.

OM85-BV Induced the Productions of IL-1β, IL-6, and TNF-α via TLR4- and TLR2-Mediated ERK1/2/NF-κB Pathway in RAW264.7 Cells

Broncho-Vaxom (OM85-BV) is an extract mixture from 8 strains of Gram(+) and Gram(-) bacteria and plays an important role in anti-infection immune response by regulating macrophage activity and cytokine productions. However, the mechanism by which OM85-BV enhances the cytokine expression is still obscure. In this study, we evaluated the effects of OM85-BV on the productions of interleukin (IL)-1β, IL-6, and tumor necrosis factor-α (TNF-α) in RAW264.7 murine macrophages. Exposure of RAW264.7 cells to 100 μg/mL OM85-BV upregulated the expression of IL-1β, IL-6, and TNF-α at the mRNA and protein levels in a time- and dose-dependent manner. In addition, OM85-BV induced extracellular signal-regulated kinase (ERK) 1/2 and nuclear factor-kappa B (NF-κB) phosphorylation. Pretreatment with U0126 or Bay11-7082, respectively, could decrease IL-1β, IL-6, and TNF-α productions induced by OM85-BV. Application of Toll-like receptor (TLR) 4 or TLR2 small-interfering RNA (siRNA) into RAW264.7 cells could inhibit the productions of cytokines and ERK1/2 and NF-κB phosphorylation induced by OM85-BV. Consistent with this, downregulating either myeloid differentiation factor 88 (MyD88) or TRIF-related adaptor molecule (TRAM) gene with MyD88-siRNA or TRAM-siRNA separately could reduce the productions of cytokines and ERK1/2 and NF-κB phosphorylation induced by OM85-BV. Our study demonstrated that the productions of IL-1β, IL-6, and TNF-α induced by OM85-BV in RAW264.7 cells were through TLR4 and TLR2 signaling pathway-mediated activation of ERK1/2 and NF-κB.

Antioxidant Neolignans from Cordia americana

Five new neolignans with a bicyclo[2.2.2]octene framework were isolated from an ethanolic extract of the bark of Cordia americana. The structures and relative configurations of the compounds were elucidated by a combination of spectroscopic methods. All the isolated compounds showed good antioxidant activities in the DPPH radical scavenging (0.5-100 µg/mL) and Ferric-reducing antioxidant power (FRAP, 1-100 µg/mL) assays. One of the compounds displayed mild fungistatic activity at 0.1 µmol/spot against Fusarium virguliforme while, at the same time, all compounds were inactive against several strains of Gram (+) and Gram (-) bacteria at all assayed concentrations (10-1,000 µg/mL).

MICROBIOLOGICAL QUALITY ATTRIBUTES OF NILE PERCH LATES NILOTICUS FISH FILLETS TREATED WITH AQUEOUS EXTRACT OF LEPIDIUM SATIVUM L. CRESS SEEDS

The antimicrobial activity of the aqueous and methanol extracts of Lepidium sativum cress seeds at various concentrations (1, 2 and 3 %) against four strains of gramnegative bacteria including Escherichia coli, E. coli 157, Salmonella typhimurium and Kelbsiella pneumonia, four strains of gram–positive bacteria including Staphylococcus aureus, Bacillus subtilus, Bacillus megaterium and Listeria moncytogenes serotype, two yeasts including Candida albicans and Sacchromyces cerevisiae and one fungi (Aspergillus niger) was assessed. Also, the effect of spraying with aqueous cress seeds extract on microbiological attributes and shelf life of Nile perch fish fillets was also studied. The results indicated that all concentrations of aqueous extract were active against all tested microorganisms except Klebsiella pneumonae. On the other hand, the methanol Lepidium sativum extract at 1 and 2 % had no effect on the growth of all gram-negative bacteria. Meanwhile, the above mentioned concentrations of methanol extract had detectable effects on the gram–positive bacteria, yeasts and fungi. Also, the antimicrobial effect of aqueous and methanol extracts was increased with increasing the concentrations. The results also showed that the distilled water was better than methanol for extracting antimicrobial substances from this seeds. Therefore, spraying of Nile perch fish fillets with various concentrations (1, 2 and 3%).of the aqueous extract was the suggested treatment to reduce the microbial load and extend the shelf life.

Preliminary phytochemical and biological screening of methanolic and acetone extracts from Leonotis nepetifolia (L.) R. Br.

This study is aimed at preliminary phytochemical analysis and determination of biological activity of methanolic extract (ME) and acetone extract (AE) from aerial parts of Leonotis nepetifolia (L.) R. Br. collected from Southern Brazil. Phytochemical analysis demonstrated the presence of terpene compounds, flavonoids, tannins, iridoids, sterols and fats. The extracts were inactive towards selected strains of Gram (+), Gram (-) bacteria and dermatophytes at concentrations up to 50 mg/ml, demonstrated antioxidative ability measured by ferric reducing ability of plasma (FRAP) and 2,2-diphenyl-1-picrylhydrazyl (DPPH) methods and exhibited cytotoxic in vitro activity towards Du145 human prostate cancer cell line. Key words: Leonotis nepetifolia, antioxidant capacity, Du145 cells.

Synthesis, Characterization and Biological Activities of Cu(II), Co(II), Mn(II), Fe(II), and UO2(VI) Complexes with a New Schiff Base Hydrazone: O-Hydroxyacetophenone-7-chloro-4-quinoline Hydrazone

The Schiff base hydrazone ligand HL was prepared by the condensation reaction of 7-chloro-4-quinoline with o-hydroxyacetophenone. The ligand behaves either as monobasic bidentate or dibasic tridentate and contain ONN coordination sites. This was accounted for be the presence in the ligand of a phenolic azomethine and imine groups. It reacts with Cu(II), Ni(II), Co(II), Mn(II), UO2 (VI) and Fe(II) to form either mono- or binuclear complexes. The ligand and its metal complexes were characterized by elemental analyses, IR, NMR, Mass, and UV-Visible spectra. The magnetic moments and electrical conductance of the complexes were also determined. The Co(II), Ni(II) and UO2 (VI) complexes are mononuclear and coordinated to NO sites of two ligand molecules. The Cu(II) complex has a square-planar geometry distorted towards tetrahedral, the Ni(II) complex is octahedral while the UO2 (VI) complex has its favoured heptacoordination. The Co(II), Mn(II) complexes and also other Ni(II) and Fe(III) complexes, which were obtained in the presence of Li(OH) as deprotonating agent, are binuclear and coordinated via the NNNO sites of two ligand molecules. All the binuclear complexes have octahedral geometries and their magnetic moments are quite low compared to the calculated value for two metal ions complexes and thus antiferromagnetic interactions between the two adjacent metal ions. The ligand HL and metal complexes were tested against a strain of Gram +ve bacteria (Staphylococcus aureus), Gram −ve bacteria (Escherichia coli), and fungi (Candida albicans). The tested compounds exhibited high antibacterial activities.

Composición química, actividad antibacteriana del aceite esencial de Citrus sinensis L. (Na­ranja dulce) y formulación de una forma farmacéutica

El presente estudio tuvo como objetivos, caracterizar los componentes químicos del aceite esencial de Citrus sinensis L. (Naranja dulce), determinar su actividad antibacteriana y formular formas farmacéuticas, principalmente de uso local. El aceite esencial se obtuvo del pericarpio , de la especie seleccionada, utilizando un sistema de hidrodestilación con arrastre de vapor de agua; así mismo, se realizaron los ensayos de miscibilidad y determinación de constantes físicas, como: gravedad específica, índice de refracción y rotación óptica. La composición química se determinó por Cromatografía de Gases/Espectrometría de Masa (CG/EM), destacándose en el cromatograma señales espectrales de identificación en la elucidación de: Limoneno, ß-linalol, decanal y 2(10)-pineno(1S,5S)-(-)-. La determinación de la actividad antibacteriana in vitro se realizó por el método de difusión en agar y en la formación de halos de inhibición contra cepas de microorganismos Gram (+), como: Staphylococcus aureus ATCC 25933 y Staphylococcus epidermidis, demostrando actividad antibacteriana significativa a concentraciones de 100 y 50%, respectivamente; no así con los microorganismos Gram (-): Bacillus subtilis, Escherichia coli y Pseudomonas aeruginosa ATCC 27853. Estos resul¬tados nos dieron la orientación para diseñar formas farmacéuticas de uso local, formulándose: un gel con base de carbomer, una loción con base de etanol y alcohol isopropílico, así como un colutorio. Los resultados de los estudios de estabilidad de las formu¬laciones, así como de tolerancia e irritabilidad con el tejido humano de los productos nos muestran resultados favorables para su utilización en enfermedades de la piel, como el acné, y en el caso del colutorio como un buen antiséptico bucal. El estudio ha permitido concluir que el aceite esencial de Citrus sinensis L. posee actividad antibacteriana contra cepas de Staphylococcus aureus ATCC 25933 y Staphylococcus epidermidis, además de permitir la elaboración de formas farmacéuticas de uso local.

(R)-(-)-carvone and (1R, 4R)-trans-(+)-dihydrocarvone from poiretia latifolia vogel

The essential oils of Poiretia latifolia Vogel, native and cultivated leaves (Samples A and B, respectively) and native flowers (sample C), were obtained by hydrodistillation and analyzed by GC, GC/MS and chiral phase gas chromatography (CPGC). Twenty-four compounds were identified, representing 99.25, 99.26 and 99.23% of the oils, respectively. The major constituents of the oils were the monoterpenes (S)-(-)-limonene (16.05, 27.60, 15.60%, respectively), (1R, 4R)-trans-(+)-dihydrocarvone (18.05, 0.66 and 77.80%, respectively) and (R)-(-)-carvone (61.05, 64.20 and 4.50%, respectively). The essential oils were evaluated against some strains of Gram (+) and Gram (-) bacteria, and yeast, but displayed only modest antimicrobial activity.

Chalcogenoxanthylium photosensitizers for the photodynamic purging of blood-borne viral and bacterial pathogens

Thio- and selenoxanthylium dyes were prepared by the addition of 2-lithiothiophene, 4- N, N-dimethylaminophenylmagnesium bromide, and 1-naphthylmagnesium bromide to the appropriate 2,7-bis- N, N-dimethylaminochalcogenoxanthen-9-one, followed by dehydration and ion exchange to the chloride salts. The corresponding chalcogenoxanthylium dyes were evaluated as photosensitizers for the inactivation of intracellular and extracellular virus in red blood cell suspensions and for the inactivation of selected strains of gram (+) and gram (−) bacteria in red blood cell suspensions. Selected combinations of photosensitizer and light gave >6 log 10 inactivation of intracellular and extracellular virus, and >4 log 10 inactivation of extracellular bacteria with varying levels of hemolyis, following a 42-day storage of red blood cell suspensions. Photocleavage experiments with plasmid DNA and the chalcogenoxanthylium dyes suggested the genomic material contained in the virus and in the bacteria as one possible target for the photodynamic action of some of these dyes.

Photocatalytic bactericidal effect of TiO 2 on Enterobacter cloacae: Comparative study with other Gram (−) bacteria

The bactericidal action of heterogeneous photocatalysis (UV-A/TiO 2) has been tested on Enterobacter cloacae, a microorganism very resistant to UV-A irradiation. Results have been compared with other representative strains of Gram (−) bacilli of different photosensitivity like E. coli, Pseudomonas aeruginosa and Salmonella typhimurium. The TiO 2 photocatalytic technology can inactivate bacteria resistant to oxidative membrane damage caused by direct UV irradiation, like E. cloacae, a common soil and aquatic microorganism, which normally is not affected by low UV-A irradiation intensity. In all cases, sublethal UV-A doses provoked an important lethality in the presence of TiO 2. Inactivation rates of the microorganisms are compared and some clues on the mechanism of bacteria destruction are discussed.

3 H-[1,2]Dithiolo[3,4- b]pyridine-3-thione and its derivatives Synthesis and antimicrobial activity

A series of 2-substituted isothiazolo[5,4- b]pyridine-3(2 H)-thiones, isothiazolo[5,4- b]pyridin-3(2 H)-ones, N-substituted 2-sulfanylnicotinamides and the corresponding carbothioamide derivatives were synthesized and evaluated for their antimicrobial activity against several strains of Gram+ and Gram−bacteria and fungi. Chemical syntheses were resumed into a comprehensive cyclic route that enables the reversible conversion for each derivative of the series considered. Among the tested compounds the N-(aralkyl)-2-sulfanylnicotinamides show the highest fungitoxicity (MIC=1.25–5 μg/ml). The best activity towards Gram-positive bacteria was in the range of 2.5–5 μg/ml. Activity against Gram-negative bacteria was generally very poor for all compounds.

Vigilancia de susceptibilidad de cocáceas grampositivas a betalactámicos, glicopéptidos y otros antimicrobianos

During the last decade, there has been a progressive increase in the resistance of gram (+) cocci to betalactamics and other antimicrobials. Therefore, vancomycin and teicoplanin have incorporated as alternative antimicrobial drugs. To assess the susceptibility of gram (+) cocci to different antimicrobials including vancomycin and teicoplanin. We studied 447 strains of gram (+) cocci coming from ambulatory and hospitalized patients. These included 308 Enterococcus sp strains, 99 Staphylococcus aureus strains and 40 coagulase negative Staphylococci strains. Enterococci susceptibility was measured using minimal inhibitory concentrations in agar and that of Staphylococci, through diffusion. Susceptibility to vancomycin and teicoplanin was measured using minimal inhibitory concentrations in all strains. Enterococcus faecalis was 100% susceptible to ampicillin, penicillin, vancomycin and teicoplanin, 23% susceptible to tetracyclin and 47% to chloramphenicol. Susceptibility of E faecium was 61% to penicillin, 49% to chloramphenicol, 41% to tetracyclin, 100% to vancomycin and teicoplanin. Of 19 Enterococcus spp strains, 90% were susceptible to ampicillin, 80% to penicillin, 55% to chloramphenicol and 45% to tetracyclin. Only one E casseiflavus strain had a low level resistance to vancomycin and was susceptible to teicoplanin. No Staphylococcus aureus strain was resistant to vancomycin or teicoplanin. A permanent surveillance of gram (+) cocci antimicrobial susceptibility is required to update therapeutic schemes.

Characterization of a new class of tetracycline-resistance gene tet(S) in Listeria monocytogenes BM4210.

The nucleotide sequence of the tetracycline (Tc)-minocycline (Mc)-resistance determinant of plasmid pIP811 from Listeria monocytogenes BM4210 has been determined. The gene, designated tet(S), was identified by analysis of the start and stop codons as a coding sequence of 1923 bp, corresponding to a protein with a calculated M(r) of 72,912. The apparent 68-kDa size estimated by sodium dodecyl sulfate-polyacrylamide-gel electrophoresis of the protein characterized in a cell-free coupled transcription-translation system was in good agreement with the calculated value. The tet(S) gene product exhibits 79 and 72% amino acid identity with Tet(M) from Streptococcus pneumoniae and Tet(O) from Campylobacter coli, respectively. The distribution of tet(S) in strains of Gram+ and Gram- genera resistant to Tc (TcR) and Mc (McR) was studied by hybridization under high stringency using a 590-bp intragenic probe. Homology with tet(S) was detected in two clinical isolates of L. monocytogenes isolated in different geographical areas.

Pathogenesis of atoxinogenic strains of gram--negative bacteria--a hypothesis.

Textbooks of medical microbiology attribute to endotoxin a primary pathogenic role in diseases caused by nontoxinogenic gram negative bacteria. There is little experimental data to support this claim while some observations indicate the contrary. The possibility cannot be ignored that our understanding of the biological effects of endotoxin is based on the administration of endotoxin as a bolus rather than as a continuous release in small amounts over a period of hours or days as probably occurs during an infection. Results are described that clearly show how different the response can be under the two conditions. It is suggested, moreover, that mediators formed primarily by macrophages stimulated by endotoxin may contribute significantly to the pathogenesis of these diseases.