Sensitivity of scopulariopsis brevicaulis to some antimicrobial agents

Sensitivity tests were done against two isolates of Scopulariopsis brevicaulis, using amphotericin B in combination with chloramphenicol, Chloramphenicol alone, amphotericin B in combination with 5-fluorocytosine, and 5-fluorocytosine, myxin and clotrimazole alone. Results indicated that the effectiveness of amphotericin B was improved in the presence of chloramphenicol or 5-fluorocytosine. Growth inhibitory values recorded for chloramphenicol alone and combined with amphotericin B did not show much variation. Resistance of the fungus has been noticed to 5-fluorocytosine; but the organism's response was much better when tested against 5-fluorocytosine in the presence of amphotericin B. Both myxin and clotrimazole proved very effective and their ED50 was 50 and 2.5 ug/ml of the medium, respectively. Thus, clotrimazole may be the drug of choice in the cases of deep scopulariopsis.     

Sensitivity of clinical strains of facultatively anaerobic bacteria to antimicrobial drugs

Six hundred and sixty five samples of clinical materials from patients with various pyoinflammatory diseases were tested for obligatory anaerobes. Anaerobes were detected in 148 samples which amounted to 22.3 per cent of the total number of the samples and to 33.2 per cent of the samples with microbial growth. A total of 171 strains of obligatory anaerobes were isolated. Among them 58.5, 24.5, 16.4 and 0.6 per cent were nonsporulating gramnegative bacilli, grampositive cocci, grampositive bacilli and gramnegative cocci respectively. Sensitivity of the isolated anaerobes was tested with the disk diffusion method. The most active drugs against the tested strains were: nitroxoline, rifampicin, metronidasole, erythromycin, carbenicillin and cefotaxim (4.2, 4.5, 9.3, 10.6, 11.5 and 11.7 per cent of the resistant strains respectively). Gentamicin, polymyxin M, novobiocin and cefazoline were the least active drugs (94.6, 78.9, 65.4 and 50.0 per cent of the resistant strains respectively). Metronidasole, levomycetin, nitroxolin, rifampicin and furazolidone showed the highest activity against bacteroids of the fragilis group (0, 0, 0, 8 and 12.5 per cent of the resistant strains respectively) while gentamicin, polymyxin M, cefazolin, oxacillin, novobiocin and penicillin showed the lowest activity (100, 100, 100, 100, 87.0 and 66.7 per cent of the resistant strains respectively).     

Resistance to antimicrobial peptides in Gram-negative bacteria

Antimicrobial peptides (AMPs) are present in virtually all organisms and are an ancient and critical component of innate immunity. In mammals, AMPs are present in phagocytic cells, on body surfaces such as skin and mucosa, and in secretions and body fluids such as sweat, saliva, urine, and breast milk, consistent with their role as part of the first line of defense against a wide range of pathogenic microorganisms including bacteria, viruses, and fungi. AMPs are microbicidal and have also been shown to act as immunomodulators with chemoattractant and signaling activities. During the co-evolution of hosts and bacterial pathogens, bacteria have developed the ability to sense and initiate an adaptive response to AMPs to resist their bactericidal activity. Here, we review the various mechanisms used by Gram-negative bacteria to sense and resist AMP-mediated killing. These mechanisms play an important role in bacterial resistance to host-derived AMPs that are encountered during the course of infection. Bacterial resistance to AMPs should also be taken into consideration in the development and use of AMPs as anti-infective agents, for which there is currently a great deal of academic and commercial interest.     

Sensitivity of some strains of the genus Epidermophyton to different antifungal agents

The inhibitory activity of some antifungal agents against 17 strains of genus Epidermophyton have been studied. The behaviour of Epidermophyton stockdaleae against antifungal agents tested is clearly different from that observed in the strains belonging to Epidermophyton floccosum, since all of the latter were sensitive to the antifungal agents used and the geophilic species showed resistance to griseofulvin, isoconazole, natamycin and nystatin, and intermediate sensitivity to ketoconazole and miconazole. The low sensitivity of E. stockdaleae (and other geophilic dermatophytes) to antifungal agents could be a problem in the current therapy if further studies or case reports demonstrate their pathogenic role.     

Sensitivity of environmental microorganisms to antimicrobial agents.

The sensitivity of different microorganisms, considered as typical representatives of the microflora of soil and water, was established to evaluate the influence of the nonmedical use of antimicrobial agents on bacterial ecology. Only seven strains, six chemoorganotrophs and one chemolithotroph, could be considered as relatively sensitive to the 21 antimicrobial compounds tested. The other 29 microorganisms may be regarded as resistant to most antimicrobial agents. Streptomyces were sensitive to high concentrations of active substances. Broad-spectrum antibiotics showed an effect on environmental bacteria similar to that on human pathogens. Cephalothin stimulated the growth of a Chlorella sp. From these experiments, it appears that spilled antimicrobial agents have little chance of causing an alteration in the microbial ecology.     

支原体对抗生素的体外敏感性研究

目的研究非淋菌性尿道(宫颈)炎(NGU)患者支原体对12种抗生素敏感性,指导临床治疗。方法男性标本取尿道拭子．女性标本取宫颈拭子,采用支原体培养鉴定及药敏试剂盒进行体外药敏测定。结果126株解脲支原体(Uu)对12种抗生素敏感性从高至低依次为交沙霉素、强力霉素、美满霉素、克拉霉素、四环素、阿奇霉素、罗红霉素、司帕沙星、甲砜霉素、红霉素、可乐必妥和壮观霉素。12株人型支原体(Mh)对12种抗生素敏感性从高至低依次为交沙霉素、强力霉素、美满霉素、司帕沙星、四环素、壮观霉素、可乐必妥、甲砜霉素、红霉素、阿奇霉素、克拉霉素和罗红霉素。结论支原体耐药情况相当普遍。Uu、Mh对相同抗生素具有不同的敏感性。治疗时可依据药敏结果选择用药。     

部分革兰氏阴性菌脂多糖运输蛋白LptD的结构及功能研究进展

在革兰氏阴性菌中,脂多糖是外膜的重要组成部分,并参与构成细菌的固有免疫。而在大多数革兰氏阴性菌中,Lpt系统都是运输脂多糖的唯一途径,在该系统中LptD作为一个跨膜的外膜蛋白,也是脂多糖输出的最后一步,因此被许多学者称作脂多糖运输的"命门"。LptD参与多种重要的生物学功能,包括有机溶剂耐受性、疏水性抗生素耐受性、膜通透性等。但近来的研究表明,LptD最重要的功能是参与了脂多糖的运输,也因为其参与脂多糖运输而具有了多种功能。本文重点介绍部分革兰氏阴性菌LptD的蛋白结构及其功能研究进程,以期为进一步研究其它革兰氏阴性菌脂多糖运输通路(Lpt通路)及该通路上各蛋白间的相互作用机制提供参考。     

Location of tyrosine phenol-lyase in some Gram-negative bacteria

Abstract From various habitats (plant material, fruits, soil), yeasts belonging to the species of Pichia kluyveri and Hanseniaspora uvarum were isolated that showed killer activity. According to the activity spectrum against other yeasts these strains belonged to 11 different groups that were distinguishable from the killer strains K₁-K₁₀. The isoelectric points of the killer proteins were in the range of pH 3.5–3.9, the activity optimum was observed at pH 4.2–4.6. Above pH 5 and above a temperature of 25–35°C the killer proteins were inactivated.     

Stress responses as determinants of antimicrobial resistance in Gram-negative bacteria

Bacteria encounter a myriad of potentially growth-compromising conditions in nature and in hosts of pathogenic bacteria. These 'stresses' typically elicit protective and/or adaptive responses that serve to enhance bacterial survivability. Because they impact upon many of the same cellular components and processes that are targeted by antimicrobials, adaptive stress responses can influence antimicrobial susceptibility. In targeting and interfering with key cellular processes, antimicrobials themselves are 'stressors' to which protective stress responses have also evolved. Cellular responses to nutrient limitation (nutrient stress), oxidative and nitrosative stress, cell envelope damage (envelope stress), antimicrobial exposure and other growth-compromising stresses, have all been linked to the development of antimicrobial resistance in Gram-negative bacteria - resulting from the stimulation of protective changes to cell physiology, activation of resistance mechanisms, promotion of resistant lifestyles (biofilms), and induction of resistance mutations.     

The susceptibility of conjugative resistance transfer in Gram-negative bacteria to physicochemical and biochemical agents

Abstract Over thirty years of studies have established that conjugative transfer of plasmid-encoded resistance to drugs and heavy metals can take place at high frequency between various organisms under laboratory conditions. The detected transfer frequencies in soil, in aquatic environments, and in the urogenital and respiratory tracts of healthy animals and man have generally been low. However, the conversion of bacteria from susceptible to resistant to antibiotics has been observed often during antimicrobial therapy. This has formed a challenge for the antibacterial treatment of pathogenic bacteria and called for the evaluation of the extent of conjugative transfer in various environments. Several biochemical and physicochemical factors inhibit conjugation, show preferential toxicity against plasmid-bearing cells, or stimulate plasmid curing. These factors include various agents such as detergents, anesthetics, mutagens and antibiotics which affect membrane potential, membrane permeability, protein synthesis and the processing of DNA. The application of the data on these agents, summarized in this review, might be helpful in preventing drug multi-resistance from spreading. Also these data might be valuable in studies which use conjugation as a tool or which treat the molecular mechanisms involved in conjugation.     

Susceptibility of various purple and green sulfur bacteria to different antimicrobial agents

Abstract Several purple and green sulfur bacteria (genera Chromatium, Thiocapsa and Chlorobium ) were tested for their sensitivity to different antimicrobial agents by a disc diffusion assay, using thioacetamide as a source of hydrogen sulfide for plate growth. Chlorobium limicola strains were more sensitive to amoxicillin, erythromycin and nalidixic acid, whereas gentamicin and netilmicin were more active against the purple bacteria tested. None of the organisms were sensitive to oxacillin and trimethoprim + sulfamethoxazole. The critical concentrations at the edge of the inhibition zone were also calculated for three organisms and the antimicrobials colistin, mitomycin C, penicillin G, rifampicin, and streptomycin. The results obtained suggest that colistin, mitomycin C, penicillin G would provide selective conditions against the growth of Chlorobium limicola strains, while streptomycin and other aminoglycoside antibiotics would select against purple bacteria.     

A molecular mechanism for lipopolysaccharide protection of Gram-negative bacteria from antimicrobial peptides

Cationic antimicrobial peptides serve as the first chemical barrier between all organisms and microbes. One of their main targets is the cytoplasmic membrane of the microorganisms. However, it is not yet clear why some peptides are active against one particular bacterial strain but not against others. Recent studies have suggested that the lipopolysaccharide (LPS) outer membrane is the first protective layer that actually controls peptide binding and insertion into Gram-negative bacteria. In order to shed light on these interactions, we synthesized and investigated a 12-mer amphipathic alpha-helical antimicrobial peptide (K(5)L(7)) and its diastereomer (4D-K(5)L(7)) (containing four d-amino acids). Interestingly, although both peptides strongly bind LPS bilayers and depolarize bacterial cytoplasmic membranes, only the diastereomer kills Gram-negative bacteria. Attenuated total reflectance Fourier transform infrared, CD, and surface plasmon resonance spectroscopies revealed that only the diastereomer penetrates the LPS layer. In contrast, K(5)L(7) binds cooperatively to the polysaccharide chain and the outer phosphate groups. As a result, the self-associated K(5)L(7) is unable to traverse through the tightly packed LPS molecules, revealed by epifluorescence studies with LPS giant unilamellar vesicles. The difference in the peptides' modes of binding is further demonstrated by the ability of the diastereomer to induce LPS miscellization, as shown by transmission electron microscopy. In addition to increasing our understanding of the molecular basis of the protection of bacteria by LPS, this study presents a potential strategy to overcome resistance by LPS, and it should help in the design of antimicrobial peptides for future therapeutic purposes.     

Transforming activity of R- and Lac-plasmids of clinical strains of Gram-negative bacteria]

The isolated plasmid DNA of clinical strains of Gram-negative bacteria were shown to have transforming activity when E. coli strain 0600 and S. typhimurium strain LT-2 were used as recipients. The frequency of transformation depended on the recipient strain and the character of the plasmids. The presence of deletion mutants was revealed among the transformants. Such mutants occurred with varying frequency, most often in S. typhimurium strain LT-20; the reason for this phenomenon is at present under discussion. The transformation of plasmids controlling lactose splitting and their conjugation transfer into recipient S. typhimurium strain LT-2 is possible only under condition of using recipient (R+). The possibility of the formation of the cointegrate (R and lac plasmids) in recipient S. typhimurium strain LT-2 is discussed.