Numerical taxonomy of Bacteroides and other genera of Gram-negative anaerobic rods.

A numerical taxonomy was performed on 157 cultures (141 different strains) of species of Bacteroides, Polyphyromonas, Prevotella [not Prevotella (Labroue, 1976)] and Fusobacterium. Isolates were each tested for 111 phenotypic characters which included possession of constitutive enzymes, fermentation of specific carbohydrates, gas chromatographic analysis of metabolic end-products and of cellular carboxylic acid composition. Computation of similarity coefficients was followed by a single-linkage cluster analysis. At the 94% similarity level, the following groupings at genus level were apparent: (1) Bacteroides ureolyticus; (2) Fusobacterium mortiferum, F. necrogenes, F. necrophorum, F. nucleatum and F. varium; (3) B. caccae, B. distasonis, B. eggerthii, B. fragilis, B. merdae, B. ovatus, B stercoris, B. thetaiotaomicron, B. uniformus and B. vulgatus; (4) B. splanchnicus; (5) Porphyromonas asaccharolytica; (6) B. bivius (Prevotella bivia); (7) B. disiens (P. disiens); (8) B. intermedius (P. intermedia);and (9) B. melaninogenicus (P. melaninogenica). Single isolates of B. ruminicola (P. ruminicola), B. denticola (P. denticola) and B. capillosus did not cluster with other strains.     

Cellular fatty acid composition in moderately halophilic Gram-negative rods

The fatty acid compositions for 40 strains of moderately halophilic Gram-negative rods were determined by gas-liquid chromatography. The strains studied were included in the genera: Vibrio, Deleya, Alteromonas, Chromobacterium, Flavobac-terium and Pseudomonas. Although there were quantitative differences all strains showed more or less similar spectra of fatty acids ranging from C₁₂ to C₂₀ chain. The major fatty acid species were C_16:0, C_16:1 and C_18:1. Most striking was the predominance of the C_18:1 component, the major fatty acid in extracts of 29 of the 40 strains.     

A staphylococcal plasmid that replicates and expresses ampicillin, gentamicin and amikacin resistance in Escherichia coli

Plasmid pPG1 from Staphylococcus aureus coding for ampicillin (Apr), gentamicin (Gmr) and amikacin (Akr) resistance was transformed into Escherichia coli. Transformation efficiency was about 2 x 10(3) transformants/micrograms of plasmid DNA. The plasmids present in the E. coli transformants were identical to pPG1 according to their restriction patterns. The copy number of pPG1 was estimated to be at least 20-times less in E. coli than in S. aureus. The minimal inhibitory concentrations (MICs) for Ap and Gm were lower in E. coli than in S. aureus. However, the MIC for Ak was higher in E. coli transformants than in S. aureus. pPG1 was maintained in the E. coli transformants for at least 80 generations at 37 degrees C without antibiotic selection pressure.     

外科重症监护病房革兰阴性杆菌的菌群分布及耐药性分析

目的监测外科重症监护病房(SICU)革兰阴性杆菌的菌群分布及耐药性。方法对中山大学附属第一医院SICU 2007年到2008年分离的革兰阴性杆菌及其耐药性进行回顾性分析。结果共分离到革兰阴性杆菌279株,前5位为大肠埃希菌(21.9%)、铜绿假单胞菌(20.8%)、鲍曼不动杆菌(15.8%)、肺炎克雷伯菌(11.8%)和嗜麦芽窄食单胞菌(11.5%)。肠杆菌科细菌对碳青霉烯类抗生素敏感性最高,尚无耐药株;非发酵菌对阿米卡星耐药率最低,对其他抗生素耐药性高。结论 SICU革兰阴性杆菌的耐药性有上升的趋势,应加强细菌耐药性监测,合理使用抗生素,防止耐药菌株的传播。     

Gram-negative bacteria resistant to antibiotics in foods

From 154 food samples, including vegetables (lettuce), milk and meals served at school it was possible to isolate and identify 400 Gram negative bacilli distributed among 339 enteric bacteria (Escherichia, Shigella, Citrobacter, Klebsiella, Enterobacter, Serratia and Proteus) and other 61 non enteric bacilli (Acinetobacter, Flavobacterium, Aeromonas and Pseudomonas). Submitting this cultures to the drugs sulfadiazine (Su), streptomycin (Sm), tetracycline (Tc), chloramphenicol (Cm), kanamycin (Km), ampicillin (Ap), nalidixic acid (Nal) and gentamycin (Gm) it was observed only six stocks susceptible to all drugs and total sensibility to Gm. Among enteric bacteria the profiles Su (27,6%) and Su-Ap (39,6%) predominated, while for the non enteric bacilli percentages of 18.0 for Ap and 9.8 for Su-Ap were detected. Aiming to better characterization of resistance, experiments of conjugation were made with standard strains of Escherichia coli K 12. Great concern was raised by the recognition of these cultures due to the elevated R+ taxes for the enteric bacilli that were close to 90% (milk and food at school) and about 70% in relation to lettuce.     

Imipenem resistance in Gram-negative rods and its consumption between 1999 and 2005

Multidrug resistant Gram-negative rods are increasingly isolated from clinical specimens, especially from hospitalized patients. The aim of this study was to evaluate the prevalence of imipenem resistant strains of Gram-negative rods isolated in dr. A. Jurasz University Hospital in Bydgoszcz between 1999 and 2005 and imipenem consumption in this period. Out of 109614 isolated microorganisms, Gram-negative rods were 28,5%, 637 (2,0%) of strains were resistant to imipenem. These strains were isolated mostly from patients hospitalized in intensive care and rehabilitation clinics. Among imipenem-resistant strains Pseudomonas aeruginosa prevailed (88,9%). P. aeruginosa strains were sensitive to colistin, 45,5% of them to aztreonam and 44,0% to ceftazidime. The imipenem consumption in the appropriate years included in this study was: 805,00; 1201,25; 940,00; 1390,00; 1660,00; 1341,25; 1841,25 DDD respectively, and was strictly connected with increasing imipenem-resistant Gram-negative rods isolation.     

Enhanced intracellular killing ofStaphylococcus aureus by canine monocytes treated with liposomes containing amikacin,gentamicin, kanamycin,and tobramycin

Entrapment and surface-charge association of the aminoglycosides; amikacin, gentamicin, kanamycin, and tobramycin with anionic neutral, and cationic multilamellar phospholipid vesicles (liposomes) were determined by bioassay and radioenzymatic assay (REA). Differences in results between the bioassay and REA were noted; however, there was general agreement of the relative amounts of aminoglycoside present in the liposomes. The highest intraliposomal concentrations were found with cationic liposomes. Intracellular killing ofStaphylococcus aureus by canine monocytes was enhanced when liposomes containing aminoglycosides were added to the cultures. Liposomes containing aminoglycosides were not toxic to canine monocytes. The phagocytic ability of canine monocytes was not decreased by the liposomes containing aminoglycosides.     

Approaches to the study of the systematics of anaerobic,Gram-negative,non-sporeforming rods: Current status and perspectives

The present article gives an overview of recent taxonomic changes among the Gram-negative, anaerobic rods, briefly highlighting areas where the biology and ecology have a bearing on recent nomenclatorial changes. The focus is among the genera Bacteroides, Prevotella, Porphyromonas, Leptotrichia, Dysgonomonas, Fusobacterium and the Synergistes group and additionally demonstrates the value of conserved indels and group-specific proteins for identifying and circumscribing many of these taxa and the Bacteroidetes–Chlorobi species in general.     

Antibiotics of the aminoglycoside group (gentamicin, sisomicin and amikacin) in the prevention and treatment of experimental plague]

Activity of aminoglycosides such as gentamicin, sisomicin and amikacin against plague microbe strains of natural origin was studied in vitro. It was also studied in prophylaxis and treatment of experimental plague infection in albino mice. The MAC of gentamicin and sisomicin for 50 strains of the plague microbe was 0.2-1.6 micrograms/ml. For the majority of the strains it was 0.4 micrograms/ml. The amikacin MICs were 0.4-3.2 and 0.8 micrograms/ml, respectively. High efficacy of gentamicin, sisomicin and amikacin was shown in prophylaxis and treatment of experimental plague infection in albino mice. The optimal doses of the antibiotics were determined. Under definite conditions such as the use of short-term regimens and higher intervals, advantages of sisomicin over gentamicin and amikacin in prophylaxis of experimental plague infection were observed.     

Sublethal injury makes Gram-negative and resistant Gram-positive bacteria sensitive to the bacteriocins, pediocin AcH and nisin

Gram-negative and some Gram-positive bacteria that are resistant to bacteriocins of lactic acid bacteria (LAB) were subjected to sublethal stresses and treated with nisin and pediocin AcH. Both bacteriocins reduced the viability of cells surviving sublethal stresses. The results explain the possible mechanisms by which bacteriocins of LAB enter through the walls (or outer membranes) to destabilize the cytoplasmic (or inner) membranes and kill cells of sensitive Gram-positive and resistant, but injured, Gram-negative and Gram-positive bacteria.     

Strategies for bypassing the membrane barrier in multidrug resistant Gram-negative bacteria

In Gram-negative bacteria, the envelope is a sophisticated barrier protecting the cell against external toxic compounds. Membrane transporters, e.g., porins or efflux pumps, are main filters regulating the internal accumulation of various hydrophilic molecules. Regarding bacterial susceptibility towards antibacterial agents, membrane permeability is part of the early bacterial defense. The bacterium manages the translocation process, influx and efflux, to control the intracellular concentration of various molecules. Antibiotics and biocides are substrates of these mechanisms and the continuing emergence of multidrug resistant isolates is a growing worldwide health concern. Different strategies could be proposed to bypass the bacterial membrane barrier, comprising influx and efflux mechanisms, in order to restore the activity of antibiotics against resistant bacteria.     

Alteration of ribosomal protein L6 in mutants of Escherichia coli resistant to gentamicin.

Summary Spontaneous and ethylmethane-sulfonate induced mutants of Escherichia coli resistant to gentamicin sulfate were isolated and investigated for alterations in the ribosomal protein pattern. It was found by two-dimensional polyacrylamide gel electrophoresis that three independently isolated strains did not show any spot for ribosomal protein L6. On cochromatography of radioactively labelled mutant and wild-type ribosomal proteins on carboxymethyl-cellulose columns a shift of the elution position of protein L6 was observed, the new elution positions being characteristic for the individual mutants analyzed which indicates that they possess different alterations in the L6 primary structure.Genetic analysis showed that the gentamicin resistant strains contain at least two mutations. One of them correlates with the altered L6 protein and causes an increased minimal inhibitory concentration of the drug by about 5 to 10-fold. The other mutation is not yet biochemically characterized. Its presence is connected with an about 10 to 20-fold increase in the resistance. Both mutations, when put together, confer resistance to 50 to 100 g/ml of the antibiotic in a low salt rich medium and to 1 mg/ml in a defined medium with a high concentration of phosphate. Cross-resistance analysis demonstrated that the three gentamicin-resistant (double-mutant) strains with the altered L6 protein are resistant to 50–100 g per ml of all other aminoglycoside antibioties tested. This forms a sharp contrast to the streptomycin resistance mutations present in strA1, strA40 or strA60 mutants which do not confer markedly increased levels of resistance to most of the other aminoglycosides.     

Polyamino geranic derivatives as new chemosensitizers to combat antibiotic resistant Gram-negative bacteria

Benzotriazol-1-yloxytris(dimethylamino)phosphonium hexafluorophosphate reagent (BOP) serves as an efficient and versatile coupling reagent for the design and synthesis of new polyamino geranic acid derivatives in moderate to good chemical yields varying from 47% to 83%. These compounds induced a significant decrease of antibiotic resistance in two Gram-negative bacterial MDR strains. Our data suggested that their mechanism of action is closely associated with the inhibition of the efflux pumps.