Comparative antibiotic sensitivity of different species of staphylococci isolated from humans]

A total of 206 strains of various staphylococcal species isolated from various sources were studied with respect to their sensitivity to 18 antibiotics. The number of strains poly-resistant to the antibiotics was almost the same among Staph. aureus and Staph. epidermidis, i. e. 54.8 and 51.3 per cent respectively. The coagulase-negative and mannitol-negative variants of Staph. aureus and Staph. epidermidis possessing high biological activity (10-14 properties) were resistant to more antibiotics as compared to the low active strains.     

Resistance to antibiotics and heavy metal salts of coagulase-positive staphylococci belonging to different biological types (ecovars)

A total of 189 strains of S. aureus isolated from cows, sheep, swines, poultry, monkeys, rabbits, foxes, and humans and 23 strains of S. intermedius isolated from minks and sables were studied. The staphylococci belonged to different biological types (according to the Hajek-Marsalek's scheme) and ecovars (according to the Meyer-Witte's scheme). The strains were studied with respect to their resistance to 10 antibiotics (benzylpenicillin, streptomycin, tetracycline, levomycetin, erythromycin, oleandomycin, neomycin, kanamycin, monomycin, and novobiocin), mercuric chloride and cadmium sulfate. As a whole the frequency of resistance to the above preparations among the staphylococci of the animal origin was not high. Differences in the frequency and range of the resistance between strains belonging to different biological types (ecovars) were shown. The highest number of the resistant cultures was detected among the strains of the biological type E (ecovar canis) and atypical strains of S. intermedius isolated from the minks. The least number of the resistant cultures was detected among the strains of the biological type C1 (ecovar bovis) isolated from the cows. It was found that almost all strains of S. intermedius were resistant to cadmium sulfate. This may be used as an additional characteristic of the species.     

Incidence of antibiotic resistance in Salmonella typhimurium strains isolated in different epidemic situations

A total of 1800 S. typhimurium strains isolated in different regions of the USSR in 1968-1979 were studied. Of these strains, 68.6% were resistant to 6-8 antibiotics, 7.8% were resistant to 2-5 antibiotics, and 23.6% proved to be resistant to all antibiotics. The number of multiresistant strains sharply increased during the last 10 years. The strains isolated from different sources and in different epidemic situations considerably differed in their sensitivity to the action of antibiotics. The infective agents isolated from the hospital foci of salmonellosis were found to possess the maximum multiresistance. The study of the genetic nature of multiresistance showed that the multiresistance strains had a conjugative R-plasmid with resistance determinants CmTc, type Fin+, incompatibility group F1me. The phage typing of the strains with phages from the collection of the Tbilisi Research Institute for Vaccines and Sera revealed that these strains belonged to phagotype 2. The problems of the relationship between the biological properties of causative agents and the character of the epidemic process of the diseases caused by these agents are discussed.     

Biological characteristics of spectinomycin-resistant strains of the tularemia pathogen

Sensitivity of 2 subspecies of the tularemia causative agent to spectinomycin, an aminoglycoside antibiotic, was studied in vitro. The MIC of the antibiotic with respect to strains 503/847 and Schu was 40 micrograms/ml and with respect to strain A-Cole 20 micrograms/ml. The frequency of spontaneous spectinomycin resistant mutants was low. The mutants grown on a medium containing spectinomycin in a concentration of 100 micrograms/ml were highly resistant to the antibiotic (at least 10000 micrograms/ml). By the main biological properties and virulence the spectinomycin resistant mutants did not differ from the initial strains.     

Biological characteristics of Streptococcus pneumoniae strains isolated from children with pneumococcal diseases

The biological properties of 97 S. pneumoniae strains isolated from 92 children with purulent meningitides, meningoencephalitides, pneumonia and otitis, hospitalized at the Leningrad Research Institute of Childhood Infections, were studied. The data obtained in this investigation were indicative of the formation of atypical forms of pneumococci (R-forms, unbalanced growth forms and L-forms) in all clinical forms of pneumococcal infection in children. In purulent meningitides and meningoencephalitides serovars 1 and 6, in pneumonia serovars 1, 3 and 6 and in otitis serovars 6 and 19 played the leading role. The determination of sensitivity to antibiotics showed that the forms under study retained high sensitivity to a number of antibiotics. The appearance of strains resistant to benzylopenicillin was registered. (10%). The isolated strains either possessed low virulence or were avirulent in bioassay on white mice.     

Evaluation of the possibility of using genetic and microbiological research methods for resolving current problems in the epidemiology of salmonellosis

S. typhimurium strains isolated in 14 regions of the USSR have, parallel with considerable similarity in their biological characteristics, a number of essential differences. These differences become manifest in the determination of the plasmid spectra of the above organisms. The transfer of R-plasmid PLE518 F1 me fin+ with a molecular weight of 96 Md to strains, sensitive to the action of typing bacteriophages, renders these strains resistant to the lytic action of a number of phages, which leads to the conversion of their phage type. In some cases it may deteriorate the validity of the method of phage typing, used for epidemiological purposes.     

Pleiotropic nature of mutation of resistance to 2,3,5-triphenyl- tetrazolium chloride of Francisella tularensis]

Natural strains of F. tularensis were characterized by sensitivity to 2,3,5-triphenyl tetrazolium chloride (TTC). Development of TTC resistance in the cells of F. tularensis was accompanied by changes in the biological properties of the culture, i.e. the colony morphology, antigenic structure, virulence and immunogenicity for laboratory animals. Moreover, there was a direct correlation between the levels of TTC resistance and resistance to chloramphenicol, erythromycin, tetracycline, furazolidone and rifampicin. The antibiotic resistant mutants of F. tularensis were in turn more resistant to TTC than the initial strains. This could be useful in isolation of polymarked strains of F. tularensis for genetic studies and investigation of the nature of the phenomenon of virulence in F. tularensis.     

Mathematical modeling of fungal infection in immune compromised individuals: implications for drug treatment

We present a mathematical model that describes treatment of a fungal infection in an immune compromised patient in which both susceptible and resistant strains are present. The resulting nonlinear differential equations model the biological outcome, in terms of strain growth and cell number, when an individual, who has both a susceptible and a resistant population of fungus, is treated with a fungicidal or fungistatic drug. The model demonstrates that when the drug is only successful at treating the susceptible strain, low levels of the drug cause both strains to be in stable co-existence and high levels eradicate the susceptible strain while allowing the resistant strain to persist or to multiply unchecked. A modified model is then described in which the drug is changed to one in which both strains are susceptible, and subsequently, at the appropriate level of treatment, complete eradication of both fungal strains ensues. We discuss the model and implications for treatment options within the context of an immune compromised patient.     

Dynamics of drug resistance of Vibrio cholerae isolated from surface water reservoirs in Siberia and the Soviet Far East in 1976-1990]

In the study on antibiotic resistance 1383 strains of El Tor Vibrio cholerae isolated from surface water reservoirs in 12 administrative territories of the Siberia and Far East within a period of 15 years were tested. The following antibiotics were used: ampicillin, streptomycin, monomycin, polymyxin, tetracycline, chloramphenicol, rifampicin and nalidixic acid. The resistance was unstable and its pattern was wave-like according to annual changes in the biological cycle. It was especially evident in regard to ampicillin, streptomycin, monomycin and polymyxin. The highest numbers of the strains were resistant to polymyxin, ampicillin and streptomycin (up to 100 per cent in some years). The lowest numbers of the strains were resistant to chloramphenicol (0.4 per cent) and tetracycline (1.9 per cent). No strains resistant to rifampicin and nalidixic acid were isolated. In some cases the antibiotic resistance level depended on the geographical zone where the strain was isolated. A direct quantitative dependence of the resistance level on the MIC was observed: the lower the MIC of the drug was, the lower the number of the strains resistant to it was. Within the 15-year period there was no general tendency to increase the resistance in V. cholerae to the antibiotics used.     

Dynamics of drug resistance in Proteus mirabilis cultures 1970-1985

Resistance of 669 clinical strains of Proteus mirabilis to 18 chemotherapeutic drugs was studied in dynamics within 1970-1985. An increase in the number of cultures resistant to ampicillin and carbenicillin was noted while the number of cultures resistant to cephalosporines did not change. Within the period from 1970 to 1975 there was observed a marked increase in the number of Proteus strains resistant to aminoglycoside antibiotics. After that period their number gradually lowered and in 1985 reached the level of 1970. Beginning from 1973 there were observed a decrease in the number of Proteus chloramphenicol resistant strains and simultaneous occurrence of cultures sensitive to this antibiotic. The predominating number of the tested strains preserved during the whole observation period their resistance to tetracycline, doxycycline, rifampicin, novobiocin, furazolidone and furagin. No increase in the number of Proteus strains with multiple drug resistance including those resistant to 5-7 drugs was noted in the observation periods of 1970-1975, 1980 and 1985. The most frequent were Proteus strains resistant to 2-4 drugs. Among them cultures resistant to chloramphenicol and aminoglycoside antibiotics of the first generation predominated. Grouping of the strains by the same resistance spectra provided dividing the rested cultures of Proteus mirabilis into 69 variants.     

The results of a 5-year study of listeriosis in Ukraine

Data on the isolation of Listeria spp. cultures on the territory of Ukraine, the frequency of Listeria contamination of alimentary raw materials and foodstuffs, the level of listeriosis morbidity, the clinical forms of the manifestation of this disease, as well as the occurrence of asymptomatic carriership among clinically healthy persons of epidemiologically significant professions, are given. The results of the study of the biological properties of 73 strains of Listeria spp., their sensitivity to antibiotics and Chlorophyllipt are presented.     

Does plasmid-based beta-lactam resistance increase E. coli infections: Modelling addition and replacement mechanisms

Infections caused by antibiotic-resistant bacteria have become more prevalent during past decades. Yet, it is unknown whether such infections occur in addition to infections with antibiotic-susceptible bacteria, thereby increasing the incidence of infections, or whether they replace such infections, leaving the total incidence unaffected. Observational longitudinal studies cannot separate both mechanisms. Using plasmid-based beta-lactam resistant E. coli as example we applied mathematical modelling to investigate whether seven biological mechanisms would lead to replacement or addition of infections. We use a mathematical neutral null model of individuals colonized with susceptible and/or resistant E. coli, with two mechanisms implying a fitness cost, i.e., increased clearance and decreased growth of resistant strains, and five mechanisms benefitting resistance, i.e., 1) increased virulence, 2) increased transmission, 3) decreased clearance of resistant strains, 4) increased rate of horizontal plasmid transfer, and 5) increased clearance of susceptible E. coli due to antibiotics. Each mechanism is modelled separately to estimate addition to or replacement of antibiotic-susceptible infections. Fitness costs cause resistant strains to die out if other strain characteristics are maintained equal. Under the assumptions tested, increased virulence is the only mechanism that increases the total number of infections. Other benefits of resistance lead to replacement of susceptible infections without changing the total number of infections. As there is no biological evidence that plasmid-based beta-lactam resistance increases virulence, these findings suggest that the burden of disease is determined by attributable effects of resistance rather than by an increase in the number of infections.     

Invasiveness and cytotoxicity as criteria in assessing Yersinia attenuation

The electron microscopic study of cells HEp-2 and the complex microbiological and morphological study of tissues and organs of guinea pigs and mice infected with the isogenic pairs of Yersinia strains (Y. pseudotuberculosis I and Y. enterocolitica 09) differing in the presence of the calcium-dependence plasmid, as well as Y. pseudotuberculosis mutants resistant to rifampicin, nalidixic acid or crystal violet without this plasmid, have revealed that the invasiveness and cytotoxicity of the infective agents are not directly related to the presence of the above-mentioned plasmid in these bacteria. The use of the quantitative characteristics of virulence, such as penetration ability, intracellular multiplication, dissemination and the formation of degenerative changes, has made it possible to find out that the mutants of Y. pseudotuberculosis I, yielding the negative result in the keratoconjunctivitis test and resistant to the above-mentioned antimicrobial substances, can be arranged in the following order according to the degree of attenuation: rifr mutants--nalr mutants--kvlr mutants. In contrast to Y. pseudotuberculosis I, the loss of the calcium-dependence plasmid by Y. enterocolitica 09 is accompanied by an essential decrease in their invasive and cytotoxic properties, but this relationship is indirect and unstable. The proposed criteria intended for use in the evaluation of the degree of the manifestation of the invasive and cytotoxic properties of bacteria can be useful for the selection of optimally attenuated Yersinia strains showing promise as vaccine strains.     

巴氏新小绥螨毒死蜱抗性选育及生物学特性

[目的]明确巴氏新小绥螨Neoseiulus barkeri毒死蜱抗性对其生物学特性的影响,为抗药性捕食螨田间应用提供理论基础.[方法]在室内采用药膜法测定毒死蜱对巴氏新小绥螨的毒力,以半致死浓度(lethal medium concentration,LC50)为选择压力,对巴氏新小绥螨敏感种群进行逐代汰选.应用生命...     

Hybrid antibiotics

Hybrid antibiotics that do not occur in nature have been obtained by combining structural genes of antibiotic producers. Some of these substances were effective against pathogenic microorganisms resistant against antibiotics produced by the parent strains. The majority of hybrid antibiotics were obtained by combining genes encoding polyketide synthases. Hybrid peptides with new biological properties have also been synthesized.     

Surface properties of bacteria sensitive and resistant to the class IIa carnobacteriocin Cbn BM1

Aims: Class IIa bacteriocins are small antimicrobial peptides synthesized by lactic acid bacteria. The proposed mechanisms of action for class IIa bacteriocins suggest that the physicochemical properties of the target bacterial surface govern the bacteriocin antimicrobial activity. The aim of this study is to decipher the relationship between both sensitivity and resistance to a class IIa bacteriocin, carnobacteriocin BM1 and physicochemical surface properties of bacteria. Methods and Results: The study was performed on 18 strains by a microbial adhesion to solvents process and with electrophoretic mobility measurements considering bacteria as soft particles. A large variation in bacterial surface properties is observed among the bacterial populations. Electro‐hydrodynamic parameters values appear to be more homogeneous for sensitive strains than for the resistant ones, which can exhibit more extreme values. Conclusions: Physicochemical surface properties of 18 strains determined show large variations between the strains. However, no direct link between these surface properties and the resistant/sensitive phenotypes of the strains can be stated. Significance and Impact of the Study: The surface physicochemical properties tested have a low predictive power to discriminate sensitive or resistant strains when determined at the bacterial population scale.     

Evaluation of hydrophobic properties of Yersinia enterocolitica strains isolated from humans and pigs]

The aim of the study was to evaluate the hydrophobic properties of Yersinia enterocolitica and to determine the influence of the culture conditions, such as: type of medium, temperature, and duration of the culture on the manifestation of these properties. The subject of the study were 117 of Y. enterocolitica strains isolated from humans and pigs. The ammonium sulphate salt aggregation test according to Lindahl modified method was used to evaluate the hydrophobic properties of Y. enterocolitica strains. Strains of Y. enterocolitica were cultured for 24 h at 25 degrees C on TSA (Difco) medium. During investigation of the influence of the culture conditions the chosen strains were incubated for 24 h and 48 h at 25 degrees C and 37 degrees C on TSA (Difco), LB (Difco), enrichment agar (Biomed), and enrichment agar with 5% sheep blood (Graso). A total of 44.5%, 17.9%, 9.4%, and 28.2% strains of Y. enterocolitica showed very strong hydrophobic properties, strong hydrophobic properties, some hydrophobic properties, and were non-hydrophobic, respectively when strains of Y. enterocolitica were cultured for 24 h at 25 degrees C on TSA medium. A total of 75.5% strains isolated from humans showed very strong hydrophobic properties and 13.5% strains were non-hydrophobic. Among strains isolated from pigs 30% showed very strong hydrophobic properties but 35% were non-hydrophobic. The hydrophobic properties of Y. enterocolitica depended on the temperature, duration of the culture and the type of media. The highest number of strains with very strong hydrophobic properties (89.6%) was obtained after 48 h of the incubation at 37 degrees C on the enrichment agar with 5% sheep blood. The highest number of non-hydrophobic strains of Y. enterocolitica (28.5%) was obtained after 24 h at 25 degrees C on TSA medium.     

沙门菌噬菌体抗性菌的筛选鉴定及致病力研究

【目的】筛选鉴定沙门菌噬菌体侵染裂解过程中的抗性菌株,研究抗性菌株的生物学特性及致病力的差异,为解决噬菌体治疗应用中的抗性菌问题提供理论依据。【方法】本研究通过次级感染法和双层平板法筛选沙门菌噬菌体抗性菌,通过生物学特性和毒力基因检测比较宿主菌ATCC 13076及其噬菌体抗性菌株R3之间的差异,并通过小鼠攻毒实验和细胞粘附实验比较致病力强弱。【结果】噬菌体抗性菌株R3的生长速度较宿主菌略慢;生化及毒力基因检测均表明抗性菌株与宿主菌无差异;与宿主菌相比,抗性菌R3的LD50增加了74.8%(P>0.05);对MODE-K细胞粘附能力稍弱,但是差异不显著。【结论】该研究表明,与噬菌体宿主菌相比,噬菌体抗性菌株的生物学特性和毒力基因并没有改变,对小鼠致病力减弱,但是对MODE-K细胞粘附能力差异不显著。     

Biological properties of bacteria of the species Shigella flexneri

Some biological properties of S. flexneri have been studied. The strains of this bacterial species have been shown to produce DNAase in 98.8 +/- 0.77% of cases and RNAase in 97.4 +/- 1.5% of cases. The capacity for the positive reaction with Congo red as early as after 24-hour incubation in the thermostat has proved to be characteristic of S. flexneri (91.1 +/- 3.6%). If stored at 4 degrees C in semiliquid agar, S. flexneri cultures have been found to retain their capacity for producing the above-mentioned enzymes as long as 10-13 years. All S. flexneri serovars under study, with the exception of serovar 6, have shown high activity in the manifestation of their properties.     

Characteristics of bacteria in the genus Proteus isolated from patients with sporadic and group intestinal diseases

The biochemical and biological properties of 148 Proteus strains isolated from patients both in sporadic intestinal infections and in a case of group infection in children's hospital was studied. The study revealed that the etiological factor of the group infection was P. mirabilis belonging to rare serovar 48:2. Proteus organisms isolated in sporadic infections belonged to a great number of serovars. No relationship between the isolated serovar and the nosological form of the intestinal disease was established. Among the Proteus strains under study, 82 strains showed atypical biochemical properties in 1 test or more. No correlation between the clinical diagnosis and the occurrence of atypical strains was established.