Evaluation of outcomes of combined specific prophylaxis with the antibiotic resistant immunogenic plague pathogen strain and emergency prophylaxis with aminoglycosides in the experimental plague model in white mice]

It was shown that aminoglycosides (streptomycin, kanamycin, gentamicin, sisomicin, tobramycin, amikacin) prevented manifestation of postvaccine immunity in albino mice immunized by vaccine strain Yersinia pestis EV. Avirulent strain Y. pestis 363 Monr with chromosome resistance to aminoglycosides of the 1st, 2nd and 3rd generations provided manifestation of antiplague immunity when streptomycin, kanamycin, gentamicin and amikacin were administered for prophylaxis. ED50 achieved 1.0-1.2 x 10(3) CFU and in control group (without treatment) 9.3 x 10(2) CFU. Gentamicin and amikacin were highly effective for experimental plague prophylaxis (90-100% animal survival), but inhibited development of postinfective immunity. Protective index (PI) value was 1.1 x 10(2). It was demonstrated that combination of specific prophylaxis (Y. pestis 363 Monr) and emergency prophylaxis with aminoglycosides in albino mice infected with approximately 1000 LD50 of virulent strain Y. pestis 358 (5 hours after infection) was highly effective and provided protective effect against subsequent infection with plague pathogen. Value of PI was 1.1 x 10(5) and practically did not differ from PI (1.7 x 10(5)) in control group (intact mice, immunized with strains EV [symbol: see text] 363 Monr).     

Effectiveness of cefotaxime in experimental plague infection]

Cefotaxime was shown highly efficient in prophylaxis and treatment of experimental plague infection in albino mice. The in vitro activity of cefotaxime against natural strains of the plague microbe was 32 to 64 times higher than that of cefazolin, cephalothin and cefmetazole. The combined use of cefotaxime with amikacin significantly increased the percentage of the survived albino mice with plague infection as compared to the use of the antibiotics alone.     

Isepamycin in prophylaxis and treatment of experimental plague due to FI+ and FI- variants of plague microbe]

The efficacy of isepamycin vs. other aminoglycosides was studied in vitro and on albino mice with experimental plague due to natural antigen valuable strains of the plague microbe and the pathogen variants deprived of the ability to produce the capsular antigen fraction I (FI- phenotype). The MICs of isepamycin for the strains of the plague microbe (20 FI+ and 20FI-) were 1.0-4.0 mg\l, that did not differ from those of streptomycin, kanamycin, amikacin and tobramycin. The ED50 of isepamycin in the prophylaxis and treatment of the experimental plague of the mice had no statistically significant differences from the ED50 of the other aminoglycosides. The efficacy index of isepamycin was > 10(4), that did not differ from that of streptomycin, amikacin and gentamicin, irrespective of the strain phenotype (Y. pestis 231 FI+ or Y. pestis 231 FI-). The same as the other aminoglycosides, isepamycin in doses equivalent to the human average daily doses, protected 80-100% of the albino mice from death when used in the prophylaxis and therapy of plague irrespective of the strain phenotype. The results of the study made it possible to consider isepamycin as an agent promising for the prophylaxis and treatment of plague.     

Doxycycline in the prevention of experimental plague induced by plague microbe variants]

A comparative study was performed on the efficacy of doxycycline in experimental plague infection induced in albino mice by strain 231 of the plague microbe and its variant 231 Fra- deprived of the ability to produce the fraction I antigen. It was shown that the LD50 for strain 231 during animal treatment with doxycycline was significantly higher than that for variant 231 Fra-. Prophylaxis of the plague infection caused by the Fra- forms of the plague microbe required significantly higher doses of doxycycline (ED50) than that of the infection caused by the Fra+ forms. The use of the daily maximum permissible doses of doxycycline (50 to 100 mg/kg a day) for 10 days in treatment of albino mice infected with the strain Fra- did not provide animal survival at the level higher than 60 to 70 per cent while the survival rate in the animals infected with the strain Fra+ of the plague microbe and treated according to the same scheme amounted to 90-100 per cent. The lower therapeutic efficacy of doxycycline in the treatment of the infection caused by the fractionless variant of the plague microbe should be considered in development of rational schemes for prophylaxis and treatment of plague.     

Ofloxacin efficacy in the prophylaxis and treatment of experimental plague due to antigen complete and defective strains of the pathogen]

Strains of the plague microbe, antigen complete and defective by fraction I and mouse toxin had the same in vitro susceptibility to ofloxacin (MIC 0.08 mg/L). The drug was superior in its activity to pefloxacin and especially nalidixic acid. In the experiments with albino mice (prophylaxis, 5 days) the ofloxacin efficacy was lower when the infection was due to the plague microbe strains deprived of the ability to produce fraction I and mouse toxin, evident from a statistically significant increase of the drug ED50 and a decrease of the animal survival percentage. When used in the doses corresponding to the human average daily doses, ofloxacin provided effective animal protection (80 to 100 per cent survival) after the prophylaxis for 7 days and the treatment of the plague infection irrespective of the strains, complete or antigen changed. However, when the infection is due to the antigen changed strain, ofloxacin should be used in the maximum daily doses at least for 7 days.     

Synergistic action of some antibacterial agents in studies on albino mice with experimental plague caused by Fr- phenotype strain of the plague microbe]

Possible use of ciprofloxacin combinations with some other antibiotics such as rifampicin, ampicillin, cefotaxime, doxycycline and amikacin was studied on albino mice with experimental plague caused by the pathogen strain (approximately 1000 LD50) deprived of the ability to produce the capsular antigen, fraction I (Fra- phenotype). The combination of ciprofloxacin with ampicillin or doxycycline had no effect on the increase of the survival rate (t<2) evident of inexpediency of its use in the infection caused by the Fra- strains of the plague microbe. The combination of ciprofloxacin and cefotaxime used in definite doses had some effect (t=2.6). The most significant synergistic effect was observed with the use of ciprofloxacin in combination with amikacin or rifampicin (t>3.3-9.0) which made the combination most promising.     

Detoxifying effect of antibiotics and their effectiveness in experimental plague at the stage of explicit intoxication]

The effect of antibiotics such as amikacin, rifampicin, doxycycline, polymyxin B and cefotaxime on the toxins of the plague microbe (lipopolysaccharide + fraction II according to Beiker) was studied in vitro and in vivo. The study on the antibiotic neutralization of plague toxins revealed that only polymyxin had toxin neutralizing capacity which depended on the dose. Investigation of the polymyxin effect at various stages of plague infection showed that when polymyxin in a dose of 1250 units and a mixture of plague toxins in lethal doses were administered simultaneously to albino mice, the positive effect amounted to 100 per cent. When the antibiotic was administered 30 or 60 minutes later, the antibiotic efficacy proved to be lower by 90 or 76.6 per cent, respectively. The intoxication in later periods (in 90-120 minutes) resulted in a decrease in animal survival up to 40-15 per cent. It was demonstrated on the model of the plague infection in albino mice that the use of amikacin, cefotaxime, rifampicin or doxycycline during polymyxin therapy at the stage of marked generalization of the infection provided a significant increase in the animal survival (60 to 80 per cent) as compared to that after the use of the same drugs alone (0 to 20 per cent).     

Effect of subinhibitory concentrations of antibiotics on catalase activity of plague microbes]

It was shown that the presence of subinhibitory concentrations of ampicillin, cefotaxime or gentamicin in the cultivation medium had a marked inhibitory effect on the catalase activity of plague microbe. The effect depended on the characteristic features of plague microbe strains and the incubation temperature. When the cells of a virulent strain of the plague microbe Y. pestis 1300 were cultivated at a temperature of 37 degrees C on a medium containing the subinhibitory concentrations of ampicillin or cefotaxime, the pathogen virulence for albino mice significantly decreased.     

Chromosomal resistance of plague agent to quinolones]

The nature of increasing chromosomal resistance to quinolones was studied in a model of the plague microbe. Five virulent strains of the natural plague microbe (Y. pestis) were used in the experiment: 363 (1/1479), 231, 2385, 2442 and 2444. The one-stage procedure for isolation of the mutants was applied. It was shown that the frequency of the one-stage mutants resistant to oxalinic acid, pefloxacin and ciprofloxacin amounted to 10(-9)-10(-11) and was 2 to 3 orders of magnitude lower than that of the mutants resistant to nalidixic acid. Two types of the plague microbe mutants resistant to the quinolones were detected: those resistant to the quinolones to the generations (Nalr-phenotype) and those resistant to the representatives of the 3rd generation quinolones (Nals-phenotype). The quinolones were not efficient in the treatment of albino mice with experimental plague caused by the quinolone-resistant forms of the plague microbe.     

Comparative study of the antibacterial activity of aminoglycoside antibiotics and their combinations with carbenicillin against Pseudomonas aeruginosa

Antibacterial activity of 7 aminoglycoside antibiotics and combinations of tobramycin or gentamicin with carbenicillin was studied with respect to 33 clinical strains of Ps. aeruginosa. Tobramycin, sisomicin, gentamicin and amicacin showed high levels of antibacterial activity. Tobramycin and sisomicin were 3-4 and 2 times more effective than gentamicin. 100 per cent of the Ps. aeruginosa isolates was sensitive to tobramycin and amicacin. The number of the isolates sensitive to sisomicin and gentamicin amounted to 97 and 94 per cent respectively. The respective numbers for streptomycin and kanamycin were 32 and 11 per cent. No monomycin sensitive isolates were detected. Combination of tobramycin or gentamicin with carbenicillin increased the antibacterial activity of the aminoglycoside antibiotics by 2-16 times and that of carbenicillin by 2-32 times. The synergistic effect of gentamicin or tobramycin with carbenicilin was observed with respect to 50 and 58 per cent of the isolates respectively. No antagonistic effect was detected on the combined use of the antibiotics. The majority of the isolates (96 per cent) were sensitive to combinations of carbenicillin in a concentration of 50 micrograms/ml with tobramycin or gentamicin in concentrations of 0.15 or 0.3 micrograms/ml respectively.     

Amikacin resistance of clinical strains of Enterobacteriaceae and Pseudomonas]

Amikacin resistance was studied in 380 bacterial strains of Enterobacter, Klebsiella, Serratia, Pseudomonas and E. coli isolated in clinics of the Moscow Region. It was shown that 69 isolates were resistant to amikacin. Plasmid DNA was detected in 10 amikacin resistant isolates. Three of them belonging to Klebsiella and 3 belonging to E. coli contained plasmids controlling resistance to amikacin. The plasmids isolated from the strains of Klebsiella determined as well resistance to kanamycin and streptomycin but did not control resistance to sisomicin, tobramycin and gentamicin while the plasmids isolated from the strains of E. coli determined resistance to amikacin, kanamycin, gentamicin, tobramycin and sisomicin.     

Effectiveness of phosphomycin and its combinations with amikacin and cefotaxime in experimental plague infection]

When administered intramuscularly in doses of 8 and 16 mg/mouse, phosphomycin was highly active in the treatment of albino mice with experimental plague infection (80-100-percent protection of the animals from death). Combinations of phosphomycin with cefotaxime in inefficient or not sufficiently efficient doses had a synergistic effect. When the albino mice were treated with combinations of phosphomycin and amikacin, the percentage of the survived animals significantly increased in comparison to that after the use of the antibiotics alone.     

Lack of levofloxacin and moxyfloxacin efficacy in experimental plague of albino mice infected with nalidixic acid resistant pathogen (Nal(r))

The efficacy of levofloxacin and moxyfloxacin vs. the previously tested fluoroquinolones was studied on albino mice with experimental plague due to the Nal(r) mutants of Yersinia pestis 231 and 231 FI-. The plague microbe mutants resistant to nalidixic acid (Nal(r)) generated at a frequency of 10(-10)-10(-9). The resistance to nalidixic acid was not accompanied by the strains loss of the virulence. The Nal(r) mutants were cross resistant to fluoroquinolones (ciprofloxacin, moxyfloxacin). The LD50 for the nontreated animals did not differ from that for the mice treated with nalidixic acid and the fluoroquinolones (when the animals were infected with Nal(r) mutants). The results showed that the criteria of the plague microbe susceptibility/resistance to fluoroquinolones should be revised.     

Experimental evaluation of prospects for the use of beta-lactams in plague infection caused by pathogens with plasmid resistance to penicillins]

High therapeutic efficacies of ceftriaxone, ceftazidime, cefotaxime and azthreonam in the treatment of experimental plague induced by beta-lactamase-producing strains of the plague microbe containing R plasmids RP-1, R57b and R40a were shown to correlate with their in vitro antibacterial activities. The therapeutic efficacy of sulbactam/ampicillin was recorded in the treatment of plague induced by the strain containing R plasmids R57b and R40a (the treatment course of 7 days). However, it was lower when the infection was due to the strain containing plasmid RP-1 (beta-lactamase TEM-2). Cefoperazone was not active in the treatment of experimental plague induced by the strains containing plasmids RP-1 and R57b (beta-lactamases TEM-2 and OXA-3). Ceftriaxone versus the antibiotics tested was considered to be the drug of choice for the etiotropic therapy of plague induced not only by the type strains of the plague microbe but also by its variants with the plasmid pattern resistance to penicillins.     

Sensitivity of Brucella melitensis to various antibiotics, drug preparations and their combinations

In vitro activity of 13 antibiotics and drug preparations as well as some of their combinations was studied with respect to Brucella melitensis. It was shown that the strains of B. melitensis were sensitive to sisomicin, amikacin, gentamicin, cefotaxime, rifaprim +, nitroxoline and trimethoprim. Variations in the doxycycline sensitivity depending on the strain were observed. The strains of B. melitensis were resistant to cephalexin, phosphomycin, chinoxydine, dioxydine and oxolinic acid. Combinations of sisomicin and trimethoprim at a ratio of 1:10 and sisomicin and nitroxoline at a ratio of 1:2 had a summation effect.     

Effect of antibiotics on Francisella tularensis]

The minimum inhibitory concentrations of rifampicin, doxycycline, sisomicin, ciprofloxacin and phosmidomycin for various strains of Francisella tularensis were 0.5 to 2.0, 0.5 to 2.0, 0.125 to 0.4, 0.625 to 0.125 and 2.0 to 12.5 micrograms/ml, respectively. Ciprofloxacin and sisomicin had a marked bactericidal effect. The bactericidal effect of rifampicin was insignificant. Doxycycline and phomidomycin had practically no such effect. All the antibiotics had a post effect. The level of the post-antibiotic effect was different and depended on the antibiotic concentration.     

Search for inhibitors of West Nile virus among antibiotics]

The activity of 24 antibiotics was studied in treatment of albino mice with experimental encephalitis caused by West Nile virus. The antiviral activity of gentamicin and kanamycin was stated. The survival rate of the animals 19. contaminated with 10-100 LD50 of the West Nile virus and treated parenterally with gentamicin in a dose of 80 to 400 micrograms/mouse was higher than that in the controls by 29.5 to 100 per cent and depended on the drug regimen. The efficacy of kanamycin was lower. The chemotherapeutic indices of gentamicin and kanamycin amounted to 100 and 10, respectively. Since there are no schemes for chemotherapy of the infection caused by the West Nile virus and the respective vaccines are not available the use of the antibiotics and gentamicin in particular appears to be promising in the disease prevention and treatment.     

Rapid evaluation of the effectiveness of antibacterial drugs in experimental tularemia

Rapid estimation of the protective effect of antibacterial drugs on Fransiella tularensis for not more than 2 days was shown possible in experiments on albino mice infected with tularemia. High efficacy of aminoglycosides (kanamycin, gentamicin, streptomycin, amikacin, netilmicin, tobramycin, sagamycin, ribostamycin and sisomicin), tetracyclines (tetracycline, doxycycline, minocycline and methacycline), rifampicin, phosphomycin and oxolinic acid was determined with the recommended rapid method. Amoxycillin, ampicillin, piperacillin, carbenicillin, erythromycin, levomycetin, cefradine, cefmetazole, cefatrizine, cefoxitin, cefsulodin and bactrim (biseptol) proved to be inefficient against the tularemia causative agent.     

Antibiotic sensitivity of plague microbe strains from foreign countries]

The method of serial dilutions on the Hottinger agar was applied to comparative assay of antibiotic sensitivity in 50 strains of the plague microbe isolated abroad and in 5 strains isolated in the plague focus in the Central Caucasus. The antibiotics used in the assay were the following: streptomycin, gentamicin, doxycycline, monomycin, kanamycin, tetracycline, erythromycin, ristomycin, lincomycin and polymyxin M. Irrespective of the origin, all the isolates were resistant to erythromycin, lincomycin and polymyxin M. The levels of the sensitivity to the other antibiotics were different. The data serve as a ground for the statement that there is no tendency to development of antibiotic resistance in the plague microbe in patients treated with high doses of the antibiotics and mainly streptomycin. Along with streptomycin, such antibiotics as gentamicin, tetracycline, doxycycline and kanamycin are useful in the therapy of plague and require further investigation.     

Biochemical determinants of aminoglycoside resistance in Gr- microorganisms isolated from urocultures

The investigation was focused on 60 strains of Gr- microorganisms isolated from urocultures and resistant to gentamicin and/or amikacin. Resistance evaluation by the method of Bauer--Kirby with respect to 7 aminoglycoside aminocyclitols (streptomycin, spectinomycin, kanamycin, gentamicin, tobramycin, sisomicin, netilmicin and amikacin) as well as determination of minimal inhibitory concentrations revealed that the most frequently occurring resistance phenotype was streptomycin kanamycin gentamicin sisomicin tobramycin (91.66% tested microorganisms). Approximately 50% of all tested organisms were found to be susceptible to netilmicin. Assays for aminoglycoside-modifying enzymes using 32P ATP and 14C ATP confirmed APH(3')(5")--I and AAD(2") as resistance determinants regarding 4,6-substituted deoxystreptamines. Acetyltransferase determination by the method of Shannon and Phillips and that by van de Klundert et al. most frequently assumes for the formation of AAC(3)-II and AAC(3)-I. Assays utilizing radioactive labels in amikacin-resistant strains determine the enzymes APH(3') and AAD(2")-II.