The influence of diethylstilboestrol on the antibacterial activity in vitro of some antibiotics.
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Anti-Bacterial Agents↗
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Modifications of hydrophobicity, in vitro adherence and cellular aggregation of Streptococcus mutans by Helichrysum italicum extract.
AIMS: The purpose of the present study was to examine whether sublethal concentrations of Helichrysum italicum extract could affect some of the cariogenic properties of Streptococcus mutans. METHODS AND RESULTS: We studied the antibacterial activity of H. italicum (ethanolic extract) against oral streptococci (Strep. mutans ATCC 35668, Strep. salivarius ATCC 13419 and Strep. sanguis ATCC 10556) and its influence on cell-surface hydrophobicity, in vitro sucrose-dependent adherence to glass surface and cellular aggregation of Strep. mutans. The results indicate that all streptococci were susceptible to ethanolic extract with minimum inhibitory concentration (MIC) values of 31.25-62.50 microg x ml(-1). Sub-MIC concentrations of H. italicum (7.81-31.25 microg x ml(-1)) reduced the hydrophobicity and the adherence (almost 90%) to glass surface of Strep. mutans. The aggregation in the presence of dextran T2000 was also affected. CONCLUSION: The inhibitory activity of H. italicum extract on Strep. mutans is worthy of further study. SIGNIFICANCE AND IMPACT OF THE STUDY: There is considerable interest in the use of natural compounds as alternative methods to control undesirable micro-organisms.
Anti-Bacterial Agents↗
Adhesion of Enterococcus faecalis 1131 grown under subinhibitory concentrations of ampicillin and vancomycin to a hydrophilic and a hydrophobic substratum.
The effect of two subinhibitory antibiotic concentrations of ampicillin and vancomycin during growth on the adhesion of Enterococcus faecalis 1131 to glass and silicone rubber was studied in a parallel plate flow chamber. Initial deposition rates and numbers of adhering bacteria after 4 h were higher on hydrophilic glass than on hydrophobic silicone rubber, regardless of growth conditions. The presence of 1/4 minimal inhibitory concentration (MIC) of ampicillin during growth reduced enterococcal adhesion to both substrata, but growth in the presence of 1/4 MIC vancomycin did not affect the adhesion of E. faecalis. Moreover, enterococcal adhesion increased after growth in the presence of 1/8 MIC vancomycin. The increased adhesion after growth in the presence of subinhibitory concentrations of vancomycin may have strong implications for patients living with implanted biomaterials, as they may suffer adverse effects from use of this antibiotic, especially since bacteria once adhered are less sensitive to antibiotics.
Ampicillin↗
The interaction of penicillin and chloramphenicol against meningococci in vitro.
Combinations of penicillin and chloramphenicol are frequently used initially in the treatment of bacterial meningitis. The simultaneous effects against meningococci of these two drugs were examined in vitro in a chemically defined, proteinfree medium. The investigation was performed with different combinations of the antibiotics, including optimal concentrations. In most instances, penicillin and chloramphenicol seemed to have an additive, but not an iso-additive, effect. No antagonism was found, and only one out of nine strains showed indifference.
Chloramphenicol↗
Development of TH1 CD4+ T cells through IL-12 produced by Listeria-induced macrophages.
Development of the appropriate CD4+ T helper (TH) subset during an immune response is important for disease resolution. With the use of naïve, ovalbumin-specific alpha beta T cell receptor transgenic T cell, it was found that heat-killed Listeria monocytogenes induced TH1 development in vitro through macrophage production of interleukin-12 (IL-12). Moreover, inhibition of macrophage production of IL-12 may explain the ability of IL-10 to suppress TH1 development. Murine immune responses to L. monocytogenes in vivo are of the appropriate TH1 phenotype. Therefore, this regulatory pathway may have evolved to enable innate immune cells, through interactions with microbial pathogens, to direct development of specific immunity toward the appropriate TH phenotype.
Animals↗
Inhibition of beta-lactamase in Neisseria gonorrhoeae by sodium clavulanate.
Sodium clavulanate at subinhibitory concentrations affected the activity of penicillin G, ampicillin, or amoxicillin on beta-lactamase-positive strains of Neisseria gonorrhoeae as demonstrated by marked reduction in the minimal inhibitory concentrations of the drugs for the organisms. The compound did not affect the activity of these penicillins on beta-lactamase-negative strains of N. gonorrhoeae. It also had no effect on the activity of cefoxitin against either beta-lactamase-negative or -positive strains. The reduction in minimal inhibitory concentrations of the penicillins for the beta-lactamase-positive organisms brought about by sodium clavulanate is probably due to inhibition of the beta-lactamase by the compound.
Anti-Bacterial Agents↗
Bactericidal effect of combinations of antimicrobial drugs and antineoplastic antibiotics against Staphylococcus aureus.
Six antineoplastic antibiotics were tested against ten strains of Staphylococcus aureus. Four showed bacteriostatic and/or bactericidal activity against each of the ten strains, and two were only bacteriostatic for seven and nine strains, respectively. Using the cellophane transfer technique, combinations of these antineoplastic antibiotics with 16 antibacterial drugs were screened for combined bactericidal activity. Synergism or antagonism was demonstrated in about one-third of the combinations. Checkerboard titrations and killing curves confirmed these findings and indicated that the effective concentrations of the antibacterial agents were similar to those attainable in the serum after therapeutic doses of these drugs. Although the pharmacokinetics of the six antineoplastic antibiotics in humans are not fully known, at least one of them has a peak serum level corresponding to those values at which a bactericidal effect was produced in vitro.
Anti-Bacterial Agents↗
Bactericidal effect of combinations of antimicrobial drugs and antineoplastic antibiotics against gram-negative bacilli.
Six antineoplastic antibiotics showed little antibacterial activity against 28 strains of four species of gram-negative enteric bacteria. By using the cellophane transfer technique, combinations of these agents with 16 antibacterial drugs usually showed indifference. However, combinations of mitomycin C, especially with the aminoglycosides, were synergistic on strains of Escherichia coli, Proteus, and Klebsiella pneumoniae. Bleomycin, on the other hand, often showed antagonism on strains of E. coli and K. pneumoniae with the beta-lactams, aminoglycosides, and other antibacterial agents. Checkerboard titrations and kinetic killing curves confirmed these findings.
Anti-Bacterial Agents↗
Effect of mixing on rifampin bactericidal activity against staphylococci.
Minimal bactericidal concentrations of rifampin were significantly increased, and serum bactericidal activity from volunteers receiving this drug was significantly decreased by vigorous mixing of microtiter plates before sampling when tested against Staphylococcus aureus and Staphylococcus epidermidis at 10(5) and 10(6) colony-forming units per ml. These results suggest that microtiter estimates of the bactericidal activity of rifampin against staphylococci should be performed after vigorous shaking.
Anti-Bacterial Agents↗
Interactions of beta-lactam antibiotics and antineoplastic agents.
The in vitro interactions of four beta-lactam antibiotics and five antineoplastic agents were examined with 100 clinically isolated strains of four species of gram-negative bacilli. Generally, by the checkerboard dilution method, beta-lactam antibiotics, when tested in combination with mitomycin C, bleomycin, or 5-fluorouracil, showed synergistic action, whereas when tested in combination with carboquone, they showed antagonistic action. Almost no combinations of adriamycin showed the interactions. Among beta-lactam antibiotics, piperacillin was more frequently synergistic than cefoperazone, cefazolin, or carbenicillin when tested in combination with each antineoplastic agent against various species.
Anti-Bacterial Agents↗
In vitro activity of teichomycin and vancomycin alone and in combination with rifampin.
The antibacterial activity of teichomycin, a glycopeptide antibiotic similar to vancomycin, has been evaluated in vitro and compared with that of vancomycin. Test strains included 130 staphylococci and 132 streptococci, with representatives of the major currently recognized species or groups, and lesser numbers of clostridia, propionibacteria, and group JK bacteria. Teichomycin was found to be more active than vancomycin. Its minimum inhibitory concentration (MIC) was two- to fourfold lower than that of vancomycin with staphylococci and anaerobic bacteria, and two- to eightfold lower with streptococci. No significant differences were observed with group JK bacteria. For most strains tested, minimum bactericidal concentrations (MBCs) of both teichomycin and vancomycin either equalled or exceeded by twofold the respective MICs. Higher MBC-to-MIC ratios were obtained for enterococci and pneumococci with both antibiotics. Both teichomycin and vancomycin showed similar in vitro interactions with rifampin in combination tests. Neither antagonism nor (with very few exceptions) synergism occurred.
Anti-Bacterial Agents↗
In vitro activity of rifampin in combination with oxacillin against Staphylococcus aureus.
The in vitro activity of rifampin alone and in combination with oxacillin was determined for 75 Staphylococcus aureus strains (64 susceptible and 11 resistant to oxacillin). Minimal inhibitory concentrations (MICs) and minimal bactericidal concentrations (MBCs) were determined by broth microdilution; antibiotic combinations were evaluated by microdilution checkerboard and time-kill studies. The 90% MIC of rifampin was less than or equal to 0.015 micrograms/ml after both 24 and 48 h of incubation. The 90% MBC of rifampin was less than or equal to 2.0 micrograms/ml on subculture at 24 h of incubation and less than or equal to 0.5 micrograms/ml on subculture at 48 h. MIC checkerboards with oxacillin-susceptible strains revealed an additive or indifferent effect in 35 strains (55%) and antagonism in 29 strains (45%). MBC checkerboards performed by subculture at 24 h demonstrated antagonism for all but one of the oxacillin-susceptible strains, with sub-MBCs of rifampin impairing the bactericidal activity of oxacillin. MBC checkerboards performed by 48-h subculture revealed antagonism with 37 strains (58%); in 26 additional strains (40%), a synergistic, additive, or indifferent effect was observed at low antibiotic concentrations, but antagonism was seen at higher concentrations. Time-kill studies tended to show indifference rather than antagonism with oxacillin plus rifampin. In checkerboards performed with oxacillin-resistant strains, the addition of rifampin did not improve oxacillin inhibitory or bactericidal activity to a clinically significant extent; however, the addition of oxacillin improved the bactericidal activity of rifampin at easily achievable serum concentrations.
Drug Interactions↗
In vitro activities of norfloxacin and ciprofloxacin against Mycobacterium tuberculosis, M. avium complex, M. chelonei, M. fortuitum, and M. kansasii.
The activities of ciprofloxacin and norfloxacin against 100 mycobacteria isolates were studied in vitro by the 1% standard proportion method. Ciprofloxacin was more active against M. tuberculosis and M. fortuitum with MICs of 1.0 and 0.25 microgram/ml, respectively, against 90% of isolates; norfloxacin had MICs of 8.0 and 2.0 micrograms/ml, respectively, against 90% of isolates.
Anti-Bacterial Agents↗
Inhibitory effects of chlorpromazine on Candida species.
Chlorpromazine was tested for antifungal activity by using Candida albicans and standard assays. The MIC of chlorpromazine was 35 micrograms/ml; the minimal fungicidal concentration was also 35 micrograms/ml. The minimal effective concentration was 2.2 to 3.5 micrograms/ml (using assays based on quantitative cultures and growth). There was a slight positive interaction between chlorpromazine and amphotericin B but no interaction between chlorpromazine and rifampin. Chlorpromazine also inhibited C. krusei, C. parapsilosis, C. tropicalis, and Torulopsis glabrata. We conclude that phenothiazines have direct anti-Candida activity and that these drugs appear to have a broad antimicrobial spectrum.
Amphotericin B↗
Comparative evaluation of a new beta-lactamase inhibitor, YTR 830, combined with different beta-lactam antibiotics against bacteria harboring known beta-lactamases.
YTR 830, a new beta-lactamase inhibitor, combined with amoxicillin or carbenicillin, showed a synergistic effect similar to that observed with clavulanic acid, and generally better than that with sulbactam, against strains harboring chromosome-encoded penicillinases and broad-spectrum beta-lactamases or plasmid-determined beta-lactamases. With ampicillin, YTR 830 showed the best synergistic activity of the inhibitors against Proteus morganii, Citrobacter freundii, and Enterobacter cloacae and their mutants with a derepressed chromosome-encoded cephalosporinase.
Anti-Bacterial Agents↗
In vitro susceptibilities of Plesiomonas shigelloides to 24 antibiotics and antibiotic-beta-lactamase-inhibitor combinations.
The antibiotic susceptibilities of 29 isolates of Plesiomonas shigelloides were studied with 24 antibiotics and antibiotic-inhibitor combinations. Results indicated that all isolates were susceptible to the cephalosporins, penicillins combined with a beta-lactamase inhibitor, aztreonam, and ciprofloxacin. Most isolates were resistant to the penicillins, possibly via production of a penicillinase.
Anti-Bacterial Agents↗
Pharmacodynamic effects of subinhibitory concentrations of beta-lactam antibiotics in vitro.
The pharmacodynamic effects of subinhibitory concentrations of different beta-lactam antibiotics were investigated. A postantibiotic effect (PAE) was induced for different bacterial species by exposure to 10x MIC of several beta-lactam antibiotics for 2 h in vitro. The antibiotic-bacterial combinations used in this study were imipenem-Pseudomonas aeruginosa, benzylpenicillin-Streptococcus pneumoniae and -Streptococcus pyogenes, cefcanel-S. pyogenes, ampicillin-Escherichia coli, and piperacillin-E. coli. After the induction of the PAE, the exposed cultures as well as the unexposed controls were washed and diluted. Thereafter, the cultures in the postantibiotic phase (PA phase) and the cultures not previously treated with antibiotics were exposed to 0.1, 0.2, and 0.3x MIC of the relevant drug and the growth curves were compared. When bacteria in the PA phase were exposed to sub-MICs, a substantial prolongation of the time before regrowth was demonstrated, especially in antibiotic-bacterial combinations for which a PAE was found. In contrast, sub-MICs on cultures not previously exposed to suprainhibitory antibiotic concentrations yielded only a slight reduction in growth rate compared with the controls. Thus, it seems important to distinguish the direct effects of sub-MICs on bacteria not previously exposed to suprainhibitory concentrations from the effects of sub-MICs on bacteria in the PA phase.
Anti-Bacterial Agents↗
Effects of magainins on ameba and cyst stages of Acanthamoeba polyphaga.
Amebic keratitis produced by Acanthamoeba spp. is an increasingly important ocular infection in extended-use contact lens wearers. Problems associated with the infection are compounded by the lack of effective and well-tolerated chemotherapeutic agents. The magainins, a group of naturally occurring and synthetic membrane-active peptide compounds, have been shown to be active in vitro against a clinical isolate of Acanthamoeba polyphaga. Two magainins tested extensively had minimal inhibitory and minimal amebicidal values of 20 and 25 micrograms/ml for magainin MSI-103 and 25 and 40 micrograms/ml for magainin MSI-94, respectively. Both amebastatic and amebicidal activities are enhanced by combining the magainins with silver nitrate (200 micrograms/ml) and/or other marginally effective antimicrobial agents. These combinations have activity against both trophic and cystic stages in the Acanthamoeba life cycle and have promise as antimicrobial agents in the treatment of amebic keratitis.
Acanthamoeba↗