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Biomedical subjects

G Masuda

Publications and source records attributed to G Masuda.

At least 73 records · Page 4Linked to original sources
PubMed1982

Assessment of timed bacteriostatic and bactericidal activities of cephalothin against gram-positive and gram-negative bacteria.

The comparative bacteriostatic and bactericidal activities of cephalothin were assessed in broth medium with special reference to the period of exposure of microbes to the drug. The bacteriostatic concentration with a brief period of exposure (6 h) was lower than the conventional MIC for Escherichia coli and Klebsiella sp. When the period of exposure was prolonged (18-42 h), the bacteriostatic concentration almost corresponded with the MIC. In contrast to these gram-negatives, the bacteriostatic concentration with a brief period of exposure roughly corresponded with the MIC for strains of Staphylococcus aureus and was higher for enterococcus. When a comparison of the bacteriostatic and the bactericidal concentrations was used as the criterion for assessment, the mode of action of cephalothin appeared to be bactericidal to most of the gram-negatives. This drug was bacteriostatic to a number of strains of gram-positives, in particular to enterococcus, especially when microbes were exposed to the drug over a brief period of time.

Cephalothin↗
PubMed1982

[Timed bacteriostatic and bactericidal activities of cefmetazole against selected gram-negative bacteria].

Antibacterial activities of cefmetazole, a new preparation of cephamycin antibiotic, were determined against selected clinical strains of Escherichia coli (27 strains), Klebsiella sp. (27 strains) and Bacteroides fragilis (27 strains). Activities were evaluated at bacteriostatic and also bactericidal levels with particular reference to time of exposure of microbes to the drug. The minimal drug concentrations producing minimal reduction of colony-forming units at time intervals of 3, 6 and 24 hours after exposure to the drug--approximations to the theoretical bacteriostatic concentrations--were designated as 3-h, 6-h and 24-h MRCs, respectively. Conventional MIC yielding no turbidity after incubation of antibiotic-containing broth for 24 hours was also determined. The minimal concentrations of the drug producing 99.9% killing at time intervals of 3, 6 and 24 hours after exposure to the drug were designated as 3-h, 6-h and 24-h MLCs, respectively. Assuming that the apparent mode of action of a drug is bactericidal when the ratio of bactericidal-bacteriostatic concentrations is low (less than or equal to 4) and bacteriostatic when high (greater than or equal to 8), then cefmetazole appeared to be a bactericidal drug to a considerable number of Gram-negative strains when the exposure time exceeded a period of 6 hours. The data that the mode of action of this drug is bactericidal with such relatively brief exposure times--indicating rapid decrease of colony-forming units--would suggest cefmetazole is an excellent antibacterial agent and would be a useful drug in treatment of bacterial infections.

Anti-Bacterial Agents↗
PubMed1981

[In vitro studies on the activities of cephalothin against selected bacteria (author's transl)].

Cephalothin antimicrobial activities were studied against selected bacteria with special reference to the time of exposure of microbes to the drug assessed in broth medium. The minimal concentration of this drug producing 10(0)-10(1) reduction of colony forming unit (CFU) per ml after given exposure times -an approximation to the theoretical bacteriostatic concentration inhibiting increase or decrease of CFU- was designated as minimally reducing concentration (MRC). The concentration was determined after 6 h, 18 h and 42 h of incubation and designated as 6-h, 18-h and 42-h MRC, respectively. Conventional minimal inhibitory concentration (MIC) with 18 h exposure time was also studied. The minimal concentration of the drug yielding 99.9% reduction of CFU after an exposure to the drug was determined and designated as minimal lethal concentration (MLC). The determinations were made at 6 h, 18 h and 42 h of incubation and designated as 6-h, 18-h and 42-h MLC, respectively. The data indicated that the bacteriostatic concentration for Escherichia coli and Klebsiella sp. with brief exposure time (6-h MRC) was 2-4 times lower than the MIC. If the exposure time was prolonged (18-42 h), the bacteriostatic concentration increased and almost agreed with the MIC. A significant effect of inoculum size was observed on the MRC values for the Gram-negatives when the values were determined with the inoculum concentrations at 10(6)-10(7) CFU/ml and 10(3)-10(4) CFU/ml. In contrast to these Gram-negatives, the 6-h MRC for most strains of Staphylococcus aureus and Enterococcus roughly agreed with the MIC. If the ratio of bacteriostatic to bactericidal concentrations was used as the criterion, the mode of action of cephalothin appeared to be bactericidal for most of the Gram-negatives. This drug was bacteriostatic for a number of the Gram-positive strains, in particular to those of Enterococcus, especially when microbes were exposed to the drug over a brief period of time.

Bacteria↗
PubMed1980

Bacteriostatic and bactericidal activities of beta-lactam antibiotics enhanced by the addition of low concentrations of gentamicin.

The combined effects of low concentrations of gentamicin on certain beta-lactam antibiotics were studied by the agar plate method. the combination of gentamicin with cephalothin produced synergism against 17 of 26 strains of Escherichia coli and 19 of 27 strains of Klebsiella sp. if assessed at the bacteriostatic (minimal inhibitory concentration) level. Synergy against many more strains was apparent when bactericidal concentrations were used. Synergy against most of these strains was observed if bactericidal concentrations with brief exposure times (3 h) to the antibiotics were used for measurement. Additive effects were observed in almost all of the remaining strains. The combination of gentamicin and carbenicillin were synergistic against most strains of Pseudomonas aeruginosa when any bacteriostatic or bactericidal measurement was used as the criterion.

Bacteria↗
PubMed1979

Comparative bactericidal activities of beta-lactam antibiotics determined in agar and broth media.

Comparative bactericidal activities were determined utilizing a relatively large number of test strains, in both agar and broth media, with special reference to the time of exposure of the bacteria to certain beta-lactam antibiotics. It was apparent that the activities increase with time. The concentrations producing a 99.9% kill with cephalothin for Escherichia coli, Klebsiella sp., and carbenicillin for Pseudomonas aeruginosa were higher in broth than in agar. In contrast, those of benzylpenicillin for alpha-streptococcus (non-enterococcal) were higher in agar than in broth. If the bactericidal concentrations with 3-hour or 6-hour exposure to antibiotics were used as the criterion, these concentrations of carbenicillin for P. aeruginosa, and benzylpenicillin for alpha-streptococcus were, in particular, unusually high compared with the conventionally determined bacteriostatic concentrations (MICs).

Agar↗
PubMed1978

Quantitative assessment of bactericidal activities of beta-lactam antibiotics by agar plate method.

Quantitative bactericidal activities of beta-lactam antibiotics were determined by the agar plate method. Broth cultures, of which the colony-forming units were counted before the study, were inoculated on antibiotic-containing agar plates, utilizing a 10(-3), 10(-2), or 10(-1) dilution or undiluted culture plated with each 0.001-ml calibrated loop. These plates were incubated at 37 degrees C overnight, and the minimal drug concentration at which no bacterial growth was observed on the plates was defined as minimal inhibitory concentration. After this procedure, the agar surface was treated with beta-lactamase spray to inactivate the antibiotic. These plates were incubated again at 37 degrees C overnight. The minimal drug concentration at which no evidence of bacterial growth was visible on the plates (resulting in a 100% kill) was defined as minimal bactericidal concentration. The lowest concentration which reduced the number of colony-forming units to 1/1,000 that in the original inoculum (resulting in a 99.9% kill) was defined as minimal lethal concentration. When compared for Escherichia coli, Klebsiella pneumoniae, Enterobacter sp., Serratia marcescens, Pseudomonas aeruginosa, Staphylococcus aureus, Staphylococcus epidermidis, alpha-hemolytic streptococcus (non-enterococcal), beta-hemolytic streptococcus, and enterococcus, the minimal bactericidal concentrations were generally several fold higher than the minimal inhibitory concentrations. Minimal lethal concentrations were virtually the same as minimal inhibitory concentrations for gram-negative strains; however, for some gram-positive strains, minimal lethal concentrations were higher than minimal inhibitory concentrations.

Cephalosporins↗
PubMed1977

Bacteriostatic and bactericidal activities of selected beta-lactam antibiotics studied on agar plates.

A novel and time-saving method for assessing bactericidal activities of beta-lactam antibiotics on agar plates is described. Minimal inhibitory concentrations (MICs) were determined by the agar dilution method. A potent beta-lactamase solution was sprayed onto the plates to inactivate the antibiotic. After further incubation at 37 degrees C overnight, the minimal concentration at which no visible growth occurred on the plates was defined as minimal bactericidal concentration (MBC). With undiluted culture as the inoculum, strains of Staphylococcus aureus, Escherichia coli, and Klebsiella pneumoniae showed a marked increase in MBC values compared with the values of MIC. There was a marked decrease in both the MICs and MBCs with diminution of inoculum size. The two concentrations were almost the same when the inoculum size was decreased to a 10(-4) dilution. In contrast, MIC and MBC for enterococci showed no marked decrease with decrease in inoculum size. Although the present study was performed with beta-lactamase-unstable penicillins and cephalosporins, the method can be applicable with any beta-lactam antibiotic if optimal and potent enzymes are available.

Ampicillin↗
PubMed1977

Possible beta-lactamase activities detectable in infective clinical specimens.

Biological beta-lactam antibiotic-inactivating activities were detected in bacteriuria and suppurating pleural fluids. Clinical specimens were sterilized with membrane filters and the amounts of ampicillin and/or cephalothin which were being inactivated by 1 ml of each filtrate were determined. In general, filtrates which originally yielded Klebsiella sp. tended to show activity against ampicillin; whereas those yielding Enterobacter sp. and Pseudomonas aeruginosa showed activity against cephalothin.

Amidohydrolases↗
PubMed1976

Studies on bactericidal activities of beta-lactam antibiotics on agar plates: the correlation with the antibacterial activities determined by the conventional methods.

A simplified method to determine minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) of beta-lactam antibiotics on agar plates is described. MIC values were determined on agar plates for benzylpenicillin, methicillin and cephalothin using Staphylococcus aureus and Klebsiella pneumoniae. A beta-lactamase solution was then sprayed onto the plates to inactivate the drug(s). After further incubation at 37 degrees C overnight, the minimal concentration at which no test bacteria were visible on the plates was defined as MBC. Both MIC and MBC values decreased with decreased inoculum size. The two values were almost coincidental when high dilutions were used as the inocula. These values were compared with those obtained by the conventional broth dilution method. In this study, MIC as well as MBC values determined by the simplified method were generally smaller than the values determined by the broth dilution technique.

Anti-Bacterial Agents↗