Mitsuto Hasegawa

Bacteriostatic and Bactericidal Activities of Selected Beta-Lactam Antibiotics Studied on Agar Plates

A novel and time-saving method for assessing bactericidal activities of β-lactam antibiotics on agar plates is described. Minimal inhibitory concentrations (MICs) were determined by the agar dilution method. A potent β-lactamase solution was sprayed onto the plates to inactivate the antibiotic. After further incubation at 37°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 β-lactamase-unstable penicillins and cephalosporins, the method can be applicable with any β-lactam antibiotic if optimal and potent enzymes are available. Images

Inhibition of Platelet Function by Sulbenicillin and Its Metabolite

The effect of sulbenicillin and its major metabolite, α-sulfobenzylpenicilloic acid, on platelet function was investigated. Sulbenicillin caused inhibition of platelet aggregation and release reaction in the same manner as carbenicillin. α-Sulfobenzylpenicilloic acid was found to cause much stronger inhibition of platelet function. The results indicate that the strong inhibitory action of α-sulfobenzylpenicilloic acid may also take part in impaired platelet functions following administration of sulbenicillin to humans.

Clinical Study of Gram Negative Rods (GNR) Septicemia at Keio University Hospital

1. A tendency of infectious organisms of GNR septicemia and the sensitivity distribution of strains recently isolated were described. 2. Therapeutic results of GNR repticemia revealed the clinical availability of the combined use of B-lactam antibiotics and Gentamicin or Tobramycin. 3. The synergetic effects was observed by the combined use of Cefazoline and Gentamicin in bacteriostatic and bactericidal action in in vitro antibacterial activity test.

Clinical Study of BBK8 on Gentamicin (GM) Resistant Gram Negative Rods (GNR)

1. Incidence of resistant strains of GNR against B-lactam antibiotics was higher in strains isolated from urine and blood rather than from sputum, especially in those isolated from blood. 2. Also, Gentamicin resistant strains were isolated more frequently from urine and blood than from sputum. 3. Strains of Proteus, Klebsiella and Pseudomonas which are resistant to Gentamicin have been increased in past two years. 4. Gentamicin resistant strains of GNR did not show the cross resistance to Amikacin (BBK8). 5. Amikacin showed therapeutic effect on P.aeruginosa septicemia which was highly resistant to Gentamicin and on Proteus mirabillis septicemia.