In this study, 6 injection antibiotics; cephaloridine (CER), cefazolin (CEZ), ceftezole (CTZ), cefoperazone (CPZ), cephalothin (CET) and cephapirin (CEPR) and 2 oral antibiotics; cephalexin (CEX) and cefadroxil (CDX), were used. Four strains of
Staphylococcus aureus were used as test organisms. Heart infusion broth (HI broth—Difco) was used as a medium for the test. A biorecorder (Toyo Kagaku Co., Ltd.) was used for measurement. The amount of bacteria added was 5×10
5 cells/ml, and the biorecorder was set to record the optical density at the moment of the growth of the added bacteria up to 5×10
7 cells/ml.
Study 1: By determination of the effect of cephalosporinase (Chemical Credentials Research) containing 290 units of activity per mg, it was confirmed that 8 cefems used in this study lose their antimicrobial activity by addition of cephalosporinase (290 units/ml) . Consequently, it was designed in this study to add 290 units of cephalosporinase per ml of broth.
Study 2: Six cefems for injection and
Staph. aureus 209P JC-1 were left in contact with shaking for 3 h at 37°C. Cephalosporinase was then added to the broth, and shaking was continued during the culture, and the delayed growth time was determined. At the concentration of 0.78μg/ml, the delayed growth time was longest with CER (14.0h), followed by CEPR (13.6h), CTZ (12.1h), CPZ (9.7 h), CET (9.4h) and CEZ (7.2h) . At 1.56μg/ml, it was longest with CEPR (14.3h), followed by CER (14.2h), CTZ (12.5h), CPZ (10.3h), CET (9.7h) and CEZ (7.3h) . At 3.13μg/ml, it was longest with CEPR or CFR (14.4h), followed by CTZ (12.6h), CPZ (12.4h), CET (9.9h) and CEZ (7.4h) . At 6.25μg/ml, it descended in the order of CEPR (14.6h) >CER (14.3h) >CTZ (12.9h) >CPZ (12.5h) >GET (10.4h) >CEZ (7.5h) . For each cefem the delayed growth time showed dose-dependent prolongation with an increase in the concentration.
Study 3: Limiting the exposure time to 3h, we studied 4 strains of
Staph. aureus with GER. It was found that there were individual variations in the delayed growth time among these strains of organisms. In addition, this study also confirmed that the delayed growth time was prolonged dose-dependently with an increase in the concentration.
Study 4: The organisms were exposed to CER for 2, 3 or 4 h. The delayed growth time was found to be dependent upon the exposure time.
Study 5: Using 2 oral antibiotics, CEX and CDX, and limiting the exposure time to 3.5h, we determined the delayed growth time. As a result, it was found that the delayed growth time was prolonged with CDX at the concentration of 1.56-6.25μg/ml.
As regards cefems for injection use, although the delayed growth time varied individually, a time-dependent relationship was noted between the delayed growth time and the time of exposure to antibiotics. Although time-dependence was noted, prolongation of the delayed growth time was short at concentrations above a certain level. From this point of view, it was considered that cefems for injection use would be more effective even at low concentrations when the exposure time was longer. Especially CER, CEPR and CTZ, resulted in long prolongation of the delayed growth time even at low concentrations, and their activity depended little upon the method of administration. Consequently, these antibiotics were confirmed to be useful in this
in vitro ex-periment.
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