A continuous flow culture has been developed as in vitro model of bacterial growth and drug concentrations in the body. On the other hand, the antibiotic sensitivity of bacteria has been tested by static culture using liquid and solid media. This study was designed to analyze the antimicrobial activities of several antibiotics (ampicillin, nalidixic acid, cefsulodin and gentamicin) on gram-nagative bacteria such as Escherichia coli and Pseudomonas aeruginosa, cultured by the continuous flow system.
When a portion of medium containing 16 times the MIC of the test antibiotic was introduced to the culture vessel containing steady state bacterial cells (2×10⁷/ml), a marked decrease in the bacterial cells in the culture vessel was observed. Escherichia coli was completely eradicated or reduced to 10² to 10³ per ml by 64 times MIC of gentamicin or other drugs such as nalidixic acid, ampicillin and cefsulodin. The effect of the antibiotics in eliminating Pseudomonas aeruginosa was not as significant as with Escherichia coli when the same antibiotic concentration was added to the reservoir medium or introduced directly to the vessel.
We also determined the time required to attain the steady state of cell growth after drastic reduction of the cell density by introduction of antibiotics to the vessel as a one-compartment model of drug absorption and excretion.
Our results suggest that the inhibitory effects of antibiotics on the growth of steady state gramnegative bacteria are quite different from the effects determined by the conventional static culture. Since the dilution rate of the drug is not proportional to the dilution rate of the cells in the culture vessel, the results obtained from such experiments should be interpreted carefully. However, the information obtained might provide a basis for making a time schedule for drug administrations to patients. Thus, we believe that use of a continuous flow culture system to study the effect of antimicrobial agents in the dynamic state is meaningful and provides important information concerning the chemotherapy of bacterial infections.

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Tobramycin has a narrow therapeutic range. For proper dosage adjustment, it is necessary to have a fast, sensitive, specific and accurate assay technique for measuring serum levels of tobramycin. We examined high-performance liquid chromatography and three enzyme immunoassay methods; EMIT, substrate-labelled fluorescent immunoassay (SLFIA) and MARKIT to measure the concentration of tobramycin in clinical serum samples.
HPLC and EIA yielded values which compared favorably to bioassay in clinical serum samples (r=0.91-0.95).
MARKIT has such an advantage that it doesn't need any particular equipments. In the view of sensitivity, specificity, simplicity, we recommend EMIT and SLFIA.

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The use of cefoxitin sodium in eight patients with a variety of obstetric and gynecological infections was studied. Cefoxitin was found to be an effective agent for the treatment of infections caused by anaerobes and mixed aerobes and anaerobes. Cefoxitin was found to be a safe antibiotic without any untoward effects when given at total dosages of 16-36 g for 4-8 days. Cefoxitin will be indicated for the treatment of mixed infections caused by susceptible strains of aerobic and anaerobic bacteria, especially Bacteroides fragilis.

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A 10μg/ml of netilmicin was incubated at 37°C for 48 hours with the 200μg/ml or 500μg/ml of carbenicillin and sulbenicillin, respectively. The residual activity of netilmicin in these mixtures was measured by bioassay. Netilmicin kept its activity completely even after 24 hours of the incubation and was slightly inactivated after 48 hours. The residual activity of netilmicin after 48 hours was 72 and 71% respectively in the mixture with 200μg/ml of carbenicillin and sulbenicillin, and 58 and 52 in the mixture with 500μg/ml of each penicillin.

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The susceptibility to 11 aminoglycoside antibiotics of 196 clinical isolates of Serratia marcescens was determined and the presence of conjugative R plasmids among the resistant strains was examined. The resistant strains and R plasmids from those strains were detected most frequently in urinary specimens. The percent detection of resistant strains and R plasmids to each antibiotic were as follows.
The resistant strains to ribostamycin and butirosin A were detected at very high frequencies (80-90%), but detection rate of R plasmids was low (15-20%).
The percent detection of resistance to kanamycin A, tobramycin and dibekacin was about 50-60% and that of R plasmids was 14-17% except kanamycin A (44%). Frequency of resistant strains to gentamicin, amikacin and the other three antibiotics (lividomycin A, paromomycin, neomycin B) was moderately low (20-30%) and R plasmids transferring gentamicin resistance were detected in relatively high percentage (40%), however, it was noticed that a small number of strains (2%) carried amikacin resistant plasmids. The resistant strains to sisomicin were isolated at 42% and R plasmids were detected at 28%. It was observed that 67 strains (34%) were multiple resistant for seven or more antibiotics and R plasmids were isolated from these strains at high frequency. It was presumed from resistance pattern of R plasmids that there were many resistant strains involving aminoglycoside phosphotransferase APH (3'). However, it was impossible in many occasions to explain the mechanisms of multiple resistance by a single enzyme.

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The nephrotoxicity of netilmicin in rabbits was examined, comparing with that of gentamicin and dibekacin. In the first experiment, the rabbits were placed in individual cages, permitted free access to tap water and pellet food for rabbit. Each of three aminoglycosides was given intramuscularly to three rabbits at a dose of 100 mg/kg/day for 10 days. These three drugs did not cause marked proteinuria, he, naturia, increase in serum creatinine and proximal tubular damage in light microscopy. In the second experiment, the rabbits were given only “okara” without water. The abnormality in urinalysis, serum creatinine and proximal tubules was more remarkable in the second experiment than in the first experiment. However, the netilmicin-injected group revealed significantly less nephrotoxicity than the other groups.

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Two transductant strains, MS 353 (pTU 053) and MS 353 (pTU 068), derived from Staphylococcus aureus resistant to gentamicin and other aminoglycosides have been examined for antibiotic modifying enzymes. From the analysis of substrate profiles and inactivated products of sisomicin and amikacin, it was found that MS 353 (pTU 053) strain is containing three enzymes mediating aminoglycoside resistance, 6'-N-acetyltransferase, 3'-phosphotransferase and 2''-phosphotransferase. Also, two enzymes mediating gentamicin resistance, 6'-N-acetyltransferase and 2'-phosphotransferase, were contained in an extract from MS 353 (pTU 068) strain. The optimal pH of acetyltransferase and phosphotransferase activities for sisomicin was near pH 6. 5. The enzymatic phosphorylation of sisomicin by a partially purified enzyme solution from MS 353 (pTU 053) strain occured at a higher rate than that of amikacin.

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