STUDIES ON IN VITRO SUSCEPTIBILITY OF VARIOUS ANAEROBIC BACTERIA AND ANTIMICROBIAL RESISTANCE OF ANAEROBES

Abstract

The rate of isolation of anaerobic bacteria from various clinical specimens became more and more significant in recent years, and anaerobic bacteria, especially Bacteroides play an important role in the opportunistic infections or polymicrobial infections. The purpose of this paper is to study1) the annual changes of the incidence of anaerobes from clinical sources, 2) the antimicrobial susceptibility of the recent isolates of various anaerobic bacteria, 3) the changes in incidence of the drug-resistant strains, and4) the, β-lactamase activity from Bacteroides species to clear the reason, for the prevalence of drug-resistant strains of Bacteroides.
1) The annual changes of the incidence of anaerobic bacteria in Juntendo University Hospital for the past 16 years (from 1965 to 1980) shoW that there has been a gradual increase in the incidence of nonsporulating Gram-negative rods including Bacteroides species, and nonsporulating Gram-positive rods (Propionibacterium, Lactobacillus, and Eubacterium). With selected types of specimens, a much higher incidence of recovery of anaerobes had been obtained from the intraabdominal and the obstetrical and gynecological infections.I also summarized the clinical background of 10 cases ofanaerobic bacteremia for the past 2 years.In 7 cases, B. fragilis was isolated as a single culture, or as one of the mixed cultures. The major focus of the infections seemed to be abdomen with previous surgery, and most important prognostic factors appeared to be the underlying diseases, surgery, or previous use of antibiotics.
2) Approximately 440 strains of anaerobic organisms, isolated from clinical specimens during January 1979 and April 1981, were selected to test the antimicrobial susceptibility to 20 antimicrobials. The minimal inhibitory concentrations (MIC) were obtained by an agar plate dilution methods, proposed by the Japanese Society of Chemotherapy.
the Japanese Society of Chemotherapy. Benzylpenicillin and ampicillin were susceptible in vitro, but many or most strains of B.fragilis were resistant to these 2 agents.Other penicillins were not always as active as benzylpenicillin and ampicillin. Cephalosporins were also quite active against many anaerobes, but most had relatively poor activity against Bacteroides.Ceftizoxime was demonstrated to be more active against B.fragilis than the other β-lactam antibiotics. Many anaerobes are now resistant to tetracycline, however, doxycycline and minocycline were more active than tetracycline. Chlorarnphenicol and thiamphenicol had excellent in vitro activity against all anaerobes. Clindamycin was represented distinctly more active than erythromycin and lincomycin, and had the greatest activity against anaerobes in all drugs. But, clindamycin-resistant strains have increased in Bacteroides species.Metronidazole also had excellent against anaerobes except for a certain Gram-positive organisms (Propionibacterium and Lactobacillus).
3) I determined the MIC ‘break point’ between susceptible and resistant strains, by the distribution of MIC for 16 years of observation.And under the criteria for resistance, the changes in incidence of resistant strains of Peptococcus, Peptostreptococcus and Bacteroides were observed.
Against Peptococcus and Peptostreptococcus, a marked increase of resistant strains was recognized in tetracycline during these periods.No resistant strains were recognized to the other drugs against Peptococcus.Against the Peptostreptococcus strains, however, slight or moderate increase in resistant strains was observed in benzylpenicillin, ampicillin and erythromycin.For the Bacteroides species, remarkable changes in resistant strains were observed in almost antimicrobials.