Effect of carbon dioxide on in vitro susceptibility of anaerobic bacteria to erythromycin

Abstract

The activity of erythromycin against 317 strains of anaerobic bacteria, including 133 strains of the Bacteroides fragilis group, was tested by the agar dilution method in an anaerobic atmosphere with two different concentrations of carbon dioxide and without C02. The effect of the atmosphere of incubation on the agar surface pH was also determined. All strains grew well in the GasPak (GP) environment. However, 3.5 and 30.3% of strains failed to grow in the 2 and 0% C02 environments, respectively. The quality of growth was best in the GP environment and poorest in the 0% C02 environment. Minimal inhibitory concentrations in the GP and 2% C02 environments were frequently the same or one dilution lower in the 0% than in the GP environment. In the 0% C02 atmosphere, minimal inhibitory concentrations were usually two to three dilutions lower than in the GP environment. Consequently, only 24% of B. fragilis strains were susceptible to erythromycin in the GP environment, whereas 77% were susceptible in the 0% C02 environment. For Fusobacterium species, 12% were susceptible to erythromycin in the GP environment, and 73% were susceptible in the 0% C02 environment. There was a comparable decrease in pH in all three atmospheres tested. In vitro susceptibility testing of erythromycin against anaerobic bacteria should be performed in an atmosphere containing carbon dioxide.Numerous variables affect the results of susceptibility testing of anaerobic bacteria. Differences due to such factors as the pH of the medium and the presence and amount of C02 in the atmosphere of incubation remain to be fully defined. Data from several laboratories show considerable variation in the susceptibility of anaerobic bacteria to erythromycin (1,5,6,16,17 MATERIALS AND METHODSThe activity of erythromycin was tested against 317 strains of anaerobic bacteria, including 133 RESULTSSusceptibility tests. The effect of atmospheric carbon dioxide on the susceptibility of anaerobic strains tested by the agar dilution method is shown in Table 1. Whereas all anaerobes grew well in the GP jar environment, some strains (3.5%) failed to grow in the 2% C02 environment, and many strains (30.3%) failed to grow in the 0% C02 environment. The quality and quantity of growth of B. fragilis and most other anaerobic bacteria were best in the GP environment. Growth was somewhat less in the 2% C02 environment, but was distinctly less in the 0% C02 environment on both control and

Activities of HMR 3004 (RU 64004) and HMR 3647 (RU 66647) Compared to Those of Erythromycin, Azithromycin, Clarithromycin, Roxithromycin, and Eight Other Antimicrobial Agents against Unusual Aerobic and Anaerobic Human and Animal Bite Pathogens Isolated from Skin and Soft Tissue Infections in Humans

“…This difference might be accounted for by the different sources of our isolates, or it might be due to their use of Oxyrase added to the test medium for macrolides and consequent incubation in an aerobic rather than a CO 2 -containing anaerobic environment. It has been shown that the CO 2 in the atmosphere of incubation can variably effect the in vitro activity of some macrolides against the isolates tested due to a pH effect (7)(8)(9). However, in their second study (5), they tested nine strains of F. nucleatum (it is unclear if these fusobacteria were the same as those used in the first study, as they noted that 60% of all isolates were new strains but did not further specify changes).…”

Activity of the investigational fluoroquinolone finafloxacin and seven other antimicrobial agents against 114 obligately anaerobic bacteria

“…As described for agar dilution tests, increased acidity of the culture medium was defined as a cause for the deviating results, especially in the case of erythromycin. Still, an environment with 5% CO 2 is recommended for testing of anaerobic bacteria in order to ensure adequate growth as a basic requirement for susceptibility testing of anaerobes [29,30].…”

Comparative In Vitro Activities of Amoxicillin-Clavulanate against Aerobic and Anaerobic Bacteria Isolated from Antral Puncture Specimens from Patients with Sinusitis

“…than clarithromycin against anaerobes but still had poor activity against 27% of fusobacteria, 29% of P. magnus (for 33 of 35, the MICs were Ն2 g/ml), and 64% of Veillonella species isolates. The effect of CO 2 in the atmosphere of incubation has been shown to decrease the activity of macrolides against anaerobes but the clinical relevance has not been determined (6,7). Levofloxacin also had reasonably good activity with the exception of some peptostreptococci.…”