The use of Sorbarod biofilms to study the antimicrobial susceptibility of a strain of Streptococcus pneumoniae.

and reported a correlation of only 74% when the media were incubated under aerobic conditions and 92.5% when the atmosphere was enriched with CO 2. 5,6 The MICs, as determined by the E test method, were a mean of one twofold dilution higher when the atmosphere contained CO 2 , compared with those determined in air. In contrast, we observed correlations of between 95% and 100% , regardless of the atmospheric condition. Moreover, the numbers of minor discrepancies detected by us were lower than those reported by other investigators. 6 This study has demonstrated that, when determining the MICs of-lactams by the agar dilution method, the results are not influenced by the atmospheric conditions during incubation. H owever, this conclusion cannot be extrapolated to other classes of antibiotics. (1991). Quantitative antimicrobial susceptibility testing of Haemophilus influenzae and Streptococcus pneumoniae by using Etest. (1994). Detection of penicillin and extended-spectrum cephalosporin resistance among Strepto-coccus pneumoniae clinical isolates by use of the Etest. Sir, Important variables of antimicrobial susceptibility testing, such as the MIC and MBC, are almost invariably determined with planktonic bacteria in broth culture. Bacteria within biofilms have been shown to be less susceptible to antibiotics; this has been attributed to the growth conditions and nutrient supply within the biofilms and to the presence of a glycocalyx which is impermeable to anti-microbial agents. 1,2 It has been proposed that the term 'biofilm eradicating concentration' (BE C) should be used in place of the conventional MIC and MBC in studies in which the antimicrobial susceptibilities of bacteria in biofilms are determined. 3 A drawback to the study of bacteria in biofilms has been the lack of a simple and reproducible technique. H owever, this has changed with the recent development of artificial biofilms or Sorbarods. A Sorbarod consists of a paper sleeve containing a com-pacted concertina of cellulose fibres. These simple biofilms have been used to establish continuous culture biofilms of both Staphylococcus aureus and Pseudom onas aeruginosa. 4 In the present study, the susceptibilities of a penicillin-susceptible clinical isolate of Streptococcus pneum oniae to four-lactams were determined in Sorbarod biofilms and the results compared with the MICs and MBCs determined by the traditional broth dilution method and with MICs determined by the E test method. The penicillin-susceptible strain of S. pneum oniae studied here was isolated from the sputum of a patient with community-acquired pneumonia and the antibiotics tested included benzylpenicillin …