A survey of susceptibility testing of anaerobes in the United Kingdom

and 27% said that they never identified anaerobes. As for susceptibility testing, six of the laboratories said that they never undertook testing. Twenty-six per cent of laboratories tested metronidazole on the primary isolation plate and, unless there was a pure culture of the organism from a site of interest, e.g. blood culture or sterile site, or if the organism appeared resistant, then no further investigation was carried out. Where testing was undertaken, the most commonly used media were Iso-Sensitest agar supplemented with 5% horse blood (ISA; 48%) and fastidious anaerobe agar (FAA; 21%). Only 5% of laboratories used media specially designed for testing anaerobic organisms (Wilkins & Chalgren agar). Ninety-nine per cent of laboratories used a disc testing method and 15% used a combination of disc testing and a gradient method of determining an MIC (Etest). The antibiotics most often tested, other than metronidazole, were penicillin (91%), clindamycin (48%), erythromycin and co-amoxiclav (both 44%). Fourteen per cent and 3% of responding laboratories said that they tested carbapenems (usually imipenem) and piperacillin/tazobactam, respectively. It is clear from these data that the susceptibility testing of anaerobes is limited to isolates from sites of special interest. Although rare, resistance in Bacteroides fragilis to carba- penems 2 and metronidazole has been observed. 3 If, in the future, resistance to these agents increases, routine testing may be necessary. Given that the majority of laboratories answering this questionnaire used either ISA or FAA, the BSAC is taking a pragmatic approach by undertaking a study to see how reliable these media are when testing fast-growing anaerobes. Further advice will be given when the results are analysed.