Antimicrobial susceptibility testing of Haemophilus influenzae: trial organised as part of United Kingdom national external quality assessment scheme for microbiology.

Six strains of Haemophilus influenzae were distributed to 417 United Kingdom laboratories who were asked to test susceptibility of the strains to ampicillin, augmentin, tetracycline, chloramphenicol, and trimethoprim and to test for beta lactamase production. Laboratories were also asked to provide details of their methods by completing a questionnaire. The incidence of reports recording sensitive strains as resistant was 8% (ampicillin), 7% (augmentin), 3% (tetracycline), 1% (chloramphenicol), and 12% (trimethoprim). The incidence of reports recording resistant strains as sensitive was 9% (ampicillin), (2% with beta lactamase producing strains, 24% with non-beta lactamase producing strains), 51% (augmentin), 10% (tetracycline), 20% (chloramphenicol), and 3% (trimethoprim). High error rates were associated with several methods or practices. These included use of general purpose growth media rather than susceptibility testing media and failure to add lysed blood to the media when testing trimethoprim susceptibility; standardise the inoculum; use suitable control strains; and the use of high content discs for testing chloramphenicol, tetracycline, and ampicillin.

Prospective study of Clostridium difficile colonization and paracresol detection in the stools of babies on a special care unit.

Infants' stools were examined for the presence of Clostridium difficile and its cytotoxin in a study performed over a one-year period on a special care baby unit. Overall, 21% of infants were colonized, but the organism was only recovered in a seven-month period during which its weekly prevalence in the group varied from zero to 44%, with a distinct clustering of colonized infants being observed. Tests for the presence of cytotoxin in the stools and in supernatants of broth that had been inoculated with each isolate were negative. The factors predisposing to colonization were a prolonged stay in the unit, low birth weight, younger gestational age and being nursed in an incubator. The organism was recovered only once from an environmental screen. An antibiogram, used in conjunction with toxin production, was helpful in distinguishing these isolates from a collection obtained from other units in the hospital. We conclude that Cl. difficile was acquired by nosocomial spread although we did not establish the precise mechanism involved. The detection of para-cresol by gas-liquid chromatography was found to be specific but insufficiently sensitive as a screening test for the organism's presence in the stools. It could only be demonstrated in infants whose birth-weights were less than 2500 g, and no association was observed between the type of feed and para-cresol presence in stools.