Increased stool sampling during a waterborne outbreak of cryptosporidiosis does not increase the detection of other faecal pathogens.

AIMS: To ascertain the effect of enhanced surveillance following an outbreak of waterborne cryptosporidiosis on the number of faecal specimens submitted to the local microbiology laboratory and the number positive for common enteric pathogens. The outbreak provided an opportunity to estimate the extent of routine under ascertainment of common enteric pathogens. METHOD: Retrospective search of the computerised microbiology system database for details of faecal examination requests for the period 26 April to 6 June in 1998 and 1999 (period of outbreak). RESULTS: Specimens were received from 378 community patients during the six week period 26 April to 6 June 1999. This was double that for the same period in 1998 (a non-outbreak year). Oocysts of Cryptosporidium parvum were detected in 59 patients, an eightfold increase compared with the same period in 1998. Despite the greater number of patients tested, the detection of other pathogens in patients with gastroenteritis was not altered when compared with the same period in the previous year. CONCLUSION: This study found no evidence of under ascertainment of gastrointestinal infection (common bacterial pathogens and rotavirus) by local general practitioners.

High incidence of antifungal drug resistance in Candida tropicalis.

Drug resistance among yeasts is an increasing problem. Isolates of Candida krusei and Candida glabrata are recognized as having reduced susceptibility to fluconazole and resistance to this drug has also arisen in Candida albicans isolated from AIDS patients on long term azole therapy. Candida tropicalis (CT) is being increasingly isolated from human disease and is associated with invasive infection, however, data regarding this organism's drug susceptibility is limited. We report our findings on 60 isolates of CT isolated from patients with serious infection in the North West of England. Over 60% of isolates were from adult Intensive Care Unit (ICU) patients, and almost half were from the respiratory tract. Susceptibility to fluconazole, flucytosine, itraconazole and ketoconazole were tested by standardised methods - 48% of the isolates were resistant to fluconazole (MIC > 12.5 mg/l), and 10% had intermediate susceptibility (MIC 6.25-12.5 mg/l). For flucytosine 17% of isolates were resistant (MIC > 8 mg/l) and 22% had intermediate susceptibility (MIC 2-8 mg/l). Three isolates were resistant to both drugs. For itraconazole 17% of isolates were resistant (MIC > 1 mg/l), and 12% showed intermediate susceptibility (MIC 0.5-1 mg/l). Resistance to ketoconazole was seen in 33% of isolates (MIC > 1 mg/l) and 10% showed intermediate susceptibility (MIC 0.5-1 mg/l). Differences in the degree of cross resistance between the azole drugs was observed. Candida tropicalis should be added to the list of yeasts in which drug resistance is commonly found. Given the high invasiveness of Candida tropicalis, its affinity for patients on ICU and the high incidence of drug resistance in this species, identification and susceptibility tests should be performed on all yeast isolates from patients on ICU.

High prevalence of antifungal resistance in Candida spp. from patients with AIDS.

Three hundred and forty-eight isolates of Candida spp. from patients treated at a regional infectious diseases unit for AIDS, immunocompromised patients admitted to the Hope Hospital and isolates referred from around the North West of England were tested for their in-vitro susceptibility to amphotericin B, fluconazole and flucytosine using standardized methods. Candida albicans comprised 73% of isolates, Candida glabrata 10% and Candida parapsilosis 7%. Ninety-six percent of isolates were susceptible to amphotericin B and resistance to > or = 12.5 mg/L fluconazole was found in 61 (17.5%) of the 348 isolates tested. Among isolates from patients with AIDS the incidence of fluconazole resistance was 33% whereas in other patients the incidence was only 11%. Flucytosine resistance was seen in only 12 (3.4%) isolates, 11 of which were C. albicans and in 6.5% of isolates from patients with AIDS. Resistance to fluconazole and flucytosine is now sufficiently prevalent among Candida spp. isolated from patients with AIDS to warrant routine susceptibility testing of yeast isolates.

Meningitis due to penicillin resistant Streptococcus pneumoniae occurring in a patient on long term ampicillin prophylaxis.

A patient with persistent dural fistula, CSF rhinorrhoea and a history of recurrent bacterial meningitis developed meningitis with a penicillin-resistant strain of Streptococcus pneumoniae while on prophylactic ampicillin. The microbiological aspects of management are discussed.

The influence of salt concentration on the detection of methicillin resistance in coagulase-negative staphylococci.

The detection of methicillin resistance by the breakpoint method was examined using three different media containing varying quantities of added salt and 4 mg/L methicillin or 1 mg/L oxacillin. Three hundred clinical isolates of eight species of coagulase-negative staphylococci were tested. In 68 strains methicillin resistance was expressed only at certain salt concentrations and four distinct susceptibility phenotypes were observed. A correlation between the susceptibility phenotype and the species of the isolate was found. Testing on Columbia agar (CA) containing 4 mg/L methicillin with 0% and 4% added salt was required to detect resistance in all 68 strains. Resistance was detected less frequently using Balanced Sensitivity Test (BST) agar or Diagnostic Sensitivity Test (DST) agar containing methicillin or CA, BST or DST agar containing oxacillin. Increased production of beta-lactamase was shown to be an unlikely cause of MR in these strains. Disc sensitivity tests were performed on the 68 strains using five different media. Columbia agar gave optimum results as the other media gave enhanced zones of inhibition for some isolates. Further tests were performed on CA containing varying salt concentrations using both oxacillin and methicillin discs. A close relationship between the staphylococcal species, and the influence of increasing salt concentration on zone size was found. Discrepancies were noted between results obtained by breakpoint and the results obtained with methicillin discs particularly with Staphylococcus simulans and some Staphylococcus epidermidis strains. Results obtained with oxacillin discs more closely correlated with those obtained by breakpoint, but only when disc tests were performed on media with low and high salt content. To identify methicillin resistance in strains of CNS by disc tests, the use of Columbia agar with 0% and 5% added salt and oxacillin discs is recommended.

Evaluation of Mast-ID 15 system for identification of fresh clinical isolates of Enterobacteriaceae and Acinetobacter.

AIMS: To assess the accuracy of the Mast-ID 15 system compared with API 20 E for the identification of stock and fresh clinical strains of Enterobacteriaceae and Acinetobacter spp; to compare the accuracy of 19 pin and 36 pin multipoint inoculator heads. METHODS: One hundred frozen stock cultures of Enterobacteriaceae and Acinetobacter spp which had previously been identified by the API 20E were classified by the Mast-ID using 19 and 36 pin multipoint inoculator heads. Reproducibility was determined by testing 36 randomly selected organisms in duplicate. Four hundred and sixty nine consecutive fresh clinical isolates of Enterobacteriaceae and Acinetobacter spp were identified by the Mast-ID using a 36 pin multipoint inoculator and by the API 20E. Reproducibility for the fresh isolates was determined by testing 96 randomly selected strains in duplicate. RESULTS: The Mast-ID 15 identified 82% and 85% of frozen strains to species level and reproducibility was 80% and 86% using 19 and 36 pin inoculator heads, respectively. Of the 469 fresh clinical isolates, the Mast-ID identified 70% of strains to species level; 19% were not identified and 11% were identified incorrectly by comparison with the API 20E. The Mast-ID achieved a reproducibility level of 80% with the fresh clinical isolates. CONCLUSIONS: The use of a 36 pin multipoint inoculator head in preference to the standard 19 pin head for the Mast-ID was advantageous as it allowed greater numbers of strains to be identified at a reduced cost. Unfortunately, in our hands, the Mast-ID system was insufficiently accurate for routine use in the clinical laboratory. Modifications to some of the problematic tests may result in a sufficient increase in accuracy and reproducibility to make the system beneficial in the routine clinical laboratory.

Evaluation of the RAPID ID 32A system for the identification of Bacteroides fragilis and related organisms.

This study evaluated the ability of a rapid identification system for anaerobic bacteria, ATB 32A, now renamed RAPID ID 32A (API-bioMérieux UK Ltd., Basingstoke), to identify accurately 74 strains of the 'B. fragilis group'. ATB 32A identified correctly 78.4% of strains to species level, without supplemental tests. The percentage of strains identified to species level rose to 94.6% when a supplementary test (advised by bioMérieux) for catalase production was used to differentiate between Bacteroides ovatus and Bacteroides uniformis. RAPID ID 32A is a rapid, accurate method for the identification of members of the 'B. fragilis group' isolated within a routine clinical laboratory.

Improved detection of Candida albicans in a blood-culture model.

Human blood reduced the numbers of colony-forming units (cfu) of Candida albicans in a blood-culture model so that the detection time was increased by 12 h. Reduction in cfu was accompanied not by reduction in cell mass but by observable clumping of cultures, which was attributable to a heat-stable serum component. The action of the latter component could be negated if the medium were supplemented by a combination of trypsin, 2-phenyl ethanol, liquoid and Tween 80, when a statistically significant improvement was noted in minimum detection time for C. albicans growing in blood-culture medium.

Comparison of three-compartment Petri dishes and individual plates for routine culture of vaginal swabs.

Recovery of aerobes and facultative anaerobes from 200 consecutive randomly selected high vaginal swabs was evaluated using three-compartment Petri dishes containing Sabouraud, dextrose agar, GC selective agar, and chocolate agar. The method was compared with the traditional method using individual Petri dishes. The two methods produced comparable results both in terms and quantities of organisms recovered from the specimens. As three-compartment Petri dishes use less agar, save time in culturing specimens, yet still maintain the same standard of culture, they provide a more economical alternative to the traditional method for routine culture of vaginal swabs.

The improved recovery of Candida albicans from fluid culture media.

This study compares the mean generation time (MGT) and lag period of the growth of Candida albicans in four blood culture media, under a variety of conditions of incubation. The media compared were Bactec 6B, brain-heart infusion, malt extract broth and Sabourauds liquid medium. All four media were incubated under the eight possible permutations of the following conditions: 37 degrees C or 30 degrees C, vented or unvented, unshaken or constantly shaken. Then, using the incubation conditions found to be most favourable, minimum detection times for C. albicans were compared in the four media. The combination of incubation of the cultures at 37 degrees C, venting and constant-shaking, produced the fastest generation time with the minimum lag period. Of the media, Bactec 6B medium had the shortest lag period under these conditions while brain-heart infusion had the lowest MGT overall. Sabourauds liquid medium, which resulted in the most favourable combination of generation time and lag period, proved superior to the other media for the recovery of C. albicans.

Netilmicin in gram-negative sepsis: comparative abilities of a dosage nomogram and clinical microbiologists to predict the preferred individual dose.

The preferred dose of netilmicin was determined in each of 39 patients with severe gram-negative sepsis treated at two centres. The dose was based upon the attainment of recommended serum concentrations. Patient age varied from 18 to 87 years (mean 58), estimated creatinine clearance from 20 to 150 ml/min (mean 71), and the preferred dose from 100 to 750 mg/24 h. The dose generated by a nomogram for netilmicin was compared in retrospect with the initial dose assigned to each patient by the clinical microbiologist concerned. With respect to the preferred dose, the nomogram underdosed, on the average, by 40 mg/24 h, and the microbiologists, by 30 mg/24 h. The correlation with the preferred dose was stronger for the nomogram dose (r = 0.66; p less than 0.001, 37 df) than for the microbiologists' dose (r = 0.47; p less than 0.005, 37 df) but there was no significant difference between the two in the frequency with which they predicted the preferred dose to within 50 mg/24 h (nomogram 19/39; microbiologists 16/39). The prescription of a fixed dose of 450 mg/day to all patients would have had a similar success rate (15/39). The performance of the nomogram was better in patients with serum creatinine concentrations of greater than or equal to 100 microM (r = 0.82; p less than 0.001, 13 df; 10/15 within 50 mg/24 h of preferred dose) than in those with creatinine concentrations less than 100 microM (r = 0.55; p less than 0.01, 22 df; 9/24 within 50 mg/24 h of preferred dose).

More rapid identification of bacteraemia by manual rather than radiometric method.

Results of blood culture examination using the radiometric (Bactec-460) system for one year showed no overall improvement compared with those of the previous three years when a manual system with early blind subculture was used. The isolates from the manual system were available more often on solid media, 24 hours earlier, than when the radiometric system was used. In a further study of 1100 blood cultures the radiometric medium was tested for growth index as well as being subcultured blindly, irrespective of growth index, on the first day. Thirty six out of 54 (67%) of the blood cultures were positive on subculture but negative for growth index at this time. The overall cost of the radiometric system is also considerably more than that of the manual system.