Susceptibility of community Gram-negative urinary tract isolates to mecillinam and other oral agents.

OBJECTIVE: To determine the susceptibility of community outpatient Gram-negative urinary tract isolates to mecillinam and other commonly used oral agents. DESIGN AND SETTING: The study was a laboratory-based study of consecutive Gram-negative urinary tract isolates. Only those isolates considered to be significant pathogens were included in the study. Susceptibility testing was performed using agar dilution methodology following guidelines published by the National Committee for Clinical Laboratory Standards. POPULATION STUDIED: Outpatients presenting to a family physician or clinic with signs or symptoms suggestive of a urinary tract infection were included in the study. MAIN RESULTS: Of 2000 consecutive community isolates (91.8% Escherichia coli, 3.9% Klebsiella species, 2.0% Proteus species, 2.3% others), in vitro susceptibilities were: mecillinam 98.8%, ampicillin 77.0%, ciprofloxacin 100%, trimethoprim/sulfamethoxazole 91.6% and nitrofurantoin 95.4%. Susceptibility to mecillinam was significantly better than all other agents except ciprofloxacin (P<0.001, McNemar's test). Organisms with reduced susceptibility to mecillinam included Citrobacter species, Pseudomonas aeruginosa and Providencia species. CONCLUSIONS: Community Gram-negative urinary tract isolates remain highly sensitive to mecillinam and ciprofloxacin, but a significant number have developed resistance to trimethoprim/sulfamethoxazole. Further studies are required to determine the clinical significance of these results.

Evaluation of accuracy and reproducibility of E test for susceptibility testing of Streptococcus pneumoniae to penicillin, cefotaxime, and ceftriaxone.

We evaluated the reproducibility with which technologists perform and interpret the E test (AB Biodisk, North America, Inc., Piscataway, N.J.) for determining the susceptibility of Streptococcus pneumoniae to penicillin, cefotaxime, and ceftriaxone. Four technologists prepared E test assays to test 124 isolates of S. pneumoniae. Each technologist then interpreted the results of the E test blinded to the interpretation of the other technologists. In addition, E test results were compared with the reference method of broth microdilution. Intraobserver and interobserver agreement were assessed by use of the kappa statistic. Interpretation of the E test and broth microdilution results showed substantial to excellent agreement, with kappa values ranging from 0.878 to 0.987. Compared with broth microdilution, no very major errors and only four major errors were made with the E test. Most minor errors with penicillin and ceftriaxone occurred for isolates with intermediate or high-level resistance, whereas for cefotaxime the minor errors were more evenly distributed between susceptible and intermediate resistance and between intermediate and high-level resistance. These results indicate that there is good agreement between technologists for the interpretation of the E test when testing the susceptibility of S. pneumoniae to penicillin, cefotaxime, and ceftriaxone and that the results of the E test agree with those of broth microdilution.

Evaluation of the automated vitek immunodiagnostic assay system (VIDAS) for the detection of measles (rubeola) IgG antibodies.

BACKGROUND: The VIDAS MSG assay is a rapid, automated assay system for the detection of measles antibodies which has not yet been fully evaluated. OBJECTIVES: To compare the VIDAS MSG assay with hemagglutination inhibition (HAI) and a commercial enzyme immunoassay (EIA) for the determination of measles immune status. STUDY DESIGN: Four hundred and seventy-seven serum samples collected from hospital employees for pre-employment screening were tested for measles antibodies using the VIDAS MSG assay and the results compared with those obtained by HAI and EIA. Intra-and inter-assay precision runs of the VIDAS instrument were evaluated using the positive standard provided by the manufacturer. RESULTS: The sensitivity of the VIDAS assay compared to HAI and EIA was 96.4% and 96.7%, respectively. The specificity of the VIDAS assay, when grouping equivocal with negative results was 77.6% and 100% compared to HAI and EIA respectively. The co-efficient of variation for both precision runs was less than 10%, indicating good reproducibility. CONCLUSIONS: The VIDAS MSG assay system is rapid and less labour intensive than HAI and manual EIA for the detection of measles antibody. The significance of equivocal results is not known, but may represent low, non-protective antibody levels. Testing of equivocal samples using another test may provide a definitive (positive or negative) result, but the degree of protection afforded by a positive result is not known. Alternatively, equivocals may be grouped with negatives for exposure or vaccination purposes. This may result in overuse of vaccine if the VIDAS MSG assay is used to determine immune status in screening programs such as pre-employment of hospital staff.

Use of the polymerase chain reaction for the detection of Chlamydia trachomatis from endocervical and urine specimens in an asymptomatic low-prevalence population of women.

The Amplicor Chlamydia trachomatis test is a polymerase chain reaction (PCR)-based methodology used for the detection of a cryptic plasmid found in C. trachomatis. It was evaluated in comparison with cell culture and the Microtrak II Chlamydia enzyme immunoassay (EIA) for the detection of C. trachomatis in urogenital specimens from women. Endocervical swabs were collected from 993 women attending the women's unit at the Mount Sinai Hospital in Toronto. In addition, concomitant first void urine specimens were collected from 394 of these women for PCR testing only. As compared with culture of the endocervical specimens, PCR and EIA had a sensitivity, specificity, positive predictive value and negative predictive value of 84.6%, 99.2%, 57.9%, and 99.8% and 61.5%, 99.7%, 72.7%, and 99.5%, respectively. As compared with the secondary gold standard of a positive culture and/or a positive PCR using a primer to the major outer membrane protein the sensitivity, specificity, positive, and negative predictive values for culture were 72.2%, 100%, 100%, and 99.5%, respectively. For the Amplicor PCR and EIA the results were 88.9%, 99.7%, 84.2%, and 99.9% and 61.1%, 99.9%, 91.7%, and 99.6%, respectively. When the urine PCR was compared with the same standard, the test had a sensitivity of 91.7% and a specificity of 99.5%. Based on this study the Amplicor C. trachomatis test was found to be sensitive and specific for the detection of C. trachomatis in both endocervical and urine specimens.

Community-acquired pneumonia: the future of the microbiology laboratory: focused diagnosis or syndromic management?

The traditional classification of community-acquired pneumonia into typical and atypical pneumonia to facilitate successful empirical treatment is no longer optimal. An accurate prediction of cause and adequate empirical therapy cannot be provided with this approach in severely ill patients. There is an increasing spectrum of recognized treatable pathogens presenting as community-acquired pneumonia including Legionella species, Chlamydia pneumoniae, and Pneumocystis carinii in addition to the traditional community pathogens. The variability of presentation in severely ill or compromised hosts makes clinical prediction of cause inadequate. A more rational approach may involve the classification of patients by the severity of illness and underlying disease with little or no microbiological workup in mild illness unless the results will contribute to the epidemiological surveillance of resistance because these investigations have not been shown to affect outcome in this setting. Etiologic diagnosis should be more aggressively sought and the microbiology laboratory can be best used by providing the efficient and rapid diagnosis of this expanded range of pathogens in more severely ill patients. The mounting antimicrobial resistance of common pathogens such as Streptococcus pneumoniae, Haemophilus influenzae, and Staphylococcus aureus will require not only a critical review of empirical therapy, but an increased emphasis on epidemiological monitoring of resistance by laboratories and effective communication with clinicians.

Evaluation of three methods for the rapid identification of Staphylococcus aureus in blood cultures.

A total of 445 blood cultures containing Gram-positive cocci in clusters were tested for the presence of Staphylococcus aureus with the Accuprobe, heat-stable thermonuclease, and latex agglutination using Staphaurex. The results show that the Accuprobe, thermonuclease, and Staphaurex correctly identified 95, 96, and 62 of the 100 specimens containing S. aureus. The corresponding specificity for the methods was 99.1%, 100%, and 98.5%, respectively.

Utilization review of the use of BACTEC PLUS high-volume blood culture bottles.

The BACTEC PLUS 26 (NR26) (Becton Dickinson, Towson, Md.) high-volume blood culture bottle replaced the less expensive smaller-volume NR6A bottle in our hospital. An audit carried out several months after their introduction revealed that only 17.5% of the NR26 bottles received the required blood volume. Several audits and educational programs were required in order to achieve a compliance rate of > 60%.

Rapid detection of infectious mononucleosis-associated heterophile antibodies by a novel immunochromatographic assay and a latex agglutination test.

A novel immunochromatographic assay, the CARDS O.S. MONO test (Pacific Biotech, San Diego, Calif.), and a latex agglutination test, the Infectious Mononucleosis Kit (Unipath Ltd., Hampshire, United Kingdom) were compared with the Paul-Bunnell-Davidsohn test. Of the 957 serum specimens studied, 78 were positive and 879 were negative by the Paul-Bunnell-Davidsohn test. After discrepancies were resolved by determining Epstein-Barr virus serology, the sensitivities of the CARDS O.S. MONO test and the Infectious Mononucleosis Kit were 91.0 and 96.2%, respectively, and both tests had a specificity and a positive predictive value of 100% and a negative predictive value and overall agreement of greater than 99%. The results show that both tests can accurately detect infectious mononucleosis-associated heterophile antibodies.

Evaluation of commercial and standard methodology for determination of oxacillin susceptibility in Staphylococcus aureus.

Agar dilution with and without 4% NaCl, broth microdilution with 2% NaCl, the dried MicroScan Rapid Positive MIC 1 panel (Baxter Health Care Corp., West Sacramento, Calif.), the Vitek GPS-SA card (Vitek Systems, Hazelwood, Mo.), and the oxacillin agar screen plate were compared with a DNA probe encoding the mec gene for their abilities to detect oxacillin resistance in 506 clinical isolates of Staphylococcus aureus. The results of testing for the mec gene showed that there were 254 oxacillin-resistant and 252 oxacillin-susceptible isolates of S. aureus. There were 14.2% very major errors with Vitek (a resistant isolate was interpreted as susceptible) and 6.7% very major errors with MicroScan. Fewer major errors were seen: 0.8% with MicroScan (a susceptible isolate was interpreted as resistant) and 0.4% with Vitek. No very major errors but 2.4% major errors occurred by agar dilution with 4% NaCl supplementation, whereas there were 0.8% very major and 0.4% major errors without 4% NaCl supplementation. By broth microdilution there were 2.0% very major and 0.8% major errors. The results of the oxacillin agar screen plate method were 100% concordant with those of the mec gene probe method.

Comparative evaluation of seven commercial tests for detection of heterophile antibody in infectious mononucleosis.

Detection of heterophile antibodies in infectious mononucleosis is the most rapid and cost-effective method for confirming the clinical diagnosis of the disease. This study compared seven commercial test kits (the Oxoid Infectious Mononucleosis Kit [Oxoid Ltd], Immunoscan Im-Latex [Baxter Travenol], Mono-Latex [Wampole Laboratories], Monospot and Im Screen Test [Ortho Diagnostics], Immunoscan Im-RBC Test [Baxter Travenol], and Infectious Mononucleosis Test [NCS Diagnostics]) to the Davidsohn differential test. All of the kits were shown to be acceptable for use, with specificities and sensitivities greater than 96.5% and 95.5%, respectively.

Comparison of the Clearview Chlamydia test, Chlamydiazyme, and cell culture for detection of Chlamydia trachomatis in women with a low prevalence of infection.

Two antigen detection systems, Clearview Chlamydia (Unipath Ltd., Bedford, United Kingdom) and Chlamydiazyme (Abbott Laboratories, North Chicago, Ill.), were compared with culture for the diagnosis of chlamydia infection in women attending gynecological clinics. Chlamydia trachomatis was isolated from 43 (4.5%) of the 965 women tested. In comparison with tissue culture, the Clearview Chlamydia and Chlamydiazyme tests had sensitivities of 79.0 and 74.4%, respectively, and both had a specificity of 99.6%. The results show that the Clearview Chlamydia test is comparable to Chlamydiazyme for the detection of C. trachomatis from endocervical specimens in a population with a low prevalence of infection.

Evaluation of five commercial systems for identification of coagulase-negative staphylococci to species level.

Five commercially available systems for identification of coagulase-negative staphylococci to the species level were evaluated using 163 clinical staphylococcal isolates. The conventional method of Kloos and Schleifer served as reference method. The API20GP system showed the highest rate of agreement with the reference method, correctly identifying 98.8% of the isolates. The Microscan system had an overall rate of agreement of 96.3%, and Staph-Trac, Sceptor and Staph-Ident rates of 88.8%, 87.6% and 84.% respectively.

Problems with rapid agglutination methods for identification of Staphylococcus aureus when Staphylococcus saprophyticus is being tested.

Six rapid agglutination tests for identification of Staphylococcus aureus were evaluated by using 62 strains of S. aureus, 63 strains of S. saprophyticus, and 67 strains of other coagulase-negative staphylococci. S. saprophyticus was responsible for 19 of 26 false-positive results and 20 uninterpretable reactions. Thus, urinary staphylococcal isolates that are positive by rapid agglutination tests may require other confirmatory tests for the identification of possible S. saprophyticus.

In-vitro activity of enoxacin against aminoglycoside-resistant gram-negative bacilli and other clinical isolates.

The in-vitro activity of enoxacin was tested against 500 clinical isolates of Gram-negative bacilli that were resistant to one or more of gentamicin, tobramycin and amikacin, and against 1060 recent consecutive clinical isolates of Gram-negative bacilli and Gram-positive cocci. Enoxacin was active against staphylococci (MICs less than or equal to 4 mg/l) but less active against Streptococcus faecalis (MICs mostly 8 mg/l). It was active against Pseudomonas aeruginosa (MICs 0.5-4 mg/l) and very active against Enterobacteriaceae. In the series of consecutive isolates 97% of Enterobacteriaceae had MICs less than or equal to 1 mg/l. The aminoglycoside-resistant series of Enterobacteriaceae included more strains with higher MICs (13% were 2-4 mg/l and 10% were greater than or equal to 8 mg/l); the majority of the isolates with MICs greater than or equal to 8 mg/l); the majority of the isolates with MICs greater than or equal to 8 mg/l were Serratia marcescens and Providencia spp. Among the non-fermenting species the least sensitive were Acinetobacter calcoaceticus and Ps. maltophilia. Enoxacin-resistant strains of Enterobacteriaceae were resistant to nalidixic acid, but nalidixic acid-resistant strains ranged from fully sensitive to highly resistant to enoxacin.