Comparison of the rapid yeast plus panel with the API20C yeast system for identification of clinically significant isolates of Candida species.

The RapID Yeast Plus system (Innovative Diagnostic Systems, Norcross, Ga.) is a qualitative micromethod employing conventional tests and single-substrate chromogenic tests and having a 4-h incubation period. This system was compared with the API20C (bioMerieux Vitek, Hazelwood, Mo.) system, a 24- to 72-h carbohydrate assimilation method. One hundred thirty-three clinical yeast isolates, including 57 of Candida albicans, 26 of Candida tropicalis, 23 of Candida glabrata, and 27 of other yeasts, were tested by both methods. When discrepancies occurred, isolates were further tested by the Automated Yeast Biochemical Card (bioMerieux Vitek). Germ tube production and microscopic morphology were used as needed to definitively identify yeast isolates. The RapID Yeast Plus system correctly identified 125 yeast isolates, with an overall accuracy of 94% (125 of 133). Excellent correlation was found in the recognition of the three yeasts most commonly isolated from human sources. The test was 99% (105 of 106 isolates) accurate with C. albicans, C. tropicalis, and C. glabrata. The RapID Yeast Plus system compares favorably with the API20C system and provides a simple, accurate alternative to conventional assimilation methods for the rapid identification of the most commonly encountered isolates of Candida species.

Comparison of rapid testing methods for enzyme production with the germ tube method for presumptive identification of Candida albicans.

The observation of germ tube production as a method for the presumptive identification of Candida albicans has been in use for many years. Methods have recently been developed for detecting the production of the enzymes L-proline aminopeptidase and beta-galactosaminidase by yeast isolates grown in culture. Both enzymes are produced by C. albicans; other yeasts may produce either L-proline aminopeptidase or beta-galactosaminidase but not both enzymes. One hundred thirty-three clinical yeast isolates, including 55 C. albicans, 27 Candida tropicalis, 22 Torulopsis (Candida) glabrata, and 29 other yeast isolates were tested by the germ tube production method and three tests for enzyme production, with the API 20C method used as a "gold standard." All three enzymatic methods evaluated provided more objective and rapid nonmicroscopic alternatives to the germ tube test and may be used to accurately distinguish C. albicans from other yeasts.

Rapid antigen testing for group A Streptococcus by DNA probe.

The Gen-probe group A Streptococcus direct test (GASD), a nucleic acid probe assay for detecting GAS from throat swabs, has recently been developed. The test uses an acridium ester-labeled DNA probe which is complementary to the rRNA of Streptococcus pyogenes. In this study, 318 single culturette throat swabs were tested by this method using culture as a "gold standard." After plating onto trypticase soy agar plates with 5% sheep blood, swabs were stored at 4 degrees C for no more than 72 h before the probe assay was performed. Our patient population consisted of symptomatic outpatients seen in the Memorial Hospital Emergency Department and in the Family Care Center. After discrepancy testing, sensitivity, specificity, and positive and negative predictive values were 91.4%, 97%, 91.4%, and 97%. The GASD is a rapid, easy-to-perform method for batch screening for streptococcal pharyngitis.

Detection of group B Streptococcus by immunoassay following enrichment in LIM-selective broth medium.

Rapid immunoassays have been developed to decrease the time to detection of Group B Streptococcus (GBS) carriage in pregnant women. In this study, a total of 162 pregnant women, considered to be high-risk obstetric patients, were seen in the Family Care Center at Memorial Hospital of Rhode Island, a 300-bed teaching hospital associated with Brown University Medical School. Vaginal and rectal specimens were taken and tested for GBS by using two rapid enzyme immunoassays (EIAs) that were compared with culture. Quidel and Hybritech ICON Group B strep tests were run following 4 h incubation in the selective enrichment LIM Group B strep broth; cultures were done both directly and after enrichment. Results with both EIAs were identical, with overall sensitivity, specificity, and positive and negative predictive values of 38%, 98%, 88%, and 84% respectively. However, when women having positive cultures were separated into moderately to heavily colonized (> or = 3 +) and lightly colonized (< or = 2 +) populations, the sensitivities were 82% and 19%, respectively. Although GBS assays are useful in the rapid diagnosis of heavily colonized women, culture following enrichment remains the most sensitive method for a lightly colonized population.

Investigation of ampicillin-intermediate strains of Haemophilus influenzae by using the disk diffusion procedure and current National Committee for Clinical Laboratory Standards guidelines.

It was noted in our laboratory that certain strains of Haemophilus influenzae yielded zone sizes interpreted as resistant to the ampicillin (AMP) disk on chocolate-Mueller-Hinton agar (CMH) but showed no evidence of beta-lactamase (beta-Lac) activity. Although it is known that a second mechanism of AMP resistance exists, strains with this mechanism are uncommon. To investigate this apparent discrepancy, a study of 100 consecutive clinical isolates of H. influenzae collected over a 6-month period was performed. Isolates were simultaneously tested against five antibiotics (AMP, chloramphenicol, cefotaxime, ciprofloxacin, and AMP-sulbactam) on CMH and on two brands of Haemophilus test medium (HTM) by using the disk diffusion procedure and National Committee for Clinical Laboratory Standards (NCCLS) standards. By using CMH and NCCLS standard M2-A3-S2, strains of H. influenzae showing zone sizes of greater than or equal to 20 mm with AMP were considered sensitive. By using HTM and NCCLS standard M2-A4, strains showing zone sizes of greater than or equal to 25 mm to AMP on HTM were considered sensitive. Intermediate strains had zone sizes of 22 to 24 mm. The majority of isolates (68%) were sensitive to all antibiotics. Two percent of the isolates were resistant to chloramphenicol. Seventeen percent of the isolates were AMP-resistant, beta-Lac-producing strains of H. influenzae. Thirteen percent of the isolates gave at least one intermediate or resistant zone for AMP but were beta-Lac negative. MIC determinations with NCCLS standard M7-A2 were performed with resistant and intermediate strains. MICs for beta-Lac-producing strains of H. influenzae were >/= 8.0 microgram/ml. MICs for beta-Lac-negative strains were

The impact of converting to a biphasic blood-culture system on the overall cost and the incidence of pseudobacteremia.

After converting from a conventional broth (CB) system to a biphasic (BP) agar-slide blood-culture system (Septi-Chek), our laboratory noted an increase in positive blood cultures in general, and in coagulase-negative staphylococci (CNS) in particular. To investigate these findings, we compared all blood cultures collected over a 21-month period using CB and then BP systems, totaling 28,199 blood cultures. The frequency of positive blood cultures increased from 9.2% to 12.7% (p less than 0.0001), whereas CNS isolation increased from 2.6% to 5.2% (p less than 0.0001). There was no significant change in the incidence of true primary or secondary bacteremia due to CNS (p = 0.9). The isolation of other pathogens, including Staphylococcus aureus, Candida albicans, Bacteroides species, and Gram-negative bacilli increased from 6.5% to 7.1% (p less than 0.05). We estimated the cost of processing 28,000 blood cultures by both CB and BP systems, using positivity rates of 9.2% and 12.7%, respectively, and standards provided by the College of American Pathologists (CAP, 1991) for workload hours of technologist time. We calculated a higher overall cost for the BP system. However, the use of this system eliminated the use of needles and syringes for subculture of bottles showing no growth, thus decreasing the risk of technologist exposure to body fluids. Despite the increased cost and more frequent occurrence of pseudobacteremia, the enhanced sensitivity and increased safety of the BP system justified its use in the prompt identification of patients with true bacteremia.

False-positive reactions in the latex agglutination test for Cryptococcus neoformans antigen.

The latex agglutination test for Cryptococcus neoformans antigen is a simple and rapid procedure for the diagnosis of cryptococcal meningitis. Although the test is sensitive, care must be taken to prevent contamination of the sample, which may result in false-positive reactions. It was discovered in our laboratory that immersion of a platinum wire inoculating loop into a sample of cerebrospinal fluid prior to testing introduced interfering substances leading to nonspecific agglutination. After further studies, it was determined that trace amounts of surface condensation (syneresis fluid) from agar, either added to the cerebrospinal fluid or adhering to the loop, were the probable source of contamination. It is suggested that the latex agglutination test for C. neoformans antigen be performed prior to culture or on a separate sample.