Polyamine depletion and growth inhibition in Candida albicans and Candida tropicalis by alpha-difluoromethylornithine and cyclohexylamine

The ability of two known inhibitors of polyamine synthesis, alpha-difluoromethylornithine (DFMO), an inhibitor of ornithine decarboxylase (ODC), and cyclohexylamine, an inhibitor of spermidine synthase, to inhibit the in vitro growth and polyamine synthesis of clinical isolates of Candida tropicalis and Candida albicans was examined. Treatment of C. tropicalis and C. albicans with either DFMO or cyclohexylamine resulted in depletion of cellular polyamines and inhibition of growth. The growth inhibition produced by each of these compounds was completely reversed by exogenous polyamines. Depletion of polyamines by low concentrations of DFMO significantly enhanced the growth inhibitory activity of cyclohexylamine versus C. albicans. DFMO inhibited ODC activity in both C. albicans and C. tropicalis. These findings document the ability of cyclohexylamine and DFMO to inhibit polyamine synthesis and growth in clinically important species of Candida.

Evaluation of laboratory methods for the classification of oxacillin-resistant and oxacillin-susceptible Staphylococcus aureus

The purpose of this study was to examine the efficacy of the oxacillin disk diffusion test and the methicillin and oxacillin agar screen tests as predictors of oxacillin resistance as defined by the reference broth microdilution method. A total of 444 clinical isolates of Staphylococcus aureus collected from individual patients over a four-year period were tested by (1) the oxacillin disk diffusion test, with particular attention to the presence of fine growth of a resistant subpopulation within the zone of inhibition (Ox Grow interpretive criteria); (2) the agar screen method using agar plates with 4% NaCl and either 6 mg/L oxacillin or 10 mg/L methicillin; and (3) the oxacillin and methicillin broth microdilution test methods with 2% NaCl supplementation. Overall, 62 (14%) isolates were resistant and 382 (86%) isolates were susceptible to oxacillin with the use of the reference broth microdilution system. The results indicate that the disk diffusion test with the use of the Ox Grow criteria had a high sensitivity (94%) and negative predictive value (98%) but a low specificity (67%) and positive predictive value (32%) when compared with the reference broth dilution test. Similarly, the agar screen tests had a high sensitivity (95-97%) and negative predictive values (99%) but low specificity (64-74%) and positive predictive values (30-37%). These data indicate that the agar screen tests and the oxacillin disk test with the use of the Ox Grow interpretive criteria may be useful as screening tests for detecting resistance to the penicillinase-resistant penicillins but that all resistant isolates should be confirmed by the reference broth dilution method because of the large number of false-resistant screening test results.

The use of the Prompt Inoculation System in preparing a standardized yeast inoculum

One of the most important steps in performing broth dilution susceptibility testing of yeast isolates is the preparation of the starting inoculum. Although not specifically developed for yeast inoculum preparation, the Prompt Inoculation System (3M) provides a novel alternative approach that may provide a more standardized yeast inoculum than previously employed methods. The authors examined the relationship between the number of colonies picked with the Prompt Inoculation Wand and the hemacytometer and viable colony counts for each of six test organisms, including Candida albicans, Candida tropicalis, Candida krusei, Candida parapsilosis, Candida glabrata, and Cryptococcus neoformans. They found that by picking five colonies 1-2 mm in diameter, inoculum densities of 1 to 5 X 10(6) CFU/mL were obtained with most of the test organisms. A considerably higher inoculum density was observed with C. glabrata (1 to 2 X 10(7) CFU/mL) because of the small size of this organism. No overfilling of the Inoculation Wand was observed when more colonies were touched. This study indicates that the Prompt Inoculation System offers a convenient and simple method for yeast inoculum preparation.

Variation from standards in Staphylococcus aureus susceptibility testing

In an effort to assess the degree of methodologic variation and adherence to current guidelines for detection of methicillin-resistant Staphylococcus aureus (MRSA), the authors surveyed the susceptibility testing practices of all 162 microbiology laboratories in the Veterans Administration (VA) system. Completed questionnaires were returned by 136 (84%) of the laboratories. Overall, 96 (71%) laboratories used disk diffusion testing, 54 (40%) used manual broth dilution, and 36 (26%) used an automated method. The percentage of MRSA detected ranged from 0 to 52%, with a mean of 10%. In general, fewer than 60% of laboratories followed the current susceptibility testing guidelines for key methodologic variables such as inoculum preparation, duration of incubation, and medium supplementation. Failure to adhere to these guidelines may result in suboptimal detection of MRSA.

Use of the appropriateness evaluation protocol for estimating the incremental costs associated with nosocomial infections

Existing methods for estimating additional days of hospital stay due to nosocomial infections (NI) have a number of documented limitations. An alternative method described in this paper uses the Appropriateness Evaluation Protocol (AEP) to determine whether each day of acute inpatient care is appropriate based on the need for care of the NI, original cause of hospitalization (OC), or combined NI-OC requirements. Using this method to identify specific days of hospitalization due to Staphylococcus aureus nosocomial infection, we find: 1) length of stay is increased for only a minority of patients (38%); 2) an average of 20 additional days of stay occurred for patients with 1 or more days attributed to NI; and 3) an average of 52% of length of stay of patients with 1 or more days attributed to NI can be attributed to the NI. Application of the AEP-based method is a useful alternative for identifying additional days of stay due to NI.

Growth inhibition of pathogenic yeast isolates by alpha-difluoromethylornithine: an inhibition of ornithine decarboxylase

A large body of evidence exists suggesting that polyamines can play essential roles in cellular growth and differentiation. We examined the ability of alpha-difluoromethylornithine (DFMO), an irreversible inhibitor of ornithine decarboxylase, the major rate-limiting enzyme in polyamine biosynthesis, to inhibit the growth of Candida albicans, C. tropicalis, and C. parapsilosis. Substantial growth-inhibition was observed for all three species at DFMO concentrations ranging from 1 to 100 mM. C. tropicalis was significantly more susceptible to DFMO than C. albicans or C. parapsilosis. Depletion of cellular polyamine pools was seen in all 3 species following exposure to DFMO and polyamine depletion enhanced the susceptibility of the organisms to DFMO. The action of DFMO was specifically antagonized by exogenous polyamines. These data suggest that polyamines are important in the growth of Candida spp. and that inhibitors of polyamine biosynthesis may be useful as antifungal agents.

Usefulness of a test for slime production as a marker for clinically significant infections with coagulase-negative staphylococci

The usefulness of a test for slime production as a marker for clinically significant infections with coagulase-negative staphylococci and its implications for therapy were examined. Hospital records were reviewed for 59 patients from each of whom more than one isolate of coagulase-negative staphylococci was obtained. In patients with a prosthetic device, 81% of 59 infectious episodes were due to a slime-positive coagulase-negative staphylococci. In contrast, 22 noninfectious episodes (in which the organisms were contaminants) were equally distributed between episodes due to slime-positive or slime-negative isolates (P = .005). Only 32% of infections caused by slime-positive organisms, in contrast to 100% of infections caused by slime-negative organisms, were improved by treatment with antibiotics alone (P = .02). Prosthetic device removal in addition to antibiotic treatment significantly improved the outcome in patients with infections due to slime-positive organisms when compared with treatment with antibiotics alone (93% vs. 32% improvement; P = .00025).

Comparison of the Quantum II Bacterial Identification System and the AutoMicrobic System for the identification of gram-negative bacilli

The Quantum II Bacterial Identification System (BID; Abbott Laboratories) is a microprocessor-based spectrophotometric system for identification within 4 to 5 h of both enteric and nonenteric gram-negative bacilli. We compared the BID with the AutoMicrobic System (AMS; Vitek Systems, Inc.), using the most recent gram-negative identification card and software (AMS-GNI), for the identification of 501 clinical isolates of gram-negative bacilli, including 382 belonging to the Enterobacteriaceae and 119 nonenteric organisms. The API 20E (Analytab Products) was used as the reference system. The BID correctly identified 375 (98.2%) of the Enterobacteriaceae isolates and 111 (93.2%) of the nonenteric isolates; the AMS-GNI correctly identified 374 (97.9%) and 115 (96.6%) isolates, respectively. The BID identified all isolates within 5 h, whereas the AMS-GNI identified only 35% within this time period. The BID performed comparably to the AMS-GNI for the identification of most gram-negative bacilli. Simplicity, speed, and relatively low reagent cost make the BID a competitive system for many clinical laboratories.

Automated instrument approaches to clinical microbiology

The introduction of instrumentation into clinical microbiology has resulted in increased standardization and to some extent more rapid processing of specimens and reporting of results. The application of available instrumentation to direct specimen processing may provide more rapid detection, identification, and susceptibility testing results on selected specimens. The feasibility of this approach to the processing of sterile body fluids, blood, urine, and respiratory specimens is discussed.

Disseminated histoplasmosis presenting as an acute tenosynovitis

Disseminated histoplasmosis is usually a multifocal process with a wide variety of clinical presentations. Despite frequent bone marrow involvement, overt bone and joint disease is uncommon and isolated synovial involvement is extremely rare. We describe in this report an unusual case of disseminated histoplasmosis presenting as acute tenosynovitis. To our knowledge, this is only the second reported case of synovial involvement by H. capsulatum without a concomitant osseous lesion.

Improved urine screening using a combination of leukocyte esterase and the Lumac system

Three rapid urine screening tests, leukocyte esterase, nitrite, and the Lumac System for detection of bacterial ATP, were evaluated alone and in combination to determine their utility in screening urine specimens from male patients for bacteruria. The combination of leukocyte esterase and Lumac testing resulted in significant improvement in the sensitivity of urine screening over each test individually and the combination of leukocyte esterase and nitrite. The leukocyte esterase/Lumac combination detected 98% of those specimens with greater than or equal to 10(5) CFU/ml and had a negative predictive value of 99%. The results obtained from this type of testing can be used with confidence to minimize the number of urine specimens cultured and to provide rapid reporting of negative results.

Use of rapid screening tests in processing urine specimens by conventional culture and the AutoMicrobic system

Two rapid urine screening tests, the Chemstrip LN (BioDynamics, Indianapolis, Ind.) and the Bac-T-Screen urine screening device (Marion Laboratories, Inc., Kansas City, Mo.), were evaluated as techniques to predict bacteriuria as quantitated by either conventional culture or the AutoMicrobic system (Vitek Systems, Inc., Hazelwood, Mo.). A total of 666 urine specimens were analyzed by both screening tests as well as the AutoMicrobic system and quantitative culture. The sensitivities of both Chemstrip LN and Bac-T-Screen for the detection of low levels of bacteriuria (greater than or equal to 10(3) CFU/ml) were comparable (73.3 and 74.4%, respectively) and were too low to recommend their use as a primary urine screen. Their excellent predictive value of a negative result at the 10(5) CFU/ml level (96 and 97.5%, respectively) makes them potentially useful in predicting urine specimens with less than 10(5) CFU/ml. The use of either of these tests in combination with the AutoMicrobic system markedly decreased the time required to classify urine specimens. Their low cost relative to the AutoMicrobic system urine card makes the use of either test cost effective as a screen for the AutoMicrobic system.

Laboratory evaluation of leukocyte esterase and nitrite tests for the detection of bacteriuria

We compared the sensitivity, specificity, and predictive values of the 1-min leukocyte esterase test and the test for urinary nitrite alone and in combination as screening tests for bacteriuria in over 5,000 clinical urine specimens. The leukocyte esterase-nitrite combination had a sensitivity of 79.2%, a specificity of 81%, and a negative predictive value of a negative test of 94.5% for specimens with greater than or equal to 10(5) CFU/ml. Although the sensitivity of this test was too low to allow its use as the only screening test for bacteriuria, it may serve as a useful adjunct to culturing and other urine-processing systems in the microbiology laboratory.

Evaluation of the Kirby-Bauer disc diffusion test as a screening test for high-level aminoglycoside resistance in enterococci

The Kirby-Bauer disc diffusion test was evaluated as a test to detect high-level aminoglycoside (streptomycin, kanamycin, tobramycin, and gentamicin) resistance in isolates of enterococci. The authors found that high-level resistance could not be predicted accurately with the diffusion test.

Laboratory evaluation of five assay methods for vancomycin: bioassay, high-pressure liquid chromatography, fluorescence polarization immunoassay, radioimmunoassay, and fluorescence immunoassay

We compared the precision and accuracy of five methods used to measure the concentration of vancomycin in serum: bioassay, high-pressure liquid chromatography, fluorescence polarization immunoassay (FPIA [TDX; Abbott Laboratories, North Chicago, Ill.]), radioimmunoassay (RIA), and fluorescence immunoassay. Based on an analysis of seven standards and of 106 patient samples, all five methods were accurate, and four (bioassay, high-pressure liquid chromatography, FPIA, and RIA) were also precise. The FPIA was the most precise and the fluorescence immunoassay was the least precise of the methods tested; intrarun coefficients of variation for these two methods were 0.9 to 3.0% versus 8.9 to 14.5%, and interrun coefficients of variation were 2.8 to 8.1% versus 12.2 to 16.2%, respectively. The RIA was inconvenient because it required an extra dilution of the specimen being tested and an additional (64 micrograms/ml) vancomycin standard for specimens with 32 to 64 micrograms of vancomycin per ml. Based on its rapid turnaround time and the stability of its standard curve, we believe that the FPIA is the best method currently available to quantitate vancomycin in the clinical laboratory.

Comparative study of the ability of four aminoglycoside assay techniques to detect the inactivation of aminoglycosides by beta-lactam antibiotics

In vitro inactivation of aminoglycosides (tobramycin, gentamicin, and amikacin) by beta-lactams (cefazolin, cefotaxime, moxalactam, carbenicillin, piperacillin, mezlocillin, and azlocillin) was measured using the enzyme-mediated immunoassay (EMIT), fluorescence polarization immunoassay ( TDX ), radioimmunoassay (RIA), and bioassay. No significant inactivation of aminoglycosides was produced by high levels of the three cephalosporins as measured by EMIT, RIA, or bioassay. Inactivation of tobramycin and gentamicin by mezlocillin and azlocillin was comparable to that seen with piperacillin but less than that with carbenicillin. In general, the bioassay detected the greatest degree of aminoglycoside inactivation and the EMIT assay detected the least for all drug combinations. The TDX and RIA techniques were equivalent in their ability to detect aminoglycoside inactivation by beta-lactam antibiotics.

In vitro antibacterial activity of cefpiramide

A microbroth dilution method was used to measure the MICs of cefpiramide (SM 1652), cefotaxime, moxalactam, ceftazidime, cefoperazone, ceftriaxone, piperacillin, and mezlocillin against 921 isolates of gram-negative (701) and gram-positive (220) bacteria. The activity of cefpiramide was equivalent to those of piperacillin and mezlocillin against members of the family Enterobacteriaceae and gram-positive isolates, including enterococci. Cefpiramide had equivalent or slightly greater activity against Pseudomonas aeruginosa than the other beta-lactam antibiotics tested.

Clinical laboratory evaluation of a urine screening device

A study was conducted to compare the Bac-T-Screen Bacterial Detection Device for Urines (BDD; Marion Laboratories, Kansas City, Mo.) with urine Gram stain as a screen for bacteriuria. We analyzed 631 urine samples with the BDD and compared the results to urine Gram stains and quantitative cultures. A total of 90 (14%) specimens could not be analyzed with the BDD due to interfering pigments (67 specimens) or clogging of the filter (23 specimens). Of the 541 specimens that were analyzed, the BDD correctly identified 67 (88.2%) of the 76 specimens with greater than or equal to 10(5) CFU/ml but only 294 (63.2%) of the 465 specimens with less than 10(5) CFU/ml. The majority of the false negative specimens had either gram-positive organisms or yeasts. The predictive value of a negative BDD reading was 97.0%. The urine Gram stain correctly identified 92.1% of all positive cultures and 77.8% of all negative cultures. The predictive value of a negative urine Gram stain was 98.4%. In summary, the BDD compares favorably with the urine Gram stain as a screen for bacteriologically negative urine specimens.

Oxygen enhances the antimalarial activity of the imidazoles

We have previously reported the antimalarial activity of imidazoles and amphotericin B against chloroquine-resistant Plasmodium falciparum. We now report the enhancement of imidazole activity in an atmosphere with 17-18% oxygen (the candle jar) vs. 3% or 0.3% oxygen. Based on both morphologic and radiometric testing, smaller amounts of the imidazoles were required to inhibit parasite growth by 50% in the candle jar vs. 3% or 0.3% oxygen. The use of older (more oxidant-sensitive) red cells also enhanced the antimalarial activity of ketoconazole. Neither increased concentrations of oxygen nor the use of older red cells affected the activity of amphotericin B. These results suggest that the imidazoles may exert their antimalarial effect by increasing the oxidant stress on the red cell-parasite complex.

Value of routine aerobic subculturing of unvented blood culture bottles

The value of performing routine aerobic subcultures of both vented and unvented blood culture bottles has not been evaluated critically. We studied 4,954 pairs of blood culture bottles consisting of one vented biphasic tryptic soy broth bottle (Roche Diagnostics) and one unvented Thiol broth bottle (Difco Laboratories). A total of 736 isolates were detected, of which 124 (17%) were in the Thiol broth bottle only. Some 15 isolates were detected only by subculturing the Thiol broth, and 13 of these isolates either were contaminants or were detected in previous positive cultures. Similar results were obtained when the unvented Thiol broth bottle was paired with a vented Difco tryptic soy broth bottle. Analysis of these pairs revealed a total of 360 isolates detected in 2,669 pairs of bottles, of which 83 isolates (23%) were in the Thiol broth bottle only. There were 11 isolates seen only in subcultures of the Thiol broth bottle, and 8 of these were probable contaminants. Thus, routine subculturing of unvented Thiol broth bottles had limited value. These results may differ with the use of other culture media or subculturing procedures. We recommend that each laboratory evaluate critically its experience with aerobic subcultures from unvented bottles.

Comparison of tryptic soy broth with tryptic soy broth supplemented with sucrose in the septi-chek blood culture system

The performance of tryptic soy broth (TSB) was compared with TSB supplemented with 10% sucrose (TSB-S) in the Septi-Chek blood culture system (Roche Diagnostics, Div. Hoffmann-La Roche Inc.). A total of 2,292 sets of blood cultures were evaluated. Although slightly more isolates were recovered in the TSB bottle in comparison with the TSB-S bottle, there was no significant difference between the two medium formulations in the recovery of either gram-positive or gram-negative bacteria. Significantly more isolates of fungi were recovered in the TSB bottles. At least 94% of all isolates were detected by day 3 of incubation in both the TSB and TSB-S bottles. Thus, the addition of sucrose to TSB did not result in greater total recovery or faster recovery of the isolates detected in this study.