Firefly luciferase ATP assay as a screening method for bacteriuria

Paper and thread as media for the frugal detection of urinary tract infections (UTIs)

Urinary tract infections (UTIs) make up a significant proportion of the global burden of disease in vulnerable groups and tend to substantially impair the quality of life of those affected, making timely detection of UTIs a priority for public health. However, economic and societal barriers drastically reduce accessibility of traditional lab-based testing methods for critical patient groups in low-resource areas, negatively affecting their overall healthcare outcomes. As a result, cellulose-based materials such as paper and thread have garnered significant interest among researchers as substrates for so-called frugal analytical devices which leverage the material's portability and adaptability for facile and reproducible diagnoses of UTIs. Although the field may be only in its infancy, strategies aimed at commercial penetration can appreciably increase access to more healthcare options for at-risk people. In this review, we catalogue recent advances in devices that use cellulose-based materials as the primary housing or medium for UTI detection and chart out trends in the field. We also explore different modalities employed for detection, with particular emphasis on their ability to be ported onto discreet casings such as sanitary products.

Nano-lantern on paper for smartphone-based ATP detection

ATP-driven bioluminescence relying on the D-luciferin-luciferase reaction is widely employed for several biosensing applications where bacterial ATP detection allows to verify microbial contamination for hygiene monitoring in hospitals, food processing and in general for cell viability studies. Several ATP kit assays are already commercially available but an user-friendly ATP biosensor characterized by low-cost, portability, and adequate sensitivity would be highly valuable for rapid and facile on site screening. Thanks to an innovative freeze-drying procedure, we developed a user-friendly, ready-to-use and stable ATP sensing paper biosensor that can be combined with smartphone detection. The ATP sensing paper includes a lyophilized "nano-lantern" with reaction components being rapidly reconstituted by 10 μL sample addition, enabling detection of 10^-14 mol of ATP within 10 min. We analysed urinary microbial ATP as a biomarker of urinary tract infection (UTI), confirming the capability of the ATP sensing paper to detect the threshold for positivity corresponding to 10⁵ colony-forming units of bacteria per mL of urine.

An ATP Aptasensor Based on the Peroxidase-like Activity of Hemin/Graphene Oxide Nanosheets

In the present work, a sensitive electrochemical aptasensor was designed for the detection of adenosine triphosphate (ATP) with hemin/graphene oxide nanosheets (HGNs). Firstly, the ATP aptamer was self-assembled on gold electrode surface, and then HGNs were captured to the modified electrode by π-π stacking. The captured HGNs could catalyze the disproportionation reaction of H2O2, and produced a detectable electrochemical signal by chronoamperometry. ATP was competitively bound to aptamer which led to the release of HGNs from the electrode surface after adding ATP. The decrease of the electrochemical signal, which was calculated by the difference of amperometric responses before and after incubation of ATP, provided a quantitative signal for ATP detection. A linear correlation was achieved between the difference of the amperometric responses and the logarithmic concentration of ATP ranging from 0.5 to 100 nM with a detection limit of 0.08 nM. Besides, the aptasensor also exhibited good selectivity toward ATP against other analogs.

Evaluating hygienic cleaning in health care settings: what you do not know can harm your patients

Recent studies using direct covert observation or a fluorescent targeting method have consistently confirmed that most near patient surfaces are not being cleaned in accordance with existing hospital policies while other studies have confirmed that patients admitted to rooms previously occupied by patients with hospital pathogens have a substantially greater risk of acquiring the same pathogen than patients not occupying such rooms. These findings, in the context recent studies that have shown disinfection cleaning can be improved on average more than 100% over baseline, and that such improvement has been associated with a decrease in environmental contamination of high touch surfaces, support the benefit of decreasing environmental contamination of such surfaces. This review clarifies the differences between measuring cleanliness versus cleaning practices; describes and analyzes conventional and enhanced monitoring programs; addresses the critical aspects of evaluating disinfection hygiene in light of guidelines and standards; analyzes current hygienic practice monitoring tools; and recommends elements that should be included in an enhanced monitoring program.

Rapid antimicrobial susceptibility determination of uropathogens in clinical urine specimens by use of ATP bioluminescence

We describe the first direct testing of the antimicrobial susceptibilities of bacterial pathogens in human clinical fluid samples by the use of ATP bioluminescence. We developed an ATP bioluminescence assay that eliminates somatic sources of ATP to selectively quantify the bacterial load in clinical urine specimens with a sensitivity of <1,000 CFU per milliliter. There was a log-log relationship between light emission and the numbers of CFU in clinical urine specimens. A clinical study was performed to evaluate the accuracy of the ATP bioluminescence assay for determination of the antimicrobial susceptibilities of uropathogens in clinical urine specimens tested in a blinded manner. ATP bioluminescent bacterial density quantitation was used to determine the inoculation volume in growth medium with and without antibiotics. After incubation at 37 degrees C for 120 min, the ATP bioluminescence assay was repeated to evaluate the uropathogen response to antibiotics. The ability of the ATP bioluminescence assay to discriminate between antimicrobial susceptibility and resistance was determined by comparison of the results obtained by the ATP bioluminescence assay with the results obtained by standard clinical microbiology methods. Receiver operator characteristic curves were used to determine the optimal threshold for discriminating between susceptibility and resistance. Susceptibility and resistance were correctly predicted in 87% and 95% of cases, respectively, for an overall unweighted accuracy of 91%, when the results were stratified by antibiotic. For samples in which the pathogen was susceptible, the accuracy improved to 95% when the results for samples with less than a 25-fold increase in the amount of bacterial ATP in the medium without antibiotics were excluded. These data indicate that a rapid bioluminescent antimicrobial susceptibility assay may be useful for the management of urinary tract infections.

[Efficacy of two semiautomatic methods for bacteriuria detection]

BACKGROUND

A quick and reliable method for detecting bacteriuria would allow to exclude the presence of microorganisms in the urine on the same day the sample is obtained.Objectives. Two semiautomatic methods have been evaluated for bacteriuria screening, taking the semiquantitative culture as reference method.

MATERIAL AND METHOD

A prospective study of urine samples from patients suspected of having a urinary infection was designed. One method is based on bioluminescence that detects the presence of ATP liberated by the bacterial cell (Utiscreen-Coral Biomedical). The other semiautomatic method uses a nephelometry technique (Uro-quick). The results of each semiautomatic method were compared with the semiquantitative culture. Samples presenting counts > 104 UFC/ml of one or two microorganisms were considered as having urinary-tract infection (equivalent to significative bacteriuria). Cultures with counts < 5,000 UFC/ml or containing three or more microorganisms were classified as non-representative of significant bacteriuria. The nephelometric system allows to obtain results at two different times. Samples were divided into two groups to compare both situations.

RESULTS

1,090 urine samples, received consecutively, were considered. In the case of the bioluminescence system, the study was prolonged to 1,565 samples. The values obtained were: a) bioluminescence: general data, sensibilitiy (S) 5 94.4%; especificity (E) 5 72.8%; positive predictive value (PPV) 5 46.2% and negative predictive value (NPV) 5 98.2%; hospitalized patients only, S 5 97.5%; E 5 77.3%; PPV 5 61.2% and NPV 5 98.8%; and b) nephelometry: 195 min, S 5 96.7%; E 5 88.8%; PPV 5 67.9% and NPV 5 99.1%; 235 min, S 5 95.5%; E 5 81.0%; PPV 5 58.7% and NPV 5 98.4%.

CONCLUSION

A negative predictive value from both methods under these conditions would allow them to be used in medical centers for the exclusion of bacteriuria.

Use of firefly luciferase in ATP-related assays of biomass, enzymes, and metabolites

The kinetics of ATP reagents not affected by product inhibition or other forms of inactivation of luciferase during the measurement time has been clarified. Under these conditions the decay rate of the light emission expressed as percentage per minute is a measure of luciferase activity and can be given as the rate constant k (min-1), directly reflecting the degradation of ATP in the luciferase reaction. Three types of reagents with different analytical characteristics and different application possibilities have been identified. Stable light-emitting reagents are suitable for measurements of ATP down to 1000 amol. This is the only type of reagent suitable for monitoring ATP-converting reactions, i.e., assays of enzymes or metabolites, assays of oxidative phosphorylation, photophosphorylation, and so on. A higher luciferase activity resulting in a slow decay of the light emission by approximately 10% per minute (k = 0.1 min-1) gives a reagent suitable for measurements down to 10-100 amol. The slow decay of light emission allows use of manual luminometers without reagent dispensers. A further increase of the luciferase activity resulting in a decay rate of approximately 235% per min (k = 2.35 min-1) and only 10% of the light emission remaining after 1 min is suitable for measurements down to 1 amol corresponding to half a bacterial cell. With this type of flash reagent the total light emission can be calculated from two measurements of the light intensity on the decay part of the light emission curve. This new measure is not affected by moderate variations in luciferase activity, but only by changes in quantum yield and self-absorption of the light in the sample. Flash-type reagents require the use of reagent dispensers. The stringent requirements for ATP-free cuvettes, pipette tips, and contamination-free laboratory techniques make it unlikely that flash reagents would be useful in nonlaboratory surroundings. A potential application for this type of reagent is sterility testing. In general, it is concluded that one should select the ideal ATP reagent carefully for each application. Obviously the reagents used in a particular application do not have to match the decay rates given earlier exactly. However, various applications of the ATP technology and the properties of manual and automatic luminometers fall quite nicely into categories corresponding to the properties of the three reagents described. The rapidly growing interest in ATP technology has already resulted in the development of a greater variety of luminometers, from hand-held instruments to high-throughput systems. The continuation of efforts in both reagent and instrument development will undoubtedly result in many new applications.

Pharmacodynamic effects of antibiotics. Studies on bacterial morphology, initial killing, postantibiotic effect and effective regrowth time

Pharmacodynamics of antibiotics deals with time course of drug activity and mechanisms of action of drugs on bacteria. In this thesis pharmacodynamic parameters have been studied after brief exposure of gram-positive bacteria to daptomycin, imipenem or vancomycin and after short exposure of gram-negative bacteria to amikacin, ampicillin, aztreonam, cefepime, cefotaxime, ceftazidime, ceftriaxone, cefuroxime, imipenem, mecillinam, or piperacillin. The studies have been focused on morphological alterations, initial killing, postantibiotic effect (PAE) and effective regrowth time (ERT) and a method, based on bioluminescence assay of intracellular ATP has been used. The basic principle behind this technique is that ATP in living cells is present in a relatively constant amount, and hence affords a measure of the number of microbial cells. The PAE describes the delayed regrowth of bacteria after brief exposure to antibiotics. The number of cells measured after this antibiotic exposure describes the initial killing and is also the start value for calculating the PAE. PAEs of 2-3 h were obtained by bioluminescence for gram-positive bacteria exposed to imipenem or vancomycin. This is in agreement with results obtained by viable count and is probably due to similar weak initial decrease in cell density when assayed by both methods. Long (greater than 3 h) concentration dependent PAEs and moderate (less than or equal to 1 log10) initial decrease in intracellular ATP were in general seen for gram-positive bacteria exposed to daptomycin and for gram-negative bacteria exposed to imipenem or amikacin when assayed by bioluminescence. These very long PAEs and rather weak initial killing have to be compared with the shorter PAEs and stronger initial killing reported by us and others using viable count. Furthermore, this study showed that there was a relatively good concordance between microscopy and bioluminescence, which are direct methods, in determining the initial killing and PAE of imipenem on Escherichia coli. The ERT, defined as the time for bacterial density to increase 1 log10 from the pre-exposure inoculum, was independent of the method used for measuring regrowth of E. coli after brief exposure to imipenem. The combination of mecillinam with ampicillin, aztreonam, ceftazidime or piperacillin and the combination of amikacin with ceftazidime, ceftriaxone or piperacillin induced longer PAEs on gram-negative bacteria than the sum of PAEs of the individual antibiotics. A strong initial killing in combination with a long PAE cause a long ERT and may allow the antibiotic concentration to stay below MIC during long periods of time without any regrowth. This may, in clinical practice, have implications for long dosing intervals.

Analyses of the FlashTrack DNA probe and UTIscreen bioluminescence tests for bacteriuria

Five hundred urine specimens were selected at random and screened for bacteriuria by a DNA probe method, FlashTrack (Gen-Probe, San Diego, Calif.), and an automated bioluminescence method, UTIscreen (Los Alamos Diagnostics, Los Alamos, N.M.), and the results were compared with those of the semiquantitative plate culture method. The performance of each test versus culturing was evaluated at colony counts of greater than or equal to 10(4), greater than or equal to 5 x 10(4), and greater than or equal to 10(5) CFU/ml. Since the interpretive breakpoint of each test was user selectable, the results were reported as receiver operator characteristic curves. Optimum interpretive breakpoints were determined for each test at each colony count by calculating a performance index that emphasized sensitivity over specificity in a 70:30 ratio. Although both tests had less-than-optimal sensitivities and specificities, the performance of FlashTrack was significantly better than that of UTIscreen at two of the three colony counts (10(4) and 10(5) CFU/ml); however, FlashTrack costs more and is a labor-intensive procedure. Neither method was evaluated for the detection of colony counts of less than 10(4) CFU/ml.

Bacteriuria testing by the ATP method as an integral part in the diagnosis and therapy of urinary tract infection (UTI)

Rapid tests for bacteriuria have the highest value, if the test result is available while the patient is with the doctor. At the bacteriological laboratory rapid testing of samples obtained by mail may be cost-effective but is of little clinical value. In a previous study performed at a health care centre using conventional urine culture as a reference the ATP test came out as the most reliable one among several rapid bacteriuria tests. The present study was performed to see how the ATP test could be fitted into the routine of the health care centre. Female patients with UTI symptoms were asked to deliver a urine sample to the health care centre laboratory and to wait for the result before seeing the doctor. After having the symptoms confirmed the doctor based the diagnosis on the ATP value. A low ATP value ruled out UTI and a high ATP value confirmed UTI. In patients with an intermediary ATP value (10-50 nmol/l) a positive nitrite test was used to confirm UTI. Only those patients with intermediary ATP values and negative nitrite test had to wait for conventional urine culture. Thus in most patients the decision on antibiotic therapy or not was based on clinical symptoms and ATP results only. Antibiotics (trimethoprim) were given as single dose or as a conventional 7-day regime in a double-blind comparison. The correlation between the ATP method and conventional culture was good.(ABSTRACT TRUNCATED AT 250 WORDS)

Bioluminescent assay of bacterial ATP for rapid detection of bacterial growth in clinical blood cultures

A bioluminescent assay of bacterial ATP for rapid detection of bacterial growth in 512 clinical aerobic blood cultures was evaluated. At the detection limit of bacterial ATP (10(-10) mol/l) in the blood cultures 94.2% of the true positive blood cultures were detected (sensitivity) and the specificity was 85.8%. If the cut-off limit was increased the sensitivity decreased and the specificity increased and at 2 x 10(-9) mol/l ATP the maximum correctly classified blood cultures was reached. At this cut-off limit the sensitivity was 82.9% and the specificity was 99.6%. In 54.3% of the true positive blood cultures bacterial growth was detected more rapidly with the bioluminescent assay than with macroscopic examination and subculture.

Rapid bioluminescence method for bacteriuria screening

A study was performed to evaluate the UTIscreen (Los Alamos Diagnostics, Los Alamos, N. Mex.), a rapid bioluminescence bacteriuria screen. The UTIscreen was compared with three other rapid bacteriuria screens: the Bac-T-Screen (Vitek Systems, Hazelwood, Mo.), an automated filtration device; the Chemstrip LN (Boehringer Mannheim Diagnostics, BioDynamics, Indianapolis, Ind.), an enzyme dipstick; and the Gram stain. A semiquantitative plate culture was used as the reference method. Of the 1,000 specimens tested, 276 had colony counts of greater than 10(5) CFU/ml by the culture method. Of these, the UTIscreen detected 96% (265 of 276) using greater than or equal to 5% of the integrated light output of the standard reading as a positive interpretive breakpoint, the Bac-T-Screen detected 96% (266 of 276), the Chemstrip LN detected 90% (249 of 276), and the Gram stain detected 96% (264 of 276). Of the 214 probable pathogens isolated at greater than 10(5) CFU/ml, the UTIscreen detected 95% (204 of 214), the Bac-T-Screen detected 98% (210 of 214), the Chemstrip LN detected 92% (198 of 214), and the Gram stain detected 98% (209 of 214). The predictive values of negative test results at greater than 10(5) CFU/ml for the UTIscreen, the Bac-T-Screen, the Chemstrip LN, and the Gram stain were 98, 97, 93, and 98%, respectively. The overall specificities at greater than 10(5) CFU/ml for the UTIscreen, the Bac-T-Screen, the Chemstrip LN, and the Gram stain were 70, 48, 51, and 69%, respectively. There were 532 specimens with colony counts of >10(3) CFU/ml, and of these, the UTIscreen, the Bac-T-Screen, the Chemstrip LN, and the Gram stain detected 72, 81, 76, and 73%, respectively. Of the 249 probable pathogens isolated at >10(3) CFU/ml, the UTIscreen, the Bac-T-Screen, the Chemstrip LN, and the Gram stain detected 91, 95, 89, and 93%, respectively. The overall specificities at > 10(3) CFU/ml for these methods were 79, 55, 57, and 78%, respectively. The cost per test for detection was approximately $0.50 for the Chemstrip LN. Overall, the UTIscreen is rapid and easy to perform; its sensitivity compared favorably with those of the other screening methods; it had higher specificity than the Bac-T-Screen and Chemstrip LN; and it allowed for bathing of specimen.

Detection of urinary tract infections by rapid methods

A review of rapid urine screens for detection of bacteriuria and pyuria demonstrates a number of available alternatives to the culture method. Selection of one or more of these systems for routine use is dependent upon the laboratory and the patient population being tested. The laboratory approach to the diagnosis of urinary tract infection should consider the clinical diagnosis of the patient whenever possible. Keeping in mind that quantitative urine cultures alone cannot be used to detect infection in some patient populations unless lower colony counts are considered, a rapid screen may be a more practical approach. It has become accepted that 10(5) CFU/ml can no longer be used as the standard for all patient groups, that pyuria often is important in making the diagnosis of a urinary tract infection, and that most of the rapid screens are more sensitive than the culture method at 10(5) CFU/ml. Presently, no one approach can be recommended for all laboratories and all patient groups. However, each diagnostic laboratory should select one approach which is best for its situation. It is not practical, efficient, or cost effective to define a protocol for each possible clinical condition; however, all should be considered when developing a protocol. This protocol should be compatible with the patient population and communicated to the physicians. Use of a rapid screen should be beneficial to the patient, the physician, and the laboratory.

The use of the firefly bioluminescent reaction for the rapid detection and counting of mycobacterium BCG

A rapid test for the counting of Mycobacterium BCG, based on firefly luciferase assay of bacterial ATP has been evaluated. Three different methods for the extraction of ATP from mycobacterial cells were examined. Extraction with n-butanol proved to be the best method. The amount of ATP extracted correlated well with the number of colony forming units. It was found that the ATP content per colony forming particle of BCG varied only slightly after various periods of cultivation.

Screening for bacteriuria with the LN strip test

Recently, the LN strip test was introduced for purposes of rapid screening of urine specimens for bacteriuria. The LN strip test permits detection of urinary leukocyte esterase and nitrite. A total of 2,481 unselected urine specimens from three tertiary care hospitals were examined using the LN strip test and the results were compared with those obtained with a conventional quantitative culture technique. When the results of the leukocyte esterase and nitrite tests were combined, the sensitivity and specificity of the LN strip test were 88.8% and 71.3%, respectively, based on culture results of greater than or equal to 10(5) CFU/ml. Test sensitivity decreased at greater than or equal to 10(4) CFU/ml, whereas test specificity increased.

Evaluation of rapid methods for the detection of bacteriuria (screening) in primary health care

The diagnostic performance of six methods for bacteriuria testing has been studied in 781 urine specimens obtained in primary health care, using conventional culture as reference method. The cut-off limits for classification of test results into positive and negative have been optimized with respect to diagnostic performance in primary health care. With optimized tests the following diagnostic efficiencies were obtained: Bacterial ATP, 0.94; Bacterial count in sediment, 0.93; Nitrite test, 0.92; Dipslide test, 0.92; White cell count in sediment; 0.87; Goffulocyte esterase test; 0.83. The diagnostic performance was also studied for all combinations of two tests. The highest diagnostic efficiency (0.96) was obtained by combining the ATP and dipslide tests. High diagnostic efficiencies can be obtained by a rapid primary test, using other tests for follow-up testing of specimens with intermediate or uninterpretable primary results. The most promising results were obtained by using ATP as the primary test, with follow-up testing of specimens with 3-25 nmol/l of ATP (12 per cent of the specimens). Follow-up testing by conventional culture resulted in overall diagnostic efficiency of 0.98. By performing the nitrite test on specimens with intermediary ATP-results, 81 per cent of the patients with UTI can be classified without culture. Only patients with intermediary ATP and negative nitrite results (10 per cent of the total number) will have to wait for final diagnosis based on conventional culture. Some alternative strategies to combine available methods are discussed in detail. Major advantages of the ATP test are that the test can be performed while the patients are waiting; it provides a numerical and objective result, and, in contrast to culture, it is not influenced by adhesion of bacteria to somatic cells.

Bioluminescence for USP sterility testing of pharmaceutical suspension products

Bioluminescence measurement significantly improved the accuracy, sensitivity, precision, and reliability of the current visual endpoint determination for the USP sterility test and eliminated the day 7 transfer/dilution step required for testing suspension products. Thirteen strains of bacteria and fungi (representing potential contaminants in sterile products), three pharmaceutical suspension products, and four media were used in the experiment. No interference from suspension products was encountered in the detection of microbial growth by the bioluminescence measurement. The poor fungal growth encountered was attributed to insufficient diffusion of oxygen into the medium and was circumvented by use of a large tube size (38 by 200 mm) or by vortexing the medium once during the 2-week incubation period. Bioluminescence measurement would facilitate automated handling of the sterility test endpoint readout operation. The optimum parameters of bioluminescence measurement for application in sterility testing were determined.

Rapid screening and microbiologic processing of pediatric urine specimens

Urinary nitrite and leukocyte esterase dipstick tests were evaluated as rapid screening procedures to select probable culture-positive urines for direct identification (AutoMicrobic System urine cards) and modified Kirby-Bauer susceptibility testing. Approximately 73% of significant culture-positive (greater than 10(5) organisms per milliliter, pure culture) urine specimens could be selected by nitrite testing alone with very high specificity (approximately 99%). The leukocyte esterase test detected 85% of culture-positive urines when used alone and approximately 91% when used in combination with nitrite testing (if either test was positive it was considered a positive screening); however, the esterase test was significantly less specific for bacteriuria than the nitrite test. Based on these results, the nitrite test was selected for use as the screening test. Rapid, direct identification and susceptibility tests on screen-positive urines showed 97% correlation with standard testing methods. Significant positive urines processed in this manner could be reported with quantitation, identification, and susceptibility results within 24 hr.

Application of bioluminescent urine screens in a tertiary care facility

Two adenosine triphosphate (ATP)-detection systems for quantitating bacteriuria, the LUMAC (noncentrifugation method) and MONOLIGHT (centrifugation method) urine screens, were separately evaluated for their capacity to detect bacteriuria in specimens from patients at a tertiary care teaching hospital. Results of each study were compared with the findings of conventional culture. Indices of test efficacy, sensitivity/predictive value for a negative test, were as follows: at greater than or equal to 10(4) CFU/ml--LUMAC 88%/93% and MONOLIGHT 82%/88%; and at greater than or equal to 10(5) CFU/ml--LUMAC 99%/99% and MONOLIGHT 97%/99%. Both systems were satisfactory urine screens for catheterized and midstream urine specimens when used at the traditional level of significance (greater than or equal to 10(5) CFU/ml). An assessment of the MONOLIGHT noncentrifugation protocol demonstrated efficacy of the system to detect significant bacteriuria at greater than or equal to 10(5) CFU/ml. Decreased numbers of false-positive results compared to the centrifugation method were obtained with this assay. False-positive and false-negative results were attributable to threshold sensitivity of the instruments. The presence of somatic cells and yeasts were associated with false-positive results. False-positive results might stem from the inability of conventional culture to recover selected microorganisms. Time and cost analyses of the LUMAC system indicated that significant savings over conventional methodology were not effected.

Leukocyte esterase-nitrite and bioluminescence assays as urine screens

The 1-min leukocyte esterase (LE)-nitrite test (Chemstrip 9; Biodynamics, Division of Boehringer Mannheim Biochemicals, Indianapolis, Ind.) and a bioluminescence assay (Monolight centrifugation method; Analytical Luminescence Laboratory, Inc., San Diego, Calif.) were tested for their efficacy as urine screens among 453 patients at a tertiary-care teaching hospital. Both methods had the capacity to exclude significant bacteriuria (greater than or equal to 10(5) CFU/ml) when compared with the results of conventional culture methods, with predictive values of 99 and 93%, respectively, for a negative test. Bioluminescence was the more accurate nonculture method used. Sensitivity and specificity values were 97 and 71%, respectively, for bioluminescence, 82 and 60%, respectively, for LE with nitrite, and 72 and 64%, respectively, for LE without nitrite. At reduced levels of bacteriuria less than 10(5) CFU/ml), the sensitivities of LE-nitrite and bioluminescence were decreased but comparable. The addition of protein and blood test results in the Chemstrip 9, along with LE-nitrite as bacteriuria indicators, were unsatisfactory because of the large numbers of false-positive results attributed to protein and blood determinations. LE activity as detected by the LE test was a poor predictor of significant bacteriuria in both male and female patients. The sensitivity (71%) and specificity (57%) of the LE test in male patients were significantly lower than those previously reported and varied with the patient population studied.

Clinical evaluation of three rapid methods for the detection of significant bacteriuria

Random urine specimens (848) were screened for significant bacteriuria by using the 30-min Lumac (3M, St. Paul, Minn.), the 2-min Bac-T-Screen (Marion Laboratories, Inc., Kansas City, Mo.), and the 13-h AutoMicrobic system (AMS) urine identification card (Vitek Systems, Inc., Hazelwood, Mo.). MacConkey and 5% sheep blood agar plates were inoculated with a 10(-4) dilution of urine and used for the reference method. Bac-T-Screen results were uninterpretable for 9.1% of the specimens owing to either urine sample pigmentation (5.3%) or clogging of the filter (3.8%). Screen-negative urine specimens made up 49.6, 57.2, and 48.5% of the total number of specimens evaluated with AMS, Lumac, and Bac-T-Screen, respectively. False-positive results with Lumac and Bac-T-Screen were 20.6 and 22.3%, respectively. False-negative results for cultures with greater than or equal to 10(4) CFU/ml were 22.0% with AMS, 29.4% with Lumac, and 25.5% with Bac-T-Screen, and false-negative results for cultures with greater than or equal to 10(5) CFU/ml were 29.6% with AMS, 9.9% with Lumac, and 7.0% with Bac-T-Screen. For each system, greater than 70% of false-negatives at greater than or equal to 10(5) CFU/ml consisted of mixed or pure cultures of common contaminants. With any of these screening methods, a clinically significant isolate at greater than or equal to 10(5) CFU/ml would rarely be missed (less than or equal to 1.7% for all systems). A cost-effective and rapid approach to urine microbiology could consist of screening out negative specimens by either Lumac or Bac-T-Screen and processing only screen-positive specimens by the AMS.

Rapid methods for counting mycobacteria--comparison of methods for extraction of mycobacterial adenosine triphosphate (ATP) determined by firefly luciferase assay

A comparison of 5 different methods of extraction of adenosine 5'-triphosphate (ATP) from mycobacterial cells was carried out using Mycobacterium bovis, BCG as a model. ATP was measured using the luciferin-luciferase bioluminescence reaction. Boiling buffer extraction was the best method. The amount of ATP extracted correlated with the number of colony forming units over a wide range of count. Although great sensitivity in terms of number of bacilli detectable was not achieved the method was rapid and appears suitable for drug sensitivity testing of tubercle bacilli.

Bioluminescent assay as a potential method of rapid susceptibility testing

A method of rapid susceptibility testing by bioluminescent assay was developed. Correlation between the 50% inhibition dose of antimicrobics for bacterial adenosine triphosphate measured by bioluminescent assay and the minimum inhibitory concentration obtained by the broth dilution method was satisfactory. In the bioluminescent assay the incubation time required was only 90 min.

Bacteriuria screening by direct bioluminescence assay of ATP

A direct bioluminescence assay for bacteriuria screening is described and compared with the MS-2 system (Abbott Laboratories, Irvine, Tex.) and the chemical strip, Gram smear, and calibrated-loop methods. A total of 973 specimens were tested. Unlike previously described bioluminescence methods, this test measures total ATP in urine without pretreatment of samples to remove somatic ATP. The result was compared with an ATP standard (20 ng/ml). A low result (less than 3% of standard) was interpreted as negative and a high result (greater than 10% of standard) as positive. Samples with intermediate results (38% of total) were incubated at 35 degrees C in thioglycolate broth (1:10). A 2% increase in ATP concentration was interpreted as positive. The sensitivity of this method for detecting greater than 10(5) pathogens per ml was 92.3% and was comparable to those of the MS-2 system (92.7%) and the Gram smear method (90.5%). The chemical strip method was less sensitive (84.0%). The direct bioluminescence method was more sensitive than were the MS-2 system and the Gram smear method for detecting low-level bacteriuria (less than 10(3) to 10(5) organisms per ml), primarily because of associated pyuria. Thioglycolate broth provided a suitable medium for ATP production, and 5% CO2 decreased bacterial ATP synthesis during log-phase growth. The direct bioluminescence assay is rapid, simple, cost-effective, and reliable for bacteriuria screening.

Comparison of the Lumac and Monolight systems for detection of bacteriuria by bioluminescence

The development of practical and rapid methods for detection of infectious-disease-producing agents in clinical specimens is the most important current goal of clinical microbiology. Bioluminescence is a technique which is rapid and potentially sensitive enough to detect significant numbers of bacteria in urine specimens. To determine whether bioluminescence is practical and cost effective for routine use, we compared two commercially available instruments and kits, Lumac and Monolight, to standard bacterial cultures on 986 urine specimens. Lumac had an overall 83.7% agreement with cultures, a sensitivity of 92.4%, and a specificity of 79.4%. Monolight had 83.5% agreement with cultures, a sensitivity of 89.1%, and a specificity of 81.8%. There were 13.8% false-positive results and 2.5% false-negative results with both systems. When only potentially significant organisms were included, the false-negative rate was reduced to ca. 1%. Both systems are sufficiently accurate to be recommended for routine use. The cost of bioluminescence is higher than that of bacterial cultures, and bioluminescence may not be cost effective in some laboratories.

Detection of bacteriuria by bioluminescence: effect of pre-analysis centrifugation of specimens

Three bioluminescence-based, rapid methods of detecting significant bacteriuria were applied in parallel to 514 urine specimens. The results were compared with those of a quantitative pour plate viable count method, defined as positive if greater than or equal to 10(5) c.f.u./ml of urine were observed. When adjusted to yield 21% falsely positive results the three rapid methods yielded 24%, 21% and 19% falsely negative results. If specimens with evidence of urethral or vaginal contamination were excluded (237 specimens remaining) the three methods yielded respectively 14%, 8% and 13% falsely negative results. A major source of disagreement between the bioluminescence-based methods and quantitative culture thus appeared to be contaminated urine specimens.

Bacteriuria screening and antimicrobial susceptibility testing of aerobic bacteria by an electrochemical method

A method is described for detecting significant bacteriuria and determination of minimal inhibition concentrations (MIC's) of aerobically growing bacteria by using electrochemical electrodes to measure changes of oxygen tensions in liquid nutrient media resulting from bacterial growth. Urine specimens (n = 577) were screened electrochemically, parallel investigations were performed by standard culture methods and by photometrical measurements. All the specimens showing significant bacteriuria in standard culture were selected within 3.5 h by the electrochemical technique. An oxygen index OI was introduced which quantitatively reflects changes in oxygen tension of nutrient media during growth. OI shows good agreement with extinction and light scattering indices, respectively. On the basis of OI as a parameter of inhibited and uninhibited growth a correlation between OI and MIC's of aerobically growing bacteria was found. The electrochemical method provides an useful aid for rapid, preliminary antimicrobial susceptibility testing and definite bacteriuria screening. The application of this method in bacteriological urine diagnostics significantly reduces laboratory work and costs, and can be recommended for the screening of urine specimens to exclude negative specimens from further processing.

Rapid detection of bacterial growth in blood cultures by bioluminescent assay of bacterial ATP

A method for rapid detection of bacterial growth in blood cultures by bioluminescent assay of bacterial ATP was developed. Samples from blood cultures were treated with a blood-lysing detergent combined with an ATP-hydrolyzing enzyme to destroy blood cell ATP. Blood cell ATP which was bound to cell debris and escaped the ATPase activity was then separated from the bacteria on Percoll density gradients. Bacterial ATP from the bacterial layer was determined by the firefly bioluminescence system. In simulated blood cultures inoculated with 10 CFU of bacteria per ml of blood, bacterial ATP levels exceeded the detection limit (10(-10) M) after 6 to 10 h of incubation. This ATP level corresponds to approximately 10(4) CFU of bacteria per ml.