Reliability of two novel methods, Alamar and E test, for detection of methicillin-resistant Staphylococcus aureus

Current perspectives in drug discovery against tuberculosis from natural products

Currently, one third of the world's population is latently infected with Mycobacterium tuberculosis (MTB), while 8.9-9.9 million new and relapse cases of tuberculosis (TB) are reported yearly. The renewed research interests in natural products in the hope of discovering new and novel antitubercular leads have been driven partly by the increased incidence of multidrug-resistant strains of MTB and the adverse effects associated with the first- and second-line antitubercular drugs. Natural products have been, and will continue to be a rich source of new drugs against many diseases. The depth and breadth of therapeutic agents that have their origins in the secondary metabolites produced by living organisms cannot be compared with any other source of therapeutic agents. Discovery of new chemical molecules against active and latent TB from natural products requires an interdisciplinary approach, which is a major challenge facing scientists in this field. In order to overcome this challenge, cutting edge techniques in mycobacteriology and innovative natural product chemistry tools need to be developed and used in tandem. The present review provides a cross-linkage to the most recent literature in both fields and their potential to impact the early phase of drug discovery against TB if seamlessly combined.

MRSA: rare in the vagina

STUDY OBJECTIVE

To determine the prevalence of vaginal Staphylococcus aureus and methicillin-resistant S. aureus (MRSA) in sexually active adolescent women.

DESIGN

A prospective surveillance study.

PARTICIPANTS

Patients included 315 sexually active young women (ages 13-24) undergoing routine pelvic examination and wet mount testing in an urban teen health center.

MAIN OUTCOME MEASURES

Prevalence of vaginal S. aureus and MRSA.

RESULTS

S. aureus was present in 16 samples for a point estimate of 5.1% (95% CI: 2.6%-7.5%). MRSA was detected in two samples, giving a vaginal prevalence estimate of 0.6% (95% CI: 0.0% -1.5%). No differences were detected in the prevalence of S. aureus by age or race, although no cases of S. aureus were observed in those under age 15.

CONCLUSION

The prevalence of MRSA in a sample of sexually active adolescents was as rare as reported in other populations. It is unlikely that vaginal MRSA is a reservoir for community acquired infections.

Rapid drug resistance detection in Mycobacterium tuberculosis: a review of colourimetric methods

Several new methods to detect drug resistance in Mycobacterium tuberculosis have been proposed in recent years. Colourimetric methods that use redox indicators or the nitrate reduction assay have received increasing attention because of their simplicity and the absence of any requirement for sophisticated equipment or highly trained personnel. Several studies have evaluated their accuracy and performance in comparison with reference standard methods, particularly for the detection of resistance to rifampicin and isoniazid, which are the two most important drugs used for the treatment of tuberculosis. This review describes the development, evaluation and implementation of these methods as rapid alternative tests for the detection of multidrug resistance in M. tuberculosis. Based on published evidence and the high accuracy of colourimetric methods for detecting drug resistance in M. tuberculosis, these methods seem to be appropriate for implementation in high-burden low-resource countries.

Guidelines for the laboratory diagnosis and susceptibility testing of methicillin-resistant Staphylococcus aureus (MRSA)

These evidence-based guidelines have been produced after a literature review of the laboratory diagnosis and susceptibility testing of methicillin-resistant Staphylococcus aureus (MRSA). We have considered the detection of MRSA in screening samples and the detection of reduced susceptibility to glycopeptides in S. aureus. Recommendations are given for the identification of S. aureus and for suitable methods of susceptibility testing and screening for MRSA and for S. aureus with reduced susceptibility to glycopeptides. These guidelines indicate what tests should be used but not when the tests are applicable, as aspects of this are dealt with in guidelines on control of MRSA. There are currently several developments in screening media and molecular methods. It is likely that some of our recommendations will require modification as the new methods become available.

In vitro evaluation of the biocompatibility of contaminated implant surfaces treated with an Er : YAG laser and an air powder system

Titanium platelets with a sand-blasted and acid-etched surface were coated with bovine serum albumin and incubated with a suspension of Porphyromonas gingivalis (ATCC 33277). Four groups with a total of 48 specimens were formed. Laser irradiation of the specimens (n = 12) was performed on a computer-controlled XY translation stage at pulse energy 60 mJ and frequency 10 pps. Twelve specimens were treated with an air powder system. After the respective treatment, human gingival fibroblasts were incubated on the specimens. The proliferation rate was determined by means of fluorescence activity of a redox indicator (Alamar Blue Assay) which is reduced by metabolic activity related to cellular growth. Proliferation was determined up to 72 h. Contaminated and non-treated as well as sterile specimens served as positive and negative controls. Proliferation activity was significantly (Mann-Whitney U-test, P < 0.05) reduced on contaminated and non-treated platelets when compared to sterile specimens. Both on laser as well as air powder-treated specimens, cell growth was not significantly different from that on sterile specimens. Air powder treatment led to microscopically visible alterations of the implant surface whereas laser-treated surfaces remained unchanged. Both air powder and Er : YAG laser irradiation have a good potential to remove cytotoxic bacterial components from implant surfaces. At the irradiation parameters investigated, the Er : YAG laser ensures a reliable decontamination of implants in vitro without altering surface morphology.

Effect of low-level GaAlAs laser irradiation on the proliferation rate of human periodontal ligament fibroblasts: an in vitro study

AIM

The aim of this in vitro study was to evaluate a potential stimulatory effect of low-level laser irradiation on the proliferation of human periodontal ligament fibroblasts (PDLF).

MATERIALS AND METHODS

PDLF obtained from third molar periodontal ligaments were cultured under standard conditions and spread on 96-well tissue culture plates. Subconfluent monolayers were irradiated with an 809-nm diode laser operated at a power output of 10 mW in the continuous wave (cw) mode at energy fluences of 1.96-7.84 Jcm-2. The variable irradiation parameters were the time of exposure (75-300 s per well) and the number of irradiations (1-3). After laser treatment, the cultures were incubated for 24 h. The proliferation rate of the lased and control cultures was determined by means of fluorescence activity of a reduction-oxidation (REDOX) indicator (Alamar Blue Assay) added to the cell culture. Proliferation, expressed in relative fluorescence units (RFU), was determined 24, 48 and 72 h after irradiation.

RESULTS

The irradiated cells revealed a considerably higher proliferation activity than the controls. The differences were significant up to 72 h after irradiation (Mann-Whitney U-test, p<0.05).

CONCLUSION

A cellular effect of the soft laser application is clearly discernible. Clinical studies are needed to evaluate whether the application of low-level laser therapy might be beneficial in regenerative periodontal therapy.

[Antibiotic resistance of Staphylococcus aureus at north Lebanon: place of the methicillin resistance and comparison of detection methods]

The aim of this study was to evaluate the susceptibility of 100 Staphylococcus aureus strains isolated from the laboratory of Microbiology of the Islami Hospital of Tripoli (Lebanon) to 19 antibiotics, and to determine the prevalence of methicillin resistant strains. 30% of strains studied were methicillin resistant, 96% were resistant to the penicillin G. Clavulanic acid restaurated the amoxicillin activity to 29%. The resistance level was 34% for amikacin, 3% for gentamycin and tobramycin, 10% for chloramphenicol, 44.33% for tetracyclin, 7% for erythromycin, 4.04% for clindamycin, 20% for trimethoprim-sulfametoxasol and 0% for vancomycin and teicoplanin. The methicillin-resistant Staphylococcus aureus possess more important resistant level in comparison with the methicillin sensitive strains. We compared the ability of latex agglutination test (Slidex(R) SARM, bioMérieux, France) to detect the production of penicillin-binding protein 2' (PBP 2') in 100 clinical isolates of S. aureus with two reference methods: the oxacillin disk diffusion test and the MIC determination by the E-test (AB BIODISK, Sweden). The two reference methods give the same results for the detection of methicillin resistant S. aureus. The Slidex test was positive for all 30 isolates determined to be methicillin resistant by the reference methods (sensitivity 100%). The latex test was negative for 42 of 70 isolates determined to be methicillin susceptible by the reference methods, and the latex test was positive for 28 isolates determined to be susceptible (specificity 60%).

Detection of complement-mediated antibody-dependent bactericidal activity in a fluorescence-based serum bactericidal assay for group B Neisseria meningitidis

Serum bactericidal assays (SBAs) for Group B meningococci are considered the methods of choice for the evaluation of functional antimeningococcal antibodies. Many investigators regard SBAs as time- and labor-intensive. Variations in SBA protocols among different laboratories make interpretation of results difficult. Here we describe a fluorescence-based serum bactericidal assay (fSBA) and compare the results obtained with the fSBA to the results obtained with a more conventional SBA. The results generated by both assays were dependent upon the surviving bacteria after incubation, and the assay mixtures contained identical components. Differences between assays lie in how the surviving bacteria are quantified. The fSBA described in the paper uses the fluorescent dye alamarBlue (M. V. Lancaster and R. D. Fields, U.S. patent 5501959, March 1996). The fluorescent signals generated in the fSBA correlate to the oxidative respiration of surviving bacteria. Viable bacteria were detected between 6 and 8 h directly from reaction mixtures in 96-well plates by the fSBA, whereas colonies isolated on semisolid media could be counted after 24 h of incubation. The bactericidal titers generated by both assays were nearly identical. The fSBA described here can be used as an assay for the screening of large quantities of individual sera as complement sources or as a method for the detection of functional antibodies directed against group B Neisseria meningitidis in both human and mouse antisera.

Discrepancies between mecA PCR and conventional tests used for detection of methicillin resistant Staphylococcus aureus

Conventional and molecular techniques are being used in the detection of methicillin resistance in Staphylococcus aureus but they do not always show concordant results. In this study, a mecA PCR-based amplification was compared with the 1 microg oxacillin disk diffusion test and the Epsilometer test (E-test) for detection of MICs. Among 31 isolates initially characterized as MRSA by the disk diffusion test, mecA was detected in only 13 (42%) isolates. The E-test showed a wide range of oxacillin MICs (0.5 - > 256 microg/ml) among these 31 MRSA isolates: seven isolates had an MIC of > 256 microg/ml, one had 64 microg/ml, two had 4 microg/ml, two had 3 microg/ml, one had 2.5 microg/ml, nine had 2 microg/ml, three had 1.5 microg/ml, five had 1 microg/ml and one had 0.5 microg/ml. Comparing the mecA PCR results with the E-test oxacillin MIC findings revealed that mecA was detected in seven of eight isolates (87.5%) with an MIC of > or = 64 microg/ml, in three of 14 isolates (21.4%) with an MIC of 2-4 microg/ml and in three of nine isolates (33.3%) with an MIC of < 2 microg/ml. Beta-lactamase production was positive in 28/31 isolates (90.3%). Because of this variation between tests and since several resistance mechanisms are known to mediate methicillin resistance in S. aureus, the reliable detection of MRSA cannot be solely based on detection of mecA gene in S. aureus. At this stage and until new guidelines are introduced by an official body, such as NCCLS, a combination of conventional methods alone or together with a molecular method should be used every time S. aureus is tested for detection of methicillin resistance.

Soft salt-mannitol agar-cloxacillin test: a highly specific bedside screening test for detection of colonization with methicillin-resistant Staphylococcus aureus

The early detection of colonization with methicillin-resistant Staphylococcus aureus (MRSA) of patients in intensive-care units is an essential step in the strategy for preventing MRSA epidemics. In this study, tubes containing soft salt-mannitol agar with cloxacillin (6 microg/ml) (SSMAC) were prepared for inoculation of clinical samples at patients' bedsides by personnel of an intensive-care unit. A total of 1,914 swabs from different sample sites of 81 patients were dipped into SSMAC tubes, and after 24 h of incubation (in an incubator located near the intensive-care unit), an evident color change was considered by the intensive-care-unit personnel to be an MRSA alarm. Sixty-three (3.3%) SSMAC tubes were considered positive for MRSA, 1,827 (95.4%) were considered negative, and 24 (1.2%) were considered intermediate. Compared with values for parallel conventional surveillance cultures for MRSA, excluding tubes with intermediate results, the SSMAC test had a sensitivity of 72.7%, a specificity of 99.2%, a positive predictive value of 76.2%, and a negative predictive value of 99.0%. When intermediate tubes were considered positive, the corresponding values were 75.3, 98.2, 63.2, and 99.0%, respectively. The sensitivity and specificity values of the test to identify MRSA-colonized patients were 89.4 and 100%, respectively. Oropharyngeal and naris specimens were the most reliable samples for MRSA detection. False-negative results were frequent in bronchial aspirates with low (< 10(3) to 10(6) CFU/ml) MRSA counts. False-positive results were mainly due to methicillin-resistant Staphylococcus haemolyticus. The SSMAC tube is a useful, rapid, and inexpensive tool for the early identification of MRSA-colonized patients and, consequently, for the implementation of measures to prevent the spread of MRSA.

Application and evaluation of the alamarBlue assay for cell growth and survival of fibroblasts

Cell proliferation assays are essential to developing an understanding of the molecular mechanisms that modulate cell growth and differentiation. In this paper, we describe the application of alamarBlue, a new and versatile metabolic dye, for the detection of Swiss 3T3 fibroblast proliferation and/or survival. As a redox indicator, alamarBlue is reduced by reactions innate to cellular metabolism and, therefore, provides an indirect measure of viable cell number. Various assay parameters were optimized for a 96-well format to achieve a detectable range of fibroblast cell number from 100 to 20,000 cells/well, which is similar to that obtained with traditional (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) and [3H]thymidine assay techniques. Standard (reference) curves generated with a known fibroblast stimulator were used to facilitate quantitation and comparison of unknown test substances. The alamarBlue assay offers the advantages of technical simplicity, freedom from radioisotopes, versatility in detection, no extraction, and excellent reproducibility and sensitivity. We anticipate that this simple and versatile alamarBlue assay, when used alone or in conjunction with other bioassays, will be a useful tool for investigating the complex mechanisms of cellular proliferation.

The reliability of Microscan conventional and rapid panels to identify Staphylococcus aureus and detect methicillin resistance: an evaluation using the tube coagulase test and mecA PCR

Microscan (Dade Diagnostics, Brisbane) Positive Combo Type 6 (312 panels) and Rapid Positive Breakpoint Type 1 (62 panels) were evaluated for Staphylococcus aureus identification, using the tube coagulase test (TC), and oxacillin susceptibility, using mecA. A total of 374 consecutive clinical staphylococci were tested, with TC and Microscan having 100% correlation (335 identified as S. aureus and 39 as coagulase negative staphylococci by both methods). A 93% correlation was observed between Microscan and mecA PCR for oxacillin susceptibility. No very major errors (0/374 false oxacillin susceptibility) and 26 (7%) major errors (26/374 false oxacillin resistance) were found showing false resistance to oxacillin to be a problem in our population. Oxacillin Etest (AB Biodisk, Sweden) was performed on all oxacillin resistant isolates. A bimodal distribution was observed between mecA positive and negative isolates. A testing algorithm (using the Microscan panels and Etest) was developed for this laboratory to detect mecA encoded methicillin resistance. Retrospective application of this algorithm to the 374 isolates gave 100% correlation with mecA detection.

Methicillin resistance in staphylococci: molecular and biochemical basis and clinical implications

Methicillin resistance in staphylococci is determined by mec, composed of 50 kb or more of DNA found only in methicillin-resistant strains. mec contains mecA, the gene for penicillin-binding protein 2a (PBP 2a); mecI and mecR1, regulatory genes controlling mecA expression; and numerous other elements and resistance determinants. A distinctive feature of methicillin resistance is its heterogeneous expression. Borderline resistance, a low-level type of resistance to methicillin exhibited by strains lacking mecA, is associated with modifications in native PBPs, beta-lactamase hyperproduction, or possibly a methicillinase. The resistance phenotype is influenced by numerous factors, including mec and beta-lactamase (bla) regulatory elements, fem factors, and yet to be identified chromosomal loci. The heterogeneous nature of methicillin resistance confounds susceptibility testing. Methodologies based on the detection of mecA are the most accurate. Vancomycin is the drug of choice for treatment of infection caused by methicillin-resistant strains. PBP 2a confers cross-resistance to most currently available beta-lactam antibiotics. Investigational agents that bind PBP 2a at low concentrations appear promising but have not been tested in humans. Alternatives to vancomycin are few due to the multiple drug resistances typical of methicillin-resistant staphylococci.

Evaluation of bacterial survival and phagocyte function with a fluorescence-based microplate assay

To compare antibacterial function in macrophages from mice deficient in the respiratory burst oxidase or inducible nitric oxide synthase, we developed a fluorescence-based microplate assay of bacterial survival. As bacteria grow, they convert a formulation of resazurin termed AlamarBlue from its nonfluorescent oxidized state to its fluorescent reduced state. The time required to achieve a given fluorescence is inversely proportional to the number of viable bacteria present when the dye is added. This relationship allows a precise, accurate assessment of bacterial numbers with greater sensitivity and throughput and at less cost than conventional assays. The assay facilitated quantification of the killing of Escherichia coli by S-nitrosoglutathione and hydrogen peroxide and of Salmonella typhimurium by human neutrophils and mouse macrophages. Mouse macrophages lacking the 91-kDa subunit of the respiratory burst oxidase were deficient in their ability to kill S. typhimurium, while those lacking inducible nitric oxide synthase were unimpaired.

Microplate alamar blue assay versus BACTEC 460 system for high-throughput screening of compounds against Mycobacterium tuberculosis and Mycobacterium avium

In response to the need for rapid, inexpensive, high-throughput assays for antimycobacterial drug screening, a microplate-based assay which uses Alamar blue reagent for determination of growth was evaluated. MICs of 30 antimicrobial agents against Mycobacterium tuberculosis H37Rv, M. tuberculosis H37Ra, and Mycobacterium avium were determined in the microplate Alamar blue assay (MABA) with both visual and fluorometric readings and compared to MICs determined in the BACTEC 460 system. For all three mycobacterial strains, there was < or = 1 dilution difference between MABA and BACTEC median MICs in four replicate experiments for 25 to 27 of the 30 antimicrobics. Significant differences between MABA and BACTEC MICs were observed with 0, 2, and 5 of 30 antimicrobial agents against H37Rv, H37Ra, and M. avium, respectively. Overall, MICs determined either visually or fluorometrically in MABA were highly correlated with those determined in the BACTEC 460 system, and visual MABA and fluorometric MABA MICs were highly correlated. MICs of rifampin, rifabutin, minocycline, and clarithromycin were consistently lower for H37Ra compared to H37Rv in all assays but were similar for most other drugs. M. tuberculosis H37Ra may be a suitable surrogate for the more virulent H37Rv strain in primary screening of compounds for antituberculosis activity. MABA is sensitive, rapid, inexpensive, and nonradiometric and offers the potential for screening, with or without analytical instrumentation, large numbers of antimicrobial compounds against slow-growing mycobacteria.

Rapid screening of natural products for antimycobacterial activity by using luciferase-expressing strains of Mycobacterium bovis BCG and Mycobacterium intracellulare

The object of this study was to investigate the ability of a rapid luciferase assay to detect antimycobacterial activity in plant extracts. Recombinant strains of Mycobacterium bovis BCG (rBCG) and Mycobacterium intracellulare expressing firefly luciferase were used as the test organisms. Assays were conducted in a 96-well minitube format under biosafety level 2 conditions. Control and test wells were sampled immediately after inoculation and after 3 (recombinant M. intracellulare) and 5 (rBCG) days of incubation to measure luminescence with a microplate luminometer, and the relative change in luminescence was calculated as a percentage of control values. As an alternative test method, Alamar blue was added after 12 days of incubation, and changes in color were read visually. A total of 480 extracts were tested. Sixteen extracts were active against rBCG, and of those, seven were also active against recombinant M. intracellulare. With activity defined as a relative change in luminescence of < or = 1% (i.e., > or = 99% inhibition) and a persistence of blue color after addition of Alamar blue, there was 99.0% agreement between the two methods. Our results suggest that the luciferase assay is rapid and accurate and has the potential to greatly accelerate the evaluation of antimycobacterial activity in plant extracts in vitro. With this method, it is possible to screen a large number of samples in a short period of time.

A new fluorometric assay for determination of osteoblastic proliferation: effects of glucocorticoids and insulin-like growth factor-I

A novel fluorometric proliferation assay, AlamarBlue (AB), was used to study the proliferative capacity of isolated human osteoblasts (hOBs). AB is an oxidation-reduction indicator that yields a fluorescent signal in response to metabolic activity. The assay was performed by replacing the experiment media in a microtiter plate with a 10% AB solution and measuring fluorescence after a 3-8-hour incubation. The assay was optimized with respect to incubation time, cell density, and AB concentration. When the results of the AB assay were compared with cell counting in a Bürker chamber there were consistently good correlations (r > 0.9), regardless of the agonist with which the cells were treated. The mean intraassay coefficient of variance (CV) values were 9.9-11.8% in experiments where osteoblasts were treated for 12 days with insulin-like growth factor-I (IGF-I; 100 nM), or dexamethasone (1 micro;M). IGF-I dose dependently, at and above 1 nM, stimulated proliferation of hOBs. This effect was detectable after 3 days and reached 130-140% of untreated controls after 12 days in culture. The effects of dexamethasone (DEX) on the proliferation rate of hOBs were more complex. In short-term cultures, 3 days, DEX dose dependently stimulated proliferation. However, at and above 6 days, DEX exerted a biphasic effect, with stimulation seen at 1-10 nM and a marked inhibition of cell proliferation at and above 100 nM. dexamethasone, hydrocortisone, prednisolone, and deflazacort had almost identical biphasic effects on osteoblastic proliferation in 12 day cultures with a stimulation seen at 1-10 nM, and a marked inhibition down to 50-60% of untreated controls at and above 100 nM. When IGF-I (0. 1-100 nM; 12 day culture) was combined with different doses of DEX, IGF-I still dose dependently stimulated the proliferation rate in hOBs regardless of the amount of DEX added. The stimulatory effect of DEX (10 nM, 12 days culture) was additive to the effect of 100 nM IGF-I. We conclude that AB is an easy and reliable assay for osteoblastic cell proliferation, well suited for large scale studies of cell growth using small amounts of cells, and that IGF-I partly reverses the glucocorticoid-induced inhibition of osteoblastic proliferation.

Comparison of efficacy and cost-effectiveness of BIOMIC VIDEO and Vitek antimicrobial susceptibility test systems for use in the clinical microbiology laboratory

Antimicrobial susceptibility testing expense may be a significant portion of a clinical microbiology laboratory's budget. This study compares the BIOMIC VIDEO system (Giles Scientific, Inc., New York, N.Y.) with the Vitek system (bioMérieux Vitek, Inc., Hazelwood, Mo.), an established automated method of antimicrobial susceptibility testing with the ability to generate MIC data. The BIOMIC system is relatively inexpensive and automates the reading of the classical disk agar diffusion test to provide both qualitative (susceptibility interpretation) and quantitative (MIC) data. The overall MIC correlation between the two systems for the 2,913 drug-organism combinations tested was 92.6%. The overall agreement for susceptibility interpretation was 97.4%. The BIOMIC system offers a 57.4% savings per test over the Vitek system. The BIOMIC system utilizes an older technology which is more efficient and yet yields results comparable to those of established automated MIC methods. The savings achievable in laboratories and hospitals nationwide may contribute significantly to the containment of national health care expenditures.

Detection of oxacillin-resistance in Staphylococcus aureus by MicroScan MIC panels in comparison to four other methods

Two hundred fifty-two isolates of Staphylococcus aureus were tested for oxacillin susceptibility by MicroScan Gram positive overnight and rapid MIC panels. Results were compared with nonautomated methods including disk diffusion, MRSA Crystal ID, and Etests using MRSA Screen Agar as reference. One hundred sixty-nine isolates (67.1%) were oxacillin-susceptible and 83 (32.9%) were resistant. All methods agreed for 234 (92.9%) isolates. Very major error rates were 1.2% for disk diffusion, 3.6% for Etest, and 0 for all other methods. Major error rates were 5.3% for MicroScan overnight panels, 3% for rapid panels, 2.4% for disk diffusion, 1.2% for Etest, and 0.6% for MRSA Crystal ID. Nine oxacillin-susceptible isolates with borderline MICs and discrepant results for 1 or more methods were tested for the mec A gene and all were negative. Each was susceptible to beta lactam/beta lactamase inhibitor combinations, suggesting that false resistance may have been due to excessive beta lactamase production. Oxacillin-resistant S. aureus with borderline MICs determined by MicroScan should be confirmed by an alternate method. The most practical and cost-effective means among those we tested is the MRSA Screen Agar.