Evaluation of a novel automated chemiluminescent assay system for antimicrobial susceptibility testing

Nasopharyngeal Streptococcus pneumoniae carriage in Japanese children attending day-care centers

OBJECTIVES

We conducted a prospective bacteriological survey to investigate antibiotic resistance-related genetic characteristics and the turnover of nasopharyngeal Streptococcus pneumoniae carriage in healthy children in day-care centers (DCCs).

METHODS

A total of 363 nasopharyngeal mucus samples were collected from children aged 0 to 6 years attending two DCCs in the summer of 2004 (n=181) and the following winter (n=182). We obtained 157 S. pneumoniae isolates and analyzed them by antibiotic susceptibility testing, PCR assay for the penicillin-binding protein (PBP) genes and macrolide-resistance gene, and pulsed-field gel electrophoresis (PFGE).

RESULTS

The overall carriage rate was 43.3% (157/363). The percentages of penicillin-intermediately resistant S. pneumoniae (PISP) strains, penicillin-resistant S. pneumoniae (PRSP) strains, erythromycin-intermediately resistant S. pneumoniae strains and erythromycin-resistant S. pneumoniae strains were 35.7% (56/157), 0.6% (1/157), 1.9% (3/157), and 69.4% (109/157), respectively. The percentages of S. pneumoniae strains with the pbp mutation(s) and mefA and/or ermB gene(s) were 92.4% (145/157) and 71.3% (112/157), respectively. Fifty strains with different PFGE patterns were obtained from among the 157 isolates. Thirteen strains were observed in both seasons, but only one of these strains was isolated from the same carrier. Twenty-one strains (42.0%) were isolated from two or more children, and 17 of these were each isolated from children attending the same DCC.

CONCLUSIONS

These results indicate the spread of S. pneumoniae, particularly those with antibiotic-resistance genes, and the vigorous genetic turnover and substantial horizontal transmission of this pathogen in healthy children attending DCCs in Japan.

A comparison of three rapid and accurate bioluminescent antibiotic susceptibility tests

INTRODUCTION

Rapid determination of microorganisms' antibiotic susceptibility remains a great challenge for the clinical diagnosis of infectious diseases. In this study, we compare three rapid bioluminescent antibiotic susceptibility tests with the conventional normalised microdilution method.

METHODS

The susceptibility of two bacterial and two fungal strains to a 6h incubation with one of eight standard antibiotics was investigated by the ATP, AK and QNO bioluminescent methods.

RESULTS

Three rapid and accurate antibiotic susceptibility testing were investigated performing ATP, AK and QNO bioluminescent assays. All the results were in accordance with those obtained using a standard microdilution assay. All these methods were sensitive and faster than the previously well-known ones.

DISCUSSION

The development of bioluminescent determination methods could lead to accurate and useful antibiotic susceptibility testing.

Rapid method for detection of minimal bactericidal concentration of antibiotics

We developed a test for rapid determination of the minimal bactericidal concentration (MBC) of antibiotics. MBC is determined by calculating the relative proportion of live and dead bacteria by means of two fluorescence dyes: Syto 9 (which detects only live bacteria) and Propidium iodide (which labels live and dead bacteria). Testing was performed in micro-titer plates. Determination of bacterial viability was performed after exposure to antibiotics for 4 h. Reference strains and clinical isolates of Escherichia coli and Pseudomonas aeruginosa were tested. Fluorescence-based determination (MBC/F) and reference methods (MBC/L) were comparable (+/-1 Dilution step), except for E. coli with piperacillin and cefotaxime, which differed up to two steps. Bactericidal activity against E. coli/P. aeruginosa was observed: Meropenem (100%/100%), gentamicin (100%/9.3%), ciprofloxacin (93.3%/86.7%), cefotaxime (E. coli only: 86.7%) ceftazidime (P. aeruginosa only: 80%), piperacillin (56.6%/76.7%). The calculation of MBC has been achieved by graphical extrapolation and mathematical approximation method.

Nasopharyngeal Haemophilus influenzae carriage in Japanese children attending day-care centers

We conducted a prospective bacteriological survey to investigate antibiotic resistance-related genetic characteristics and the turnover of nasopharyngeal Haemophilus influenzae carriage in healthy children in day-care centers (DCCs). A total of 363 nasopharyngeal mucus samples were collected from children aged 0 to 6 years attending two DCCs in the summer of 2004 (n = 184) and the following winter (n = 179). We obtained 172 H. influenzae isolates and analyzed them by antimicrobial susceptibility testing, PCR for bla(TEM-1) and the penicillin-binding protein (PBP) gene, and pulsed-field gel electrophoresis (PFGE). The overall carriage rate was 47.4% (172/363), and 37.2% of the isolates (64/172) were ampicillin (AMP) resistant. All the resistant isolates had a PBP mutation(s), while only three isolates had TEM-1. The carriage rate was significantly higher in the winter than in the summer (56.4% and 38.6%, respectively), owing to the increase in the numbers of AMP-susceptible H. influenzae isolates in the winter. Children aged < or = 3 years showed a higher rate of carriage of H. influenzae isolates with an AMP resistance gene(s) than those aged > or = 4 years (21.9% and 12.6%, respectively). Forty-two strains with different PFGE patterns were obtained from among the 172 isolates. Only five strains were observed in both seasons. None of the strains isolated in the summer was isolated from the same carrier in the winter. Twenty-seven strains (64.3%) were isolated from two or more children, and 25 of these were each isolated from children belonging to the same DCC. These results indicate the spread of H. influenzae, particularly those with a PBP mutation(s), and the highly vigorous genetic turnover and substantial horizontal transmission of this pathogen in healthy children attending DCCs in Japan.

Rapid detection of Staphylococcus aureus strains having reduced susceptibility to vancomycin using a chemiluminescence-based drug-susceptibility test

Current drug-susceptibility tests used routinely in clinical laboratories sometimes fail to identify strains of Staphylococcus aureus with reduced susceptibility to vancomycin. To solve this problem, we have developed a more sensitive and rapid method that measures bacterial metabolic activity by a chemiluminescence-based technique. This method is able to discriminate such strains from vancomycin-susceptible S. aureus with a sensitivity and specificity of > 95%. This rapid and reliable method appears to be promising for detection of vancomycin-intermediate S. aureus strains in clinical laboratories, and may supersede classical susceptibility testing.

[Obtention of bacterial antibiotic susceptibility following standard conditions directly from infected biological fluids and positive blood cultures]

OBJECTIVE

Determining the conditions, which would allow us to apply bacterial antibiotic susceptibility tests directly to infected biological fluids and positive blood cultures and in accordance with the standard conditions of these tests.

METHODS

For infected fluids (N=23), a correlation was determined between the bacterial count observed by microscopic field on a cystopin centrifugation pellet and the dilution required to obtain bacterial inocula corresponding to those used in the standard antibiogram and E-test methods. For blood cultures detected positive with the BactALERT system (26 Enterobacteriaceae, 29 Staphylococcus and 11 Pneumococcus), the broth dilution required to obtain such inocula was determined for each bacterial type.

RESULTS

For infected fluids, the dilution required for the antibiogram of enterobacterial and staphylococcal isolates was respectively of 10(-1) and 10(0) when there were 50 to 100 bacteria/field, 10(-2) and 10(-1) for 100 to 500, 10(-3) and 10(-2) for 500 to 1000, and 10(-4) and 10(-3) for>1000. A minimum of 50 to 100 bacteria/field was required to determine beta-lactam MICs towards a pneumococcal isolate present in cerebrospinal fluid. For blood cultures, a broth dilution of 10(-4) for Enterobacteriaceae and of 10(-2) for Staphylococcus and Pneumococcus allowed to reproduce the standard antibiogram. To reproduce the standard conditions of the E-test method for beta-lactam MICs towards a pneumococcal isolate, the broth dilution was 10(-1).

CONCLUSION

Following the procedure described, antibiotic susceptibility can be available 24 h earlier.

Menadione-catalyzed luminol chemiluminescence assay for the rapid detection of viable bacteria in foods under aerobic conditions

A menadione-catalyzed luminol chemiluminescence assay was developed for the rapid detection and estimation of viable bacteria in foods. The principle of this assay is based on the extracellular menadione-catalyzed active oxygen spieces (O2- and H2O2) generated by the activity of NAD(P)H:menadione oxidoreductase in viable cells. This luminol chemiluminescence assay requires 10 min for the incubation of cells with menadione and then 2 s for the measurement of chemiluminescence intensity after an injection of luminol solution without the treatment of cell lysis. This method was evaluated using liquid food samples of milk, vegetable juice, green tea, and coffee spiked with Escherichia coli ATCC 25922. The study result revealed that E. coli contamination at 1 to 10 CFU/ml in these foods could be detected after incubation at 37 degrees C for 7 h in an enrichment medium; however, the green tea and coffee samples requires filtration. This method could be a useful tool for the rapid evaluation of microbial food contamination.

A rapid antimicrobial susceptibility test based on chemiluminescence assay and its application to screening of genotypes in vancomycin-resistant enterococci

Minimum inhibitory concentrations (MICs) of vancomycin (VCM) and teicoplanin (TEIC) were measured using a novel susceptibility test based on the chemiluminescence assay (CA) method (Rapid-Lumi Eiken; Eiken Chemicals, Tokyo, Japan) against 33 strains in total: 7, 5, and 10 strains of which are VCM-resistant enterococci (VRE) with vanA, vanB, and vanC genes, respectively, and the other 11 strains are vancomycin-susceptible enterococci (VSE). The results were in good accordance with the values determined by the standard broth dilution method approved by the National Committee for Clinical Laboratory Standards (NCCLS): i.e., 88% (29/33) of consistency for VCM and 97% (32/33) for TEIC, respectively. In addition, genotypes in VRE strains (vanA, vanB, vanC-1, and vanC-2/3 genes) were properly estimated from the results of the CA method and the NCCLS interpretive categories, even though the incubation time was very short (2-4 h). In conclusion, it was found that the new method is reliable and rapid to detect VRE strains in clinical laboratories.