Antimicrobial susceptibility testing of vancomycin-resistant Enterococcus by the VITEK 2 system, and comparison with two NCCLS reference methods

Antibiotic Susceptibility Patterns and Virulence-Associated Factors of Vancomycin-Resistant Enterococcal Isolates from Tertiary Care Hospitals

This study explored the prevalence of multi-drug resistance and virulence factors of enterococcal isolates obtained from various clinical specimens (n = 1575) including urine, blood, pus, tissue, catheter, vaginal wash, semen, and endotracheal secretions. Out of 862 enterococcal isolates, 388 (45%), 246 (29%), 120 (14%), and 108 (13%) were identified as Enterococcus faecalis, Enterococcus faecium, Enterococcus durans, and Enterococcus hirae, respectively, using standard morphological and biochemical methods. The antibiotic resistance profile of all these enterococcal isolates was checked using the disc diffusion technique. High-level resistance was observed for benzylpenicillin (70%) and vancomycin (43%) among E. faecalis and E. faecium isolates, respectively. This study also revealed the prevalence of 'multi-drug resistance (resistant to 3 antibiotic groups)' among the vancomycin-resistant enterococcal strains, and this was about 11% (n = 91). The virulence determinants associated with vancomycin resistance (VR) were determined phenotypically and genotypically. About 70 and 39% of E. faecalis and E. faecium isolates showed to be positive for all four virulence factors (gelatinase, protease, hemolysin, and biofilm). Among the several virulence genes, gelE was the most common virulence gene with a prevalence rate of 76 and 69% among E. faecalis and E. faecium isolates, respectively. More than 50% of VRE isolates harbored other virulence genes, such esp, asa, ace, and cylA. Similarly, the majority of the VR enterococcal isolates (n = 88/91) harbored vanA gene and none of them harbored vanB gene. These results disclose the importance of VR E. faecalis and E. faecium and the associated virulence factors involved in the persistence of infections in clinical settings.

An automated and portable antimicrobial susceptibility testing system for urinary tract infections

Urinary tract infections (UTIs) are bacterial infections that 1) commonly affect females, 2) can pose high risks to impair kidney function, 3) are often treated with broad-spectrum antibiotics, and 4) are associated with high recurrence rates due to the evolution of drug-resistant strains. To choose the appropriate antibiotic, the minimum inhibitory concentration (MIC) among a panel of antibiotics should be determined before administration to avoid inadequate dosing or use of wrong antibiotics. To meet with the unmet needs, we developed a bead-based method for bacterial preconcentration with capture rates ranging from 20-50% and then automatically performed on-chip AST on an automated device which was composed of a pneumatic control module, a temperature control module and a chip image processing module. The developed portable system was capable of automatically conducting AST and MIC measurements using urine samples (via image analysis) in only 4.5-9 h and tested on four common UTIs bacterial strains. This compact system may therefore be promising for point-of-care personalized medicine in the near future.

Characterization of Clinical Isolates of Enterococci with Special Reference to Glycopeptide Susceptibility at a Tertiary Care Center of Eastern Nepal

Background

Enterococci, once considered as a harmless commensal of intestine, have now emerged as medically important pathogens and are associated with both community-acquired and nosocomial infections. They bear the potential to exhibit resistance against all commonly used antibiotics either by inherent or acquired mechanism, posing a therapeutic challenge.

Objectives

This study aimed to characterize enterococci up to the species level and study their antibiogram with special regard to vancomycin.

Methods

A descriptive cross-sectional study was conducted in the Department of Microbiology, B.P. Koirala Institute of Health Sciences, Dharan, Nepal, from February to May 2017. A total of 91 enterococcal isolates recovered from clinical specimens were investigated in this study. Their identification and speciation were done according to standard microbiological guidelines. Kirby–Bauer disc diffusion technique was used to study antimicrobial susceptibility pattern, whereas minimum inhibitory concentration of vancomycin was determined by the agar dilution method, with reference to Clinical and Laboratory Standards Institute guidelines.

Results

Seven different species of enterococci were isolated, E. faecalis and E. faecium accounting about 45% each. The other species encountered were E. avium, E. cecorum, E. dispar, E. durans, and E.

Conclusions

Enterococcus faecalis and E. faecium were the predominant species in causing enterococcal infections. The alarming rise in prevalence of vancomycin and multidrug resistance strains warrants immediate, adequate, and efficient surveillance program to prevent and control its spread.

On-chip spectroscopic assessment of microbial susceptibility to antibiotics within 3.5 hours

In times of rising antibiotic resistances, there is a high need for fast, sensitive and specific methods to determine antibiotic susceptibilities of bacterial pathogens. Here, we present an integrated microfluidic device in which bacteria from diluted suspensions are captured in well-defined regions using on-chip dielectrophoresis and further analyzed in a label-free and non-destructive manner using Raman spectroscopy. Minimal sample preparation and automated sample processing ensure safe handling of infectious material with minimal hands-on time for the operator. Clinical applicability of the presented device is demonstrated by antibiotic susceptibility testing of Escherichia coli towards the commonly prescribed second generation fluoroquinolone ciprofloxacin. Ciprofloxacin resistant E. coli were differentiated from sensitive E. coli with high accuracy within roughly three hours total analysis time paving the way for future point-of-care devices. Spectral changes leading to the discrimination between sensitive and resistant bacteria are in excellent agreement with expected metabolic changes in the bacteria due to the mode of action of the drug. The robustness of the method was confirmed with experiments involving different chip devices with different designs, both electrode as well as microfluidics design, and material. Furthermore, general applicability was demonstrated with different operators over an extended time period of half a year.

Sources of systematic errors in the epidemiology of vancomycin-resistant enterococci

PURPOSE

The rates of vancomycin resistance among enterococci (VRE) have been increasing worldwide. However, reports on vancomycin-resistant enterococci (VRE) are easily biased and meta-data reporting is insufficient. Additionally, no standardised protocol for VRE testing currently exists. The aim of our study was to investigate, for the first time, the impact of introduced bias in VRE reports. We also analysed the sensitivity of our in-house screening test for VRE, namely, a broth-enriched PCR assay.

METHODS

Retrospective review of microbial and clinical data on all patients tested for VRE who had been admitted to a large university hospital over a 5-year period and an analysis of the possible impact of introduced bias. Our screening test was also evaluated using clinical isolates.

RESULTS

A total of 27,636 screening tests were carried out over the 5-year study period, of which 2,459 were VRE-positive. The number of screening tests increased dramatically over the study period, with 1,053 tests carried out on 435 patients in 2006 and 9,444 tests carried out on 5,104 patients in 2010. VRE prevalence was 8.1 % over the 5-year period. The introduction of measurement bias caused a clear overestimation of absolute VRE numbers. The sensitivity of our screening test was 95.5 % with a positive predictive value of 39 %.

CONCLUSION

Biased reports lead to the implementation of high-cost containment measures that may be both unnecessary and detrimental to the patient. Our data show that systematic errors in VRE reports caused a clear overestimation of absolute VRE numbers, thereby indicating an outbreak situation even though the actual prevalence of VRE was decreasing. We suggest that reports of VRE must take measurement and analysis biases into account, otherwise any conclusion drawn is unreliable and inconclusive.

Expert systems in clinical microbiology

This review aims to discuss expert systems in general and how they may be used in medicine as a whole and clinical microbiology in particular (with the aid of interpretive reading). It considers rule-based systems, pattern-based systems, and data mining and introduces neural nets. A variety of noncommercial systems is described, and the central role played by the EUCAST is stressed. The need for expert rules in the environment of reset EUCAST breakpoints is also questioned. Commercial automated systems with on-board expert systems are considered, with emphasis being placed on the "big three": Vitek 2, BD Phoenix, and MicroScan. By necessity and in places, the review becomes a general review of automated system performances for the detection of specific resistance mechanisms rather than focusing solely on expert systems. Published performance evaluations of each system are drawn together and commented on critically.

Comparison of the VITEK 2 system with the E-test for the determination of glycopeptide susceptibility of vanA and vanC positive enterococci

The performance of the VITEK 2 System (bioMérieux) version 3.01 software was compared to that of the E-test (AB Biodisk, Solna, Sweden) for antibiotic susceptibility testing of 17 clinical isolates of vancomycin resistant enterococcus (VRE). Antibiotic Susceptibility Testing (AST) by VITEK 2 produced 10 minor (59%) errors, resulting in false phenotypes. Reporting of vancomycin resistance in enterococcal strains has enormous therapeutic and epidemiological consequences. Therefore, at laboratories using automated systems (e.g. VITEK 2) for routine microbiological susceptibility testing data must be confirmed by independent validated methods, e.g. E-test, or microdilution.

Analysis of methods commonly used for glycopeptide and oxazolidinone susceptibility testing in Enterococcus faecium isolates

The susceptibility to teicoplanin, vancomycin and linezolid of 30 clinical isolates of Enterococcus faecium was tested by Vitek 2, Phoenix, Etest, broth microdilution and disc diffusion tests. The vanA and vanB resistance genes and the 23S rRNA gene G2576T mutation were detected by PCR and PCR-RFLP, respectively. Resistance rates to teicoplanin ranged from 3 % for Vitek 2 to 57.6 % for the Phoenix test, and those to vancomycin ranged from 56.7 % for Vitek 2 to 86.7 % for the Phoenix test. Only two out of 25 strains carrying the vanA gene were univocally recognized as the VanA phenotype. The only strain with the G2576T mutation did not carry the vanA gene and showed resistance to linezolid by the disc diffusion, Vitek 2 and broth dilution methods (MIC >8 μg ml−1), but was susceptible when tested with the Phoenix test and Etest (MIC ≤4 μg ml−1). Therefore, the resistance to glycopeptides and linezolid was not univocally detected by the susceptibility testing methods used in this study.

Identification, antimicrobial resistance and genotypic characterization of Enterococcus spp. isolated in Porto Alegre, Brazil

In the past two decades the members of the genus Enterococcus have emerged as important nosocomial pathogens worldwide. In the present study, we evaluated the antimicrobial resistance and genotypic characteristics of 203 Enterococcus spp. recovered from different clinical sources from two hospitals in Porto Alegre, Rio Grande do Sul, Brazil. The species were identified by conventional biochemical tests and by an automated system. The genetic diversity of E. faecalis presenting high-level aminoglycoside resistance (HLAR) was assessed by pulsed-field gel electrophoresis of chromosomal DNA after SmaI digestion. The E. faecalis was the most frequent specie (93.6%), followed by E. faecium (4.4%). The antimicrobial resistance profile was: 2.5% to ampicillin, 0.5% to vancomycin, 0.5% teicoplanin, 33% to chloramphenicol, 2% to nitrofurantoin, 66.1% to erythromycin, 66.5% to tetracycline, 24.6% to rifampicin, 30% to ciprofloxacin and 87.2% to quinupristin-dalfopristin. A total of 10.3% of the isolates proved to be HLAR to both gentamicin and streptomycin (HLR-ST/GE), with 23.6% resistant only to gentamicin (HLR-GE) and 37.4% only to streptomycin (HLR-ST). One predominant clonal group was found among E. faecalis HLR-GE/ST. The prevalence of resistance among beta-lactam antibiotics and glycopeptides was very low. However, in this study there was an increased number of HLR Enterococcus which may be spreading intra and inter-hospital.

Validation of VITEK 2 version 4.01 software for detection, identification, and classification of glycopeptide-resistant enterococci

We evaluated the ability of the new VITEK 2 version 4.01 software to identify and detect glycopeptide-resistant enterococci compared to that of the reference broth microdilution method and to classify them into the vanA, vanB, vanC1, and vanC2 genotypes. Moreover, the accuracy of antimicrobial susceptibility testing with agents with improved potencies against glycopeptide-resistant enterococci was determined. A total of 121 enterococci were investigated. The new VITEK 2 software was able to identify 114 (94.2%) enterococcal strains correctly to the species level and to classify 119 (98.3%) enterococci correctly to the glycopeptide resistance genotype level. One Enterococcus casseliflavus strain and six Enterococcus faecium vanA strains with low-level resistance to vancomycin were identified with low discrimination, requiring additional tests. One of the vanA strains was misclassified as the vanB type, and one glycopeptide-susceptible E. facium wild type was misclassified as the vanA type. The overall essential agreements for antimicrobial susceptibility testing results were 94.2% for vancomycin, 95.9% for teicoplanin, 100% for quinupristin-dalfopristin and moxifloxacin, and 97.5% for linezolid. The rates of minor errors were 9% for teicoplanin and 5% for the other antibiotic agents. The identification and susceptibility data were produced within 4 h to 6 h 30 min and 8 h 15 min to 12 h 15 min. In conclusion, use of VITEK 2 version 4.01 software appears to be a reliable method for the identification and detection of glycopeptide-resistant enterococci as well as an improvement over the use of the former VITEK 2 database. However, a significant reduction in the detection time would be desirable.