Clinical and Microbiological Characteristics of Hospital-Acquired Methicillin-Resistant Staphylococcus aureus Bacteremia Caused by Community-Associated PVL-Negative Strain

Background ST72-SCCmecIV, a community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) strain in Korea, originated in the community and has been spreading in the healthcare settings. Herein, we describe the clinical and microbiological characteristics of patients with hospital-acquired MRSA bacteremia (MRSAB) caused by community-associated strains. Methods We analyzed hospital-acquired MRSAB cases caused by ST72-SCCmecIV using a prospective cohort of patients with SAB at in a tertiary hospital in Korea from July 2008 to December 2018. We compared the clinical and microbiological characteristics of ST72-SCCmecIV with ST5-SCCmecII, a representative hospital-associated genotype strain. Results Of the 1782 S. aureus bacteremia (SAB) cases, 628 (35.2%) were hospital-acquired MRSAB. Of the 628 isolates, 431 (68.6%) were ST5-SCCmecII and 152 (24.2%) were ST72-SCCmecIV. Patients with ST72-SCCmecIV were younger than those with ST5-SCCmecII and less likely to have a history of recent surgery, antibiotic treatment, nasal MRSA colonization, and central venous catheter placement. Compared with ST5-SCCmecII, ST72-SCCmecIV isolates were more likely to have vancomycin MICs ≤ 1.0 mg/L (P < 0.001). Osteoarticular infection as site of infection [7.2% (11/152) vs. 1.4% (6/431)] was more common in patients with ST72-SCCmecIV. There were no significant differences in the rate of recurrence (≤ 90 days), persistent bacteremia (≥ 7 days), and 30- and 90-day mortality rates between the two groups. Conclusions Osteoarticular infections were more prevalent in ST72-SCCmecIV MRSAB. Mortality rates between the ST72-SCCmecIV and ST5-SCCmecII groups were not significantly different.

Effect of genetic background on the evolution of Vancomycin-Intermediate Staphylococcus aureus (VISA)

Vancomycin-intermediate Staphylococcus aureus (VISA) typically arises through accumulation of chromosomal mutations that alter cell-wall thickness and global regulatory pathways. Genome-based prediction of VISA requires understanding whether strain background influences patterns of mutation that lead to resistance. We used an iterative method to experimentally evolve three important methicillin-resistant S. aureus (MRSA) strain backgrounds—(CC1, CC5 and CC8 (USA300)) to generate a library of 120 laboratory selected VISA isolates. At the endpoint, isolates had vancomycin MICs ranging from 4 to 10 μg/mL. We detected mutations in more than 150 genes, but only six genes (already known to be associated with VISA from prior studies) were mutated in all three background strains (walK, prs, rpoB, rpoC, vraS, yvqF). We found evidence of interactions between loci (e.g., vraS and yvqF mutants were significantly negatively correlated) and rpoB, rpoC, vraS and yvqF were more frequently mutated in one of the backgrounds. Increasing vancomycin resistance was correlated with lower maximal growth rates (a proxy for fitness) regardless of background. However, CC5 VISA isolates had higher MICs with fewer rounds of selection and had lower fitness costs than the CC8 VISA isolates. Using multivariable regression, we found that genes differed in their contribution to overall MIC depending on the background. Overall, these results demonstrated that VISA evolved through mutations in a similar set of loci in all backgrounds, but the effect of mutation in common genes differed with regard to fitness and contribution to resistance in different strains.

Comparative evaluation of the Phoenix®, VITEK® 2, E-test® and microdilution test for vancomycin susceptibility testing in Staphylococcus aureus isolated from bloodstream infection

Introduction: Staphylococcus aureus bacteremia causes significant morbidity and mortality, mainly by methicillin-resistant S. aureus (MRSA). Currently, vancomycin is the main choice for the treatment of infections by MRSA. Broth microdilution (BMD) remains the gold standard for measuring vancomycin MIC. However, most clinical laboratories employ practical methods in the routines, but these methods may not determine accurate vancomycin MIC values. Objectives: This study aimed to evaluate the accuracy of VITEK®2, Phoenix® and Etest® methods against BMD. Materials and Methods: A total of 78 strains (27 methicillin-sensitive S. aureus and 51 MRSA) were isolated from bloodstream infections. The vancomycin MIC was determined following CLSI and the manufacturers' recommendations. We also performed SCCmec typing, in order to identify their vancomycin MIC ratio values. Results: Most of all isolates showed values of MIC = 1 μg/mL by BMD and Phoenix®, while Etest® and VITEK® 2 determined the majority with MIC = 1.5 and 0.5 μg/mL, respectively. Thus, Etest® and VITEK® 2 tended to overestimate and underestimate, respectively, the MIC values. Three MRSA isolates that were vancomycin susceptible by the BMD were vancomycin-intermediate by Etest®. The SCCmec II (39%) and IV (51%) were the most frequent, and there was no relationship between the type of SCCmec and the MIC values. Conclusions: The results showed that vancomycin MICs vary according to the test method. It is essential that clinicians consider the differences in MIC results determined by different methods, since the MIC value is generally the parameter used by clinicians to select the appropriate therapy.

Failure of Vitek2 to reliably detect vanB-mediated vancomycin resistance in Enterococcus faecium

Objectives The increasing prevalence of VRE necessitates their reliable detection, especially for low-level resistance mediated by vanB in Enterococcus faecium. In this prospective study we analysed if vanB-mediated vancomycin resistance can be reliably detected by Vitek2. Methods One thousand, three hundred and forty-four enterococcal isolates from routine clinical specimens were tested by Vitek2 (bioMérieux, Nürtingen, Germany). Additionally, a bacterial suspension (with a turbidity equivalent to that of a 0.5 McFarland standard) was inoculated on chromID VRE screening agar (bioMérieux) and incubated for 48 h. If vancomycin tested susceptible by Vitek2 but growth was detected on the screening agar, PCR for vanA/vanB was performed (GeneXpert vanA/B test, Cepheid, Frankfurt, Germany). For isolates that tested susceptible to vancomycin by Vitek2 but were vanA/B positive, MICs were determined before and after cultivation in broth with increasing concentrations of vancomycin. Results One hundred and fifty-six out of 491 E. faecium were VRE and were predominantly vanB positive (81.0%). Of these, Vitek2 did not identify 14 as VRE (sensitivity 91.0%). By broth microdilution 9/14 isolates demonstrated high MICs (≥32 mg/L) and 5/14 showed low vancomycin MICs, which did not increase despite vancomycin exposure. Three of the 14 isolates demonstrated growth on chromID VRE; after vancomycin exposure seven additional isolates were able to grow on chromID VRE. Conclusions Vitek2 fails to detect vanB-mediated vancomycin resistance consistently, especially, but not limited to, low-level resistance. As this may lead to treatment failure and further dissemination of vanB VRE, additional methods (e.g. culture on VRE screening agar or PCR) are necessary to reliably identify vanB-positive enterococci in clinical routine.

Effect of the vancomycin minimum inhibitory concentration on clinical outcomes in patients with methicillin-susceptible Staphylococcus aureus bacteraemia: a systematic review and meta-analysis

ObjectiveThe use of the vancomycin minimum inhibitory concentration (MIC) as a prognostic predictor in patients with methicillin-susceptible Staphylococcus aureus (MSSA) has been debated in the last decade. We performed a systematic review and meta-analysis to investigate whether an elevated vancomycin MIC is associated with a worse prognosis for patients with MSSA bacteraemia.DesignSystematic review and meta-analysis.Data sourcesPubMed, Embase and the Cochrane Library were searched from inception to December 2019.Eligibility criteriaRandomised controlled trials or observational studies were considered eligible if they provided clinical outcomes of patients with MSSA bacteraemia, stratified by vancomycin MIC.Data synthesisPrimary outcome was mortality. Secondary outcomes included septic thrombophlebitis, persistent bacteraemia and complicated bacteraemia. Pooled ORs and 95% CIs were calculated. Subgroup analyses included the susceptibility testing method.ResultsFifteen observational studies were included. Bacteraemia due to MSSA isolates with high vancomycin MICs was associated with higher mortality than isolates with low MICs (OR 1.44; 95% CI 1.12 to 1.84; I2=40.3%). Additionally, significantly greater septic thrombophlebitis (OR 3.16; 95% CI 1.11 to 9.00; I2=58.6%) and a trend towards more persistent bacteraemia (OR 1.79; 95% CI 0.97 to 3.31; I2=0%) were observed in patients with high vancomycin MICs than in patients with low MICs. Differences in complicated bacteraemia were not significant. Similar findings were obtained in subgroup analyses using Etest. However, significant differences in outcomes were not observed between the high and low vancomycin MICs detected using broth microdilution.ConclusionThe available data suggest an association between elevated vancomycin MICs detected using Etest and adverse clinical outcomes for patients with MSSA bacteraemia. Future studies should validate these findings and explore the potential mechanisms.PROSPERO registration numberCRD42018090547.

Synergistic effect of Zinc Oxide nanoparticles and Vancomycin on Methicillin resistant Staphylococcus aureus

The study was carried out on (120) various clinical samples collected from patients attended Al Salam and Al-Khansa Hospitals and the Public Health Laboratory in the Mosul city during the of 4 months (September - December 2019). Samples were cultured on Mannitol Salt Agar medium, 105 samples give a positive result (grew the bacteria). 50 isolates were fermented mannitol sugar, at a rate of 47.6%, depending on the phenotypic characteristics and production of Coagulase, 14 isolates were identified, at a rate of 13.3%, belonging to Staphylococcus aureus the diagnosis were confirmed using VITEK system. The highest isolation rate from wounds was 57%, then abscesses 21%, blood samples 14%, and urinary tract infections 7%. The sensitivity of the isolates was tested for 16 antibiotics, the isolates showed variation in their resistance to antibiotics. Most of the isolates showed high resistance at 92.8% to each of Oxacillin, Vancomycin, which were diagnosed as MRSA and VRSA. Vancomycin MICs against MRSA and VRSA ranged (2500-5000) g /mL. MIC for nanoparticles sized (30, 20, 50-150) nm ranged (5000-10000) g / mL for isolates that are positive coagulase. In this study the efficacy of vancomycin was improved in combination with ZnO nanoparticles. results showed a decrease in vancomycin MICs from (2500-5000) g / mL to (39-78.125) g \ mL when mixed with ZnO 20 nm.

MINIMUM INHIBITORY CONCENTRATIONS OF VANCOMYCIN AND DAPTOMYCINAGAINST METHICILLIN-RESISTANT STAPHYLOCOCCUS AUREUS ISOLATED FROM VARIOUS CLINICAL SPECIMENS

Background Staphylococci are Gram-positive cocci arranged in clusters. They are colonized in humans and animals. Also, Staphylococcus aureus (S. aureus) is frequently associated with various superficial to deep-seated infections in humans. Due to the potential for easy transmission, Staphylococci are associated with both hospital-acquired and community-associated infections. Strains of S. aureus resistant to methicillin (MRSA) pose treatment challenges. In such cases, vancomycin isthe treatment of choice. Due to the indiscriminate use of vancomycin, recently, we are seeing the emergence of vancomycin-intermediate sensitive S. aureus (VISA) and vancomycin-resistant S. aureus (VRSA). The present study aims to evaluate the minimum inhibitory concentrations (MICs) of vancomycin and daptomycin among MRSA strains isolated from human clinical specimens Methods The study included 115 MRSA isolates collected over 24 months from October 2018 to September 2020. The strains were isolated from pus, urine, wound swabs, catheters, blood, and sputum. The bacteria were acquired from different inpatient and outpatient departments of Darbhanga Medical College and Hospital (DMCH), Laheriasrai, Bihar. Kirby-Bauer disk diffusion method using cefoxitin was used to confirm the MRSA isolates. The agar dilution and the Epsilometer method (E-test) were used to test the MICs of MRSA isolates against vancomycin and daptomycin, respectively, by the standard procedures recommended by the clinical laboratory standards institute (CLSI). Results Of the 115 S. aureus isolates, seven (6.08%) strains were resistant to vancomycin (VRSA) and 53 (46.08%) were found to be VISA using the new CLSI breakpoints. The MIC of the daptomycin was found to be ≤1 µg/ml for all the MRSA isolates. Conclusion The study results depicted an increasing trend in the vancomycin MICs among the MRSA isolates. Several tested strains show MICs in the intermediate sensitive range (VISA). The daptomycin was effective against all the MRSA isolates.

Bloodstream Infections Caused by S. aureus: Daptomycin Nonsusceptibility and Clinical Aspects

Background:Staphylococcus aureus is one of the leading pathogens isolated from bloodstream infections (BSIs), and vancomycin has been the main choice to treat MRSA (methicillin-resistant S. aureus) infections. Vancomycin-intermediate S. aureus (VISA) and heteroresistant-VISA (hVISA) have been described, limiting this antibiotic use. We evaluated aspects associated with the resistance and its clonality of the S. aureus isolated from BSIs, and we determined their association with clinical aspects of patients attended at Rio de Janeiro between 2016 and 2018. The detection of MRSA and trimethoprim-sulfamethoxazole resistant isolates was performed using the disk diffusion test, while the minimum inhibitory concentrations (MICs) were evaluated for 5 antimicrobials using the broth microdilution method. The MICs for ceftaroline and vancomycin of the MRSA isolates were determined using the E test. The presence of hVISA isolates was evaluated for isolates with vancomycin MICs of 1 and 2 μg/mL by screening on BHI agar added with vancomycin. The population profile was divided by the area under the curve (ie, PAP/AUC test). SCC mec was evaluated by PCR and the clonal profile by PFGE method. Among 123 S. aureus isolates from BSI, 31% were MRSA. MIC50 and MIC90 were daptomycin 2 and 2 μg/mL; linezolid, 1 and 1 μg/mL; oxacillin 1 and 256 μg mL; teicoplanin, 0.5 and 0.5 μg/mL and vancomycin 1 and 1 μg/ml. MIC values for ceftaroline and vancomycin were 0.75 and 2 μg/mL. The frequency of isolates not susceptible to daptomycin was 75%. The clonal lineages and SCCmec types found were USA100/ST5-II (50%), USA800/ST5-IV (22%), USA300/ST8-IV (15.8%), USA1100/ST30-IV (5.3%), BEC/ST239-III (5.3%), and 1 isolate carrying SCCmecV/ST1. We found 1 VISA isolate, and the PAP/AUC analysis detected 3 hVISA isolates that were associated with the USA100 and USA300 lineages. Overall, 85% of patients had a vascular catheter. More advanced age was associated with MRSA infection as was higher mortality. Patients with end-stage renal disease were more affected by MSSA infection. Daptomycin nonsusceptibility and VISA and hVISA phenotypes associated with prevalent clonal lineages were described. In addition, MRSA infections presented higher mortality, which emphasizes the importance of epidemiological studies.Funding: NoneDisclosures: None

Assessment of Vancomycin MIC Creep Phenomenon in Methicillin-Resistant Staphylococcus aureus isolates in a Tertiary Care Hospital of Lahore

Objective: To assess vancomycin MIC creep phenomenon in methicillin-resistant Staphylococcus aureus isolated from clinical specimens. Methods: This descriptive study was conducted in Microbiology department of University of Health Sciences, Lahore from January 2016- December 2019. In this study, vancomycin MICs were revealed by E test method for clinical MRSA strains. For the final evaluation, a single isolate from each patient was taken. The reported vancomycin MICs results were used and the values were not rounded up to the next upward value. For every study year, MIC50, MIC90, median and geometrical mean MIC, percentages of susceptible and resistant strains were calculated. Results: A total of 352 MRSA strains were isolated out of 2704 staphylococcal isolates. Our study showed elevated vancomycin MIC among MRSA isolates. The majority of isolates showed MIC values ≥1.5µg/ml. MIC50, MIC 90 was constant throughout four years period. However, geometric mean MIC increased gradually during the study period. The MIC greater than base year median was overall 17.3%. A complete shift can be observed between MIC “1.0” and “2.0” the percent of cases with MIC “1.0” decreased and with MIC “2.0” increased over time crossing each other in 2017. Conclusion: Vancomycin MIC creep was identified in clinical isolates of MRSA, during four years of study period. Even though there is an absence of VISA and VRSA strains; this significant increase in vancomycin MIC trend is indeed worrying for the clinicians about the threat of potential failure of treatment in MRSA infections. doi: https://doi.org/10.12669/pjms.36.7.3273 How to cite this:Arshad F, Saleem S, Jahan S, Tahir R. Assessment of Vancomycin MIC Creep Phenomenon in Methicillin-Resistant Staphylococcus aureus isolates in a Tertiary Care Hospital of Lahore. Pak J Med Sci. 2020;36(7):---------. doi: https://doi.org/10.12669/pjms.36.7.3273 This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.