Vancomycin Minimum Inhibitory Concentration Values Research Articles

Prevalence and factors associated with human colonisation and vancomycin minimum inhibitory concentration of <em>Staphylococcus aureus</em> in Colombo, Sri Lanka

Introduction: Staphylococcus aureus is known to cause a wide variety of diseases of varying severity in humans. The objectives of this study were to determine the prevalence of S. aureus and methicillin resistant S. aureus (MRSA) colonisation, assess factors associated with MRSA colonisation, identify antibiotic susceptibility patterns of MRSA isolates, determine distribution of vancomycin minimum inhibitory concentrations (MIC) of S. aureus and factors associated with high vancomycin MIC values (≥2 µg/ml). Methods: A descriptive cross sectional study was conducted among 341 participants aged 18 to 84 years selected randomly from the Colombo district from 11th December 2018 to 10th April 2019. Samples were collected from the nose, axilla, groin of participants and identification and sensitivity testing of S. aureus were performed based on standard operation procedures given in the Laboratory manual in microbiology published by the Sri Lanka College of Microbiologists (2011). Results: Prevalence of S. aureus and MRSA colonisation in the sample population was 34.6% and 13.78% respectively. All MRSA isolates were susceptible to linezolid. MRSA susceptibility to gentamicin (86%), co-trimoxazole (88 %), and chloramphenicol (80%) was high. Erythromycin had the lowest susceptibility (20%). Inducible clindamycin resistance was demonstrated in 31% of isolates. Meat consumption and consumption of antibiotics within the previous six months showed a significant association with MRSA colonisation. Vancomycin MIC of S. aureus ranged from ≤ 0.5 to 2 µg/ml. Conclusion: As prevalence of MRSA colonisation is 13.78%, more attention should be paid when managing patients with suspected S. aureus infections presenting from the community. Further research on associated factors and environmental triggers are warranted with a larger sample size and different study design to formulate national regulations and guidelines.

Antibiotic Susceptibility of Staphylococcus Aureus with VanA and MecA Genes.

Staphylococcus aureus (S.aureus) is an emerging antibiotic resistant bacterium responsible for various infections in human. Resistance to methicillin and vancomycin are of prime concern in S. aureus. The study aims to determine the minimum inhibitory concentration (MIC) of Vancomycin and evaluate the existence of mecA and vanA genes, associated with antibiotic resistance. Clinical specimens from three Kathmandu hospitals were processed and S. aureus was identified using conventional microbiological procedures. MRSA was phenotypically identified with cefoxitin (30µg) disc diffusion, while vancomycin susceptibility was assessed using the Ezy MICTM stripes. The mecA and vanA genes were detected by polymerase chain reaction (PCR). Out of 266 S. aureus samples from various clinical specimen subjected for analysis, 77 (28.9%) were found methicillin-resistant (MRSA) and 10 (3.8%) were observed vancomycin-resistant (VRSA). Vancomycin resistant isolates showed a significant correlation between resistance to ampicillin, chloramphenicol, and cefoxitin. The mecA gene was found in 39 of the MRSA isolates, having 50.64% of MRSA cases, while the vanA gene was detected in 4 of the VRSA cases, constituting 40% of VRSA occurrences. The strains with higher vancomycin minimum inhibitory concentration values (≥ 1.5 μg/ml) displayed increased resistance rates to various antibiotics compared to strains with lower minimum inhibitory concentration values (< 1.5 μg/ml). The presence of vanA genes was strongly associated (100%) with vancomycin resistance, while the 10.3% mecA gene was identified from MRSA having resistance towards vancomycin also.

Automated Susceptibility Testing With Vitek 2 Compared to MicroScan Reduces Vancomycin Alternative Therapy For Methicillin-Resistant Staphylococcus Aureus Bacteremia

Variability in minimum inhibitory concentration (MIC) with automated susceptibility testing instruments may influence methicillin-resistant Staphylococcus aureus (MRSA) treatment. The purpose of this study was to evaluate the difference in vancomycin MIC values and the impact on vancomycin alternative therapy for MRSA bacteremia using the MicroScan and VITEK 2 automated systems. This was a retrospective multicenter cohort study of adult patients with MRSA bacteremia. Patients were stratified by susceptibility testing with MicroScan (May 2013-December 2016) or VITEK 2 (June 2017-February 2020). The primary outcome was vancomycin alternative therapy use. Secondary endpoints included MRSA MIC, 30-day mortality, 30- and 90-day readmission, and hospital length of stay (LOS). A total of 193 patients were included for analysis: 89 in the MicroScan group and 104 in the VITEK 2 group. Vancomycin alternative therapy use was higher in the MicroScan group than the VITEK 2 group (56.2% vs 20.2%; p <0.001). Median MIC value was 2 mg/L and 1 mg/L for MicroScan and VITEK 2, respectively (p <0.001). Median hospital LOS was shorter in the VITEK 2 period (16 vs 12 days; p=0.02). Thirty-day mortality (10.1% vs 7.7%; p=0.555) and 90-day readmission (34.8% vs 29.8%; p=0.457) did not significantly differ between MicroScan and VITEK 2 groups. VITEK 2 use was associated with lower reported vancomycin MICs and less use of vancomycin alternative therapy.

Assessment of Antibiotics Susceptibility Pattern of Vancomycin Resistant Enterococci Isolated from Clinical Specimens in Port Harcourt

Aim: The aim of this study was to assess the prevalence of vancomycin resistance among Enterococcal species isolated from clinical specimens of patients attending two hospitals in Port Harcourt, Rivers State.&#x0D; Study Design: The study employs statistical analysis of the data and interpretation.&#x0D; Place and Duration of Study: Two hospitals which are Meridian hospital Port Harcourt and University of Port Harcourt Teaching Hospital, located in the city of Port-Harcourt, Rivers State were used for this study. Specimen collection lasted for 3 weeks and the analysis was carried out daily and it lasted for six months.&#x0D; Methodology: A total of one hundred and eighteen (118) urine and stool specimens (60 urine and 58 stool specimens) were collected from Fifty nine (59) patients for a period of three months from Meridian hospital and University of Port Harcourt Teaching Hospital, Port-Harcourt, Rivers State. The specimens collected were grouped inpatients and outpatients and were subjected to standard microbiological procedures which include standard plate counts, identification, and sensitivity testing using Kirby-Bauer disk diffusion method, Minimum inhibitory concentration and molecular identification of the isolates.&#x0D; Results: A total of 48 enterococcal isolates were isolated from the different specimens (hospitalized and non-hospitalized patients) of urine and stool specimens. All Enterococcal isolates showed high level of resistance to Ceftazidime and Cefuroxime (100%) followed by cloxacillin (95.8%), augumentin (85.4%) and Ceftriaxone (75.0%). The isolates showed higher sensitive rates to Ofloxacin (95.5%), followed by Gentamicin (77.1%) and Vancomycin (39.6%). All Enterococal isolates from this study had a MAR index &gt; 0.2. A total of the 48 Enterococci were isolated, the 23 (47.9%) isolates were identified as vancomyin resistant during this study were subjected to MIC (Minimum Inhibitory Concentration) for vancomycin as a confirmatory test. Of the 23 isolates, 12 isolates were vancomycin resistant with 11 isolates showing vancomycin MIC values of 8-16μg /ml (vancomycin intermediate).&#x0D; Conclusion: Conclusively, this study revealed varying Antibiotic susceptibility pattern of the isolated bacteria. Treatment guidelines for use of antibiotics should be based on the hospital formulary and the sensitivity patterns is advocated. This should be reviewed occasionally to ensure rational use of antibiotics

Association between high vancomycin minimum inhibitory concentration and clinical outcomes in patients with methicillin-resistant Staphylococcus aureus bacteremia: a meta-analysis.

To assess the relationship between high vancomycin minimum inhibitory concentrations (MIC), in patients with methicillin-resistant Staphylococcus aureus bacteremia (MRSAB), and both mortality and complicated bacteremia. Embase, Medline, EBM, Scopus and Web of Science were searched for studies published from January 1st 2014 to February 29th 2020. "High" vancomycin MIC cut off was defined as ≥ 1.5mg/L. Three referees independently reviewed studies that compared outcomes in patients with MRSAB stratified by vancomycin MIC. Subgroup analyses were performed for rates of mortality and complicated bacteremia. A total of 13 studies with 2089 patients were included. Overall, mortality was 27.7% and 23.3% in the high and low vancomycin MIC group, respectively. No significant difference was found between vancomycin MIC groups for overall mortality, in-hospital mortality, late mortality, persistent bacteremia, severe sepsis or septic shock, acute renal failure, septic emboli or endocarditis, and osteomyelitis or septic arthritis. Early mortality was significantly associated with low vancomycin MIC. Mortality in studies using broth microdilution method (BMD) and need for mechanical ventilation were significantly associated with high vancomycin MIC. Overall mortality and complicated bacteremia were not significantly associated with high vancomycin MICs in a patient with MRSAB. Randomized controlled trials to assess the utility of vancomycin MIC values in predicting mortality and other adverse clinical outcomes are warranted.

Effect of the lantibiotic nisin on inhibitory and bactericidal activities of antibiotics used against vancomycin-resistant enterococci

ObjectivesAntibiotic resistance is a serious issue facing clinicians all over the world. Vancomycin-resistant enterococci (VRE) are amongst the most common resistant pathogens that are isolated from patients suffering from infections in our locality. New antimicrobial agents such as the lantibiotic nisin have been previously examined against resistant bacteria as it has strong antibacterial action with no chance of resistance development. This study aimed to explore the effect of nisin in combination with the conventional antibiotics against VRE, with a view to using it as an auxiliary therapy with such antibiotics for combating resistant isolates. MethodsTwenty-three VRE had been examined for the combined effect of nisin with the routine sets of antibiotics using the microplate dilution technique for minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) testing. Checkerboard microbroth assay was conducted for inspection of synergism between nisin and either ampicillin or chloramphenicol. ResultsAn obvious improvement of inhibitory and bactericidal activities of the tested antibiotics after addition of lantibiotic nisin was observed, with a remarkable reduction in the MIC values of vancomycin against all of the isolates. Nisin recorded a synergistic outcome when combined with either ampicillin or chloramphenicol using the checkerboard assay. ConclusionNisin could be effectively considered as a supplementary agent to traditional antibiotics in the management of VRE-associated infections, as it had a synergistic outcome with commonly prescribed antibiotics such as ampicillin and chloramphenicol.

Development, optimization, standardization, and validation of a simple in-house agar gradient method to determine minimum inhibitory concentration of vancomycin for Staphylococcus aureus.

BACKGROUND:The Clinical and Laboratory Standards Institute recommends reporting minimum inhibitory concentration (MIC) values of vancomycin for Staphylococcus aureus. Commercial MIC strips are expensive, and the traditional broth microdilution method is cumbersome. With this background, we attempted to develop and standardize an in-house agar gradient method to determine MIC values of vancomycin for S. aureus.OBJECTIVES:To develop and validate an in-house vancomycin MIC strip, based on simple agar gradient method for S. aureus as per bioassay development guidelines.MATERIALS AND METHODS:Filter paper gradient strips were made in house and impregnated with varying concentrations of vancomycin to create an antibiotic gradient. During standardization, MICs of ninety clinical strains of S. aureus and ATCC 29213 were tested by the broth microdilution and commercial strip followed by the in-house strip. During the validation stage, MICs of ninety different clinical strains of S. aureus and ATCC 29213 were determined by the in-house strip followed by MIC detection by broth microdilution and commercial strips. A reading of more than ± 1log2 dilution compared with broth microdilution was considered as an outlier.RESULTS:During the initial stage, there were 7/90 outliers in the clinical strains, and no outliers were seen with the ATCC 29213 control strain. Corrective action included increasing precaution during the antibiotic impregnation on the strip. During validation stage, only 4/90 outliers were observed in the clinical strains. The commercial strips had 29/90 among clinical and 15/30 outliers in the control strain during the prevalidation phase. Despite maintaining cold chain during the validation phase, the outliers for commercial strip were 18/90 and 4/30 for clinical and control strains, respectively.CONCLUSION:Reporting vancomycin MIC for S. aureus may be attempted using the in-house method after validating it with a gold standard broth microdilution method and quality control as per protocol.

PAMAM-dendrimer Enhanced Antibacterial Effect of Vancomycin Hydrochloride Against Gram-Negative Bacteria.

The antibacterial activity of some antibiotics is specific to either Gram-positive or Gram-negative bacteria. There are different mechanisms behind such insensitivities like inability of antibiotics to permeate through some bacterial membranes, as is the case for vancomycin in Gram-negative bacteria. The present investigation tries to overcome this problem by dendrimers, in order to make Gram-negative bacteria responsive to vancomycin. The effects of generations 3 (G3) and 5 (G5) polyamidoamine amine-terminated dendrimers (NH2-PAMAM), on the antibacterial activity of vancomycin, were evaluated. Vancomycin-PAMAM dendrimers complexes were prepared and their antibacterial activities were evaluated by determination of their "minimum inhibitory concentration (MIC)", "minimum bactericidal concentration" and "fractional inhibitory concentration index" values against two Gram-positive and four Gram-negative bacteria, using broth micro-dilution method. The complexation of vancomycin and dendrimers was also assessed by in vitro release studies across dialysis tubing using a developed HPLC method. Results showed that vancomycin solution was effective against Gram-positive bacteria, but, was not effective in Gram-negative ones. Vancomycin-PAMAM dendrimers exhibited significant antibacterial efficacy against Gram-negative bacteria resulting in a decline of vancomycin MIC values by about 2, 2, 4 and 64 times in E. coli, K. pneumonia, S. typhimurium and P. aeruginosa, respectively. Results also showed that enhanced effect by G5 is more than G3. Dendrimers did not affect antibacterial activity of vancomycin in Gram-positive bacteria, as no permeation problem exists here. The present study revealed that both G3 and G5 cationic PAMAM dendrimers are able to make Gram-negative bacteria sensitive to vancomycin, resulting in decline of MIC values up to 64 times, possibly by increasing its permeation through bacterial membrane. These results look promising for broadening the antibacterial spectrum of vancomycin and such a strategy might be used for increasing the overall life of antibiotics.

Vancomycin Capped with Silver Nanoparticles as an Antibacterial Agent against Multi-Drug Resistance Bacteria.

Purpose: Many antimicrobial medications are available to combat infections. However, the indiscriminate use of antibiotics has produced antibiotic resistance in the case of many bacterial pathogens. This study focuses on the development of nanoparticles (NPs) that enhance the in vitro antibiotic activity of vancomycin against multi-drug resistant (MDR) organisms.Methods: Spherical shaped thioglycolic acid-stabilized silver nanoparticles (TGA-AgNPs) were prepared by using a simple chemical reduction method. Then, vancomycin was conjugated to the terminal carboxyl of TGA in the presence of N-Hydroxysuccinimide (NHS) and N-(3-dimethylaminopropyl)-N’-ethylcarbodiimide hydrochloride (EDC). Afterwards, the antibacterial activity of these nanoconjugates was examined by using the minimum inhibitory concentration (MIC) assay against MDR bacteria.Results: The rate of vancomycin bound to the AgNPs was 19.6%. The MIC values of vancomycin (Van)-capped AgNPs against tested pathogens were in the range of (3.2, 1.6, 0.8, 0.4, 0.2, 0.1, 0.05, and 0.025 µl/ml). The MIC was 0.1 µg/ml for VRE, MIC≤0.02 µg/ml for MRSE, and 0.05 µg/ml for S. aureus. The MIC corresponded to the MBC for all bacterial species.Conclusion: This study indicated that some antimicrobial agents like vancomycin can be conjugated with AgNPs. This can lead to increased antimicrobial activity against MDR microorganisms.

Reproducible measurement of vancomycin MICs within the susceptible range in Staphylococcus aureus by a broth microdilution method with a "quasi-continuum" gradient of antibiotic concentrations.

The availability of reproducible broth microdilution (BMD) methods including inter log2 antibiotic dilutions for measuring Staphylococcus aureus (SA) vancomycin minimum inhibitory concentrations (MICs) within the susceptible range is needed to elucidate the impact of vancomycin MICs on clinical outcomes of invasive SA infections. Here, we report on the development of a very precise BMD method that incorporates the following incremental antibiotic concentrations: 0.50, 0.62, 0.75, 0.87, 1.0, 1.25, 1.40, 1.50, 1.60, 1.75, and 2.0μg/mL. The intra- and inter-assay coefficients of variation of this method were around 20%. The mean of the differences in MIC values for all isolates obtained across two independent runs performed at one center was 0.04μg/mL [95% confidence interval (CI), 0.011-0.07μg/mL] and that for ten isolates measured at two different centers was 0.04μg/mL (95% CI, 0-13μg/mL). Vancomycin MIC values differed by less than 0.1μg/mL between runs for most isolates. Storage of isolates at -20°C for up to 3months had no impact on the vancomycin MIC values. The mean vancomycin MIC values obtained by the Etest using a standard inoculum (0.5 McFarland) were significantly higher (p≤ 0.001) than those measured by BMD and the MIC values measured by the two methods correlated poorly (Rho, 0.319; p=0.148). Nevertheless, the mean MIC values measured by the Etest using lower inocula (107 or 106CFU/mL) and those measured by BMD were comparable and correlated significantly (p=0.004 for 107CFU/mL and p=0.029 for 106CFU/mL).

In vitro effect of vancomycin and daptomycin on biofilm formation of coagulase-negative staphylococci strains

Coagulase-negative staphylococci (CNS) are one of the primer agents of blood stream infections (BSI) and catheter-related bloodstream infections (CR-BSI) which are associated mostly with the usage of central venous catheters and, important causes of morbidity and mortality despite the usage of antibacterial and supportive treatment. It is important to determine the properties of these causative microorganisms in order to make appropriate treatment of such infections. The aims of our study were to evaluate the biofilm formation of coagulase negative staphylococci (CNS) which were causative agents of bloodstream (BSI) and catheter related bloodstream infections (CR-BSI), to determine the minimum inhibitory concentration (MIC) of planktonic forms and minimal biofilm eradication concentration (MBEC) of sessile forms for vancomycin and daptomycin and to evaluate the efficacy of these antibiotics in infections with biofilm-forming isolates in vitro. A total of 65 CoNS (n= 26 catheter colonizers, n= 28 CR-BSI, n= 11 BSI agents) were identified by conventional methods and also with BD Phoenix (Becton Dickinson, USA) and Bruker Microflex MS (Bruker Daltonics, Germany) systems. Methicillin resistance was determined by the presence of mecA gene with PCR. MIC values of vancomycin and daptomycin were investigated by broth microdilution, for daptomycin medium containing 25 and 50 μg/ml Ca++ were used. Assessment of biofilm formation and detection of MBEC were determined by microplate method. The clonal relationship was investigated by the PFGE method. A total of 65 isolates; 26 catheter colonizers, 28 CR-BSI agents and 11 BSI agents were evaluated and identified as Staphylococcus epidermidis (n= 33), Staphylococcus haemolyticus (n= 16), Staphylococcus hominis (n= 15), and Staphylococcus capitis (n= 1). 81.5% of the isolates were found to be methicillin resistant and all of them were found to be sensitive to vancomycin (MIC= 0.125-4 μg/ml) and daptomycin (MIC= 0.062-0.25 μg/ml in 25 μg/ml Ca++ and MIC= 0.031-0.50 μg/ml in 50 μg/ml Ca++ containing medium). MIC values were lower in medium containing 50 μg/ml Ca++ for daptomycin. As it is known that the efficacy of daptomycin depends on the physiological levels of Ca++, which causes conformational changes in the structure of these antibacterials. Our findings also suggested that high levels of Ca++ are needed to ensure the efficacy of daptomycin. All of the isolates produced biofilm at different strengths of positivity (n= 12/18.5% weak, n= 35/%53.8 moderate, n= 18/%27.7 strong). MBEC and MBEC/MIC values for vancomycin were found to be higher than daptomycin (p< 0.001). Strong biofilm producers had higher MBEC and MBEC/MIC, MBEC50/MIC50 ve MBEC90/MIC90 values (p< 0.05). Especially in infections with biofilm forming isolates, the detection of only MIC values are not always sufficient in the treatment of biofilm-related infections as they reflect the sensitivity of planktonic bacteria. The inconsistency between the MIC and MBEC values and the high rates of MBEC/MIC found in our study supported this prediction.The lower detection of MBEC and MBEC/MIC values of daptomycin compared to the same values of vancomycin suggested that daptomycin might be effective at lower doses than vancomycin in the treatment of biofilm infections.

Update of the activity of telavancin against a global collection of Staphylococcus aureus causing bacteremia, including endocarditis (2011\u20132014)

The efficacy and safety of telavancin is under evaluation for the treatment of subjects with complicated Staphylococcus aureus bacteremia and S. aureus right-sided infective endocarditis. This study evaluated the telavancin activity against a global collection of S. aureus causing bloodstream infections (BSI), including endocarditis, to support the development of bacteremia/endocarditis clinical indications. This study included a total of 4191 S. aureus [1490 methicillin-resistant S. aureus (MRSA)], which were unique (one per patient) clinical isolates recovered from blood samples collected during 2011–2014 in a global network of hospitals. All isolates were deemed responsible for BSI, including endocarditis, by local guidelines. Isolates were tested for susceptibility by broth microdilution. Telavancin (MIC50/90, 0.03/0.06 μg/ml) inhibited all S. aureus at ≤0.12 μg/ml, the breakpoint for susceptibility. Equivalent minimum inhibitory concentration (MIC) values (MIC50/90, 0.03/0.06 μg/ml) were obtained for telavancin against methicillin-susceptible S. aureus (MSSA) and MRSA isolates, as well as MRSA from community and healthcare origins. Similar telavancin activities (MIC50, 0.03 μg/ml) were observed against MRSA subsets from North America and Europe, while isolates from the Asia-Pacific (APAC) and Latin America regions had MIC50 values of 0.06 μg/ml. MRSA with vancomycin MIC values of 2–4 μg/ml and the multidrug resistance (MDR) subset had telavancin MIC50 results of 0.06 μg/ml, although the MIC100 result obtained against these subsets remained identical to those of MSSA (MIC100, 0.12 μg/ml, respectively). This study updates the telavancin in vitro activity, which continues to demonstrate great potency against invasive S. aureus, regardless of the susceptibility phenotype or demographic characteristics (100.0% susceptible), and supports the sought-after subsequent indications.

Antimicrobial resistance in Enterococcus strains isolated from healthy domestic dogs.

Enterococci are opportunistic bacteria that cause severe infections in animals and humans, capable to acquire, express, and transfer antimicrobial resistance. Susceptibility to 21 antimicrobial agents was tested by the disk diffusion method in 222 Enterococcus spp. strains isolated from the fecal samples of 287 healthy domestic dogs. Vancomycin and ampicillin minimum inhibitory concentrations (MICs) and high-level aminoglycoside resistance (HLAR) tests were also performed. Isolates showed resistance mainly to streptomycin (88.7%), neomycin (80.6%), and tetracycline (69.4%). Forty-two (18.9%) isolates showed an HLAR to streptomycin and 15 (6.7%) to gentamicin. Vancomycin and ampicillin MIC values showed 1 and 18 resistant strains, respectively. One hundred and thirty-six (61.2%) strains were classified as multidrug resistant and six (2.7%) strains as possibly extensively drug-resistant bacteria. Enterococcus faecium and Enterococcus faecalis were the most prevalent antimicrobial resistant species. Companion animals, which often live in close contact with their owners and share the same environment, represent a serious source of enterococci resistant to several antibiotics; for this reason, they may be a hazard for public health by providing a conduit for the entrance of resistance genes into the community.

Decreased Vancomycin MICs among Methicillin-Resistant Staphylococcus aureus Clinical Isolates at a Chinese Tertiary Hospital over a 12-year Period.

The increased vancomycin minimum inhibitory concentration values (MICs) for methicillin-resistant Staphylococcus aureus (MRSA) isolates are associated with treatment failure and mortality of MRSA infections. In the present study, 553 non-duplicate MRSA isolates from various specimens of patients with infections at a Chinese tertiary hospital from January 2003 to December 2014, were selected randomly for investigating the shift of vancomycin MICs determined by E-test method. The percentages of the MRSA isolates with vancomycin MICs of ≥2.0, 1.5, 1.0, and ≤0.75 mg/L were 16.3% (90/553), 38.5% (213/553), 35.6% (197/553), and 9.9% (55/553), respectively. The highest geometric mean MIC (GM MIC) value (1.648 mg/L) and the lowest GM MIC (0.960 mg/L) were found in the first year (2003) and the last year (2014) over the study period, with significant difference (p < 0.05). The GM MICs over the study period fluctuated by year, with the elevated values in 2005, 2011, and 2013 and the decreased values in other years relative to the respective former year. The vancomycin GM MIC (1.307 mg/L) for MRSA isolates from sputum was the highest relative to that for the MRSA isolates from other specimens. By contrast, the vancomycin GM MIC value (1.156 mg/L) for MRSA isolates from pus was the lowest, with similar value to that for the isolates from blood. The vancomycin GM MICs in period I (2003–2005), period II (2006–2008), period III (2009–2011), and period IV (2012–2014) were 1.501, 1.345, 1.177, and 1.139 mg/L, respectively, with the continuous decreased trend. Compared with period I, the vancomycin GM MIC for MRSA isolates in period IV was significantly lower (p < 0.01), with a 1.318- fold decrease. The percentages of the isolates with vancomycin MIC ≥2 mg/L in four periods were 25, 15.6, 15.2, and 12%, respectively, with a continuous decrease. While the percentages of the isolates with vancomycin MIC ≤0.75 mg/L in four periods increased from 1.7% in period I to 19.3% in period IV. Taken together, a decreased trend in vancomycin MICs for MRSA isolates from a Chinese tertiary teaching hospital has been found. This pnenomenon was mainly associated with a decrease in the proportion of the MRSA isolates with vancomycin MIC ≥2 mg/L and an increase in the proportion of the MRSA isolates with vancomycin MIC ≤0.75 mg/L.

Optimizing the detection of methicillin-resistant Staphylococcus aureus with elevated vancomycin minimum inhibitory concentrations within the susceptible range.

BackgroundDetermination of vancomycin minimum inhibitory concentration (MIC) can influence the agent used to treat methicillin-resistant Staphylococcus aureus (MRSA) infection. We studied diagnostic accuracy using E-test and VITEK® 2 against a gold standard broth microdilution (BMD) methodology, the correlation between methods, and associations between vancomycin MIC and MRSA phenotype from clinical isolates.MethodsMRSA isolates were obtained from April 2012 to December 2013. Vancomycin MIC values were determined prospectively on all isolates by gradient diffusion E-test and automated VITEK® 2. The Clinical and Laboratory Standards Institute reference BMD method was performed retrospectively on thawed frozen isolates. Diagnostic accuracy for detecting less susceptible strains was calculated at each MIC cutoff point for E-Test and VITEK® 2 using BMD ≥1 µg/mL as a standard. The correlation between methods was assessed using Spearman’s rho (ρ). The association between MRSA phenotype and MIC for the three methods was assessed using Fisher’s exact test.ResultsOf 148 MRSA isolates, all except one (E-test =3 µg/mL) were susceptible to vancomycin (MIC of ≤2 µg/mL) irrespective of methodology. MICs were ≥1.0 µg/mL for 9.5% of BMD, 50.0% for VITEK® 2, and 27.7% for E-test. Spearman’s ρ showed weak correlations between methods: 0.29 E-test vs VITEK® 2 (P=0.003), 0.27 E-test vs BMD (P=0.001), and 0.31 VITEK® 2 vs BMD (P=0.002). The optimal cutoff points for detecting BMD-defined less susceptible strains were ≥1.0 µg/mL for E-test and VITEK® 2. E-test sensitivity at this cutoff point was 0.85 and specificity 0.29, while VITEK® 2 sensitivity and specificity were 0.62 and 0.51, respectively. Multiresistant MRSA strains tended to have higher MIC values compared to nonmultiresistant MRSA or epidemic MRSA 15 phenotypes by E-test (Fisher’s exact P<0.001) and VITEK® 2 (Fisher’s exact P<0.001).ConclusionOverall diagnostic accuracy and correlations between MIC methods used in routine diagnostic laboratories and the gold standard BMD showed limited overall agreement. This study helps optimize guidance on the effective use of vancomycin.

Development of a sandwiched microarray platform for studying the interactions of antibiotics with Staphylococcus aureus

It still confronts an outstanding challenge to screen efficient antibacterial drugs from millions of potential antibiotic candidates. In this regard, a sandwiched microarray platform has been developed to culture live bacteria and carry out high-throughput screening antibacterial drugs. The optimized lectin-hydrogel microarray can be used as an efficient bacterial capturing and culturing platform, which is beneficial to identify spots and collect data. At the same time, a matching drug-laden polyacrylamide microarray with Luria–Bertani (LB) culture medium can be generated automatically and accurately by using a standard non-contacting procedure. A large number of microscale culture chambers (more than 100 individual samples) between two microarrays can be formed by linking two aligned hydrogel spots using LB culture medium, where live bacteria can be co-cultured with drug candidates. Using Staphylococcus aureus (S. aureus) and four well-known antibiotics (amoxicillin, vancomycin, streptomycin and chloramphenicol) as model system, the MIC (minimum inhibitory concentration) values of the antibiotics can be determined by the drug induced change of bacterial growth, and the results demonstrate that the MIC values of amoxicillin, vancomycin and streptomycin are 1.7 μg mL−1, 3.3 μg mL−1 and 10.3 μg mL−1, respectively.

An investigation of vancomycin minimum inhibitory concentration creep among methicillin-resistant Staphylococcus aureus strains isolated from pediatric patients and healthy children in Northern Taiwan.

The phenomenon of vancomycin minimum inhibitory concentration (MIC) creep is an increasingly serious problem in the treatment of methicillin-resistant Staphylococcus aureus (MRSA) infections. In this study, we investigated the vancomycin and daptomycin MIC values of MRSA strains isolated from pediatric patients and MRSA colonized healthy children. Then, we assessed whether there was evidence of clonal dissemination for strains with an MIC to vancomycin of ≥ 1.5μg/mL. We collected clinical MRSA isolates from pediatric patients and from healthy children colonized with MRSA during 2008-2012 at a tertiary medical center in northern Taiwan and obtained vancomycin and daptomycin MIC values using the Etest method. Pulse-field gel electrophoresis (PFGE) and staphylococcal cassette chromosome (SCCmec) typing were used to assess clonal dissemination for strains with an MIC to vancomycin of ≥ 1.5μg/mL. A total 195 MRSA strains were included in this study; 87 were isolated patients with a clinical MRSA infection, and the other 108 strains from nasally colonized healthy children. Vancomycin MIC≥1.5μg/mL was seen in more clinical isolates (60/87, 69%) than colonized isolates (32/108, 29.6%), p<0.001. The PFGE typing of both strains revealed multiple pulsotypes. Vancomycin MIC creeps existed in both clinical MRSA isolates and colonized MRSA strains. Great diversity of PFGE typing was in both strains collected. There was no association between the clinical and colonized MRSA isolates with vancomycin MIC creep.

Prospective Evaluation of Staphylococcus aureus Antibiotic Resistance Patterns from Respiratory Specimens in ICU Patients

Background: Staphylococcus aureus is the leading pathogen responsible for hospital-acquired pneumonia (HAP). Vancomycin is the primary antimicrobial choice for methicillin-resistant S. aureus (MRSA) HAP worldwide, but S. aureus isolates have been reported susceptible or even resistant to vancomycin. Objectives: This study compares automated and non-automated susceptibility patterns for MRSA isolates to vancomycin to determine comparability of testing methods for this drug. Methods: Respiratory samples submitted to Clinical Microbiology from patients in the ICU were plated onto sheep blood agar and chocolate agar media and visually inspected at 12-24 hours. The presence of S. aureus was determined serologically. S. aureus isolates were subcultured for susceptibility testing to detect MRSA respiratory isolates. Consecutive MRSA respiratory isolates were analyzed for susceptibility and minimum inhibitory concentration (MIC) using E-test strips and BD Phoenix automated system testing for vancomycin and the vancomycin alternative agents teicoplanin, linezolid and tigecycline. Results: Ninety-five MRSA respiratory isolates were collected. Three were obtained by bronchoalveolar lavage and the remainder by protected alveolar lavage. There was no heteroresistance detected by E-test at 24 hours, but there were 4 isolates at 48 hours demonstrating elevated vancomycin MIC values of 6 ug/ml. Conclusions: Vancomycin heteroresistance was not a problem in this series of isolates. Agreement between vancomycin automated MICs and E-test MICs was not universal. Although under-calls were few based upon automated MIC, several instances were indeed identified.These data show that Phoenix under-reports vancomycin MIC values for MRSA compared to E-test methodology.

Methicillin Resistant Staphylococcus aureus: Inconsistencies in Vancomycin Susceptibility Testing Methods, Limitations and Advantages of each Method.

Vancomycin may be ineffective against an increasing proportion of methicillin resistant Staphylococcus aureus (MRSA) with minimum inhibitory concentrations (MICs) well within the susceptible range. On the other hand it is common knowledge that determination of vancomycin MICs is method dependent. Therefore, given the apparent variability in vancomycin MIC results obtained with the different methods, the use of the vancomycin MIC to predict the outcome of serious S. aureus infections needs to take into account the method used and the results of studies using that particular method. Comparative study was carried out to evaluate the MICs obtained by BMD method, E-test, and Vitek 2 method and to detect inconsistencies in these vancomycin for 66 MRSA isolates obtained from various samples of patients attending the OPDs & IPDs within a period of one year. A comparative study was carried out to evaluate the MICs obtained by BMD method, E-test, and Vitek 2 method to detect vancomycin susceptibility in 66 clinical isolates of MRSA obtained from various samples of patients attending the OPDs & IPDs within a period of one year. The study was conducted in Department of Microbiology, Subharti Medical College, Meerut from January to December 2012. On determination of MICs for vancomycin for the MRSA isolates, all were identified as VSSA by BMD, E-Test & Vitek 2 methods. However, the vancomycin MIC values obtained by E-test correlated better with BMD method (correlation factor= 0.6727) than Vitek 2 (correlation factor=0.5316), indicating E-Test to be a better method for determination of vancomycin MICs as compared to Vitek 2. MRSA isolates with higher vancomycin MICs, even within the susceptibility range, are being observed more frequently which result in treatment failures with vancomycin. Because of the discrepancy that exists in vancomycin MIC results from different methods, the prediction of outcome of serious S.aureus infections should take into account the method used & results of studies using that particular method.

Association Between Vancomycin Minimum Inhibitory Concentration and Mortality Among Patients WithStaphylococcus aureusBloodstream Infections

Staphylococcus aureus bacteremia (SAB) is a worldwide problem. It is unclear whether higher-vancomycin minimum inhibitory concentration (MIC) is associated with mortality. This potential association has direct consequences for patients and public health. PubMed, Embase, the Cochrane Library, Evidence-based Medicine BMJ, and the American College of Physicians Journal Club were searched from inception through April 2014. Studies reporting mortality and vancomycin MIC in patients with SAB were included. Two authors performed the literature search and the study selection separately. Random-effects modeling was used for all analyses. All-cause mortality. Among 38 included studies that involved 8291 episodes of SAB, overall mortality was 26.1%. The estimated mortality was 26.8% among SAB episodes (n = 2740) in patients with high-vancomycin MIC (≥1.5 mg/L) compared with 25.8% mortality among SAB episodes (n = 5551) in patients with low-vancomycin MIC (<1.5 mg/L) (adjusted risk difference [RD], 1.6% [95% CI, -2.3% to 5.6%]; P = .43). For the highest-quality studies, the estimated mortality was 26.2% among SAB episodes (n = 2318) in patients with high-vancomycin MIC compared with 27.8% mortality among SAB episodes (n = 4168) in patients with low-vancomycin MIC (RD, 0.9% [95% CI, -2.9% to 4.6%]; P = .65). In studies that included only methicillin-resistant S aureus infections (n = 7232), the mortality among SAB episodes (n = 2384) in patients with high-vancomycin MIC was 27.6% compared with mortality of 27.4% among SAB episodes (n = 4848) in patients with low-vancomycin MIC (adjusted RD, 1.6% [95% CI, -2.3% to 5.5%]; P = .41). No significant differences in risk of death were observed in subgroups with high-vancomycin MIC vs low-vancomycin MIC values across different study designs, microbiological susceptibility assays, MIC cutoffs, clinical outcomes, duration of bacteremia, previous vancomycin exposure, and treatment with vancomycin. In this meta-analysis of SAB episodes, there were no statistically significant differences in the risk of death when comparing patients with S aureus exhibiting high-vancomycin MIC (≥1.5 mg/L) to those with low-vancomycin MIC (<1.5 mg/L), although the findings cannot definitely exclude an increased mortality risk. These findings should be considered when interpreting vancomycin susceptibility and in determining whether alternative antistaphylococcal agents are necessary for patients with SAB with elevated but susceptible vancomycin MIC values.