Occurrence of vancomycin MIC creep in methicillin resistant isolates in Saudi Arabia

BACKGROUND

"MIC creep" is a phenomenon that describes an increase of an organism MICs over time and have been reported from different parts of the world. High MIC in MRSA has been theoretically liked to treatment failure and may be a precursor to hVISA and VISA. This study was conducted to assess presence of vancomycin minimum inhibitory concentration (MIC) creeps among clinical isolates of methicillin-resistant Staphylococcus aureus (MRSA) in Saudi Arabia.

METHODS

Minimum inhibitory concentration (MIC) of vancomycin by E test of all MRSA isolates of from 2013 to 2018 were reviewed.

RESULTS

Of the 736 isolates evaluated, no isolates with MIC above 2 were found. Majority of MRSA isolates were susceptible to vancomycin with MIC less than 1. There was a significant increase in both Arithmetic and geometric mean MIC for vancomycin during the first three years which progressively declined in the next three years.

CONCLUSIONS

Although most of MRSA isolated remained very susceptible to vancomycin there was evidence of dynamic vancomycin MIC creep over time.

Staphylococcus aureus at an Indian tertiary hospital: Antimicrobial susceptibility and minimum inhibitory concentration (MIC) creep of antimicrobial agents

OBJECTIVES

Staphylococcus aureus causes a variety of symptoms and diseases and has been associated with high morbidity and mortality. A global population drift in clinical S. aureus isolates towards reduced antimicrobial susceptibility is being reported. In this study, the antimicrobial susceptibility profile and minimum inhibitory concentration (MIC) creep of vancomycin, linezolid, teicoplanin and rifampicin against clinical S. aureus isolates at an Indian tertiary centre from January 2012 to December 2016 were investigated.

METHODS

All consecutive, non-duplicate S. aureus isolates (n=1466) recovered from hospitalised patients identified by VITEK^®2 were included in the study. Clinical isolates were tested against 20 antibiotics and were evaluated according to Clinical and Laboratory Standards Institute (CLSI) guidelines. Statistical significance of the MIC creeps of four antimicrobials (vancomycin, linezolid, teicoplanin and rifampicin) was ascertained.

RESULTS

S. aureus isolates recovered from all clinical samples demonstrated high resistance to ampicillin, ciprofloxacin and penicillin (75-100%) and low resistance to amikacin, linezolid, netilmicin, nitrofurantoin, teicoplanin and vancomycin (0-13%). The MIC₉₀ values (MIC required to inhibit 90% of the isolates) for vancomycin, linezolid and rifampicin decreased, whereas the MIC₉₀ for teicoplanin increased. The change in the geometric mean MIC of rifampicin was found to be statistically significant. A statistically significant and progressive MIC creep was observed for teicoplanin and rifampicin.

CONCLUSION

Despite remaining susceptible, S. aureus is not inert to antibiotic pressure. Implementation of preventive measures in healthcare settings is required worldwide to combat the increasing number of infections by this pathogen.

A 5-year Survey Reveals Increased Susceptibility to Glycopeptides for Methicillin-Resistant Staphylococcus aureus Isolates from Staphylococcus aureus Bacteremia Patients in a Chinese Burn Center

Methicillin-resistant Staphylococcus aureus (MRSA) infections are prevalent in burn wards, and are especially serious in S. aureus bacteremia (SAB) patients. Glycopeptides and daptomycin are effective against MRSA infections, but MIC creeps can reduce their efficacy. Our object was to perform a molecular epidemiological investigation of S. aureus isolates in our burn center and to evaluate MICs for antimicrobials against SAB-associated MRSA isolates. A total of 259 S. aureus isolates, obtained from August 2011 to July 2016, were used in this study. Multiple molecular typing was used for molecular epidemiological analysis. E-tests were used to determine MICs of vancomycin, teicoplanin, and daptomycin for SAB-associated MRSA isolates. MIC values were stratified by collection date or source and compared. Spearman's test was used to analyze MICs correlations amongst tested antimicrobials. ST239-MRSA-III-t030-agrI clone was found to be dominant in both SAB and non-SAB patients, and significantly more in SAB patients (P < 0.0001). SAB-MRSA isolates exhibited decreased MICs for vancomycin, teicoplanin, and daptomycin during the 5-year period. Compared to those isolated from catheters or wounds, SAB-MRSA isolates from the bloodstream were less susceptible to vancomycin and daptomycin, but more susceptible to teicoplanin. MICs Correlation was found only between vancomycin and daptomycin in MRSA isolates from the bloodstream (rho = 0.250, P = 0.024). In conclusion, our results suggest that MRSA infections are still serious problems in burn centers. In contrast to most other studies, we observed increased susceptibility to glycopeptides and daptomycin against SAB-associated MRSA in our center from 2011 to 2016, suggesting the use of glycopeptides does not lead to MIC creeps. Isolates from different sites of the body may exhibit different levels of susceptibility and change trend over time for different antimicrobials, antimicrobials selection for MRSA infections should be considered comprehensively.

Evaluation of vancomycin MIC creep in Staphylococcus aureus

OBJECTIVES

Vancomycin is the primary treatment for methicillin-resistant Staphylococcus aureus (MRSA). However, an increasing proportion of MRSA isolates with high minimum inhibitory concentrations (MICs) within the susceptible range (vancomycin 'MIC creep') is being observed. The aim of this study was to assess the vancomycin MIC distribution for S. aureus isolates over a period of 4 years in Centro Hospitalar Baixo Vouga (Aveiro, Portugal) and to identify differences in vancomycin MIC determined by different susceptibility testing methods.

METHODS

For each S. aureus isolate, the vancomycin MIC was assayed by the VITEK^®2 automated system and the broth microdilution testing method.

RESULTS

The results showed significant differences in vancomycin MIC by different methods (P=0.021, sign test) and did not suggest the presence of vancomycin MIC creep during the study period.

CONCLUSIONS

Vancomycin MIC creep is a regional problem, therefore it can only be assessed through the evaluation of local susceptibility profiles, and antibiogram based on real MIC assay should be an essential element in local MRSA infection clinical management.

Glycopeptide and daptomycin susceptibility trends among clinical isolates of methicillin-resistant Staphylococcus aureus in a tertiary care center in North India

Increased vancomycin minimum inhibitory concentration (MIC) levels in Staphylococcus aureus and their association with vancomycin treatment failure are well-known problems. Few studies have recognized progressive increases in glycopeptide MIC levels for S. aureus strains in recent years. This study determined glycopeptide and daptomycin susceptibility among methicillin resistant S. aureus (MRSA) strains. A total of 776 clinical isolates of MRSA recovered from 2009 to 2012 were studied for glycopeptide and daptomycin susceptibility using the E-test method. The vancomycin MIC geometric mean (GM) of the MRSA isolates was 0.923, 0.944, 1.134 and 1.294 mg/L in the years 2009, 2010, 2011 and 2012, respectively, and the trend significantly increased over the years (P < 0.0001). Similarly, the teicoplanin MIC GM was 1.47, 1.49, 1.8 and 2.04 mg/L in the years from 2009 to 2012, respectively (P < 0.0001). MIC shifts were not found for daptomycin (P > 0.232). A significant increase in the MIC for glycopeptides was observed among the clinical MRSA isolates at our center over a 4-year period. However, the daptomycin MIC did not increase in the observed MRSA isolates.