Resistance to vancomycin S. aureus : prevalence and clinical significance
The number of reports regarding the isolation of vancomycin-resistant Staphylococcus aureus (VRSA) is significantly higher than the frequency of confirmed cases of resistance to this antibiotic in vitro or an ineffective treatment of vancomycin for staphylococcal infections.
The number of reports of the isolation of vancomycin-resistant Staphylococcus aureus (VRSA) is significantly higher than the frequency of confirmed cases of resistance to this antibiotic in vitro or ineffective treatment of staphylococcal vancomycin infections.
Currently, there are no more than 5-6 S.aureus strains in the world with confirmed MIC values for vancomycin of 8 mg / l (all are linked to the Mu 50 strain ). For the other strains (similar to Mu 3), the MPC does not exceed 3 mg / L.
The "detection" of strains resistant to vancomycin from S. aureus can be explained by the constant modification of the procedures for determining the sensitivity of staphylococci to this antibiotic and the criteria for interpreting the results. The main question requiring further study is whether strains of S.aureus with intermediate resistance to glycopeptides (GISA) cause more frequent clinical ineffectiveness of vancomycin therapy.
As you know, reports of a decrease in the therapeutic efficacy of vancomycin have been found in the literature over the past 40 years. As with other antibacterial drugs, this may be due not only to a direct decrease in the susceptibility of pathogens to vancomycin, but also to other factors, such as an insufficient level of antibiotics in the plasma, monitoring impaired medication, the severity of the patient's condition, the presence of foreign bodies or undrained abscesses, the use of antagonist combinations with aminoglycosides and / or β-lactams, as well as the use of teicoplanin less active in patients is obviously serious and pathological.
Given the high level of vancomycin binding to plasma proteins and the increased non-specific affinity of the drug for the modified cell wall, the effective concentration of vancomycin in plasma should exceed the BMD by 20 to 40%, or, which is much better, at least three times the concentration. the vast majority of 100% dense S. aureus inoculum cells (107-108 CFU / ml).
Currently, there are no clinical studies in which the importance of S.aureus reduced susceptibility to vancomycin as the sole or primary cause of ineffective treatment of infections caused by this pathogen would be studied adequate.
Many GISAs are sensitive to linezolid, chloramphenicol, quinupristine / dalphopristine, cotrimoxazole and sometimes tetracyclines, rifampicin and fusidine, which can be used to treat certain patients, especially in combination with vancomycin. The latest generation fluoroquinolones have little activity against multidrug-resistant staphylococci and new drugs with supposed efficacy against such strains (tigecycline, oritavancin and daptomycin) are at different stages of clinical trials and their clinical importance for the treatment of infections caused by GISA remains to be determined.
It is always difficult to predict the future course of events, however, with the emergence and spread of resistance of staphylococci not only to vancomycin, but also to other new and "old" antibacterial drugs, the clinical significance of GISA will become undeniable.