The identification of a high percentage of MRSA and presence of VRSA and VISA isolates is a serious warning about the treatment of future MRSA infections and reveals the need for new and effective therapeutic agents.
Both compounds were active against clinical isolates of methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-intermediate and vancomycin-resistant S. aureus (VISA and VRSA respectively) and vancomycin-resistant Enterococcus faecalis (VRE).
MRSA with reduced susceptibility to glycopeptide antibiotics such as vancomycin (vancomycin intermediate S. aureus, VISA) have also emerged in the ocular infections, and there has been a rise in S. aureus resistance to new and old generation fluoroquinolones that are commonly used for prophylaxis after intravitreal injections and intraocular surgeries.
Traditionally, it has been used as a drug of last resort; however, clinical isolates of methicillin-resistant Staphylococcus aureus (MRSA) strains with decreased susceptibility to vancomycin (vancomycin intermediate-resistant S. aureus [VISA]) and more recently with high-level vancomycin resistance (vancomycin-resistant S. aureus [VRSA]) have been described in the clinical literature.
PPNA2332 (≥1 µM) essentially cleared lethal MRSA/VISA Mu50 infection in epithelial cell cultures, and eliminated viable bacterial cells in a time- and concentration- dependent manner, without showing any apparent toxicity at 10 µM.
An isolate of the methicillin-resistant Staphylococcus aureus (MRSA) clone USA300 with reduced susceptibility to vancomycin (SG-R) (i.e, vancomycin-intermediate S. aureus, VISA) and its susceptible "parental" strain (SG-S) were recovered from a patient at the end and at the beginning of an unsuccessful vancomycin therapy.
Resistance to vancomycin, the principal drug used to treat MRSA infections, has only recently emerged, is mainly low level, and characteristically appears during vancomycin therapy (vancomycin-intermediate S. aureus [VISA] and hetero-resistant VISA).
Not surprisingly, the spread of MRSA from the hospital to the community setting, coupled with the emergence of VISA and VRSA, has become a major cause of concern among clinicians and microbiologists.