Quantitation of mecA transcription in XXXX -resistant @entity794 clinical isolates.

@entity6101 @entity794 @entity3337
The transcription of mecA, the gene required for @entity6101 resistance in staphylococci, was quantified in a collection of 65 geographically and genetically diverse clinical and 8 defined laboratory @entity794 isolates. mecA transcription was measured by real-time reverse transcription-PCR, confirmed by Northern blot analysis, and correlated with the presence and DNA sequence of the two mecA repressors, mecI and blaI. Isolates were first examined that contained mecI and/or blaI with wild-type sequence. BlaI provided significantly more repression of mecA transcription than did MecI, unrelated to blaI genetic location. Both together repressed mecA better than either one alone. In clinical isolates containing only wild-type mecI, mecA transcription repression was 10- to 25-fold less effective than that seen in previously studied constructs derived from strain N315. There was a difference in the mecI @entity3337 ( @entity3337 ) between the clinical isolates (GGAA) and N315 (GGAG). The GGAA @entity3337 was associated with 5.5- to 7.3-fold less mecA repression than GGAG in isogenic constructs. The values generated for wild-type repressors were compared to those in 26 isolates containing mecI mutations. mecA transcription appeared to be repressed only by BlaI in isolates with mecI nonsense and frameshift mutations. In contrast, mecI repression seemed to be partially or fully retained in many of the isolates with mecI and one isolate with blaI missense mutations, providing structure-function correlates with the site and type of mutation. We conclude that mecA repressor activity is highly variable in clinical @entity794 isolates due to mecI mutations, @entity3337 polymorphisms, and unidentified genomic adaptations.
