The distribution of mecA, mecR1 and mecI and sequence analysis of mecI and the mec promoter region in staphylococci expressing resistance to methicillin

Abstract

The presence and sequences of genes that regulate the expression of methicillin resistance was investigated in 42 isolates of Staphylococcus aureus and 102 isolates of coagulase-negative staphylococci (CNS). PCR was used to detect mecA and the regulatory genes mecR1 and mecI. In a selected group of isolates, the sequences of mecI and the mec promoter region were also determined and compared with the sequences obtained from pre-MRSA strain N315. The genetic diversity of the collection was assessed by pulsed-field gel electrophoresis (PFGE). mecA was present in 21 S. aureus and 44 CNS. mecR1 was associated with mecA in all S. aureus and in all CNS, except two isolates of Staphylococcus haemolyticus. mecI was present in 48% of mecA-positive S. aureus and 50% of mecA-positive CNS. In six S. aureus isolates, mecI contained a termination codon at nucleotide 202 which would truncate the MecI protein. No mutation was found in the mecI gene of the four other S. aureus and 15 CNS sequenced. Seven isolates of Staphylococcus simulans had a single nucleotide substitution in the mec promoter region. Expression of methicillin resistance could be explained for all mecA-positive staphylococci with mutations within mecI or in the mec promoter region or in which mecI was deleted. However, the 'wild type' sequences observed in four S. aureus and eight CNS suggest that there is another mechanism for overcoming the repression of resistance caused by mecI.

Comparative Analysis of Multidrug-Resistant, Non-Multidrug-Resistant, and Archaic Methicillin-Resistant Staphylococcus aureus Isolates from Central Sydney, Australia

“…The eight nmMRSA group 1 isolates with mecI deletions may share a common ancestor, but a detailed analysis of deletion junctions would be needed to verify this. Among the mutations in the two nmMRSA group 1 isolates with an intact mecI gene, a C3T substitution in J28 at position 202 has been reported in MRSA isolates from several countries around the world (7,12,31,34). In marked contrast to findings in nmMRSA, 13 of the 14 mMRSA isolates retained the mecI gene.…”

“…Analysis of mecI in contemporary MRSA from other countries has shown deletion rates ranging from 16 to 73% (11,13,26,31,34). Our study of mec mutations has novel features: it provides the first such data from this part of the world and, unlike previous surveys, distinguishes multidrug-resistant from non-multidrug-resistant strains.…”

mecA - blaZ Corepressors in Clinical Staphylococcus aureus Isolates

“…In addition to regulating blaZ transcription, BlaI also binds to mecA-mecR1 promoter-operator (P-O) sequences and regulates their transcription (9,13,14,19). Coregulation of mecA by both MecI and BlaI has been demonstrated in defined laboratory strains (14), but neither the presence nor the nucleotide sequences of the two coregulators have been investigated in clinical isolates.Mutations and deletions in mecI and deletions of both mecI and mecR1 appear to be common in clinical Staphylococcus aureus isolates (1,12,16,21,22). In contrast, while there has been no systematic assessment of blaI and blaR1 in clinical isolates, these regulators have been found to be intact in sequence or function whenever they have been examined.…”

Detección de los genes mecA, mecRl y mecí en cepas de Staphylococcus aureus resistentes a meticilina de origen bovino aisladas en unidades de producción lechera familiar, México

“…La transcripción del gen mecA se produce cuando la proteína MecR1 se expone a los β-lactámicos con su dominio extracelular de unión a penicilina (PB), activando su dominio citoplásmico (MS) en forma de proteasa; a continuación se escinde la proteína represora MECI, la que bloquea la región operadora del gen mecA expresando la PBP2a (Zhang y col 2001). Los genes mecR1 y mecI han sido identificados en S. aureus de origen humano (Weller 1999, Petinaki y col 2001 y bovino (Lee 2006). En México se ha identificado SARM en bovinos con mastitis, pero la identificación del gen mecA y sus elementos regulatorios mecR1 y mecI aún no han sido estudiados.…”