Methicillin resistance study in clinical isolates of coagulase-negative staphylococci and determination of their susceptibility to alternative antimicrobial agents

Abstract

Aims: To achieve reliable detection of methicillin resistance in clinical isolates of coagulase‐negative staphylococci. Methods and Results: Strains (105) were evaluated by normatized antimicrobial susceptibility methods, and for the presence of the methicillin resistance‐determining mecA gene, using the polymerase chain reaction. Correlation between phenotypic and genotypic methods was obtained in 87·6% of the samples. Six strains, classified as methicillin‐susceptible by phenotypic assays, revealed the presence of the mecA gene, indicating that methicillin resistance expression was probably repressed. Another seven isolates failed to show mecA amplification after displaying methicillin resistance in phenotypic evaluations. The susceptibility of the methicillin‐resistant isolates to other antimicrobial agents was variable. Conclusions: Genotypic determination of the mecA gene proved to be the most reliable method for detection of methicillin resistance. Significance and Impact of the Study: Correct assessment of methicillin resistance, such as that attained through genotyping, is essential for defining therapeutic strategies, particularly when treating severely compromised patients.

Detection of methicillin resistant and slime factor production of coagulase negative Staphylococcus spp. in bovine clinical mastitis by using PCR

“…In recent years, increased numbers of β-lactamase-producing CoNS and mecA-gene positive CoNS [MRCoNS] resistant to all groups of β-lactam antibiotics have been observed [33] .In the present study, three [50%] CoNS strains were positive phenotypically by disc diffusion method and negative byPCR for detection of methicillin resistance, Table [4]. The differences between molecular and phenotypic determinations of methicillin resistant was reported by [11] . The isolates that did not carry mecA were phenotypically resistant to methicillin [33] .…”

“…Indiscriminate use of the antibiotics in the farm animal practice coupled with the increasing pathogenicity of the CoNS was suspected to be the issue of major concern [40] . The frequency of methicillin-resistant strains in CoNS varies widely among [11] .…”

“…[3]. The positive detection rates of mecA in MRCoNS were 79% and 63.2% by [11,33] , respectively. In recent years, increased numbers of β-lactamase-producing CoNS and mecA-gene positive CoNS [MRCoNS] resistant to all groups of β-lactam antibiotics have been observed [33] .In the present study, three [50%] CoNS strains were positive phenotypically by disc diffusion method and negative byPCR for detection of methicillin resistance, Table [4].…”

“…Methicillin resistance is associated with the presence of the mecA gene which encodes a penicillin-binding protein [PBP2a] with altered properties responsible for the observed resistance [10] . Incidence of methicillin resistance in CoNS is high, as well as the accompanying antimicrobial resistance [11] .…”

“…Although the use of PCR-based determinations represents a significant increase in reagent costs relative to phenotypic reagents, their reliability, as well as considerations of the time and labour, make these molecular methods increasingly recommendable for early detection of methicillin resistance [11] .…”