Evaluation of various phenotypic methods with genotypic screening for detection of methicillin-resistant Staphylococcus aureus

Abstract

<jats:title>Abstract</jats:title><jats:sec><jats:title>Background</jats:title><jats:p><jats:italic>Staphylococcus aureus</jats:italic> is one of the common opportunistic gram-positive pathogens which are often associated with nosocomial infections. Detection of methicillin-resistant <jats:italic>S. aureus</jats:italic> (MRSA) has become complicated due to the complex phenotypic and genomic pattern.</jats:p></jats:sec><jats:sec><jats:title>Objective</jats:title><jats:p>To evaluate the sensitivity and specificity pattern of various phenotypic methods used in screening <jats:italic>mec</jats:italic> genes harboring MRSA.</jats:p></jats:sec><jats:sec><jats:title>Methods</jats:title><jats:p>Clinical isolates of <jats:italic>S. aureus</jats:italic> were collected from diagnostic centers in Tamil Nadu. Phenotypic identification methods such as Minimal Inhibitory Concentration for oxacillin, oxacillin screen agar (OSA), oxacillin disk diffusion, and cefoxitin disk diffusion (CFD) tests were compared. The clinical isolates were classified into MRSA and methicillin-susceptible <jats:italic>S. aureus</jats:italic> (MSSA) based on the polymerase chain reaction (PCR) amplification of the <jats:italic>mec</jats:italic>A gene.</jats:p></jats:sec><jats:sec><jats:title>Result</jats:title><jats:p>Out of 50 <jats:italic>S. aureus</jats:italic>, 21 were found to be MRSA based on the presence of the <jats:italic>mec</jats:italic>A gene. All 21 <jats:italic>mec</jats:italic>A-positive isolates were found to be resistant through minimum inhibitory concentration (MIC) and CFD test, having a sensitivity of 100% and specificity of 52% and 62%, respectively. OSA and oxacillin disk tests were found to have a sensitivity of 86% and specificity of 48% and 52%, respectively.</jats:p></jats:sec><jats:sec><jats:title>Conclusion</jats:title><jats:p>The combination of two phenotypic methods, CFD and oxacillin MIC, can be used for the detection of MRSA in clinical laboratories.</jats:p></jats:sec>

Mutation-Based Antibiotic Resistance Mechanism in Methicillin-Resistant Staphylococcus aureus Clinical Isolates

“…In addition, all 30 mecA -positive MRSA isolates were found to be resistant to cefoxitin. These data suggest that the cefoxitin disk-diffusion (CFD) method is a sensitive phenotypic testing used for the identification of MRSA, as previously reported [ 18 ]. This CDF method is able to avoid misdiagnosis that could be the significant factor for the emergence of infections with MRSA [ 23 ] and could lead to the development of resistance against other important available antibiotics.…”

“…Of the 33 S. aureus , 30 isolates were found to be resistant to cefoxitin ( Table 1 ) and to be mecA -positive. Therefore, these 30 isolates are MRSAs because polymerase chain reaction (PCR) amplification of the mecA gene and cefoxitin resistance determined by disk diffusion tests are considered a gold standard method for the rapid detection of MRSA infections [ 18 , 19 ]. Of the 30 MRSA, three isolates (MR-13, -14, and -33) demonstrated high-level cefoxitin resistance with inhibition zone diameters ranging from 3 mm to 4 mm ( Table 1 ) and high minimum inhibitory concentrations (MICs) (≥64 mg/L) ( Table 2 ).…”

Facile Synthesis of Functionalized Phenoxy Quinolines: Antibacterial Activities against ESBL Producing Escherichia coli and MRSA, Docking Studies, and Structural Features Determination through Computational Approach

“…In short, MRSA was poured into the Mueller Hinton agar (MHA) plate and a cefoxitin (30 µg) disc was placed. If the zone of inhibition was ≤21 mm, it was considered MRSA positive [44].…”

Identification of the respiratory tract infection due to methicillin-resistant Staphylococcus aureus by TaqMan real-time PCR

“…S. aureus is detected in the clinical laboratory by growth characteristics and identification of catalase and coagulase actions. Resistance to methicillin or oxacillin is routinely measured by traditional S. aureus susceptibility tests when disk diffusion tests, agar dilution methods have been used in compliance with the guidelines of the national committee of clinical laboratory standards [5]. However, routine susceptibility test takes time to complete.…”