GeneXpert Captures Unstable Methicillin-Resistant Staphylococcus aureus Prone to Rapidly Losing the mecA Gene

Abstract

A cefoxitin-susceptible Staphylococcus aureus strain was identified by the Cepheid GeneXpert as methicillinresistant S. aureus (MRSA). This strain was highly unstable and rapidly lost SCCmec upon subculturing in vitro, indicating that unstable MRSA is best detected by gene amplification-based methods. CASE REPORTA 62-year-old woman underwent posterior lumbar decompression and stabilization L3 to L5 for intractable lumbar pain and neurogenic claudication due to severe stenosis and instability. One month after surgery, the patient experienced progressive lumbar pain; the wound area showed signs of inflammation without purulent secretion. The C-reactive protein (CRP) level was elevated to 98 mg/dl, and body temperature was elevated up to 40°C. Computer tomography showed correct decompression and placement of transpedicular screws and intervertebral cages, with no signs of loosening or abscess formation. A postoperative superficial and potentially deep wound infection was diagnosed. Blood cultures were taken, and empirical intravenous antibiotic therapy with vancomycin, flucloxacillin, and rifampin was administered for 4 days. Fever subsided, blood cultures became positive for Staphylococcus aureus, and intravenous therapy was continued with only flucloxacillin and rifampin for 13 days. The patient was then discharged with levofloxacin and rifampin per os, which was continued for a total of 6 weeks. The CRP level normalized 3 weeks after initial antibiotic treatment, and local pain subsided within 2 months. Further follow-up over 1 year with CRP and clinical and radiological controls was uneventful, and the patient fared well.

Gene-Z: a device for point of care genetic testing using a smartphone

“…Tracking a pathogen by single marker has lead to improper diagnosis in some instances. [4][5][6] Up and coming techniques that have recently been published for POC genetic testing are promising due to the use of microfluidic chips with smaller assay volumes and reduced reagent consumption and/or rapid…”

Detection of Methicillin-Resistant Staphylococcus aureus Infections Using Molecular Methods

“…The junction region between orfX in the S. aureus chromosome and the inserted SCC mec element was targeted early on for detection of MRSA by PCR directly in nasal swabs [ 13 , 18 ]. While this approach has overall been very successful [ 13 , 19 , 20 , 21 ], the loss of the mecA gene from the SCC mec element (so called “empty cassettes”) resulted in some false positive results in commercial tests [ 22 , 23 , 24 ]. This was addressed in some tests by adding additional primer sets targeting either mecA [ 25 ] or both mecA and mecC to complement those for the junction region to ensure that the methicillin resistance gene was still present in those strains in which the orfX /SCC mec junction was detected [ 26 , 27 ].…”

A Comprehensive Overview of Antibiotic Selection and the Factors Affecting It

“…Currently, we are finding ourselves in a transition period between using classic laboratory techniques to determine susceptibility and using automated machines that can expedite and aid us in providing a diagnosis. Machines such as GeneXpert® (Cepheid, Sunnyvale, CA) have begun to be employed that allow for not only the determination of a pathogen, but also the determination of resistance to certain antibiotics such as methicillin - a popular use of the machine is to help diagnose methicillin-resistant Staphylococcus aureus (MRSA) [ 22 , 23 ]. Moreover, BioFire machines (BioFire Diagnostics, Salt Lake City, UT) can identify pathogens directly from blood cultures and can detect resistance to methicillin, vancomycin, and carbapenem [ 24 ].…”