Detection of amino acid substitutions in the GyrA protein of fluoroquinolone-resistant typhoidal Salmonella isolates using high-resolution mass spectrometry

• A LC–MS methodology was developed to identify fluoroquinolone-resistant Salmonella.
• Reliable and rapid detection of fluoroquinolone resistance is feasible using LC–MS.
• LC–MS can be a useful tool in future detection of antibiotic resistance.

Infections with typhoidal Salmonella isolates that are resistant to fluoroquinolone antibiotics have become very common in several Asian countries. In the majority of these cases, resistance to fluoroquinolone-based antibiotics is associated with genetic mutations in the quinolone resistance-determining region (QRDR) of the bacterial DNA gyrase gene gyrA. The objective of this study was to detect these amino acid substitutions by high-resolution mass spectrometry instead of sequencing of the gyrA gene. A liquid chromatography–mass spectrometry (LC–MS) methodology was developed and evaluated for the detection of amino acid substitutions in the GyrA protein of 23 typhoidal Salmonella isolates. These isolates included typhoidal Salmonella that possessed different antibiotic sensitivities to fluoroquinolone antibiotics. The LC–MS methodology correctly identified peptide sequences associated with phenotypic QRDR mutations of the GyrA protein in all 23 phenotypically diverse typhoidal Salmonella isolates tested. In conclusion, a reliable and rapid LC–MS methodology has been developed that is able to identify GyrA QRDR mutations that are involved in the development of fluoroquinolone resistance in typhoidal Salmonella spp. Furthermore, this ‘proof of principle’ study indicates the potential usefulness of LC–MS in future detection of antibiotic resistance.