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Our study indicated high rates of dapsone resistance in patients with relapse, compared with patients with new and recent cases of leprosy. Moreover, it was observed that many of the patients with relapse who had dapsone-resistant mutations had histories of treatment with dapsone monotherapy.

Aim Fluoroquinolone (FQ) is a potent antibiotic class. However, resistance to this class emerges quickly which hinders its application. In this study, mechanisms leading to the emergence of multidrug-resistant (MDR) Staphylococcus aureus (S. aureus) strains under FQ exposure were investigated. Methodology S. aureus ATCC 29213 was serially exposed to ciprofloxacin (CIP), ofloxacin (OFL), or levofloxacin (LEV) at sub-minimum inhibitory concentrations (sub-MICs) for 12 days to obtain S. aureus -1 strains and antibiotic-free cultured for another 10 days to obtain S. aureus-2 strains. The whole genome (WGS) and target sequencing were applied to analyze genomic alterations; and RT-qPCR was used to access the expressions of efflux-related genes, alternative sigma factors, and genes involved in FQ resistance. Results A strong and irreversible increase of MICs was observed in all applied FQs (32 to 128 times) in all S. aureus-1 and remained 16 to 32 times in all S. aureus-2. WGS indicated 10 noticeable mutations occurring in all FQ-exposed S. aureus including 2 insdel mutations in SACOL0573 and rimI; a synonymous mutation in hslO; and 7 missense mutations located in an untranslated region. GrlA, was found mutated (R570H) in all S. aureus-1 and -2. Genes encoding for efflux pumps and their regulator (norA, norB, norC, and mgrA); alternative sigma factors (sigB and sigS); acetyltransferase (rimI); methicillin resistance (fmtB); and hypothetical protein BJI72_0645 were overexpressed in FQ-exposed strains. Conclusion The emergence of MDR S. aureus was associated with the mutations in the FQ-target sequences and the overexpression of efflux pump systems and their regulators.

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Aim: Recently, the rise in Staphylococcal infection incidence accompanied by a rise of antibiotic-resistant strains is a major threat to public health. In this study, mechanisms leading to the occurrence of high-level multidrug-resistant (MDR) Staphylococcus aureus (S. aureus) strains after fluoroquinolone (FQ) exposure were investigated. Methodology: Serially exposing S. aureus ATCC 29213 to ciprofloxacin (CIP), ofloxacin (OFL), or levofloxacin (LEV) at sub-minimum inhibitory concentrations (sub-MICs) for 12 days was performed to obtain S. aureus -1 strains and culturing for another 10 days without antibiotics to obtain S. aureus-2 strains. The genomic alterations in FQ-exposed strains were reached using whole genome sequencing and target sequencing. The expressions of efflux-related genes, alternative sigma factors, and genes involved in FQ resistance were evaluated using RT-qPCR. Results: After serial FQ exposure, we observed a strong and irreversible increase of MICs to all applied FQs, i.e 32 to 128 times in all S. aureus-1 and remained 16 to 32 times in all S. aureus-2. WGS indicated 10 significant mutations including 2 deletions, 1 insertion, and 7 missense mutations that occur in all S. aureus-1 and -2 but not in initial strain. The FQ target, GrlA, was also mutated (R570H) in all S. aureus-1 and -2 which can partly explain the development of FQ resistance over the FQ exposure. Besides, FQ exposure also resulted in overexpression of genes encoding for (1) efflux pumps and their regulator (norA, norB, norC, and mgrA); (2) alternative sigma factors (sigB and sigS); (3) acetyltransferase (rimI); (4) methicillin resistance (fmtB); and (5) hypothetical protein BJI72_0645. Conclusion: The mutations occurred in the FQ-target sequence were associated with high-level FQ resistance while the activation of efflux pump systems and post-translational modification proteins played an important role in the emergence of MDR in S. aureus.