Abstract
Staphylococcus aureus nasal carriage is a risk factor for individuals suffering from trauma, surgical procedures, invasive devices, and/or decreased immunity. Recently, we demonstrated that artificial nasal colonization with an attenuated S. aureus mutant reduced by bacterial interference with the colonization of pathogenic strains of S. aureus. This could be an optional tool to diminish the rate of S. aureus infections in hospitalized patients. The aim of this study was to construct a safe ΔaroA mutant of S. aureus and to discriminate it from nasal colonizing and osteomyelitis S. aureus isolates by SmaI pulsed-field gel electrophoresis (PFGE) typing. The ΔaroA mutant, named RD17, exhibited an LD50 (3.2 × 106 colony-forming unit (CFU)) significantly higher than that of the parental strain (2.2 × 103 CFU). The colony number of the RD17 mutants recovered from nares of leukopenic mice was similar to that observed in the animals of the control group. Therefore, the ΔaroA mutant was demonstrated to be safe due to maintaining low growth levels in the nares regardless of immune status of the animals. PFGE typing allowed the unequivocal identification of the S. aureus and differentiation of aroA mutants in nasal colonizing and osteomyelitis isolates. This information could be important to discriminate endogenous infections from laboratory strains of S. aureus.
Highlights
Staphylococcus aureus is part of the human microbiota and remains one of the most important community and nosocomial-acquired pathogens, with high rates of hospital-associated infections [1]
In order to characterize the auxotrophic phenotype, the isolated mutants were replicated onto defined minimum medium (DMM) agar plates for S. aureus [18] with or without aromatic amino acids Trp, Phe, Tyr and its precursors p-aminobenzoic acid (PABA) and dihydroxybenzoic acid (DHB)
The number of genetic differences of the RD17 and NK41 mutant genomes (RN6390 and Newman background, resp.), compared with those S. aureus isolates was three or more, which made them clonally different according to the criteria set by Tenover et al [27]. These results show that RD17 and NK41 mutants could be discriminated from osteomyelitis and nasal colonizing S. aureus isolates using SmaI macrorestriction pulsed-field gel electrophoresis (PFGE) typing
Summary
Staphylococcus aureus is part of the human microbiota and remains one of the most important community and nosocomial-acquired pathogens, with high rates of hospital-associated infections [1]. Carriers of methicillinresistant S. aureus (MRSA) have a higher risk of infection than those colonized by methicillin-sensitive (MSSA) strains [4, 5]. Bloodstream infections are an important cause of morbidity and mortality during immunosuppressive conditions (diabetes mellitus, liver diseases, renal failure, corticotherapy, haemodialysis treatment, etc.), for S. aureus nasal carriers [7, 8]. This susceptibility appears to be directly related to the severity and length of leukopenia [9]. Leukocytes, mainly neutrophils, are the main source of proinflammatory mediators and are essential for resistance to bacterial infections [10, 11]
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