Generation and Characterization of Stable Small Colony Variants of USA300 <i>Staphylococcus aureus</i> in RAW 264.7 Murine Macrophages
Dalida Bivona,
Carmelo Bonomo,
Lorenzo Colombini,
Paolo G. Bonacci,
Grete F. Privitera,
Giuseppe Caruso,
Filippo Caraci,
Francesco Santoro,
Nicolò Musso,
Dafne Bongiorno,
Francesco Iannelli,
Stefania Stefani
Affiliations
Dalida Bivona
Medical Molecular Microbiology and Antibiotic Resistance Laboratory (MMARLab), Department of Biomedical and Biotechnological Sciences (BIOMETEC), University of Catania, 95123 Catania, Italy
Carmelo Bonomo
Medical Molecular Microbiology and Antibiotic Resistance Laboratory (MMARLab), Department of Biomedical and Biotechnological Sciences (BIOMETEC), University of Catania, 95123 Catania, Italy
Lorenzo Colombini
Laboratory of Molecular Microbiology and Biotechnology, Department of Medical Biotechnologies, University of Siena, 53100 Siena, Italy
Paolo G. Bonacci
Medical Molecular Microbiology and Antibiotic Resistance Laboratory (MMARLab), Department of Biomedical and Biotechnological Sciences (BIOMETEC), University of Catania, 95123 Catania, Italy
Grete F. Privitera
Department of Clinical and Experimental Medicine, University of Catania, 95123 Catania, Italy
Giuseppe Caruso
Department of Drug and Health Sciences, University of Catania, 95125 Catania, Italy
Filippo Caraci
Department of Drug and Health Sciences, University of Catania, 95125 Catania, Italy
Francesco Santoro
Laboratory of Molecular Microbiology and Biotechnology, Department of Medical Biotechnologies, University of Siena, 53100 Siena, Italy
Nicolò Musso
Biochemical Section, Department of Biomedical and Biotechnological Sciences (BIOMETEC), University of Catania, 95123 Catania, Italy
Dafne Bongiorno
Medical Molecular Microbiology and Antibiotic Resistance Laboratory (MMARLab), Department of Biomedical and Biotechnological Sciences (BIOMETEC), University of Catania, 95123 Catania, Italy
Francesco Iannelli
Laboratory of Molecular Microbiology and Biotechnology, Department of Medical Biotechnologies, University of Siena, 53100 Siena, Italy
Stefania Stefani
Medical Molecular Microbiology and Antibiotic Resistance Laboratory (MMARLab), Department of Biomedical and Biotechnological Sciences (BIOMETEC), University of Catania, 95123 Catania, Italy
Intracellular survival and immune evasion are typical features of staphylococcal infections. USA300 is a major clone of methicillin-resistant S. aureus (MRSA), a community- and hospital-acquired pathogen capable of disseminating throughout the body and evading the immune system. Carnosine is an endogenous dipeptide characterized by antioxidant and anti-inflammatory properties acting on the peripheral (macrophages) and tissue-resident (microglia) immune system. In this work, RAW 264.7 murine macrophages were infected with the USA300 ATCC BAA-1556 S. aureus strain and treated with 20 mM carnosine and/or 32 mg/L erythromycin. Stable small colony variant (SCV) formation on blood agar medium was obtained after 48 h of combined treatment. Whole genome sequencing of the BAA-1556 strain and its stable derivative SCVs when combining Illumina and nanopore technologies revealed three single nucleotide differences, including a nonsense mutation in the shikimate kinase gene aroK. Gene expression analysis showed a significant up-regulation of the uhpt and sdrE genes in the stable SCVs compared with the wild-type, likely involved in adaptation to the intracellular milieu.
