Double-Serine Fluoroquinolone Resistance Mutations Advance Major International Clones and Lineages of Various Multi-Drug Resistant Bacteria.

The major international sequence types/lineages of methicillin-resistant (MRSA), extended-spectrum β-lactamase (ESBL)-producing and ESBL-producing were demonstrated to have been advanced by favorable fitness balance associated with high-level resistance to fluoroquinolones. The paper shows that favorable fitness in the major STs/lineages of these pathogens was principally attained by the capacity of evolving mutations in the fluoroquinolone-binding serine residues of both the DNA gyrase and topoisomerase IV enzymes. The available information on fitness balance incurred by individual and various combinations of mutations in the enzymes is reviewed in multiple species.

Fitness cost associated with resistance to fluoroquinolones is diverse across clones of Klebsiella pneumoniae and may select for CTX-M-15 type extended-spectrum β-lactamase.

Lowered fitness cost associated with resistance to fluoroquinolones was recently demonstrated to influence the clonal dynamics of methicillin-resistant Staphylococcus aureus (MRSA) in the health care setting. We investigated whether or not a similar mechanism impacts Klebsiella pneumoniae. The fitness of K.