<prompt> Which one of the following is a mechanism underlying the resistance of strains of S. pneumoniae to the widely used antibiotic, ciprofloxacin?Reduced topoisomerase sensitivity to inhibitorsIncreased synthesis of PABAFormation of methyltransferases that change receptor structureStructural changes in porins  <response>: Microbial resistance to fluoroquinolones is increasing, and some strains of Streptococcus pneumoniae are now resistant to ciprofloxacin. The mechanism can involve changes in the structure of topoisomerase IV, one of the targets of fluoroquinolones, which inhibit nucleic acid synthesis. Pneumococcal resistance to penicillins is also increasing via changes in penicillin-binding proteins PBPs. The other mechanisms listed underlie microbial resistance to other antibiotics as follows: sulfonamides choice B, macrolides choice C, extended-spectrum penicillins choice D, and beta-lactams choice E. 