Antibiotic antibiotic therapy. The antibiotic treatment may select for bacterial strains with physiologically or genetically enhanced capacity to survive high doses of antibiotics. Under certain conditions, it may result in preferential growth of resistant bacteria, while growth of susceptible bacteria is inhibited by the drug. For example, antibacterial selection for strains having previously acquired antibacterial-resistance genes was demonstrated in 1943 by the Luria–Delbrück experiment. Antibiotics such as penicillin and erythromycin, which used to have a high efficacy against many bacterial species and strains, have become less effective, due to the increased resistance of many bacterial strains. Resistance may take the form
Quinolone antibiotic not be used as a first-line agent for community-acquired pneumonia, instead recommending macrolide or doxycycline as first-line agents. The Drug-Resistant "Streptococcus pneumoniae" Working Group recommends fluoroquinolones be used for the ambulatory treatment of community-acquired pneumonia only after other antibiotic classes have been tried and failed, or in cases with demonstrated drug-resistant "Streptococcus pneumoniae". Resistance to quinolones can evolve rapidly, even during a course of treatment. Numerous pathogens, including "Escherichia coli", commonly exhibit resistance. Widespread veterinary usage of quinolones, in particular in Europe, has been implicated. Fluoroquinolones had become the class of antibiotics most commonly prescribed to adults in 2002. Nearly