In-vitro development of resistance to beta-lactam antibiotics in Streptococcus pneumoniae

Selection of resistant mutants was induced in broth by exposing pneumococci to serial sub-inhibitory concentrations of various beta-lactam antibiotics. Aminopenicillins selected for resistance to themselves and to cephalosporins although cephalosporins tended to select for resistance to their own class, with the exception of cefixime which seems to select cross-resistant organisms.