Klebsiella pneumoniae is a gram-negative nosocomial pathogen and causative agent of many hospital acquired infections. K. pneumoniae infections have become increasingly of interest due to the rise of hypervirulent variants and multidrug resistant strains. Modeling how antibiotic resistance evolves in K. pneumoniae will allow us to better understand exactly how the bacterium acquires resistance to various antibiotics. A previous experiment in our lab exposed a strain of K. pneumoniae to low but increasing concentrations of the antibiotic cephalothin. As a result, the strain evolved to be mucoid with elongated cellular morphology and resistant to multiple antibiotics. This study aimed to repeat the same experimental approach with multiple cultures, to determine if different genomic mutations could result in the same endpoint of antibiotic resistance. Five cultures of K. pneumoniae 43816 were exposed to increasing amounts of the antibiotic cephalothin over a 14-day period. After the 14 day experiment, cultures were assayed for changes in antibiotic susceptibility, colony, and cellular-level morphology. Preliminary results indicate evolved resistance to cephalothin and tetracycline, but not kanamycin. Further, alterations in the colony morphology have been noted with a mix of small and large colony phenotypes. This variation of colony morphology in the adapted population may indicate different genetic mutations that correspond to these large and small colony variants. Current work is determining the relationship between colony morphology and antibiotic resistance
