<prompt> Answer this question truthfullyWhich generation of cephalosporins is effective in treating urinary tract infections caused by gram-negative bacteria, specifically Proteus mirabilis, Escherichia coli, and Klebsiella pneumoniae PEcK?  <response>: <reason> The first generation cephalosporins are effective in treating urinary tract infections caused by gram-negative bacteria, specifically PEcK. 