Proteus vulgaris has potential to produce "broad-spectrum" beta-lactamases that can hydrolyze penicillins and cephalosporins. Treatment of such organisms can often be challenging.
While resistance may not be detectable initially, it can appear after a period of exposure to beta-lactam antibiotics. Use of penicillins (with or without beta-lactamase inhibitors) and cephalosporins should generally be avoided.
Fosfomycin and nitrofurantoin should be used for cystitis only.