[In vivo-acquired resistance to cefsulodin by a strain of Pseudomonas aeruginosa].

We isolated a Pseudomonas aeruginosa strain which was initially cefsulodin-susceptible (J1, MIC = 4 g/l) and became resistant (J2, MIC greater than 64 g/l) after 12 days of treatment of the patient with cefsulodin. Strain J2 had a constitutive beta-lactamase with hydrolytic activities similar to those of a cephalosporinase and an isoelectric point at 8.1. This enzyme (Case) may be related to the ld type. Concomitant development of resistances to various beta-lactams stable to Case suggests that other mechanisms of resistance may be involved.