TRENDS IN BETA-LACTAM RESISTANCE AMONG ENTEROBACTERIACEAE

beta-Lactam resistance among Enterobacteriaceae is related primarily t o the emergence of novel beta-lactamases. The class A extended-spectru m beta-lactamases hydrolyze extended-spectrum beta-lactams and are inh ibited by clavulanic acid. These beta-lactamases are divided in two gr oups: TEM and SHV derivatives and non-TEM and non-SHV extended-spectru m beta-lactamases (CTX-M1, CTX-M2, MEN-1, PER-1, PER-2, TOHO-1, and VE B-1). The plasmid-mediated cephalosporinases (MIR-1, FOX-1, MOX-1, BIL -1, CMY-1, CMY-2, and LAT-1) hydrolyze extended-spectrum cephalosporin s and cephamycins and are not inhibited by clavulanic acid. They have been reported in Europe and in the United States. The 15 inhibitor-res istant penicillinases are TEM derivatives (except for SHV-10) and plas mid mediated, and they are mainly from Escherichia coli isolates. The carbapenemases noted among Enterobacteriaceae are either the chromosom ally located penicillinases (Sme-1, NmcA, IMI-1) found in rare Enterob acter cloacae or Serratia marcescens isolates or the plasmid-mediated metalloenzyme IMP-1 that is widespread in Japan. The incidence of resi stance among Enterobacteriaceae related to the other more common beta- lactam-resistance mechanisms has continued to rise worldwide.