| A novel extracellular β-lactamase (AmpC2′) and two periplasmic β-lactamases (AmpC1 and AmpC2) were purified and characterized from the β-lactam-resistant clinical strain Enterobacter cloacae 212. AmpC2′ and AmpC2, sharing the same molecular weight (39.4 kDa) and basic pI value (9.3), are considered to be the same protein. AmpC1, with a slightly larger molecular weight (40 kDa) and similar pI value (9.3), may be a precusor of AmpC2/AmpC2′ . Cloning and nucleotide sequencing indicate the AmpC proteins are encoded by the chromosomal ampC 212. Analysis of the 1.2 kb ampC 212 reveals high nucleotide and amino acid sequence identity to other ampC genes reported in E. cloacae . Based upon the physical characteristics and nucleotide sequence, ampC 212 is assigned into the Group 1 cephalosporinases of the Bush-Jacoby-Medeiros classification scheme. The minimum inhibitory concentration (MIC) values observed for transformants harboring ampC 212 increased against natural penicillins, aminopenicillins, carboxypenicillins, ureidopenicillins, and first and second generation cephalosporins. However, the lack of resistance conferred by ampC 212 to third generation cephalosporins, cephamycins, carbapenems, and monobactams suggests ampC 212 is not responsible for the entire range of resistance found in the 212 strain. Penicillin-binding-proteins (PBPs) of E. cloacae 212 when compared to other 13-lactam resistant E. cloacae strains, showed differences exist among the strains which may also contribute to the high levels of resistance found in E. cloacae 212. The presence of an extracellular β-lactamase produced by E. cloacae has clinical significance and may have an impact on the development of antimicrobial agents and chemotherapeutic strategies. |
