OBJECTIVE To study the classification of the ?-lactamases produced by Citrobacter freundii.METHODS To detect the ?-lactamases produced by 33 strains of C.freundii with nitrocefin test,a multi-disk test(synergy test and antagonized test) for the inducible AmpC ?-lactamases(IABLs),AmpC ?-lactamases(ABLs) phenotype test,extended-spectrum ?-lactamases(ESBLs) screening test,and carbapenem-hydrolyzing ?-lactamases(CHBLs).RESULTS In the 33 strains,29 strains produced the ?-lactamases(87.9%);the nitrocefin tests of 27 from the 29 strains were positive(81.8%);two strains produced penicillinases,3 strains produced cephalosporinases,5 strains produced broad-spectrum ?-lactamases(BSBLs),11 strains produced ESBLs alone,and 6 strains produced ESBLs+ high-productive ABLs,the rate of ESBLs produced by the 33 strains of C.freundii was 51.5%,and 2 strains produced CHBLs(all produced ESBLs+ metallo-?-lactamase).CONCLUSIONS The rate of ?-lactamases,rate of ESBLs and co-produced rate is very high.There are six kinds of ?-lactamases produced by the 33 strains of C.freundii,mainly BSBLs and ESBLs.

OBJECTIVE To study the classification the ?-lactamases produced by Providencia spp.METHODS To detect the ?-lactamases produced by 19 strains of Providencia spp with nitrocefin test,a multi-disk test(synergy test,antagonized test for the inducible AmpC ?-lactamases(IABLs),AmpC ?-lactamases(ABLs) phenotype test and extended-spectrum ?-lactamases(ESBLs) screening test,carbapenem-hydrolyzing ?-lactamases(CHBLs).RESULTS The nitrocefin tests of all of 19 strains were positive,producing the ?-lactamases(100.0%);eight strains produced broad-spectrum ?-lactamases(BSBLs,42.1%) and ESBLs(42.1%),respectively,one strain produced overexpression of AmpC,3 strains produced CHBLs.CONCLUSIONS The rate of ?-lactamases produced by the 19 strains of Providencia spp is very high,there are three kinds of ?-lactamases,mainly BSBLs and ESBLs.