Prevalence of β-Lactamases among 1,072 Clinical Strains of Proteus mirabilis: a 2-Year Survey in a French Hospital

β-Lactam resistance was studied in 1,072 consecutive P. mirabilis clinical strains isolated at the Clermont-Ferrand teaching hospital between April 1996 and March 1998. The frequency of amoxicillin resistance was 48.5%. Among the 520 amoxicillin-resistant isolates, three resistance phenotypes were detected: penicillinase (407 strains [78.3%]), extended-spectrum β-lactamase (74 strains [14.2%]), and inhibitor resistance (39 strains [7.5%]). The penicillinase phenotype isolates were divided into three groups according to the level of resistance to β-lactams, which was shown to be related to the strength of the promoter. The characterization of the different β-lactamases showed that amoxicillin resistance in P. mirabilis was almost always (97%) associated with TEM or TEM-derived β-lactamases, most of which evolved via TEM-2.