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Three commercially available microbiology identification and susceptibility testing systems were compared with regard to their ability to detect extended-spectrum ␤-lactamase (ESBL) production in Enterobacteriaceae, i.e., the Phoenix Automated Microbiology System (BD Diagnostic Systems, Sparks, MD), the VITEK 2 System (bioMérieux, Marcy l'Etoile, France), and the MicroScan WalkAway-96 System (Dade Behring, Inc., West Sacramento, CA), using routine testing panels. One hundred fifty putative ESBL producers were distributed blindly to three participating laboratories. Conventional phenotypic confirmatory tests such as the disk approximation method, the CLSI double-disk synergy test, and the Etest ESBL were also evaluated. Biochemical and molecular characterization of ␤-lactamases performed at an independent laboratory was used as the reference method. One hundred forty-seven isolates of Escherichia coli, Klebsiella pneumoniae, Klebsiella oxytoca, Enterobacter cloacae, Enterobacter aerogenes, Citrobacter freundii, Serratia marcescens, Proteus mirabilis, Proteus vulgaris, and Morganella morganii were investigated. Of these isolates, 85 were identified as ESBL producers by the reference method. The remaining isolates were identified as non-ESBL producers; they were either hyperproducers of their chromosomal AmpC, Koxy, or SHV enzymes or lacked any detectable ␤-lactamase activity. The system with the highest sensitivity for the detection of ESBLs was the Phoenix (99%), followed by the VITEK 2 (86%) and the MicroScan (84%); however, specificity was more variable, ranging from 52% (Phoenix) to 78% (VITEK 2). The performance of the semiautomated systems differed widely with the species investigated. The sensitivities of the conventional test methods ranged from 93 to 94%. The double-disk synergy test showed the highest specificity and positive predictive value among all test methods, i.e., 97% and 98%, respectively.In the Enterobacteriaceae, resistance to ␤-lactams is mainly due to ␤-lactamases that hydrolytically cleave the ␤-lactam ring, thus rendering the antibiotic inactive. A strategy to prevent hydrolysis caused by wide-spread ␤-lactamases, like the TEM-1 and SHV-1 enzymes, was the development of intrinsically stable ␤-lactams, such as the extended-spectrum cephalosporins. However, plasmid-encoded derivatives of these enzymes that show an enhanced spectrum of catalytic activity have been known since the early 1980s (7). Due to alterations at the active site caused by specific point mutations, these extended spectrum-␤-lactamases (ESBLs) are also able to hydrolyze oxyimino-␤-cephalosporins (e.g., cefotaxime, cefpodoxime, ceftazidime) and aztreonam (6). In addition to the large number of ESBL-TEM and -SHV variants, other plasmid-encoded ESBL such as CTX-M enzymes (http://www .lahey.org/studies/) are now frequently reported (13). The successful spread of ESBLs in a wide range of Enterobacteriaceae can be attributed to the fact that the genes coding for ESBLs are often located on self-transmissible or mobilizable broadh...

We evaluated the antimicrobial susceptibility of 87 pathogens isolated from 37 patients with odontogenic abscesses. The most prevalent bacteria were viridans group streptococci and Prevotella species. Considering all bacterial isolates, 100% were susceptible to amoxicillin-clavulanic acid, 98% were susceptible to moxifloxacin and to levofloxacin, 76% were susceptible to doxycycline, 75% were susceptible to clindamycin, and 69% were susceptible to penicillin.

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