Carbapenem resistance in Bacteroides fragilis is associated with cfiA-encoded class B metallo-beta-lactamase. cfiA-negative and cfiA-positive isolates belong to genotypically distinct groups. Of a total of 248 B. fragilis isolates included in this study, 214 were susceptible, 10 were intermediate, and 24 were resistant to meropenem. We show that matrix-assisted laser desorption ionization-time of flight mass spectrometry is able to differentiate between cfiA-negative and cfiA-positive isolates and predict carbapenem resistance in a routine laboratory setting.Bacteroides fragilis is a strictly anaerobic Gram-negative bacillus present in the human gut. It is recovered from various infection sites and frequently associated with abscess formation and sepsis. Carbapenem resistance in B. fragilis is emerging and associated with cfiA-encoded class B metallo-betalactamase, which is activated by insertion sequence (IS) elements. However, elevated MICs or resistance was also observed in strains that did not have activating IS elements in the upstream region of cfiA (17). In the 2003-2005 Belgian multicenter survey (18), the prevalence of the cfiA resistance gene was 7.4% (10/135) (19), which is high compared with the prevalence of cfiA positivity (2 to 7%) in other countries (5,6,13,15,20). In the survey, 4% (6/135) of B. fragilis isolates were intermediate or resistant to meropenem according to CLSI breakpoints (18).By using various molecular typing methods, such as arbitrarily primed PCR, ribotyping, multilocus enzyme electrophoresis, and sequencing of recA and glnA genes, cfiA-negative and cfiA-positive strains were shown to belong to two genotypically distinct groups (9, 10, 13). Matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) has the capacity to discriminate closely related species based on the spectrum of constantly expressed highly abundant proteins, such as ribosomal proteins. This technique was recently introduced as a rapid and accurate method for the identification of bacteria (2,7,14) and can also be applied in the identification of Bacteroides isolates (12). The aim of the present study was to examine the discriminatory power of MALDI-TOF MS to differentiate cfiA-positive from cfiA-negative B. fragilis strains in order to predict carbapenem susceptibility.The 135 B. fragilis clinical isolates from the survey mentioned above (18, 19), originating from nine Belgian hospitals, as well as 113 B. fragilis isolates from routine cultures collected at our laboratory since 2005 were analyzed. Identification was performed by appropriate biochemical and enzymatic tests (11) and confirmed by MALDI-TOF MS. Meropenem susceptibility was determined by Etest methodology (bioMérieux, Marcy l'Etoile, France). The CLSI breakpoints for susceptible and resistant strains are Յ4 mg/liter and Ն16 mg/liter, respectively (4). PCR analysis was performed to detect the presence of the cfiA gene. The annealing temperature of the cfiA gene detection method described by Sóki et al. (16) was increa...

Background: Guidelines established for the treatment of HIV-1 infection and genotype interpretation do not apply for HIV-2. Data about antiretroviral (ARV) drug efficacy and resistance mutations is scarce.

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