ESBL producers

Extended Spectrum Beta-Lactamase (ESBL)

The picture below is a method to detect ESBL producers by using disk potentiation technique. Aztreonam (ATM 30ug) disk and Amoxicillin/Clavulanic acid or Augmentin (AMC 30ug) disk are placed 1.5 cm apart on a susceptibility plate. Incubated for 18-24 hours. Positive results can be seen as shown exhibiting a "keyhole effect" between Aztreonam disk (ATM) and Augmentin disk (AMC). *A keyhole effect can also be seen between Ticarcillin/Clavulanic acid (TIM) disk and Aztreonam (ATM) disk.

    * I will try to upload more (and better) pics of ESBL positive screening results.

ESBL are enzymes derived from mutations of TEM-1, SHV-1, capable of hydrolyzing extended spectrum cephalosporins such as cefotaxime, ceftriaxone but not cephamycins such as cefoxitin and cefotetan. These may be present and detected among enterobacteriaceae.

ESBL detection is very important in the surveillance of antimicrobial resistance. In 2007, CLSI (Clinical and Laboratory Standards Institute) recommended that all confirmed ESBL-producing strains should be interpreted and reported as resistant for all penicillins, cephalosporins (except cephamycins and Beta-Lactam/Beta-lactamase inhibitors, carbapenems) and Aztreonam regardless of in vitro results. This means that back then, an aztreonam with a zone of inhibition of 25mm, which is suppose to be susceptible, would be reported as resistant if confirmed as an ESBL-producer. But in 2010, these was changed. All results of confirmed ESBL-producers should be reported as is. This is still the recommendation up to now.  




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