Microbiological diagnosis

Extended-spectrum Beta-lactamases are enzymes produced by some bacteria with a spectrum of hydrolysis that provide resistance to 3rd generation Cephalosporins.

In the presence of β-lactamases the ß-Lactam ring is hydrolyzed except for carbapenem and cephamycin antibiotics.

The ESBLs are frequently plasmid encoded, facilitating its transfer from one bacterium to another. This mechanism is responsible for spreading resistance among patients. Furthermore, genes for resistance to other antibiotics (co-resistors) are frequently plasmid-induced.

Fig 1: image of bacterial conjugation

(plasmid exchange between bacterias)

Just as penicillinases, the β-Lactamases are inhibited in vitro by clavulanic acid. In the antibiogram this inhibition appears as the so called "champagne cork aspect" when performing a double disk synergy test.(Fig 2).

Fig 2 : antibiogram of E. coli β-Lactamase and synergistic effect shown as « champagne cork aspect »

In the laboratory, the β-Lactamase phenotype can be detected in an antibiogram carried out with clinical specimens of enteric bacteria strains.

The presence of Enterobacteria producing β-Lactamase may also be sought specifically in the context of a screening policy for multi-resistant bacteria.

In this case, the search is performed from a rectal swab plated on selective media containing 3GC (Fig 3).

Fig 3: chronology for obtaining results after sample testing

J 0: rectal swab sample testing

J 1: positive culture on specific medium

J 2: Antibiogram performed