Extended spectrum beta lactamase (ESBL):
1. This is one important group of beta lactamase that is occasionally found in certain species of gram negative bacilli.
2. These enzymes are called Extended spectrum beta lactamases because they confer upon the bacteria the additional ability to hydrolyze the beta lactum rings of cefotaxime, ceftazidime or aztreonam.
History and present condition:
1. ESBLs were first described in the mid-1980s and during the 1990s were mostly found in Klebsiella species, mostly in hospitals and often in intensive care units treating the most vulnerable patients.
2. Until recently, the numbers of patients affected remained small and the problem showed little sign of growing.
3. However, a new class of ESBL (called CTX-M enzymes) has emerged and these have been widely detected among E. coli. These ESBL-producing E. coli are able to resist penicillins and cephalosporins and are found most often in urinary tract infections – though not simple cystitis.
4. Of the most concern is the emergence of KPC (Klebsiella pneumoniae carbapenemases), which confer resistance to 3rd and 4th generation cephalosporins and carbapenems.
5. Of concern, they have been found even in the community as well as in hospitals.
Laboratory diagnosis of ESBL strains:
The presence of an ESBL is suggested if bacterial growth is observed despite a concentration of 1 microgram/ml of atleast one of the 3 extended spectrum cephalosporins (Ceftazidime/ Ceftriaxone/ Cefotaxime) or growth occurs despite a concentration of 4 microgram/ ml of Cefpodoxime.
1. Carbapenems (imipenem, meropenem etc.) are the most effective and reliable as they are highly resistant to the hydrolytic activity of the beta lactamases.
2. Amongst them, meropenem is the most active carbapenem active against ESBLs.