Reverse - CAAAAGTCCCGCTCCAACGA

Class B2 – possess asparagine instead of histidine at first position of principal Zn binding motif,

Class B3 – MBL L1 unique among all β-lactamases in being functionally represented as a

The numbering scheme has been recently updated to accommodate newly discovered MBLs.

MBLs are inhibited by EDTA (Ethylene diamino tetraacetic acid), 2 Mercaptoethanol, 5- Mercaptoacetic acid, 2 Mercapto propionic acid, Copper Chloride and Ferric Chloride. MBLs are classified mainly into two types – Chromosomally encoded and Plasmid encoded or Acquired or Transmissible type. Usually metallobetalactamase producing strains are suscep‐ tible to Colistin or Polymyxin B. MBLs do not hydrolyze aztreonam very well, which charac‐

The acquired MBLs are further classified into different types depending on their place of origin as VIM (Italy or Greece), SPM (Brazil), GIM (Germany), SIM (Korea), DIM (Dutch), NDM/PCM

**NDM – 1:** NDM – 1 was named after New Delhi, capital of India as NDM – 1 and was first described by Young et al in December 2009 in an individual who acquired infection in a

In March 2010, researchers from Mumbai found that most of Carbapenam resistant bacteria carried blaNDM–1 gene. The gene is carried on plasmids and is readily transferred between different strains of bacteria by horizontal gene transfer. All these strains were resistant to most of routinely used antibiotics like Aminoglycosides, β-lactams, Quinolones but sensitive to Tigecycline and Colistin [50]. Recently, Espinal et al identified a new variant of NDM-1 in *Acinetobacter baumannii* and designated it as NDM-2. They reported that, the clonal dissemi‐ nation of a NDM-2 producing *A. baumannii* was isolated in an Israeli rehabilitation ward [51]. Recently, a new variant of the New Delhi metallo-enzyme (NDM) carbapenemase, NDM-4 and NDM-5, was identified in *E.coli* from two patients both of them had a history of

Carbapenems often used as an antibiotic of last resort for treating serious infections caused by multi-drug resistant (MDR) organism. Reduced susceptibility to any Carbapenem can be used as a screen for carbapenemases. Positive screening tests are to be followed by a confirmatory

Although a variety of phenotypic methods have been proposed for the detection of carbape‐ nemases, none have been recommended by CLSI. The classical Hodge [54], Modified Hodge test (MHT) [55] are economical approach for detection and confirmation of carbapenemase activity and Re – Modified Hodge test [56] for detection of MBL. However, the first two tests cannot differentiate between a class A carbapenemase and MBL, making a further confirma‐ tory test necessary. Imipenem is more sensitive but less specific Carbapenem for this test

NXHXD. e.g. Aeromonas species and *Serratia fonticola* enzyme SFH – 1.

teristic is different than ESBLs or Class A β-lactamases [48].

hospitalization in India [52,53].

test for MBL production.

**Detection of Metallo β-lactamase production**

allowing detection of even OXA carbapenemases.

(New Delhi metallobetalactamases/Plasmid coded metallobetalactamases).

Hospital in India due to Carbapenam resistant *Klebsiella pneumoniae* strain [49].

tetramer.

52 Trends in Infectious Diseases

PCR is specific for gene family IMP, VIM, etc. and hence, many other specific primers can be used for different MBL genes. The main disadvantage of PCR is that it requires tailor-made DNA primers and cannot differentiate between variants and may not detect new variants.

#### **E. Detection of Klebsiella pneumoniae carbapenamases (KPCs) [61]**

KPCs can be mainly detected by Combined disk method using Imipenem and Imipenem with Phenyl boronic acid, Molecular methods like PCR etc.

Recently, Carbapenem Resistant Enterobacteriaceae (CRE) pose a real threat to Medical fraternity as the increased frequency with which Enterobacteriaceae cause infection and the mortality associated with infection caused by CRE. Most of the studies reported newer βlactamases including MBL production in nonfermenters like *Pseudomonas aeruginosa*, *Acineto‐ bacter species* etc. There are very few studies that report MBL production in Enterobacteriaceae [19]. Hence, we have conducted the study to detect newer β - lactamases producing *E.coli* strains by phenotypic methods, isolated from different clinical specimens.
