Table of Contents  
Year : 2012  |  Volume : 5  |  Issue : 1  |  Page : 10-13  

Metallo β-lactamases: A perspective and implications

Department of Microbiology, Pad. D. Y. Patil Medical College, Pimpri, Pune, Maharashtra, India

Date of Web Publication20-Jun-2012

Correspondence Address:
Rabindra N Misra
Department of Microbiology, Pad. D. Y. Patil Medical College, Pimpri, Pune, Maharashtra
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/0975-2870.97498

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The emergence of Carbapenem-resistant organisms from the family Enterobacteriaceae is a major challenge in the intensive care facilities. They produce carbapenemases which inhibit carbapenems belonging to the Ambler classification group B and they depend on heavy metals like Zn ++for hydrolysis of β-lactam ring. Most of the clinically important metallo-β-lactamases (MBL) belong to five different families (IMP, VIM, SPM, GIM, and SIM). They are typically transmitted by mobile genetic elements inserted into integrons and spread through Pseudomonas spp, Acinetobacter spp. In a study from New Delhi, 36 out of 56 P. aeruginosa species were MBL positive and from Vellore MBL was detected in 20 out of 61 P. aeruginosa 20 (32%). Inappropriate antibiotic usage, defensive practices by medical practitioners, promotion of antibiotics by pharmaceutical companies are major hurdles in the direction of rational use of antibiotics. Intensified infection control strategy should be adopted to prevent emergence and spread of carbapenemase-producing organisms.

Keywords: Carbapenemase, enterobacteriaceae, metallo-β-lactamases

How to cite this article:
Misra RN. Metallo β-lactamases: A perspective and implications. Med J DY Patil Univ 2012;5:10-3

How to cite this URL:
Misra RN. Metallo β-lactamases: A perspective and implications. Med J DY Patil Univ [serial online] 2012 [cited 2020 Jul 2];5:10-3. Available from:

  Introduction Top

The emergence of Carbapenem resistant organisms particularly from the family Enterobacteriaceae is a major challenge in the intensive care facilities. The carbapenemase producing Klebsiella pneumoniae are associated with increased morbidity, mortality, and increased hospital stay in acute care settings. These patients are usually critically ill and exposed to invasive devices such as central venous catheters or ventilators. [1]

Carbapenems are group of broad-spectrum antibiotics which are not inactivated by commonly encountered β-lactamases including AmpC and are very effective against a wide range of bacteria particularly in critical care cases. The carbapenems traverse the outer membrane barrier of bacteria by OprD protein and bind the penicillin-binding proteins (PBPs) to produces their effect on a wide ranging Gram-positive and Gram-negative bacteria and are incredibly stable to many β-lactamases. Often they are used as last resort against multi-drug resistant (MDR) bacteria particularly in a critical care setting. The commonly used antibiotics in this group are imipenem, meropenem, ertapenem, etc which are produced from Streptomyces cattleya and derivatives of thienamycin. [2]

The metallo-β-lactamases (MBL) or carbapenemases which inhibit carbapenems belongs to the Ambler classification group B and they depend on heavy metals like Zn ++for hydrolysis of β-lactam ring. They are susceptible to iron chelators like ethylene diamine tetra-acetic acid (EDTA). They are resistant to well-known β-lactamase inhibitors like clavulanic acid, sulbactam, and tazobactam and confer resistance to all β-lactam antibiotics except monobactams. They are distinct from other β-lactamases in that they do not compete with PBPs for their mode of action. [3]

Chromosomally encoded MBL are primarily found in environmental isolates of Aeromonas spp, Stenotrophomonas maltophilia, Bacillus spp, etc which are of low pathogenic potential. [2] Most of the clinically important MBL belong to five different families (IMP, VIM, SPM, GIM, and SIM). They are typically transmitted by mobile genetic elements inserted into integrons and spread through Pseudomonas spp, Acinetobacter spp, other Gram-negative non-fermenters, and enteric pathogens. A few K. pneumoniae strains also acquired plasmid borne class A carbapenemase known as KPC-1, KPC-2, and KPC-3. They are prevalent in Greece, USA, and Israel and were later detected in E. coli also. During 1990, MBL IMP1 was first detected in Japan in Gram-negative bacilli strains. Another MBL VIM1 was detected in Italy in 1995 and later in other countries. MBL VIM2 was found in France and Greece. It was found in Korean hospital in 1995. The VIM MBL continued to evolve and VIM3 was found in Taiwan and VIM4 in USA. [4],[5]

New Delhi metallo-β-lactamase (NDM-1) was recently named because it was discovered from an Indian patient who was transferred to UK for treatment. It was coded by gene bla ndm1 which has a potentiality to spread horizontally from one bacterium to the other by means of conjugative plasmids. [4]

  The Perspective Top

In a multicenter study in Korea, Korean Nationwide Surveillance of Antimicrobial Resistance Group hospitals, 11.4% of 387 Pseudomonas aeruginosa species and 14.2% of 267 Acinetobacter spp were positive for MBL VIM-2 or IMP-1 during 2001-03. [6]

In an North-East Indian study, it was found that among surgical site infections, there were 27% of Enterobacteriaceae isolates had newly recognized MBL (blaNDM-1). The organisms were one each of Enterobacter cloacae, Klebsiella sp, and  Escherichia More Details coli. In the medicine wards with intravascular device infections one E coli had NDM-1. These organisms were only sensitive to colistin and tigecycline. [7]

In a hospital-based multicenter study in South East Asia, it was found that bacteria from Enterobacteriaceae family particularly Klebsiella and E. coli were showing resistance to carbapenems and were detected to have NDM-1. In this study, there were 44 isolates with NDM-1 in Chennai, 26 in Haryana, 37 in the UK, and 73 in other sites in India and Pakistan among which 36 were E. coli and 111 were K. pneumonia. They were further confirmed by molecular studies using PCR and PFGE. [8]

CLSI has the recommended modified Hodge test (MHT) for detection of susceptible Enterobacteriaceae strains with raised MIC for carbapenems. However, for intermediate or resistant organisms to carbapenems, MHT is not required (CLSI). [9]

In one of the studies carried out in our institution where multi-drug resistance organisms from the Enterobacteriaceae family were selected for their capability to produce MBL by phenotypic double disk synergy test. Imipenem and Imipenem + EDTA combined disk synergy test is simple, inexpensive, and reliable for phenotypic detection of MBL production in all MDR isolates. In this study, during the period January 2010-June 2010, 52 MDR Gram-negative bacilli were included. These isolates showed resistance to important groups of antibiotics e.g., third-generation cephalosporins, aminoglycosides, quinolones, and carbapenem which is characteristic of MBL-producing isolates. 14.32% of Gram-negative bacilli were MDR and 23.07% of MDR were MBL producers. K. pneumoniae 7 out of 28 isolates, E. coli 1 out 14 isolates, Citrobacter sp. 1 out of 6 isolates, Pseudomonas sp. 2 out 2 and Acinetobacter sp. 1 out of 2 isolates produced MBL. These patients had very limited antibiotic treatment options like tigecycline or colistin. Some of the patients lost their lives due to not only sepsis but associated multi-organ dysfunction (DYP, Unpublished data 2010).

bla NDM-1 gene detection is usually carried out by polymerase chain reaction (PCR) and also useful for epidemiological clonality studies. However, the phenotypic detection of MBL will help in deciding the appropriate therapy in a particular clinical situation. Bacterial resistance due to other mechanisms may also be detected by phenotypic methods.

  Implications Top

Selection Pressure

There may be outbreaks due to unrecognized colonization of carbapenemase-resistant K. pneumoniae (CRKP) in health care facilities. In a hospital in Puerto Rico in 2008, 39 cases of CRKP were detected from two colonizers. However, they could control it by stringent infection control compliance like hand hygiene and contact precautions, weekly perirectal surveillance cultures and patient cohorting. [5] Molecular techniques and chromogenic agar may be used for active surveillance of CRKP but it is not yet approved by Food and Drug administration. Screening tests should be carried out by using rectal or perirectal swabs for detection of CRKP than from other body sites like anterior nares or skin. [10] Active surveillance testing should be carried out whenever a health care associated carbapenem-resistant Enterobacteriaceae (CRE) is detected. The patients in the same unit or patients who have been cared by the same health care personnel should be included under the active surveillance. [9]

Other studies including India and abroad, the MBL production among Gram-negative organisms vary from 20% to 80%. In a study from New Delhi, 36 out of 56 P. aeruginosa species were MBL positive, study by Irfan from Pakistan 83 (96.6%) out of 90 Acinetobacter spp, and all of 25 P. aeruginosa were positive for MBL. Manoharan et al. from Vellore detected MBL in 20 out of 61 P. aeruginosa 20 (32%). Fang et al. found that 39 out of 59 P. aeruginosa were MBL-positive from Beijing. [11],[12],[13],[14]

Administration of parenteral third-generation cephalosporins in post-operative cases and in patients with intravascular devices may lead to selection pressure and development of resistance to these antibiotics and spread through bacterial populations. [15] Ironically, these cases are infected with organisms which not only carry plasmids for ESBLs like CTXbla-15 but also for NDM-1. The MBL IMP and VIM subtypes are coded by genes which are horizontally transferable as they are located in integrons on conjugative plasmids. Plasmid typing methods are enhancing our understanding the growing prevalence of ESBL producers. In North-East India, some SSI infections and patients with IV devices were not given carbapenems but the organisms detected were having resistance to NDM-1. [7] Even it was observed that some strains from community which infected the patients were also having NDM-1. The increase in resistance of Gram-negative bacteria is serious problem due to the widespread use of reserved antibiotics. More than that due to air travel and medical tourism, these bacteria spread rapidly between countries and create a public health concern. [16]

  Prevention Top

During 1990s, the ESBLs conferring resistance to third-generation cephalosporins were detected and the bla-CTX-15 is a global problem at present. Since carbapenemases like NDM-1 is also spreading among Enterobacteriaceae, it should warn the health authorities that we soon will be approaching an era when antibiotics will no longer be effective. The normal human gut flora mainly consists of Enterobacteriaceae and if they acquire these plasmids with genes for multiple antibiotic resistance and transfer among themselves it becomes a serious situation. Selection pressure due to antibiotic administration will worsen this situation. There is referendum by the Central Govt. on this issue but implementation may take some time. Rational antibiotic usage, avoidance of defensive practices by medical practitioners, promotion of antibiotics by pharmaceutical companies are major hurdles in the direction of rational use of antibiotics.

The hospitals in our country are woefully inadequate in implementing proper hospital control policies. Wherever disinfection practices can reduce infection, antibiotics are prescribed as a safety measure particularly in the post-operative period. Many times, stop signals are not given even after required period of antibiotic administration is over.

As per CDC, Hospital Infection Control Practices Advisory Committee (HICPAC) in hospitals with CRE recommended guidelines which are as follows.

If there is sporadic detection of CRE, it should be placed on contact precautions (tier 1). The epidemiology and infection control staff should be alerted. The acute facilities should review records for the last 6-12 months for the occurrence of such cases. If found positive, then point prevalence survey should be carried out (i.e., one single round of active surveillance cultures) to identify patients colonized with CRE.

If CRE are routinely recovered including many cases admitted from community i.e., where CRE is endemic, intensified infection control strategy should be adopted (tier 2). This includes allocating additional resources for surveillance and control for aggressive infection control strategy and in US hospitals this has given dividend as CRE is low in these hospitals.

  • Aggressive Infection Control Strategy
  • Contact precautions in managing patients CRE
  • Implementing CLSI guidelines for detection of Carbapenemase production.

  Conclusion Top

The production of newer antibiotics is very few and takes long incubation period before it is commercially available. The only viable alternative left is stringent infection control coupled with antibiotic stewardship program which will play an important role in limiting the spread of metallo-β-lactamase-producing organisms which make best use of the available antimicrobial armamentarium.

  References Top

1.Schwaber MJ, Carmeli Y. Carbapenem-resistant Enterobacteriaceae: A potential threat. JAMA 2008;300:2911-3.  Back to cited text no. 1
2.Walsh TR. The emergence and implication of metallo b-lactamases in gram negative bacteria. Clin Microbiol Infect 2005;11 Suppl 6:S2-9.  Back to cited text no. 2
3.Walsh TR, Toleman MA, Poirel L, Nordmann P. Metallo b-lactamase: The quiet before the storm? Clin Microbiol Rev 2005;18:306-25.  Back to cited text no. 3
4.Tato M, Coque TM, Ruiz-Garbajosa P, Pintado V, Cobo J, Sader HS, et al. Complex clonal and plasmid epidemiology in the first outbreak of Enterobacteriaceae infection involving VIM-1 metallo b-lactamase in Spain towards endemicity? Clin Infect Dis 2007;45:1171-8.  Back to cited text no. 4
5.Samra Z, Ofir O, Lishtzinsky Y, Madar-Shapiro L, Bishara J. Outbreak of carbapenem resistant Klebsiella pneumoniae producing KPC-3 in a tertiary medical centre in Israel. Int J Antimicrob Agents 2007;30:525-9.  Back to cited text no. 5
6.Lee K, Lee WG, Uh Y, Ha GY, Cho J, Chong Y, Korean Nationwide Surveillance of Antimicrobial Resistance Group. VIM- and IMP-Type Metallo-â-lactamase-producing Pseudomonas spp. and Acinetobacter spp. in Korean hospitals. Emerg Infect Dis 2003;9:868-71.  Back to cited text no. 6
7.Sarma JB, Bhattacharya PK, Kalita D, Rajbangshi M. Multi-drug resistant Enterobacteriaceae including metallo-â-lactamase production are predominant pathogens of healthcare-associated infectionsin an Indian teaching hospital. Indian J Med Microbiol 2011;29:22-7.  Back to cited text no. 7
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8.Kumarasamy KK, Toleman MA, Walsh TR, Bagaria J, Butt F, Balakrishnan RK, et al. Emergence of a new antibiotic resistance mechanism in India, Pakistan, and the UK: A molecular, biological, and epidemiological study. Lancet Infect Dis 2010;10:597-602.  Back to cited text no. 8
9.CLSI document, Clinical and Laboratory Standard Methods. Performance Standards for antimicrobial susceptibility testing: Seventeenth informational supplement. Wayne PA: Clinical and Laboratory Standard Institute; 2007. p. M100-S17.  Back to cited text no. 9
10.Calfee D, Jenkins SG. Use of active surveillance culturs to detect asymptomatic colonization with carbapenem-resistant Klebsiella pneumoniae in intensive care unit patients. Infect Control Hosp Epidemiol 2008;29:966-8.  Back to cited text no. 10
11.Manoharan A, Chatterjee S, Mathai D, Benjamin M, Aggarwal A, Deotale V, et al. Detection and characterization of metallo beta lactamases producing Pseudomonas aeruginosa. Indian J Med Microbiol 2010;28:241-4.  Back to cited text no. 11
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12.Fang D, Wei XX, Song WQ, Ping LU, Sang YU, Yong HY, et al. Characterization of multidrug-resistant and metallo-beta-lactamase-producing Pseudomonas aeruginosa isolates from a paediatric clinic in China. Chin Med J 2008;121:1611-6.  Back to cited text no. 12
13.Irfan S, Zafar A, Guhar D, Ahsan T, Hasan R. Metallo-beta-lactamase-producing clinical isolates of Acinetobacter species and Pseudomonas aeruginosa from intensive care unit patients of a tertiary care hospital. Indian J Med Microbiol 2008;26:243-5.  Back to cited text no. 13
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14.Behera B, Mathur P, Das A, Kapil A, Sharma V. An evaluation of four different phenotypic techniques for detection of metallo-â-lactamase producing Pseudomonas aeruginosa. Indian J Med Microbiol 2008;26:233-7.  Back to cited text no. 14
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15.Srinivasan A, Patel JB. Klebsiella pneumoniae carbapenemase-producing organisms: An ounce of prevention really worth a pound of cure. Infect Control Hosp Epidemiol 2008;29:1107-9.  Back to cited text no. 15
16.Queenan AM, Bush K. Carbapenemases, the versatilebeta lactamases. Clin Microbiol Rev 2007;20:440-58.  Back to cited text no. 16


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