Classification of the β-lactamases.
Abstract
Klebsiella pneumoniae (K. pneumoniae) pose an emerging threat to public health sector worldwide. They are one of the potent nosocomial pathogens and cause variety of infections including pneumonia, septicaemia, wound infections, urinary tract infections and catheter-associated infections. From the last two decades, these pathogens are becoming more powerful due to the acquisition of resistomes on different types of plasmids and transposons. There are four main mechanisms of antibacterial resistance such as efflux pump, target alteration, membrane permeability and notably enzymes hydrolysis. K. pneumoniae produce different types of enzymes but most importantly extended spectrum-β-lactamase (ESBL), carbapenemase and metallo-β-lactamase (MBL). K. pneumoniae carbapenemases (KPCs) and New Delhi metallo-β-lactamase (NDM) producing isolates displayed resistance not only against the β-lactam drugs (penicillins, cephalosporins and carbapenems) but also to other classes of antibiotics (aminoglycosides and quinolones). Therapeutic options available to treat serious infections caused by these extensively drug-resistant pathogens are limited to colistin, tigecycline and fosfomycin. Hence, combination therapy has also been recommended to treat such bacteria with clinical side effects, therefore, new treatment regime must be required. Moreover, we are relying on conventional diagnostic tools, however, novel techniques must be required for robust identification of multi-drug-resistant bacteria.
Keywords
- Klebsiella pneumoniae
- antimicrobial resistant mechanisms
- mortality and morbidity
- economic burden
1. Introduction
2. Antimicrobial resistance
Antimicrobial resistance (AMR) defined when a bacterial strain shows resistance against antibiotics that normally inhibit or stop their growth and allow them to withstand against drugs. Last 2 decades, there are various AMR pathogens have been emerged around the globe such an ESBL producing pathogens, multi-drug resistant and extensively drug resistant
3. Mortality, morbidity and economic burden due to antimicrobial resistant bacteria
AMR pathogens are one of the main cause of morbidity and mortality in both developed and developing countries. According to a published data, around 700,000 people die due to infections caused by AMR pathogens every year worldwide and most of the data is still underreported because of poor reporting and surveillance studies [7]. On the other hand, as per The Centre of Disease and Control (CDC), above 2 million people get infected due to AMR bacteria with a mortality rate of 23,000 each year [8]. Similarly, an Indian study revealed that around 60,000 neonates die due to AMR infections per year [9]. Likewise, a study conducted in Pakistan in 2009 was also documented that 40% neonates die due to MDR and XDR pathogens (
Every year, millions of dollars are spent to tackle the burden of AMR bacterial infections around the globe. European Union invested around €1.5 billion annually to tackle the infections caused by AMR pathogens which are responsible for around 23,000 mortalities only in Europe [15]. However, United States of America also expenditures above $20 billion to treat the 20 million patients who get infected with AMR infection each year [16].
4. Mechanisms of antimicrobial resistance
Since 1990s, bacteria have been becoming gradually more lethal, due to acquisition of resistomes and develop resistance to different sets of antibiotics. Now a day, many bacterial pathogens notably
4.1 Target alteration of the antibiotics
In general, many antibiotics bind to different bacterial target sites with high affinity. So, most of the bacteria including
4.2 Modification in membrane permeability
Outer membrane of the bacteria is first line barrier to protect the microorganisms against unfavourable environment including chemical and biological materials. In comparison, majority of the Gram-negative rods (GNR) are intrinsically less permeable to various antibiotics because of outer membrane barrier than Gram positive bacteria [22]. In the cell wall of
4.3 Increased efflux pumps
Efflux pumps are the active transport mechanisms that expel out antibiotics from bacterial cell and play a vital role to develop intrinsic resistance against broad range of antibiotics in GNR [18]. Currently, there are several MDR efflux pumps are present in bacteria including FuaABC in
4.4 Enzymatic hydrolysis of the antibiotics
In
4.4.1 Classification of β-lactamases
These enzymes are broadly classified into two main scheme one is Ambler Molecular classification scheme which is based on amino acid sequence and is widely acceptable and secondly, Bush Jacoby classification scheme which is based on biochemical properties [30]. Ambler class is further divided in to four major sub-classes A, B, C, and D based on conserved and distinguished amino acid motifs. Among these, class A, C, and D are the serine carbapenemases that hydrolyzed their substrate through active site by forming acyl groups and require serine as a cofactor for their activity. However, class B enzymes are the MBLs that utilised at least one zinc ion at their active site to hydrolyze the β-lactam antibiotics. MBLs are further classified into three super families B1, B2 and B3 [31]. However, Bush-Jacoby-Medeiros classification scheme is divided into three major groups; class C (Group 1 cephalosporinases), class A and D (Group 2 Serine β-lactamases) and class B (Group 3 MBLs). These are further divided in to several different subgroups as shows in Table 1 [30].
Molecular class (subclass) | Bush Jacoby groups | Main substrate | Defining characteristic(s) | Representative | Bacteria |
---|---|---|---|---|---|
A | 2a | Penicillins | Increased hydrolysis of benzylpenicillin | PC1 | |
A | 2b | Penicillins and early Cephalosporins | Hydrolysis of the penicillins and cephalosporins | TEM and SHV | |
A | 2be | Extended spectrum-β- lactam drugs, monobactam | Hydrolysis of extended spectrum-β- lactam drugs | TEM, SHV and CTX-M | |
A | 2br | Penicillins | Resistant to β-lactam inhibitor | TEM and SHV | |
A | 2c | Carbenicillin | Hydrolysis of carbenicillin | CARB | |
A | 2ce | Carbenicillin and Cefepime | Hydrolysis of carbenicillin and cefepime | RTG | |
B (B1) | 3a | Carbapenems | Carbapenems but not aztreonam | IMP, VIM and NDM | |
B (B2) | 3b | Carbapenems | Prefer to hydrolyze carbapenems | CphA and Sfh | |
C | 1 | Cephalosporins | More hydrolyze the cephalosporins | AmpC, | |
C | 1e | Cephalosporins | Highly hydrolyzed the ceftazidime | GC1, CMY-37 | |
D | 2d | Oxacillin | Hydrolysis of oxacillin | OXA-1, OXA-10 | |
D | 2de | Extended spectrum-β- lactam drugs | Hydrolysis of extended spectrum-β- lactam drugs | OXA-11, OXA-50 | |
D | 2df | Carbapenems | Hydrolysis of oxacillin and carbapenems | OXA-23 and OXA-48 |
4.4.2 Extended spectrum-β-lactamase producing K. pneumoniae
ESBL are the enzymes that hydrolyze the extended spectrum drugs mainly cephalosporins. ESBL producing
4.4.3 AmpC producing K. pneumoniae
AmpC are the β-lactam enzymes that belong to the ambler class C of β-lactam. These enzymes hydrolyze cephalosporins antibiotics and produce resistance against penicillin, second and third generation cephalosporins and cephamycin. Moreover, these enzymes can also convey resistance to combination of these antibiotics along with β-lactam inhibitors. The versatility of the
4.4.4 Class A carbapenemases producing K. pneumoniae
Since the sporadic spread of ESBL producing
4.4.5 Class B carbapenemase producing K. pneumoniae
Class B are the MBLs that require Zn+ as a cofactor for their activity. There are many types of MBLs have been identified such as IMP, VIM, and NDM in
4.4.6 Class D carbapenemases producing K . pneumoniae
These carbapenemase enzymes swiftly hydrolyzed the isoxazolylpenicillins drugs such as oxacillin, cloxacillins and dicloxacillin than benzylpenicillin. There are more than 574 variants have been identified around the globe but few of them have the carbapenemase activity. Therefore, class D are reclassified in to 12 main groups; Oxacillinase (OXA)-23, OXA-24, OXA-48, OXA-51, OXA-58, OXA-143, OXA134, OXA-211, OXA-213, OXA-214, OXA-229, OXA-235 [43]. Among these most potent variants is OXA-48 which was firstly identified in
5. Tacking of antibiotic resistance
AMR is becoming a menace to global health. According to United Nation (UN), in 2050, if we do not tackle the AMR now, more than 10 million people will die each year and the global income cost would be $100 trillion. So, in 2050, one person will die after every 3 seconds [7]. Firstly, it is need of the hour to give a public awareness through paper and electronic media to stop the irrational use of antibiotics. Secondly, people should improve their hygiene practices which will reduce the 60% antibiotics burden to reduce the diarrhoea. Thirdly, more than 70% world’s antibiotics are being utilised in agriculture and live stocks, so overuse of antibiotics must be avoided in these settings. Fourthly, Global surveillance of AMR should be conducted and maintained throughout the world. Fifthly, there are many countries which do not have the rapid and effective diagnostics facilities of microbiology which allow the physician to prescribe the broad-spectrum empirical therapy. Sixthly, there is an urgent need to develop an alternative method to treat the AMR such as vaccines, phage therapy, probiotics, antibodies and lysins. Seventhly, there are shortages of microbiologists, infectious diseases specialists, infections control specialists, vegetarians, pharmacists and epidemiologists. Eighthly, A global funding must be required to support and encourage the less commercially attractive. Ninthly, the world gives better incentive to pharmaceutical companies to develop new and existing antibiotics. Finally, world leading organisations such as WHO, G20, UN must work together with coordination.
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