K. Karthik

Introduction

• A bacterium carrying resistance to more than one antibiotic is called as superbug or super bacteria.

• Presently- a pile of bacteria line up in this list• No ESKAPE from superbug1. Enterococcus faecium2. Staphylococcus aureus3. Klebsiella pneumoniae4. Acinetobacter baumanii,5. Pseudomonas aeruginosa, 6. Enterobacter species

Bugs web the world

Supe-R-evolution

• Basis of Darwin’s theory- survival of fittest

• Selection pressure

Antibiotics

Mechanism

• Spontaneous mutation

• Lateral gene transfer- conjugation, transformation, transduction

• Uptake of resistance gene form plasmid, transposons, integrons

• CRISPR(Clustered Regularly Interspaced Short Palindromic Repeats)- act against gene uptake

Mutation

• Change in the nucleotides at a single position can lead to mutation- resistance

• gyrA (DNA gyrase) –mutation in 83 and 87 nucleotide lead to change in aminoacids-resistance development - quinalonessimilarly for parC (topoisomerase IV )

Mutation

PBP

PBP

Thickened peptidoglycan-vancomycin trapped in peptidoglycan

Beta lactam

Beta lactamase Peptidoglycan

Vancomycin

Alter in peptidoglycanshape

Mutated mRNA

Protein

Normal DNA

Mutation and methylation of rRNA

Linezolid, quinupristin–dalfopristin, daptomycin,tigecycline

1

3

2

Resistance development

• Widespread use of antibiotics

• Antibiotics as growth promoters

• Irregular dosing and period of antibiotic usage

• Over the counter sale of antibiotics

• Direct use of higher generation antibiotics

MRSA

• 1981, USA- in i/v drug users

• Commonly referred as superbug in press

• Common strains EMRSA15 and EMRSA16 (Johnson et al., 2001)

• Types:

– Community-associated MRSA (CA-MRSA)

– Health care-associated MRSA (HA-MRSA)

Trend in S. aureus resistance development

CA/HA-MRSA

• CA-MRSA- seen in healthy people- usually skin infections

• RISK factors: Crowding, contact, compromised skin, contaminated surfaces, shared items and poor hygiene

• HA-MRSA- seen in hospitalized patience (Immunocompromised)

• Risk: hospitalization, surgery, dialysis, long-term care, indwelling devices, and history of previous MRSA infection

PVL-MRSA

• Panton Valentine Leukocidine +ve MRSA- CA MRSA type- highly virulent

• Targets white blood cells- depletion of WBC-low immunity

• Causes boils, abscess, tissue necrosis

• Extreme condition: septic arthritis, septicemia and lethal necrotizing pneumonia

USA300

• New strain of MRSA

• Do not have the capability to acquire genes from other MRSA

• They inherit from USA500 strain

• Bacterial toxin alpha haemolysin (Hla)- can serve as weapon against MRSA

• Immunization with Hla reduced skin infection

Human animal

• 1972- I report of MRSA in cattle

• Now reported in almost all livestock's

• Old thoughts: MRSA- human to animal through hands to nostrils

• New ideas: Bi-directional

• Healthy animals- reservoir (Klevens et al., 2007, Smith et al., 2009)

• Wild animals: USA300 strain isolated- elephants

Extended spectrum beta lactamase

• ESBL joins MRSA, VRSA, VISA and vancomycinresistant Enterococcus

• ESBL hydrolyses all penicillins, cephalosporinsand monobactams

• E. coli and Klebsiella are the important organism –ESBL

• Mortality rate : 25-75%

NDM-1

• New Delhi Metello betalactamase -1

• 2009, swedish patient- urinary tract infection-carbapenem-resistant K. pneumonia

• Resistant to all antibiotics except tigecyclineand colistin.

• Resistance gene located on plasmid

• E. coli and K. pneumonia commonly acquires this gene (blaNDM-1)

Genes carried by NDM-1 superbugs

• blaTEM-1, blaOXA-1, blaOXA-10 and blaCMY (various β-lactamases)

• qnrA6 and qnrB1 (quinolone resistance)

• armA, rmtA and rmtC (nearly all aminoglycoside antibiotics)

• arr-2 (rifampicin ribosyltransferase)

• sul-2(sulfonamide-resistant dihydopteroate synthase)

• cmlA (chloramphenicol acetyltransferase)

• ereC (macrolide resistance)

• A few plasmids carrying blaNDM-1 also encode other carbapenemases, including OXA-181- and VIM-types

Variants

• NDM-2• Acinetobacter baumannii from Germany- showed

sequence change NDM-1 gene by substitution of C to G at 82

• Leads to amino acid change- no plasmid in these strains

• First variant of NDM-1 in A. baumannii• NDM-3 and NDM-4 in Enterobacteriaceae from

Australia and India (Nordman et al., 2011)• Consequences -?

MDR-TB/ XDR-TB

• 440,000 MDR-TB cases as per WHO, 2008

• India & China- 50% global contribution

• Spontaneous mutation; no HGT

• Drug usage as monotherapy- leads to resistance

• India, Gujarat state: 2006 Survey – MDR-TB:216

– XDR in MDR: 7

– % XDR in MDR: 3·2% (1·2–6·6)

Resistance development- clinical threat

Incorrect treatmentMycobacterium

infection

Healthcare center

Clinical threats

• One resistant MRSA kills> people than AIDS, Parkinson's and homicide together

• MRSA can spread through sharing of clothing, personal items and sports equipment

• Surgical site infection (SSI)- crucial post operative complication.

• Spread of NDM-1 through endoscope camera-UK

• >29% of SSIs are complicated with MRSA

Threats..

• Flesh eating bugs- causes severe infection to human and treatment failure

• Spread by sneezing, coughing and contact

Organism/ resistance Resistance mechanism Future AntimicrobialAgents with Potential Clinical Use

Hospital-associated MRSA

Vancomycin (both VISAand VRSA)

Thickening of cell wall Linezolid, quinupristin–dalfopristin, daptomycin,tigecycline, ceftobiprole, ceftaroline,dalbavancin, telavancin, oritavancin,iclaprim

Daptomycin changes in cell wall and cellmembrane

Linezolid, quinupristin–dalfopristin, tigecycline,ceftobiprole, ceftaroline, dalbavancin,telavancin, oritavancin, iclaprim

Linezolid Mutations in the 23S ribosomal RNA genes

Daptomycin, quinupristin–dalfopristin, tigecycline,ceftobiprole, ceftaroline, dalbavancin,telavancin, oritavancin, iclaprim

Organism/ resistance Resistance mechanism Future AntimicrobialAgents with Potential Clinical Use

Vancomycin-resistant Enterococcus faecium

Ampicillin Mutation and overexpression of pbp5

Linezolid, quinupristin–dalfopristin, daptomycin,tigecycline

High-level resistance toaminoglycosides

Acquisition of aminoglycoside-modifying enzymes;ribosomal mutations

No alternative for a reliable bactericidal effectalone or in combination

Linezolid Mutations in the 23S ribosomal RNA genes

Quinupristin–dalfopristin, daptomycin, tigecycline

Quinupristin–dalfopristin Enzymes that inactivate quinupristin–dalfopristin,target modification

Daptomycin, linezolid, tigecycline

Escherichia coli, Klebsiella species and Enterobacter species

Cephalosporins Extended-spectrum β-lactamases (includeshyperproduction of the AmpC enzymes)

Carbapenems, tigecycline

Carbapenems Production of carbapenemases, decreasedpermeability

Polymyxins, tigecycline

Acinetobacter species/ Pseudomonas aeruginosa

Carbapenems Decreased permeability, increased efflux,and production of carbapenemases

Polymyxins

Tigecycline and colistin- nephrotoxic

Non clinical threats

• Presence of MRSA without clinical signs

• Condition remains unnoticed till admitted in clinics (Leonard and Markey, 2008)

• Marine mammals also inhabit MRSA without signs and can transmit to sea divers

• Strastkova et al. (2009) reported MRSA from goat milk- no signs- potential to transmit

• Pigs are also a major source without signs

• Affect medical tourism

Through food products• MRSA can also be transmitted through meat

products

• USA300 and USA100- isolated from meat shops

• Studies from Japan, Turkey reveals the same

• Recently NDM-1 DNA has been recovered from drinking water and sewage in INDIA

• MRSA is found everywhere and can be isolated commonly from all places in hospitals where hygienic conditions are poor.

CONCLUSION

• Hygienic measures are required

• Use of antibiotics in a proper way

• Need to find new antibiotics

• Time to shift towards antibiotic alternatives?

• Infectious disease society of America (IDSA)

– Bad bugs, No drugs- 2004

– Bad bugs, need drugs- 2010