11 - Introduction to Superbugs

• Multi-Drug Resistance (MDR)


  Any strain of bacteria that has become resistant to the antibiotics that are used to treat it
• Superbugs


  • Staphylococcus aureus (MRSA)
  • Escherichia coli
  • Acinetobacter spp.
  • Klebsiella pneumoniae
  • Pseudomonas aeruginosa
  • Mycobacterium tuberculosis
• Penicillin


  A wonder drug discovered in 1928 by Sir Alexander Fleming
• Norman Heatley worked out how to purify penicillin, how to assay it accurately and how to scale up production in 1940
• Penicillin was isolated by Sir Howard Walter Florey and Ernst Boris Chain, who won the Nobel Prize in 1945
• Alexander Fleming: '"Then there is the danger that the ignorant man may easily underdose himself … He buys some penicillin and gives himself, not enough to kill the streptococci but enough to educate them to resist penicillin"'
• Resistance to vancomycin developed in Enterococcus and it is now quite common in Enterococcus
• Vancomycin resistance was transferred to other species and eventually to MRSA in 2002 (VRSA)
• VRSA such strains are still rare
• Mechanisms of resistance


  1. Exposure to antibiotics selects for bacteria with mutated key genes and/or their control systems (e.g. up-regulation and/or mutation of β-lactamases; down-regulation of porins; up-regulation of efflux pumps)

  2. Exposure to antibiotics selects for bacteria with horizontally acquired antibiotic resistance determinants
• Multidrug-resistant (MDR) Klebsiella pneumoniae


  A rising threat that is resistant to third-generation cephalosporins, fluoroquinolones and aminoglycosides
• A nosocomial infection is a hospital-acquired infection
• Klebsiella pneumonia


  Causes destructive changes to human lungs, inflammation and haemorrhage that sometimes produces a thick, bloody, mucoid sputum (currant jelly sputum)
• In recent years, klebsiellae have become important pathogens in nosocomial infections
• Spread of MDR Klebsiella pneumoniae


  • 1999
  • 2005
  • 2006
  • 2008
  • 2010
  • 2011
  • 2014
  • 2017
• Drivers of antimicrobial resistance (AMR)


  Behaviour, commercial practices, medical practices
• Anthropogenic drivers of antibiotic resistance


  • Farming practices (13 million Kg of antibiotic as growth promoters in USA)
  • Horticultural practices (Californian soft fruit routinely sprayed with tetracycline in USA)
  • Veterinary practices (Over-prescription of antibiotics for treatment of pets in UK)
  • Healthcare practices (Over-prescription of antibiotics worldwide)
• Community-acquired resistance generates antibiotic resistant strains that spread into the community
• Unnecessary Antibiotic Prescriptions


  • ear infection
  • common cold
  • bronchitis
  • sore throat
  • sinusitis
• Bacterial characterisation: Typing by Gram Stain


  Gram stain detects peptidoglycan. Gram positive cell wall vs Gram negative cell wall
• Not all bacteria can be classified by Gram staining, such as Gram-variable and Gram-indeterminate groups
• Gram staining provides poor species resolution
• Typing Methods


  • Biotyping (26.8%)
  • Antibiogram typing (50.7%)
  • Phage-typing (0.7%)
  • Serotyping (7.2%)
  • RAPD (6.5%)
  • PFGE (10.9%)
  • AFLP (2.9%)
  • Ribotyping (1.4%)
  • MLST (0.7%)
  • Other (0.7%)
• Biotyping


  Strain discrimination by examining growth profiles on different substrates, metabolic activities, colony morphology and environmental tolerances
• Antibiotyping (antibiogram typing)


  Strain discrimination on the basis of antibiotic resistance, comparing susceptibility of different isolates to a set of antibiotics
• Phage-typing


  Strain discrimination on the basis of resistance to various bacteriophages, characterising strains by their resistance or susceptibility to a standard set of bacteriophages
• Serotyping


  Strain discrimination on the basis of binding of antibodies of known specificity to their cell surface antigens such as lipopolysaccharides, membrane proteins, capsular polysaccharides, flagellae and fimbriae
• Some Salmonella strains are autoagglutinable (rough) and untypeable by serotyping
• Serotyping sometimes has poor discriminatory power due to the large number of serotypes and cross-reaction of antibodies with surface antigens
• Molecular typing methods


  • RAPD: random amplification of polymorphic DNA
  • PFGE: pulsed field gel electrophoresis
  • AFLP: amplified fragment length polymorphism
  • Ribotyping: fingerprinting of genomic DNA restriction fragments containing 16S and 23S rRNA genes
  • MLST: multilocus sequence typing