12 - gram neg superbugs

• There are global present and rising threats from multi-drug resistant pathogenic bacteria
• Antibiotic resistance was detected in the 1940s and confirmed within a decade
• Antibiotic overuse is the primary cause: farming, soft fruit, veterinary and health practices
• Biotyping


  Takes us some way towards identification, but nucleic acid techniques show superior strain discrimination
• Pseudomonas aeruginosa has multiple environmental reservoirs
• There has been a rapid and disturbing threat of carbapenem and quinolone resistance in Pseudomonas aeruginosa
• Carbapenem resistance in Pseudomonas aeruginosa

  1. Porin loss

  2. Acquisition of ESBLs

  3. Acquisition of carbapenemases

  4. Upregulation of efflux
• Quinolone resistance in Pseudomonas aeruginosa


  • Mutations in GyrA (the mutated DNA gyrase resists quinolone binding)
  • Mutations in NfxB (globally dysregulated physiology that upregulates the efflux pumps encoded by OprN and OprJ)
• These resistance phenotypes have spread to other Gram negative pathogens
• Carbapenems are β-lactam antibiotics with a broad spectrum of activity. Their structures are generally resistant to β-lactamases
• Carbapenemases in Pseudomonas aeruginosa

  • AmpC enzymes (not inhibited by β-lactamase inhibitors)
  • Metallo-β-lactamases
  • KPC (Klebsiella pneumoniae carbapenemase)
  • OXA-48 β-lactamases
• Quinolones (e.g. ciprofloxacin) inhibit DNA gyrase (topoisomerase II) and DNA topoisomerase IV
• A previously healthy 38-year-old male presented to the emergency room with a 10-hour history of fevers, chills, and significant pubic area pain. He also complained of painful urination and feelings of incomplete emptying after voiding
• He denied any history of sexually transmitted diseases, recent urinary tract infections, or genitourinary trauma
• He was hospitalized for 10 days and became septicemic
• Bacterial samples taken soon identified Pseudomonas aeruginosa as a likely culprit
• He purchased a newly hot tub and used it a lot over the previous week, filling it from a local stream
• Pseudomonas aeruginosa can multiply to 10^4 to 10^6 organisms/ml when chlorine levels drop to <1 ppm
• Pseudomonas aeruginosa has minimal nutritional requirements and a wide growth temperature range (4 to 42°C)
• Pseudomonas aeruginosa is responsible for one in ten hospital-acquired infections
• Pseudomonas aeruginosa can cause a range of infections including pneumonia, septic shock, urinary tract infections, gastrointestinal infections, and skin/soft tissue infections
• Pseudomonas aeruginosa is an opportunistic pathogen of animals and plants
• RFLP (Restriction Fragment Length Polymorphism) and PFGE (Pulsed Field Gel Electrophoresis) are molecular biology techniques used for typing bacteria
• PFGE is good for analysing recent evolutions like hospital outbreaks, is highly discriminative, and faster than MLST, but requires many hours of work, is very technical and hard to reproduce, and the results may be subjective
• PFGE typing of the Pseudomonas aeruginosa isolates showed the source of the infection was the patient's hot tub
• Legionella can also grow in hot tubs and infect people when they breathe in steam or mist from a contaminated hot tub
• There has been a rapid and disturbing rise in carbapenem resistance in Pseudomonas aeruginosa
• Antibiotics have specific modes of action including inhibiting cell wall synthesis, RNA synthesis, cell membrane disruption, folate synthesis, nucleic acid synthesis, and protein synthesis