Antibiotics are used to fight bacterial infections.

There are 2 main types:

  • Bactericidal: Antibiotic that kills bacteria
  • Bacteriostatic: Inhibits growth of bacteria


When bacteria are no longer affected by an antibiotic they are resistant.

Resistance happens because:

  • Mutations
  • Pathogens have evolved to evade immune systems – struggle is the evolutionary race


Hospital Acquired Infections

They try to combat antibiotic resistance by:

  • Only using antibiotics when needed and ensure course of treatment is completed (reduced selection pressure on organisms and destroys all bacteria causing infection)
  • Isolating patients with resistant diseases (prevents transmission)
  • Good hygiene
  • Screening of patients entering a hospital (detection and treatment)


Investigating bacteria and antibiotics:


  • A sterile nutrient agar plate is seeded with bacteria
  • Antibiotic applied to sterile paper discs, lay on agar using sterile forceps
  • Seal petri dish but not completely
  • Incubate at 30oC for around 24 hours
  • Look for inhibition zones around the antibiotic discs (clear zones). Bigger areas indicate a better antibiotic against this species