Micro & Immunology · single question
What is the most resistant bacterial form to sterilization?
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Correct answer: D. Bacilli
BACTERIAL SPORES (endospores) are the most resistant forms to sterilization methods. Spores are produced by certain gram-positive bacteria including Bacillus and Clostridium species. They can survive boiling water, many disinfectants, desiccation, UV radiation, and require high-pressure steam (autoclave at 121°C for 15-20 minutes or 134°C for 3 minutes) for destruction. This is why the biological indicator (spore test) for autoclaves uses Geobacillus stearothermophilus spores — they represent the ultimate test of sterilization efficacy.
- A. INCORRECT. Streptococcus is a gram-positive coccus. Vegetative bacteria like Streptococcus are killed by most sterilization and disinfection methods — they are among the LEAST resistant forms.
- B. INCORRECT. Flagella are bacterial appendages for motility — they are not a 'form' of bacteria and have no special resistance to sterilization.
- C. INCORRECT. Biofilm is highly resistant to antimicrobials but can be disrupted by mechanical debridement and appropriate disinfectants. It does not approach the resistance level of bacterial spores.
- D. CORRECT. BACILLI (specifically spore-forming bacilli like Bacillus and Clostridium) produce endospores that are the most resistant biological entities to sterilization. The 'Bacilli' answer refers to the spore-forming ability of these bacteria. Spores resist heat, chemicals, and radiation.
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