Cross-contamination occurs when:

• A. antibiotics are used to kill bacteria in a culture
• B. sterile techniques are used to prevent the spread of microbes
• C. microorganisms are unintentionally transferred from one object or surface to another
• D. all microorganisms are completely removed from a surface

Answer: (C)

Verified step by step guidance

1. Understand the definition of cross-contamination in microbiology: it refers to the unintentional transfer of microorganisms from one object or surface to another, which can lead to the spread of microbes.
2. Review each option given in the problem and analyze whether it matches the definition of cross-contamination:
3. Option 1: 'antibiotics are used to kill bacteria in a culture' – this describes antimicrobial treatment, not cross-contamination.
4. Option 2: 'sterile techniques are used to prevent the spread of microbes' – this describes prevention methods, not the occurrence of cross-contamination itself.
5. Option 3: 'microorganisms are unintentionally transferred from one object or surface to another' – this matches the definition of cross-contamination and is the correct choice.