The presence of organic matter such as saliva and pus can interfere with the actions of disinfectants.

Physical methods of microbial control, such as autoclaving, dry heat, or filtration, can achieve sterilization by completely eliminating all forms of microbial life, including bacterial spores. In contrast, chemical methods, like alcohols, chlorine, or phenolic compounds, primarily disinfect surfaces by killing or inhibiting vegetative bacteria, fungi, and some viruses, but they do not reliably destroy highly resistant spores. The effectiveness of chemical disinfectants depends on concentration, contact time, and the presence of organic material. Therefore, while physical methods can sterilize under controlled conditions, chemical methods are generally limited to disinfection rather than true sterilization.

Not all mutations are harmful to the cell. Mutations are changes in the DNA sequence, and their effects depend on the location and nature of the change. Some mutations are neutral, causing no noticeable effect on cellular function. Others can be beneficial, providing an adaptive advantage under specific environmental conditions, such as antibiotic resistance in bacteria. Harmful mutations do exist and can disrupt protein function, leading to cell dysfunction or death, but the presence of a mutation does not automatically equate to harm. The impact of a mutation is determined by how it affects gene expression and protein activity.