What is the purpose of adding sodium thiosulfate to a bacteria sample bottle?

The addition of sodium thiosulfate to a bacteria sample bottle primarily serves the function of removing any chlorine residual present in the sample. Chlorine is commonly used in water treatment processes to disinfect and eliminate harmful pathogens. However, if chlorine remains in the sample when testing for bacteria, it can adversely affect the growth of the microorganisms in question, leading to inaccurate or misleading results.

By neutralizing the chlorine, sodium thiosulfate ensures that the sample accurately reflects the true bacterial content without the interference of chlorine, thus allowing for a proper evaluation of the sample's microbiological quality. This is essential for reliable testing, as it helps in getting an accurate count and assessment of the microbial population in the water sample.

In contrast, the other options do not accurately describe the role of sodium thiosulfate in this context. Preserving the sample, enhancing bacteria growth, and stabilizing pH levels involve different chemical processes that are not the primary function of sodium thiosulfate when it comes to bacterial analysis.