Final answer:
The appropriate strength of a chemical sanitizer varies based on its intended use and effectiveness against specific microbes, as defined by high, intermediate, and low levels of germicidal activity. The use-dilution test measures this effectiveness, with a passing grade requiring consistent results showing no growth in the majority of test replicates.
Step-by-step explanation:
The strength of a chemical sanitizer should be such that it is effective against the intended type of microorganisms, considering factors like the sanitizer's concentration, pH, temperature, and exposure time. The effectiveness of disinfectants can be grouped into three levels - high, intermediate, and low. High-level germicides are capable of killing vegetative cells, fungi, viruses, and endospores, potentially leading to sterilization with extended use. Intermediate-level germicides are less effective against endospores and certain viruses, while low-level germicides kill vegetative cells and certain enveloped viruses, but are ineffective against endospores.
The use-dilution test is a specific method used to measure the effectiveness of a chemical agent. This involves immersing stainless steel cylinders in a culture of the target organism, then in a disinfectant solution at various concentrations, followed by incubation in a sterile medium to detect any surviving bacteria.
As per the Association of Official Agricultural Chemists International (AOAC), for a disinfectant to pass its effectiveness test, 59 of 60 replicates must show no growth, and the results must be consistent across different batches and on different days.