Final answer:
The zone of inhibition for determining the susceptibility to optochin should be referenced from authoritative sources such as the CLSI standards. The question does not provide the correct measurement for optochin, and the keyword optochin is omitted, thus, a precise answer cannot be given without the correct standards as context.
Step-by-step explanation:
The zone of inhibition required for susceptibility to optochin (not provided in the question's options) is typically defined by established clinical guidelines, such as those set out by the Clinical Laboratory Standards Institute (CLSI). For the particular measurements listed in the question with various disk sizes, no standard size matches those exact conditions. In a standard Kirby-Bauer disk diffusion test, which is the test typically used to determine the susceptibility of bacteria to antibiotics, a filter paper disk impregnated with optochin is placed on an inoculated agar plate. After incubation, a clear area devoid of bacterial growth indicates susceptibility, and the diameter of this zone of inhibition is measured. The specific measurement for optochin susceptibility should be referenced from the latest CLSI standards or similar authoritative sources.
For instance, with a 6-mm disk, if a 14 mm or greater zone of inhibition is observed, it may indicate susceptibility to optochin; however, this is a general example and may not reflect current standards for optochin or the specific conditions of the test, as standard values can vary depending on the antibiotic and organism being tested. It's important to ensure that the recorded zone of inhibition is compared against the most recent standardized chart to determine accurate antibacterial susceptibility.