In a standard broth dilution, what is the most commonly used visual indicator that bacteria have grown in a tube or well?

A bright color change to blue in the broth caused by antibiotics binding to amino acids released by bacteria, which is the standard colorimetric growth indicator used universally.

Visible turbidity (cloudiness) of the broth indicating bacterial proliferation.

Formation of crystalline precipitates in the broth as bacteria metabolize the antibiotic into insoluble products.

Complete clearing of the broth due to production of extracellular enzymes that digest the medium constituents.