Serotypes are a type of phenotype that is based on the antigens present on the surface of a microorganism, such as bacteria or viruses. These antigens, known as surface proteins, determine the immune response to the microorganism and can be used to classify and identify different serotypes.

Serotypes are different from genotypes, which are the genetic makeup of an organism. While genotypes are determined by the DNA sequence, serotypes are determined by the proteins on the surface of the organism.

In some cases, serotypes can be used to predict the virulence or susceptibility of an organism to certain drugs. For example, some serotypes of the bacterium Streptococcus pneumoniae are more likely to cause severe infections, while others are more susceptible to antibiotics.

Overall, serotypes are an important aspect of the study of microorganisms, and they can provide valuable information about their characteristics and behavior.