PSI Barbering Practice Exam 2026 - Free Barbering Practice Questions and Study Guide

The organism known for being pus-forming and growing in clusters resembling bunches of grapes is Staphylococci. This group of bacteria is characterized by their spherical shape and the tendency to form clusters due to their division in multiple planes. This distinctive arrangement is what gives them the appearance of grapes under a microscope. Staphylococci are known to be involved in various infections, especially skin infections, and are associated with the formation of pus, which is a result of the body's immune response to bacterial infection.

The other options represent different types of organisms. Streptococci, while also spherical bacteria, grow in chains and are not typically known for pus formation. Bacilli are rod-shaped bacteria, differing significantly in shape and structure from cocci. Viruses, on the other hand, are entirely different in that they are not bacteria and do not have a cellular structure; they require a host cell to replicate and do not typically cause pus formation in the same way bacteria do. Each of these distinctions helps to clarify why Staphylococci is the correct answer.