What bacterium is commonly associated with pustules, rashes, and boils?

The presence of pustules, rashes, and boils in the context of skin conditions is commonly associated with Staphylococcus bacteria, particularly Staphylococcus aureus. This bacterium is known for causing various skin infections including folliculitis (inflammation of hair follicles), impetigo (a contagious rash), and abscesses (localized infections that can lead to pus formation).

Staphylococcus bacteria are part of the normal skin flora but can become pathogenic under certain conditions, such as when the skin barrier is compromised or when there is an underlying health issue that affects the immune system. The ability of Staphylococcus to produce toxins and enzymes that can damage host tissues significantly contributes to the formation of lesions like pustules and boils.

The other options represent different types of bacteria. Streptococcus is often associated with throat infections and can cause skin infections, but it is typically not the primary bacterium behind pustules and boils. Bacillus is a genus that includes some species that can cause food poisoning and other illnesses rather than skin issues. Escherichia, primarily known for its role in gastrointestinal infections, does not typically cause pustular skin conditions. Thus, Staphylococcus is the most relevant and correct choice for the symptoms provided.