Which type of bacteria are considered harmful and may be contagious?

Pathogenic bacteria are a specific type of bacteria that can cause disease and infections in humans, animals, and plants. These bacteria are known for their ability to invade host tissues, multiply, and produce toxins that can lead to various health issues. Because of their nature, pathogenic bacteria can be contagious, meaning they can be spread from one individual to another, often through direct contact or contaminated surfaces.

In contrast, non-pathogenic bacteria are generally harmless and often play essential roles in various ecological and biological processes, such as digestion or nutrient cycling. Symbiotic bacteria form beneficial relationships with their hosts and can contribute positively to health and well-being. Beneficial bacteria, like probiotics, support digestive health and strengthen the immune system. Given these distinctions, pathogenic bacteria remain the only category recognized for their harmful effects and contagious potential, making them a crucial focus in the study of microbiology within the esthetics and health fields.