Final answer:
Resident microbiota protects against pathogens by competing for nutrients and space (competitive exclusion) and producing bacteriocins that attack pathogenic bacteria.
Step-by-step explanation:
The resident microbiota acts as a barrier to pathogens through two main methods. First, by the process known as competitive exclusion, they outcompete potential pathogens for space and nutrients within the body. Secondly, members of the resident microbiota may produce substances such as bacteriocins, which are protein toxins that inhibit the growth of susceptible bacteria by binding to their receptors.
In addition to these mechanisms, the microbiota influences the pH and secrete various substances that create an unfriendly environment for pathogens, contributing to the protection of the host from infections. Practices such as good hygiene and proper diet can affect the composition of both resident and transient microbiota, impacting this natural defence system.