Host defenses against bacteria

Human defense system against bacteria or the immune system is a well developed system. It consists of two arms;

1. Innate (nonspecific) defenses
2. Acquired (specific) defenses

Innate (nonspecific) immunity

This system provides a general protection against infections. This is the first to react against microorganisms which tend to invade our body. It consists of following components;

1. physical barriers (intact skin and mucous membranes)
2. phagocytic cells (neutrophils, macrophages)
3. proteins (complements, lysozymes)

Damage to skin/mucous membrane can result following infections

Predisposing factors	Site of infection	example
Intravenous catheters	Skin	Staphylococcus aureus
Diabetes	Skin	Staphylococcus aureus
Burns	Skin	Pseudomonas aeruginosa
Cystic fibrosis	Respiratory tract	Pseudomonas aeruginosa
Trauma to jaw	Gingival crevices	Actinomyces isralii
Dental extraction	Oropharynx	Viridans sterptococci
Oral mucositis	Mouth and entire GIT	Viridans sterptococci

Acquired (specific) immunity

Acquired immunity results either from exposure to the organism or from receipt of preformed antibody made in another host. This system consists of two components;

1. passive acquired immunity
2. active acquired immunity

Essential host defense mechanisms against bacteria

Mechanism	Bacteria/toxin	Example
Antibody mediated (humoral immunity)	Encapsulated pyogenic bacteria	Streptococcus pneumonia Staphylococcus aureus Haemophilus influenzae
Antibody mediated	Exotoxins	Clostridium tetani Clostridium botulinum
Cell mediated	Intracellular bacteriae	Mycobacterium tuberculosis Legionella pneumophila