Most of the α-hemolytic streptococci present in the normal flora are known as viridans because they cause green hemolysis on blood agar plates. It causes endocarditis generally in persons with diseased heart valves.

Proteus mirabilis causes up to 10% of community-acquired UTIs and presumably colonises the normal human gastrointestinal tract.

These include proteases, collagenases and hyaluronidases. For example, Clostridium perfringens produces a potent collagenase, whilst Staphylococcus aureus produces a hyaluronidase.

Droplet transmission involves coughing, sneezing  resulting in a spray of secretions capable of contacting conjunctiva, nasal mucosa and lips within a 3-foot radius. This is an important means of transmission of meningococci, influenza viruses and pertussis.

These organisms causes neonatal meningitis and septicemia after transmission from the normal vaginal flora of the mother. The organism can be identified on the basis of beta hemolysis.

Enterohemorrhagic Escherichia coli (EHEC) serotype O157:H7 is a human pathogen responsible for outbreaks of bloody diarrhea and hemolytic uremic syndrome (HUS) worldwide.

Gamma interferon and tumor necrosis factor alpha secreted by host immune cells activates the infected endothelial cell to destroy intracellular rickettsiae by the creation of autophagosomes. Later, fusion of lysosomes with autophagosomes results in the digestion of dying rickettsia  .

Granuloma is a chronic inflammatory lesion characterised by large numbers of cells of various types including macrophages, lymphocytes, fibroblasts, giant cells and some degrading and some repairing the tissues.

It is a gram-negative, spiral to pleomorphic, prokaryote. H. pylori infection is the main cause of chronic superficial gastritis and it is associated with both gastric and duodenal ulcers.

Infections by P. aeruginosa are a common cause of bacteremia that is bacterial blood infections. Heart valves, particularly of intravenous drug users can also become infected. Symptoms include general malaise with fever, joint and muscle pain.

A group of 11 proteins, which are coded by plasmids, are essential for rodent pathogenesis and are responsible for cytotoxicity, inhibition of phagocyte migration and engulfment and platelet aggregation.

 Francisella tularensis is the causative agent of tularemia. Primary reservoirs are rabbits, hares and ticks. Man most commonly acquires tularemia via insect bites (ticks primarily, but also deer flies, mites, blackflies, or mosquitoes) or by handling infected animal tissues.  

Legionella pneumophila facultative intracellular pathogens, which stain poorly as Gram negative rods. It resides in the environment in pools of stagnant water worldwide. It is found as an intra-cellular agent within protozoa and a component of biofilms.

Erysipelothrix rhusiopathiae, is a Gram-positive anaerobic rod, which infects through skin abrasion while handling contaminated animal products or soil. Generally, the organism produces an inflammatory skin lesion, on fingers or hand, which is violaceus and has a raised edge. It spreads peripherally, as the discolouration in the central area fades.

Reiter's syndrome is a triad of symptoms that include conjunctivitis, polyarthritis and genital inflammation. The disease is associated with HLA-B27.