Very few microbes are always pathogenic Many microbes are potentially pathogenic Most microbes are never pathogenic

A lesion anywhere on the body that does not spread.

 Symptoms of bacterial infection are localized Redness, Heat, Swelling and  Includes local pain, pain that is in a specific part of the body.  For example, if you get cut and the cut gets infected with a bacterium, it will be painful right where the infection is. If you have a sore throat and the infection is bacterial, one side of the throat is often more sore than the other. An ear infection is usually bacterial if one ear hurts and the other doesn't. An infection that produces pus is always bacterial.

 Impetigo is a common bacterial infection of the upper layers of the skin caused by Streptococcus pyogenes and Staphylococcus aureus. It is highly contagious and usually treated with a topical antibiotic.  Impetigo tends to occur in areas of minor breaks in the skin such as insect bites, cuts, or abrasions. Impetigo can also occur in breaks in the skin caused by skin conditions such as scabies, herpes, chickenpox.  Often people harbor the Staphylococcus bacteria inside their nose and don't even know it because it does not cause an infection inside the nose. However, direct contact with infected nasal fluid can infect other parts of the body or other people. The following are common contributing factors: Warm, humid climate or environment

 Tooth decay is caused by specific types of acid- producing bacteria that cause damage in the presence of fermentable carbohydrates such as sucrose, fructose, and glucose.  The mineral content of teeth is sensitive to increases in acidity from the production of lactic acid  A person experiencing caries may not be aware of the disease. The earliest sign of a new carious lesion is the appearance of a chalky white spot on the surface of the tooth, indicating an area of demineralization of enamel. This is referred to as incipient decay.

 As the lesion continues to demineralize, it can turn brown but will eventually turn into a cavitation ("cavity").  Before the cavity forms, the process is reversible, but once a cavity forms, the lost tooth structure cannot be regenerated  A lesion which appears brown and shiny suggests dental caries was once present but the demineralization process has stopped, leaving a stain.  A brown spot which is dull in appearance is probably a sign of active caries.

 is a chronic bacterial infection caused by Treponema pertenue,  Yaws is contagious via direct skin contact with an infective skin lesion.  The bacteria typically gains entry through a cut, bite or scratch. Yaws mainly infects your skin, bones and joints.

 Staphylococcal scalded skin syndrome (SSSS), also called Lyell's disease or toxic epidermal necrolysis,  starts as a localized lesion, followed by widespread erythema and exfoliation of the skin.  This disorder is caused by phage group II staphylococci which elaborate an epidermolytic toxin. The disease is more common in infants than in adults.

 The most superficial form of skin infection is staphylococcal folliculitis, manifested by minute erythematous follicular pustules without involvement of the surrounding skin.  The scalp and extremities are favorite sites. Gram- negative folliculitis occurs mainly as a superinfection in acne vulgaris patients receiving long-term, systemic antibiotic therapy.  These pustules are often clustered around the nose. The agent is found in the nostril and the pustules.

 The primary lesion is a white to yellow follicular pustule, flat or domed. Gram stain of pus reveals numerous intracellular and extracellular Gram- positive pleomorphic rods.  The lesions are more common in men than in women. The process may start at the age when acne usually appears, yet most cases occur years late

 Pitted keratolysis is a superficial infection of the plantar surface, producing a punched-out appearance.  The pits may coalesce into irregularly shaped areas of superficial erosion.  The pits are produced by a lytic process that spreads peripherally. The areas most often infected are the heels, the ball of the foot, the volar pads, and the toes. Humidity and high temperature are frequent aggravating factors. Gram- positive coryneform bacteria have been isolated from the lesions.

 A common disorder, occurs most often in the beard area of black people who shave.  The characteristic lesions are usually erythematous papules or, less commonly, pustules containing buried hairs.  This occurs when a strongly curved hair emerging from curved hair follicles reenters the skin to produce an ingrown hair.  Gram-positive microorganisms that belong to the resident flora are associated with this disorder.

Skin Tuberculosis

 Many cases of M marinum skin disease occur in children and adolescents who have a history of using swimming pools or cleaning fish tanks.  Often, there is a history of trauma, but even in the absence of trauma the lesions appear frequently on the sites most exposed to injury.  The usually solitary lesions are tuberculoid granulomata that rarely show acid-fast organisms. The skin tuberculin test is positive.

 Lesions in M ulcerans skin disease occur most often on the arms or legs and occasionally elsewhere, but not on the palms or soles.  Most patients have a single, painless cutaneous ulcer with characteristic undermined edges.  Geographic association of the disease with swamps and watercourses has been reported. In some tropical areas, chronic ulcers caused by this organism are common.  In scrofuloderma, tuberculosis of lymph nodes or bones is extended into the skin, resulting in the development of ulcers.

 Actinomyces israelii usually is the agent of human actinomycosis.  The characteristic appearance of the lesion is a hard, red, slowly developing swelling. The hard masses soften and eventually drain, forming chronic sinus tracts with little tendency to heal. The sinus tracts discharge purulent material containing “sulfur” granules.  In about 50 percent of cases, the initial lesion is cervicofacial, involving the tissues of the face, neck, tongue, and mandible.  About 20 percent of cases show thoracic actinomycosis, which may result from direct extension of the disease from the neck or from the abdomen or as a primary infection from oral aspiration of the organism.  In abdominal actinomycosis, the primary lesion is in the cecum, the appendix, or the pelvic organs.