Acne vulgaris is a chronic inflammatory disorder usually present in the late teenage years characterized by comedones, papules, nodules, and cysts.
 - subdivided into obstructive type with closed comedones (whiteheads) and open comedones (blackheads) and the inflammatory type consisting of papules, pustules, nodules, cysts and scars.
 - pathogenesis of inflammatory acne relates to blockage of the hair follicle with keratin and sebaceous secretions, which are acted upon by Propionibacterium acnes (anaerobe) that causes the release of irritating fatty acids resulting in an inflammatory response.
 - pathogenesis of the obstructive type (comedones) is related to plugging of the outlet of a hair follicle by keratin debris.
 - chocolate, shellfish, nuts iodized salt do not aggravate acne.
 - obstructive type is best treated with benzoyl peroxide and triretnoin (vitamin A acid)
 - treatment of inflammatory type is the above plus antibiotics (topical and/or systemic; erythromycin, tetracycline, clindamycin).

Parvoviruses
 - smallest DNA virus
 - erythema infectiosum (fifth disease) is characterized by a confluent rash usually beginning on the cheeks ("slapped face") which extends centripetally to involve the trunk; fever, malaise and respiratory problems; and arthralgias and joint swelling (50%).
 
 other associations:
 - aplastic anemia in patients with chronic hemolytic anemias (e.g., sickle cell disease, spherocytosis).
 - repeated abortions associated with hydrops fetalis.
 - pure RBC aplasia by involving the RBC precursors (no reticulocytes peripherally).
 -chronic arthritis

HYPERPLASIA
It is the increase in the size of an organ or tissue due to increase in the number of its constituent cells. This is seen in organs made up of labile and stable cells.

Causes
I. Increased demand:
- Bone marrow in hypoxia and haemolytic states.
- Thyroid gland in puberty

2. Persistant Trauma:
- Acanthosis of the epidermis in chronic inflammations and in warts.
- Hyperplasia of oral mucosa due tooth and denture trauma.
- Mucosa at the edges of a gastric ulcer.

3. Endocrine target organ:
- Pregnancy hyperplasia of breast.
- Prostatic hyperplasia.

4. Compensatory:

Hyperplasia of kidney when the other kidney has been removed.

5. Idiopathic:
Endocrine organs like thyroid, adrenals, pituitary etc. can undergo hyperplasia with no detectable stimulus. .
 

Staphylococcal Infection

Staphylococci, including pathogenic strains, are normal inhabitants of the nose and skin of most healthy people
Virulence factors include coagulase (which clots blood), hemolysin, and protein A (which ties up Fc portions of antibodies). Although we have antibodies against staphylococci, they are of limited usefulness. 

Staphylococci (and certain other microbes) also produce catalase, which breaks down H2O2, rendering phagocytes relatively helpless against them. 

The coagulase-positive staphylococcus (Staphylococcus pyogenes var. aureus) is a potent pathogen. It tends to produce localized infection
It is the chief cause of bacterial skin abscesses. Infection spreads from a single infected hair (folliculitis) or splinter to involve the surrounding skin and subcutaneous tissues

Furuncles are single pimples
carbuncles are pimple clusters linked by tracks of tissue necrosis which involve the fascia.

Impetigo is a pediatric infection limited to the stratum corneum of the skin -- look for honey-colored crusts

Staphylococcal infections of the nail-bed (paronychia) and palmar fingertips (felons) are especially painful and destructive

These staph are common causes of wound infections (including surgical wounds) and of a severe, necrotizing pneumonia. Both are serious infections in the hospitalized patient.

Staph is the most common cause of synthetic vascular graft infections. Certain sticky strains grow as a biofilm on the grafts

Staph aureus is pathogenic, β-hemolytic, and makes coagulase.
Staph epidermidis are non-pathogenic strains that don’t make coagulase.  Often Antibiotics resistant, and     can become opportunistic infections in hospitals.

Staph aureus is normal flora in the nose and on skin, but can also colonize moist areas such as perineum.  Causes the minor infections after cuts.  Major infections occur with lacerations or immune compromise, where large number of cocci are introduced.

While Staph aureus can invade the gut directly (invasive staphylococcal enterocolitis), it is much more common to encounter food poisoning due to strains which have produced enterotoxin B, a pre-formed toxin in un-refrigerated meat or milk products

Staph epidermidis (Coagulase-negative staphylococci)
Universal normal flora but few virulence factors.  Often antibiotic resistant.
Major cause of foreign body infections such as prosthetic valve endocarditis and IV line sepsis.

Staph saprophyticus
Common cause of UTI in women.

Pathogenicity
Dominant features of S. aureus infections are pus, necrosis, scarring.  The infections are patchy.  Serious disease is rare because we are generally immune.  However, foreign bodies or necrotic tissue can start an infection.  Staph infections include wound infections, foreign body sepsis, pneumonia, meningitis.
Occassionally, S. aureus can persist within cells.

Major disease presentations include:
    --Endocarditis
    --Abscesses (due to coagulase activity)
    --Toxic Shock
    --Wound infections
    --Nosocomial pneumonia

Prevention of Staph aureus infections
S. aureus only lives on people, so touching is the main mode of transmission.  Infected patients     should be isolated, but containment is easy with intense hand washing.
 

Acute pericarditis

1. Characterized by inflammation of the pericardium.
2. Causes include:
a. Viral infection.
b. Bacterial infection, including Staphylococcus, Pneumococcus.
c. Tuberculosis.
d. MI.
e. Systemic lupus erythematosus.
f. Rheumatic fever.

3. Signs and symptoms include:
a. Pericardial friction rub on cardiac auscultation.
b. Angina.
c. Fever.

4. Consequences include constrictive pericarditis,which results from fusion and scarring of the pericardium. This may lead to the restriction of ventricular expansion, preventing the heart chambers from filling normally.

Pyelonephritis

- A bacterial infection that affects the renal tubules, interstitium, and renal pelvis.
- One of the most common renal diseases. 
- Usually caused by gram-negative, rod-shaped bacteria that are part of the normal flora of the enteric tract. Most commonly caused by Escherichia coli, followed by Proteus, Klebsiella, and Enterobacter.
- The infecting bacteria are usually from the patient’s own enteric flora an example of an endogenous infection.
- Usually associated with a urinary tract infection (acute pyelonephritis) or involved with another precipitating condition, such as obstruction (chronic pyelonephritis).