Chapter Capsule

A. Infections: Target is skin; local abscess occurs at site of invasion of hair follicle, gland; manifestations are folliculitis, furuncle, carbuncle, and bullous impetigo. Other common infections are osteomyelitis, a focal infection of bone; bacteremia, leading to endocarditis; and pneumonia.

B. Toxic Disease: Food intoxication due to enterotoxin; staphylococcal scalded skin syndrome (SSSS), a skin condition that causes desquamation; toxic shock syndrome, toxemia in women due to infection of vagina, associated with wearing tampons.

C. Principal Coagulase-Negative Staphylococci: S. epidermidis, a normal resident of skin and follicles; an opportunist and one of the most common causes of nosocomial infections, chiefly in surgical patients with indwelling medical devices or implants. S. saprophyticus is a urinary pathogen.

D. Treatment: S. aureus has multiple resistance to antibiotics, especially penicillin, ampicillin, and methicillin; drug selection requires sensitivity testing; cephalosporins often used; abscesses require debridement and removal of pus; extreme resistance of staphylococci to harsh environmental conditions makes control difficult, requiring a high level of disinfection and antisepsis.

A. b-Hemolytic Streptococci: S. pyogenes is the most serious pathogen of family; produces several virulence factors, including C-carbohydrates, M-protein (fimbriae), streptokinase, hyaluronidase, DNase, hemolysins (SLO, SLS), pyogenic toxin.

1. Microbe resides in nasopharynx of carriers; transmitted through close contact; invades skin and mucous membranes.

2. Skin infections include pyoderma (strep impetigo) and erysipelas (deeper, spreading skin infection).

3. Systemic conditions include strep throat or pharyngitis, severe inflammation of throat membranes; may lead to toxemia, called scarlet fever—generalized flushing of skin and high fever due to erythrogenic toxin; also causes pneumonia.

4. Sequelae caused by immune response to streptococcal toxins include rheumatic fever, a delayed allergy that damages heart valves and joints, and glomerulonephritis, an inflammation that leads to malfunction or destruction of kidney tubules.

B. Streptococcus agalactiae (group B), a pathogen increasingly found in the human vagina; causes neonatal, wound, and skin infections, particularly in debilitated persons.

1. Enterococcus faecalis and other enteric group D species are normal flora of intestine; cause opportunistic urinary, wound, and surgical infections.

2. Group A and group B are treated primarily with some type of pencillin (G is very effective); sensitivity testing may be necessary for enterococci; no vaccines available.

C. a-Hemolytic Streptococci: The viridans streps S. mitis, S. salivarius, S. mutans, and S. sanguis constitute oral flora in saliva.

1. Principal infections are subacute endocarditis, mass colonization of heart valves following dental procedures.

2. Mutans and sanguis species are the main contributors to plaque and dental disease.

D. S. pneumoniae, the pneumococcus, has heavily encapsulated, lancet-shaped diplococci; capsule is an important virulence factor—84 types; reservoir is nasopharynx of normal healthy carriers.

E. The pneumococcus is the most common cause of bacterial pneumonia; attacks patients with weakened respiratory defenses; entrance of bacteria into lungs initiates acute, massive inflammatory response that fills lungs (and bronchioles) with fluid; consolidation of fluid leads to lobar pneumonia and compromised respiration. Other symptoms include fever/chills, cyanosis, cough; otitis media, inflammation of middle ear, is common in children; vaccination available for patients at risk.

A. Neisseria gonorrhoeae: The gonococcus, cause of gonorrhea; microbe invades mucous membranes by attaching with pili; tends to be located intracellularly in pus cells; among the top five most common STDs; may be transmitted from mother to newborn; asymptomatic carriage is common in both sexes.

1. Symptoms of gonorrhea in males are urethritis, discharge; infection of deeper reproductive structures may cause scarring and infertility. Symptoms of gonorrhea in females include vaginitis, urethritis. Ascending infection may lead to salpingitis (PID), mixed anaerobic infection of abdomen; common cause of sterility and ectopic tubal pregnancies due to scarred fallopian tubes. Extragenital infections may be anal, pharyngeal, conjunctivitis, septicemia, arthritis.

2. Infections in newborns cause eye inflammation, occasionally infection of deeper tissues and blindness; can be prevented by prophylaxis immediately after birth.

3. Preferred treatment is a combination of cephalosporin and tetracycline due to increasing PPNG (penicillin-resistant) strains; no vaccine exists; safe sex practices, lack of promiscuity are important controls.

B. Neisseria meningitidis: The meningococcus is a prevalent cause of meningitis. Agent can be carried in the nasopharynx; invades when resistance is lowered; is spread by close contact; bacterium adheres by capsule and pili. Disease begins when bacteria enter bloodstream, pass into the cranial circulation, multiply in meninges; very rapid onset; initial symptoms are neurologic; endotoxin released by pathogen causes hemorrhage and shock; can be fatal; treated with penicillin and/or chloramphenicol; vaccines exist for groups A and C.

C. Other Gram-Negative Cocci and Coccobacilli: Branhamella catarrhalis, common member of throat flora; is an opportunist in cancer, diabetes, alcoholism. Moraxella, short rods that colonize mammalian mucous membranes. Acinetobacter, gram-negative coccobacilli that occasionally cause nosocomial infections.