Streptococcus Infections

Streptococcus is a genus of spherical gram-positive bacteria. In these bacteria, cellular division occurs along a single axis, thus they grow in chains or pairs. Certain Streptococcus[Page 450]species are responsible for many diseases, including the common streptococcal pharyngitis (“strep throat”), meningitis, bacterial pneumonia, endocarditis, erysipelas, and necrotizing fasciitis. However, many streptococcal species are nonpathogenic. Streptococci are also part of the normal commensal flora of the mouth, skin, intestine, and upper respiratory tract of humans.

Individual species of Streptococcus are classified based on their hemolytic properties. Alpha hemolysis is caused by a reduction of iron in hemoglobin, giving it a greenish color on blood agar. Beta-only hemolysis is complete rupture of red blood cells, giving distinct, wide, clear areas around bacterial colonies on blood agar.

Group A streptococcal bacteria and infections are a form of beta hemolytic Streptococcus bacteria responsible for most cases of streptococcal illness. Group A causes strep throat, scarlet fever, impetigo, toxic shock syndrome, cellulitis, and necrotizing fasciitis. It also causes pneumonia, tonsillitis, septic arthritis, osteomyelitis, meningitis, and sinusitis. Group A not only causes acute infections but also is responsible for nonsuppurative postinfectious sequelae such as rheumatic fever and glomerulonephritis.

The physical findings include erythema, edema, and swelling of the pharynx. Tonsils are enlarged, and grayish-white exudates may be present. Upon palpation, enlarged lymph nodes at the mandibular angle are found. Patients may develop chills and fever. Patients may all present with small papule that turn into pustules and develop a thick crust. To date, the number one treatment of choice is penicillin.

These bacteria are spread through direct contact with mucus from the nose or throat of persons who are infected or through contact with infected wounds or sores on the skin. Ill persons, such as those who have strep throat or skin infections, are most likely to spread the infection. Persons who carry the bacteria but have no symptoms are much less contagious. After a person has been treated with an antibiotic for 24 hours or longer, the infected person generally loses the ability to spread the bacteria. However, it is important to complete the entire course of antibiotics as prescribed.

To reduce the spread of group A streptococcal infections, hands should be washed thoroughly, especially after coughing and sneezing and before preparing or eating food. A patient with a sore throat should consult a doctor so that a test can be performed to determine if it is strep throat. If the test is positive, the person should stay away from work, school, or daycare for 24 hours after beginning antibiotics. All wounds should be kept clean and monitored for possible signs of infection, such as redness, swelling, drainage, and pain at the wound site. A person with an infected wound site and a fever should seek medical attention immediately.

Group B streptococcal bacteria is a form of beta hemolytic Streptococcus bacteria best known as the cause of postpartum infection and the most common cause of neonatal sepsis. Group B streptococci are found commonly in the gastrointestinal tract and have been found to colonize the urethra in both men and women without causing infection. Group B can also colonize the upper respiratory tract. Colonization by group B Streptococcus is also observed in wound and soft tissue cultures, in the absence of obvious infection.

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