Microbiology and Immunology

Streptococci and streptococcal infections WORLD OF MICROBIOLOGY AND IMMUNOLOGY

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Numerous strains of strep bacteria have been identi-

fied. Those streptococci from groups A, B, C, D, and G are

most likely to cause disease. While some of these infections

do not produce symptoms, and the infected person can

become a carrier of the disease-causing bacteria, other strep

infections can be fatal.

Primary strep infections invade healthy tissue, and

most often affect the throat. Secondary strep infections invade

tissue already weakened by injury or illness. They frequently

affect the bones, ears, eyes, joints, or intestines. Both primary

and secondary strep infections can travel from affected tis-

sues to lymph glands, enter the bloodstream, and spread

throughout the body.

Group A streptococci contains those strep bacteria that

are most apt to be associated with serious illness. Between

10,000 and 15,000 infections attributable to group A strepto-

cocci occur in the United States every year. Most are mild

inflammations of the throat or skin, the environments where

the bacteria are normally found. However, other infections can

be deadly.

One example of a serious infection is known as necro-

tizing fasciitis (which is also referred in the popular press as

flesh-eating disease). The disease results from the invasion of

host tissue cells by the bacteria. There, shielded from the

immune responses of the host, toxic bacterial products cause

the destruction of muscle tissue and fat. The infection is able

to quickly spread outward from the point of origin. Unless

intervention is undertaken quickly, which includes antibiotic

therapy and, in severe cases where a limb is involved, ampu-

tation of the affected limb, the infection can be fatal.

A second example of a serious group A streptococcal

infection manifests toxic shock syndrome.

Another division of streptococci is known as group B.

Infections caused by group B streptococci most often affects

pregnant women, infants, the elderly, and chronically ill adults.

Group B was designated in the 1970s. The intervening years

have revealed group B streptococci to be the primary cause of

life-threatening illness and death in newborns. The bacteria

reside in the reproductive tract of a quarter of all pregnant

women. Only a small percentage of these women develop inva-

Chains of Streptococcus pyogenes.

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