Deciphering virulence: heart-harming bacteria flaunt unique viral genes. (This Week).Scientists have mapped the genome of a bacterium responsible for the heart-damaging illness known as acute rheumatic fever. In the process, they've identified telling genetic differences--many of them introduced by viruses--that distinguish the dangerous pathogen from its less virulent relatives.
People who suffer from rheumatic fever sometimes develop rheumatic heart disease rheumatic heart disease
Permanent damage to the valves of the heart usually caused by repeated attacks of rheumatic fever.
Rheumatic heart disease , which causes about 3,600 deaths in the United States each year. Epidemics of the fever hit Salt Lake City in 1986-1987 and 1998-1999 (SN: 11/28/98, p. 346).
The offending bacteria belong to the group A streptococci Streptococcus (plural, streptococci)
A genus of spherical-shaped anaerobic bacteria occurring in pairs or chains. Sydenham's chorea is considered a complication of a streptococcal throat infection. . Why some infections by these bacteria cause only strep throat while others cause more severe conditions--including rheumatic fever and the flesh-destroying disease known as necrotizing necrotizing /nec·ro·tiz·ing/ (nek´ro-tiz?ing) causing necrosis.
Causing the death of a specific area of tissue. Human bites frequently cause necrotizing infections. fasciitus--isn't clear, but certain subtypes of the group are more likely than others to trigger the fever.
Led by James M. Musser of the National Institute of Allergy and Infectious Diseases in Hamilton, Mont., researchers from several U.S. institutions sequenced the genome of a rheumatic-fever-causing streptococcus streptococcus (strĕp'təkŏk`əs), any of a group of gram-positive bacteria, genus Streptococcus, some of which cause disease. that belongs to a group A subtype known as M18.
The researchers compared the sequence of that strain with the previously sequenced genome of a strain of subtype M1. Strains of the M1 type are not normally associated with rheumatic fever.
The two sequenced strains share 1,532 genes, the researchers found. The M18 bacterium also has 178 genetic elements that the M1 microbe microbe /mi·crobe/ (mi´krob) a microorganism, especially a pathogenic one such as a bacterium, protozoan, or fungus.micro´bialmicro´bic
n. lacks, while the latter possesses 112 unique elements of its own.
Viruses that infect bacteria often insert genetic material, but these contributions make up a surprising amount of the variation between M1 and M18 streptococci, says Musser. Many of the virus-related genes unique to the M18 strain produce toxins that could account for its virulence, he says.
The sequence of the type-M18 genome provides a useful map for investigators who wish to mine for factors underlying Streptococcus virulence, comments infectious disease researcher James B. Dale of the University of Memphis The University of Memphis is a public research university located in Memphis, Tennessee, United States, and is a flagship public research university of the Tennessee Board of Regents system. (Tenn.).
Musser's team also compared genetic characteristics of 36 type-M18 streptococci. These included the strain they've fully sequenced and bacteria from both outbreaks of rheumatic fever in Salt Lake City. There's less variation in the virus-contributed genes among the M18 strains than between those strains and the M1 strain, the researchers report in the April 2 Proceedings of the National Academy of Sciences The Proceedings of the National Academy of Sciences of the United States of America, usually referred to as PNAS, is the official journal of the United States National Academy of Sciences. .
Musser notes that the bacteria behind the two Salt Lake City epidemics are virtually identical, indicating that the second outbreak there essentially recycled the strain that caused the first. This similarity suggests that the strain has achieved a stable evolutionary state and can smolder smol·der also smoul·der
intr.v. smol·dered, smol·der·ing, smol·ders
1. To burn with little smoke and no flame.
2. at a low frequency in some populations until unknown factors trigger an outbreak, he says.