|Biological Diversity 2006|
Streptococcus pyogenes is a gram positive bacteria. It is a cocci or sphere shaped bacterium that does not produce spores. It reproduces by asexual reproduction along a central axis creating either pairs of bacterium or long chains depending on culture media. It is a facultative anaerobe that produces lactate as part of its fermintation pathway. They lack cytochromes (heme transport proteins that carry electrons, characteristic of electron transport chains) and obtain energy fron substrate level phosphorylation.
has recently undergone some profound changes as information gleaned
from recent breakthroughs in genetic technology become available.
What was once a process that involved classification based on phenotypic
differences is now being rearranged based on genomic and proteomic
information. Please keep this in mind as you read the below.
1) They are all unicellular
The other prokaryote kingdom is Archaebacteria. They differ from bacteria in four key respects.
1) Although they both have plasma membranes containing a lipid-bilayer,
they differ in the kind of lipids used to compose their membranes
The bacterial kingdom is subdevided into main catagories by a process
called Gram Staining (named after Hans Christian Gram, a Danish bacteriologist).
The process is a stain that illustrates the composition of the composition
of the cell wall.
Crystal violet - stains both gram negative and positive bacteria
The mechanism is as follows, gram positive bacterial membrane pores shrink in response to the ethanol or acetone and prevent the stain from being washed. Gram negative bacterial cell walls are made more porous by the decolorization step and the stain is washed away.
The three groupings are Gracilicutes, Firmicutes and Mollicutes. Gracilicutes possess a second cell membrane containing lipids, they stain gram-negative. Firmicutes have a single membrane and a thick peptidoglycan cell wall, they stain gram-postitive. Lastly, Mollicutes have no second membrane or cell wall, they stain gram-negative. Gracilicutes have been divided into many different phyla. Gram positive bacteria are devided into Firmicutes and Actinobacteria (soil bacteria). Mollicutes are now a class of Firmicutes.
The Firmicute phylum is divided into three classes, the Clostridia, Bacilli and Mollicutes. The Clostridia are anaerobic. The Bacilli which are obligate or facultative (capable of both aerobic respiration and fermentation under anaerobic conditions) aerobes. The Mollicutes are described above.
Bacilli comes from the term bacillus which is used to describe any
rod-shaped bacteria. It is divided into two orders the Bacillus and
the Lactobacillales. Bacillus produce endospores and Lactobacillales
do not. An endospore is a heat and chemical resistant, thick walled
spore that bacteria produce when they undergo dormancy.
The lactobacillales contain the families Aerococcaceae, Carnobacteriaceae, Enterococcaceae, Lactobacillaceae, Leuconostocaceae and Streptococcaceae. The family Streptococcaceae contains the genera Lactococcus, Lactovum, Pilibacter and Streptococcus.
The Streptococcus species are clustered into four groups: pyogenic, oral, anaerobic and other. Pyogenic streptococci are pathogens that are associated with pus formation. Most of these species are Beta hemolytic and Streptococcus pyogenes is part of this group. Oral streptococci inhabit the oral cavity and upper respiratory tract of humans and other animals, but other than habitat are not simliar.
The Streptococcus species are also classified on their hemolytic properties (their ability to lyse erythrocytes or red blood cells on media). There are three types of hemolysis alpha, beta and gama. Bacteria are grown on blood agar plates and the media is observed for signs of hemolysis.
Alpha - if there is a greenish darkening of the media, it is incomplete
or partial hemolysis and is generally caused by peroxides
Other means of organization include serological studies, antigen identification, biochemical and physiological tests, carbohydrate fermentation patterns and sensitivity to bacitracin, sulfa drugs and optochin. Some representative Streptococcus species are agalactiae, bovis, dysgalactiae, equi, gordonii, mitis, mutans, oralis, pneumoniae, pyogenes, salivarius, sanguinis, suis, thermophilus and viridans.
Pathogenesis and Treatment
Streptococcus pyogenes is widely distributed among humans, but most hosts are asymptomatic. Only acute infections spread the pathogen and transmission occurs via respiratory droplets, and direct or indirect contact.
Diseases caused by Streptococcus pyogenes are:
Cellulitis - a diffuse, spreading infection of subcutaneous skin tissue.
It results in inflammation characterized by erythema (defined area
of redness) and edema (accumulation of fluid). The most common infection
from Streptococcus pyogenes is impetigo, a superficial cutaneous infection
common to children characterized by crusty legions and vesicles surrounded
by a red border.
Poststreptococcal diseases are:
Diseases caused by invasive Streptococcus A infections are:
Necrotizing fasciitis - infection that destroys the sheath covering
Invasive Strep A is characterized by the
development of specific virulent strains (M-1 and M-3 serotypes)
and predisposing host factors (such
as surgery, wounds, or diabetes). These infections move so fast they
have the colloquial name "galloping gangrene."
Its pathogenecity is due to the following factors:
1) extracellular enzymes that break down host molecules
A means of rapid identification is the Culturette Group A Strep ID
Kit (produced by Marion Scientific, Kansas City, MO) and Directigen
(produced by Hynson, Wescott, and Dunning, Baltimore, MD) that detect
group A streptococci from throat swabs.
Prescott, Harley and Klein. Microbiology,
McGraw Hill Higher Education, NY, 2005.
Images Obtained from
CDC Public Health Image Library #2110, 1979.
Copyright ©-2001 Earlham College. Revised 1 March 2006