Biological Diversity 2006 

Pappenheim's Stain of Streptococcus pyogenes

Kingdom: Bacteria
Phylum:
Firmicutes
Class: Bacilli
Order: Lactobacillales
Family: Streptococcaceae
Genus: Streptococcus
Species: pyogenes

Representative Photos

Bacterial Cell wall
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Gram stain
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Hemolysis
Top to bottom:
Alpha, Beta and Gamma

Cellulitis
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Impetigo
(mouse over to reveal)

Scarlet fever
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Necrotizing fasciitis
(mouse over to reveal)


 

 

Streptococcus pyogenes

Introduction

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.

Bacterial Classification

Bacterial classification 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.

Bacteria are one of two prokaryote kingdoms. Prokaryotes are the simplist and most abundant organisms on earth. They differ from eukaryotic life in seven distinct ways.

1) They are all unicellular
2) They are, on average, only 1 micrometer in diameter
3) They lack a membrane bound nucleus and their DNA is not arranged in chromosomes, but rather localized in a cytoplasmic zone called the nucleoid
4) Cell division is mainly accomplished through binary fission and transfer of genetic information to other organisms is carried out by a process called conjugation
5) They have no cytoplasmic compartmentalization or cytoskeleton, and the only organelle present is the ribosome
6) They have flegella composed of the flagellin protein, the flegella move like propellers
7) They have the ability to perform multiple kinds of photosynthesis and can be chemoautotrophic (energy production from inorganic compounds) as well

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
2) They also both usually have cell walls, bacterial cell walls are made of the carbohydrate-protein complex peptidoglycan and archaebacterial cell walls are made of chitin
3) Bacterial ribosomal proteins and RNA polymerase are distinct from their eukaryotic counterparts, whereas archeabacterial ribosomal proteins and RNA are closely related to eukaryotes
4) Bacterial genes lack introns, while some archaebacterial genes contain them

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.
The gram stain consists of these steps.

Crystal violet - stains both gram negative and positive bacteria
Gram's iodine - fixes the stain in gram positive bacteria
Ethanol or acetone - washes the stain from gram negative bacteria
Safranin - counterstain, will restain gram negative bacteria while not interfering with the previous stain in gram 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.
(Although they fall under this taxonomic group they are cocci shaped bacterium)

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
Beta - if there is a transparent or lightened area, it is complete hemolysis and is caused by hemolysins
Gama - if there is no change in the media, hemolysis did not occur

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.
Erysipelas - an acute infection and inflammation of the dermal layer of the skin. It occurs primarily in infants and individuals over thirty with a history of streptococcal soar throat and is characterized by painful reddish patches that enlarge and thicken with a sharply defined edge.
Scarlet Fever - a scarlet rash on the upper chest that spreads to the remainder of the body, other symptoms include sore throat, chills, fever, headache, and a strawberry-colored tongue. It is caused by a strain of Streptococcus pyogenes that carries a lysogenic bacteriophage which codes for the production of an erythrogenic or rash-inducing toxin that causes a shedding of the skin.
Streptococcal Sore Throat - bacteria in the throat and or the tonsils stimulate an inflammatory response and the lysis of leukocytes and erythrocytes causing the release of the inflammation exudate from the blood vessels which is deposited on the surrounding tissue. Symptoms include general feeling of discomfort or malaise, fever, headache with the physical manifestations of redness, edema and lymph node enlargement in the throat.

Poststreptococcal diseases are:
Glomerulonephritis (Bright's disease) - the destruction of the glomerular membrane by a type-III (immune complex based) hypersensitivity reaction possibly caused by streptococcal M protein. Symptoms are edema, fever, hypertension and hematuria (blood in the urine).
Rheumatic Fever - an autoimmune disease characterized by inflammatory lesions involving heart valves, joints, subcutaneous tissues and the central nervous system. Mechanism of development is unknown but it usually results from prior streptococcal sore throat infection. There are a variety of symptoms that make diagnosis difficult.

Diseases caused by invasive Streptococcus A infections are:

Necrotizing fasciitis - infection that destroys the sheath covering skeletal muscles
Myositis - inflammation and destruction of skeletal muscle and fat tissue
Toxic Shock-like Syndrome (TSLS) - caused by an invasive Strep A that produces pyrogenic exotoxins that leads to a precipitous drop in blood pressure, multiple organ failure and very high fever. This condition has a 30% mortality rate.

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."
A reason for the high mortality of these infections is due to 85% of the strains carry genes for the production of streptococcal pyrogenic exotoxins A and B. Exotoxin A acts as a superantigen, causing T cells to produce abnormally large quantities of cytokines which damage the endothelial cells that line blood vessels causing fluid loss and rapid tissue death due to lack of oxygen. Exotoxin B is an enzyme that rapidly destroys tissues by breaking down proteins.

Its pathogenecity is due to the following factors:

1) extracellular enzymes that break down host molecules
2) streptokinases, enzymes that activate a host-blood factor that dissolves blood clots
3) cytolysins streptolysin O and streptolysin S to kill host leukocytes
4) capsules and M protein that help retard phagocytosis

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.
Treatment for infection is penicillin or erythromycin if there is a penicillin allergy. There is no vaccine for Streptococcus pyogenes, only Streptococcus pneumoniae (responsible for Streptococcal pneumonia).
Streptococcus pyogenes is less contagious than the cold or flu viruses, so the best preventative measures include covering food, washing hands and cleansing and medicating wounds.

Literature Cited

Prescott, Harley and Klein. Microbiology, Sixth Edition. McGraw Hill Higher Education, NY, 2005.

Raven, Johnson, Losos and Singer. Biology, Seventh Edition. McGraw Hill Higher Education, NY, 2005.

Wikipedia.org Accessed 26-3-2006.

Department of Health and Human Services Center for Disease Control and Prevention.
Homepage= http://www.cdc.gov Accessed 26-3-2006.

Images Obtained from

CDC Public Health Image Library #2110, 1979.
CDC Public Health Image Library #I4648.
CDC Public Health Image Library #5155, 1975.
CDC Public Health Image Library #5163, 1975.


MJCR/MBMB 403:Medical Microbiology Southern Illinois University Carbondale 2006.
Homepage= www.cehs.siu.edu/fix/medmicro/genmicr.htm Accessed 26-3-2006.

Loyola University Health System Microbiology & Immunology Medical Education Pages 2006. http://www.meddean.luc.edu/lumen/DeptWebs/microbio/med/gram/tech.htm Accessed 26-3-2006

Author: Seth Stephens
Creation Date:
02 March 2006
Revision Date: 26 March 2006


Earlham Biology Department Biology 226: Biological Diversity

Copyright -2001 Earlham College. Revised 1 March 2006