Everyone has heard the trivial terms, "staph and strep germs." Use of the term,
"germ," is a way of trivializing the idea of an infectious biological agent for
children. We aren't quite sure why that sort of
trivialization is continued into adulthood.
Click for ideas on teaching bacteriology.
|Staphylococcus aureus .
Staphylococcus is a very well known genus of bacteria. Colonies are
"gold," or yellow on sheep blood agar solid media, hence the name. A common
pathogen, boils, acne, wound infections, food poisoning are among a host of
conditions caused by this organism. The organism is both pathogenic and
invasive. It produces leukotoxin which can kill white blood cells and a wide
variety of other toxins. S. aureus is quite pyogenic and in decades past
was named Staphylococcus pyogenes, however that specific name is currently
applied to one GPC, Streptococcus pyogenes.
|Increasingly, and especially in hospital, strains of both
S. aureus and S. epidermidis have become resistant to the antibiotic
DOC, methicillin. Such strains have been labelled Staph MR. Other clinically
significant species include, S. haemolyticus, S. hominis and
(Coagulase-negative) Staphylococcus epidermidis, appears as white
colonies on sheep blood agar plates. While both S aureus and S
epidermidis are normal inhabitants of the skin, epidermidis had been
considered the lesser of the two in virulence. Most S aureus strains
test positive for coagulase, clot formation in tube of citrated rabbit plasma.
The other species test negative. "Infections by S. epidermidis, S.
haemolyticus, and S. hominis, are associated with intravascular
devices (prosthetic heart valves and intra-arterial or intravenous lines) and
shunts. Also quite common are infections of prosthetic joints, wound
infections, osteomyelitis associated with foreign bodies, and endocarditis." Dr
sp. is a contaminant virtually every time. One definite exception is when it
arrives in hospital accreditation test samples in which it is a "freebie." So
it deserves mention. If you have ever looked at it under the microscope, you
might wonder about the Micro- part of the name, since on gram stain, the cocci
can be quite large. Pairs and clusters are seen. Catalase positive. Growth on
mannitol agar. What else. "Three common species of Micrococcus are M.
luteus, M. roseus, and M. varians." |
View a gram stain, such as it is, M. luteus,
| "Streptococcus, plural streptococci, any member of a genus
(Streptococcus) of spheroidal bacteria in the family
Streptococcaceae. The term streptococcus ("twisted berry") refers to the
bacteria's characteristic grouping in chains resembling a string of beads."
"Streptococci can also be classified by the type of carbohydrate contained in
the cell wall, a system called the Lancefield classification."
Encyclopedia Britannica Agglutination
and immunofluorescent antibody microscopic methods can quickly identify Lancefield groups.|
|Streptococcus pyogenes |
pyogenes electron micrographs, Rockefeller University, A downloadable set
of eleven electron micrographs of Streptococcus pyogenes of exceptional
quality.Click link or thumbnail:
Group A, S. pyogenes species of streptococci cause rheumatic
fever, scarlet fever, erysipelas, strep throat, tonsillitis, and other upper
respiratory infections. In case you are wondering which streptococcal species
is the worst, Streptococcus pyogenes, Lancefield group A is the bad boy
in the Strep family. It is so important that physicians don't want any silly
mistakes with names. "Pyogenes? What's that?" Physicians are programmed to
react to the term "Strep group A."
A recently sensationalized strain of an
especially invasive Lancefield group A Streptococcus carries the terms
"pyo-," pus. "-gen-," forming. "necrotizing fascitis," flesh eating, to a very
rare extreme. Once established under the skin, a focus of infection can spread
liquifying flesh as it moves outwardly at a rate as rapid as one inch per hour.
Sounds scary. You have five times more probability of getting hit by
In common practice Streptococcus group A is usually found
in samples from the throat, nasopharanyx, or in sputum in which a plethora of
unimportant normal flora is also present. Its characteristic type of hemolysis
is key for detection. If there is an area of clear or "beta," hemolysis, the
possibility of the presence of group A organisms exists, although the same type
of hemolysis pattern may also be exhibited by some other organisms such as some
gram negative rods which may also be present. The bacterial colony is carefully
scooped up, placed on a glass slide and mixed with a fluorescent antibody. If
the organisms fluoresce when examined by fluorescent microscope, the presence
of Streptococcus group A is confirmed. In laboratories which lack the
relatively high tech fluorescent microscopes, the colonies are replated and
streaked for isolation and identified with older methods. In these cases an
extra incubation period, (day) is required.
|Streptococcus pneumoniae is a member of the
Viridans group, so called because of green or, "alpha," hemolysis on sheep
blood agar, causes lower respiratory infection pneumonia and upper respiratory
infections bronchitis, laryngitis, otitis media (middle ear) and sinusitis.|
The encapsulated, gram-positive coccoid bacteria have a distinctive morphology
on gram stain, the so-called, "lancet shape," which actually looks more like a
blunt arrow head.
Streptococcus pneumoniae, in blood culture.
Enlargement, 1400x900 pixels
Streptococcus pneumoniae, Bacillus sp., SEM x48,000
Streptococcus pneumonaie in bacterial meningitis:
"Before the 1990s, Haemophilus influenzae type b (Hib) was the leading
cause of bacterial meningitis, but new vaccines being given to all children as part of their
routine immunizations have reduced the occurrence of invasive disease due to H.
influenzae. Today, Streptococcus pneumoniae and Neisseria
meningitidis are the leading causes of bacterial meningitis."
fever, headache, and stiff neck are common symptoms of meningitis in anyone
over the age of 2 years.""The diagnosis is usually made by growing bacteria
from a sample of spinal fluid. The spinal fluid is obtained by performing a
spinal tap, in which a needle is inserted into an area in the lower back where
fluid in the spinal canal is readily accessible. Identification of the type of
bacteria responsible is important for selection of correct antibiotics."
|Streptococcus agalactiae, group B|
agalactiae, Lancefield group B, in blood culture.
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"GBS is the most common cause of sepsis (blood infection)
and meningitis (infection of the fluid and lining surrounding the brain) in
newborns. GBS is a frequent cause of newborn pneumonia and is more common than
other, better known, newborn problems such as rubella, congenital syphilis, and
spina bifida. Before prevention methods were widely used, approximately 8,000
babies in the United States would get GBS disease each year. One of every 20
babies with GBS disease dies from infection. Babies that survive, particularly
those who have meningitis, may have long-term problems, such as hearing or
vision loss or learning disabilities.""Approximately one of every 100 to 200
babies whose mothers carry GBS develop signs and symptoms of GBS disease."" In
pregnant women, GBS can cause bladder infections, womb infections (amnionitis,
endometritis), and stillbirth. Among men and among women who are not pregnant,
the most common diseases caused by GBS are blood infections, skin or soft
tissue infections, and pneumonia. Approximately 20% of men and nonpregnant
women with GBS disease die of the disease."
"Many people carry GBS in their bodies but do not become
ill. These people are considered to be "carriers." Adults can carry GBS in the
bowel, vagina, bladder, or throat. People who carry GBS typically do so
temporarily -- that is, they do not become lifelong carriers of the bacteria."
"GBS disease is diagnosed when the bacterium is grown from
cultures of sterile body fluids, such as blood or spinal fluid. Cultures take a
few days to complete. GBS infections in both newborns and adults are usually
treated with antibiotics (e.g., penicillin or ampicillin) given through a vein."
"Group B streptococcus (GBS) is a type of bacterium that
causes illness in newborn babies, pregnant women, the elderly, and adults with
other illnesses such as diabetes or liver disease. GBS is the most common cause
of life-threatening infections in newborns."
Group B Streptococcus website:
|Streptococcus mutans , Normal
mouth flora. Is responsible for cavities. A vaccine is thought possible for
Streptococcus mutans for the prevention of cavities.|
|Peptostreptococcus sp. is anaerobic. It is sometimes
opportunistically involved in the infection of wounds.|