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Micro ch.19 Gram positive cocci
Terms in this set (23)
Know how catalase differentiates the Gram Positive cocci.
The catalase test is a particularly important test used to determine whether the Gram + cocci is a staphylococci or a streptococci. Catalase is an enzyme that converts hydrogen peroxide to water and oxygen gas. The test is easy to perform; bacteria are simply mixed with H 2O 2. If bubbles appear (due to the production of oxygen gas) the bacteria are catalase positive. If no bubbles appear, the bacteria are catalase negative. Staphylococcus and Micrococcus spp. are catalase positive, whereas Streptococcus and Enterococcus spp. are catalase negative.
What is the classic, definitive test for Staphylococcus aureus?
Slide Coagulase test
What is Toxic Shock Syndrome, and what toxin must be present to cause it?
(Non-Streptococcal) When strains of Staphylococcus that produce TSS toxin grow in a wound or in an abraded vagina, the toxin can be absorbed into the blood and cause toxic shock syndrome, non-streptococcal (TSS), characterized by fever, vomiting, red rash, extremely low blood pressure, and loss of sheets of skin. TSS is fatal to 5% of patients when their blood pressure falls so low that the brain, heart, and other vital organs have an inadequate supply of oxygen—a condition known as shock.
(Streptococcal Toxic Shock Syndrome) Group A streptococci can spread, albeit rarely, from an initial site of infection, particularly in patients infected with HIV or suffering with cancer, heart disease, pulmonary disease, or diabetes mellitus. Such spread leads to bacteremia and severe multisystem infections producing streptococcal toxic shock syndrome (STSS). Patients experience inflammation at sites of infection as well as pain, fever, chills, malaise, nausea, vomiting, and diarrhea. These signs and symptoms are followed by increased pain, organ failure, shock—and over 40% of patients die.
How does S. aureus cause food poisoning, what foods are most commonly contaminated, and what are the symptoms? How is this illness treated medically?
Commonly affected foods include processed meats, custard pastries, potato salad, and ice cream that have been contaminated with bacteria from human skin. The food must remain at room temperature or warmer for several hours for the bacteria to grow, reproduce, and secrete Enterotoxin. Warming or reheating inoculated food does not inactivate enterotoxins, which are heat stable, although heating does kill the bacteria. Symptoms, which include nausea, severe vomiting, diarrhea, headache, sweating, and abdominal pain, usually appear within four hours following ingestion. Consumed staphylococci do not continue to produce toxins, so the course of the disease is rapid, usually lasting 24 hours or less.
complete lysis of red blood cells around a colony, results in a clear zone surrounding colonies. i.e: S. pyogenes, S. agalactiae, S. equisimilis, S. anginosus
Partial lysis of red blood cells, leaving a greenish ring in the blood agar medium around the colonies. i.e: Viridans Streptococci (esp. S. mutans), S. pneumoniae (aerobic), Streptococcus bovis
no lysis of red blood cells producing no change in blood agar plate i.e: Enterococcus (faecalis, E. faecium)
Pharyngitis: Group A Strep
Inflammation of the pharynx—that is accompanied by fever, malaise, and headache. The back of the pharynx typically appears red, with swollen lymph nodes and purulent (pus-containing) abscesses covering the tonsils
A complication of untreated S. pyogenes pharyngitis in which inflammation leads to damage of heart valves and muscle. Rheumatic fever is most common in five- to fifteen-year-old children. It appears that rheumatic fever is not caused directly by Streptococcus but instead is an autoimmune response in which antibodies directed against streptococcal antigens cross-react with heart antigens, though the exact cause of heart damage is unknown. Damage to the heart valves may be so extensive that they must be replaced when the patient reaches middle age. Rheumatic fever was much more prevalent before the advent of antimicrobial drugs.
scarlet fever (scarlatina)
Often accompanies streptococcal pharyngitis when the infection involves a lysogenized strain of S. pyogenes. After one to two days of pharyngitis, pyrogenic toxins released by the streptococci trigger a diffuse rash that typically begins on the chest and spreads across the body. The tongue usually becomes strawberry red. The rash disappears after about a week and is followed by sloughing of the skin.
A confined, pus-producing lesion that usually occurs on the exposed skin of the face, arms, or legs. One cause is group A streptococcal infection following direct contact with an infected person or contaminated fomites (i.e. doorknob). This condition is also known as impetigo because its appearance is similar to that of the staphylococcal disease of the same name. After a pus-filled lesion breaks open, it forms a yellowish crust. This stage is highly contagious, and scratching may convey bacteria to the surrounding skin, spreading the lesions.
A contagious disease of the skin and subcutaneous tissues caused by infection with streptococci organisms; also involves surrounding lymph nodes and triggers pain and inflammation.
Streptococcal toxic shock syndrome
Group A streptococci can spread, albeit rarely, from an initial site of infection, particularly in patients infected with HIV or suffering with cancer, heart disease, pulmonary disease, or diabetes mellitus. Such spread leads to bacteremia and severe multisystem infections producing streptococcal toxic shock syndrome (STSS). Patients experience inflammation at sites of infection as well as pain, fever, chills, malaise, nausea, vomiting, and diarrhea. These signs and symptoms are followed by increased pain, organ failure, shock—and over 40% of patients die.
Necrotizing fasciitis AKA "flesh-eating bacterial disease"
A serious disease usually characterized by redness, intense pain, and swelling at the site of infection. Initially, the pain does not seem proportionate to the appearance of the infected area. As the bacterium digests muscle fascia—the connective tissue surrounding muscles—and fat tissue, the overlying skin becomes distended and discolored. Patients develop fever, nausea, and malaise, and they may become mentally confused as their blood pressure drops severely.
For an undetermined reason, antibodies bound to the antigens of some strains of group A Streptococcus are not removed from circulation but instead accumulate in the glomeruli (small blood vessels) of the kidneys' nephrons (filtering units). The result is inflammation of the glomeruli and nephrons—which obstructs blood flow through the kidneys and leads to hypertension (high blood pressure) and low urine output. Blood and proteins are often secreted in the urine. Young patients usually recover fully, but progressive and irreversible kidney damage may occur in adults.
What effects can S. agalactiae have on a baby whose mother is colonized with this form of strep in her vaginal tract?
S. agalactiae is most often associated with neonatal bacteremia, meningitis, and pneumonia, at least one of which occurs in approximately 3 of every 1000 newborns in the United States. Mortality has been reduced to about 5% as a result of rapid diagnosis and supportive care, but about 25% of infants surviving group B streptococcal meningitis have permanent neurological damage, including blindness, deafness, or severe mental retardation.
Know the appearance of S. pheumoniae on gram stain. What characteristics can greatly enhance virulence?
Virulent strains of Streptococcus pneumoniae have adhesin, which attaches the bacterium to the cells of the pharynx, and phosphorylcholine, which binds to receptors in the lungs, meninges, and blood vessels, triggering endocytosis of Streptococcus. Inside a human cell, a polysaccharide capsule protects the bacterium from digestion, enabling it to cross the cell and enter the blood and brain. Virulent S. pneumoniae also secretes the proteins secretory IgA protease and pneumolysin. The latter lyses cells in the lungs.
What infection does S. pneumonia cause?
Pneumococcal Pneumonia, Sinusitis, Otitis Media, Bacteremia, Endocarditis, and Pneumococcal Meningitis
The most prevalent disease caused by S. pneumoniae, which constitutes about 85% of all cases of pneumonia. It results when pneumococci are inhaled from the pharynx into lungs damaged either by a previous viral disease, such as influenza or measles, or by other conditions, such as alcoholism, congestive heart failure, or diabetes mellitus. As the bacteria multiply in the alveoli (air sacs), they damage the alveolar lining, allowing fluid, red blood cells, and leukocytes to enter the lungs. The leukocytes attack Streptococcus, in the process secreting inflammatory and pyrogenic chemicals. The onset of clinical symptoms is abrupt and includes a fever of 39-41°C and severe shaking chills. Most patients have a productive cough, slightly bloody sputum, and chest pain.
What species of strep is implicated in dental caries, and how does a mother transmit this organism to her baby?
Veridans Streptococci, especially S. mutans.. It can be vertically transmitted to babies of infected mother
Why is Enterococcus such a good indicator organism for recreational water testing?
Because it is highly associated with feces, it survives very well at a wide temperature range, and is salt resistant which allows to evaluate water quality in fresh and marine water
Many microorganisms secrete exotoxins that are central to their pathogenicity in that they destroy host cells or interfere with host metabolism. Exotoxins are of three principal types:
• Cytotoxins, which kill host cells in general or affect their function
• Neurotoxins, which specifically interfere with nerve cell function
• Enterotoxins, which affect cells lining the gastrointestinal tract
Examples of pathogenic bacteria that secrete exotoxins are the clostridia that cause gangrene, botulism, and tetanus; pathogenic strains of S. aureus that cause food poisoning and other ailments; and diarrhea-causing E. coli, Salmonella enterica, and Shigella species. Some fungi and marine dinoflagellates (protozoa) also secrete exotoxins.
Gram-negative bacteria have an outer (wall) membrane composed of lipopolysaccharide, phospholipids, and proteins. Endotoxin, also called lipid A, is the lipid portion of the Gram-negative's outer layer of lipopolysaccharide. Endotoxin can be released when Gram-negative bacteria divide, die naturally, or are digested by phagocytic cells such as macrophages. Lipid A stimulates the body to release chemicals that can cause fever, inflammation, diarrhea, hemorrhaging, shock, and blood coagulation. Most Gram-negative pathogens can be potentially life threatening because the release of endotoxin from dead bacteria can produce serious, systemic effects in the host.
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