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25 Cards in this Set

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  • Back
What are some basic characteristics of Corynebacterium and Listeria
Both are aerobic, gram positive, non-spore forming rods
What does Corynebacterium diphtheriae primarily cause
Diphtheria, a model for toxin-mediated bacterial diseases. Immunization with diphtheria toxoid prevents disease, and treatment with anti-toxin is therapeutic
What can Listeria monocytogenes cause
Typically a food-borne pathogen and can cause miscarriage and stillbirths in pregnant women, severe systemic disease in the immunosuppressed, and occasionally gastroenteritis in healthy people.
Septicemia and/or meningitis in newborns (from mother)
Serves as model for how certain bacteria move within and between cells
What are some Corynebacteria that cause disease in humans
Corynebacterium diphtheriae
C. ulcerans and C. pseudotuberculosis- occasionally cause disease
C. jeikeium- infections in severely immunosuppressed patients and is frequently resistant to antibiotics
C. urealyticum- UTIs and alkaline encrusted cystitis.
What are the properties of Corynebacterium diphtheriae
URT and skin of humans
Gram-positive, club shaped bacteria that are nonmotile, nonsporulating, and produce catalase. Bacteria arranged in Chinese letters
Biotypes gravis, mitis, and intermedius
Grey to black colonies on selective medium containing tellurite. Must notify lab
Diphtheria toxin is a major virulence factor that is only produced by some strains
How does diphtheria in an upper respiratory tract infection present
Characterized by sore throat, low-grade fever, and an adherent pseudomembrane on the tonsils, pharynx, and nose. Respiratory diphtheria is usually caused by toxinogenic strains. Epidemic in Russia and the Ukraine
How does Cutaneous diphtheria present
It usually results from infection of insect bites, wounds, or other skin lesions by C. diphtheriae. Can present with deep ulcers containing typical pseudomembranes. Cutaneous diphtheria is often caused by nontoxinogenic strains
What are complications caused by the systemic action of diphtheria toxin
Myocarditis and polyneuritis. The lethal dose is about 0.1 ug/kg
Where is the gene for diphtheria toxin present
Several tox+ corynephages, including phage Epsilon. Toxinogenic strains of C. diphtheriae are lysogenic for tox+ phages (phage conversion)
When is toxin produced by Corynebacterium diphtheriae
Under iron-limiting growth conditions. Toxin synthesis is inhibited by an iron-dependent repressor
In what form is toxin secreted by Corynebacterium diphtheriae
As a single polypeptide. It is processed by proteolysis and reduction to form fragments A and B.
What does Fragment B of diphtheria toxin do
Binds to receptors on the plasma membrane of susceptible cells and initiates uptake of the toxin by receptor-mediated endocytosis
What does Fragment A of diphtheria toxin do
Once it is transported to the cytosol it catalyzes the transfer of adenosine diphosphate ribose from (NAD) to EF-2. The ADP-ribosylation of EF-2 causes inhibition of protein synthesis and death of the intoxicated cell. This is the same as exotoxin A of Pseudomonas aeruginosa, but the receptors are different
How is immunity to diphtheria toxin given
There is only one antigenic type of diphtheria toxin, and antitoxic antibodies neutralize its toxicity. Diphtheria toxoid is nontoxic, and when administered it elicits antitoxic antibodies. These prevent intoxication, but do not prevent colonization of C. diphtheriae
What is the mainstay of treatment for diphtheria
Passive immunization with horse antitoxin. Mortality increases each day the antitoxin is delayed. Allergic reactions can occur. Antitoxin is no longer made in the US. Antibiotics do not eliminate the need for antitoxin
What is the mainstay for prevention of diphtheria
Active immunization with diphtheria toxoid. Primary immunization during childhood is accomplished by administering a primary series of diphtheria and tetanus toxoids and pertussis vaccine (DTaP). Boosters given every ten years
What does Listeria monocytogenes cause in domestic animals
Septicemia and abscesses, meningoencephalitis, and infections of the uterus and fetus
How does Listeriosis in humans often present
Meningitis or septicemia, and is most likely to occur in immunosuppressed patients. Most infections foodborne, but infection in a pregnant patient can lead to abortion, stillbirth, transplacental infection, or infection of the infant during childbirth
What are the properties of Listeria monocytogenes
Psychrophilic or mesophilic and widely distributed in nature. Often foodborne
Short, gram-positive, motile rod that is nonsporulating, aerobic to microaerophilic and catalase positive. Has end-over-end tumbling motility
Beta hemolytic on blood agar. Grows on tellurite, may show palisades (Chinese letters)
13 serotypes based on somatic and flagellar antigens. Ia, Ib, IVb affect humans most
Care must be taken to distinguish Listeria monocytogenes from what?
Streptococci, Corynebacterium diphtheriae, and diphtheroid. Listeria monocytogenes is CAMP test positive, which helps distinguish it from environmental isolates
What is the pathogenesis of Listeria monocytogenes
It is a facultative intracellular pathogen. Enter cells via internalin which interacts with E-cadherin to promote internalization. Then produces a sulfhydryl-dependent hymolyin (LLO) that releases it from the phagosome into the cytoplasm. LLO is responsible for the hemolytic phenotype of L. monocytogenes on blood agar plates, and is an essential virulence factor.
Moves using host actin polymerization mediated by ActA. Spread from cell to cell without reentering the extracellular space. Encased in a double host membrane which is lysed
What is important for development of Listeriosis
Host factors. About 70% of cases in humans occur in immunocompromised patients. Meningitis is the most common presentation in humans. Bacteremia, focal infections, and perinatal sepsis can also occur
How are infections by Listeria monocytogenes terminated
Cell-mediated responses of the host
What antibiotics are used to treat infections caused by Listeria monocytogenes
Ampicillin or penicillin; combo of gentamicin with penicillin; combo of trimethoprim with sulfamethoxazole
Cephalosporins are not effective
An outbreak of what microorganisms was linked to eating sliceable turkey deli meat
Listeria monocytogenes. It caused seven deaths, and three stillbirths or miscarriages in eight states