Infectious Disease: Transmission via Direct Contact Flashcards
Nonsporulating Gram Positive Bacteria:
- Staphylococcus ?
- aerobic, cocci
- resistant to reduced water potential
- tolerate high salt
- many species are pigmented
- staphylococcus aureus (yellow)
- methicillin resistant Staphylococcus aureus (MRSA)
- catalase positive
Staphylococcus aureus is part of the normal flora of about 20% of people, True or false?
- true
Staphylococcus aureus:
- describe the disease inflicted by it
- staphylococci: usually harmless inhabitants of the upper respiratory tract and skin
- disease: Pyogenic infection aka pus forming. Acne, boils, pimples, impetigo, pneumonia, osteomylitis, carditis, meningitis and arthritis
- some caused by staphylococcal superantigens
Explain the structure of a boil.
pus contents: mixture of white blood cells being broken down
-fibrilligen forming fibrin
L> protective response via preventing spread to epidermis but protects the infection from immune system
Explain toxic shock syndrome,
- causes: Staphylococcus aureus, Streptococcus pyogenes
- Symptoms: high fever, rash, vomiting, diarrhoea, death (70%)
- rare, associated with local infection: complication of surgery and associated with tampons
- Toxic shock syndrome toxin: TSST-1, superantigen
Explain the virulence factors of Staphylococcus aureus.
L> Toxins
L>Coagulase
L>Superantigens
- toxins: haemoylsins (cell lysis), leukocidin (destroys leukocytes)
- Coagulase: converts finrin to fibrinogen, localised clot
- superantigens: eg toxic shock syndrome antigen, elicit a very strong immune response, stimulate T cells to grow and divide, T cells produce cytokines, excessive inflammatory response
What is direct contact?
- with person or with blood or excreta
L> Staphylococcus aureus, Helicobacter pylori, Hepatitis Viruses - sexually transmitted infections : Treponema pallidum, Chlamydia trachomatis
Methicillin-Resistant S. aureus (MRSA)
L> discuss B-lactans
- B-lactan antibodies (eg penicillin) target transpeptidases (PBPs)
- MRSA have a PBP that is not inhibited by penicillins : continue to make cell wall in presence of penicillin
- ## B-lactans are ineffective in MRSA
Methicillin-Resistant S. aureus (MRSA)
L> alts to B-lactans?
- more toxic
-more expensive
-more difficult to administer
L> eg. vancomycin : acts on cell wall in a completely diff way.
Spirilla: Campylobacter and Helicobacter
L> discuss their adverse effects on hosts
and uniting characteristics
-motile
-microaerophilic
L> require O2 at lower than atmospheric concentrations (3-15%)
- most species are pathogenic to animals or humans
- Campylobacter: entertitis (bloody diarrhoea)
-Helicobacter: causes gastritis, peptic ulcers, can survive the acidic conditions of the stomach,
Helicobacter pylori
L> whats up with this lil broski?
- gram negative, highly motile, spiral shaped bacterium
- associated with gastritis, duodenal ulcers and gastric cancers
- colonizes gastric epithelium
- orally transmitted person to person, in families (usually)
Helicobacter pylori linked with what!??
L> Aussies ?
- peptic ulcers
- conventional thinking: bacterium can’t live in human stomach (pH1) and the ulcers are caused by stress.
- 1979: Robin Warren seen it in a stomach biopsy…unintentionally left their plates incubating for five days and growth was found
Helicobacter pylori linked with peptic ulcers:
- What did Marshall discover in 1985?
L>treatment?
- he drank a beaker of H. pylori
L> developed nausea, vomiting
L> endoscopy found gastritis and the presence of H.pylori
L> AKA ULCERS ARE NOT CAUSED BY STRESS
-antibiotics are effective in the treatment gastritis
L>prevention of relapse of ulcers
Helicobacter pylori virulence factor??
- Flagellar motility and chemotaxis: needed to reach mucosa (needs to get out of gastric lumen into mucosa bc it will protect it from the acid..produces urease which neutralizes acid
- Urease: neut acids, scavenges nitrogen, ammonia damages mucosa
- Toxins, CagA and VacA: damage epithelium
- Enzymes: mucinase, proteases: helps work through the epithelium
Hepatitis
L> What type of disease? Symptoms?
- liver disease: destruction of liver cells leads to cirrhosis
- hepatitis viruses are phylogenetically diverse
- can also be caused by bacteria
- Symptoms: fever, Jaundice (excess billrubin released by the liver causing yellowing of the skin)
Hepatitis C
L> virus??
- HCV hepacivirus
L>ssRNA positive sense, enveloped
-Transmission: parenterally (blood transfusion, dirty needles), STD
What is the difference between viral capsid and bacterial capsule ?
- bacterial capsule: usually polysaccharide, protects the bacterium from: host immune system, desiccation. Outermost layer of bacterium.
What are the symptoms of Hep C
- mild symptoms
- chronic hepatitis
- chronic liver disease and cirrhosis
- liver cancer
Pathogenesis of Hep CCCCCCCCCCCCCCCCCC
- non cytopathic, can remain host associated but prevent cell death
- damage to tissues caused by immune response
- cancer may result from constant tissue repair
Organisms causing sexually transmitted diseases - describe theeeem.
- are often gram positive bacteria they are resistant to drying
- are generally sensitive to environmental stresses such as drying, heat and light
- are usually viruses bc they can only be transmitted by close contact
Syphilis - what’s up with that?
- serious disease
-can be passed to fetus = congenital syphilis
-primary chancre is unsightly
L> patients seek medical intervention (patients seek medical attentions..aids in diagnosis) - susceptible to penicillin : Benzathine penicillin G…longer course required for tertiary syphilis
What causes syphilis?
- T. pallidum
What are T. pallidum’s virulence factors?
- outer membrane proteins promote adherence
- corkscrews into host tissue
- surface coated with host proteins tissue destruction and lesions are primarily result of host’s immune response
What are the factors affecting the incidence of gonorrhoea and syphilis?
- often transmitted together
- syphilis: lower incidence than gonorrhoea, chancre is an obvious symptom, can be cured by penicillin
- Gonorrhoea: higher incidence, often asymptomatic, antibodies are strain specific - don’t prevent further infection. Oral contraceptives alter conditions in urogenital tract
Chlamydia - give a description of it’s basic characteristics.
- gram negative type cell walls
L> does not strain with gram stain, outer lipopolysaccharide membrane - lacks peptidoglycan
-Obligate parasites: poor metabolic capacities, require biosynthetic intermediates and probably ATP
L> some of the simplest biochemical capacities of all known bacteria
Chlamydial infections —-> GO.
- currently one of the leading sexually transmitted diseases
- non specific urethritis, associated with reactive arthritis
- other strains cause trachoma (blindness)
- key virulence factor ( type III secretion system)
Chlamydial Urethritis: Clinical Features?
- incubation: 1-4 weeks
- Men: 25% asymptomatic, 75% urethritis with a mucopurulent discharge, usually less severe than in gonorrhoea
- Women: usually asymptomatic, 30% vaginal discharge, 10-20% urethritis
Chlamydial Urethritis
L> Complications?
L> Treatment?
- pelvic inflammatory disease, conjunctivitis and pneumona in neonates, reactive arthritis
- Treatment: azithromycin as a single dose or with doxycycline for 7 days or erythromycin for 14 days
