Lecture 14 Flashcards
• What are five different defenses of the skin?
“SHEDDING” as a mechanical defense: Millions of cells of the stratum corneum slough off daily, taking microorganisms with them
ANTIMICROBIAL PEPTIDES
Positively charged peptides that act by disrupting the negatively charged membranes of bacteria
Play a major role in keeping the microbial count on the skin relatively low
SEBUM: oily substance secreted by sebaceous glands
Low pH can be inhibitory to many microorganisms
Lipids in sebum serve as nutrients to normal microbiota
Toxic byproducts of fatty acid metabolism inhibit the growth of microorganisms not adapted to the skin environment
SWEAT
Inhibitory to microorganisms due to low pH and high salt concentration
LYSOZOME: Enzyme found in sweat, tears, saliva
Breaks down peptidoglycan in bacterial cell walls (breaks bonds between sugars in the glycan chains)
• What are four major genera that are components of the normal skin microbiota? For each of these covered in class: are they Gram positive or negative, to which phylum do they belong, what is their relationship to oxygen, and what is an example of each that is pathogenic?
Streptococcus (Phylum Firmicutes; Gram +)
Aerotolerant anaerobe (“lactic acid bacteria”)
Homofermentative – lactic acid as sole product
Genus includes the pathogens S. pneumoniae, S. pyogenes
Propionibacterium (Phylum Actinobacteria; Gram +)
Facultative or aerotolerant anaerobes
Live in follicles, pores; ferment sebum, acids, carbs
P. acnes is implicated in acne
Staphylococcus (Phylum Firmicutes; Gram +)
Facultative anaerobe (fermentation)
Commensals (S. epidermidis) and pathogens (S. aureus)
Corynebacterium (Actinobacteria; Gram +)
Obligately aerobic or facultatively anaerobic
Includes the pathogen C. diphtheriae, cause of diptheria
• What are the signs, symptoms, and causative agent of the macropapular disease measles? Know that many fatalities are due to secondary infections, such as pneumonia.
.Sore throat, dry cough, headache, fever, conjunctivitis (inflammation of the conjunctiva, or outer layer of eye), lymphadenitis (enlargement of lymph nodes)
Red, maculopapular exanthem (widespread rash) that erupts on the head and progresses to the trunk and extremities
Causative Agent: Measles virus
Genus Morbillivirus, family Paramyxovirus
Enveloped, single-stranded RNA virus
• What are some differences between measles and rubella?
There are two “forms” of measles: rubeola (the “ordinary” kind), which causes more serious symptoms and can do permanent damage, and rubella (“German” measles), which is very benign if you have it as a child or an adult but can induce severe birth defects in womem infected early in pregnancy. Aside from some similarity in symptoms, there isn’t much in common betwen the two viruses.
Measles (also known as rubeola)
Sore throat, dry cough, headache, fever, conjunctivitis (inflammation of the conjunctiva, or outer layer of eye), lymphadenitis (enlargement of lymph nodes)
Red, maculopapular exanthem (widespread rash) that erupts on the head and progresses to the trunk and extremities
Rubella
Latin for “little red”, also known as German measles
Relatively minor rash disease with few complications
Teratogenic: causes harm to the fetus
Virus is transmitted from the mother to fetus in utero, even if the mother is asymptomatic
Infection in the first trimester can result in miscarriage or multiple permanent defects
Most common defect is deafness, but cardiac abnormalities, ocular lesions, and mental and physical retardation can occur in varying combinations
• What are the target microbes/diseases of the MMR vaccine, and what type of vaccine is this?
MMR (mumps, measles, rubella) vaccine contains live, attenuated measles virus that confers protection for up to 20 years
• What is the main sign of impetigo, and what are the main two causative agents of this disease?
Superficial bacterial infection that causes the skin to flake or peel
Staphylococcus au or Streptococcus
• Which of these causative agents is important in initiating the disease, and which of them typically causes the disease in newborns?
S. pyogenes begins all cases of the disease, but later S. aureus takes over and produces a bacteriocin that destroys S. pyogenes
S. pyogenes is more often the cause of impetigo in newborns; S. aureus is more often the cause of impetigo in older children
• What are some of the important virulence factors of Staphylococcus aureus in impetigo, and how do they function?
Exfoliative toxins A and B:
Coded for by a phage that infects some strains of S. aureus
Attack a protein important in cell-to-cell binding in the epithelium
Leads to characteristic blistering
Breakdown of skin architecture facilitates spread of the bacterium
Coagulase:
Coagulates plasma
Helps pathogen evade immune system
97% of all human isolates produce this enzyme; considered diagnostic of the species
Hyaluronidase:
Digests the intracellular “glue” (hyaluronic acid) that binds connective tissue in host tissues
Staphylokinase:
Digests blood clots
DNase, a nuclease that digests DNA
Lipase, an enzyme that helps the bacteria colonize oily surfaces
• What are some characteristics regarding Staphylococcus aureus’s resistance to heat, desiccation, salt concentrations, and antimicrobial drugs?
among the sturdiest of all non-spore-forming pathogens
Withstands high salt (7 – 10%),
Tolerates high temperatures (survives 60 °C for 1 hour)
Remains viable after months of air drying
Resists the effects of disinfectants and antibiotics (e.g. MRSA)
• What are two tests that can be used to differentiate Staphylococcus aureus from Streptococcus pyogenes in impetigo?
Coagulase test
Key technique that separates S. aureus from other species of Staphylococcus
Isolates that coagulates plasma are likely S. aureus
Others are coagulase negative
This test aids in diagnosis
Catalase test
Enzyme breaks down hydrogen peroxide accumulated during oxidative metabolism
Used to differentiate the staphylococci from the streptococci Primary isolation is achieved by inoculation on blood agar
Will produce a clear area in the agar around the colonies due to lysis of red blood cells (hemolysis)
• What is the causative agent of smallpox?
Variola virus, an orthopoxvirus
Enveloped DNA virus
This group also includes monkeypox and vaccinia
Hardy virus, surviving outside the host longer than most viruses
What are two different viruses that have been used as vaccines for smallpox?
. First successful vaccine produced by Edward Jenner in 1796, by exposure of patient to related but non-virulent cowpox
Vaccine now is another related virus, vaccinia virus (mild infection)
A massive vaccination effort from 1967-1977 eradicated the disease
How prevalent is smallpox in the world today?
Vaccination had been discontinued when the disease was eradicated, but is now offered to certain U.S. populations
• What does the term “immunologically privileged” mean?
Only able to mount a partial or different immune response when exposed to an immunological challenge
CNS functions are so vital that even temporary damage that could result from normal immune responses could be detrimental
Macrophages are present but not as active as in other body parts
• Is there a normal microbiota in the central nervous system?
none known
