Basic biology of pathogens Flashcards
In what environment will you find Blastomyces?
Moist soil
Decomposing wood + leaves
In what environment will you find Coccidioides?
Dust
Dry soil.
In what environment will you find Histoplasma?
Soil with bird/bat droppings
Where do body lice live?
In clothes
(They just come to your body to feed, then go back and hide in seams)
Describe the microscopic morphology of: Blastomyces
Mould phase: (25-30C)
- Lollipops + double thick “broad based” buds.
- Septate hyaline hyphae with unbranched short or long conidiophores @ 90degrees
- “Lollipop” (round/pear) unicellular conidia at apex, emerging directly from the hyphae.
Yeast phase: (37C in tissue or on enriched agar)
- Thick-walled.
- Broad-based budding.
- Often see pairs since buds remain attached until same size as parent cell.
Describe the microscopic morphology of: Coccidioides
Mould form: (in environment)
- Septate, branched hyphae.
- Thick-walled, barrel-shaped arthroconidia that alternate with empty (“disjunctor”) cells.
Yeast form: (in tissues/body fluids)
- Large, round, thick-walled spherules which contain endospores
Describe the microscopic morphology of: Histoplasma
Mould form: (environment)
Young:
- Septate hyphae bearing round/pear smooth microconidia on short branches or right on the sides of the hyphae.
Mature (after several weeks):
- Large, thick-walled, round macroconidia: tuberculate, knobby, with short cylindrical projections.
Yeast form: (tissues, culture 35C)
- Narrow-based budding yeast.
- Thick/double wall appearance.
How many cells make up a single protozoan?
One
How does Blastomyces exposure lead to infection & disease?
- Spores (from mould form) are inhaled from damp soil with decomposing matter.
(OR may be inoculated into the skin). - Warmer temperature -> changes into yeast form.
- Yeast remains colonized in lungs.
- Yeast may disseminate in the bloodstream to other parts of the body.
How does Clostridium tetani cause disease?
Bacteria grow locally, releases tetanospasmin toxin
How does Coccidioides exposure lead to infection & disease?
- Spores (from the mould form) are inhaled.
- Temperature change -> change to spherules.
- Spherules divide (internally) until they are filled with endospores.
- Spherule ruptures ->
- releases endospores ->
- disseminate into the surrounding tissue.
- Endospores develop into new spherules + repeat this cycle.
What are the virulence factors for Enterococcus spp.?
Few:
- adhesins
- cytolysins
- proteases
- (antibiotic resistance)
But very susceptible to phagocytosis
Virulence factors of S. pyogenes?
M protein: a virulence determinant!
- adherance to host cells
- inhibits phagocytosis
- antigenic, but mimics human tissues, so immune response can cross react with human tissues, causing rheumatic fever, rheumatic heart disease, glomerulonephritis.
Capsule:
- inhibits phagocytosis
- made from hyaluronic acid
- indistinguishable from mammalian hyaluronic acid
- a poor immunogen
Fimbriae/pili, Lipoteichoic acid, F protein :
- for attachment to host cells
- fibrils support M protein, other proteins
Virulence factors of Streptococcus agalactiae?
Capsule = major virulence factor
- inhibits phagocytosis
How does Histoplasma exposure lead to infection & disease?
- Spores (from the mould form) are inhaled.
- Warmer temperature ->yeast form.
- Yeast are phagocytosed by immune cells
- ->regional LNs.
- Yeast survive inside the immune cells and travel in the blood to other parts of the body.
Describe the pathophysiology of LTBI activation ->active pulmonary TB disease
- Granuloma bursts
- Releases bacteria
- Causes hemoptysis
- Bacteria replicate further in the lungs.
What are the purposes of protozoan cysts?
- To protect them against a harsh/unstable environment (for days/weeks).
- For morphogenesis/nuclear division (i.e. the formation of their structures).
- For transmission to a new host
Which protozoa live in human blood/tissues?
- Plasmodium
- Leishmania
- Toxoplasma
- Babesia
- Trypanosoma
Which are the free-living protozoa?
- Acanthamoeba
- Balamuthia
- Naegleria
Which of these intestinal protozoa are pathogenic?
- Entamoeba histolytica
- Entamoeba dispar
- Entamoeba coli
- Entamoeba polecki
- Endolimax nana
- Iodamoeba buetschlii
- Dientamoeba fragilis
- Entamoeba histolytica
- Dientamoeba fragilis
Which protozoa can live in/infect the human GI tract?
- Entamoeba
- Giardia
- Blastocystis
- Neobalantidium
- Microsporidians
- Coccidians
Which protozoa live in the human GU tract?
- Trichomonas
What are the virulence factors of S.pneumoniae?
Symptoms mainly from host’s immune response
Virulence factors mostly protect against immune response
-
Polysaccharide capsule:
- prevents phagocytosis
-
secretory IgA protease
- breaks down IgA, so no adhesion of bacteria to mucin
- prevents muco-ciliary clearance
Describe the infection process of M.tuberculosis to the establishment of a latent infection.
- Transmitted through respiratory droplets –> inhaled into the URT.
- MTB phagocytosed by lung macrophages, but MTB blocks fusion with lysosomes.
- MTB persists + replicates within macrophages.
- Infected macrophages try to kill MTB by producing IFN-gamma (to kill intracellular pathogens), and recruit backup (other immune cells) to the area wit by releasing other cytokines.
- Incoming cells wall off the area by forming a large granuloma around the site of infection.
- Eventually, cells inside the granuloma die –>caseating lesion.
What are some virulence factors for VGS?
(very few)
No capsule (no Lancefield antigens)
-
Biofilms
- adherance to endocardium, tooth enamel
- resist immune defences, antibiotics
How is S. agalactiae prevented?
- Screening mothers for colonization @ 35-37 weeks pregnancy
- abx given to colonized moms & moms at risk (preterm birth, fever, previous GBS)
- ensures protective levels of antibiotics in neonates
What are the member genera of the aerobic actinomycetes?
Suborder Corynebacterineae:
- Nocardia
- Gordonia
- Rhodococcus
- Tsukamurella
- Dietzia
- Williamsia
- Segniliparus
- (Corynebacterium & Mycobacterium are also in this suborder, but not consider aerobic actinomycetes)
Suborder Streptosporangineae:
- Nocardiopsis
- Actinomadura
What are the pathogenic species of Coccidioides and the differences between them?
C. immitis
- California (San Joaquin Valley).
C. posadasii
- More widespread.
- Endemic throughout the Americas.
What are the pathogenic species of Histoplasma and the differences between them?
- H. capsulatum* var. capsulatum
- North + South America
- H. capsulatum* var. duboisii
- Africa
What are the three kinds of lice that infect humans?
- Pubic ~ (Pthirus pubis).
- Body ~ (Pediculus humanus corporis).
- Hair/head ~ (Pediculus humanus capitis)
What are the 5 asexual types of moulds?
- Hyaline
- Dematiaceous
- Dimorphic
- Mucormycetes
- Dermatophytes
Name 6 blood/tissue endoparasites:
- Naegleria
- Toxoplasma
- Trypanosoma
- Leishmania
- Plasmodium
- Babesia
What are the 3 mechanisms of motility for protozoa?
Give an example genus for each type.
-
Pseudopods
E.g. Entamoeba -
Flagella
E.g. Giardia, Trichomonas -
Cilia
E.g. Neobalantidium
What are some reservoirs of Aeromonas hydrophila?
Fresh & salt water
How is Aeromonas hydrophila transmitted?
Traumatic wounds in fresh water
Reservoir of Bartonella henselae?
Cats mouths (commensal)
How is Bartonella henselae transmitted?
- Cat scratches,
- bites,
- feces contact
What is the Babesia vector?
Tick
How is Candida albicans transmitted?
Direct human-to human contact
How is Entamoeba histolytica transmitted?
- Fecal-oral
- Oral-anal
How is Francisella tularensis transmitted?
Animal and tick bites, scratches.
In Tasmania by possums
Reservoir for S. pyogenes?
Upper Respiratory Tract
How is S. pyogenes transmitted?
- Respiratory droplets.
- Skin
Reservoir of S. agalactiae?
- lower GI tract
- GU tract
Commensal in 30% of healthy women of childbearing age
How is Haemophilus influenzae transmitted?
Respiratory secretions
How are Leishmania tropica, L. braziliensis, and L. donovani transmitted?
- Bite of an infected female sandfly (Phlebotomus)
- Direct contact with infected lesion
How is Mycobacterium leprae transmitted?
Nasal secretions
Reservoirs for Mycobacterium marinarum?
Fresh & salt water
How is Mycobacterium marinarum transmitted?
Trauma in contaminated water, esp. cleaning aquariums
Reservoirs of Mycobacterium ulcerans?
- koalas
- possums
How is Malassezia furfur transmitted?
Direct/indirect contact with infected skin
How are Wuchereria bancrofti & Brugia malayi transmitted?
Various Anopheles species (mosquitoes)
How is Neisseria gonorrhoeae transmitted?
Sexually transmitted
How is Neisseria meningitidis transmitted?
Respiratory secretions
Reservoirs for Pasteurella multocida
- dogs
- cats
- rabbits (normal mouth flora)
How is Pasteurella multocida transmitted?
Bites or scratches
What is the Plasmodium vector?
Female Anopheles mosquitoes.
Reservoirs of Rickettsia & Orientia
wild animals (many)
How are Rickettsia & Orientia transmitted?
Arthropods (ticks, mites, lice, fleas)
Reservoir for Streptococcus pneumoniae?
Upper respiratory tract
How is Sarcoptes scabiei transmitted?
- Direct contact
- Contact with infected clothing
- Sexual contact
How are Trypansoma brucei gambiense and T. brucei rhodesiense transmitted?
Both are spread by the tsetse fly
How is Trypanosoma cruzi transmitted?
Reduviids, so called kissing bugs.
While biting, the bug defecates into the wound allowing transmission of T. cruzi.
Spread is aided by scratching the irritated site of the bite.
How is Treponema pallidum transmitted?
Sexually transmitted
How is M.tuberculosis transmitted?
Respiratory droplets (e.g. coughing, sneezing)
–>inhaled into the URT.
What are the main Toxoplasma vectors?
- Cats
- Pigs
- sheep
- water
- fruit
Reservoirs of Vibrio vulnificus?
Salt water
How is Vibrio vulnificus transmitted?
Exposure of wound to seawater
Treatment of C.difficile?
discontinue implicated antibiotic
multiple abx courses required: spores not killed
Fecal transplant
Treatment of Clostridium perfringens
rapid aggressive debridement
high dose penicillin
Treatment of Clostridium tetani?
- debridement
- abx: only prevents growth, toxin still active
- tetanus immunoglobulin
How is Enterococcus spp. treated?
Combo therapy often,
e.g. gentamicin + a penicillin.
How is S. pyogenes treated?
Penicillin
- all strains susceptible
Erythromycin if allergic
Prompt treatment of pharyngitis avoids rheumatic fever etc.
What is the best treatment for body louse infection?
- Improve hygiene
- Get rid of clothes (better than boiling/ironing)
What is the best treatment for hair/head louse infection?
- Shampoos with permethrin
- Ivermectin
- Mechanical removal with fine-toothed comb
How is Streptococcus pneumoniae treated?
IV penicillins
- (very effective in most cases)
Use cephalosporin if hypersensitive to penicillins
What is the first-line treatment for active TB disease?
‘RIPE’:
- Rifampin
- Isoniazid
- Pyrazinamide
- Ethambutol
What do the H.influenzae serotypes differ in?
How many are there?
Which are more predominant in North America? {}
Capsule polysaccharides
6 serotypes (a-f)
What do the N.meningitidis serogroups differ in?
How many are there?
Which are more predominant here in North America?
Capsular types.
13 identified, 6 can cause epidemics (A, B, C, W, X, Y)
B > C > others in USA.
Increase in serogroup W in Canada since 2010 due to vaccine escape.
How many S.pneumoniae serotypes exist?
~90 capsular serotypes (#s 1-48 w sub-types)
Vaccines cover the 13-23 most common
What do the different S.pneumoniae serotypes reflect?
Capsular structure.
(No capsule = no disease.)
What is the motile form of a protozoan called?
A trophozoite
