Bacteria + Protozoa Flashcards
what are pros to intracellular survival
-survive or die
-gain access to a protected/nutritious environment
-some protection from immune response
hostile takeover
what are the cons to intracellular survival
-must overcome host barriers
-modulate innate immunity
-modulate cell mediated immunity
-overcome normally bactericidal stress
examples of facultative intracellular pathogens
-salmonella
-legionella
-shigella
-yersinia
examples of obligate intracellular pathogens
-mycobacterium
-chlamydia
examples of pathogens that survive and grow in phagocytic cells after phagocytosis
-salmonella
-listeria monocytogenes
-mycobacterium
-legionella pneumophila
examples of pathogens that survive and grow in non-phagocytic cells
-salmonella
-shigella
-listeria
what’s the morphology of macrophages
large, mononuclear with granular cytoplasm
what’s the morphology of neutrophils
small with multilobed nucleus and granular cytoplasm
location of kupffer cells
liver
location of alveolar macrophage
lung
location of osteoclasts
bone
location of microglia
brain`
location of neutrophils
found in blood-require recruitment to site of infection
killing ability of macrophages
require activation by IFNg
killing ability of neutrophils
activated during recruitment
after killing what happens to macrophages
migrate to local lymph nodes
after killing what happens to neutrophils
die at site by apoptosis
do macrophages present antigens
yes
do neutrophils present antigens
not normally
mechanism of phagocytosis
-internalization of pathogen into phagosome
-acidification of phagosome
-fusion of phagosome with lysosomes/ granules containing anti-microbial compounds=phagolysosome
-oxygen and nitrogen species generated
what is the role of toll-like receptors
recognise pathogen-associated molecular patterns resulting in cytokine production and cellular activation
what is the receptor- ligand interaction utilised during phagocytosis dependent upon
bacterial species and macrophage phenotype
do macrophages and neutrophils have phagosome acidification
yes
do macrophages and neutrophils have primary granules
only neutrophils
do macrophages and neutrophils have secondary granules
only neutrophils
do macrophages and neutrophils have lysosomes
only macrophages
do macrophages and neutrophils have oxygen dependent and independent mechanisms
yes
do macrophages and neutrophils have nitrogen dependent mechanisms
yes
what are the different strategies for intracellular survival in phagocytes
-avoid/prevent phagocytosis
-able to proliferate in vacuole
-escape vacuole and survive in cytoplasm
mechanisms for resisting bactericidal activities during phagocytosis
-detoxification of killing agents
-prevention of access to killing agents
-prevention of iNOS activity
salmonella as an intracellular pathogen
-survives in and modifies phagosome
-resists bactericidal activities
-invades non-phagocytic cells
shigella as an intracellular pathogen
-escapes phagosome
-kills macrophages
-invades non-phagocytic cells
-intracellular motility
first phase of typhoid fever
slow fever, rose spots, mild, bacteraemia
second phase of typhoid fever
organism reaches gall bladder, re-invasion of intestine, ulcer, haemorrhage, death (20%)
what’s enteric fever
similar to typhoid fever nut less severe and rarer. S. paratyphi
how long is incubation period of salmonella
12-36 hours
- chills/fever, nausea/vomiting, abdominal pain, diarrhoea (1-7days)
salmonella and toll-like receptors
TLR stimulation by salmonella PAMPs trigger burst of ROI and RNIss
salmonella and ROIs
SPI-2 and PhoPQ involved in evasion of ROIs as is the salmonella containing vacuole
salmonella and RNIs
salmonella induces arginase II which limits substrate for iNOS activity. arginase is also recruited into the salmonella containing vacuole
salmonella and P-L fusion
salmonella actively avoids salmonella containing vacuole fusion with lysosomes
salmonella and metal ions
macrophages try to establish balance to starve bacteria
salmonella and cell death
salmonella effectors modify cell death pathways, e.g activation of PKR kinase leads to phosphorylation of eIF2a, hampering protein synthesis
define endotoxin
the lipid A portions of lipopolysaccharides that are part of the outer membrane of the cell wall of gram-negative bacteria with the exception of listeria, liberated when bacteria die and cell wall breaks
define exotoxin
proteins produced inside pathogenic bacteria, most commonly gram+ but can be gram-negative, exotoxin secreted into surrounding medium during log phase
what is the toxicity of exotoxin
high, specific activity targeting specific sites
what is the toxicity of endotoxin
moderate, non-specific
what’s the antigenicity of exotoxin
highly antigenic
what’s the antigenicity of endotoxin
poorly antigenic
heat stability of exotoxin
heat liable
heat stability of endotoxin
heat stable
how does endotoxin trigger gram-negative bacterial sepsis
induces systemic inflammatory response characterized by pro-inflammatory cytokines, nitric oxide, fever, hypotension, intravascular coagulation, organ failure, and culminating in septic shock
what are the direct mechanisms of bacterial exotoxins
-facilitate spread of bacteria through tissue (hyaluronidase)
-damage cell membranes/body structures (collagenase)
-immunomodulatory (IgA protease)
-inhibit protein synthesis (diphtheria, shigatoxin)
-inhibit release of neurotransmitters (botulinum)
cytokine induction by endotoxin
-endotoxins mainly activate antigen-presenting cells to produce cytokines
cytokine induction by exotoxin
super-antigens affect antigen-presenting cells and t-cells and induce macrophage and t-lymphocyte cytokines leading to cytokine storm
what are type I exotoxins
bind to surface receptors, are not translocated into the host cell and stimulate transmembrane signals
what are type II exotoxins
act directly on cell membranes
what are type III exotoxins
A-B toxins which translocate an active enzymatic component into target cell which modifies an intracellular target molecule
what are the features of A-B (type III) toxins
-A part = active component
-B part = binding component
-A attacks host structure or function and B binds to host cell receptor
-toxin enters cell
-vacuole becomes acidified and membrane breaks down
-A + B dissociate from one another, A enters cytoplasm to inflict its activity and everything else removed via exocytosis
structure of AB toxin
-product of a single gene
-single protein with A + B domains
-A linked to B by disulphide bond
structure of AB5 toxin
-product of several genes
-separate subunits covalently linked
-could be 5 different B’s so multiple host cell receptors
ADP-ribosylation
enzyme that catalyses removal of an ADP-ribose moiety from NAD+ and subsequent transfer to a specific target molecule in host cells resulting in activation or inactivation of cell functions modulated by these proteins
what is the target and effect of cholera toxin
Gs protein, constitutive adenylate cyclase activation
what is the target and effect of E.coli LT toxin
Gs protein, constitutive adenylate cyclase activation
what is the target and effect of Pertussis toxin
Gi protein, prevent adenylate cyclase deactivation
what is the target and effect of Diphtheria toxin and Pseudomonas exotoxin A
elongation factor 2, stops protein synthesis
what is the causative agent in cholera
Vibrio cholerae
what is death by cholera due to
-hypovolemic shock (due to abnormally low volume of circulating fluid)
-metabolic acidosis (loss of bicarbonate and thus buffering capacity)
how is cholera treated
rehydration therapy, antibiotics may make it worse
mechanisms of cholera
-attaches to intestinal epithelial cells and release of CTX
-B binds to specific ganglioside
-A subunit transferred into cell
-A protein adds an ADP-ribose molecule to the G-protein making it permanently active
-adenyl cyclase converts ATP to cAMP
-normal transport of sodium from lumen blocked and Cl- and Na+ enter intestinal lumen
-water flows by osmosis from blood stream due to loss of ions
what’s the structure of the cholera toxin
-A-B type
- A unit is enzymatic
-B unit binds to host GM1 ganglioside
produced in inactive form but nicked by bacterial endopeptidase during processing in body to produce active form
how is chxA. another virulence factor for V.cholerae
1/3 of non 01 and non-0139 V.cholerae encode this PE like toxin ChxA
-ADP-ribosylation of EF2, inhibits translation and kills cells, potential cancer treatment
what is the causative agent of whooping cough
Bordetella pertussis
what’s the catarrhal stage of whooping cough
-1-2 weeks
-fever
-malaise with mild cough
what’s the paroxysmal stage of whooping cough
-1-6 weeks
-5-20 forceful coughs with no time to breath
-whoop when air rushes back into lungs
-vomiting and exhaustion
mechanism of B.pertussis virulence
-inhalation of aerosols containing B.pertussis
-adherence to ciliated epithelial cells + colonisation of upper respiratory tract
-toxin produced
-damage to mucosal cells or action on neurons
describe the pertussis toxin
-5 different subunits (A-5B)
-A (S1) is a ribosyl transferase
-S1 activated by calmodulin
-increases cAMP production + disrupts cell function
-S2 (B) binds to lactosylceramide
-S3 binds to macrophages
what’s the causative agent of diphtheria
Corynebacterium diphtheriae
describe diphtheria
-2-6 days incubation
-fever, malaise, sore throat, formation of pseudomembrane. damage to mucosal cells, damage to organs by toxin, breatrhing obstruction, death
what’s the mechanism of C.diphtheriae virulence
-inhaled
-adherence to throat epithelial cells + colonisation
-elaboration of toxin and organ damage
-formation of pseudomembrane
what’s the mode of action diphtheria toxin
-binds to heparin-binding epidermal growth factor precursor
-complex taken up by endocytosis
-acidification changes conformation of T-domain allowing it to insert into the membrane
- A is translocated into cytoplasm activating it
describe toxins as a therapy
-bacterial protein toxins utilized as vaccine antigens
-vehicles for taking in heterologous proteins into cell
-immunotoxins enable targeting of diseased cells
-botox used in treatment of neurological disorder
what’s a type III secretion system
a multi-protein complex that’s formed between inner + outer membrane of bacteria delivering bacterial proteins directly to host cell
what are the functional attributes of the T3SS components
-translocon interacts with host cell
-tip complex caps needle filament to stop it growing larger
-base body holds apparatus in place
-export apparatus is a gated pore that controls export of effectors
what are the 7 main families of T3SSs
-Ysc
-Inv-Mxi-spa
-Esc-Ssa
-Hrp1
-Hrp2
-chlamydia
-Rhizobiales
what is the function of the Ysc T3SS family
dampen host immune responses- indicative of an extracellular pathogen
what is the function of the Inv-Mxi-Spa T3SS family
trigger bacterial uptake by non-phagocytic- indicative of an invasive pathogen
what is the function of the Ssa-Esc T3SS family
promotes adherence to epithelial cells or allows survival inside host cells
what is the function of the chlamydiales T3SS family
alters host membrane structure to allow uptake into a membrane-bound vacuole
what is the function of the Hrc-Hrp1 and Hrc-Hrp2 T3SS family
manipulate host cell signalling, nutrient accessibility
what is the function of the Rhizobiales T3SS family
form symbiotic relationships with plants causing formation of nodules on roots of leguminous plants
describe the process of T3SS assembly
-outer membrane (OM) secreting ring joins inner membrane (IM) protein at same time, inner ring assembles on IM
-OM ring and IM complex join together
-integration of the 2 assemblies into one complex allows recruitment of cytoplasmic components
what’s the role of the LEE-encoded Map effector
induces transient filopodia formation
-causes mitochondrial dysfunction
-affects fluid secretion
-disrupts tight junctions
-causing loss of epithelial barrier
what’s the role of the LEE-encoded EsgG effector
-disrupts microtubules, tight junctions and paracellular permeability, also Golgi function and protein secretion
what’s the role of the LEE-encoded EspH effector
disrupts focal adhesion proteins
-remodels brush border
-promotes actin nucleation and pedestal elongation
what’s the role of the LEE-encoded EspF effector
-disrupts mitochondrial function, nucleolus, tight junctions and intermediate filaments
-inhibits phagocytosis
-induces apoptosis
what’s the role of the LEE-encoded EspZ effector
-inhibits apoptosis and cytotoxicity
-regulates type III secretion via translocation stop activity
what’s the role of the LEE-encoded EspZ effector
-inhibits apoptosis and cytotoxicity
-regulates type III secretion via translocation stop activity
describe the tubercle bacillus
-unicellular rods
-gram positive
-complex cell walls- sugars, proteins and lots of lipid
what are the clinical manifestations of TB
-fever, weight loss, weakness, cachexia
-disease is pneumonia, impairment of the lung tissue itself
-can spread anywhere in body
mechanism of TB
-aerosols travel to alveoli of lungs
-M. tuberculosis engulfed by alveolar macrophages
-if inactivated, bacteria survive and replicate in macrophages attracting more cells, damage tissue and form granulomatous tubercle
M.tb survival in macrophages
-enter via receptors that avoid stimulation of oxidative burst
-detoxifies reactive oxygen by producing superoxide dismutase and catalase
-induces an efficient stress response to resist effects of damaged proteins
describe phagosome maturation
-uptake
-small GTPase Rab5 recruited to phagosome membrane
-rab5 directs stimulation of PI3K, enzyme that generates PI3P
-Rab5 recruits Rab7
Rab 5 + EEA1 lost
-Rab 7 important for fusion of late endosome to lysosomes forming the phagolysosome
what does M.tb inducing macrophage necrosis ESX-1 dependent contribute to
-dissemination-infection of new cells
-inflammation, attracting new immature phagocytes
-formation of cellular architecture of the granuloma
-caseation in granuloma centre
-transmission
what is the treatment regimen for TB
-first line of oral anti-TB drugs
what are the signs and symptoms of meningococcal meningitis
-vomiting
-intense headache
-skin rash, confusion, sensitivity to light
-neck stiffening
-convulsions
-if untreated fluid build-up in ventricles of the brain resulting in unconsciousness or death
describe meningococcal sepsis
-N.meningitidis invade blood stream
-meningococcaemiacan rapidly progress toward a septic shock leading to a purpura fulminans, an acute systemic inflammatory response associated with intravascular coagulation and tissue necrosis
-40% mortality
what’s the Labatory diagnosis of meningococcal disease
-CSF and blood samples
- microscopy
-culture
-PCR
-detection of soluble bacterial polysaccharides in CSF by latex agglutination
what’s the Labatory diagnosis of gonococcal disease
-direct examination of exudates in GUM clinics
-endocervical, cervical, anal and eye swabs and urines
-nucleic amplification tests
-QRT PCR
describe the infection with Neisseria meningitidis
-natural habitat is in human nasopharynx, transmitted by aerosol droplets or direct contact with contaminated fluid
-grows on top of mucus-producing epithelial cells surrounded by complex microbiota
-formation of micro-colonies that extend overtime to fill micro vessels
describe the interactions between N. meningitidis and human host
-meningococci survive by expressing capsule, LOS, the MtrCDE efflux pump, and factors that capture nutrients
-express 2 families of polymorphic toxins; MafB and CdiA
-meningococci cross epithelial layer into bloodstream where they adhere to vascular wall
-adhesive bacteria proliferate + induce an active signalling leading to better adhesion and opening of vascular barrier, vessel leakage and massive thrombosis
capsule of N. meningitidis
-can be encapsulated or not
-N. gonorrhoea lacks capsule
-serogroup B not antigenic
-serogroups associated with disease are A, B, C, W, Y, and X
-capsule switching can occur- vaccines based on capsular type causes problem
how does Neisseria use adhesion
-pili traverse the capsule + act as adhesins
-integral outer membrane adhesins mediate interactions with specific host cell receptors
-lipoolygosaccharide may interfere with adhesion functions of OM proteins, can also contribute to cellular interactions by interacting with cellular receptors
how does meningococci survive in serum
-uptake nutrients + iron from extracellular environment
-avoid complement killing by antigenic variation and complement resistance
treatment of meningococcal disease
-IV antibiotics
maintenance therapy for shock
-vasoactive treatments IV adrenaline
-steroids
-experimental therapies, such as anti-cytokine + anti-endotoxin
describe the Bexsero B vaccine
-developed by reverse vaccinology
-possible protection against serogroup W and cross-protection against neisseria gonorrhoeae infection
what are the symptoms of pelvic inflammatory disease
-abnormal vaginal discharge
-bleeding between periods
-pain in lower part of abdomen
-uncomfortable/painful sex
-pain or difficulty when urinating fever
describe Neisseria gonorrhoeae infection
-adherence to urogenital epithelium
-colonisation and invasion of epithelium
-release of peptidoglycan, LOS + OMVs
-cytokine, chemokine + inflammatory transcription factor activation
-peptidoglycan, LOS + OMVs cause NOD + TLR activation on epithelial cells, macrophages + DCs; HBP causes activation of TIFA-dependent innate immunity in epithelial cells and macrophages
-influx of neutrophils; adherence and phagocytosis of N. gonorrhoeae
-neutrophil rich purulent exudate facilitates transmission
how does N. gonorrhoeae modulate the immune system
-prevents complement activation, opsonization and bacterial killing
-modulates activities of macrophages, DCs and neutrophils
-modulates T cell function + varies its surface components to avoid adaptive immune system
what is LpxC
a zinc metalloamidase that catalyses the second step of critical lipid A biosynthesis
what natural protection exists against malaria
-sickle cell anaemia
-thalassemia
-lack of duffy factor
-glucose-6-dehydrogenase deficiency
what are the 3 main antigen groups present on malaria infected RBC
-P.falciparum erythrocyte membrane protein (PfEMP1)
-repetitive interspersed families of polypeptides (RIFINs)
-subtelomeric variant open reading frame (STEVOR)
what’s the life cycle of Cryptosporidiosis
-penetrate intestinal wall
-mature in extra-cytoplasmic vacuoles
-develop into 8 merozoites
-second round infection- some cells develop into gametocytes
-further multiplication and release with faeces
what’s toxoplasmosis
-toxoplasma gondii
-toxon= bow, plasma= cell
-apicomplexan- obligate intracellular parasite
describe toxoplasmosis in neonates
-infection during 1st and 2nd trimesters is most serious
-possible outcomes; ocular abnormalities, brain damage, foetal damage
-infection in 3rd trimester has milder symptoms
identification of alpha streptococcus
-partially break down blood agar, produces large amounts of polysaccharide capsule, gram positive
identification of beta streptococcus
complete breakdown of haemoglobin
what’s necrotising fasciitis
-post pharyngitis or direct inoculation
-rampant unfettered tissue damage, vascular dissemination + systemic disease
-high morbidity and mortality
what’s acute rheumatic fever
-potential sequelae to pharyngitis
-4-8 weeks post infection; inflammation of heart + joints
-can reoccur + cause permanent damage to heart valves
what’s acute glomerulonephritis
-post pharyngitis or skin infection
-few weeks post infection; haematuria, proteinuria, hypertension, impaired renal function
-risk factor for chronic kidney disease + end stage renal failure
describe the colonisation and carriage of GAS
-assymptomatic carriage low in healthy adults, higher in kids
-in nasopharyngeal mucosa, skin and vaginal tract
-saliva important reservoir of GAS
-saliva is carbohydrate limited environment
-reliant on amylase to degrade starch
give some examples of non-invasive GAS infections
-pharyngitis
-scarlet fever,
-impetigo
-otitis media
give some examples of severe invasive GAS infections
-meningitis
-puerperal fever
-septicaemia
-necrotizing fasciitis
-TSS
describe the adherence of GAS
-LTA establishes weak attachment between bacteria + host
-long surface attachment mediated by longer pili like surface structures + other surface fibronectin binding proteins + the M protein
-allows higher affinity attachment by numerous protein adhesins that permit bacterial interactions with multiple host components= GAS colonise diverse tissue sites
how is the M protein in S. pyogenes a major virulence factor
-enables GAS to resist complement-mediated killing by polymorphonuclear leukocytes + macrophages
- required for attachment of GAS to keratinocytes
-causes GAS to aggregate when they attach to tonsillar epithelial cells
how does GAS resist phagocytosis
-M protein- thwarts complement binding
-capsule- shields bacteria by molecular mimicry, blocks antibody access, inhibits complement deposition, enhances survival in NETs
-secreted proteases-inhibit phagocyte recruitment
-Mac1/2 blocks phagocytosis
-SpyCEP, ScpA- degrades cytokine
describe super antigens
-potent immuno-stimulatory molecules
-produced by variety of microorganisms
-bind TCR irrespective of its antigenic specificity
what infections are caused by S.pneumoniae
-meningitis
-occult bacteraemia
-sepsis with haemorrhagic shock
-pneumonia
-arthritis
-peritonitis
transmission of S. pneumoniae
-colonizes mucosa of URT
-carriers can shed S.pneumoniae in nasal secretions
-dissemination by aspiration, bacteraemia or local spread
what are risk factors for S.pneumoniae infection
-no spleen
-viral infection
-heart disease
-very young/ elderly
-diabetes
-alcoholism
-HIV infections
-smoking
describe the identification of S.pneumoniae
-alpha haemolytic streptococcus
-very mucoid colonies due to production of large amounts of capsule
-production of hydrogen peroxide causes greening around colonies (haemoglobin broken down into methaemoglobin)
how does pneumococcus compete
-produce pneumocins which target other membranes of same species
-commit fratricide (kill and lyse non-competent sister cells and members of closely related species)
