G- pathogens of mucosal surfaces pt.1 Flashcards
what enterobacteriaceae are prolific colonizers of mucosal surfaces?
- escherichia coli
- salmonella spp.
- shigella spp.
- klebsiella spp.
- proteus spp.
what vibrionoaceae are prolific colonizers of mucosal surfaces?
vibrio spp.
what is a mucosal surface?
surface that interacts with air that has associated glands for secreting mucus
what are some mucosal surfaces?
- oral cavity
- resp. tract
- reproductive/urinary tract
- gastrointestinal tract
what are the defenses of the mucosal surfaces?
- innate immunity
- adaptive immunity
- nonspecific barrier defenses
why study gastrointestinal diseases?
estimate 76 million cases of intestinal tract infection in the US each year. approx. 500,000 require prolonged hospitalization and 5000 will die
what are ways that gram negative mucosal pathogens are transmitted?
feces to mouth via any of the 7 F’s
- feces
- food
- fluids
- fingers
- flies
- fomites
- fornication
what does a small inoculum (50-100 orgs) mean?
resistant to most defenses on body and can be directly spread from fecal to oral
ex: shigella dysenteriae, EHEC, EIEC
what does a large inoculum (millions of orgs) mean?
most of the pathogens are killed but survivors are enough to cause disease
ex: ETEC, EPEC, vibrio spp.
why aren’t we always infected with gram negative pathogens?
- natural barrier defenses: secretory substances, anatomical and physiological barriers, indigenous microbiota
- innate immunity
- adaptive immunity
how do natural anatomical and physiological properties assist with creating a physical barrier?
- acidity: pH 1-2 or 9
- motility: GI from peristalsis, respiratory from microcillia
- mucous layer and underlying glycolayx
- tight junction: protein between epi cells so will have to invade across epi cells or between them
T/F: there is only a single layer that separates outside world from inside body from billions of microbes found on all mucosal surfaces
T
T/F: bacteria resistant to gastric acid are those with low infectious doses
T
why are most pathogens not in upper/middle small intestine?
because of motility… they can’t grab onto cells
pathogens colonize which area of the GI tract the most?
ileum and colon
T/F: the natural GI flora out compete pathogens for nutrients/binding sites creating a physical barrier to colonization
T
when normal microbiota is suppressed is there an incr. or decr. in susceptibility to pathogens?
incr.
what effect does lysozyme (muramidase) have as an antimicrobial?
cleaves beta 1,4-glycosidic linkages between NAG and NAM therefore more effective against G+ because more peptidoglycan
what effect does lactoferrin have as an antimicrobial?
bacteriostatic effects via sequestering iron (binds Fe and keeps it away from bacteria)
what effect does cathelicidin have as an antimicrobial?
distrupts bacterial membranes of G+ and G- (as well as fungi)
what effect do defensins have as antimicrobials?
- create pores in microbes (all microbes can be affected)
- alpha-defensins produced by neutrophils and paneth cells (in intestines)
- beta-defensins produced by epithelial cells
- highly expressed on mucosal surfaces
what effect do immunoglobulins have as antimicrobials?
secretory IgA on mucosal surfaces to bind/coat pathogens so its harder for them to attached to mucosal tissue
how do pathogenic bacteria overcome these innate barrier defenses?
- acid resistance: microbes with low infectious dose tend to acid resistant (shigella spp. and enteroinvasive e. coli)
- fimbriae/pili: adhesins adhere to host
- bacterial structures:
- G+/G- cell membrane sensitivities to bactericidal compounds
- cationic amino acids into cell membrane to reduce effects of cationic antimicrobial peptides
- siderophores to sequester iron in low iron environments (eg enterobactin produced by e. coli)
- development of capsule to resist phagocytosis
- development of mechanisms capable of neutralizing the phagocytic compartment of macrophages (reactive oxygen and nitrogen)
why are macrophages an important component of mucosal immunity?
- they recognize microbes via PRRs which leads to activation of the macrophages and the ability to kill many microbes
- this initiates the inflammatory response
what do inflammatory cytokines do?
- activate macrophages
- bring in more inflammatory cells due to non-specific recognition of microbes thru PRRs
Which TLR is important in G- bacteria?
TLR-4: binds G- bacteria LPS
what is the negative side effect to initiating the inflammatory response at mucosal surfaces?
inflammatory cytokines such as TNF-alpha can disrupt the tight junctions between epithelial cells
where are the densest clusters of lymph nodes found?
near mucosal tissues
which immune response is generated in the lymph nodes?
the adaptive immune response
what are the 3 ways that toxins cause disease?
- invasive bacterial pathogens
- toxin-producing bacterial pathogen
- “hybrid” misfits
describe invasive bacterial pathogens?
- ex: salmonella spp, shigella spp.
- large intestine
- small volume of stool
- bloody stool
- leukocytes in stool
- tissue ulcerations
describe toxin-producing bacterial pathogens?
- ex: vibrio spp (but primarily v. cholerae), enterotoxigenic e. coli (ETEC)
- small intestine
- copious amounts of watery stool
- no blood in stool
- no leukocytes in stool
- no tissue damage
describe “hybrid” misfit pathogens?
- ex: enterohemmorhagiv e. coli (EHEC) and enteropathogenic e. coil EPEC)
- lower small intestine/upper large intestine
- colonization causes attaching and effacing lesion
- blood in stool (and possibly in urine with EHEC)
- change leads to water loss and produces toxin
there are four species of shigella distinguished by which antigen?
- O antigen
1. s. dysenteriae
2. s. flexneri
3. s. boydii
4. s. sonnei (in USA)
is the shigella inoculum size very large or small?
small
what facilitates shigella’s survival through the stomach?
- acid resistance which is controlled by a global regulatory system of genes under the control of RpoS made in the stationary phase. occurs when shigella are grown anaerobically
- genes triggered help with acid resistance because of anaerobic environment. once reach acid environment start expressing genes for invasion
where does shigella multiply/colonize?
distal part of terminal ileum and colon because its anaerobic
how do Shigella spp. invade?
- mucosal surface is resistant to infection, but basal surface is not
- enter M cells, via outer membrane proteins called invasive plasmid antigens
- released into lamina propria, ingested by macrophages. inflammatory response causes illness
- epithelial cells will ingest the bacteria, facilitated by bacterial factors
- bacterial proteins lyse the phagosomal vesicle so can go from one epi cells to next
- intracellular spread facilitated by IcsA, an ATPase that causes actin polymerization
-only a few Shigella need to be passed through
what damage is done from Shigella invading?
- an ulcer develops when invaded cells die and slough off
- neutrophils can be seen by microscopy in stool samples
- all species will induce an inflammatory diarrhea with leukocytes in the stool.
- S. sonnei induces a watery stool (still has leukocytes) = EXCEPTION
why is Shigella dysenteriae type 1 different?
- gastroenteritis caused by S. dysenteriae type 1 presents as an invasive diarrhea
- S. dysenteriae type 1 also produces Shiga toxin
what does Shiga toxin do?
- kills intestinal epithelial and endothelial cells
- disrupts Na absorption
- more pronounced watery/bloody diarrhea
name and briefly describe the 4 types of infections caused by salmonella.
- gastroenteritis: typhimurium and enteritidis serovars; chicken meat, eggs, dairy products
- focal infection of vascular endothelium: cholerasuis and typhimurium
- infections of organ systems: typhimurium
- typhoid fever: typhi and paratyphi; human carrier state, high mortality, bacteremia and multiorgan dysfunction
how is salmonella infection transmitted?
fecal (human or animal)- oral transmission
does salmonella need a large or small inoculum size?
large
is salmonella more or less acid sensitive than shigellae?
MORE
- low pH induces the expression of at least 40 proteins found on pathogenicity islands on large virulence plasmids
- acidity in stomach triggers these genes
how do salmonella spp. invade?
- when orgs approach the cell’s surface, they induce activity of cell signaling pathways, and cause an incr. in cellular Ca2+
- these events induce surface “ruffles” and uptake of the orgs (microbe-directed phagocytosis)
- remain within cell vesicles for many hours (unlike Shigella)
- orgs released to lamina propria somehow induces NaCl loss from the host cells
- macrophages engulf host, but some escape to cause transient bacteremia
- typhoid serovars will survive and grow in macrophages
where are macrophages located for mucosal immunity?
directly under epi cells and will control salmonella replication present to adaptive immune system
specifically how does salmonella typhi cause typhoid fever?
- enters into lymphatic system
- replicates within macrophages throughout the body
can salmonella typhi replicated in animals?
no, strictly a human pathogen
how are typhoid mary’s or salmonella asymptomatic carriers ID’ed to carry it?
carriers have colonized gall bladders and the organisms can be cultured from their feces
salmonella typhi replicates where?
- liver
- spleen
- bone marrow
**unique property of the strains that cause typhoid fever
what are some similarities between shigella and salmonella?
- both are invasive, so both cause invasive diarrhea not much stool but bloody (neutrophils)
- both are able to respond to environmental changes (acid or anaerobic environment)
what are some dissimilarities between shigella and salmonella?
- inoculum size
- bacteremia
- species that cause severe disease are very dissimlar
how are invasive enteric pathogens ID’ed?
based on symptoms and based on stool cultures
what is the treatment recommended for invasive enteric pathogens?
- oral rehydration (always a good idea)
- most of the time no treatment because gets better within week
- antibiotic resistance first ID’ed in Shigella: fluoroquinolones, beta-lactams
- salmonella gastroenteritis: antibiotics not indicated by 2nd generation fluoroquinolones can be used
- typhoid fever/typhoid mary: fluorquinolones or surgical removal of gallbladder, vaccine to the capsule of s. typhi
