Typhoid Mary and Enterobacteriacae: Infectious disease Module 2 :

where is enterobacteriacae found?

in soil, water, plants, and in the normal flora of most animals

are enterobacteriacae opportunistic?

sort of, some can be human disease, others are opportunistic causing disease only in some circumstances

what are the common structural features of enterobacteriacae?

• O antigen (lipopolysaccharide)

• K antigens

• H antigens

what is the O antigen?

another name for the polysaccharide component of the LPS

• varies among different members

what is the K antigen?

a type-specific polysaccharide in the capsule

what is the H antigen?

a variable protein making up flagella

what is so specific about the reference antibodies to be able to bind to strain specific targets?

being able to be a main method of identification

in general mode of pathogenesis in enterobacteriacae, how is the endotoxin recognized?

• is recognized by TLR4 that is found on many leukocytes

in general mode of pathogenesis in enterobacteriacae, what happens when TLR4 initiates the response?

initiates an inflammatory response that mobilizes the immune system and begins pathogen elimination

in general mode of pathogenesis in enterobacteriacae, what happens when the infection becomes systemic?

the global activation of leukocytes and vascular endothelium leads to thrombosis in the small vasculature feeding vital organs

• vascular leakage leads to shock

in general mode of pathogenesis in enterobacteriacae, what ae capsules comprised of?

comprised of a layer of hydrophilic polysaccharides that protect the bacterium from phagocytosis

• it can also interfere with complement activation and binding antibodies to structures below the outer layer

in general mode of pathogenesis in enterobacteriacae, what are iron scavangers?

• iron is a growth limiting nutrient for bacteria since host proteins like transferrin proteins sequester it

what is enterobactin?

a siderophore or iron-capturing compound

• it steals iron even when available only at very low concentrations

in general mode of pathogenesis in enterobacteriacae, what is the type III secretion system?

some enterobacteria produce protein toxins that affect target cells in the host

• they have a unique delivering system whereby upon physical contact of the bacterium with the target cell

• a molecular syringe directly injects the toxin

what is the antigenic phase variation of the enterobacteria survival strategy?

the expression of O,H,and K antigens under genetic control

• and the genes that are encoding the antigens or the enzymes used to produce them can be switches on or off

• by turning some genes off, the bacterium can avoid being attacked by antibodies

what is the antimicrobial resistance of enterobacteria survival strategies?

• many of the genes that encode resistance to antibiotics are encoded in plasmids, the small chromosomal rings of self replicating DNA

• these can be passed from bacterium to bacterium and also between families of bacteria

what is e.coli?

one of the most common gut bacterium in healthy individuals

how is e.coli caused?

is caused opportunistically or because of tremendous strain variability within the species that includes harmless and disease causing types

what is the difference between harmless and disease causing E.coli?

the expression of number of possible virulence factors

why is E.coli divided into categories?

because of the different complement of virulence factors which defines the pathology of the disease states they cause

what is the first enterotoxogenic e.coli?

is common known as “traveler’s diarrhea”

• contacted from contaminated food or water

• high infectious dose

what are the symptoms of enterotoxogenic e.coli

watery diarrhea without blood, stomach cramps, nausea, vomitting

how does ETEC cause diease?

thru two classes of enterotoxins

• heat labile toxin ( LT 1 and LT2)

• heat stable toxins (STa and STb)

what is LT1 of ETEC?

it is similar to cholera toxin that an A/B toxin the B subunit binds to GM1 gangliosides and A subunit increases cAMP levels which leads to the leaking of chloride anions followed by sodium then water

what is the STb of ETEC?

a small monomeric peptide that binds to a trasnmembrane guanylate cyclase receptor that leads to generation of cGMP within the target enterocyte

• increased cGMP leads to hypersecretion of fluid

what are colonization factors of ETEC?

• CFA/I, II, and III

• are fimbriae that bind to specific glycoprotein receptors and allow bacteria to adhere to cells on gut wall

what is the category 2 of e.coli?

enteropathogenic e.coli ( EPEC)

• cause of infant diarrhea

• occurs in developed countries mostly in daycares

• includes symptoms of watery diarrhea with vomiting and fever

what is attachment/effacement histopathology in EPEC?

when the EPEC attach to the epithelial cells of the small intestine and destroy microvilli

in EPEC, how is the establishment of microcolonies on the gut wall mediated?

by bundle-forming pilli, a virulence factor encoded by a plasmid

what is the third category of e.coli?

enteroaggregative e.coli ( EAES)

• causes persistent watery diarrhea in infants

• chronic diarrheal disease can lead to growth retardation in children

how is the EAEC stimulates the adhesion?

the bacteria form associations into a “stacked brick” formation

• its mediated by aggregative adherence fimbriae 1 which is an adhesion

EAEC adhere to the surface of the intestine and stimulate production of mucus

what does the mucus in conjunction with the aggregated E.coli leads to?

leads to the production of thick biofilm

• the biofilm protects the bacteria from phagocytosis

• also retards entry of antibiotics

what are the two toxins EAEC produces?

entergoaggregative heat stable toxin and plasmid-encoded toxin

what is the fourth category of e.coli?

enterohemorrhagic e.coli

• most are infected thru ingestion of undercooked ground meat or other meat products, contaminated water, milk or produce contaminated with cattle feces

• very low infectious dose

what doe the EHEC disease syndromes result from?

from EHEC infectious range from uncomplicated diarrhea to hemorragic colitis with severe abdominal pain

what can people who recover from hemolytic uremic syndrome develop?

sequelae

• are disease syndromes that appear after the infection has been defeated

• can arise from lost lasting damage or by an immune response directed against the virus

what is Stx-1 in EHEC?

a virtually identical to toxin shigella

• toxin is encoded by lysogenic bacteriophage

• A/B toxins with one A subunit and 5 B subunits

what is the category 5 of e.coli?

enteroinvasive e.coli

• very rare

• begins with watery diarrhea, can progress to dysenteric form with fever, cramps, and bloody diarrhea

what serological variant or serovar?

defines as reactivity with a particular antibody reagent

• serovars differ from one another by the expression of one or more different antigens

what is the treatment of control for different enterobacteri

since most enterobacteriae are confined in the gut, antibiotics are avoided because it will only encourage development of resistance

what is nosocomial infection?

infections acquired by virtue of being in a hospital

what is the iatrogenic infection?

infection acquired as a result of medical procedure

what is proteus?

proteus mirabilis is most commonly associated with uriinary tract

what is cystitis ?

when the bacterial infections reach the bladder

what is pyelonephritis?

when the bacterial infections reach to the kidneys

how do kidney stones happen?

the organism digests urea to form free ammonia

• the resulting pH precipitates calcium and magnesium