Emerging pathogens

Emergence of infectious disease ~

habitat / niche

BoundaryBarrier

adaptationhost / bacteria

time

homeostasis emerginginfectiousdisease

re-establishbalance

homeostasisbacteria & host

Mechanisms of host adaptation

Analysis of host adaptation

Mechanisms of bacterial adaptation

Analysis of bacterial adaptation

Emerging bacterial disease

avoids host response aggressive pathogen

stealth route

overwhelm innate immune responserapid infection - no adaptive immunity

frontal attack strategies

engages innate immune responseavoids / manipulates adaptive immunity

carrier state / chronic infections

Development of stealth pathogens / bacteria

BoundaryBarrier

natural habitat

homeostasis colonizes inhost

goal -persistance

chronic infectionsymbiotic relationship

Mycobacterium tuberculosis - tuberculosisListeria monocytogenes - listeriosis

Salmonella typhi - typhoid fever Helicobacter pylori - gastric ulcers / cancer

Chronic infectious agents

Symbionts

Rhizobium spp. - nitrogen fixing bacteria on roots / legumes Wolbachia spp. - induce sex ratio distortions in insects

Mitochondria - energy production

Stealth bacteria / pathogens

Bacterial adaptation to host cells associated with lateral gene transfer (mobile and unstable genetic elements)

Establishment of chronic infections

(Batut et al, Nature Reviews Microbiology, 2004)

First contact with host cellAdherence / invasion

Life in the environment

Establishing life within the hostAvoid host defenses

Establishing life within the hostAdapt to host environment

Extending the nicheModulate host biology

Extending the nicheMultiply / survive in replication niche

Avoid host defenses:- Invade host cells rapid - Rho, Rac, Cdc42 mediated invasomes - engulf bacterial aggregates zipper - silent cell entry- Evade innate immunity lack TL4 reactive LPS- Block adaptive immunity- Evade adaptive immunity by genetic rearrangement

Establish life within host:- Within phagosome arrest - phagosome acidification / fusion redirect - phagosome trafficking utilize - phagosome environment lyse phagosome - move via actin tails- Induce host cell proliferation- Inhibit host cell apoptosis- Adapt to host conditions (stomach acidity)

Common strategies of stealth bacteria

Manipulate host cell:- Type III secretion- Type IV secretion

(J. Batut, S. Andersson, D. O’Callghan, Nature Reviews, 2004)

Proteobacteria

Chronic infection with Mycobacterium tuberculosis

(Wilson, McNab, Henderson, Bacterial Disease Mechanisms, 2002)

M. tuberculosis phagosome arrest

Development of aggressive pathogens

BoundaryBarrier

becomes

natural habitat

homeostasiscolonize in

new environment

aggressivepathogen

microorganism-rich environment(soil / water / intestine)

acquire new virulence genesprovide a survival advantage

competes against normal flora& host defenses

Vibrio cholerae

adhere / colonize in intestinerapid onset / severe diarrhea

massive fluid loss - dehydrationhypotension

collapse of the circulatory systembacteria eventually wash out

self-limiting disease

(www.cameroon-info.net/ img/news/cholera_victim)

Disease - cholera

(UCLA Department of Epidemiology website)

Transmission

contaminated waterraw seafood

Cholera pandemics - begin in coastal communities - link between marine environment (algal blooms) - V. cholerae survival / spread

(Source: Dr. Rita Colwell, Director, National Science Foundation and Professor of Microbiology, University of Maryland)

Sea surface temperature (SST) changes in Indian Ocean vs. number of cholera cases in Bangladesh.

marine reservoirVibrio cholerae

(www.hinduonnet.com/.../ 07/stories/0807048f.htm)

Tcp - (toxin coregulated pili) - adherence origin - filamentous phage (VPI)

cholera toxin - A-B toxin encoded on CTX phage Tcp = receptor for CTX phage

Acquisition of virulence factors

B5 - subunit (GM1 ganglioside)

A - subunit

(ADPRT activity - Gs)

Vibrio cholerae

1992 - novel epidemic strain emerged in India - serotype 0139 - Bengal strain carries conjugative transposon

allowed - horizontal gene transfer of DNA encoding 0139 antigenusurped El Tor until 1994

(Obtained from CDC)

The global spread of cholera during the seventh pandemic(1960 - 1990’s) - El Tor biotype

Emerging Vibrio cholerae disease

Epidemiologyremains a major problem in developing countries

155 serotypes most epidemics - serotype 01 Classical biotype - 1881-1896 & 1899-1923 pandemics

El Tor biotype - ongoing cholera pandemic

WHO estimates that officially reported cases represent~ 5-10% of actual cases worldwide

(www.who.int/topics/ cholera/surveillance/)

Areas reporting cholera cases in 2004Cholera, 2000-2001

Cholera

Epidemiology

Grey areas: countries with cholera cases Black dots: countries with imported cholera cases

Emergence of pathogenic Vibrio cholera

BoundaryBarrier

ancestral species lacked CTinfection excluded by normal flora

becomes

natural habitatsalt / fresh water

homeostasiscolonizes in

smallintestine

aggressivepathogen

acquired VPI phage encoded Tcpthen CTX phage encoded CT

allows bacteria to flourish in intestineshed in large numbers back to natural

habitat (salt / fresh water)

acquired virulence factors

Tcp / cholera toxin - phage0139 serotype - conjugation

Emergence of pathogenic Escherichia coli

Not colonized

Streptococcus, Lactobacillus

Streptococcus, Lactobacillus, Bacteroides, Bifidobacter

E. coli, Lactobacillus, Bacteroides, Bifidobacterium, EnterococcusClostridium,

40+ species, >90% anaerobesBacteroides, Eubacterium, Fusobacterium,Bifidobacterium, Peptostreptococcus,Ruminococcus, Enterococcus, Streptococcus, Clostridium, Enterococcus

Microbial GI tract ecosystem (probiotics)

Not colonized

Helicobacter pylori

E. coli - EHEC, ETEC, Vibrio choleraC. perfringes, B. cereus, S. aureus

E. coli - EHEC, EIEC, Shigella,Clostridium difficile

Pathogenic bacteria of the GI tract

E. coli - EPEC, Salmonella Campylobacter jejuni

(Dennis Kunkel Microscopy, 2001)

Escherichia coli

Associated disease:diarrhea / hemorrhagic colitis

Transmission:contaminated food or water

Bacteriology:Gram-negative rod - motilefacultative anaerobeserotype - based on O, H, K antigens - LPS; H - flagellum (hauch); K - capsule (i.e. O157:H7)virotype - based on virulence factors (i.e. ETEC)

(www.geocities.com/ CapeCanaveral/3504/gallery.htm)

Emergence of pathogenic Escherichia coli

ancestral species not pathogenic

not cleared by host

becomes

natural habitatGI tract - warm-blooded

animals

homeostasisexposed toGI bacteria

acquired phage / plasmid encoded virulence factors from intestinal pathogenic

bacterianow competes more effectively in

host shed into environment

transferred to other hosts

virulence factors

virotype dependent

aggressivepathogen

Escherichia coli enteropathogens

Enteropathogenic E. coli (EPEC)

Enterotoxigenic E. coli (ETEC)

Enteroaggregative E. coli (EAggEC)

Enterohemorrhagic E. coli (EHEC)

Enteroinvasive E. coli (EIEC)

EPEC - Enteropathogenic E. coli

Disease:major cause of diarrhea in children(> 1 million children die / year from EPEC)

associated with attaching-effacing (A/E) lesion

loss of microvilli host actin-mediated pedestal formation

(Knutton et al, Oxford University Press, 1998)

EPEC bundle forming pili

(Anantha et al, Infect. Immun., 1998)

Virulence:not toxigenic / not invasive

type III secretion - genes encoded - chromosomal pathogenicity island (PAI) (35 kb - LEE - locus of enterocyte effacement)

adhesion - contact with host cell induces: bundle-forming pilus - (plasmid encoded)

EPEC - Pathogenesis

Type III secretion: Apparatus - EspA, EspB, EspD (EspF)

Tir- phosphorylated by host tyrosine kinase, becomes receptor for bacterial adhesin - intimin leads to intimate attachment - activation PKC (PLCIP3)

results in chloride secretion - causing diarrhea -

(Wilson, McNab, Henderson, Bacterial Disease Mechanisms, 2002)

Acquisition of virulence: type III secretion - encoded on LEE PAI

bundle forming pilis - plasmid encoded

ETEC - Enterotoxigenic E. coli

Disease:childhood diarrhea in developing countries‘traveler’s’ diarrhea’

(From: info.med.yale.edu/ library/zeiss)

Virulence:toxigenic - heat labile toxin (LT) heat stable toxin (ST)

(both toxins - plasmid encoded)

fimbriae CFA - colonization factor antigen (plasmid encoded)

ETEC - pathogenesis

ST- heat-stable toxin

guanilyn hormone-like) - stimulates guanylate cyclase retains toxicity - 100o C for 30 min processed 18-19 amino acid peptide / stabilized by disulfide bonds

ST1a

ST1b

LT- heat-labile toxin

cholera-like (AB5) toxin B-subunit receptor - GM1 gangliosideA-subunit enzyme - ADP-ribosyltransferase ADP-ribosylates / activates Gsstimulates - adenylate cyclase

secondary effects - stimulates prostaglandins, leukotrienes, cytokines

AB5-toxin

Acquisition of virulence:LT / ST - plasmid encodedfimbriae CFA - plasmid encoded

ETEC - pathogenesis

Disease:childhood diarrhea in developing countries- linked to growth retardation

mucous diarrhea - can persist for > 14 days

persistent colonization - forms mucous biofilm

EAggEC - Enteroaggregative E. coli

(J. Nataro, T. Steiner, R. Guerrant Emerging Infectious Diseases, 1998)

EAEC adherence to HEp-2 cells

Virulence:Adhesion / mucous biofilm relatedAAF/I - (aggregative adherence fimbriae) characteristic - adherence to epithelial cells as aggregates - plasmid encoded

EAST1 - heat stable (ST) enterotoxin encoded on 100 kD plasmid

Acquisition of virulence: - AAF/I and EAST1 - plasmid encoded

Disease:watery followed by bloody diarrheaintense abdominal pain

O157:H7 - most important serotype

hemorrhagic colitis (HC)

severe cases - hemolytic uremic syndrome (HUS)

edema, hemorrhage, acute kidney failurehemolytic anemia, thrombocytopenia(5-10% mortality rate)

EHEC - Enterohemorrhagic E. coli (STEC)

Virulence:Toxigenic / non invasiveShiga-like toxin (Stx1, Stx2-vero toxins) bacteriophage encoded

EAST1 - heat stable toxinLEE - pathogenicity island - A/E lesion

(www.yamagiku.co.jp/pathology/case/case006)

Bacteria attached to crypt epithelium in region of active inflammation (HE, high power)

Colon biopsy patient suffering from O157:H7 infected patient shows focal

inflammation in lamina propria (HE, low power)

Shiga-like (Stx) AB5- toxin

L enzyme activity N-glycosidase

A-subunit B-subunit receptor bindingGb3 (glycolipid globotriaosylceramide)

Receptor - Gb3 (not on enterocytes - high expression on kidney cells)

Enzyme activity - N-glycosidase - cleaves adenine from residue 4324 of 28S rRNA - inhibits protein synthesis

- retrograde transfer to cytosol - ERAD (ER associated protein degradation)

(Wilson, McNab, Henderson, Bacterial Disease Mechanisms, 2002)

Acquisition of virulence:Stx - phage encodedT3S - encoded on LEE PAIEAST 1 - plasmid encoded

EHEC - Pathogenesis

EIEC - Enteroinvasive E. coli

Disease:inflammatory diarrhea - closely related to Shigellosis(infectious dose 2-3 logs higher than Shigella)

E. coli - biochemical characterization

Shigella - genotype / phenotype characterization

Virulence:

Invasive disease

invasion genes - located on 140 MDa plasmid encodes type III secretion system - mxi / spa loci

does not produce Shiga toxin

EIEC invasion

(Prasadarao et al, Infect. Immun. 1999)

Virulence relates to:

- hybrid - Shigella - E. coli organism

- type III secretory process - affecting invasion plasmid encoded

Summary emerging Escherichia coli pathogens

normal flora E. coli - host

GI homeostasis

ETECplasmid -

LT / ST

LT - CT-like

EAggECplasmid -

AAF/1 fimbriae

EHECLEE PAI - T3Sphage - Stx

Stx - Shiga-like toxin

EIECShigella-like

plasmid - T3S

Shigellaaggressive

GI pathogen

EPECLEE PAI - T3Splasmid - bfp

SalmonellaAggressive

GI pathogen

100 million years

Concepts - emerging pathogens

• How new bacterial diseases emerge

• Strategies used by stealth / chronic pathogens

• Origin / strategies used by aggressive pathogens