Gastrointestinal Bacterial Gastrointestinal Bacterial InfectionsInfections

Liliana RodrLiliana Rodrííguez, MPH, RM (AAM), guez, MPH, RM (AAM), M(ASCP)M(ASCP)

UT Health Science Center at HoustonUT Health Science Center at HoustonLiliana.F.Rodriguez@uth.tmc.eduLiliana.F.Rodriguez@uth.tmc.edu

Learning ObjectivesLearning Objectives

• Understand the definition of diarrhea Understand the definition of diarrhea and other gastrointestinal syndromes. and other gastrointestinal syndromes.

• Learn the classification of diarrhea Learn the classification of diarrhea and the microorganisms associated and the microorganisms associated with each type. with each type.

• Learn the mechanisms utilized by Learn the mechanisms utilized by microorganisms to cause disease in microorganisms to cause disease in the GI tract, and be able to list the GI tract, and be able to list examplesexamples..

Learning ObjectivesLearning Objectives

• Learn the definitions of endotoxin, Learn the definitions of endotoxin, exotoxin, enterotoxin and exotoxin, enterotoxin and cytotoxin and be able to list cytotoxin and be able to list examples of each.examples of each.

• Understand the mechanisms of Understand the mechanisms of defense in the GI tract and the defense in the GI tract and the role of the normal flora.role of the normal flora.

• Understand the global impact of Understand the global impact of diarrheal disases.diarrheal disases.

Learning ObjectivesLearning Objectives

• Understand the general morphology, Understand the general morphology, physiology, and virulence factors of major physiology, and virulence factors of major bacterial pathogens of the GI tract.bacterial pathogens of the GI tract.

• Understand the molecular pathogenesis of Understand the molecular pathogenesis of the major GI bacterial diseases.the major GI bacterial diseases.

• Learn the epidemiology, clinical features, Learn the epidemiology, clinical features, diagnosis, basic treatment and prevention diagnosis, basic treatment and prevention of GI bacterial infections.of GI bacterial infections.

The Gastrointestinal Tract

GI Tract (Enteric) InfectionsGI Tract (Enteric) Infections

Most common infections seen by primary Most common infections seen by primary care physicians in USA.care physicians in USA.

Leading cause of infant mortality Leading cause of infant mortality worldwide, killing 2-3 million children/year.worldwide, killing 2-3 million children/year.

In some countries, a 7 years-old or In some countries, a 7 years-old or younger child’s chance of dying of a younger child’s chance of dying of a diarrheal illness can be as high as 50%.diarrheal illness can be as high as 50%.

300 children die of diarrhea in the U.S. 300 children die of diarrhea in the U.S. each year along with 4000 elderly, AIDS each year along with 4000 elderly, AIDS and transplant patients.and transplant patients.

GI Tract (Enteric) InfectionsGI Tract (Enteric) Infections

Diarrheal disease control is a major Diarrheal disease control is a major goal of the World Health Organization.goal of the World Health Organization.

Traveler's diarrhea has a high Traveler's diarrhea has a high economic impact.economic impact.

GI Tract can be the major portal of GI Tract can be the major portal of entry but not prime target (Polio, entry but not prime target (Polio, hepatitis A, botulism), ORhepatitis A, botulism), OR

Major portal of entry Major portal of entry andand prime target prime target in most cases (Shigellosis, Cholera, in most cases (Shigellosis, Cholera, Traveler’s Diarrhea).Traveler’s Diarrhea).

Clinical FeaturesClinical Features

feverfever vomitingvomiting abdominal painabdominal pain diarrheadiarrhea presence of these symptoms varies presence of these symptoms varies

with different diseases, and the with different diseases, and the different stages of infectiondifferent stages of infection

Definition of DiarrheaDefinition of Diarrhea

An abnormally frequent discharge of An abnormally frequent discharge of semisolid or fluid fecal matter. semisolid or fluid fecal matter.

Usually involving increased fluid and Usually involving increased fluid and electrolyte loss.electrolyte loss.

Can be watery or bloody.Can be watery or bloody. Method by which the host forcibly Method by which the host forcibly

expels the infecting microorganism(s).expels the infecting microorganism(s).

Classification of DiarrheaClassification of Diarrhea

I.I. WateryWatery diarrhea diarrhea

no blood or pusno blood or pus caused by enterotoxinscaused by enterotoxins small bowel (proximal or distal)small bowel (proximal or distal) self-limitingself-limiting examples: Traveler’s diarrhea, examples: Traveler’s diarrhea,

choleracholera

Classification of DiarrheaClassification of Diarrhea

II. Bloody diarrhea II. Bloody diarrhea

structural damage to the intestine structural damage to the intestine large bowel large bowel invasion or damage to the mucosa by invasion or damage to the mucosa by cytotoxinscytotoxins usually requires treatment usually requires treatment examples: non-typhoid examples: non-typhoid

Salmonella, Salmonella, Yersinia and CampylobacterYersinia and Campylobacter

Classification of DiarrheaClassification of Diarrhea

III. Dysentery - inflammatory disorderIII. Dysentery - inflammatory disorder frequent passage of stool, blood and pusfrequent passage of stool, blood and pus tenesmus, fever, cramps tenesmus, fever, cramps colon colon serious, requires antibiotic treatmentserious, requires antibiotic treatment typically caused by Shigella, typically caused by Shigella, Entamoeba Entamoeba

histolytica histolytica (amoeba)(amoeba)

IV.IV. Diarrhea can also be classified as Diarrhea can also be classified as acuteacute (<2 (<2 weeks) and weeks) and chronicchronic (>6 weeks) (>6 weeks)

Pathophysiology of DiarrheaPathophysiology of Diarrhea

Impaired fluid absorptionImpaired fluid absorption Increased fluid production*Increased fluid production*

• toxin-mediatedtoxin-mediated• mucosal injury (adhesion to mucosal injury (adhesion to

enterocytes)enterocytes) Motor disturbancesMotor disturbances

Important TermsImportant Terms

• GastroenteritisGastroenteritis – A syndrome characterized – A syndrome characterized by GI symptoms including nausea, diarrhea by GI symptoms including nausea, diarrhea and abdominal discomfort.and abdominal discomfort.

• Enterocolitis Enterocolitis - Inflammation involving the - Inflammation involving the mucosa of the mucosa of the smallsmall and and largelarge intestines intestines

• Enteric feverEnteric fever ( (typhoid fevertyphoid fever) – Disseminated ) – Disseminated infection involving multiple organs. infection involving multiple organs. Associated with Associated with Salmonella typhiSalmonella typhi..

Other GI Clinical SyndromesOther GI Clinical Syndromes

Gastric ulcers – Gastric ulcers – H. pyloriH. pylori Antibiotic-associated diarrhea – Antibiotic-associated diarrhea – Cl. Cl.

difficiledifficile Food poisoning – Food poisoning – Bacillus cereusBacillus cereus, ,

Clostridium perfringens, Cl. botulinum,S. Clostridium perfringens, Cl. botulinum,S. aureusaureus

In addition to bacteria, certain parasites In addition to bacteria, certain parasites and viruses are classified as enteric and viruses are classified as enteric agentsagents

GI Defenses Against GI Defenses Against InfectionInfection Mouth- flow of fluids, Mouth- flow of fluids,

salivasaliva Esophagus – flow of Esophagus – flow of

liquids, peristalsisliquids, peristalsis Stomach – acid pHStomach – acid pH Small intestine- Small intestine-

peristalsis, bile, IgA, peristalsis, bile, IgA, Peyer’s patches, Peyer’s patches, shedding, normal florashedding, normal flora

Large intestine- NF, Large intestine- NF, peristalsis, shedding, peristalsis, shedding, mucusmucus

Normal FloraNormal Flora

• 101011 11 to 10to 1012 12 viable viable bacteria/gm of bacteria/gm of fecesfeces

• BacteriocinsBacteriocins• Occupation of the Occupation of the

mucosal surfacemucosal surface• ImmunogensImmunogens• Vitamin KVitamin K

Distribution of Intestinal FloraPredominant Concentration Organisms (per gram)Obligate anaerobesStreptococciStaphylococciNeisseria

LactobacilliStreptococci

Anaerobes BacteroidesColiforms E. coliStreptococciCandidaProtozoa

None

>106

102

<104

106

109

1011

Cast of CharactersCast of Characters

Family Family EnterobacteriaceaeEnterobacteriaceae• Escherichia coliEscherichia coli (many serotypes) (many serotypes)• SalmonellaSalmonella spp. (many serotypes) spp. (many serotypes)• Shigella Shigella spp. (4 species)spp. (4 species)• Yersinia enterocoliticaYersinia enterocolitica (minor cause of diarrhea) (minor cause of diarrhea)

Family Family VibrionaceaeVibrionaceae• Vibrio choleraeVibrio cholerae• Vibrio parahemolyticusVibrio parahemolyticus

Family Family CampylobacteriaceaeCampylobacteriaceae• Campylobacter jejuniCampylobacter jejuni

Acquisition of GI PathogensAcquisition of GI Pathogens

Infections are acquired by the fecal-oral Infections are acquired by the fecal-oral route (fecally-contaminated food, fluids, route (fecally-contaminated food, fluids, fingers, fomites, flies)fingers, fomites, flies)

Infective doseInfective dose

• HighHigh, 10 , 10 6-8 6-8 ((ETEC, Vibrio cholerae)ETEC, Vibrio cholerae)

• IntermediateIntermediate 10 10 3-53-5 ( (Salmonella, Salmonella, Campylobacter)Campylobacter)

• LowLow,, 10-100 cells (Shigella, EHEC)10-100 cells (Shigella, EHEC)

Evasion of host defensesEvasion of host defenses

Mechanisms of PathogenesisMechanisms of Pathogenesis

A. ColonizationA. Colonization1.1. Adhesins Adhesins fimbria or pilifimbria or pili colonizing factor colonizing factor

antigen (CFA)antigen (CFA)

22. Receptors. Receptors glycoproteinsglycoproteins

D- mannoseD- mannose

PathogenesisPathogenesis

B. Toxin ProductionB. Toxin Production Endotoxin Endotoxin - LPS Gram-negative - LPS Gram-negative

bacteria, extremely toxic to humansbacteria, extremely toxic to humans Exotoxins –Exotoxins –excreted excreted

• Enterotoxins -Enterotoxins - proteins that affect the proteins that affect the small intestine without demonstrable small intestine without demonstrable histopathology. histopathology. Vibrio choleraeVibrio cholerae, ETEC, ETEC

• Cytotoxins Cytotoxins –produced by –produced by Shigella Shigella dysenteriaedysenteriae type 1 and certain type 1 and certain E. coliE. coli serotypes; kill mammalian cells by serotypes; kill mammalian cells by inhibiting protein synthesis. inhibiting protein synthesis.

PathogenesisPathogenesisC. Invasion of Intestinal Mucosa

Mucu

Microbial cell

Epithelial cell

Mucus

EnterobacteriaceaeEnterobacteriaceae

• Largest family of GNRLargest family of GNR• Found in soil, water, Found in soil, water,

vegetation, humans, vegetation, humans, animalsanimals

• Large rods, non-spore Large rods, non-spore forming, facultativeforming, facultative

• Major reservoirs for Major reservoirs for

R-factorsR-factors• They ferment glucoseThey ferment glucose• Most have surface pili Most have surface pili

for attachmentfor attachment• Oxidase negativeOxidase negative

Enterobacteriaceae (cont...)Enterobacteriaceae (cont...)

Colon normal flora (Colon normal flora (E. coliE. coli, Klebsiella, , Klebsiella, Enterobacter). Enterobacter).

Frank pathogens (Salmonella, Shigella, Frank pathogens (Salmonella, Shigella, Yersinia, certain serotypes of Yersinia, certain serotypes of E. coliE. coli).).

Some typically encapsulated (Some typically encapsulated (K. K. pneumoniaepneumoniae). ).

Most are motile by peritrichous flagella Most are motile by peritrichous flagella except Shigella, Klebsiella and some except Shigella, Klebsiella and some E. E. colicoli. .

Can cause disease in other organs, such Can cause disease in other organs, such as the urinary and respiratory tract.as the urinary and respiratory tract.

ClassificationIdentification to species level by biochemical characteristics

Below species level by ID of surface antigens, called serotyping

cell wall antigens: O(somatic)

flagellar antigens: H

capsular antigens: K

Production of fever by Lipid AProduction of fever by Lipid A

Escherichia coliEscherichia coli

Most abundant facultative bacteria in Most abundant facultative bacteria in GI tractGI tract

Large rods, non-spore forming, Large rods, non-spore forming, facultativefacultative

Lactose fermenter (unlike Lactose fermenter (unlike SalmonellaSalmonella and and ShigellaShigella) )

Nornal flora of colon (human and many Nornal flora of colon (human and many animals)animals)

Escherichia coliEscherichia coli Five groups cause intestinal disease. Five groups cause intestinal disease.

All share the property of adherence All share the property of adherence to the epithelium of the intestine.to the epithelium of the intestine.

• Enterotoxigenic Enterotoxigenic ETECETEC• EnteroaggregativeEnteroaggregative EAECEAEC• EnteroinvasiveEnteroinvasive EIECEIEC• EnteropathogenicEnteropathogenic EPECEPEC• EnterohemorrhagicEnterohemorrhagic EHECEHEC

Enterotoxigenic Enterotoxigenic E. coliE. coli (ETEC)(ETEC)

• The most important cause of diarrhea in children in developing countries.

• Main cause of traveler’s diarrhea.

• Affects 50% of Americans traveling to Africa or Latin America.

• Spread by contaminated water or food.

ETEC: EpidemiologyETEC: Epidemiology

High infecting dose Worldwide distribution All ages affected No seasonal incidence Infects only humans Affects small intestine 80,000 cases/yr in the US

ETEC: Virulence FactorsETEC: Virulence Factors

General type 1 pili General type 1 pili

bind to D-mannosebind to D-mannose

Colonization factor Colonization factor

antigens (CFA), bind antigens (CFA), bind to glycoproteins in to glycoproteins in the host’s cellsthe host’s cells

ETEC: EnterotoxinsETEC: Enterotoxins

LT - Heat-labileLT - Heat-labile

• Similar to Similar to choleragencholeragen

• ImmunogenicImmunogenic

• Plasmid-Plasmid-mediatedmediated

• LTI and LTIILTI and LTII

ST- Heat-stableST- Heat-stable

• Non-immunogenicNon-immunogenic

• Plasmid-mediatedPlasmid-mediated

• ST-a and ST-bST-a and ST-b

ETEC: Clinical featuresETEC: Clinical features

Watery diarrhea. Watery diarrhea.

No white or red cells in stool. No No white or red cells in stool. No inflammatory process in the gut.inflammatory process in the gut.

Incubation period 1-4 days. Incubation period 1-4 days.

Abdominal cramps, nausea, profuse Abdominal cramps, nausea, profuse diarrhea for 3-4 days. diarrhea for 3-4 days.

No fever.No fever.

Immunity mediated by sIgA antibodies Immunity mediated by sIgA antibodies against LT-toxin.against LT-toxin.

Enteropathogenic Enteropathogenic E. coliE. coli (EPEC)(EPEC) Major cause of diarrhea in Major cause of diarrhea in

poor countriespoor countries Infects primarily infantsInfects primarily infants Fever, nausea, vomiting and Fever, nausea, vomiting and

self-limiting watery diarrheaself-limiting watery diarrhea Small intestineSmall intestine Also called enteroadherentAlso called enteroadherent 12 species identified by

serotype (O111:H2, O55:H6)

EPEC O:111 in small intestineEPEC O:111 in small intestine

EPEC: PathogenicityEPEC: Pathogenicity

Attachment to Attachment to enterocytes through enterocytes through bundle-forming pili (Bfp)bundle-forming pili (Bfp)

Proteins inserted into Proteins inserted into the cell membranethe cell membrane

Effacement of Effacement of microvillusmicrovillus

No enterotoxinNo enterotoxin Diarrhea from Diarrhea from

malabsorptionmalabsorption

Attachment-Effacing Lesions

Enteroaggregative Enteroaggregative E. coliE. coli (EAggEC)(EAggEC)

Cause of persistent diarrhea in Cause of persistent diarrhea in developing countriesdeveloping countries

Affects mainly infants Affects mainly infants Small intestine Small intestine Patients suffer of vomiting, low grade Patients suffer of vomiting, low grade

fever, watery (sometimes bloody) fever, watery (sometimes bloody) diarrhea and dehydrationdiarrhea and dehydration

EAggEC: PathogenicityEAggEC: Pathogenicity

Adherence to Adherence to enterocytesenterocytes

Cytotoxin (?)Cytotoxin (?)

Secretion of mucus Secretion of mucus and trapping of the and trapping of the bacteria in a biofilmbacteria in a biofilm

Shortening of the villi, Shortening of the villi, mononuclear mononuclear infiltration and infiltration and sometimes sometimes hemorrhagehemorrhage

Enteroinvasive Enteroinvasive E. coliE. coli (EIEC) (EIEC)

Classical serotype Classical serotype O29:HO29:H--

Able to invade and Able to invade and destroy colonic destroy colonic epitheliumepithelium

Food-borne diseaseFood-borne disease Important cause of Important cause of

pediatric diarrhea in pediatric diarrhea in developing countriesdeveloping countries

EIEC: EpidemiologyEIEC: Epidemiology

Infects only humans Infects only humans

Associated with travelAssociated with travel

Infections restricted Infections restricted to children under 5 to children under 5 years of age living in years of age living in poor conditionspoor conditions

One outbreak in USA One outbreak in USA traced to traced to contaminated contaminated imported cheeseimported cheese

EIEC: PathogenesisEIEC: Pathogenesis

Similar to Similar to ShigellaShigella Attachment to the Attachment to the

large intestine mucosa large intestine mucosa (plasmid-mediated)(plasmid-mediated)

Invasion of cells after Invasion of cells after endocytosisendocytosis

Lysis of the endocytic Lysis of the endocytic vacuole, multiplication vacuole, multiplication and spread to adjacent and spread to adjacent cellscells

EIEC: Clinical FeaturesEIEC: Clinical Features

Resembles shigellosis, but less severeResembles shigellosis, but less severe From mild, watery diarrhea, to severe From mild, watery diarrhea, to severe

bloody diarrheabloody diarrhea Fever Fever Cramps Cramps Blood and leukocytes in stoolBlood and leukocytes in stool

Enterohemorrhagic Enterohemorrhagic E. coliE. coli (EHEC)(EHEC)

EHEC: Historical PerspectiveEHEC: Historical Perspective

1982- First identified 1982- First identified as a pathogen as a pathogen

1985- Associated 1985- Associated with HUSwith HUS

1990 outbreak in 1990 outbreak in Missouri.Missouri.

1991 outbreak in 1991 outbreak in Massachusetts.Massachusetts.

1993 - Multistate 1993 - Multistate outbreak, 731 cases outbreak, 731 cases linked to linked to hamburgers.hamburgers.

EHEC: General EHEC: General CharacteristicsCharacteristics

About 50 serotypesAbout 50 serotypes Also known as Also known as

Verotoxin Verotoxin E. coli E. coli

(VTEC)(VTEC) The most important The most important

are O157:H7 are O157:H7 O111:NM, O26:H11, O111:NM, O26:H11, O104, O45O104, O45

Acquisition of the Acquisition of the Shiga-toxin gene?Shiga-toxin gene?

EHEC: EpidemiologyEHEC: Epidemiology

Outbreaks or sporadic zoonosis Outbreaks or sporadic zoonosis Main reservoir: GI tract of cattleMain reservoir: GI tract of cattle Worldwide outbreaksWorldwide outbreaks Most prevalent in warmer months; Most prevalent in warmer months;

greater incidence among children <5 greater incidence among children <5 Person-to-person infection commonPerson-to-person infection common Very low infective dose (~100 cells)Very low infective dose (~100 cells) Sources: beef, unpasteurized milk, apple Sources: beef, unpasteurized milk, apple

cider, untreated watercider, untreated water

EHEC: Virulence FactorsEHEC: Virulence Factors

Low infective dose; acid-toleranceLow infective dose; acid-tolerance Two cytotoxins (verotoxins) encoded in Two cytotoxins (verotoxins) encoded in

lysogenic bacteriophageslysogenic bacteriophages• Shiga-like-toxin I (SLT-I) homologous Shiga-like-toxin I (SLT-I) homologous

to Shiga toxin except for one a.a.to Shiga toxin except for one a.a.• Shiga-like-toxin II (SLT-II) 60% Shiga-like-toxin II (SLT-II) 60%

homologyhomology Attachment (Attachment (eaeeae gene) attaching- gene) attaching-

effacingeffacing HemolysinHemolysin

EHEC: PathogenesisEHEC: Pathogenesis

Colonization of Colonization of distal ileum, colon distal ileum, colon and cecum. and cecum.

Confined to the gut Confined to the gut mucosa.mucosa.

Attachment to Attachment to epithelial cells and epithelial cells and local multiplication.local multiplication.

No systemic No systemic invasioninvasion..

The problem is…..The problem is…..

Shiga-like toxin (SLT, Shiga-like toxin (SLT, cytotoxin, verotoxin) cytotoxin, verotoxin) promotes inflammation of promotes inflammation of the colonic mucosa the colonic mucosa resulting in purulent resulting in purulent exudate and bleedingexudate and bleeding

Damage of the intestinal Damage of the intestinal lining cellslining cells

2-7% 2-7% →→HUS due to HUS due to systemic absorption of SLTsystemic absorption of SLT

SLT damage to small renal SLT damage to small renal arteries arteries

E. coli Diarrheal Diseases E. coli Diarrheal Diseases DiagnosisDiagnosis

Stool culture in special Stool culture in special media (EIEC difficult)media (EIEC difficult)

Clinical (EHEC)Clinical (EHEC) Serotypes determined Serotypes determined

w/polyvalent w/polyvalent antiserum and antiserum and adhesion in cell adhesion in cell culturescultures

Test for toxins (ETEC, Test for toxins (ETEC, EHEC) in tissue EHEC) in tissue culture, ELISA, latex culture, ELISA, latex agglutination testagglutination test

DNA probesDNA probes

EMB Agar with E. coli

EPEC, EAggEC, EIEC, EPEC, EAggEC, EIEC, EHECEHEC

Fluid Replacement.Fluid Replacement. No need for antibiotics or No need for antibiotics or

antispasmodics except in EIEC cases, antispasmodics except in EIEC cases, where some antibiotics reduce where some antibiotics reduce duration of diarrhea.duration of diarrhea.

HUS HUS SupportiveSupportive Dialysis in renal failureDialysis in renal failure Antibiotics contraindicatedAntibiotics contraindicated

Prevention and ControlPrevention and Control

Pure water supplyPure water supply Adequate systems Adequate systems

for sewagefor sewage Boiling waterBoiling water Promotion of Promotion of

breast feeding breast feeding ((EPEC, EAggECEPEC, EAggEC))

Improved Improved sanitationsanitation

E. coli type Symptoms epidemiology pathogenesis primary site

Enterotoxigenic (ETEC)

traveler's diarrheainfant diarrhea; watery, no fever, no WBC

worldwide; all ages; humans only

LT or ST toxinspili

small intestine

Enteropathogenic (EPEC)

Fever, nausea, vomiting. Watery diarrhea, no WBC

Important cause of pediatric diarrhea

adherence to enterocytes,destroys villi

small intestine

Enteroinvasive (EIEC)

bloody diarrhea, and fever (resembles Shigella)

humans onlyassociated with travel

plasmid-mediated invasion. Destruction of colon cells

large intestine

Enterohemorrhagic (EHEC) O157:H7

Little or no feverHemorrhagic colitis. HUS

Zoonosis foodborne

Cytotoxic Shiga-like verotoxin

large intestine

Enteroaggregative (EAEC)

Vomiting, low grade fever. Watery/bloody diarrhea

infant diarrhea in underdeveloped countries

adherence to enterocytesheat-stable toxin

small intestine

Summary