Gastrointestinal Bacterial Infections

SalmonellaSalmonella Shigella Shigella Yersinia enterocoliticaYersinia enterocolitica

Liliana Rodríguez, MPH, RM (AAM), M(ASCP)Liliana Rodríguez, MPH, RM (AAM), M(ASCP) UT Health Science Center at HoustonUT Health Science Center at Houston

Liliana.F.Rodriguez@uth.tmc.eduLiliana.F.Rodriguez@uth.tmc.edu

Salmonella Motile Gram-negative rods, members of the Motile Gram-negative rods, members of the

Family Family EnterobacteriaceaeEnterobacteriaceae Common speciesCommon species

• S. cholerasuis (pigs) • S. typhimurium (cattle, pigs, poultry)• S. typhi, S. paratyphi A and B (humans)• S. enteritidis (1500 serotypes) many hosts

Non-lactose fermentors; production of HNon-lactose fermentors; production of H22SS

Laboratory Identification

Non-lactose fermenting colonies on MacConkey

agar

Biochemical reactions on TSI

Serotyping

Salmonella: Epidemiology

Ubiquitous pathogensUbiquitous pathogens All are associated with animals, except All are associated with animals, except S. S.

typhi, S. paratyphi typhi, S. paratyphi A, B, and CA, B, and C Transmitted to humans via contaminated Transmitted to humans via contaminated

food, water (less frequent), or person-to-food, water (less frequent), or person-to-personperson

Killed by gastric acidKilled by gastric acid High infectious doseHigh infectious dose

Virulence factors

Virulence polysaccharide (Vi antigen)Virulence polysaccharide (Vi antigen) Adhesion to M-cellsAdhesion to M-cells MotilityMotility Tolerance to acid in phagocytic cellsTolerance to acid in phagocytic cells Survival in macrophages (Survival in macrophages (S. typhiS. typhi)) Endotoxin Endotoxin

Salmonella: Clinical Syndromes

1.1. GastroenteritisGastroenteritis

2.2. Extra-intestinalExtra-intestinal SepticemiaSepticemia Typhoid fever (enteric fever)Typhoid fever (enteric fever) Chronic carriageChronic carriage

Gastroenteritis Most common Most common

manifestationmanifestation Highest rates of infection Highest rates of infection

in childrenin children S. enteritidis S. enteritidis (many (many

serotypes)serotypes) Contaminated food - Contaminated food -

eggs, poultry, dairyeggs, poultry, dairy Exotic petsExotic pets Incubation period 12-48 Incubation period 12-48

hrshrs

Gastroenteritis PathogenesisAttachment to the brush border

Ruffles

Invasion and penetration of enterocytes

←

bacterial death

Inflammatory Response

PMN confine infection to GI tractPMN confine infection to GI tract Mediates release of prostaglandinsMediates release of prostaglandins Stimulates cAMP, activates fluid secretion Stimulates cAMP, activates fluid secretion

resulting in diarrhearesulting in diarrhea S. enteritidisS. enteritidis can become can become invasiveinvasive in in

immunocompromised patientsimmunocompromised patients

Salmonella enteritis ingestion

diarrhea

bacteria penetrate cells and migrate to lamina propria layer of ileoceal region

multiply in lymphoid follicles causing reticuloendothelial hyperplasia and hypertrophy

polymorphonuclear leucocytes confine infection to GI tract

inflammatory response also mediates release of prostaglandins

stimulates cAMP and active fluid

secretion

absorbed to epithelial cells in terminal portion of small intestine

Summary

Gastroenteritis: Clinical Presentation

Nausea, vomiting (rare)Nausea, vomiting (rare) Fever (50%)Fever (50%) Abdominal crampsAbdominal cramps Acute but self-limiting watery or bloody Acute but self-limiting watery or bloody

diarrhea with fecal leukocytesdiarrhea with fecal leukocytes Symptoms subside in 7 days, but stool Symptoms subside in 7 days, but stool

cultures remain (+) several weekscultures remain (+) several weeks

Bacteremia Caused by salmonellas Caused by salmonellas

highly adapted to animals:highly adapted to animals: S. cholerasuisS. cholerasuis S. typhimuriumS. typhimurium S. enteritidis S. enteritidis

heidelbergheidelberg Severe disease in humansSevere disease in humans Portal of entry: GI tract Portal of entry: GI tract Phagocytes in lamina Phagocytes in lamina

propria cannot stop propria cannot stop infectioninfection

Pathogenesis

Bacteremia: Pathogenesis

Penetrates mucosa - invades bloodstreamPenetrates mucosa - invades bloodstream Localizes in abnormal cardiovascular Localizes in abnormal cardiovascular

surfaces of some patients (It has a surfaces of some patients (It has a predilection for the artherosclerotic plaque)predilection for the artherosclerotic plaque)

It can cause metastasic infection in bones It can cause metastasic infection in bones (osteomyelitis)(osteomyelitis)

Sepsis can be seen in those with cell-Sepsis can be seen in those with cell-mediated immune system deficienciesmediated immune system deficiencies

Clinical Presentation High fever without localizing findingsHigh fever without localizing findings Minimal or absent GI symptoms Minimal or absent GI symptoms MeningitisMeningitis ArthritisArthritis EndocarditisEndocarditis

Typhoid Fever

Systemic infection of mononuclear phagocytesSystemic infection of mononuclear phagocytes Etiologic agentEtiologic agent:: S. typhi S. typhi Parathypoid feverParathypoid fever caused by S. caused by S. paratyphi A,paratyphi A, S. scottmulerii S. scottmulerii (paratyphi(paratyphi B) and B) and S. hirschfeldiiS. hirschfeldii

(paratyphi C)(paratyphi C) Humans-humans (no animal reservoir)Humans-humans (no animal reservoir) S. typhiS. typhi virulence virulence

• binds to intestinal M-cells (adhesin)binds to intestinal M-cells (adhesin)• motilitymotility• intracellularityintracellularity

Typhoid Fever: Pathogenesis

Infective dose: 10Infective dose: 1055

Penetration of gut mucosa (jejunum, ileum)Penetration of gut mucosa (jejunum, ileum)

Reaches intestinal lymph nodes, survives Reaches intestinal lymph nodes, survives and multiply within macrophagesand multiply within macrophages

Typhoid Fever: Pathogenesis

After 5-7 days reaches blood, taken up by After 5-7 days reaches blood, taken up by liver, bone marrow, and spleen, where liver, bone marrow, and spleen, where intracellular replication continues intracellular replication continues (asymptomatic incubation period)(asymptomatic incubation period)

Multiplication within macrophages Multiplication within macrophages continues continues → → release into the bloodstreamrelease into the bloodstream

Resolves, gets complicated, or patient Resolves, gets complicated, or patient becomes a chronic carrier (becomes a chronic carrier (1-3 %) 1-3 %)

Typhoid Fever: Pathogenesis

Typhoid Fever: Clinical Manifestations

Incubation period: 1-2 weeks after Incubation period: 1-2 weeks after ingestioningestion

A sustained period of high fever (4-8 A sustained period of high fever (4-8 weeks if untreated)weeks if untreated)

Malaise, achesMalaise, aches Respiratory symptoms (flu-like) Respiratory symptoms (flu-like) Occasional diarrhea or constipationOccasional diarrhea or constipation Rose spots (50%)Rose spots (50%)

Diagnosis GastroenteritisGastroenteritis

• Stool cultureStool culture• Biochemical idBiochemical id

BacteremiaBacteremia• Blood culturesBlood cultures• Stool cultures usually Stool cultures usually

negativenegative• Leukocytosis (many WBC)Leukocytosis (many WBC)

Diagnosis of Typhoid Fever

Clinical historyClinical history Blood cultures Blood cultures

during the first 2 during the first 2 weeksweeks

Stool and urine Stool and urine culture during weeks culture during weeks 3-43-4

Bone marrowBone marrow aspiration if neededaspiration if needed

Serology: Widal test

The Widal test measures the patient’s antibodies against Salmonella typhi “O” and “H” antigen preparations. Dilutions 1:20-1:1280 and negative control. In this case “O” antigen titer = 1:80.

1:20 1:40 1:80

Salmonella Infections: Therapy

SyndromeAntibioticsIndicated

Useful Antibiotics

Enterocolitis No

Yes

Yes

ImmunosuppressionDebilitated hostInfants, elderly

Chronic bacteremiaExtra-intestinal infectionTyphoid fever

AmpicillinChloramphenicolTrimethoprimCiprofloxacinCeftriaxone

Prevention

Hand washingHand washing Adequate standards of Adequate standards of

public health and public health and educational programseducational programs

Food workers should Food workers should be excluded from be excluded from handling foodhandling food

Prolonged treatment Prolonged treatment for chronic carriersfor chronic carriers

Prevention Typhoid fever immunizationTyphoid fever immunization

• inactivated –parenteralinactivated –parenteral• live – orallive – oral• Vi antigen- parenteralVi antigen- parenteral

Preventing gastroenteritis presents a Preventing gastroenteritis presents a challenge because of animal reservoirschallenge because of animal reservoirs

Shigella Closely related to Closely related to E. coliE. coli Non-lactose fermenterNon-lactose fermenter No gas from glucoseNo gas from glucose Non-motileNon-motile Causes bacillary dysenteryCauses bacillary dysentery

Stool Gram stain showing numerous white blood cells and GNR

Shigella: Classification

Group

A

B

C

D

Species

S. dysenteriae

S. flexneri

S. boydii

S. sonnei

Shigella species S. S. dysenteriae dysenteriae (Shiga bacillus) (Shiga bacillus) first discovered in 1890 Japan; re-first discovered in 1890 Japan; re-

emerged in 1969emerged in 1969 causes most serious diseasecauses most serious disease S.S. dysenteriae type 1 produces Shiga toxin (cytotoxin) type 1 produces Shiga toxin (cytotoxin) associated with 10-20% mortalityassociated with 10-20% mortality

S. flexneriS. flexneri is the dominant species internationally. Associated with is the dominant species internationally. Associated with severe infections in gay man.severe infections in gay man.

Shigella species cont..

SS. boydii. boydii causes severe infections. Occurs primarily in India causes severe infections. Occurs primarily in India S. soneiiS. soneii is the most important in the United States (70% of the cases). is the most important in the United States (70% of the cases).

Shigellosis in the U.S. is primarily a pediatric diseaseShigellosis in the U.S. is primarily a pediatric disease Species distinguished from one another by serology, not Species distinguished from one another by serology, not

biochemically.biochemically.

Epidemiology

Humans only reservoirHumans only reservoir Spread from person-to-person by the fecal-oral routeSpread from person-to-person by the fecal-oral route Extremely low infective dose (10-100 cells)Extremely low infective dose (10-100 cells) No seasonal incidence for isolated causesNo seasonal incidence for isolated causes Epidemics occur in the summerEpidemics occur in the summer The most virulent of all enteric pathogensThe most virulent of all enteric pathogens

Age distribution of diarrheal disease caused by Campylobacter, Salmonella, and Shigella

Shigella: Virulence Factors

Gastric acid resistantGastric acid resistant Attachment – invasion plasmid antigens (Ipa) Attachment – invasion plasmid antigens (Ipa) Intracellular pathogen (local invasion)Intracellular pathogen (local invasion) ToxinsToxins

• cytotoxins – “Shiga” toxin (cytotoxins – “Shiga” toxin (S. dysenteriae)S. dysenteriae)• enterotoxins role unknownenterotoxins role unknown

Shigella: Local Invasion

Shigella: Pathogenesis

Attachment and invasion of mucosal Attachment and invasion of mucosal epithelium of distal ileum and colonepithelium of distal ileum and colon

Destruction of enterocytes and release of Destruction of enterocytes and release of TNF, PGTNF, PG

Vascular abnormalitiesVascular abnormalities Locally invasiveLocally invasive Rarely invade bloodstream (except Rarely invade bloodstream (except S. S.

dysenteriaedysenteriae type 1) type 1)

Shigella

Shigella: Clinical Features

Incubation period 1-2 daysIncubation period 1-2 days Mild diarrhea to dysenteryMild diarrhea to dysentery Diarrhea, abdominal cramps, fever, malaise, Diarrhea, abdominal cramps, fever, malaise,

anorexia, and sometimes myalgiasanorexia, and sometimes myalgias Stool contains mucus and blood. Most Stool contains mucus and blood. Most

display many white blood cellsdisplay many white blood cells Self-limiting but dehydration can occur, Self-limiting but dehydration can occur,

especially in the young and elderlyespecially in the young and elderly No chronic carrier stateNo chronic carrier state

Shigella: Diagnosis Rectal swabs or stoolRectal swabs or stool Requires transport mediaRequires transport media Fecal leukocytes (+)Fecal leukocytes (+) CultureCulture Biochemical testsBiochemical tests Agglutination testsAgglutination tests Other: PCR, DNA probesOther: PCR, DNA probes

Shigella on MacConkey Agar

Non-lactose fermenter Non-motile

Shigellosis: Prevention

Education in personal Education in personal hygienehygiene

Proper disposal of Proper disposal of diapers at day-care diapers at day-care centerscenters

Hand-washing Hand-washing Safe sex for gay manSafe sex for gay man

Yersinia enterocolitica: “the cold bug”

Gram negative Gram negative encapsulated encapsulated cocobacillus with polar cocobacillus with polar stainingstaining

Prefers to grow Prefers to grow between 22-25 between 22-25 ººCC

Requires a special Requires a special medium to growmedium to grow

Y. enterocolitica: Epidemiology Food-associated infection in Food-associated infection in coldercolder parts of parts of

the worldthe world More common during More common during coldercolder months months Found in rodents, rabbits, pigs, sheep, Found in rodents, rabbits, pigs, sheep,

cattle, horses, dogs.cattle, horses, dogs. Humans are accidental hostsHumans are accidental hosts Survives and multiplies at refrigerator Survives and multiplies at refrigerator

temperaturestemperatures

Y. enterocolitica: Virulence Factors

Invasin - early attachment protein to cells Invasin - early attachment protein to cells expressing receptorexpressing receptor

ST-like enterotoxin (chromosomal)ST-like enterotoxin (chromosomal)

Complement resistance factorComplement resistance factor

Yersinia outer proteins or Yersinia outer proteins or YopsYops (anti- (anti-phagocytic & toxic action)phagocytic & toxic action)

Y. enterocolitica: Pathogenesis

Invasion of M-cells of Peyer’s patchesInvasion of M-cells of Peyer’s patches

In contrast to Shigella, Yersinia does not In contrast to Shigella, Yersinia does not replicate in the M-cells but passes to the replicate in the M-cells but passes to the underlying tissueunderlying tissue

Engulfed by macrophages and carried to Engulfed by macrophages and carried to MLN where they replicateMLN where they replicate

Y. enterocolitica: Clinical Syndromes

Enterocolitis - young children.Enterocolitis - young children.

Mesenteric adenitis (Mesenteric adenitis (mimics appendicitismimics appendicitis) - ) - older children.older children.

Focal necrosis of Peyer’s patches.Focal necrosis of Peyer’s patches.

Bacteremia - high fatality rate.Bacteremia - high fatality rate.

Arthritis, reactive polyarthritis (post-Arthritis, reactive polyarthritis (post-infection in adults)infection in adults)

Y. enterocolitica: Diagnosis Challenging - few Challenging - few

laboratories screen laboratories screen for for YersiniaYersinia

Can be isolated from Can be isolated from stoolstool

Non-lactose Non-lactose fermenterfermenter

Cold enrichmentCold enrichment increases chances of increases chances of isolationisolation

Y. enterocolitica: Treatment

Usually self-limitingUsually self-limiting Not clear if antibiotics helpNot clear if antibiotics help If needed, aminoglycosides, tetracycline, If needed, aminoglycosides, tetracycline,

chloramphenicol and broad-spectrum chloramphenicol and broad-spectrum cephalosporins cephalosporins

Resistant to ampicillin and cephalosporins Resistant to ampicillin and cephalosporins (beta-lactamase)(beta-lactamase)