Microbiology: Basic and Clinical Principles
First Edition
Chapter 19
Digestive System Infections
Presented by
Shannon Ulrich, Ph.D.
St. Petersburg College
Copyright © 2019 Pearson Education, Inc. All Rights Reserved.
The digestive system
includes the GI tract
and accessory organs
• GI tract is associated with
lymphatic tissues
– Tonsils, appendix, and
Peyer’s patches
– Serves as a major
entry portal for
pathogens
Accessory organs
Immune-related
tissues
Upper
system
Lower
system
Mumps is a viral infection of the salivary
glands
• Progression
– Mumps virus enters the nose or mouth
– Replicates in the upper respiratory tract
– Enters the bloodstream to infect salivary glands
• Prevention
– Measles, mumps, and rubella (MMR) vaccine
Many viruses cause gastroenteritis
• The immune system tends to mount a rapid and effective
response to GI-tract viral infections
• These illnesses are usually acute rather than chronic
– Sudden outset of symptoms
– Quickly resolve (usually within a few days)
Rotavirus
• Rotavirus (acute viral gastroenteritis)
• Etiological agent - Rotavirus - RNA virus
• Characteristics
– Leading cause of enteritis in children under five years old
• Transmission
– Fecal–oral transmission
– Contaminated fomites (e.g., doorknobs)
• Complications
– Dehydration
Rotavirus
Table 19.1 Dehydration Signs and Symptoms
• Transmission
– Fecal–oral
transmission
– Contaminated
fomites (e.g.,
doorknobs)
• Complications
– Dehydration
Type
Signs and Symptoms
Mild
Dry mouth and skin
Dehydration Decreased urine; no wet diaper for 3
hours
Little or no tears when crying
Headache
Severe
Extreme thirst
Dehydration Little urination, darker urine
Decreased skin turgor
Sunken eyes, sunken fontanels on
babies
Low blood pressure that may lead to
hypovolemic shock and organ failure
Norovirus
• Norovirus (acute viral gastroenteritis)
• Etiological agent – Norovirus - RNA virus
• Characteristics
– Leading cause of acute viral gastroenteritis in the U.S.
– >50% of all outbreaks occur in long-term-care facilities
• Transmission
– Infectious dose of 20 viral particles
– Feces and vomit spread the virus via the fecal–oral
route
Norovirus
• Signs and symptoms
– Develop within 12–48 hours
– Acute diarrhea and projectile vomiting lasting 36–72
hours
Hepatitis is a liver infection most commonly
caused by three unrelated viruses
• Hepatitis
– Term meaning inflammation of the liver
– Infectious and noninfectious sources
– Primary cause of infectious hepatitis:
 Hepatitis A (Picornaviridae family)
 Hepatitis B (Hepadnaviridae family)
 Hepatitis C viruses (Flaviviridae family)
Hepatitis A:
Foodborne and Waterborne Hepatitis
• Hepatitis A
• Etiological agent
– Hepatitis A virus (HAV) (Picornaviridae family)
– Nonenveloped, single-stranded RNA virus
• Characteristics
– HAV is fairly stable
– Remains infectious for months outside the body
– HAV is inactivated by high temperature
Hepatitis A:
Foodborne and Waterborne Hepatitis
• Transmission
– Fecal–oral route
• Signs and symptoms
– Most children under age 6 are asymptomatic
– Patients older than age 6 have ~70% chance of developing
signs and symptoms:
 Low-grade fever
 Nausea and vomiting
 Abdominal pain
 Fatigue
 Clay-colored feces and jaundice
• Prevention - Vaccine
Hepatitis A:
Foodborne and Waterborne Hepatitis
• Mechanism of disease
– HAV multiplies within intestinal cells
– Virions enter the bloodstream (viremia)
– Infect hepatocytes
– Inflammation develops
– Liver function is impaired
 Bilirubin clearing is limited
 Causes yellowing of the skin
and sclera
Hepatitis B:
Acute and Chronic Infections
• Hepatitis B
• Etiological agent
– Hepatitis B virus (HBV) (Hepadnaviridae family)
– Double-stranded enveloped DNA virus
• Characteristics
– Since 1991, HBV vaccinations have reduced infections
by ~82%
– Chronic HBV affects up to 2.2 million people in the U.S.
Hepatitis B:
Acute and Chronic Infections
• Transmission
– Direct contact with bodily fluids or open sores from an
infected individual (e.g., sexual contact, HBVcontaminated needles, razors, toothbrushes)
– Accidental percutaneous exposures
– Vertical transmission during childbirth
– No evidence of transmission through breastmilk
Hepatitis B:
Acute and Chronic Infections
• Progression
– In up to 10% of patients age 6 and over
 Virus is not cleared
 Establishes a chronic infection
– Children under age 5 are more likely to become
chronically infected than adults
– HBV can cause an acute infection (clears up in a few weeks)
Hepatitis B:
Acute and Chronic Infections
• Complications
– Chronic infection with intermittent inflammation
– Cirrhosis
– Eventual liver failure
– Hepatocellular carcinoma
Healthy liver
Liver cirrhosis
Hepatitis C: The Silent Killer
• Hepatitis C
• Etiological agent
– Hepatitis C virus (HCV) (Flaviviridae family)
– Single-stranded, enveloped RNA genome
– Continually mutates
Hepatitis C: The Silent Killer
• Transmission
– Direct contact with
HCV-infected
blood and bodily
fluids (e.g., shared
HCV-infected
needles)
– Vertical
transmission from
mother to child
Injecting
drug use
Other*
Unknown
Transfusion
(before screening)
Sexual
*Nosocomial: Healthcare work; Perinatal
Hepatitis C: The Silent Killer
• Signs and symptoms
– Early infection is usually asymptomatic
– Chronic infections are not diagnosed until liver
problems begin
• Progression
– 75–85% of patients develop a chronic form of infection
• Complications
– Liver cancer and cirrhosis
Hepatitis C: The Silent Killer
• Treatment
– Up to 20% of patients spontaneously clear the virus
without treatment
– Drug treatment (protease, polymerase, and other viral
protein inhibitor medications)
 90% effective treatment
 Possible severe side effects
• Prevention
– No vaccine
Dental caries are prevalent in children while
periodontal disease is prevalent in adults
• Periodontal disease
– Starts with gingivitis (inflammation of gums)
– May progress to periodontitis
 Further inflammation and eventual erosion of the
bone that surrounds the tooth
 leading cause of tooth loss in adults
• Genera of the oral microbiota:
– Streptococcus and Actinomyces species -first to attach
to the tooth enamel
– Viellonella and Haemophilus may attach next
 Create dental plaque
Ie. Streptococcus mutans)
metabolize sugar
Create acids
Bacteria in plaque
biofilms ferment sugars.
The acid by-products
they release erode tooth
enamel, forming caries.
Caries
As enamel erodes,
the underlying dentin
is damaged.
If left untreated, the pulp
becomes infected and
an abscess may form.
Caries extension
Dentin
Pulp
Inflamed pulp
Swollen
gums pull
away from
tooth
Abscess
Periodontal Disease
• Periodontal disease
• Signs and symptoms
– Tender, swollen gums with a bright red or purplish
coloration
– Gums may pull away from teeth
Swollen gums
Tartar buildup
Recessed gums
Helicobacter pylori can cause gastritis and
stomach ulcers
• Stomach ulcers
• Etiological agent
– Helicobacter pylori
– Microaerophilic
– Gram-negative, curved rod-shaped bacteria
• Characteristics
– CDC estimates ~66% of the world’s population is
infected with H. pylori
Helicobacter pylori can cause gastritis and
stomach ulcers
• Transmission
– Fecal–oral route
• Signs and symptoms
– Many Abdoare asymptomatic
– Symptomatic individuals may develop:
 Belching
 Vomiting
 minal pain due to gastritis
 Stools tinged with blood
• Progression
– Inflammatory response causes ulcers to form in areas
where the stomach lining is damaged by the bacterium
Helicobacter pylori
infects the
mucosal linings of
the stomach to
colonize.
Inflammation
causes tissue
damage and
stomach lining
erosion.
The epithelial layer
of the stomach
becomes exposed
to stomach acid,
and is further
damaged.
Colony
H. pylori
Mucus
layer
Epithelial
cells
Connective
tissue
An ulcer
develops.
Ulcer as
seen by
endoscopy
Ulcer
Bacteria are common causes of
foodborne illnesses
– Norovirus is the most common causative agent
– Bacteria cause a significant proportion of foodborne
illnesses
• Food-borne illnesses can be sorted into:
– Foodborne infection
– Food poisoning (food intoxication)
• Majority of foodborne illnesses are due to fecal
contamination of food or water
Leading Causes of
Foodborne Bacterial Infections
• Most common etiological agents
–
–
–
–
–
Campylobacter species
Shigella species
E. coli
Salmonella
Listeria monocytogenes
Leading Causes of Food Poisoning
– Symptoms are triggered by ingested enterotoxins (a
type of exotoxin)
• They may be emetic (trigger vomiting)
– Causes inflammation of intestinal cells
– Prevents water absorption
– Leads to diarrhea and abdominal pain
• often associated with:
– Prepared foods that require a lot of handling
– Leaving foods at room temperature
– toxins are not affected by heat
Leading Causes of Food Poisoning
Staphylococcus aureus
• Leading causes of food poisoning are:
– Staphylococcus aureus
– Clostridium perfringens
Clostridium perfringens
– Bacillus cereus
– Clostridium botulinum
– Aspergillus flavus
Bacillus cereus
• S. aureus food poisoning
– Linked to creamy salads (e.g., tuna, chicken), dairybased foods, poultry and meat products
• C. perfringens food poisoning
– Commonly found in animal intestines and found on raw
meat
– Most cases linked to gravy and meat products that are
left too long at room temperature
• B. cereus food poisoning
– Spore-forming organism
– Present in soil and can contaminate produce
– Cooking does not always kill its spores
Leading Causes of Food Poisoning (7 of 9)
• Botulism
• Etiological agent
– Spore-forming Clostridium botulinum
• Mechanism of disease
– Exotoxin enters the blood and targets nerves
Campylobacter jejuni is a leading cause of
bacterial foodborne illness
– Campylobacter jejuni
– Gram-negative, flagellated, spiral-shaped bacteria
• Characteristics
– One of the leading causes of foodborne infection in
the U.S. (1.6 million /yr /US
– Often underreported
– Found in the intestinal tract of healthy birds (e.g.,
chickens)
Campylobacter jejuni is a leading cause of
bacterial foodborne illness
• Transmission
– Consuming undercooked poultry
– Contaminating foods with raw poultry juices
• Signs and symptoms
– Diarrhea
– Abdominal cramps
– Fever
– Nausea and vomiting
Campylobacter jejuni is a leading cause of
bacterial foodborne illness
• Mechanism of disease
– Bacteria burrow through the mucosal layer of the
intestine
– Migrate through intestinal epithelial cells
– Multiply beneath the epithelial layer
– Inflammatory response within 2–5 days
• Treatment
– Symptoms usually resolve within a week
Campylobacter jejuni is a leading cause of
bacterial foodborne illness
• Complications
– Guillain-Barré syndrome (GBS)
 Rare autoimmune neurological disease
 Symptoms develop weeks after diarrhea clears
 Begins with a tingling in the legs and feet
 Progresses to paralysis
 Symptoms are temporary, but individuals must be
hospitalized
CLINICAL VOCABULARY
• Hematuria: blood in the urine
• Purpura: a rash of purple spots/bruising caused by red
blood cell lysis and/or capillary destruction rather than by
external physical trauma
• Edema: generalized swelling, often in the extremities, in
response to fluid accumulation in tissues
Various Escherichia coli strains cause
• E. coli pathotypes can be grouped by their O and H
antigens
• Six main E. coli pathotypes are diarrheagenic
– Transmitted via the fecal–oral route
– Some may also cause fever and/or dysentery
• Pathotypes determine:
– Specific symptoms
– Disease severity and length
– Treatment
E. coli O157:H7
• E. coli O157:H7
– Shiga toxin–producing E. coli (or STEC)
• Characteristics
– Most common dysentery-associated serovar in the U.S.
– Resistant to gastric acids
– Deadly outbreaks have been associated with
contaminated hamburgers, unpasteurized juices, and
petting zoos
E. coli O157:H7
• Transmission
– Normal gut microbiota of healthy cattle
– Intestines contaminate ground beef
– Agricultural runoff contaminates vegetables
– Person-to-person transmission
– Infectious dose of 10–100 cells
E. coli O157:H7 (3 of 3)
• Signs and symptoms
– Abdominal pain
– Watery diarrhea followed by bloody diarrhea
– No fever or low-grade fever
• Progression
– Illness typically resolves within a week
• Complications
– Children, elderly, and immune-compromised patients
are at the greatest risk for HUS
Some Salmonella cause common foodborne
gastroenteritis, others cause typhoid fever
• Salmonellosis
• Etiological agent
– Salmonella enterica
– Gram-negative rods
– >2,600 serovars
– Most common diarrheagenic serovars in the U.S. are:
 Enteritidis and Typhimurium
– Serovar Typhi causes typhoid fever
Salmonella enterica Serovars
Enteritidis and Typhimurium (
• Nontyphoid Salmonellosis
• Etiological agent
– S. enterica serovar Enteritidis
– S. enterica serovar Typhimurium
• Characteristics
– Wide array of animals harbor the bacterium in their gut
(e.g., birds, mammals, reptiles)
– Commonly detected in raw chicken and eggs (inside
and outside of shells)
Salmonella enterica
Serovars Enteritidis and Typhimurium
• Transmission
– Poultry products are most likely to harbor Salmonella
serovars that infect people
– Consuming contaminated produce, raw eggs,
undercooked meat or seafood
– Pet reptiles
• Signs and symptoms
– Appear within 1–2 after consuming contaminated food
or water
– Fever, abdominal cramps, and diarrhea lasting 4–7 days
– May progress to dysentery
– Vomiting, chills, and headache are common
Salmonella enterica Serovars Enteritidis and Typhimurium
• Mechanism of disease
– Salmonella bacteria induce endocytosis in intestinal
epithelial cells - allows avoidance of the immune
factors
– Salmonella can escape phagocytosis and multiply
inside macrophages
Salmonella enterica Serovar Typhi
• Typhoid fever
• Etiological agent
– S. enteritidis serotype Typhi
– Typhoid toxin production increases virulence
• Characteristics
– Humans are the only known source and host for the
bacterium
– Rare in the U.S. but common in developing countries
Salmonella enterica Serovar Typhi (2 of 4)
• Transmission
– Human to human
– Sewage contaminated water or food
– Up to 5% of recovered patients become asymptomatic
carriers
 Shed bacteria in their feces
Salmonella enterica Serovar Typhi (3 of 4)
• Signs and symptoms
– Begin 1–2 weeks following exposure
– Fever
– Headache
– Rose-colored spotted rash
– Constipation
– Abdominal pain that can last weeks
– Vomiting is usually absent
Salmonella enterica Serovar Typhi (4 of 4)
• Complications
– Intestinal rupture
– Internal bleeding
– Shock
• Treatment
– Antibiotics (e.g., azithromycin)
• Prevention
– Salmonella Typhi vaccine
End Here
Clostridium difficile increasingly causes
serious, healthcare-acquired infections (1 of 8)
• Clostridium difficile pseudomembrane colitis
• Etiological agent
– Clostridium difficile
– Spore-forming, Gram-positive anaerobe
– Most pathogenic C. difficile strains release two
exotoxins (A and B toxins)
– An emerging strain makes binary toxin
Clostridium difficile increasingly causes
serious, healthcare-acquired infections (2 of 8)
• Characteristics
– ~500,000 develop C. difficile infections per year in the
U.S.
 ~29,000 of them die
– Considered the most common healthcare-acquired
infection
Clostridium difficile increasingly causes
serious, healthcare-acquired infections (3 of 8)
• Transmission
– 75% of cases occur in older people with a history of a
hospital stay or residents of long-term-care facilities
– Fecal–oral route
– Contact with contaminated fomites
– Contaminated hands
Clostridium difficile increasingly causes
serious, healthcare-acquired infections (4 of 8)
• Signs and symptoms
– Usually develop toward the end of an antibiotic
treatment
– Mild cases
 Diarrhea and moderate abdominal pain
– Serious cases
 Severe abdominal pain, fever, nausea, and
abundant watery diarrhea
 May progress to dysentery
 Pseudomembranous colitis
Clostridium difficile increasingly causes
serious, healthcare-acquired infections (5 of 8)
• Progression
– C. difficile forms dormant endospores
– Resist antibiotics
– Normal microbiota are removed via a course of
antibiotics
– C. difficile is given the opportunity to thrive
Clostridium difficile increasingly causes
serious, healthcare-acquired infections (6 of 8)
• Mechanism of disease
– A and B toxins cause an inflammatory response
– Damage the integrity of the colon’s lining
– Form pus-filled pseudomembranous lesions
Pseudomembranous colitis
Healthy colon
Clostridium difficile increasingly causes
serious, healthcare-acquired infections (7 of 8)
• Complications
– Toxic megacolon
 Large intestine loses ability to expel gas and feces
 Becomes distended
 Leads to colon perforation
 Bacteria seep into the abdominal cavity
 Patient may progress to septic shock and die
Clostridium difficile increasingly causes
serious, healthcare-acquired infections (8 of 8)
• Treatment
– Probiotics
– Fecal transplants
• Prevention
– Limit unnecessary antibiotic prescriptions