Bacteriology of the Colon Flashcards
Gut bacteria that can cause systemic disease
Listeria
Salmonella Typhi/non typhoidal salmonella serotypes
Pathogens that invade cells/ cause inflammation/intoxicate
Shigella
Enterohemorrhagic E. Coli
Campylobacter/Helicobacter
Bacteria whose pathology and symptoms are due to exotoxin production
Vibrio Cholerae
What are the sites of terminal digestion and absorption of nutrients
The mucosal villi and crypts lined by a single layer of columnar epithelial cells
What absorbs most of the water from chyme
The large intestine (90%)
Differences in absorption between small and large intestine
In large intestine, villi are absent, and the colonic mucosa is full of Crypts of Lieberkhun
Fluid Balance
How many Liters of fluid enter the upper gastrointestinal tract each day?
What is the the average daily fecal excretion?
8.5 L
150mL
Infections alter normal intestinal physiology in one of three ways:
- Penetration through an intact mucosa
- Inflammatory or cytotoxic destruction of the ileal or colonic mucosa
- Shift in bidirectional water and electrolyte fluxes in the upper small bowel by intraluminal toxins or minimally invasive organisms
Barriers to invading pathogens (6)
- Epithelial barrier and intestinal motility (epithelium continuously regenerating)
- Structural barrier (Tight cell junctions)
- Chemical barrier (Gastric acidity)
- Paneth cells (Secrete antimicrobial peptides)
- Adaptive immunity (Mucosal associated lymphatic tissue)
- Microbial recognition (Pattern Recognition Receptors)
5 Take home points about normal microbiota
- Neonates are colonized following delivery
- Colonization drives the maturation of the mucosal immune system
- Intact microbiota monopolizes physical and nutritional niches at the mucosal surface
- Normal microbiota contributes to nutrient acquisition by fermenting non-digestible dietary components, contributing to normal growth and differentiation
- Normal microbiota provide powerful host defense mechanism to limit the ability of pathogens to take up residence and invade the human body
Listeriosis
Aerobic non spore forming Gram positive rod
Listeriosis
Human Pathogen:
Growth range:
How it enters the body:
Human Pathogen: L. monocytogenes
Growth range: 1-45° and high salt concentrations
How it enters the body: Penetration through an intact mucosa to the reticuloendothelial system
Listeriosis is restricted to well defined populations:
- Neonates
- Elderly
- Pregnant Women
- Persons with defects in cellular immunity
Listeria pathogenesis
- Ingest contaminated food
- L. monocytogenes are able to survive in stomach acid and bile salts
- Adherence to host cells
- Entry into enterocytes or M cells in Peyer patches
- Phagosome is initially intact
- pH drop in the phagosome activates listeriolysin O and 2 different phospholipase C enzymes
- Bacteria replicate free in cytoplasm
- ActA located on one pole of the bacterium polymerizes host actin allowing intracellular movement to membrane
- Actin polymerization pushes the bacterium to uninfected cells and the cycle begins again
- Systemic infection - passage through the intestinal lining, entry into macrophage and spread
Listeria - Epidemiology
Human listeriosis is sporadic
Undercooked processed meats, unpasteurized milk, contaminated cheese…
Can be isolated from the feces of animals
Can grow inside of wide range of temperatures
Human to human transmission of Listeria occurs from _____ to ____ in _____
mother; child; utero
Lysteria Clinical Diseases
Neonatal:
Pregnant Women:
Adults:
- Neonatal disease
Early onset disease acquired in utero - abortion, stillborn or premature birth
Granulomatosis infantiseptica = granuloma formation in multiple organs
Late onset disease -2-3 weeks after birth - characterized by meningitis - Pregnant women (third trimester - influenza-like)
- Adults
Healthy - mild influenza like illness
Immunocompromised - meningitis
Listeria - Laboratory Diagnosis
Gram stain of CSF for meningitis patients
Culture - 1 to 2 days - cold enrichment
Biochemical Tests
Serologic tests - 13 serotypes
Listeria - treatment, prevention, control
Ubiquitous in environment so control is difficult
No vaccine
Combination treatment = gentamicin with penicillin
Naturally cephalosporin resistant
Salmonella:
Method of Entry:
- Gram negative rods, found in soil ,water, normal intestinal flora
- Method of Entry: Penetration through an intact mucosa
- Inflammatory or cytotoxic destruction of the ileal or colonic mucosa
Serotyping schemes to identify individual salmonella isolates
H antigen = flagellar proteins
K or Vi = capsular antigens for E. coli and S. typhi, respectively
O antigens = Lipopolysaccaride
Salmonella does not ferment _________
lactose
Salmonella Pathogenesis
- Broad host range EXCEPT for Typhi and Paratyphi
- Salmonella can resist stomach acid; attach to the mucosa of the small intestine and invade into M cells and enterocytes
- Replicates within endocytic vacuoles
- Endocytic vacuoles are modified and stabilized by the injection of bacterial proteins through two type III systems = spacious vacuole
Pathogenicity Island 1 genes = ______
Pathogenicity Island 2 genes = ______
invasion; evasion of immune response
Gastroenteritis due to Salmonella
- Infection and replication induces an inflammatory response
- Disruption of the enterocytes and malabsorption
- Release of prostoglandins, stimulation of CAMP and fluid secretion
Pathogenesis of Enteric or Typhoid Fever
- Bacteria invade cells and replicate as in gastroenteritis
- Typhi also replicates in macrophages and spreads through the reticuloendotheilal system to liver, spleen, blood and bone marrow
- Bacteremia causes the fever and may lead to localized suppurative infections or in rare cases perforation of the intestine
Gastroenteritis to salmonella Epidemiology (6)
- Ingestion
- Incidence is greatest in children (under 5) and adults (older than 60)
- Occurs most frequently during the summer months
- Common food sources include poultry, eggs, dairy products, ground beef
- Nontyphoidal US infections > 1.4 million with 600 deaths/year
- Infectious dose is high (10^6 - 10^8 bacteria)
Typhoid or Enteric Fever Epidemiology
- Relative to strains causing gastroenteritis, the inoculum for Typhi is low
- Transmission person to person and through fecal contamination
- Enteric fever is endemic to India, South/Central America, Africa
- Travelers should be vaccinated when going to endemic areas
Salmonella outbreaks in children can occur with the introduction of _____
PET TURTLES!
Salmonella clinical diseases:
S. Gastroenteritis:
S. Septicemia:
Enteric Fever:
- S. Gastroenteritis: Symptoms - 6 - 48 hours after consumption of contaminated food (fever, cramps, headache, nausea, vomiting) - persists for 7 days but self limiting
- S. Septicemia: ALL SALMONELLA SPECIES CAN CAUSE A BACTEREMIA
- Immunocompromised patients at risk for septicemia
- Enteric Fever:
10-14 days after ingestion - gradual fever, headache, myalgias, anorexia, rose spots - After bacteremic phase gastrointestinal symptoms occur: colonization of gall bladder and reinfection of the intestines
Mary Mallon - Typhoid Mary
- First person identified in US as asymptomatic carrier of S. Typhi
- She was a cook - infected 51 people, three of whom died
- Typhoid fever was traced to the places where she worked
- Arrested and quarantined
She died of pneumonia and complications of a stroke
Salmonella - Laboratory Diagnosis
- Stool culture - must use selective medium to recover salmonella versus normal flora
- Lactose negative, motile, makes H2S, other differential biochemical tests
- Epidemiological investigations use pulsed-field electrophoresis
Salmonella - Treatment, Prevention, Control
- Symptomatic relief but no antibiotics for Salmonella gastritis
- Careful food preparation and storage, hand washing
- Ampicillin, trimethoprim-sulfamethoxazole for systemic infections
Traveler vaccinations for Salmonella
Live attenuated vaccine Ty21a: good for 5yrs, 6 capsules every other day, booster at 4 yrs, not recommended for children
Typhim - Vi polysaccharide capsular vaccine, not recommended for children under 2 years of age
Shigella Characteristics
- Family member of the Enterobacteriaceae (Gram negative)
- Non motile (no flagella), does not ferment lactose, no capsule
- Infectious dose is low, easily spread person to person by the fecal oral route
- 4 recognized biogroups - dysenteriae, flexneri, boydii, sonei
Shigella -
4 recognized biogroups
dysenteriae, flexneri, boydii, sonei
Shigella - Pathogenesis
- Shigella replicate intracellularly in the colon
- They invade M cells in Peyer patches and initially colonize the small intestine
- Bacteria inject type III “effectors” into cells to instruct the cytoskeleton to engulf them
- The effectors are called Invasion Protein Antigens or IpaA, IpaB, IpaC and IpaD
- Once inside of host cells the bacterium lyses the vacuole and replicates free in the cytoplasm
- Similar to Listeria, Shigella polymerize host actin to move to the membrane to penetrate uninfected cells
- Shigella induce apoptosis in phagocytic cells which leads to a release of IL-1β resulting in intense inflammatory response
Shigella - Toxins
Ipa proteins - induce bacterial uptake - injected by the type III secretory system
Shigella secrete Shiga toxin
- Exported by a type II secretory pathway
- Shiga toxin is a typical A:5B toxin
*B = recognizes the host glycolipid GB3
*A = enzymatic activity of the toxin; cleaves 28S ribosomal RNA disrupts protein synthesis and colonic epithelium dies and cells and mucous are lost from the large intestine
____ are the only reservoir for Shigella
______ is a pediatric disease (60% of cases in children under 10
Humans
Shigellosis
Shigella Transmission
Infectious dose is low (100-200 bacteria) so person to person transmission is easy through fecal-oral route
Shigella - Clinical Disease
Incubation period after ingestion 1-3 days Symptoms - Abdominal cramps - Tenesmus or straining to defecate - Diarrhea - Pus and blood in stools - Neutrophils and mucous in stool
Dysentery
Term coined by Hippocrates to describe the frequent passage of stool containing blood and mucous
Shigella laboratory Diagnosis
- Lactose negative colonies on selective medium (colorless as opposed to pink colonies on MacConkey agar)
- Shigella is NOT motile while salmonella is flagellated and motile and Shigella does not produce H2S
Shigella - Treatment, Control and Prevention
- Mild infections are usually self limiting
- Antibiotic treatment may shorten illness but are only used for severe illness
- Antidiarrheal agents such as loperamide or diphenoxylate with atropine can make illness worse
- In presence of antidiarrheal agents, Shiga toxin is not flushed from the system, leading to more extensive cell death and inflammation
Enterohemorrhagic E. Coli (EHEC) - Characteristics
Family member of the Enterobacteriaceae (Gram Negative)
Infectious dose is low (100-200 bacteria) - spread person to person by fecal oral route
Member of the family of pathogenic E. coli
EHEC pathogenisis
Culture filtrates from these bacteria were cytotoxic to Vero cells
Toxic activity could be neutralized with antibodies to Shiga toxin
Produce a distinct histopathology called attaching and effacing lesions
EPEC = EHEC that do not synthesize Shiga toxins
Alterations in the cellular cytoskeleton due to bacterial type III secretion
EHEC also injects a protein called Tir
Bacteria grow in place and release shiga toxin
Tir
EHEC protein that integrates into the mammalian cellular membrane and binds tightly to a bacterial outer membrane protein called intimin
Shiga toxins are encoded on lysogenic bacteriophage in E. Coli (2 types)
Stx-1 = Shiga toxin Stx-2 = 60% homology to Shiga toxin (A:5B)
Shiga toxin
Stops host protein synthesis by cleaving host ribosomal RNA
Binds to cell with GB3 receptor
Strains expressing both toxins are more virulent
Stimulate the expression of inflammatory cytokines
EHEC epidemiology
EHEC associated with certain H and C serotypes
Certain serotypes may be selected for in the intestinal tract of cattle
Undercooked beef, meat, cattle feces
EHEC clinical diseases
Hemorrhagic colitis:
Hemolytic uremic syndrome (HUS):
Hemorrhagic colitis: Characterized by severe abdominal pain and bloody diarrhea that occurs 3-4 days after ingestion of contaminated food
Hemolytic uremic syndrome (HUS): Occurs in children under 10 years of age - acute renal failure; thrombocytopenia; microangiopathic hemolytic anemia
*vomiting in about 50% of patients
EHEC laboratory diagnosis
Culture - differential identification based on the inability to ferment sorbitol
EHEC is colorless and normal
Look for certain serotypes associated with HC or HUS
Immunoassays to detect the presence of Stx-1 or Stx-2
EHEC treatment, prevention and control
Treatment consists of supportive care
Monitoring of the development of microangiopathic complications (HUS)
Antiperistaltic agents increase the risk of systemic complications
Antibiotic therapy is generally not beneficial - may increase shiga toxin production and release
Careful cooking of food
Campylobacter: Physiology and Structure
Gram negative curved rod
Microaerophilic, can grow at 42°
Non-fermentative
Motile with single flagellum at one or both poles
Major isolates of Campylobacter associated with human disease
C. jejuni
C. upsalensis
C. coli
C. fetus
Campylobacter pathogenisis
- Inflammation - gastrointestinal infections produce histologic damage to the mucosal surfaces of the jejunum, ileum and colon
- Infection is associated with the development of autoimmune disorders (Guillan-Barre syndrome; reactive arthritis)
- Other than LPS and antigenic cross-reactivity, one toxin has been discovered that stops cell division - cytolethal distending toxin (cdt)
Campylobacter Epidemiology
Infections are associated with the consumption of contaminated food, particularly chicken
Not a reportable disease - difficult to grow and identify bacteria
Highest isolation rates of Campylobacter are in ______ and ______ _____
Summer and early fall
Campylobacter clinical diseases
Acute enteritis:
Extraintestinal infections:
Acute enteritis: Gastrointestinal infection characterized by bloody stools, inflammation, ulcerated mucosa, diarrhea
Extraintestinal infections: C. fetus in compromised patients - resistant to serum antibody and complement killing
Campylobacter - laboratory diagnosis
Microscopy - darting motility in fresh fecal samples
- S shaped organism in stool
- Presence of RBCs and WBCs in stool
Antigenic detection
Culture - difficult - slow growth; microaerophilic
Campylobacter - Treatment, Prevention and Control
Treatment recommendations - Fluid replacement as long as diarrhea lasts
Severe cases are treated with azithromycin or erythromycin
Severe infections include: high fever; bloody stool; symptoms lasting over 1 week
Helicobacter - Physiology and Structure
Gram negative curved rods Multiple polar flagella, highly motile Microaerophilic Produce a powerful urease enzyme that converts urea to NH3 and CO2 Difficult to culture and isolate
Helicobacter - pathogenesis
Gastric colonization can be lifelong so part of the pathogenesis involves survival in this extreme environment
- Urease expression allows the bacterium to survive in acidic gastric juice
- They swim through the mucus using flagella
- They adhere to the gastric epithelium via specific receptors that include the Lewis blood-group Ags and laminin
- pH at the epithelial surface is 7.0
Helicobacter - pathogenesis
The production of ______ ______ in humans in strongly correlated with the possession of ___ genetic loci
Peptic ulcers; two
VacA (Helicobacter)
A multifunctional toxin
- Forms anion specific channels
- forms large vacuoles in cultured cells
- alters tight junctions
- induces gastric epithelial erosion in animal models
Second locus associated with peptic ulcers (Helicobacter)
Second locus encodes many genes including:
Specialized secretion system called a type IV secretory system
This secretion system injects CagA which induces IL-8 release - also induces pedestal formation
Other products also enhance IL-8 transcription in epithelial cells
Helicobacter pathogenesis
Urease:
Flagella:
Adhesins:
Urease: secretion to survive in gastric juice
Flagella: allows them to propel into mucus layer and to reach the gastric epithelial cells
Adhesins: allow bacterium to stick to the apical region of epithelial cell
Heliobacter - Epidemiology Reservoir: Transmission: Highest Incidence: Asymptomatic: Increased risk: Associated diseases:
Reservoir: Humans only
Transmission: fecal-oral route
Highest Incidence: Developing countries
Asymptomatic: 70-80% of infected individuals
Increased risk: Persons with gastritis, gastric ulcer or duodenal ulcers
Associated diseases: infection is also associated with gastric adenocarcinoma and gastric B-cell lymphomas
Helicobacter - Clinical diseases
Gastric Helicobacters:
Enterohepatic Helicobacters:
Clinical outcome depends on site of colonization
Gastric Helicobacters: H. pylori; gastritis, peptic ulcer, gastric adenocarcinoma, gastric mucosa-associated lymphoid tissue (MALT) B-cell lymphomas
Enterohepatic Helicobacters: Isolates from homosexual men with procititis, proctocolitis, or enteritis
A chronic inflammatory response to Helicobacter may contribute to the development of ______
cancer
Helicobacter - Laboratory Diagnosis
- Urea breathing test
- Histologic examination of gastric biopsy
- Biochemical detection of urease activity from gastric biopsy
- Detection of H. pylori antigens from stool samples
Helicobacter - Treatment, Prevention and Control
Recommended treatment: Proton pump inhibitor + macrolide + β-lactam
NO vaccine - not sure whether eradication is good
Vibrio
Structure:
Important human pathogens:
Structure: Gram negative curved rods
Important human pathogens:
- Vibrio cholerae serogroups 01 and 0139 - produce cholera toxin
- Vibrio vilnificus - associated with wound infections and septicemia
- Vibrio parahaemolyticus - gastroenteritis, wound infection, septicemia
Vibrio - Physiology and structure
Curved rods with single polar flagella Require NaCl for growth Oxidase positive Toxin co-regulated pili Serogroups are based on LPS
Vibrio serotypes
Serotypes O1 and O139 produce cholera toxin and are associated with epidemic disease
Serotype O1 is subdivided into Classical and El Tor biotypes
- Current pandemic is due to El Tor
Vibrio pathogenisis (Cholera toxin)
Cholera Toxin is an A:5B protein
Cholera toxin and Labile toxin (ETEC) are structurally and functionally similar
Toxins bind ganglioside receptors on intestinal epithelial cells = GM1
The A subunit ADP-ribosylates the G protein and induces cAMP production
Camp stimulates the CFTR inducing Cl- secretion, inhibiting NaCl absorption and causing water efflux - tremendous loss of water
Other factors encoded on Vibrio phage
TCP = Toxin coregulated pilus; used by bactera to adhere to the mucosal epithelium and used by the phage to infect the bacteria
Chemotaxis proteins - also used for adherence to host epithelial cells
Zona Occludens toxin (ZOT) - disrupts tight junctions
Accessory cholera enterotoxin (Ace) - increases fluid secretion
Why is Vibrio pathogenesis hard to prevent?
The expression of toxins prevents the development of live attenuated vaccines
Vibrio epidemiology
Vibrio grows in nature in estuarine and marine environments
Pathogenic vibrios infect shellfish
Asymptomatic individuals can shed the organism
Cholera is transmitted by contaminated water and food
Infectious dose = approximately 10^8 with normal stomach acid levels
Vibrio clinical diseases:
V. Parahaemolyticus:
V. Vulnificus:
2-3 days after ingestion, abrupt onset of watery diarrhea and vomiting
DIarrhea becomes colorless and odorless and contains small specks of mucous = rice water stool
Dehydration, cramps, metabolic acidosis
Mortality rate can be 60% if untreated
V. Parahaemolyticus: gastritis ranging from mild to severe
V. Vulnificus: wound infection/septicemia
Vibrio laboratory diagnosis
Microscopy - curved gram-negative rods in large numbers in stool material from wound infections
Culture - Relatively easy to isolate in the laboratory; confirmation by a relatively small number of biochemical tests
Vibrio treatment, prevention and control
- Fluid electrolyte replacement
- Antibiotics can reduce toxin production and decrease transmission
- Improvements in sanitation
- Vaccines
- Formalin inactivated whole cell vaccine (IM)
- Dukoral given PO - also given for travelers diarrhea due to ETEC
Dukoral
Heat and formalin killed O1 classical and El Tor strains - IgA response prevents colonization
Non-toxic B subunits - IgA response prevents toxin binding
Klebsiella Pneumonia Resistant to Carbapenems (CRKP) and Carbapenem resistant Enterobacteriaceae (CRE)
Cephalosporins and Carbapenems are antibiotics usually reserved to treat the sickest patients
Difficult to control, can be fatal in up to 40% of cases
Family of Pathogenic E.Coli (5):
- Enterotoxigenic E. coli (ETEC) - Labile toxin (LT‐1) and stable toxin (STa)
- Enteropathogenic E. coli (EPEC) - attaching and effacing lesion
- Enteroinvasive E. coli (EIEC) - like Shigella, invasive, inflammatory
- Enteroaggregative E. coli (EAEC) - adherence, colonization
- Uropathogenic E. coli (UPEC) - fimbrial adherence, UTI
