Bacterial GI Pathogens Flashcards
Epidemiology of Pediatric Diarrheal Diseases
1.7 billion cases of childhood diarrheal diseases each year
Leading cause of malnutrition in children <5 years old
2nd leading cause of mortality in children <5 years old
Secretory Gastroenteritis
Proximal small intestine
Watery diarrhea
No fecal leukocytes
Mechanism: enterotoxin (produced in or affecting intestines) or bacterial adherence/invasion causes shift in water and electrolyte excretion/adsorption
Classic pathogens: Vibrio cholerae ETEC Clostridium perfringens Staphyloccocus aureus Bacillus cereus
Inflammatory Gastroenteritis
Colon (large intestine)
Dysentery
Fecal polymorhonuclear leukocytes
Bacterial invasion or cytotoxins cause mucosal damage that leads to inflammation
Classic pathogens: Shigella EHEC Salmonella (not S. Typhi/Paratyphil) Campylobacter
Invasive Gastroenteritis
Distal small intestine
Enteric fever (Typhoid fever)
Fecal mononuclear leukocytes
(if a patient has diarrhea)
Bacteria penetrate mucosa and invade the reticuloendothelial system
Classic pathogens:
Salmonella S. Typhi/Paratyphil
Yersinia enterocolitica
Enterobacteriaceae
Enteric bacteria or Enterics
Ubiquitous (GI, soil, plants): simple nutritional requirements
Primary pathogens
Opportunistic pathogens
Gram-negative rods Non-sporeforming Facultative anaerobes Growth on McConkey agar Ferment glucose Reduce nitrate Catalase-positive Oxidase-negative
Clinical significance?
Sorbitol MacConkey (SMAC)
Used for Gram- enteric rods
Contains bile salts and crystal violet to SUPPRESS Gram+ bacteria
Lactose+ (pink/purple) [E. Coli, Klebsiella]
Lactose- (colorless) [Salmonella, Shigella, Proteus]
Escherichia coli
Agent for:
Diarrhea, UTI, meningitis, HUS, septicemia, pneumonia
Different strains associated with different diseases
Serotype classification useful in epidemiology: Somatic O antigen Flagellar H protein Capsular K antigens Ex. E. coli O157:H7
Virotypes based on virulence factors present in a particular strain
Ferments lactose
Etiology and symptoms of HUS
Hemolytic Uremic Syndrome
Occurs in 10% of children <10 years old who are infected with EHEC
Death occurs in 3-5% of HUS patients
Toxemia affecting the kidney
- Destruction of glomerular endothelial cells
- Decreased glomerular filtration
- Acute renal function
Anemia, thrombocytopenia, acute renal failure due to microthrombi forming on damaged endothelium
> Mechanical hemolysis > Platelet consumption > Decreased renal flow
Enterohemorrhagic E. coli (EHEC)
- O157:H7 (colonizes cattle intestinal tract)
Most common type of serotype in US - Consumption of undercooked Hamburgers, unpasteurized milk, apple cider, municipal water, raw, leafy veggies
- Low ID (low inoculum) 100 bacteria is sufficient
- Adhere to Large Intestinal Cells
- Mild diarrhea 3-4 days after incubation, Hemorrhagic colitis within 2 days after mild diarrhea
- Common causative agent for HUS by directly activating platelet aggregation
- No antibiotics; electrolyte and fluid maintenance
Hemorrhagic, Hamburgers, HUS
EHEC Virulence Factors
Virulence factors transmitted by bacteriophages: take the virulent and spread to non-virulent colonies
Inject shiga toxins
- LEE Pathogenicity Island:
Locus of Enterocyte Effacement
T3SS (type 3 secretion system)
Intimin adhesion (A/E factor) - A1B5 toxins
B subunits bind to Gb3 glycolipid on intestinal villus and renal endothelial cells
A1 subunit binds to 28s rRNA and disrupts protein synthesis
{Stx1 = almost identical to Shigella shiga toxin
Stx2 = associated with HUS}
Enterotoxigenic E. coli (ETEC)
- From fecally contaminated food or water
- Traveler’s diarrhea in adults and potentially fatal diarrhea in children
- High ID (have to consume a large amount of contaminated food/water)
- Adhere to Small Intestinal mucosa
- Cramps, nausea, watery diarrhea, vomiting (rare)
- No antibiotics; electrolyte and fluid maintenance
- 1-2 day incubation, 3-4 day persistence
Pathogenesis: due to enterotoxins
No histological changes or inflammation
ETEC Virulence Factors (Adhesins and Exotoxins)
Type 1 pili
1. Fimbriae:
Colonization factor antigens (CFAs)
Located on plasmids
- Heat-labile (LT) {can be altered at high temps} or stable (ST) toxins
Genes found on same plasmids as CFA genes
LT and ST; LT is 75% similar to cholera toxin, with the same mechanism of action
ETEC Heat-labile toxin
Heat-Labile Toxin (LT-1)
A1B5 toxin and homologous to cholera toxin
- B subunit binds host GM1 molecule expressed by small intestinal mucosal cells (glycolipid/ganglioside receptor)
- A subunit activated by cleavage upon entry
- Locks adenylate cyclase in ON state
- cAMP levels INCREASE
Affects transport of Na+ and Cl- and causes ION IMBALANCE
ETEC Heat-stable toxin
Methanol-soluble ST (STa)
Family of SMALL PEPTIDE toxins
1. Binds and activates host guanylate cyclase (GC)
2. cGMP levels increase
3. Affects many cellular functions including ion transport
EPEC
- Watery diarrhea in children <5, fever, nausea, vomiting
P=pediatrics - Small intestinal cells
Attachment and effacement like EHEC
Adheres to apical surface, flattens villi, prevents absorption - No toxins produced
- No antibiotics; electrolyte and fluid maintenance
EAEC
- Persistent diarrhea in children <5
- Small intestinal cells
Autoaggregation “stacked bricks”
Minimal mucosal damage, bacteria form adherence lesions > deformed vili> malabsorption - Shiga-like toxin, hemolysin
Mucus secretion > biofilm formation - No antibiotics, electrolyte and fluid maintenance
- Contaminated food/water
- Diarrhea in developing countries, common in children
DAEC
- Watery diarrhea in children <5
- Small intestinal cells
Elongation of microvilli
Adhere over entire surface of epithelial cells -more diffusely (vs stacked bricks like in EAEC) - No antibiotics, electrolyte and fluid maintenance
EIEC
- Mild form of dysentery
Fever, cramping, watery diarrhea, blood, mucus - LARGE intestinal cells
Facultative intracellular pathogen
Cell to cell spread via actin polymerization
Epithelial cell destruction > inflammatory infiltration > colonic ulceration
- VF: Invasion genes on plasmid
- No antibiotic
**Related to Shigella, but require higher inoculum because aren’t pH resistant
DO NOT produce Shiga toxin
E. Coli Prevention and Treatment
Avoid contaminated foods and water
No medium to rare burgers
Fluid and electrolyte maintenance
HUS: dialysis and blood transfusions
Antibiotics not normally use since infections are mostly self limited (resolved without treatment)
Strains usually resistant to multiple drugs
Salmonella
- Gram- bacilli in Enterobacteriacea family
S. typhi and S. parathypi; non-typhoid
Salmonellosis
1. Contaminated food (poultry, eggs) causes S. typhimurium
- Very small inoculum
- Virulence factors and toxins - mucosal damage
T3SS
Flagellin activates TLR5 > inflammation
LPS activates TLR4 > inflammation - Nausea, vomiting, non bloody diarrhea 6-48 hours after ingestion
Progression to severe abdominal pain and bloody diarrhea, Gastroenteritis, Septicemia, Enteric fever - Self-limited; Symptoms last 2-7 days before spontaneous resolution
Commensals of a wide variety of domestic and wild animals
Common cause of diarrhea in US
DNA hybridization: strains are closely related
> 2400 O serogroups; variations in the distal end of the LPS
Biochemical tests:
Lactose-negative (in contrast to E. coli; unable to ferment lactose)
Salmonella Typhoid (Enteric) Fever
- Caused by S. typhi or S. paratyphi
Encapsulated (by the Vi antigen used in one vaccine formulation) - Humans are the only host
- Low ID: person to person spread
- Asymptomatic carriers “Typhoid Mary”
- Incubation 1-3 weeks
- Gradually increasing fever, anorexia, headaches, myalgias (muscle pain), constipation
- Systemic disease may precede gastroenteritis
Salmonella Virulence factors
Fimbrial adhesions, some encoded by plasmids
Facultative intracellular, replicates in phagosome
2 x T3SS: encoded by two separate pathogenecity islands (SPI-1 internalization, and SPI-2 block of phagosome-lysosome fusion)
Other SPIs - Mg2+ transporter (intravacuolar growth)
Protection against:
- Intracellular killing: superoxide dismutase (on lysogenic phage) and catalase
- Stomach acid: acid tolerance response (ATR)
Endotoxin
Membrane ruffles
Endotoxins vs endotoxins
An exotoxin is a toxin secreted by bacteria. An exotoxin can cause damage to the host by destroying cells or disrupting normal cellular metabolism. They are highly potent and can cause major damage to the host. Exotoxins may be secreted, or, similar to endotoxins, may be released during lysis of the cell.
Salmonella: Treatment and prevention
S. Typhoid usually requires antibiotics and vaccines: 1. Antibiotic Ciprofloxacin Levofloxacin Azithromycin (Asian) Cefriaxone (Asian) Carbapenem (critically ill)
- Vaccinations
Heat killed
Capsular Vi antigen
Live attenuated strain (TY21a)Proper handling of foods
Shigella
Four species:
S. sonnei: industrial world
S. flexneri: developing world
S. dysenteriae: most severe infection
- Gram- in Enterobacteriaceae family
- Contaminated food/water, person to person; fecal oral
- Low ID <200 to establish infection (very small inoculum)
- Humans are the only reservoir
- Invade mucosal cells, proliferate, cause mucosal damage (T3SS) - intracellular growth
- Mucosal ulcers may form pseudomembranes
- Resistant to gastric acid (survive low stomach pH)
- Diarrhea, dysentery, fever, ab pain, prolonged course; common cause of diarrheal death in children
- HUS from Shiga toxin
- Non-motile, lactose negative
Shigella diseases
- Shigellosis:
Gastroenteritis incubation 1-3 days
Watery diarrhea>ab cramps with bloody stools and tenesmus
2. Dysentery: Mostly caused by S. dysenteriae Frequent passage of small volume of bloody, mucous stools and tenesmus Causes seizure in children <2 years Some strains cause HUS
Post infection sequelae: Reiter’s syndrome (arthritis, conjunctivitis, urethritis)
Shigella Pathogenesis
- Orally ingested bacteria survive low stomach pH
- Taken up by M cells only (microfold)
- Escape from vesicle
- Phagocytosis into macrophage
- Entry into epithelial cell
- Escape from vesicle
- Actin transport into next epithelial
Shigella Virulence factors and toxins
- T3SS-mediated invasion (plasmid)
Important effectors cause macrophage apoptosis, endocytosis, phagosome lysis - Shiga toxin: cause host cell damage and death
Causes HUS
B binds GB3, A1 inactivates 60s ribosomal subunit
Hemolysin: vacuolar escape (pore forming toxin)
intracellular spread via actin polymerization (ICS)
Shigella Treatment and Prevention
- Appropriate environment and personal hygiene
- Rehydration for mild to moderate shigellosis
- Antibiotic treatment for bloody diarrhea and dysentery
DOC:
Ciprofloxacin
Levofloxacin
Ceftriaxone
Virbrio cholerae (Cholera)
S Asia (indian subcontinent), Gulf of Mexico
Contaminated water; small inoculum
Non-invasive, minimal mucosal changes
Vomiting, watery diarrhea, massive fluid loss
“Rice water stools”
Dehydration, hypovolemic shock, death
Oral rehydration key to recovery
NOt common in US
Rotavirus
- dsRNA virus, encapsulated
- Common cause of diarrheal mortality in CHILDREN worldwide
- Protection by maternal antibodies in first 6 mo of life
- Vaccine available (2 oral)
- Contaminated food/water; person to person
Fecal oral - Small inoculum
- Short incubation period
- Nausea, vomiting, watery diarrhea, ab pain, low grade fever
- Destruction of mature enterocytes with loss of absorptive surface
- Infection of mucosal cells of small intestines
Norovirus
- ssRNA of Caliciviridae
- MOST common cause of acute gastroenteritis in US; second most common cause in severe diarrhea among children
- Contaminated food/water; person to person; fecal oral
- Low inoculum
- Cruise ships, schools, camps, hospital
- Short incubation period
24-72 hours then recovery - Nausea, vomiting, watery diarrhea, ab pain
Low grade fever - Mild mucosal abnormalities/bowel
- Self-limited, could lead to intermittant diarrhea w nutritional disturbances if not cleared
No vaccine
Salmonella Pathogenesis
- Attachment (fimbriae), membrane ruffling (SPI-1 T3SS effectors), phagocytosis
- Block of phagosome-lysosome fusion (SPI-2 T3SS effectors) and intravacuolar growth
- Host cell death and spread to adjacent epithelial cell and lympoid tissue
- Inflammatory response, release of prostaglandins, stimulation of cAMP, diarrhea
OR
S. typhi:
3. Taken up by submucosal macrophages
- Transported to liver, spleen, bone marrow, replication, release
- Gallbladder infection > reinfection of intestines
Adenovirus
- DNA non enveloped virus
- Military uses vaccines
- Fecal oral or direct inoculation
- Attaches to cell then penetrates, uncoats, DNA migrates in; New virions are released with cell lysis
- Pharyngitis, respiratory disease, conjuctivitis, hemorrhagic cystitis, nonbloodly diarrhea
CMV
- DNA enveloped
- Saliva, semen, cervical, blood and organ TRANSPLANTation
- Oral, esophagus, bowel, liver (mononucleosis syndrome)
- Can be asymptomatic
Enters latent stage in monocytes and can be reactivated - After early protein synthesis, viral DNA polymerase replicates genome, DNA and late protein synthesis start
- Structural proteins assemble virion which buds through the nuclear membrane and exits via tubules
- Retinitis, esophagitis, mononucleosis, colitis, pneumonitis, systemic disease with fever, BONE marrow suppression
- 80% of adults have been infected; acute disease can transmit fetal disease; likely reactivation
Mumps
- RNA enveloped
- Vaccination lasts >10 years
- Oral (parotitis)
- Soluble Ag can be detected by complement fixation
EBV
- Enveloped DNA
- Oral (hairy leukoplakia, pharyngitis), liver (mononucleosis syndrome), cervical adenopathy (lymph nodes in neck)
- Viral capsid antigen
- Infects mainly B lymphocytes and epithelial cells of throat
- 90% of Americans have antibody to EBV. Associated with hairy leukoplakia and cancers
Coxsackie Virus
- Fecal oral or respiratory transmission
- Oral herpangina
Hand Foot Mouth - Virion enters cell, uncoats, mRNA translated to large polypeptide cleaved and forms capsid + noncapsid proteins
Complementary RNA strands formed and RNA is coated with capsid proteins which are released at cell death
A: Herpangina (blistered legions in back of throat), Conjuctivitis
B: Myocarditis, pericarditis, pleurodynia, aseptic meningitis
No vaccine
Ancyclovir
- Anti-herpes
- Inhibition of viral Genome Replication
- Oral, IV or topical
- Guanosine analogue; activted by viral thymidine Kinase (TK)
Initial phosphorylation requires viral kinase. Acyclovir is substrate for viral polymerase. Incorporation of acyclovir causes chain termination and inhibition of DNA polymerase. TK- viruses resistant - Manage/suppress (cannot cure) HSV 1 and HSV 2. Given to transplant patients for prevention
Valacyclovir
- Anti-herpes
- Inhibition of viral Genome Replication
- Dosed twice a day instead of 3-5. More expensive
- Pro-drug. Cleaved by esterases to yield acyclovir
- Treat HSV 1 and HSV 2. Same effect as acyclovir, but more expensive and requires less dosage
Ganciclovir
- CMV Treatment - IV
- Inhibition of viral Genome Replication
- Myelosuppression (25-40% of patients)- bone marrow suppression
- Requires phosphorylation by viral specific enzyme. Doesn’t have thymidine kinase like HSV so acyclovir doesn’t work. CMV gene codes for phosphotransferase that converts ganciclovir to a monophosphate
Then enzymes in infected cell convert monophosphate to triphosphate that gets high levels in cell and helps stop CMV DNA from elongating. - Treatment for CMV. Not as selective as acyclovir so more toxic.
Side effects: GI, neuropathies, some CNS, carcinogenic in animals at high doses.
Forcarnet
- CMV and Resistant Herpes Viruses
- Not nucleoside analogy - instead pyrophosphate
- IV
- Binds to and directly inhibits viral polymerases (DNA, RNA and RT)
- Treatment:
Effective against ganciclovir - resistant CMV and acyclovir resistant HSV, VZV
Cidofovir
- Anti-herpes
- Cytosine nucleotide analog
- IV
- Phosphorylated by host kinases (so also active against thymidine kinase deficient HSV) competitive inhibitor of viral DNA synthesis, incorporated into viral DNA
- CMV third string drug. If Ganciclovir and forcarnet don’t work
Trifluridine
- Anti-herpes
- Competes with TPP at viral polymerase
- Topical
- Competes with TPP at viral polymerase
Inhibits DNA synthesis in HSV1 HSV 2 CMV
Incorporates into both viral and host DNA - Used for HSV 1 and HSV 2 conjuctivitis, epithelial keratitis.
Effective for acyclovir-resistant HSV
Pseudomembranous colitis
- Antibiotic-associated, usually due to C. diff
- C. diff overgrowth due to disruption of normal bowel flora
- Pseudomembranes
Adherent layer of inflammatory cells and debris - Fever, leukocytosis, ab pain, watery diarrhea, dehydration
- Major concern in healthcare facilities
Giardia
Parasite
- Non-invasive diarrhea
- Treat with oral rehydration and anti-protozoan agents
Cryptosporidium
Parasite
1. Water borne, spores resistant to chlorine
Spread through pools
- Acute self-limited diarrhea or chronic in immunosuppressed host
HSV
- DNA enveloped virus
- Bind on cell surface, travel to nucleus to become circular, activates viral immediate early genes by host RNA polymerase and create proteins
DNA + thymidine kinase - HSV1: Oral>sexual; Very sore mouth gingivostomatitis, herpes labialis on vermillion border, keratitis and encephalitis
HSV2: Sexual>oral; herpes genitalis/labialis, neonatal encephalitis, aseptic meningitis
Serotypes
IgM = more fast acting than IgG
Core = Actually had the illness
Surface antigen = active disease
No igG or igM = no immunity, never been infected or vaccinated
Surface antibody = shows vaccination or previous manifestation
Treatment for HepC
Telaprevir Simeprevir Sofosbuvir Daclatasvir Velapatasvir
Knowing genotype
Current HepC viral lode
Degree of fibrosis/cirrohosis
Liver biopsy will show cirrhosis
Ultrasound elastography can show fibrosis
Na+ shows prognosis in patients with end stage liver disease
Alpha fetal protein tumor makers helpful with HCC
FibroTest-ActiTest used to stage fibrosis and evaluate for cirrhosis
HepA
Fecal oral
Acute
2-6 week incubation
Councilman bodies (represents a dying hepatocyte surrounded by normal parenchyma)
HepE
Fecal oral
Acute
2-8 week incubation
Could only progress to chronic hep in immunocompromised patients
India
No vaccination
HepC
No vaccination
Levels in Data Recommendations
The level A suggests that Data is derived from multiple randomized clinical trials, meta-analyses or equivalent.
Level B would be a single randomized trial, nonrandomized studies, or equivalent
Level C would mean Consensus opinion of experts and case studies.
Exposure to HepC
After needle stick, risk of infection is 1.8%
If HepC is acquired, 15-25% chance of clearing it
Wouldn’t make sense to treat it even though newer medications have better side effect profiles
Baseline testing with follow up 2-3 weeks for Hep RNA
Old Hep B/C Treatment
Ribavirin with interferon A
Campylobacter
- Common in adults, common cause of traveler’s diarrhea
- Contaminated food/water; small inoculum
- Mucosal colonization and adherence
- Watery diarrhea, dysentery (uncommon); usually self-limited
- Arthritis - HLA-B27
Guillain-Barre syndrome - Curved Gram- rod
Jejuni
1. Symptoms like ulcerative colitis or Crohn’s disease
