YERSINIA ENTEROCOLITICA: Gram-Negative Rod
ENTEROBACTERIACEAE
YERSINIA ENTEROCOLITICA: Gram-Negative Rod
Epidemiology / At Risk: Infected from animals especially during cold season.
Manifestations: Outcome of disease depends on age
Less than 5: Acute watery diarrhea that goes on for about a week.
5-15 years old: Acute mesenteric adenitis. Can be mistaken for appendicitis.
10-20 years old: Acute terminal ileitis,"Pseudo-Crohn's" disease.
Adult: Diarrhea. Liver disease can predispose to sepsis.
HLA B27 gene: Post-infectious arthritis.
Processing:
Specimen: Feces, joint fluid (for HLA B27), lymph.
Stain: Must first be put in enrichment broth before staining.
Culture:
Enrichment Broth: Bugs are put in enrichment broth before staining, as number of collected organisms is low.
COLD TEMP: 28C
Identification: Biochemical tests for species.
Virulence:
Invasin Gene: Adhesin and invasion.
Attachment-Invasin Loci: Genes that control the invasin gene.
Yersinia factors: shared in common with, or similar to, Y. Pestis.
Yersinia Outer Proteins (YOP's): Adhesin proteins, regulated by presence of calcium and temperature.
YOP-1: Four important properties
Confers serum resistance
Autoagglutinates the bug, which makes it harder to phagocytose.
Mannose-resistance Hemagglutination (not attracted to mannose)
Adhesin
Yersinia Adherence Protein (Yad-A): Adhesin, binds to fibronectin, fibrinogen, collagen. Blocks both alternate and classical complement.
V & W Antigens: Lipoprotein, antiphagocytic.
Arthritogenic Factor: Factor important in arthritis in HLA B27 patients.
beta-subunit of urease.
Stimulates TH1 CD4+ cells.
Enterotoxin: Stimulates cGMP to cause diarrhea.
CAMPYLOBACTER JEJUNI: Wavy Gram (-) Rod
Name-Derivation: Campylobacter = curved bacterium
Epidemiology / At Risk: From cattle.
Manifestations:
Invasive gastroenteritis, causing ulcers, crypt abscesses, hemorrhagic necrosis.
Blood and pus found in feces.
Processing:
Specimen: Feces or rectal swab.
Stain: Gram-negative rod with spiral or helical appearance, due to heavy tuft of flagella at one end.
Culture: Campy Agar
HIGH TEMP 42C -- must notify lab!
Identification: Microaerophilic
Virulence:
Antigenic Diversity is key virulence property. They are hard to type epidemiologically. Constant change of O and H antigen types.
Flagellum for motility and propulsion into mucosa.
Enterotoxin: Stimulates cAMP.
Heat-labile, denatured by boiling the milk.
Cytotoxin: Injurious to enterocytes.
Host Immune Response: Fairly easily killed by PMN's if they can be phagocytosed.
CAMPYLOBACTER FETUS: Wavy Gram (-) Rod
Name-Derivation: Campylobacter = curved bacterium
Epidemiology / At Risk: Contaminated food, milk, or water.
Manifestations: Bacteremia -- no diarrhea symptoms, even though the initial infection is via GI tract.
Bacteremia disseminates to, in order of importance:
Meninges, aided by propulsion of flagella.
Lungs, with contiguous spread to pleura
Joints
Suppurative Arthritis early on; specimen can be collected.
Rheumatoid Arthritis can occur post-infection.
Heart Valves, causing endocarditis.
C. Fetus like to get inside vascular endothelial cells, causing hemorrhagic necrosis. It isn't essential, but they like it.
Processing:
Specimen: Blood, CSF if you suspect meningitis, joint fluid when suppurative.
Stain: Gram-negative rod with spiral or helical appearance, due to heavy tuft of flagella at one end.
Culture: Campy Agar.
LOW TEMP 25C -- must notify lab!
Identification: Microaerophilic
Virulence:
Antigenic Diversity is key virulence property. They are hard to type epidemiologically. Constant change of O and H antigen types.
Protein Capsule: Unique among Gram (-)'s. Antiphagocytic, confers serum resistance.
Tropic for endothelial cells. It likes to live inside vascular endothelial cells.
Host Immune Response: Fairly easily killed by PMN's if they can be phagocytosed.
HELICOBACTER PYLORI: Wavy Gram (-) Rod
Name-Derivation: Originally part of Campylobacter, then given its own genus. Helical = wavy.
Epidemiology / At Risk:
Manifestations:
Type-B Gastritis: Inflammatory, pyogenic infection of antrum and goblet cells. pH remains normal.
Type-A Gastritis: Autoimmune disease against parietal cell resulting in pernicious anemia. pH is high due to damaged parietal cells.
Processing:
Specimen: Must be taken by gastric endoscopy. No specimen is usually collected.
Stain:
Culture: Campy Agar
NORMAL TEMP 37, as compared to the Campylobacter
Identification: Microaerophilic
UREASE (+)
Catalase (+)
UREA BREATH TEST: Give patient radiolabeled 14C urea, then monitor for the appearance of the 14C in their breath or blood, indicating that it has been broken down. Quick and easy test.
Virulence:
Flagellum: Number one property allowing it to invade gastric mucosa.
Mucinase helps penetrate mucin layer.
Fibrillar Hemagglutinin: Adhesin. It hooks to a glycero lipid in host cell membrane.
Catalase: Can survive (not replicate) inside PMN's.
Urease: Thought to create a basic microenvironment which damages intracellular junctions in stomach.
Oxidase
Treatment: Three antibiotics, plus Bisthmus (Pepto-Bismol) as a coating against acid damage.
CLOSTRIDIUM DIFFICILE: Gram (+) Rod, Spore-former. Not an Enterobacteriaceae.
Epidemiology / At Risk: Spores found in soil and are usually ingested. Can be opportunistic.
Endogenous Infection: Spores that were otherwise silent become activated when normal flora is depressed by antibiotics.
Exogenous Infection: Nosocomial infection in the hospital.
Manifestations:
Processing:
Specimen: Fecal filtrate is taken for toxin assay.
Stain:
Culture: Egg-yolk agar with antibiotics.
Identification:
Obligate anaerobe
Serogroups A - G
Can be identified through Gas Liquid Chromatography.
Toxin Test: Toxin is present only in some of the strains. Must determine whether it is present.
Put feces specimen filtrate in two dishes. Add antitoxin to one of the dishes.
Positive Test: One dish remains toxic, while the other dish is neutralized.
Negative Test: Neither dish is toxic.
Low Specificity: The antitoxin can cross react with other toxins.
ELISA can identify C. Difficile toxin.
Virulence:
Exotoxin A: Protein that damages the intestinal mucosa. It attracts PMN's and causes them to degranulate, resulting in more damage.
Exotoxin B: AB-Toxin that disrupts the cytoskeleton of enterocytes.
Fragment-A gets inside with the help of a host-cell protease. Mechanism of damage unknown.
Treatment: Treatment has a high relapse rate.
Discontinue broad-spectrum antibiotic therapy. Replace lost fluid and electrolytes.
Do not interfere with diarrhea. Let it run its course.
Vancomycin (some resistance has shown) or metronidazole is used when necessary.
ESCHERICHIA COLI (ENTERIC): Gram (-) Rods
Epidemiology / At Risk:
UTI's
Gastroenteritis
Wound Infections
Pneumonia
Meningitis in Infants
Sepsis
Manifestations: GI manifestations depends on strain. Virulence factors included.
Enteropathogenic E. COLI (EPEC): Cause Travelers's Diarrhea -- loose stools, plus mild GI complaints, such as nausea, vomiting, or even tenesmus.
Has also been called Entero-Aggregative E. COLI (EAEC) because of their tendency to aggregate.
Enterotoxigenic E. COLI (ETEC): Watery diarrhea, as opposed to loose stools. Diarrhea acts on the small intestine.
Labile Toxin (LT): Heat labile AB-toxin kicks water out by up-regulating cAMP.
Fragment-B: Binds GM1 Ganglioside in small intestinal enterocytes.
Fragment-A: ADP-Ribose Transferase. Transfers ADP to a Gs Stimulatory subunit ------> cAMP.
LT is also a large molecule and a potent antigen.
LT-IIa and Iib: Antigenic variants of labile toxin.
Stable Toxin (ST): Heat stable AB-Toxin, prevents water from being reabsorbed in small intestine.
Fragment-A: Up regulated cGMP ------> inhibit reabsorption of Na, Cl, and water in brush border.
Enteroinvasive E. COLI (EIEC): Causes dysentery in addition to the watery diarrhea. The new cytotoxin acts in the colon, while watery diarrhea continues to occur from the small intestine.
Verotoxin: Phage-mediated Shiga-Like Toxin is cytotoxic to colonic enterocytes. It inactivates protein synthesis at the 60s ribosome and kills the cell, resulting in hemorrhagic necrosis.
Invasin: Gene allows the E. COLI to live intracellularly inside colonic enterocytes.
Entero hemolytic E. COLI (EHEC): Causes Hemolytic Uremic Syndrome (HUS). In addition to the dysentery, it has a hemolysin and is tropic for transitional epithelial cells.
Symptoms:
Hemolytic Crisis
Thrombocytopenia
Disseminated Intravascular Coagulopathy (DIC)
Acute Renal Failure
Hemolysin: Plasmid-mediated factor that lyses red-blood cells. It is also a nephrotoxin.
Processing:
Specimen:
Stain: Gram-Stain is not done on fecal specimens.
Culture: Selective Medium (always used on Enterics), which inhibits Gram (+) and contains lactose, in order to differentiate lactose-fermenting genera.
Identification: Lactose-Fermenting
Motile
Huge Antigenic Diversity: Flagellar H-Antigen is divided L, A and B subtypes.
With Neonatal sepsis and meningitis, lab will report a B-subtype as it is associated with prognosis.
The LAB subtypes indicate how easily the flagellar antigens come off with heat.
Mannose-sensitive hemagglutination, because of F1 pilus antigen.
Virulence: Only cell-associated factors.
Pili (F-Antigen): Fimbriae. 10 F Antigen types. Adhesin.
F1 Antigen is found in all E. Coli. (chromosomally coded). It is Mannose-Sensitive, i.e. does not agglutinate RBC's in the presence of mannose (because it prefers to stick to the mannose).
Mannose sensitive is important to us as normal carriers of E. COLI. It helps E. COLI stick to mucosal (vaginal, GI, buccal) surfaces and protect them.
F2 - F10 Antigens: They are all mannose-resistant.
One of them is the P-Antigen, associated with Pyelonephritis.
Capsule (K-Antigen): Important in UTI's and Meningitis. Antiphagocytic, serum resistance.
Outer Membrane Proteins: Protein-A confers serum resistance.
Siderophore: Aerobactin
LPS: Lipid-A is the specific component which is a superantigen and makes up endotoxin.
Vaccine / Prevention:
The Core Polysaccharide, common to all strands, has been looked at. But whenever we target it, E. COLI respond by making new surface (O-Antigen) polysaccharides.
Treatment: Run the risk of inducing endotoxic shock when treating bacteremia.
SHIGELLOSIS:
Different Species:
S. Sonnei: Found in U.S.
S. Flexneri: Found in U.S.
S. Boydii: Found in U.S.
S. Dysenteriae: Found mostly abroad, and contains the extra Shiga Toxin.
Epidemiology / At Risk: Communicable. Very low infective dose of only 200 - 500 bugs.
Manifestations: Ulcerative colitis. Invasive disease.
Children in U.S. with Shigellosis can experience bacteremia and CNS toxicity.
Processing:
Specimen: Ulcer swab or feces.
Special transport medium required. The organic acid by-products of other normal flora are toxic to the Shigella bugs.
Stain:
Culture: Selective Medium
Identification: Non-Lactose Fermenting
Non-Motile, thus no H-Antigen.
Virulence:
Surface Polysaccharide: Plasmid-mediated, adhesin and invasin.
Outer Membrane Proteins: Invasin allows mucosal penetration by receptor-mediated endocytosis. Details uncertain.
Hemolysin: Plasmid-mediated (only some strains have it). Disrupts phagolysosome formation and allows intracellular replication in PMN's.
They can also actually infect neighboring cells, eventually leading to an ulcer.
SHIGA TOXIN: Only present in the S. Dysenteriae strain, making it the most virulent.
In the small intestine, it blocks absorption of NaCl, glucose, and water.
In the colon, AB-Toxin.
Fragment-B binds a glycolipid on colonic enterocyte.
Fragment-A gets internalized and is then known as Fragment-A1, which is an N-Glycosidase. It removes adenine from the 28s rRNA and irreversibly in activates protein synthesis at the 60s ribosomal subunit.
Some of the U.S. bugs produce a Shiga-Like toxin that produces similar effects -- not but Shiga toxin, and details are not characterized.
Treatment: Shigellosis is a public health issue. Antibiotic treatment is required.
SALMONELLA ENTEROCOLITICA (ENTERICA GROUP 1): Gram negative rods.
Epidemiology / At Risk: Communicable
Animal to human transmission.
There are over 2000 species of Salmonella. Ubiquitous in environment and many people act as carriers (bugs live in bile duct).
Large infective dose is required for infection.
Manifestations: Enterocolitis self limiting to 2-7 days.
Nausea, vomiting, non-bloody diarrhea, fever, abdominal cramps, headache.
Can be asymptomatic.
Can penetrate mucosa but doesn't cause much damage.
No Bacteremia
Processing:
Specimen: Feces or blood.
Stain: Not on the feces; direct microscopy not helpful.
Culture: Selective Medium, including bile and lactose. These bugs really love bile.
Identification:
Non-lactose fermenting
Motile: Compare to Shigella.
Serogrouping: Very high antigenic diversity.
O-Antigen: 4 serogroups
DNA Hybridization: 6 groups. Type 1 is most common in U.S.
Biphasic expression of the flagellar (H) antigen. Changes throughout growth.
Virulence:
Flagellum (H-Antigen): Motility. Biphasic antigen expression in early and late growth makes the bugs hard to fingerprint.
Polysaccharide (O-Antigen): Adhesin to mucosa.
Capsule (K-Antigen)
Outer Membrane Proteins: Adhesin helps them adhere to neighboring cells in the lamina propria.
Causes degeneration of the brush border (diarrhea) and fever.
Pili: Mannose-Sensitive hemagglutinins. Adheres to intestinal epithelium.
LPS Endotoxin: Common to all the serogroups.
Enterotoxin: Cause diarrhea, similar to the E. COLI enterotoxins.
Cytotoxin: In the colon, inhibits protein synthesis.
Host Immune Response:
Vaccine / Prevention:
Treatment: Do NOT treat. It only prolongs the carrier state. Only treat symptomatically.
SALMONELLA TYPHI:
Epidemiology / At Risk: Human to human transmission only.
Large infective dose.
Mortality Rate: 2-10%
Relapse Rate: 20%
Manifestations: Typhoid Fever
Symptoms:
First Week: Constipation with step-wise fever and malaise.
Second week: Bacteremia. Sustained fever.
Rose Spot Rashes are discrete rashes on the trunk.
Diarrhea: Intestinal necrosis, severe bleeding, thrombophlebitis, cholecystitis, pneumonia, focal abscesses.
Carrier State following resolution -- may last up to a year. Bugs localize to the bile ducts.
PATHOGENESIS:
Organisms multiple in the lamina propria, lymphatics, and monocytes of the small intestine.
They then invade and disseminate to reticuloendothelial system, leading to sustained bacteremia.
At the liver, organisms re-invade the GI-Tract via the gallbladder.
COMPLICATIONS:
Intestinal perforations
Thrombophlebitis.
Cholecystitis and gallstones
Patchy necrosis caused by complement fixation and PMN inflammation.
DIC and focal abscesses.
Processing:
Specimen:
Blood can be taken in early in infection.
Feces can be taken in late infection (when diarrhea starts)
Stain: Not useful.
Culture: Enteric Selective Culture containing lactose and bile.
Culture under aerobic conditions 1- 7 days.
Will show motile bugs with smooth colonies.
Identification:
Non-Lactose fermenting
Motile
Facultative intracellular parasite.
Virulence:
Capsule Antigen (Vi): Polysaccharide, antiphagocytic, serum resistance. This enhances survival inside monocytes.
Immunogenic and basis for partial-vaccine.
Intracellular in Monocytes: Facultative intracellular parasites of monocytes. The capsule protects them from destruction.
Flagellar (H) Antigen: Biphasic antigenic expression.
Outer Membrane Proteins (O-Antigens): Antiphagocytic inside monocytes. Enhances resistance to non-oxidative cationic proteins (defensins) inside PMN's.
Endotoxin.
Vaccine / Prevention:
TAB Vaccine: For travelers, short-term temporary protection. Passive antibody to the Vi antigen, allowing for phagocytosis and good complement response.
Prevention: Chlorinate water, sewage disposal, cook your food.
Treatment: Carrier state may be prolonged by antibiotic treatment. Cholecystectomy may be needed.
VIBRIO CHOLERAE: Halophilic (salt-loving) Gram-negative rod.
Epidemiology / At Risk: Highly communicable in areas of poor sanitation.
Cholera tends to spread in epidemics.
Humans are host; crustaceans are a vector. Infection via seafood or infected water.
Manifestations:
Cholera: Very watery profuse diarrhea. Rice-water stools.
Vomiting and muscular cramps
Dehydration can lead to oliguria and collapse.
Non-invasive. No damage to intestinal epithelium. Diarrhea is strictly via the exotoxin.
Processing:
Specimen: Food, water, stool.
Transport medium at pH > 8, which suppresses contaminating organisms.
Stain: Dark-field stain only, will see small curving rods with darting motility.
It's a comma-shaped bug with long flagellum.
Culture:
Identification:
Motile
Oxidase (+)
Non-lactose fermenting
SEROLOGY: Test for O1 serotype to identify presence of Tox gene.
If positive, we test for the Cholera El Tor strain via a hemolysis test. Cholera el Tor properties:
beta-hemolytic.
Endemic to U.S. and South America.
Less virulent, as it has only one copy of the Tox gene.
If negative, then the Tox gene probably isn't present, although another strain is supposed to have acquired it.
Virulence:
Polar Flagellum: Provides motility and penetration through mucin.
Pilus: Along with an accessory colonizing protein, this is an adhesin that allows adhesion to brush border.
Mucinase: Aids invasiveness -- but not beyond the intestinal lumen.
Cholera Toxin: Exotoxin causes diarrhea.
AB-Mechanism:
B-Fragment binds GM1-ganglioside of enterocyte.
A-Fragment enters the cell, and a disulfide bond is broken so that it cleaves into two parts.
A1 Fragment transfers ADP-Ribose to the Gs-subunit, making it permanently activated ------> perpetually high cAMP, diarrhea.
Cholera toxin also prevents absorption of water in the brush-border. Double-duty diarrhea.
Vaccine / Prevention: Live attenuated vaccine currently provides short-term protection.
Treatment:
Oral Rehydration Therapy: Glucose and water. IV replacement fluids are only used in most severe cases.
Tetracycline may be used, but can also produce resistant strains. Use with caution.
VIBRIO PARAHAEMOLYTICUS: Halophilic Gram-negative rod.
Epidemiology / At Risk:
Associated with raw shellfish.
High infective dose.
People with underlying liver disease are at risk.
Manifestations:
Self-limiting diarrhea + GI symptoms lasting 3 days.
Wound infections in fisherman.
Processing:
Specimen:
Stain: Small gram (-) rods with single large flagellum.
Culture: Salty (3% NaCl) selective medium.
No hemolysis in vitro -- only in vivo.
Identification:
V. Parahaemolyticus grows in 8% NaCl whereas V. Cholera does not.
Facultative Anaerobe.
Virulence:
Hemolysins: they only act in vivo.
Treatment: Not usually treated.
YERSINIA ENTEROCOLITICA: Gram-Negative Rod
Epidemiology / At Risk: Infected from animals especially during cold season.
Manifestations: Outcome of disease depends on age
Less than 5: Acute watery diarrhea that goes on for about a week.
5-15 years old: Acute mesenteric adenitis. Can be mistaken for appendicitis.
10-20 years old: Acute terminal ileitis,"Pseudo-Crohn's" disease.
Adult: Diarrhea. Liver disease can predispose to sepsis.
HLA B27 gene: Post-infectious arthritis.
Processing:
Specimen: Feces, joint fluid (for HLA B27), lymph.
Stain: Must first be put in enrichment broth before staining.
Culture:
Enrichment Broth: Bugs are put in enrichment broth before staining, as number of collected organisms is low.
COLD TEMP: 28C
Identification: Biochemical tests for species.
Virulence:
Invasin Gene: Adhesin and invasion.
Attachment-Invasin Loci: Genes that control the invasin gene.
Yersinia factors: shared in common with, or similar to, Y. Pestis.
Yersinia Outer Proteins (YOP's): Adhesin proteins, regulated by presence of calcium and temperature.
YOP-1: Four important properties
Confers serum resistance
Autoagglutinates the bug, which makes it harder to phagocytose.
Mannose-resistance Hemagglutination (not attracted to mannose)
Adhesin
Yersinia Adherence Protein (Yad-A): Adhesin, binds to fibronectin, fibrinogen, collagen. Blocks both alternate and classical complement.
V & W Antigens: Lipoprotein, antiphagocytic.
Arthritogenic Factor: Factor important in arthritis in HLA B27 patients.
beta-subunit of urease.
Stimulates TH1 CD4+ cells.
Enterotoxin: Stimulates cGMP to cause diarrhea.
CAMPYLOBACTER JEJUNI: Wavy Gram (-) Rod
Name-Derivation: Campylobacter = curved bacterium
Epidemiology / At Risk: From cattle.
Manifestations:
Invasive gastroenteritis, causing ulcers, crypt abscesses, hemorrhagic necrosis.
Blood and pus found in feces.
Processing:
Specimen: Feces or rectal swab.
Stain: Gram-negative rod with spiral or helical appearance, due to heavy tuft of flagella at one end.
Culture: Campy Agar
HIGH TEMP 42C -- must notify lab!
Identification: Microaerophilic
Virulence:
Antigenic Diversity is key virulence property. They are hard to type epidemiologically. Constant change of O and H antigen types.
Flagellum for motility and propulsion into mucosa.
Enterotoxin: Stimulates cAMP.
Heat-labile, denatured by boiling the milk.
Cytotoxin: Injurious to enterocytes.
Host Immune Response: Fairly easily killed by PMN's if they can be phagocytosed.
CAMPYLOBACTER FETUS: Wavy Gram (-) Rod
Name-Derivation: Campylobacter = curved bacterium
Epidemiology / At Risk: Contaminated food, milk, or water.
Manifestations: Bacteremia -- no diarrhea symptoms, even though the initial infection is via GI tract.
Bacteremia disseminates to, in order of importance:
Meninges, aided by propulsion of flagella.
Lungs, with contiguous spread to pleura
Joints
Suppurative Arthritis early on; specimen can be collected.
Rheumatoid Arthritis can occur post-infection.
Heart Valves, causing endocarditis.
C. Fetus like to get inside vascular endothelial cells, causing hemorrhagic necrosis. It isn't essential, but they like it.
Processing:
Specimen: Blood, CSF if you suspect meningitis, joint fluid when suppurative.
Stain: Gram-negative rod with spiral or helical appearance, due to heavy tuft of flagella at one end.
Culture: Campy Agar.
LOW TEMP 25C -- must notify lab!
Identification: Microaerophilic
Virulence:
Antigenic Diversity is key virulence property. They are hard to type epidemiologically. Constant change of O and H antigen types.
Protein Capsule: Unique among Gram (-)'s. Antiphagocytic, confers serum resistance.
Tropic for endothelial cells. It likes to live inside vascular endothelial cells.
Host Immune Response: Fairly easily killed by PMN's if they can be phagocytosed.
HELICOBACTER PYLORI: Wavy Gram (-) Rod
Name-Derivation: Originally part of Campylobacter, then given its own genus. Helical = wavy.
Epidemiology / At Risk:
Manifestations:
Type-B Gastritis: Inflammatory, pyogenic infection of antrum and goblet cells. pH remains normal.
Type-A Gastritis: Autoimmune disease against parietal cell resulting in pernicious anemia. pH is high due to damaged parietal cells.
Processing:
Specimen: Must be taken by gastric endoscopy. No specimen is usually collected.
Stain:
Culture: Campy Agar
NORMAL TEMP 37, as compared to the Campylobacter
Identification: Microaerophilic
UREASE (+)
Catalase (+)
UREA BREATH TEST: Give patient radiolabeled 14C urea, then monitor for the appearance of the 14C in their breath or blood, indicating that it has been broken down. Quick and easy test.
Virulence:
Flagellum: Number one property allowing it to invade gastric mucosa.
Mucinase helps penetrate mucin layer.
Fibrillar Hemagglutinin: Adhesin. It hooks to a glycero lipid in host cell membrane.
Catalase: Can survive (not replicate) inside PMN's.
Urease: Thought to create a basic microenvironment which damages intracellular junctions in stomach.
Oxidase
Treatment: Three antibiotics, plus Bisthmus (Pepto-Bismol) as a coating against acid damage.
CLOSTRIDIUM DIFFICILE: Gram (+) Rod, Spore-former. Not an Enterobacteriaceae.
Epidemiology / At Risk: Spores found in soil and are usually ingested. Can be opportunistic.
Endogenous Infection: Spores that were otherwise silent become activated when normal flora is depressed by antibiotics.
Exogenous Infection: Nosocomial infection in the hospital.
Manifestations:
Processing:
Specimen: Fecal filtrate is taken for toxin assay.
Stain:
Culture: Egg-yolk agar with antibiotics.
Identification:
Obligate anaerobe
Serogroups A - G
Can be identified through Gas Liquid Chromatography.
Toxin Test: Toxin is present only in some of the strains. Must determine whether it is present.
Put feces specimen filtrate in two dishes. Add antitoxin to one of the dishes.
Positive Test: One dish remains toxic, while the other dish is neutralized.
Negative Test: Neither dish is toxic.
Low Specificity: The antitoxin can cross react with other toxins.
ELISA can identify C. Difficile toxin.
Virulence:
Exotoxin A: Protein that damages the intestinal mucosa. It attracts PMN's and causes them to degranulate, resulting in more damage.
Exotoxin B: AB-Toxin that disrupts the cytoskeleton of enterocytes.
Fragment-A gets inside with the help of a host-cell protease. Mechanism of damage unknown.
Treatment: Treatment has a high relapse rate.
Discontinue broad-spectrum antibiotic therapy. Replace lost fluid and electrolytes.
Do not interfere with diarrhea. Let it run its course.
Vancomycin (some resistance has shown) or metronidazole is used when necessary.
ESCHERICHIA COLI (ENTERIC): Gram (-) Rods
Epidemiology / At Risk:
UTI's
Gastroenteritis
Wound Infections
Pneumonia
Meningitis in Infants
Sepsis
Manifestations: GI manifestations depends on strain. Virulence factors included.
Enteropathogenic E. COLI (EPEC): Cause Travelers's Diarrhea -- loose stools, plus mild GI complaints, such as nausea, vomiting, or even tenesmus.
Has also been called Entero-Aggregative E. COLI (EAEC) because of their tendency to aggregate.
Enterotoxigenic E. COLI (ETEC): Watery diarrhea, as opposed to loose stools. Diarrhea acts on the small intestine.
Labile Toxin (LT): Heat labile AB-toxin kicks water out by up-regulating cAMP.
Fragment-B: Binds GM1 Ganglioside in small intestinal enterocytes.
Fragment-A: ADP-Ribose Transferase. Transfers ADP to a Gs Stimulatory subunit ------> cAMP.
LT is also a large molecule and a potent antigen.
LT-IIa and Iib: Antigenic variants of labile toxin.
Stable Toxin (ST): Heat stable AB-Toxin, prevents water from being reabsorbed in small intestine.
Fragment-A: Up regulated cGMP ------> inhibit reabsorption of Na, Cl, and water in brush border.
Enteroinvasive E. COLI (EIEC): Causes dysentery in addition to the watery diarrhea. The new cytotoxin acts in the colon, while watery diarrhea continues to occur from the small intestine.
Verotoxin: Phage-mediated Shiga-Like Toxin is cytotoxic to colonic enterocytes. It inactivates protein synthesis at the 60s ribosome and kills the cell, resulting in hemorrhagic necrosis.
Invasin: Gene allows the E. COLI to live intracellularly inside colonic enterocytes.
Entero hemolytic E. COLI (EHEC): Causes Hemolytic Uremic Syndrome (HUS). In addition to the dysentery, it has a hemolysin and is tropic for transitional epithelial cells.
Symptoms:
Hemolytic Crisis
Thrombocytopenia
Disseminated Intravascular Coagulopathy (DIC)
Acute Renal Failure
Hemolysin: Plasmid-mediated factor that lyses red-blood cells. It is also a nephrotoxin.
Processing:
Specimen:
Stain: Gram-Stain is not done on fecal specimens.
Culture: Selective Medium (always used on Enterics), which inhibits Gram (+) and contains lactose, in order to differentiate lactose-fermenting genera.
Identification: Lactose-Fermenting
Motile
Huge Antigenic Diversity: Flagellar H-Antigen is divided L, A and B subtypes.
With Neonatal sepsis and meningitis, lab will report a B-subtype as it is associated with prognosis.
The LAB subtypes indicate how easily the flagellar antigens come off with heat.
Mannose-sensitive hemagglutination, because of F1 pilus antigen.
Virulence: Only cell-associated factors.
Pili (F-Antigen): Fimbriae. 10 F Antigen types. Adhesin.
F1 Antigen is found in all E. Coli. (chromosomally coded). It is Mannose-Sensitive, i.e. does not agglutinate RBC's in the presence of mannose (because it prefers to stick to the mannose).
Mannose sensitive is important to us as normal carriers of E. COLI. It helps E. COLI stick to mucosal (vaginal, GI, buccal) surfaces and protect them.
F2 - F10 Antigens: They are all mannose-resistant.
One of them is the P-Antigen, associated with Pyelonephritis.
Capsule (K-Antigen): Important in UTI's and Meningitis. Antiphagocytic, serum resistance.
Outer Membrane Proteins: Protein-A confers serum resistance.
Siderophore: Aerobactin
LPS: Lipid-A is the specific component which is a superantigen and makes up endotoxin.
Vaccine / Prevention:
The Core Polysaccharide, common to all strands, has been looked at. But whenever we target it, E. COLI respond by making new surface (O-Antigen) polysaccharides.
Treatment: Run the risk of inducing endotoxic shock when treating bacteremia.
SHIGELLOSIS:
Different Species:
S. Sonnei: Found in U.S.
S. Flexneri: Found in U.S.
S. Boydii: Found in U.S.
S. Dysenteriae: Found mostly abroad, and contains the extra Shiga Toxin.
Epidemiology / At Risk: Communicable. Very low infective dose of only 200 - 500 bugs.
Manifestations: Ulcerative colitis. Invasive disease.
Children in U.S. with Shigellosis can experience bacteremia and CNS toxicity.
Processing:
Specimen: Ulcer swab or feces.
Special transport medium required. The organic acid by-products of other normal flora are toxic to the Shigella bugs.
Stain:
Culture: Selective Medium
Identification: Non-Lactose Fermenting
Non-Motile, thus no H-Antigen.
Virulence:
Surface Polysaccharide: Plasmid-mediated, adhesin and invasin.
Outer Membrane Proteins: Invasin allows mucosal penetration by receptor-mediated endocytosis. Details uncertain.
Hemolysin: Plasmid-mediated (only some strains have it). Disrupts phagolysosome formation and allows intracellular replication in PMN's.
They can also actually infect neighboring cells, eventually leading to an ulcer.
SHIGA TOXIN: Only present in the S. Dysenteriae strain, making it the most virulent.
In the small intestine, it blocks absorption of NaCl, glucose, and water.
In the colon, AB-Toxin.
Fragment-B binds a glycolipid on colonic enterocyte.
Fragment-A gets internalized and is then known as Fragment-A1, which is an N-Glycosidase. It removes adenine from the 28s rRNA and irreversibly in activates protein synthesis at the 60s ribosomal subunit.
Some of the U.S. bugs produce a Shiga-Like toxin that produces similar effects -- not but Shiga toxin, and details are not characterized.
Treatment: Shigellosis is a public health issue. Antibiotic treatment is required.
SALMONELLA ENTEROCOLITICA (ENTERICA GROUP 1): Gram negative rods.
Epidemiology / At Risk: Communicable
Animal to human transmission.
There are over 2000 species of Salmonella. Ubiquitous in environment and many people act as carriers (bugs live in bile duct).
Large infective dose is required for infection.
Manifestations: Enterocolitis self limiting to 2-7 days.
Nausea, vomiting, non-bloody diarrhea, fever, abdominal cramps, headache.
Can be asymptomatic.
Can penetrate mucosa but doesn't cause much damage.
No Bacteremia
Processing:
Specimen: Feces or blood.
Stain: Not on the feces; direct microscopy not helpful.
Culture: Selective Medium, including bile and lactose. These bugs really love bile.
Identification:
Non-lactose fermenting
Motile: Compare to Shigella.
Serogrouping: Very high antigenic diversity.
O-Antigen: 4 serogroups
DNA Hybridization: 6 groups. Type 1 is most common in U.S.
Biphasic expression of the flagellar (H) antigen. Changes throughout growth.
Virulence:
Flagellum (H-Antigen): Motility. Biphasic antigen expression in early and late growth makes the bugs hard to fingerprint.
Polysaccharide (O-Antigen): Adhesin to mucosa.
Capsule (K-Antigen)
Outer Membrane Proteins: Adhesin helps them adhere to neighboring cells in the lamina propria.
Causes degeneration of the brush border (diarrhea) and fever.
Pili: Mannose-Sensitive hemagglutinins. Adheres to intestinal epithelium.
LPS Endotoxin: Common to all the serogroups.
Enterotoxin: Cause diarrhea, similar to the E. COLI enterotoxins.
Cytotoxin: In the colon, inhibits protein synthesis.
Host Immune Response:
Vaccine / Prevention:
Treatment: Do NOT treat. It only prolongs the carrier state. Only treat symptomatically.
SALMONELLA TYPHI:
Epidemiology / At Risk: Human to human transmission only.
Large infective dose.
Mortality Rate: 2-10%
Relapse Rate: 20%
Manifestations: Typhoid Fever
Symptoms:
First Week: Constipation with step-wise fever and malaise.
Second week: Bacteremia. Sustained fever.
Rose Spot Rashes are discrete rashes on the trunk.
Diarrhea: Intestinal necrosis, severe bleeding, thrombophlebitis, cholecystitis, pneumonia, focal abscesses.
Carrier State following resolution -- may last up to a year. Bugs localize to the bile ducts.
PATHOGENESIS:
Organisms multiple in the lamina propria, lymphatics, and monocytes of the small intestine.
They then invade and disseminate to reticuloendothelial system, leading to sustained bacteremia.
At the liver, organisms re-invade the GI-Tract via the gallbladder.
COMPLICATIONS:
Intestinal perforations
Thrombophlebitis.
Cholecystitis and gallstones
Patchy necrosis caused by complement fixation and PMN inflammation.
DIC and focal abscesses.
Processing:
Specimen:
Blood can be taken in early in infection.
Feces can be taken in late infection (when diarrhea starts)
Stain: Not useful.
Culture: Enteric Selective Culture containing lactose and bile.
Culture under aerobic conditions 1- 7 days.
Will show motile bugs with smooth colonies.
Identification:
Non-Lactose fermenting
Motile
Facultative intracellular parasite.
Virulence:
Capsule Antigen (Vi): Polysaccharide, antiphagocytic, serum resistance. This enhances survival inside monocytes.
Immunogenic and basis for partial-vaccine.
Intracellular in Monocytes: Facultative intracellular parasites of monocytes. The capsule protects them from destruction.
Flagellar (H) Antigen: Biphasic antigenic expression.
Outer Membrane Proteins (O-Antigens): Antiphagocytic inside monocytes. Enhances resistance to non-oxidative cationic proteins (defensins) inside PMN's.
Endotoxin.
Vaccine / Prevention:
TAB Vaccine: For travelers, short-term temporary protection. Passive antibody to the Vi antigen, allowing for phagocytosis and good complement response.
Prevention: Chlorinate water, sewage disposal, cook your food.
Treatment: Carrier state may be prolonged by antibiotic treatment. Cholecystectomy may be needed.
VIBRIO CHOLERAE: Halophilic (salt-loving) Gram-negative rod.
Epidemiology / At Risk: Highly communicable in areas of poor sanitation.
Cholera tends to spread in epidemics.
Humans are host; crustaceans are a vector. Infection via seafood or infected water.
Manifestations:
Cholera: Very watery profuse diarrhea. Rice-water stools.
Vomiting and muscular cramps
Dehydration can lead to oliguria and collapse.
Non-invasive. No damage to intestinal epithelium. Diarrhea is strictly via the exotoxin.
Processing:
Specimen: Food, water, stool.
Transport medium at pH > 8, which suppresses contaminating organisms.
Stain: Dark-field stain only, will see small curving rods with darting motility.
It's a comma-shaped bug with long flagellum.
Culture:
Identification:
Motile
Oxidase (+)
Non-lactose fermenting
SEROLOGY: Test for O1 serotype to identify presence of Tox gene.
If positive, we test for the Cholera El Tor strain via a hemolysis test. Cholera el Tor properties:
beta-hemolytic.
Endemic to U.S. and South America.
Less virulent, as it has only one copy of the Tox gene.
If negative, then the Tox gene probably isn't present, although another strain is supposed to have acquired it.
Virulence:
Polar Flagellum: Provides motility and penetration through mucin.
Pilus: Along with an accessory colonizing protein, this is an adhesin that allows adhesion to brush border.
Mucinase: Aids invasiveness -- but not beyond the intestinal lumen.
Cholera Toxin: Exotoxin causes diarrhea.
AB-Mechanism:
B-Fragment binds GM1-ganglioside of enterocyte.
A-Fragment enters the cell, and a disulfide bond is broken so that it cleaves into two parts.
A1 Fragment transfers ADP-Ribose to the Gs-subunit, making it permanently activated ------> perpetually high cAMP, diarrhea.
Cholera toxin also prevents absorption of water in the brush-border. Double-duty diarrhea.
Vaccine / Prevention: Live attenuated vaccine currently provides short-term protection.
Treatment:
Oral Rehydration Therapy: Glucose and water. IV replacement fluids are only used in most severe cases.
Tetracycline may be used, but can also produce resistant strains. Use with caution.
VIBRIO PARAHAEMOLYTICUS: Halophilic Gram-negative rod.
Epidemiology / At Risk:
Associated with raw shellfish.
High infective dose.
People with underlying liver disease are at risk.
Manifestations:
Self-limiting diarrhea + GI symptoms lasting 3 days.
Wound infections in fisherman.
Processing:
Specimen:
Stain: Small gram (-) rods with single large flagellum.
Culture: Salty (3% NaCl) selective medium.
No hemolysis in vitro -- only in vivo.
Identification:
V. Parahaemolyticus grows in 8% NaCl whereas V. Cholera does not.
Facultative Anaerobe.
Virulence:
Hemolysins: they only act in vivo.
Treatment: Not usually treated.