Bacteriology - Gram Negative

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TSI test

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Triple Sugar Iron test.Tests microorganism's ability to ferment sugars and produce H2S. If only ferments glucose - yellow on top and in butt. If ferments lactose/sucrose, yellow all over. If produces H2S, black in butt.

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Can TSI determine specific strain of bacteria?

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No. Can tell us the bacteria - ie, shigella or salmonella - but to detect specific strain, need serological identification. This means that we use antibodies and look for agglutination.

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Enteric Fever Pathogenesis

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Cause: Salmonella typhi
Found only in humans.
Transmitted via fecal-oral route.
The bacteria perforate through intestinal wall, and are phagocytosed by macrophages, where they are able to resist destruction. They then travel in the lymphatics, thus gaining access to various body organs. This is all during the incubation, asymptomatic period. Then they get into blood, causing bacteremia, followed by redeposition into lymph nodes.

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Enteric Fever symptoms

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High fever, sweating, non-bloody diarrhea, abdominal pain.

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Enteric Fever Diagnosis

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Can be made with blood, bone marrow, or stool cultures, but these are tricky, as they go up and down throughout the disease. The Widal test is a demonstration of agglutinating antibodies against antigens O and H in the blood and peaks after three weeks.

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Salmonella Typhi Virulence

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1. Motile (H-antigen)
2. Capsule (called Vi antigen) - protects from intracellular kiling.
3. Siderophore

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Is S. typhi part of the normal intestinal flora?

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No. Never.

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S. typhi can live in the ______ for years after infection. Can try _____ to get rid of it. If it persists, may require ______.

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Gall bladder
Ampicillin
Colecystectomy

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LPS

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Lipopolysaccharides (LPS) are large molecules consisting of a lipid (A) and a polysaccharide (with O-antigen) joined by a covalent bond; they are found in the outer membrane of Gram-negative bacteria, act as endotoxins and elicit strong immune responses in animals.

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O-antigen

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Polysaccharide side chain of LPS. The composition of the O side chain varies between different Gram-negative bacterial strains. The presence or absence of O chains determine whether the LPS is considered rough or smooth.

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Lipid A

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A disaccharide with multiple fatty acid tails reaching into the outer membrane of gram negative bacteria. This is the key in the toxicity. When bacterial cells are lysed by our efficiently working immune system, fragment of membrane containing lipid A are released into the circulation, causing fever, diarrhea, and possible fatal endotoxic shock.

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Can we get typhoid from animals?

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No. Only human-to-human transmission.

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What is the most effective immune response against enteric bacilli?

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Secretory IgA

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Paratyphoid Fevers

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Group of enteric illnesses caused by strains (A, B, C) of the bacterium Salmonella paratyphi. Transmitted by contaminated food/water. Shorter incubation and disease duration (7-10 days) than typhoid fever. Is also milder.

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The "four F's" cause enteric diseases:

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Food
Fingers
Feces
Flies

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Salmonellosis

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Infection with Salmonella bacteria (non-typhoidal). Most persons infected develop diarrhea, fever, vomiting, and abdominal cramps 12 to 72 hours after infxn. In most cases, it lasts 3 to 7 days—most affected persons recover without treatment. Sources are animals (unlike typhoid).

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Shigellosis

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Infection with Shigella bacteria. In most severe form, causes Bacillary dysentery. Is a food-borne illness, and infects via fecal-oral route.

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Infective dose of Shigella:

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>10^3

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Is Shigella limited to the GI tract?

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Yes.

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Is Shigella highly communicable?

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Yes.

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Pathological process of Shigella

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Invades mucosal lining of intestinal wall and creates micro-abscesses. Then we see necrosis, superficial ulceration, bleeding and formation of pseudomembrane

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Bacillary Dysentery

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Most severe form of Shigellosis. Here we see severe diarrhea that contains mucus and blood.

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Which is the only enteric disease that invades the lymphatics?

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Typhoid fever - caused by Salmonella typhi

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Endotoxins

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Classically, an "endotoxin" is a toxin which, unlike an "exotoxin", is not secreted in soluble form by live bacteria, but is a structural component in the bacteria, which is released mainly when bacteria are lysed. The prototypical example is LPS, although there are others.

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Endotoxemia

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Presence of endotoxins in the blood, which can lead to septic shock if immune response is severe.

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K antigen

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Capsular antigen - antigen found only in bacterial capsules. In s. typhi, they are called Vi antigens.

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H antigen

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Flagellar antigen.

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Salmonella pathogenesis

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Salmonella attaches to epithelial cells lining terminal portion of small intestine. This triggers phagocytosis and then the bacteria multipy within phagocytic vacuoles. Then kills host cell, inducing diarrhea, and can move into bloodstream.

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Most common manifestation of Salmonella?

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Gastroenteritis

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Treatment for Shigellosis

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First, need to replace fluids and salts lost in diarrhea. In most cases, disease will resolve on its own without antibiotics. If antibiotics are needed: chloramphenicol, ampicillin, tetracycline, trimethoprims, and sulphamethoxazole can be used.

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Three main pathogenic strains of Vibrio.

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V. cholerae
V. parahaemolyticus
V. vulnificus.

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Vibrio morphology

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curve-shaped rod

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Vibrio infective dose

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10^8-10^10

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Is vibrio invasive?

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No. It is localized in the GI tract.

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Vibrio cholerae

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causes infectious gastroenteritis. the enterotoxin activates adenylcyclase, which increases ATP, which increases cAMP, leading to hypersecretion - outpouring of electrolytes and liquid, causing profuse diarrhea. is very very dangerous.

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Mortality rate of cholera without treatment?

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25-50%

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Vaccination against cholera?

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Problem is that it's only good for six months.

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Vibrio parahemolyticus

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Halophilic; get from eating sea food, or less often through wounds. The incubation period of ~24 hours is followed by explosive, watery diarrhea accompanied by nausea, vomiting, abdominal cramps, and sometimes fever. Symptoms usually subside within 72-hrs but can persist for up to 10 days in immuno-compromised hosts.

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Vibrio Vulnificus

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Only found in salt-water. Get from eating fish or from open wounds exposed to salt water. Symptoms include vomiting, diarrhea, abdominal pain, and a blistering dermatitis. Severe symptoms and even death can occur if the bacterium enters the bloodstream - something more common in people with compromised immune systems or liver disease.

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Symptoms to look for after eating raw or undercooked seafood for vibrio vulnificus infxn:

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Nausea
Vomiting
Diarrhea
Stomach pain

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Symptoms to look for from infected cuts or sores for vibrio vulnificus infxn:

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Redness, pain or swelling around the cut that spreads quickly
Cuts or sores that get larger and deeper or blister

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People at higher risk for serious infection from vibrio vulnificus are those with:

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Chronic liver disease
Alcoholism
Weakened immune system

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E. coli can cause:

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UTIs
Traveler's diarrhea - acute gastroenteritis
Sepsis
Meningitis in infants

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E. coli causing UTIs:

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Uropathogenic e. coli - UPEC; is responsible for 90% of UTIs

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Strains of E. coli causing gastroenteritis (5):

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Entero Pathogenic (EPEC)
Entero Toxigenic (ETEC)
Entero Invasive (EIEC)
Entero Hemorrhagic (EHEC
Entero Aggregative (EAEC

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EPEC
-site of action
-disease
-pathogenesis

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small intestine
infant diarrhea in underdeveloped countries
plasmid-mediated disruption of normal microvillus resulting in malabsorption and diarrhea

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ETEC
-site of action
-disease
-pathogenesis

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Enterotoxic
small intestine
traveler's diarrhea, infant diarrhea in developing countries - low-grade or no fever
plasmid-mediated, heat stable or heat-labile enterotoxins that inhibit reabsorption- they have pili so can bind well for exotoxin release

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EHEC
-site of action
-disease
-pathogenesis

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Entero Hemorrhagic
large intestine
initial watery diarrhea, followed by grossly bloody diarrhea and little to no fever; may progress to hemolytic uremic syndrome (HUS)
mediated by cytotoxic shiga toxins which disrupt protein synthesis resulting in decreased absorption

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EIEC
-site of action
-disease
-pathogenesis

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large intestine
disease in underdeveloped countries - watery diarrhea and may progress to dysentery
plasmid-mediated invasion and destruction of epithelial cells lining colon

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EAEC
-site of action
-disease
-pathogenesis

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small intestine
infant diarrhea in underdeveloped countries; traveler's diarrhea - persistent with vomiting
plasmid-mediated aggregative adherence of rods with shortening of microvilli, hemorrhage and decreased fluid absorption

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Campylobacter Jejuni

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twisted bacilli
infection by oral route
infective dose = 10^4
one of the most common causes of human gastroenteritis in the world
they multiply in the small intestine, invade the epithelium and cause inflammation. rbcs in stool.
treatment with erythromycin, but can be resolved without treatment

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Yersinia enterocolitica

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Not really an enteric, but causes diarrhea. Symptoms are similar to those of salmonellosis and shigellosis. More widespread among children.

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Which of the gram negative rods that cause diarrhea are enterotoxin-mediated? (2)

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1. e. coli
2. vibrio cholerae

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Which of the gram-negative rods that cause diarrhea are invasive-inflammatory? (3)

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1. Salmonella
2. Shigella
3. Campylobacter jejuni

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Helicobacter pylori

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twisted, rod-shaped, microaerophilic bacterium that inhabits various areas of the stomach and duodenum. most common cause of duodenal ulcers and chronic gastritis. second leading cause of stomach ulcers behind aspirin.

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Helicobacter pylori virulence factors (6):

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1. urease
2. acid-inhibitory protein
3. flagella - allows penetration into gastric mucous layer
4. adhesins - mediate binding to host cells
5. mucinase - degrades gastric mucus
6. catalase - prevents phagocytic killing

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Helicobacter pylori diagnostic tests:

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1. Biopsy - urease test, giemsa stain for histology, culture
2. Serology (ELISA)
3. Urea breath test

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Drugs used to treat H. pylori peptic ulcers

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1. antibiotics: metronidazole, tetracycline, clarithromycin, amoxicillin
2. H2 blockers: cimetidine, ranitidine, famotidine, nizatidine
3. Proton pump inhibitors: omeprazole, lansoprazole, rabeprazole, esomeprazole, pantoprozole
4. stomach-lining protector: bismuth subsalicylate

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What is the correlation between endotoxin presence and pathogenic potential?

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No correlation. Endotoxins are available in all gram negative bacteria; pathogenic and non-pathogenic.

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Limulus lysate test

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Gram-negative endotoxin induces gel formation of Limulus polyphemus (horseshoe crab) lysates. Can detect concentrations as low as 10^-12, which is also the toxic limit.