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198 Cards in this Set

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What is the difference between dysentery and typhoid fever?
Dysentery has fever, abdominal cramps, and bloody, mucopurulent diarrhea that is produced by invasive organisms that target the colon.
Typhoid fever is a systemic febrile illness of prolonged (3 to 5 weeks) with fever, persistent bactermia, and metastatic spread BUT NO DIARRHEA.
What is the causative agent of typhoid fever?
Salmonella typhi
What is the most common agent of acute infectious diarrhea in the US?
Campylobacter
How does Yersina enterocolitica cause dysentery?
Y. Entercolitica organisms penetrate the surface epithelium of the distal small bowel and quickly make their way to deep tissues, including regional lymphatics
Why does Yersina enterocolitica infection mimic acute appendicitis?
Y. enterocolitica can penetrate their way through the distal small bowel to the regional lymphatics.
clinical features include diarrhea and prominent right lower quadrant abdominal pain. the Clinical spectrum of these organisms includes mesenteric adenitis mimicking acute appendicitis.
Where is the common location for Yersinia enterocolitica infections?
certain European countries and Canada
Which of the infectious enteric bacteria can be transmitted from person to person?
Shigella , this is unique among the enteric pathogens
What layers of the bowel are affected in invasive bacteria?
The initial lesions caused by these inflammatory pathogens are confined to the epithelial layer; however, as the disease progresses, the lamina propria becomes involved extensively with an inflammatory response --> crypt abscesses are common
What are some common causes of protozoan diarrhea?
The most common protozoa are Giardia, Cryptosporidium, and Cyclospora
Enterotoxic E.Coli causes _________ but Enterohemorrhagic E.Coli causes ________.
Traveler's diarrhea
Acute hemorrhagic colitis
What is the most common cause of viral cause of diarrhea?

Rotavirus
Rotavirus mainly affects ______ and Norovirus mainly affects ______
pediatric populations
adult populations
What is the mechanism for bacterial secretory diarrhea?
These organisms colonize the proximal small bowel and stimulate fluid and electrolyte secretion resulting in watery diarrhea.
Why are fecal leukocytes not usually not seen in amebic colitis?
The amebae engulf the white cells and RBCs for food.
What is the causative agent of the amebic colitis?
Entamoeba histolytica is a common invasive protozoan that causes dysentery (amebic colitis) with complications (liver abscess)
Which types of hepatitis can lead to liver cancer?
Hepatitis B and C
What are the risk factors for hepatitis A?
eating contaminated seafood or imported berries
What does the presence of leukocytes indicate in diarrhea?

Inflammatory diarrhea
What does the presence of frank or occult blood or mucus indicate in the diarrhea?

Dysentery syndrome
Describe Campylobacter.

Bacteria in the genus Campylobacter are motile, Gram- negative curved rods ( comma or seagull shaped organisms)
What is the difference in the virulence factors of Campylobacter fetus and Campylobacter jejuni?
A major virulence factor of Campylobacter fetus a proteinaceous capsule- like structure. The virulence factor of C. jejuni is its flagella
How is Campylobacter cultured?
Growth of Campylobacter strains requires selective media, microareophilic conditions (5% oxygen, 5% to 10% CO2) and incubation at 42 C
How do we differentiate between the species of Campylobacter?
Differentiation of Campylobacter species is based on biochemical reactions
How are most cases of Campylobacter transmitted?
Most cases are associated with improper food handling and preparation of poultry
What is the infectious dose of Campylobacter jejuni?
Ingestion of only 500 organisms
How does Campylobacter damage intestinal mucosa?
A cytolethal distending toxin and an endotoxin likely contribute to tissue injury
What is the incubation period of Campylobacter?
2 to 5 days
How does Campylobacter penetrate the intestinal mucosa?
The microaerophilic organisms are adapted for survival in the GI mucosa layer and they colonize the intestinal mucosal layer , mediated by flagella and putative adhesins
What type of tissue damage is seen with Campylobacter infection?
An acute, nonspecific neutrophilic and monocytic inflammatory reaction causing tissue damage in lamina propria and jejunal epithelium is seen
What is the role of antibiotics in Campylobacter infection?
It is generally self-limited infection but if antibiotics are indicated, they should be given early in the course for maximum benefit.
Erythromycin should be given if antimicrobial therapy is required and quinolones in complicated cases
What groups are likely to have bacteremia with Campylobacter jejuni?
Elderly and patients with AIDS
What bacterial infection had Guillain-Barre syndrome been associated with?
Campylobacter jejuni
What complications are likely in patients with HLA-B27 with Campylobacter infection?
Reactive Arthritis
What is Guillain- Barre syndrome?
It is one of the most common cause of flaccid paralysis in the US and manifests as symmetrical ascending muscle weakness and facial diplegia
What is treatment of choice in Campylobacter enteritis?
Rehydration
Describe the Salmonella bacteria.
Gram negative rods
How are the different strains of Salmonella differentiated?
Antigenic analysis of strains are based on cell wall (O) and flagellar (H) antigens
Which antigen of Salmonella undergo phase variation?
H antigens undergo phase variation via DNA rearrangements
Salmonella ferment _____, but not ferment______ and reduce______, they are facultative ______ organisms.
glucose
lactose
nitrates
anaerobic
What are the main reservoir for Salmonellae?
Animals are the main reservoir
what is the role of antibiotics in nontyphoidal Salmonella infection?
Antibiotics are not usually required to treat
How is salmonella infection acquired?
Infection is acquired by ingestion of contaminated food or water, by contact with infected animals or person to person
What is the infective dose of Salmonella?
10^5 organisms
How does Salmonella cause infection?
The organisms adhere to a distal portion of small intestinal mucosa, this is mediated by fimbriated adhesins. A localized infection in the intestinal epithelial cells are mediated by bacterial invasins
What defines complicated enteritis of Salmonella?
Dissemination throughout the reticuloendothelial system and bacteremia
Salmonella typically causes ______ diarrhea.
bloody
How does the immune system react to Salmonella?
There is an overwhelming influx of neutrophils to the intestines
What causes complicated enteritis of Salmonella?
Phagocytosis of macrophages
How does Salmonella typhi differ from other salmonella?
S. typhi is an encapsulated organism but all the others are non- encapsulated
How are clinical isolates of Salmonella typhi identified?
S. typhi is identified by biochemical reactions and by agglutination with O, H, and Vi antibodies
The incubation period for S. typhi is _____ but the incubation period for nontyphoidal Salmonella is ______
3 days to 3 months
6 to 48 hours
How does Salmonella typhi reach the submucosal lymph nodes of the intestine?
The typhoidal salmonellae bind to intestinal M cells by an unknown adhesin. After invasion, the M cells die and deliver the salmonellae into the Peyer patch.They then migrate through the intestinal mucosa of the terminal ileum into the submucosal lymph nodes
What is the preferred antibiotic empirical therapy?
Ciprofloxacin
What group of people are susceptible to chronic infection of Salmonella typhi?
Those individuals with biliary obstruction or gallstones are particularly prone to becoming long term carriers
What is the skin manifestations of S. typhi?
Rose spots
What are rose spots?
They are erythematous maculopapular lesions caused by thrombocytopenia and vascular capillary leakage caused by S. typhi
What are the intestinal changes with an infection of S. typhi?
An infiltration of mononuclear cells into the colonic mucosa
How does Salmonella typhi survive and multiply?
It survives and multiplies within macrophages by inhibiting the oxidative burst
How does S. typhi cause hepatomegaly and splenomegaly?
They are carried inside the monocytes and delivered to the RES.
What is the causative agent of enteric fever?
The signs and symptoms of enteric fever including abdominal pain are caused by the secretion of cytokines and pyrogens by macrophages
How does one vaccinate against S. typhi ?
There is a live vaccine that is taken orally and consists of the attenuated mutant of S. typhi
There is also an IM vaccine based on the Vi capsular polysaccharide antigen
Why can S. typhi cause chronic infection in those with biliary obstruction or with those that have gallstones?
The typhoidal salmonellae are resistant to bile
How does S. typhi cause diarrhea days after the febrile illness?
It reenters the intestines in bile, causing diarrhea
How does the body eventually overcome a Salmonella typhoidal infection?
Humoral antibody and activated macrophages
How long does it take to overcome a Salmonella typhoidal infection?
3 weeks
What is the causative agent for bacillary dysentery?
Shigella flexneri
What is the most virulent species of Shigella?
S. dysenteriae
It belongs in serogroup A
What is the most predominant form of shigella in the United States?
Shigella sonnei
Which type of Shigella secretes the Shiga toxin?
S. dysenteriae type 1
How does Shiga toxin work?
Stx is an inhibitor of protein synthesis, targeting the 23S ribosomal RNA. It kills intestinal epithelial cells and endothelial cells
Which Shigella strain produces watery and less severe diarrhea?
S. sonnei
How is Shigella cultured?
On Hektoen agar
Shigella is a _______ anaerobe
facultative
How does the Shigella bacteria cause local spread?
Infected intestinal epithelial cells produce attractants for neutrophils, which migrate between the epithelial cells, causing a breakdown of the tight junctions and facilitating the local spread of the bacteria
Which host protein is essential for the spread of Shigella?
cadherin L-CAM
How does the Shigella bacteria move from infected intestinal cell to uninfected intestinal cell?
Passage of the bacteria into adjacent epithelial cells occurs through finger-like projections from the surface of an infected cell to the surface of the an uninfected cell
What are the systemic complications of S. dysenteriae type 1?
Hemolytic-uremic syndrome and TTP are the systemic complications
What is the antimicrobial of choice in the treatment of Shigella?
TMP/SMX
What antimicrobial is recommended for the treatment of Bactrim resistant Shigella?
quinolones
Where does the Shigella bacteria initially invade the colonic mucosa?
In the COLONIC mucosa, the invasive bacteria penetrate the M cells and are taken up by the macrophages in the lamina propria
What happens the Shigella bacteria ingested inside the dead macrophages?
the bacteria released from the dead macrophages also invade the intestinal epithelial cells via their basolateral membrane
All Shigella bacteria do not ferment lactose except _______
S. sonnei
What is the most common pathogen that is isolated from bloody diarrhea?
E. coli O157:H7
How is E. coli O157:H7 cultured?
On sorbitol - MacConkey agar medium
How is the diagnosis of E. coli O157:H7 made?
Identification of E. coli O157:H7 is made on the basis of an indole-positive, lactose positive, sorbitol- nonfermenting isolate that is positive for agglutination of O157- specific antibodies
Describe the course of hemorrhagic colitis.
It is characterized by abdominal cramps and watery diarrhea that after a few days became streaked with blood or grrossly bloody
What are the major vehicles of infection for E. coli O157:H7?
Ground beef and unpasteurized milk
Which E. coli infection is like mild cholera and which is like mild shigellosis?
Enterotoxigenic E. Coli is like mild cholera and Enteroinvasive E. coli is like mild shigellosis
Which form of E. coli infection has the complications of hemolytic-uremic syndrome and TTP?
E. coli O157:H7, EHEC
What other form of E.coli invades the colonic mucosa like the Enterohemorrhagic E.coli?
Enteroinvasive E.coli
What is the serotype of Enteropathogenic E.coli?
O26:H111
How does Enterohemorrhagic E. coli invade colonic mucosa?
EHEC strains produce virulence factors that allow them to attach and efface the brush border of the intestinal epithelium
What happens to the enterocyte after Enterohemorrhagic E.coli attaches to it?
The affected enterocytes show a dramatic loss of microvilli and rearrangement of cytoskeleton elements, with a proliferation of filamentous actin under the areas of attachment
How does E. coli O157:H7 ( EHEC) kill enterocytes?
With Shiga toxin -1 and Stx-2
Why does hemolytic uremic syndrome occur in EHEC?
The Stx-1 or Stx-2 binds to a glycolipid receptor molecule on the surface of endothelial cells in the kidney
Shiga toxins are cytotoxic to colonic and _______ cells
renal endothelial
How does enterotoxigenic E.coli kills colonic endothelial cells
With enterotoxins
The heat labile LT stimulates adenyl cyclase and this increases cAMP
If a colonoscopy was done in a patient with E.coli, and it showed a necrotic mucosa what should we suspect?
Enteroinvasive E.coli
If a colonoscopy was done in a patient with E.coli, and it showed a necrotic mucosa what should we suspect?
Enteroinvasive E.coli
What are the different types of E.coli that can result in bloody diarrhea?
Enteroinvasive E. coli
Enterohemorrhagic E. coli
What is the antimicrobial therapy for E.coli?
Most cases do not require antimicrobial therapy.
Describe Vibrio bacteria.
The bacteria inthe genus Vibrio are curved, Gram negative rods with a single flagellum
Vibrio are nonspore forming, oxidase-_______ and facultative ________.
positive
anaerobes
How is Vibrio cultured?
On Thiosulfate-citrate-bile agar--> this supports Vibrio growth but inhibits the commensal colonic bacteria
What type of cholera cause epidemics?
Organisms that agglutinate in 0:1 antiserum.
What type of cholera causes pandemics?
Organisms that agglutinate in 0:1 antiserum.
Where is the current pandemic of cholera located?
The seventh global pandemic is in Asia, Africa and Latin America and it began in Sulawesi, Indonesia
What is the causative agent in the current pandemic of cholera?
El Tor 0:1
What medication would predispose a person to cholera?
Antacids or any drug that would reduce stomach acidity
What are the risk factors for developing cholera in the United States?
Ingestion of contaminated raw seafood
Where would we expect to see cases of cholera in the United States?
Along the Gulf Coast, mainly in Texas and Louisiana
How does reduced stomach acidity give Vibrio cholera an advantage to infection?
V. cholorae lacks a mechanism for acid resistance so they need a very large inoculum size for infection EXCEPT for patients with reduced gastric acidity
Where does V.cholerae colonize in the body?
In the small intestine
How does V. cholerae colonize the GI tract?
V. cholerae colonizes the small intestine via long filamentous pili
Describe the cholera toxin.
CTX is an A-B type ADP-ribosylating enterotoxin
How does CTX enter an intestinal cell?
The B pentamer binds to Gm1 ganglioside, a glycolipid on the surface of jejunal epithelial cells that serve as the toxin receptor and facilitates the delivery of the A subunit to its target
What is the toxin receptor for the Cholera toxin?
Gm1 ganglioside on the jejunal epithelial cell
How does the cholera toxin cause the secretory diarrhea?
Via the functional A subunit.
It activates the adenyl cyclase cascade system by irreversible transfer of an ADP- ribose subunit from NAD to membrane Gs protein --> raising intracellular concentrations of cAMP --> activates excretory chloride transport system in the crypt cells--> NaCl accumulates in the lumen
Describe the diarrhea caused by the cholera toxin
Rice water diarrhea
How much fluid loss can occur with cholera in an hour?
1 L/hr
What is the antibiotic of choice with cholera?
Doxycycline
Why is cholera vaccine NO LONGER recommended for travelers?
Killed cholera vaccine has limited value --> protects only 50% of those vaccinated of short duration (3-6 months)
In the current pandemic of cholera, virulence is ____ but carrier rate is _____.
low
high
What is the most common cause of watery diarrhea in travelers?
Enterotoxigenic E. coli
Why does food poisoning due to S.aureus and B.cereus have a rapid onset of 1- 6 hours?
They have a pre- formed toxin
How can you identify Staphylococci on blood agar?
They are yellowish colonies that are identified based on a coagulase- positive reaction.
What mechanism allows S aureus to cause food poisoning via a meat dish despite reheating the dish to a high temp before serving?
If the dish was left out at a warm temp for hours, the heat stable enterotoxin would have already formed
What would be the source of S. aureus food poisoning?
S. aureus is of human origin, from a purulent discharge of an infected finger or eye, abscesses, acneiform facial eruptions, or nasopharyngeal secretions of food preparers
What is the antibiotic of choice for S. aureus infection ?
There is none
The syndrome is self-limiting
How long does the upper GI symptoms caused by the enterotoxin of S. aureus last?
12 to 24 hours
What are the common food sources of S. aureus enterotoxin?
Ham (meats), mayonnaise, custard
What are the common food sources that cause Bacillus cereus food poisoning between 1-6 hours
Reheated fried rice
What are the common food sources that cause Bacillus cereus food poisoning between 8-24 hours
Cream sauce
The heat-stable enterotoxin of Bacillus cereus causes _______but the heat- labile enterotoxin causes _______
Acute upper GI symptoms
Watery Diarrhea
What types of toxin does Bacillus cereus produce?
Two
Heat stable (emetic)
Heat labile (diarrheogenic)
What type of symptoms does a Clostridium perfringens infection cause?
Watery diarrhea
What are the common food sources of Clostridium perfringens?
Reheated meat dishes, gravy
When would we see symptoms from a Clostridium perfringens infection?
Within 8-12 hours
Clostridium botulinum is a Gram _____, spore- forming _____ .
positive
rod
Clostridium botulinum is an ______ anaerobe.
obligate
What is associated commonly with cases of wound contamination of Clostridium botulinum?
Skin-popping black tar heroin
What is the most frequently encountered form of botulism?
Infant botulism
What places infants at risk for contracting botulism?
Ingestion of honey and to a lesser extent corn syrup
What is the disease causing agent in Clostridium botulinum infection?
A heat labile neurotoxin
What are the primary sources of adult botulism?
Ingestion of preformed toxin in home- canned fruit, sausage, and fish products
What is the action of Clostridium botulinum neurotoxin at the neurotoxin junction?
It cleaves the components of the neuroexocytosis apparatus, irreversibly preventing release of ACh from the neuromuscular junction
What are the clinical effects of Clostridium botulinum food poisoning?
descending symmetrical flaccid paralysis
diarrhea
vomiting
blurred vision
bulbar weakness
dysarthria
ptosis
dysphagia
dry mouth
Where should we first see the effects of Clostridium botulinum paralysis?
It usually beginning with the cranial nerves, that may progress rapidly
How does Clostridium botulinum move the GI tract to the NMJ?
It doesnt. The spores germinate and produce the neurotoxin, which then circulates in the bloodstream.
Describe the involvement of the CNS with Clostridium botulinum neurotoxin.
the CNS is not involved.
What are the targets for the Clostridium botulinum neurotoxin.
Peripheral cholinergic nerve terminals, including NMJ, postganglionic parasympathetic nerve endings, and peripheral ganglia.
What is the role of antibiotics in infant botulism?
Antibiotics are contraindicated because these drugs may increase the levels of toxin in the gut by bacterial lysis
What is the treatment of adult botulism?
Use purgatives to expel retained food
You can use equine antitoxin serum to neutralize toxin that is not yet internalized in neurons
How does the Clostridium botulinum neurotoxin enter a nerve cell?
It attaches specifically to peripheral cholinergic synapses and is internalized inside the nerve cell to endocytic vesicles, from where it is translocated into the cytosol.
Why does Clostridium botulinum neurotoxin cause dry mouth, ptosis?
It affects peripheral cholinergic nerve terminals
What is the role of antibiotics in wound botulism?
Penicillin, metronidazole with wound debridement is an effective modality for management.
What effect does boiling have on food that is already contaminated with Clostridium botulinum?
It can inactivate the toxin but the spores are more difficult to destroy
Why can adults eat honey but infants can't?
The spores of Clostridium botulinum are not able to germinate in older children or adults like they can in infants
Clostridium difficile is a strict _______ bacterium
anaerobe
Clostridium difficile is Gram ______ and a spore- forming ____
positive
rod
How does Clostridium difficile cause disease?
via either one of its two toxins: toxin A or toxin B
What is the carrier rate for Clostridium difficile in the adult population
4%
What is the carrier rate for Clostridium difficile in the neonate population
50%
What is the carrier rate for Clostridium difficile among hospitalized adults that have received antibiotic therapy?
46%
What are the commonly incriminated antibiotics involved in Clostridium difficile associated diarrhea?
Clindamycin,
3rd generation Cephalosporin
Ampicillin
Primary cases of Clostridium difficile associated diarrhea occur via________ but secondary cases occur via _______.
endogenous mode in precolonized patients exposed to antibiotics
exogenous transmission of spores in the hospital
Which is the more potent toxin of Clostridium difficile?
Toxin B
How do broad spectrum antibiotics encourage Clostridium difficile associated diarrhea?
Broad-spectrum antibiotics suppress normal flora
How does the toxins of Clostridium difficile attack the epithelial cell of the colonic mucosa?
They bind to the cellular GTP -binding proteins and inactivate them by glycosylation, and dysregulate the action of the cytoskeleton in epithelial cells. This causes depolymerization of actin.
What is the receptor of Clostridium difficile in an epithelial cell?
Both toxins exert their effects by binding to cellular GTP - binding proteins.
What is the antibiotic of choice in Clostridium difficile associated diarrhea?
Metronidazole
What should one expect to see in a colonoscopy of a patient withClostridium difficile associated diarrhea?>
Multiple elevated , yellowish white plaques (pseudomembranes) within the colon
What is a potentially serious complication in a patient with psuedomembranous colitis?
toxic megacolon
What are the cumulative effects seen in the bowel lining that has been exposed to the toxin of Clostridium difficile?
the bowel lining becomes erythematous and friable, with ulceration and hemorrhagic necrosis due to the breakup of actin filaments within the cell
In the _____ months, rotavirus can be very severe and is very common.
winter
Describe Rotavirus nucleocapsid structure.
The viral nucleocapsid is composed of two concentric shells.
Rotavirus is a noneveloped ______ virus in the family of _________
RNA
Reoviridae
Describe the Rotavirus virion structure.
The double shelled particles are shaped like wheels with short spokes on an outer rim are the complete infectious virions
there are ____ major subgroups of rotavirus and _______serotypes of human rotaviruses
three
nine
Describe the genome of Rotavirus.
Rotaviruses have a segmented genome with 11 segments of a double- stranded RNA genome
What defines the antigenic types of rotaviruses?
Two structural proteins on the outermost shell defines the antigenic types of the virus.
How is Rotavirus diagnosed?
An assay that detects rotavirus viral antigen in stool specimens
Why was a rotavirus vaccine unsuccessful?
It was withdrawn due to reports of intussusception as a sideeffect
How is rotavirus transmitted?
through fecal- oral transmission and through fomites
What is the single most important cause of severe dehydrating diarrhea in infants and in children younger than 3 years?
rotavirus
What is the cellular target of a rotavirus that has been ingested?
The virus infects the mature villus tip cell of the small intestine.
How does Rotavirus cause osmotic diarrrhea?
The rotavirus invasion of the epthelial cells of the small intestine results in destruction of the mature absorptive cells.
The damaged cells on villi are replaced by immature crypt cells that cannot absorb carbohydrates or other nutrients efficiently --> osmotic diarrhea
What is frequently seen with active rotavirus infection?
Respiratory tract symptoms but with negative chest exams and radiologic studies
What is the antiviral therapy of choice for rotavirus infection.
There is none
Supportive care only via IV or oral rehydration therapy
What is the incubation period of Norwalk virus?
24 to 48 hours, but most cases occur within 12 hours of exposure
Why are Noroviruses considered highly contagious?
An inoculum of as few as 10 viral particles may be sufficient to infect an individual
How are Noroviruses transmitted?
Primarily through the fecal- oral route or by direct person- person spread
What is the structure of Noroviruses?
NV is a spherical, nonenveloped virus
Describe the genome of Noroviruses
It has a positive sense, single-stranded RNA genome
How are Noroviruses visualized?
Human antibodies are needed to concentrate and visualize the Noroviruses.
How can an outbreak caused by Noroviruses be distinguished from other viruses?
1. The incubation period is 24 to 48 hours
2. Vomiting occurs in 50% or more of the cases
3. The duration of illnesses last from 12 to 60 hours
4.Diarrheal illness rapidly spreads among many individuals
What morphological changes are seen in the mucosa of the small bowel in a Norovirus infection?
The biopsy should show shortening and atrophy of the villi, crypt hyperplasia,and infiltration of the lamina propria by PMN and mononuclear cells
What is poorly absorbed as a result of a Norovirus infection?
There is carbohydrate malabsorption