7 Enteric Gram Negative Bacilli (34) Flashcards
Case
A 45-year-old woman presents with a 2-day history of abdominal cramps and bloody diarrhea. She has just returned from her vacation in India, where she ate many of the local foods. Her blood pressure is 120/80 mmHg, pulse rate is 84/minute, and temperature is 37.8°C. Stool examination reveals many polymorphonuclear leukocytes and aerobic Gram-negative non-motile organisms. From the stool culture, a Gram-negative rod was isolated that forms non-lactose fermenting colorless colonies on eosin-methylene blue (EMB) agar.
What organism is the most likely cause?
1 Shigella dysenteriae
2 Escherichia coli
3 Vibrio cholerae
4 Vibrio parahaemolyticus
5 Campylobacter jejuni
Shigella dysenteriae
Shigella dysenteriae is the causative organism in this case. Shigella are Gram-negative non-motile rods that form non-lactose fermenting (colorless) colonies on MacConkey’s or EMB agar. On TSI agar, they cause alkaline slant and an acid butt, with no gas and no H2S. After an incubation period of 1-4 days, symptoms begin with fever and abdominal cramps, followed by diarrhea, which may be watery at first but later contains blood and mucus. The disease varies from mild to severe depending on 2 major factors: the species of Shigella and the age of the patient. Young children and elderly people are the most severely affected. Treatment includes correction of dehydration, electrolyte imbalance, and antibiotic therapy in severe cases.
Escherichia coli are Gram-negative rods that ferment lactose, a property that distinguishes it from the 2 major intestinal pathogens, Shigella and Salmonella. It produces dark blue-black colonies with a greenish metallic sheen on EMB agar.
Vibrio cholerae is a Gram-negative, highly motile, non-spore forming comma-shaped rod, which causes characteristic watery diarrhea/cholera. It does not ferment lactose.
Vibrio parahaemolyticus is a comma-shaped Gram-negative rod involved in a foodborne illness known as seafood poisoning. It produces watery diarrhea.
Campylobacter jejuni is a comma-shaped Gram-negative rod. It needs to be cultured on a special agar (e.g., Skirrow’s agar) at 42°C in high CO2 and low O2 conditions. It produces enterocolitis.
The major property that distinguishes E. coli from the two other intestinal pathogens–Shigella and Salmonella–is that it ferments:
1 Lactose
2 Maltose
3 Fructose
4 Glucose
5 Acetate
Lactose
The major property that distinguishes E. coli form the two other intestinal pathogens Shigella and Salmonella is that it ferments lactose. It does not ferment maltose, fructose, glucose and acetate.
Impaired blood supply and the presence of Escherichia coli (E. coli) predisposes to infection by Bacteroides fragilis (B. fragilis) because
1 E. coli is a facultative anaerobe, it uses up oxygen and reduces it to a level so that B. fragilis an anaerobe can grow
2 E. coli and B. fragilis are symbiotic
3 E. coli is an aerobe, it uses up oxygen and reduces it to a level so that B. fragilis an anaerobe can grow
4 B. fragilis is a facultative anaerobe, it uses up oxygen and reduces it to a level so that E. coli an anaerobe can grow
5 B. fragilis is an aerobe, it uses up oxygen and reduces it to a level so that E. coli an anaerobe can grow
E. coli is a facultative anaerobe, it uses up oxygen and reduces it to a level so that B. fragilis an anaerobe can grow
Impaired blood supply and the presence of E. coli predisposes to infection by B. fragilis because E. coli is a facultative anaerobe, it uses up oxygen and reduces it to a level so that B. fragilis an anaerobe can grow.
Which of the following group of Escherichia coli is the common cause of diarrhea in infants and is implicated in outbreaks of diarrhea in nurseries?
1 Enterotoxigenic
2 Enteroinvasive
3 Enteropathogenic
4 Enterohemorrhagic
5 Enteroaggregative
Enteropathogenic
Enteropathogenic Escherichia coli (EPEC) is common cause of infantile diarrhea in infants in developing countries. EPEC is associated with outbreaks of diarrhea in nurseries and day care center. EPEC adheres to epithelial cells of the intestine via adhesive factor and causes destruction of microvilli. This results in watery diarrhea and fever.
Which of the following strains of Escherichia coli is commonly implicated in traveler’s diarrhea mediated by heat stable enterotoxin and heat labile exotoxin?
1 Enterotoxigenic
2 Enteroinvasive
3 Enteropathogenic
4 Enterohemorrhagic
5 Enteroaggregative
Enterotoxigenic
Enterotoxigenic Escherichia coli (ETEC) is common cause of traveler’s diarrhea. It is also associated with diarrhea in infants in developing countries. It causes watery diarrhea, abdominal cramps and low grade fever.
The virulence factor implicated are as follows:
Heat stable enterotoxin stimulates fluid secretion by activating guanylate cyclase in enteric epithelial cells.
Heat labile exotoxin binds to the ganglioside at the brush border of epithelial cells of small intestine and leads to activation of adenylate cyclase.
Colonization factors facilitate the attachment of ETEC to epithelial cells of intestine.
The virulence factor produced by Escherichia coli includes
1 P pili
2 Aerobactin
3 α-hemolysin
4 K1 capsular polysaccharide
5 All of the above
All of the above
P pili is adhesin and E. coli strains possessing P pili is mostly implicated in urinary tract infections which includes pyelonephritis.
Aerobactin provides the bacterial cell with iron by extracting iron from the host.
α-hemolysin is associated with lysis of red blood cells and tissue injury.
K1 capsular polysaccharide is antiphagocytic and anticomplementary.
If a stool specimen containing E. coli Serotype O157:H7 is plated on sorbitol-MacConkey agar and observed at 48 hours. What will happen?
1 Do not ferment sorbitol and appear pink
2 Do not ferment sorbitol and appear colorless
3 Ferment sorbitol and appear pink
4 Ferment sorbitol and appear colorless
5 Do not grow on the medium
Do not ferment sorbitol and appear colorless
Serotype O157:H57 of enterohemorrhagic E. coli (EHEC) strain is associated with colitis, hemorrhagic diarrhea and hemolytic uremic syndrome. When a stool specimen is cultured on MacConkey agar containing sorbitol other E. coli ferments sorbitol and appears pink in color. However, E. coli O157:H7 does not ferment sorbitol and appears colorless. These isolates of E. coli O157:H7 can be tested by latex agglutination test for rapid presumptive identification.
The major virulence factor of Enterotoxigenic Escherichia coli (ETEC) includes heat labile toxin and heat stable toxin. The action of heat labile toxin is similar to
1 Exotoxin A of Pseudomonas aeruginosa
2 Vibrio cholerae toxin
3 Diphtheria toxin
4 Botulinum toxin
Vibrio cholerae toxin
Heat labile toxin of Enterotoxigenic Escherichia coli (ETEC) is similar to toxin produced by Vibrio cholerae. It binds to the ganglioside at the brush border of epithelial cells of small intestine and leads to activation of adenylyl cyclase. Adenylate cyclase in turn activates the conversion of adenosine triphosphate to cyclic adenosine monophosphate (cAMP) resulting in cAMP accumulation. This lead to hypersecretion of fluids and electrolytes into the lumen causing watery diarrhea.
Salmonella enterocolitis is characterized by
1 Presence of large number of leukocytes in the stool
2 Headache, nausea, vomiting and profuse diarrhea
3 Positive blood cultures always
4 Negative stool cultures throughout the course of disease
Headache, nausea, vomiting and profuse diarrhea
The most common manifestation of Salmonella infection is enterocolitis. Symptoms of enterocolitis appear 8-48 hours after the ingestion of the organism and it includes nausea, headache, vomiting and profuse diarrhea. The stool contains few leukocytes and gives positive culture. It is accompanied by low grade fever and course of disease usually lasts 2-3 days. Mostly blood cultures yield negative results since bacteremia is not commonly seen (except in immunodeficient patients).
Stool specimen of a patient with profuse diarrhea was cultured on MacConkey agar and Bismuth sulfite medium. Lactose fermenting colonies and non-lactose fermenting colonies were observed on MacConkey medium. Bismuth sulfite media grow black colonies. The isolate fermented glucose and mannose but not lactose and sucrose. What is the most probable causative agent of diarrhea?
1 Escherichia coli
2 Enterobacter aerogenes
3 Shigella boydii
4 Proteus mirabilis
5 Salmonella typhi
Salmonella typhi
Bismuth sulfite is a selective medium and is used for rapid detection of Salmonella typhi. The colonies appear black due to production of H2S. It is non-lactose fermenter and appears clear on MacConkey medium.
Escherichia coli and Enterobacter aerogenes are lactose fermenters and are normal flora of intestine.
Shigella boydii and Proteus mirabilis are non-lactose fermenters and do not produce H2S.
Treatment of chronic carriers of Salmonella typhi with gall stones includes
1 Ampicillin
2 Fluoroquinolones
3 Cholecystectomy
4 A and B
5 A and C
A and C
Salmonella typhi is carried in gall bladder and biliary tract in most carriers. The organism persists in the gall bladder especially if the person has gall stones. In these cases the effective treatment includes combination of ampicillin and cholecystectomy.
Which of the following species of Shigella is a lactose fermenter?
1 Shigella boydii
2 Shigella dysenteriae
3 Shigella flexneri
4 Shigella sonnie
Shigella sonnie
Shigella sonnie type D is only lactose fermenting species of Shigella, as shown in the following:
Group and Type Glucose Lactose Mannitol Ornithine
Decarboxylase
S. boydii C + - + -
S. dysenteriae A + - - -
S. flexneri B + - + -
S. sonnei D + + + +
The urine specimen of a patient admitted in the hospital grew large, mucoid, pink colony on MacConkey agar. The isolate was oxidase negative, non motile gram negative rod. Which of the following organism you will suspect?
1 Proteus mirabilis
2 Klebsiella pneumoniae
3 Hemophilus ducreyi
4 Salmonella typhi
5 Streptococcus agalactiae
Klebsiella pneumoniae
Klebsiella pneumoniae contains large polysaccharide capsule contributing to its mucoid growth.
It is gram negative rod that is non motile and ferments lactose.
Proteus mirabilis is
Gram negative rod
Motile
Non lactose fermenter
Exhibits swarming on the medium
Hemophilus ducreyi is
Gram negative coccobacillus
Oxidase positive
Non lactose fermenter
Salmonella typhi
Gram negative rod
Motile
Non lactose fermenter
Streptococcus agalactiae
Gram positive cocci
Non motile
Klebsiella oxytoca is
1 Non lactose fermenter
2 Gram positive rod
3 Spore former
4 Capsulated
5 Motile
Capsulated
Klebsiella oxytoca is part of the family Enterobacteriaceae. It has the following characteristics:
Gram negative rod
Non motile
Capsulated
Non spore former
Lactose fermenter
The urine specimen of a 55-year-old AIDS patient yields non-lactose fermenting colonies on MacConkey agar. Typical swarming of the colonies was observed. The organism isolated was a gram-negative rod and gave a negative oxidase and positive urease test. Which of the following is the most probable organism isolated?
1 Escherichia coli
2 Klebsiella pneumoniae
3 Hemophilus ducreyi
4 Proteus mirabilis
5 Pseudomonas aeruginosa
Proteus mirabilis
Proteus mirabilis species is associated with urinary tract infections, bacteremias, and pneumonia in debilitated hosts and individuals receiving antibiotic treatment.
Klebsiella pneumoniae is
Gram-negative rod
Non-motile
Capsulated
Lactose fermenter
Mucoid colony on MacConkey medium
Escherichia coli is
Gram-negative rod
Motile
Lactose fermenter
Hemophilus ducreyi and Pseudomonas aeruginosa are oxidase positive.
Case
A 15-year-old boy was admitted to a healthcare facility with a 2-day history of nausea, vomiting, diarrhea, headache, and a continued fever with 39.5°C (103.1°F) temperature. The patient was found to have rose-colored spots on his abdomen. The physician suspected it to be a case of Salmonella infection based on the symptoms. Microscopic examination of the stool revealed Gram-negative bacilli. The organism did not show any motility and produced mauve colonies on CHROMagar Salmonella (CAS) media and black transparent colonies on Hektoen enteric agar (HEA), Salmonella-shigella (SS) agar, and xylose-lysine-desoxycholate agar (XLD). On XLD agar, yellow-colored zones surrounded the colonies.
What is the causative organism in this patient?
1 Salmonella enteritidis
2 Salmonella gallinarum
3 Salmonella paratyphi
4 Salmonella typhi
5 Salmonella typhimurium
Salmonella typhi
The patient has been infected by Salmonella typhi. Salmonella species are a group of non-spore forming, facultative anaerobic, Gram-negative bacilli that are predominantly motile; they are found in the intestinal tracts of humans and other warm-blooded animals. They are responsible for the outbreak of food poisoning instances. S. typhi infection causes typhoid with symptoms like abdominal pain, headache, loss of appetite, and in some cases appearance of rose-colored spots across the abdomen. Diagnostic test for all the species of Salmonella involve microscopic examination of stool for the detection of organisms, and later biochemical tests are used to identify the species. All species of Salmonella produce mauve colonies on CAS medium. S. typhi and paratyphi produce black-colored colonies on XLD, SS, and HEA media as a result of hydrogen sulfide (H2S) production, but only S. typhi produces yellow-colored halos around its colonies on XLD media due to fermentation of the sugar xylose present in it.
The best way to prevent Salmonella infections is by properly cooking food, good hygiene practices, and heating food to appropriate temperatures or prompt refrigeration.
Salmonella enteritidis is transmitted to humans from infected hens via raw or undercooked eggs and causes gastroenteritis. These organisms contaminate the eggs before the shells are formed in the infected hens, resulting in transmission of the organisms to humans. Infection by S. enteritidis results in diarrhea and fever. These organisms form mauve colonies on CAS, but serological tests confirm the infection by S. enteritidis. Preventive measures include eating well-boiled eggs and avoiding consumption of cracked eggs.
Salmonella gallinarum is found to infect only chickens, turkeys, and other animals. This organism causes fowl typhoid, resulting in mortality or drop in egg production by the birds. These organisms have not been found to infect humans.
Salmonella paratyphi infection results in symptoms similar to typhoid. The infected person develops rose-colored spots on the chest. The organism is transmitted by direct or indirect contact with feces of the infected person or by contaminated food and water. Differential tests include growing the organism on CAS and XLD media. S. paratyphi do not produce yellow halos around colonies on XLD media. Preventive measures involve hygienic practices when handling food.
Salmonella typhimurium are generally found to infect mice but can be transmitted to humans from contaminated foods of animal origin and cause salmonellosis. Symptoms include diarrhea, fever, headache, abdominal pain, and vomiting. In rare cases, blood is seen in stools. Symptoms are evident 12-72 hours after ingestion of the organism and may last for 4-7 days. Diagnosis involves microscopic examination of stool and serological tests. Preventive measures include proper handling of food.
A 12-year-old girl is taken to the emergency room with a fever (104°F), abdominal cramps, fatigue, muscle aches, and headache. She was on vacation in Venezuela 1 week ago. A blood culture showed Salmonella typhi. Which is the reservoir for these bacteria?
1 Chicken
2 Deer
3 Human
4 Rabbit
5 Rat
Human
Salmonella Typhi is a Gram negative rod, non-lactose fermenter and motile, that lives only in humans. It produces typhoid fever which is more common in developing countries. It is found in bloodstream and intestinal tract, is transmitted by eating or drinking food contaminated with feces. The symptoms are non-specific, fever (103°F), abdominal pain, headache, fatigue. If salmonella is suspected, the bacteria should be found in blood or stool to confirm the diagnosis. A Widal test is one of the methods used to make the diagnosis The test detects H and O agglutinins, but in endemic areas many false positive and false negative results can be found. Mortality is between 12 and 30%. Treatment is with antibiotics such as ciprofloxacin, but resistance to flouroquinolones has increased.
Which of the following groups of Escherichia coli is a common cause of diarrhea in infants and is implicated in outbreaks of diarrhea in nurseries?
1 Enterotoxigenic
2 Enteroinvasive
3 Enteropathogenic
4 Enterohemorrhagic
5 Enteroaggregative
Enteropathogenic
Enteropathogenic Escherichia coli (EPEC) is common cause of infantile diarrhea in infants in developing countries. EPEC is associated with outbreaks of diarrhea in nurseries and day care center. EPEC adheres to epithelial cells of the intestine via adhesive factor and causes destruction of microvilli. This results in watery diarrhea and fever.
Which of the following strain of Escherichia coli is commonly implicated in traveler’s diarrhea mediated by heat stable enterotoxin and heat labile exotoxin?
1 Enterotoxigenic
2 Enteroinvasive
3 Enteropathogenic
4 Enterohemorrhagic
5 Enteroaggregative
Enterotoxigenic
Enterotoxigenic Escherichia coli (ETEC) is common cause of traveler’s diarrhea. It is also associated with diarrhea in infants in developing countries. It causes watery diarrhea, abdominal cramps and low grade fever.
The virulence factor implicated are as follows:
Heat stable enterotoxin stimulates fluid secretion by activating guanylate cyclase in enteric epithelial cells.
Heat labile exotoxin binds to the ganglioside at the brush border or epithelial cells of small intestine and leads to activation of adenylate cyclase.
Colonization factors facilitate the attachment of ETEC to epithelial cells of intestine.
If stool specimen containing E. coli Serotype O157:H7 is plated on sorbitol-MacConkey agar and observed at 48 hours, the isolates
1 Do not ferment sorbitol and appear pink
2 Do not ferment sorbitol and appear colorless
3 Ferment sorbitol and appear pink
4 Ferment sorbitol and appear colorless
5 Do not grow on the medium
Do not ferment sorbitol and appear colorless
Serotype O157:H57 of enterohemorrhagic E. coli (EHEC) strain is associated with colitis, hemorrhagic diarrhea and hemolytic uremic syndrome. When stool specimen is cultured on MacConkey agar containing sorbitol other E. coli ferments sorbitol and appears pink in color. However, E. coli O157:H7 does not ferment sorbitol and appears colorless. This isolates of E. coli O157:H7 can be tested by latex agglutination test for rapid presumptive identification.
The major virulence factor of Enterotoxigenic Escherichia coli (ETEC) includes heat labile toxin and heat stable toxin. The action of heat labile toxin is similar to
1 Exotoxin A of Pseudomonas aeruginosa
2 Vibrio cholerae toxin
3 Diphtheria toxin
4 Botulinum toxin
Vibrio cholerae toxin
Heat labile toxin of Enterotoxigenic Escherichia coli (ETEC) is similar to toxin produced by Vibrio cholerae. It binds to the ganglioside at the brush border of epithelial cells of small intestine and leads to activation of adenylyl cyclase. Adenylate cyclase in turn activates the conversion of adenosine triphosphate to cyclic adenosine monophosphate (cAMP) resulting in cAMP accumulation. This lead to hypersecretion of fluids and electrolytes into the lumen causing watery diarrhea.
Salmonella enterocolitis is characterized by
1 Presence of large number of leukocytes in the stool
2 Headache, nausea, vomiting and profuse diarrhea
3 Positive blood cultures always
4 Negative stool cultures throughout the course of disease
Headache, nausea, vomiting and profuse diarrhea
The most common manifestation of Salmonella infection is enterocolitis. Symptoms of enterocolitis appear 8-48 hours after the ingestion of the organism and it includes nausea, headache, vomiting and profuse diarrhea. The stool contains few leukocytes and gives positive culture. It is accompanied by low grade fever and course of disease usually lasts 2-3 days. Mostly blood cultures yield negative results since bacteremia is not commonly seen (except in immunodeficient patients).
Stool specimen of a patient with profuse diarrhea was cultured on MacConkey agar and Bismuth sulfite medium. Lactose fermenting colonies and non lactose fermenting colonies were observed on MacConkey medium. Bismuth sulfite media grow black colonies. The isolate fermented glucose and mannose but not lactose and sucrose. The most probable causative agent of diarrhea is:
1 Escherichia coli.
2 Enterobacter aerogenes.
3 Shigella boydii.
4 Proteus mirabilis.
5 Salmonella typhi.
Salmonella typhi.
Bismuth sulfite is a selective medium and is used for rapid detection of Salmonella typhi. The colonies appear black due to production of H2S. It is non lactose fermenter and appears clear on MacConkey medium.
Escherichia coli and Enterobacter aerogenes are lactose fermenters and are normal flora of intestine.
Shigella boydii and Proteus mirabilis are non lactose fermenters and do not produce H2S
Which of the following species of Shigella is a lactose fermenter?
1 Shigella boydii
2 Shigella dysenteriae
3 Shigella flexneri
4 Shigella sonnei
Shigella sonnei
Shigella sonnei type D is only lactose fermenting species of Shigella as shown:
Group
and
Type Glucose Lactose Mannitol Ornithine
Decarboxylase
S. boydii C + - + -
S. dysenteriae A + - - -
S. flexneri B + - + -
S. sonnei D + + + +
