MCQs on Enterobacteriaceae, gut flora

Enteric bacteria/ Gut flora - E. coli, Salmonella spp, and Shigella spp

1) A large family of enteric bacteria is present as normal flora in the intestines of humans and other mammals.
Which of the following is less likely to be found as the normal flora of the intestine? 
a) Escherichia spp
b) Salmonella spp
c) Staphylococcus spp
d) Proteus spp

2) Which of the following bacteria is not a clinically important enterobacteriaceae?
a) E.coli
b) Streptococcus pyogenes
c) Salmonella typhi
d) Proteus mirabilis

3) All are the important general characteristics of enteric bacteria, EXCEPT?
a) Aerobic and facultatively anaerobic
b) Non-spore forming
c) Grow in media with bile salts
d) Do not produce nitrates
e) Ferment glucose
f) Most of them are catalase positive and oxidase negative

4) Enteric bacteria are mainly classified based on their ability to ferment various sugars including lactose. 
Which of the following bacteria is a non-lactose fermenter?
a) Klebsiella spp
b) Salmonella spp
c) Enterobacter spp
d) Citrobacter spp

5) Escherichia coli is one of the widely distributed enteric bacteria that causes diarrhea worldwide. 
Name the other common gram negative bacteria that causes diarrhea developing countries like India, Nepal, and Bangladesh? 
Select all the correct answers:
a) Shigella spp
b) Salmonella spp
c) Mycobacterium spp
d) Proteus spp

6) Enteropathogenic E. coli (EPEC) is a common foodborne pathogen, when ingested through contaminated water or food, it attaches to the mucosal cells of the small intestine. 
Symptoms such as watery diarrhea, vomiting, and non-bloody stools lasting for 1-3 days. 
What are the two important virulent factors of pathogenesis of EPEC?
a) The chromosomal locus of enterocyte effacement (LEE)
b) The bundle-forming pilus encoded by a plasmid adherence factor (EAF)
c) Both of the above
d) None of the above

7) Enteroinvasive E. coli (EIEC) are nonmotile, non-lactose, or late lactose fermenters that are predominantly found in developing countries infecting children and travelers. 
Which of the following infection is similar to the EIEC infection?
a) Bacillary dysentery
b) Shigellosis
c) Typhoid
d) Hay fever

8) Enterobacteriaceae expresses a variety of virulent antigens, all of the following are the antigens of enteric bacteria, EXCEPT?
a) O antigens (in lipopolysaccharide)
b) K antigens (capsular antigens)
c) H antigens (flagellar proteins)
d) D antigens 

9) E. coli is one of the most common enteric bacteria isolated in urinary tract infections (UTIs) followed by the bacteria Proteus mirabilis
All of the following are the cultural characteristics of Proteus mirabilis, EXCEPT?
a) Facultative aerobe
b) Urease positive
c) Motile
d) Citrate positive

10) Shigellosis is caused by Shigella dysenteriae in humans, the common symptoms are fever, abdominal cramps, diarrhea sometimes with blood. The infection is attributed to the …................................. activity of Shiga toxin which increases the severity by tissue invasion in the large intestine.
a) Exotoxic
b) Enterotoxic
c) Cytotoxic
d) Neurotoxic

11) Enterotoxigenic E. coli (ETEC) produces two major types of toxins, heat-labile (LT) and heat-stable (ST) toxins. 
LT or cholera-like toxin activates adenylate cyclase (cAMP) whereas ST activates................................. that causes Travelers’ diarrhea.
a) Ribosomal dysfunction
b) Decarboxylase reaction
c) Guanylate cyclase
d) Fermentation of sugars

12) The following bacteria has the following morphological characteristics:
  • a rapid lactose fermenter
  • motile with flagella
It is one of the major pathogens that causes a broad range of hospital-acquired infections such as pneumonia, urinary tract infections, and wound infections. 
Name the possible pathogen
a) Streptococcus pyogenes
b) Pseudomonas aeruginosa
c) Mycobacterium tuberculosis
d) Enterobacter aerogenes

13) Salmonella typhi is an important foodborne and waterborne pathogen, during the pathogenesis it penetrates into the intestine, reaching the lymphatics and the bloodstream that ultimately causes the infection in the intestine, also known as "Typhoid". 
Which of the following is the most likely site where the pathogenesis can easily occur?
a) Mononuclear phagocytic cells in the liver and Peyer’s patches of the small intestine
b) Liver, spleen, lymph nodes, and large intestine
c) Isolated follicles and Peyer’s patches of a large intestine
d) None of the above

14) Which type of salmonellae is primarily infectious to humans?
a) Salmonella typhi A
b) Salmonella paratyphi A, B, and C
c) Salmonella paratyphi A and B
d) Salmonella paratyphi

15) The symptoms of typhoid fever usually develop in one to three weeks after exposure to S. typhi.
Which of the following is the least common symptom of the disease?
a) Weight gain
b) Headache
c) High-grade fever
d) Rashes

16) Which of the following Shigella spp produces a heat-labile exotoxin that can affect both the gut and central nervous system resulting in diarrhea and meningismus?
a) Shigella sonnie
b) Shigella dysenteriae type 1
c) Shigella dysenteriae type 2
d) Shigella dysenteriae type 3

17) S. enteritidis and S. typhimurium cause enterocolitis and gastroenteritis in humans. 
What is the most common food for source of transmission of the infection to humans?
a) Fruits and vegetables
b) Poultry and eggs
c) Canned beans
d) Yogurt

18) The biochemical properties of enteric bacteria are helpful in the differentiation of the specific pathogen.
Which of the following biochemical test method demonstrates the production of tryptophan into an indole compound?
a) IMViC test
b) MRVP test
c) TSI test
d) Citrate test

19) Which of the following culture media is not the selective media most commonly used for the isolation of salmonellae and shigellae?
a) Deoxycholate citrate agar
b) Xylose-lysine decarboxylase agar
c) Salmonella –Shigella agar
d) Potato dextrose agar

20) The Widal test is used for the detection of Salmonella typhi and other subspecies. 
This test is based on which of the following 'principles'?
a) the antigens are detected using the neutralization assay
b) the antigen combines with its soluble antibody and forms a lattice with a visible precipitate
c) the antigens bind to RBCs and form the agglutination
d) None of the above

21) The bloody dysentery epidemics occurred in different parts of India during the 1980s. 
Name the predominant pathogen identified during the dysentery outbreaks in India in the 2000s
a) Shigella dysentery type 1
b) Shigella boydii
c) Shigella dysentery type 3
d) Shigella sonnei

22) All of the following statements regarding coliform bacteria are true, Except?
a) They are used as the indicator for the sanitation of the water
b) Consists of gram-negative, rods, non-spore-forming bacteria
c) Can survive in soil and plant vegetation
d) The acceptable number of coliform counts in drinking water is <1

23) There are numerous research studies that have been done by scientists around the world on gut flora, in recent years several studies have shown that there is a strong relationship between gut flora and the health conditions of an individual.
What are the common types of poor health conditions that have been strongly associated with the imbalance and changes in the gut flora?
a) Overweight 
b) Mental stress
c) Inflammation
d) Road accidents

24) Cholera is a virulent disease that is most prevalent in Asia, mainly affecting children under 5 and older people, according to WHO (world health organization) there have been more than 5 pandemics reported in history. 
Select all the correct statements regarding the prevention and control of cholera that can help to reduce the spread of the disease in children.
a) Provide oral rehydration solution to the patients
b) Proper and regular hand washing practices
c) Provide oral cholera vaccines to the older patients
d) Organizing awareness program for hygiene practices

25) Salmonella typhi and S.paratyphii are the two major pathogens that cause enteric fever.
Which of the following are Not possible specimens taken for the routine diagnosis of the disease?
a) Blood
b) Sputum
c) Feces
d) Urine

Multiple Choice Answers:
1)-c) Staphylococcus spp. It is a gram positive bacteria

2-b) Streptococcus pyogenes is a  gram positive bacteria, enterobacteriaceae are gram negative bacteria.

3-d) Nitrate production, most of the enteric bacteria, such as Escherichia coli (E. coli) and other related species, have the ability to convert dietary nitrates (NO3-) present in food and water into nitrites (NO2-) and other nitrogen compounds.

4-b) Salmonella spp. When inoculated in MacConkey agar, the colonies of Salmonella spp appear colorless because of the inability to produce lactose in the media.
5- a, and b. c) Mycobacterium spp is a acid fast bacilli, not a enteric pathogen, and d) Proteus spp is gram negative bacilli, a common pathogen of UTI.

6-c)Both of the above

7-b)Shigellosis. EIEC and shigellosis (Shigella bacteria) infections both have common symptoms such as watery and bloody diarrhea, abdominal cramps and pain, fever, nausea and vomiting.
8-d)D antigen

9)-a)Facultative aerobe. P. mirabilis is facultative anaerobe. Facultative anaerobes are microorganisms that have the ability grow in environments with or without oxygen (aerobic or anaerobic).

11-c) Guanylate cyclase
12-d) Enterobacter aerogenes
13-a)Mononuclear phagocytic cells in the liver and Peyer’s patches of the small intestine
14-c) Salmonella paratyphi A and B
15-a) Weight gain
16-b) Shigella dysenteriae type 117)-b)
18-a) IMViC test
19-d) Potato dextrose agar
20-b)the antigen combines with its soluble antibody and forms a lattice with a visible precipitate
21-a)Shigella dysentery type 1
22-d) The acceptable number of coliform counts in drinking water is <1
23-a), b), and c)
24- a), b), and d)
25- b) Sputum


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