Write a answer according to apurva shastri microbiology book Write que

+4 more

Write a answer according to apurva shastri microbiology book Write questions with answers

Reading File

analyse_media

Searching PubMed

bacterial virulence sterilization enteric fever Escherichia coli

Searching the Web

CDC sterilization disinfection flexible endoscopes high-level disinfection typhoid conjugate vaccine WHO

Finding Sources

Answer Key with Explanations

The answers below are written in the standard style used in Apurba Sastry, Essentials of Medical Microbiology. Some questions in the images are incomplete or their options are cut off, so I have answered all clearly visible questions.

1. Bacterial morphology

Question: A Gram-stained smear shows spherical bacteria arranged in chains. Which arrangement is characteristic?

Answer: b. Streptococci in chains

Explanation: Cocci dividing repeatedly in one plane and remaining attached form chains, called streptococci. Staphylococci divide in multiple planes and occur in grape-like clusters.

2. Physiology of bacteria

Question: A bacterium grows rapidly in the presence of oxygen but can also grow in its absence. What is it?

Answer: c. Facultative anaerobe

Explanation: Facultative anaerobes use oxygen when it is available, but can grow anaerobically by fermentation or anaerobic respiration when oxygen is absent. Example: Escherichia coli.

3. Horizontal gene transfer

Question: A multidrug-resistance plasmid is transferred from one bacterium to another by direct cell-to-cell contact. What is the mechanism?

Answer: c. Conjugation

Explanation: In conjugation, plasmid DNA, commonly an R plasmid carrying antibiotic-resistance genes, is transferred through a sex pilus from donor to recipient bacterium.

4. Horizontal gene transfer

Question: A plasmid carrying multiple antibiotic-resistance genes is transferred through a sex pilus. What mechanism is involved?

Answer: c. Conjugation

Explanation: The sex pilus and direct bacterial contact are characteristic of bacterial conjugation.

5. Exotoxin

Question: Which feature best describes bacterial exotoxins?

Answer: b. They are generally proteins with specific cellular targets

Explanation: Exotoxins are protein toxins secreted by bacteria. They are highly potent and usually act on specific host cells or biochemical pathways. They may be produced by both Gram-positive and Gram-negative bacteria.

6. Bacterial virulence factor

Question: A strain of Streptococcus pyogenes prevents phagocytosis by interfering with opsonization. Which factor is responsible?

Answer: b. M protein

Explanation: M protein is the major virulence factor of Group A streptococci. It inhibits opsonization and phagocytosis, partly by interfering with complement deposition.

7. Physical sterilization

Question: A surgical instrument is to be sterilized using moist heat under pressure. Which method is appropriate?

Answer: b. Autoclaving

Explanation: Autoclaving uses saturated steam under pressure, commonly at 121 degrees C for 15 minutes at 15 psi, and destroys bacteria, viruses, fungi, and spores.

8. Chemical sterilization

Question: A heat-sensitive medical device requires sterilization. Which chemical method is most suitable?

Answer: a. Ethylene oxide

Explanation: Ethylene oxide gas is used for sterilization of heat- and moisture-sensitive materials, such as plastic devices, catheters, tubing, and certain electronic equipment. It is sporicidal.

9. Enteric fever

Question: A 15-year-old boy has prolonged fever, abdominal discomfort, constipation, relative bradycardia, and rose spots over the abdomen. What is the diagnosis?

Answer: b. Enteric fever

Explanation: Enteric fever due to Salmonella Typhi typically presents with sustained fever, headache, abdominal symptoms, relative bradycardia, hepatosplenomegaly, and sometimes rose spots.

10. Diarrheagenic E. coli

Question: A child develops profuse watery diarrhea after contaminated food and water. The organism produces heat-labile and heat-stable enterotoxins. Which pathotype is responsible?

Answer: b. ETEC - Enterotoxigenic Escherichia coli

Explanation: ETEC causes traveller's diarrhea and infantile diarrhea.

Heat-labile toxin (LT) increases intracellular cAMP, similar to cholera toxin.
Heat-stable toxin (ST) increases intracellular c GMP.

11. Cholera

Question: A patient has profuse, painless watery diarrhea described as “rice-water stools.” Which virulence factor is responsible?

Answer: b. Cholera toxin

Explanation: Cholera toxin of Vibrio cholerae activates adenylate cyclase through ADP-ribosylation of the Gs protein. This increases cAMP, causing chloride, bicarbonate, water, and electrolyte secretion into the intestinal lumen.

12. Gas gangrene

Question: A patient has severe pain, swelling, crepitus, and foul-smelling discharge from a traumatic wound. Which organism is most commonly associated with gas gangrene?

Answer: Clostridium perfringens, especially Type A.

Explanation: C. perfringens causes clostridial myonecrosis or gas gangrene. Its alpha toxin, a lecithinase or phospholipase C, produces massive tissue destruction, hemolysis, edema, and gas formation.

13. High-level disinfection

Question: A flexible gastrointestinal endoscope contacts mucosa. What is the minimum routine reprocessing requirement?

Answer: c. High-level disinfection

Explanation: Endoscopes contacting mucous membranes are semicritical items according to Spaulding classification. They require meticulous cleaning followed by high-level disinfection. Sterilization is preferred where feasible for some devices.

14. Stethoscope and reusable thermometer

Question: A stethoscope and reusable thermometer contact intact skin and are shared between patients. What is appropriate?

Answer: b. Cleaning followed by compatible low-level disinfection

Explanation: Items that contact intact skin are noncritical items. They require cleaning and low-level disinfection, commonly with an appropriate alcohol-based or other compatible disinfectant.

15. Spill management

Question: A small blood spill occurs on a nonporous hospital surface. After visible organic matter is removed, what should be done?

Answer: a. Use an appropriate hospital disinfectant or recommended sodium hypochlorite

Explanation: Blood spills should first be cleaned safely with protective precautions. The surface is then disinfected using sodium hypochlorite at the recommended concentration or an approved hospital disinfectant.

16. Enteric fever vaccine

Question: Which vaccine is preferred by WHO for routine typhoid vaccination because of better immunological properties and suitability in younger children?

Answer: a. Typhoid conjugate vaccine - TCV

Explanation: Typhoid conjugate vaccine contains Vi polysaccharide conjugated to a carrier protein. It produces a T-cell-dependent immune response, longer protection, and can be given to younger children than unconjugated Vi polysaccharide vaccine.

17. Diarrheagenic E. coli and Shiga-like toxin

Question: A child develops bloody diarrhea after eating undercooked beef. The organism produces a Shiga-like toxin that inhibits protein synthesis. Which pathotype is likely?

Answer: EHEC - Enterohemorrhagic E. coli, also called STEC - Shiga toxin-producing E. coli.

Explanation: EHEC, particularly E. coli O157:H7, is associated with undercooked beef and hemorrhagic colitis. Shiga-like toxin inhibits protein synthesis by acting on the 60S ribosomal subunit. It may cause hemolytic uremic syndrome.

18. Cholera-like toxin

Question: A diarrheagenic E. coli strain produces heat-labile toxin that increases intracellular cAMP and resembles cholera toxin. Which pathotype is likely?

Answer: a. ETEC

Explanation: ETEC produces heat-labile enterotoxin that resembles cholera toxin and increases cAMP. It may also produce heat-stable toxin, which increases cGMP.

19. Polio vaccination

Question: Which statement best distinguishes OPV from IPV?

Answer: b. OPV induces intestinal mucosal immunity and helps interrupt transmission, while IPV mainly provides systemic protection

Explanation:

OPV: Live attenuated oral vaccine. It induces intestinal IgA immunity, reduces intestinal carriage, and can interrupt community transmission. It can rarely cause vaccine-associated paralytic poliomyelitis.
IPV: Inactivated injectable vaccine. It gives good systemic humoral immunity and prevents paralytic disease but produces less intestinal immunity than OPV.

20. Staphylococcal superantigen

Question: A patient develops fever, hypotension, diffuse rash, and multiorgan involvement after tampon use. Which toxin is most likely responsible?

Answer: b. TSST-1

Explanation: Toxic shock syndrome toxin-1 is a superantigen produced by Staphylococcus aureus. It causes massive cytokine release by nonspecific activation of T lymphocytes, resulting in fever, rash, hypotension, and multiorgan dysfunction.

21. Staphylococcal food poisoning

Question: Several people develop sudden vomiting 3 hours after eating cream-filled pastries. What is the likely cause?

Answer: a. Staphylococcus aureus - preformed heat-stable enterotoxin

Explanation: Staphylococcal food poisoning occurs after ingestion of preformed enterotoxin in food. It has a short incubation period, usually 1-6 hours, with prominent nausea and vomiting. The toxin is heat stable.

22. Bacillus cereus food poisoning

Question: Students develop prominent vomiting 2-4 hours after eating reheated fried rice. What is the cause?

Answer: a. Bacillus cereus - emetic toxin

Explanation: B. cereus causes two food-poisoning syndromes:

Emetic type: Preformed, heat-stable toxin; incubation 1-6 hours; vomiting predominates; classically linked to reheated fried rice.
Diarrheal type: Enterotoxin formed in intestine; incubation 8-16 hours; watery diarrhea and abdominal cramps predominate.

The images do not clearly show questions numbered 11, 12, and 14, or all answer choices for gas gangrene and EHEC. Send those portions if you want the remaining questions answered in the same format.

This is a shared conversation. Sign in to Orris to start your own chat.