MCQ for UG students and Case discussions on common infectious diseases.

1. Case Discussion and MCQs
Dr.Suprakash Das

2. MCQs
1. In the Gram stain procedure, bacteria are exposed
to 95% alcohol or to an acetone/alcohol mixture.
The purpose of this step is:
(A) to adhere the cells to the slide
(B) to retain the purple dye within all the bacteria
(C) to disrupt the outer cell membrane so the purple dye
can leave the bacteria
(D) to facilitate the entry of the purple dye into the gram-
negative cells
(E) to form a complex with the iodine solution

3. MCQs
2. In the process of studying how bacteria cause disease, it was
found that a rare mutant of a pathogenic strain failed to form a
capsule. Which one of the following statements is the most
accurate in regard to this unencapsulated mutant strain?
(A) It was nonpathogenic primarily because it was easily phagocytized.
(B) It was nonpathogenic primarily because it could not invade tissue.
(C) It was nonpathogenic primarily because it could only grow
anaerobically.
(D) It was highly pathogenic because it could secrete larger amounts of
exotoxin.
(E) It was highly pathogenic because it could secrete larger amounts of
endotoxin.

4. MCQs
3. Of the following bacterial components, which
one exhibits the most antigenic variation?
(A) Capsule
(B) Lipid A of endotoxin
(C) Peptidoglycan
(D) Ribosome
(E) Spore

5. MCQs
4. β-Lactamases are an important cause of
antibiotic resistance. Which one of the
following is the most common site where β-
lactamases are located?
(A) Attached to DNA in the nucleoid
(B) Attached to pili on the bacterial surface
(C) Free in the cytoplasm
(D) Within the capsule
(E) Within the periplasmic space

6. MCQs
5. Bacteria that cause nosocomial (hospital-acquired)
infections often produce extracellular substances that
allow them to stick firmly to medical devices, such as
intravenous catheters. Which one of the following is the
name of this extracellular substance?
(A) Axial filament
(B) Endotoxin
(C) Flagella
(D) Glycocalyx
(E) Porin

7. MCQs
6. Lysozyme in tears is an effective mechanism
for preventing bacterial conjunctivitis. Which
one of the following bacterial structures does
lysozyme degrade?
(A) Endotoxin
(B) Nucleoid DNA
(C) Peptidoglycan
(D) Pilus
(E) Plasmid DNA

8. MCQs
7. Several bacteria that form spores are important human
pathogens. Which one of the following is the most accurate
statement about bacterial spores?
(A) They are killed by boiling for 15 minutes.
(B) They are produced primarily by gram-negative cocci.
(C) They are formed primarily when the bacterium is exposed to
antibiotics.
(D) They are produced by anaerobes only in the presence of oxygen.
(E) They are metabolically inactive yet can survive for years in that
inactive state.

9. MCQs
8. The main reason why some bacteria are anaerobes
(i.e., they cannot grow in the presence of oxygen) is
because:
(A) they do not have sufficient catalase and superoxide
dismutase.
(B) they have too much ferrous ion that is oxidized to
ferric ion in the presence of oxygen.
(C) they have unusual mitochondria that cannot function
in the presence of oxygen.
(D) transcription of the gene for the pilus protein is
repressed in the presence of oxygen.

10. MCQs-9
Identify the
Clinical Condition
Caused by a GPC
In clusters.

11. Case Discussion-1
Identify the disease caused by
Gram
Positive , Coagulase +ve
organism

12. Case Discussion-1
 The case of a 4-year-old Caucasian boy with a blistering skin
syndrome. He had no relevant medical history and no use of
medication prior to this event. No allergies were known and he had
been vaccinated, according the Dutch vaccination program.
 He presented to an emergency room with a history of loss of
appetite, constipation, and agitation of 1-week duration.
 Furthermore, he experienced pain at his buttocks, lower back,
thorax, and face. In addition, skin lesions started inthe peribuccal
area and appeared after rubbing of the skin (Nikolsky’s sign).
 At physical examination, erythema and exfoliation were present. He
was apyretic. Mucous membranes were not affected. Exfoliation
affected 10% of his total body surface area (TBSA).

13. Case Discussion-1
 Laboratory tests revealed no signs of infections: leukocyte count (L)
of 7.4 × 109 and C-reactive protein (CRP) was 3 mg/l.
 Further investigation was performed, including skin cultures and
biopsies. Because of superficial scalding, Nikolsky’s sign, and no
involvement of mucous membranes, SSSS was considered a
working diagnosis and
 antibiotic treatment was initiated with intravenously administered
flucloxacillin and clindamycin.
 His pain was managed with acetaminophen and morphine
intravenously administered. Fluids management was monitored.

14. CASE
DISCUSSION-2

15. CASE DISCUSSION-2
 A 65-year-old man presented with fever and painful
swelling at the back for last 2 weeks.
 His prior history was significant for long-standing type
2 diabetes of 20 years duration and systemic
hypertension.
 Clinical examination showed red, swollen, painful
carbuncle with gangrenous patch at the centre and
multiple pus points.
 Investigations revealed elevated white blood cell count
with neutrophil predominance and high random blood
sugar, 340mg/dL (normal, <140 mg/dL).

16. CASE DISCUSSION-2
 He was started on insulin and good glycaemic control
was achieved. Aggressive debridement of the local
affected area was done.
 Tissue culture was positive for Staphylococcus aureus
and he was treated with amoxicillin and clavulanic acid
to which he responded well.
 On follow-up, his debrided wound was granulating
well.
 Carbuncle, also called as infective gangrene of skin and
subcutaneous tissue, is most commonly caused by S.
aureus that usually starts as a furuncle/boil around the
root of a hair follicle

17. CASE DISCUSSION-3
Biochemical Test- Catalase (-ve), PYR Test (+ve), Beta-Haemolytic, Sensitive to Penicillin
Patient’s age- 3 years.

18. Biochemical Test- Catalase (-ve), PYR Test (+ve), Beta-Haemolytic, Resistant to
Penicillin
Patient’s age- 43 years.
CASE DISCUSSION-3

19. CASE DISCUSSION-3
 A 43-year-old male, a fireman with no remarkable medical history,
presented to the Emergency Department of our hospital on April 2016
secondary to an insidious onset of fever, persistent painful wounds on his
left leg with swelling, redness, tenderness and difficulty walking around.
 He was admitted to Infectious Diseases Department because of a
suspected severe pyoderma and subsequently was diagnosed as having a
cutaneous infection due to drug-resistant Streptococcus pyogenes.
 He had a recent history of minor repeated traumas on his left leg related to
his sport activities.
 At admission, he was febrile but with normal vital signs; he reported
intense pain on his left lower limb and walking difficulties.
 On the medial surface of the distal third of his left leg there were four
ulcers which were intensely inflamed and discharging pus.
 Another less tender wound was seen at the base of the first finger of his
left foot, medially.

20. CASE DISCUSSION-3
 His left leg and foot were swollen, red and tender;
 a lymphangitic streak extended to his groin and there was inguinal
lymphadenitis;
 Laboratory test showed haemoglobin value of 15.0 g/dL, MCV 87.0
fl, platelets 215,000/mm3, white blood cell count of 11,100/mm3
(neutrophils 75%, lymphocytes 14%, monocytes 9%),
 elevated inflammatory markers (ESR, CRP), fibrinogen and LDH;
 normality of the hepato-renal parameters and electrolytes.
 Urine and blood cultures were negative,
 as well as an histological examination carried out on skin biopsy on
the edge of the ulcers on purpose to rule out infectious agents as
Leishmania and atypical mycobacteria.
 Both of the swab cultures from ulcers were positive for S. pyogenes
resistant to macrolides, penicillin and levofloxacin.

21. ANSWER KEY
1- C
2-A
3-A
4-E
5-D
6-C
7-E
8-A
9- Folliculitis
Case Discussion-3- S. pyogens sore throat.