MCQ Bacteriology 31: A diagnosis of diphtheria is confirmed by:
A) Microscopic appearance of organisms stained with methylene blue
B) Isolation of a typical colony on Tinsdale’s agar
C) Isolation of typical organisms from materials such as blood, showing invasiveness
D) Detection of β phage plaques in cultures of suspicious isolates
E) Demonstration of toxin production by a suspicious isolate.
MCQ Bacteriology 32: Listeria monocytogenes shows which of the following characteristics?
A) It can grow at refrigerator temperatures (4°C)
B) It is an extracellular pathogen
C) It is catalase-negative
D) It is a gram-negative coccus
E) It is strictly a human pathogen
MCQ Bacteriology 33: Which one of the following is characteristic of N.meningitidis but not N.gonorrhoeae?
A) Ferments glucose
B) Contains a polysaccharide capsule
C) Is oxidase-positive
D) Most isolates show resistance to penicillin
E) No effective vaccines are available
MCQ Bacteriology 34: Which of the following is true of Haemophilus influenzae?
A) Invasive infections are most commonly associated with encapsulated strains
B) Most invasive infections occur in infants during the neonatal period
C) Most human infections are acquired from domestic pets
D) The organism can be readily cultured on sheep blood agar in an environment of elevated CO2
E) Older adults are rarely at risk for infection with this organism because they typically have a high level of immunity.
MCQ Bacteriology 35: For which of the following organisms is there no known animal reservoir?
A) Francisella tularensis
B) Pasteurella multocida
C) Bordetella pertussis
D) Brucella melitensis
E) Yersinia pestis
MCQ Bacteriology 36: A distinguishing feature of human mycoplasma species is that they:
A) Stain well with Giemsa, but not by Gram stain
B) Contain no bacterial pepidoglycan
C) Are not immunogenic because they mimic host cell membrane components
D) Cannot be cultivated in vitro
E) Are dependent on host sources of ATP
MCQ Bacteriology 37: Which one of the following is most characteristic of Mycoplasma pneumoniae infection?
A) Infection results in a fever of sudden onset accompanied by a productive cough
B) Infection most commonly occurs in the upper respiratory tract
C) Infection is definitively diagnosed by direct microscopic examination of sputum
D) Re-infection is rare and less severe than primary infection
E) Infection causes extensive scarring and calcification of affected lung tissue
Q. No. 31: E
Observation of diphtheria toxin production is required to prove the diagnosis. Options A and B are presumptive indicators. Beta phage is a temperate phage, and lytic activity is not observed. Corynebacterium diphtheriae is noninvasive, and the organism (but not the toxin) is recovered only from the surface infections such as those of the oropharynx and skin lesions.
Q. No. 32: A
Listeria monocytogenes grow optimally at 30 to 37°C but is capable of growth at 4°C. Thus, refrigeration does not reliably suppress the growth in food. L. monocytogenes is catalase-positive, gram-positive, obligate intracellular pathogens. These organisms are found in cattle, other warm-blooded animals, and fish, where they can cause disease.
Q. No. 33: B
N.meningitidis contains a polysaccharide capsule, whereas N. gonorrhoeae does not. N. meningitidis ferments both glucose and maltose, but N.gonorrhoeae metabolizes only glucose. Most isolates of N.meningitidis remain sensitive to penicillin, although resistance is increasing. Effective vaccines exist for N.meningitidis serogroups A, C. W-135, and Y, but not for N. gonorrhoeae.
Q. No. 34: A
The capsule is antiphagocytic and facilitates hematogenous dissemination of Haemophilus influenzae. Although H.influenaze is an important pathogen of infants and young children, passive transfer of maternal immunoglobulin G may afford neonates protection. Immunity begins to wane in older adults, increasing the risk of infection for this population. Humans are the only natural hosts for H.influenzae. H.influenzae requires both hemins, X factor, and nicotinamide adenine dinucleotide (NAD), V factor, which are unavailable in blood agar. Heating the blood lyses the RBC, releasing both X and V factors and simultaneously inactivating a NAD-inactivating enzyme in the blood. Media made with such heated blood is termed “chocolate agar“. The organism does prefer elevated CO2.
Q. No. 35: C
Francisella tularensis has a broad host range, including wild and domestic animals, birds, and house pets. Pasteurella multocida primarily colonizes mammals and birds, both domestic and feral. Brucella melitensis primarily infects sheep and goats. Yersinia pestis infects a variety of mammals.
Q. No. 36: B
The distinguishing feature of mycoplasma is its complete lack of a cell wall.
Q. No. 37: B
Atypical pneumonia is the best-known form of Mycoplasma pneumoniae infection. However, upper respiratory tract and ear infections are much more frequent. Atypical pneumonia is characterized by a gradual onset and a scantily productive cough. Direct microscopic examination of clinical specimens for M. pneumoniae is of limited value. Sputum is scanty and nonpurulent, and the pathogen stains poorly or not using standard bacteriologic stains. Reinfection causes more severe lesions and a more extensive chronic inflammatory response. Recovery is slow but without residual damage.
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