Systemic bacteriology: Gram-negative and other bacteria

75 Kerala MSc MLT Entrance practice questions on Systemic bacteriology: Gram-negative and other bacteria, part of Microbiology. The first 25 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

1. Question 1 · Medium

   A sputum isolate grows on Lowenstein-Jensen medium in 3 weeks as rough, buff, dry colonies. It is niacin positive and nitrate reductase positive, and shows no catalase activity after heating to 68 °C. The isolate is most likely:

   1. AMycobacterium avium complex
   2. BMycobacterium tuberculosis
   3. CMycobacterium bovis
   4. DMycobacterium kansasii

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   Answer: B · Mycobacterium tuberculosis

   Rough, buff, slow-growing colonies with positive niacin and nitrate reduction tests and a heat-labile catalase are typical of M. tuberculosis. M. bovis is niacin negative and nitrate negative and grows better with pyruvate. M. kansasii is a photochromogen with a heat-stable catalase. M. avium complex is niacin negative and forms smooth colonies.

   • A: M. avium complex is niacin negative and forms smooth, non-pigmented colonies.
   • C: M. bovis is niacin and nitrate negative.
   • D: M. kansasii turns yellow in light and has a heat-stable catalase.

2. Question 2 · Hard

   A 2-day-old baby has swollen eyelids with a thick purulent discharge from both eyes. A Gram stain shows gram-negative diplococci inside neutrophils. Growth on chocolate agar in CO2 is oxidase positive and produces acid from glucose only. The most likely cause is:

   1. ANeisseria gonorrhoeae
   2. BMoraxella catarrhalis
   3. CNeisseria meningitidis
   4. DChlamydia trachomatis

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   Answer: A · Neisseria gonorrhoeae

   Ophthalmia neonatorum in the first days of life with intracellular gram-negative diplococci points to N. gonorrhoeae acquired during birth. Acid from glucose only confirms the gonococcus. N. meningitidis produces acid from glucose and maltose, and Moraxella produces acid from no sugar. Chlamydial conjunctivitis appears later, at about 5 to 14 days, and is not seen on Gram stain.

   • B: Moraxella catarrhalis does not produce acid from any sugar.
   • C: N. meningitidis produces acid from both glucose and maltose.
   • D: Chlamydia appears later and is not seen as gram-negative diplococci.

3. Question 3 · Medium

   On primary isolation, Brucella abortus differs from Brucella melitensis in that it:

   1. AGives a negative urease test
   2. BGrows within 24 hours of plating
   3. CNeeds 5 to 10% CO2 to grow
   4. DGrows well on MacConkey agar

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   Answer: C · Needs 5 to 10% CO2 to grow

   Most strains of B. abortus need added CO2 on primary isolation, while B. melitensis grows in air. B. abortus also produces H2S and is inhibited by thionin but not basic fuchsin, which help in biotyping. All Brucella species grow slowly, often taking several days, and grow poorly or not at all on MacConkey agar. Most are urease positive.

   • A: Both species are usually urease positive.
   • B: Brucellae grow slowly, often needing several days.
   • D: Brucellae grow poorly or not at all on MacConkey agar.

4. Question 4 · Hard

   A 40-year-old sewage worker in Kottayam had fever, myalgia and conjunctival suffusion. MAT on serum taken on day 4 is negative; on day 14 it is 1:800 against serovar Icterohaemorrhagiae. How should these results be interpreted?

   1. AA prozone that hid antibody on day 4
   2. BRecent leptospirosis shown by seroconversion
   3. CCross-reaction caused by scrub typhus
   4. DPast infection with no current disease

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   Answer: B · Recent leptospirosis shown by seroconversion

   A negative MAT early in the illness followed by a high titre two weeks later is seroconversion, which confirms recent leptospirosis. Antibodies are often undetectable in the first week, so a single early negative MAT does not exclude the disease. MAT uses live leptospires of several serovars, and the serovar with the highest titre suggests the likely infecting serogroup. Occupational exposure to sewage or flood water is the classic history in Kerala.

   • A: Prozone affects undiluted or low dilutions; seroconversion is the simple explanation.
   • C: Scrub typhus does not produce agglutinins against leptospiral serovars.
   • D: A titre that appears during the illness indicates current, not past, infection.

5. Question 5 · Hard

   Slit-skin smears from six sites of a patient with leprosy are graded on Ridley's logarithmic scale as 3+, 2+, 2+, 1+, 0 and 4+. What is the bacteriological index?

   1. A2.0
   2. B12
   3. C2.4
   4. D4.0

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   Answer: A · 2.0

   The bacteriological index is the sum of the grades divided by the number of sites examined. Here 3 + 2 + 2 + 1 + 0 + 4 = 12, and 12 / 6 = 2.0. Dividing by the five positive sites gives 2.4, which overstates the load. The BI falls slowly, by about 1 a year, with effective treatment.

   • B: 12 is the sum of grades before dividing by the number of sites.
   • C: 2.4 divides by positive sites only; all sites examined are counted.
   • D: 4.0 is the highest single grade, not the index.

6. Question 6 · Medium

   Charcoal is added to the Regan-Lowe medium used for Bordetella pertussis in order to:

   1. ASupply the X factor the organism needs
   2. BAbsorb fatty acids and peroxides that inhibit it
   3. CCreate an anaerobic layer under the agar
   4. DMake the small colonies easier to see

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7. Question 7 · Medium

   Haemophilus ducreyi, the cause of chancroid, differs in its growth needs from H. influenzae because it requires:

   1. AV factor only
   2. BNeither X nor V factor
   3. CX factor only
   4. DBoth X and V factors

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8. Question 8 · Easy

   The infectious, extracellular form of Chlamydia is the:

   1. AInclusion body
   2. BReticulate body
   3. CElementary body
   4. DInitial body

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9. Question 9 · Easy

   Treponema pallidum cannot be grown on artificial media. The Nichols strain is maintained for test antigen by growth in:

   1. AEmbryonated eggs
   2. BGuinea pig peritoneum
   3. CRabbit testes
   4. DMonkey kidney cells

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10. Question 10 · Medium

    In the second week of leptospirosis, which specimen is most likely to yield leptospires on culture?

    1. AThroat swab
    2. BStool
    3. CBlood
    4. DUrine

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11. Question 11 · Easy

    In the Weil-Felix test, antibodies in scrub typhus agglutinate which Proteus strain?

    1. ABoth OX19 and OX2
    2. BProteus vulgaris OX19
    3. CProteus vulgaris OX2
    4. DProteus mirabilis OXK

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12. Question 12 · Easy

    The Kanagawa phenomenon (beta haemolysis on Wagatsuma agar) is a marker of pathogenic strains of:

    1. AAeromonas hydrophila
    2. BVibrio vulnificus
    3. CVibrio parahaemolyticus
    4. DVibrio cholerae O1

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13. Question 13 · Hard

    A diabetic paddy farmer from coastal Karnataka has fever and a splenic abscess. Blood culture grows an oxidase-positive gram-negative bacillus with bipolar staining, forming dry, wrinkled colonies with an earthy smell. It is resistant to gentamicin and colistin and susceptible to amoxicillin-clavulanate. The most likely organism is:

    1. APseudomonas aeruginosa
    2. BAcinetobacter baumannii
    3. CBurkholderia pseudomallei
    4. DKlebsiella pneumoniae

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14. Question 14 · Medium

    Inclusions of Chlamydia trachomatis, unlike those of C. psittaci and C. pneumoniae, stain brown with iodine because they contain:

    1. AMucin
    2. BLipid
    3. CVolutin
    4. DGlycogen

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15. Question 15 · Hard

    During a monsoon outbreak in a coastal village, a man passes profuse rice-water stools. A hanging drop shows darting motility that stops when polyvalent O1 antiserum is added. Stool culture gives yellow colonies on TCBS agar that are oxidase positive. The most likely organism is:

    1. AAeromonas hydrophila
    2. BVibrio cholerae O139
    3. CVibrio cholerae O1
    4. DVibrio parahaemolyticus

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16. Question 16 · Medium

    Shigella sonnei differs from the other Shigella species in that it:

    1. AIs motile and produces gas from glucose
    2. BFerments lactose late and is ornithine positive
    3. CProduces hydrogen sulphide in TSI agar
    4. DDoes not ferment mannitol and is indole positive

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17. Question 17 · Easy

    Venkatraman-Ramakrishnan (VR) fluid, developed in India, is a holding medium for transporting:

    1. AGenital swabs for gonococci
    2. BStool for Shigella species
    3. CStool for Vibrio cholerae
    4. DNasal swabs for Bordetella

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18. Question 18 · Medium

    A Klebsiella pneumoniae colony lifted with a loop stretches into a sticky string more than 5 mm long. This positive string test points to:

    1. AA hypermucoviscous, hypervirulent strain
    2. BA strain producing an ESBL enzyme
    3. CA non-capsulated rough variant
    4. DContamination with Vibrio cholerae

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19. Question 19 · Easy

    In a leprosy slit-skin smear, the morphological index (MI) is the percentage of:

    1. AOil-immersion fields that contain acid-fast bacilli
    2. BFragmented or granular bacilli among all bacilli
    3. CSolidly stained bacilli among all bacilli counted
    4. DBacilli lying in globi rather than lying singly

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20. Question 20 · Medium

    The main advantage of Castaneda's biphasic medium for Brucella blood culture is that:

    1. ASubculture is made by tilting, without opening the bottle
    2. BMalachite green inhibits skin contaminants
    3. CColonies appear within 24 hours of incubation
    4. DIt supplies X and V factors for slow growers

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21. Question 21 · Medium

    Which TSI agar reaction is typical of Salmonella Typhi?

    1. AAlkaline slant, acid butt, heavy H2S and gas
    2. BAlkaline slant, acid butt, little H2S, no gas
    3. CAlkaline slant, alkaline butt, no H2S
    4. DAcid slant, acid butt, gas, no H2S

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22. Question 22 · Hard

    A 24-year-old woman with SLE has a routine antenatal VDRL that is reactive at 1:4. TPHA on the same serum is non-reactive, and she has no history or signs of syphilis. A repeat sample a month later gives the same results. How should this be interpreted?

    1. ABiological false-positive VDRL
    2. BProzone reaction in secondary syphilis
    3. CTreated old syphilis
    4. DEarly primary syphilis

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23. Question 23 · Medium

    Which property separates Pseudomonas aeruginosa from P. fluorescens and P. putida?

    1. AMotility by polar flagella
    2. BProduction of pyoverdin
    3. CGrowth at 42 °C
    4. DA positive oxidase test

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24. Question 24 · Medium

    An adult who had TAB vaccine a year ago now has a Widal test with H agglutinin 1:320 and O agglutinin below 1:40. This pattern most likely reflects:

    1. APast vaccination rather than current enteric fever
    2. BThe prozone phenomenon in the O tube
    3. CThe first week of acute enteric fever
    4. DA chronic gall bladder carrier state

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25. Question 25 · Medium

    Like Shigella, enteroinvasive E. coli gives a positive Sereny test. This test detects:

    1. AHeat-stable enterotoxin in infant mouse gut
    2. BFluid accumulation in a ligated rabbit ileal loop
    3. CInvasion of epithelium, as keratoconjunctivitis in a guinea pig
    4. DCytotoxicity of Vero cells in tissue culture

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