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Question 1Bacteriology

A wound culture Gram stain shows gram-positive cocci arranged in clusters. Which organism is most consistent with this finding?

  1. Streptococcus pyogenes
  2. Escherichia coli
  3. Staphylococcus aureus Correct answer.
  4. Neisseria gonorrhoeae

Explanation

Clustered (staphylo-) arrangement of gram-positive cocci is characteristic of staphylococci, and S. aureus is the species most often recovered from purulent wounds. Streptococci divide in chains, neisseriae are gram-negative diplococci, and E. coli is a gram-negative rod.

Question 2Bacteriology

Which reagent is applied to a colony to perform the catalase test?

  1. 3% hydrogen peroxide Correct answer.
  2. 10% potassium hydroxide
  3. Kovac's reagent
  4. Ferric chloride

Explanation

Catalase splits hydrogen peroxide into water and oxygen, so bubbling after adding 3% H2O2 indicates a catalase-positive organism. Kovac's reagent detects indole, KOH is used for the string test and KOH preparations, and ferric chloride detects phenylpyruvic acid.

Question 3Bacteriology

Which test result best separates Staphylococcus aureus from coagulase-negative staphylococci?

  1. Bile esculin hydrolysis
  2. Bacitracin susceptibility
  3. Coagulase production Correct answer.
  4. Optochin susceptibility

Explanation

S. aureus produces bound and free coagulase, which converts fibrinogen to fibrin, whereas coagulase-negative species such as S. epidermidis do not. Optochin and bile esculin tests are used for streptococci, and bacitracin for S. pyogenes.

Question 4Bacteriology

Beta-hemolysis on sheep blood agar is best described as:

  1. Complete lysis of red cells Correct answer.
  2. No visible change in the agar
  3. A brown pigment diffusing into the agar
  4. Greenish discoloration of the medium

Explanation

Beta-hemolysis is complete destruction of erythrocytes, producing a clear, transparent zone around the colony. Greenish discoloration indicates alpha-hemolysis, and no change at all indicates gamma-hemolysis.

Question 5Bacteriology

The oxidase test detects the activity of which enzyme?

  1. Cytochrome oxidase Correct answer.
  2. Beta-galactosidase
  3. Urease
  4. Catalase

Explanation

The oxidase reagent tetramethyl-p-phenylenediamine is oxidized by cytochrome c oxidase of the electron transport chain, forming a dark purple product. Urease, catalase, and beta-galactosidase are detected by separate tests.

Question 6Bacteriology

MacConkey agar inhibits gram-positive organisms because the medium contains:

  1. Bile salts and crystal violet Correct answer.
  2. Colistin and nalidixic acid
  3. Potassium tellurite
  4. Sodium azide

Explanation

Bile salts and crystal violet are the selective agents in MacConkey agar that suppress gram-positive bacteria while allowing gram-negative bacilli to grow. Lactose and neutral red then provide the differential reaction.

Question 7Bacteriology

A gastric biopsy isolate is a curved gram-negative rod that is strongly urease positive. Which organism is most likely?

  1. Campylobacter jejuni
  2. Yersinia enterocolitica
  3. Vibrio parahaemolyticus
  4. Helicobacter pylori Correct answer.

Explanation

Helicobacter pylori is a curved gram-negative rod that is strongly and rapidly urease positive, a property used in biopsy urease (CLO) testing. It colonizes gastric mucosa and is associated with peptic ulcer disease.

Question 8Bacteriology

Streptococcus pyogenes is classically presumptively identified by susceptibility to which disk?

  1. Optochin
  2. Trimethoprim-sulfamethoxazole
  3. Bacitracin Correct answer.
  4. Novobiocin

Explanation

Group A streptococci are susceptible to the 0.04-unit bacitracin disk, a long-used presumptive identification test. Optochin susceptibility indicates S. pneumoniae, and novobiocin resistance indicates S. saprophyticus.

Question 9Bacteriology

On Hektoen enteric agar, a blue-green colony with a black center is most suggestive of:

  1. Enterococcus faecalis
  2. Salmonella species Correct answer.
  3. Shigella species
  4. Escherichia coli

Explanation

Hektoen enteric agar contains lactose, sucrose, and salicin plus ferric ammonium citrate; Salmonella does not ferment these sugars and produces hydrogen sulfide, giving blue-green colonies with black centers.

Question 10Bacteriology

Which incubation condition is optimal for recovering Campylobacter jejuni from a stool specimen?

  1. 37 °C in an anaerobic jar
  2. 42 °C in reduced oxygen Correct answer.
  3. 35 °C in ambient air
  4. 35 °C in 5% carbon dioxide

Explanation

C. jejuni is thermophilic and microaerophilic, growing best at 42 °C in an atmosphere of roughly 5% oxygen and 10% carbon dioxide. Ambient air, CO2 alone, and strict anaerobiosis do not provide these conditions.

Question 11Bacteriology

A catalase-positive, gram-positive rod is motile with a tumbling, end-over-end motion at 25 °C and grows at 4 °C. This organism is:

  1. Erysipelothrix rhusiopathiae
  2. Corynebacterium diphtheriae
  3. Bacillus cereus
  4. Listeria monocytogenes Correct answer.

Explanation

Listeria monocytogenes is a catalase-positive, non-spore-forming rod that shows tumbling motility at room temperature and is unusual in its ability to multiply at refrigeration temperatures.

Question 12Bacteriology

A comma-shaped gram-negative rod grows on TCBS agar as large yellow colonies. Which organism is most likely?

  1. Vibrio vulnificus
  2. Vibrio parahaemolyticus
  3. Escherichia coli
  4. Vibrio cholerae Correct answer.

Explanation

TCBS agar uses sucrose fermentation with bromothymol blue; Vibrio cholerae ferments sucrose and forms yellow colonies. Non-sucrose-fermenting vibrios such as V. parahaemolyticus form green colonies.

Question 13Bacteriology

Which set of characteristics is typical of Pseudomonas aeruginosa?

  1. Oxidase negative and lactose fermenting
  2. Coagulase positive and catalase negative
  3. Oxidase positive and nonfermentative Correct answer.
  4. Hydrogen sulfide positive on TSI agar

Explanation

P. aeruginosa is an oxidase-positive gram-negative rod that oxidizes rather than ferments carbohydrates, so it is nonfermentative on oxidative-fermentative media and on TSI agar.

Question 14Bacteriology

A beta-hemolytic streptococcus produces an arrowhead-shaped zone of enhanced hemolysis where its streak approaches a Staphylococcus aureus streak. This identifies:

  1. Group B streptococcus Correct answer.
  2. Streptococcus pneumoniae
  3. Group A streptococcus
  4. Enterococcus faecalis

Explanation

The CAMP test detects the CAMP factor of Streptococcus agalactiae (group B), which enhances the sphingomyelinase-mediated hemolysis of S. aureus and produces an arrowhead zone of intensified lysis.

Question 15Bacteriology

An alpha-hemolytic colony is optochin susceptible and dissolves in bile salts. This organism is:

  1. Streptococcus sanguinis group
  2. Streptococcus mutans
  3. Streptococcus bovis
  4. Streptococcus pneumoniae Correct answer.

Explanation

S. pneumoniae is the alpha-hemolytic streptococcus that is both optochin susceptible and bile soluble. Viridans group streptococci are optochin resistant and bile insoluble.

Question 16Bacteriology

Methicillin resistance in Staphylococcus aureus results from:

  1. Overexpression of an efflux pump
  2. Chromosomal induction of ampC
  3. Loss of outer membrane porins
  4. Production of an altered penicillin-binding protein Correct answer.

Explanation

The mecA gene encodes PBP2a, a penicillin-binding protein with low affinity for beta-lactams, so these drugs cannot efficiently inhibit cell wall cross-linking.

Question 17Bacteriology

Haemophilus influenzae requires which growth factors for growth in culture?

  1. V factor only
  2. Both X and V factors Correct answer.
  3. X factor only
  4. Neither X nor V factor

Explanation

H. influenzae requires both X factor (hemin) and V factor (nicotinamide adenine dinucleotide). Chocolate agar supplies them because heating lyses erythrocytes and releases these factors.

Question 18Bacteriology

Black colonies surrounded by a brown halo on Tinsdale agar indicate:

  1. Pseudomonas aeruginosa
  2. Streptococcus pyogenes
  3. Corynebacterium diphtheriae Correct answer.
  4. Staphylococcus aureus

Explanation

Tinsdale agar contains potassium tellurite and cystine; C. diphtheriae reduces tellurite to metallic tellurium, giving black colonies, and its cystinase produces the brown halo.

Question 19Bacteriology

An anaerobic gram-negative bacillus grows in 20% bile, hydrolyzes esculin, and is resistant to kanamycin and vancomycin. This organism belongs to which group?

  1. Bacteroides fragilis group Correct answer.
  2. Prevotella melaninogenica
  3. Fusobacterium nucleatum
  4. Porphyromonas gingivalis

Explanation

Bile tolerance and resistance to kanamycin and vancomycin are key identifying features of the B. fragilis group. Most other gram-negative anaerobes are bile sensitive and are inhibited by those antibiotics.

Question 20Bacteriology

Legionella pneumophila is recovered from respiratory specimens only on media supplemented with:

  1. X and V factors
  2. Sodium polyanethol sulfonate
  3. Vitamin K and hemin
  4. L-cysteine and iron Correct answer.

Explanation

L. pneumophila has an absolute requirement for L-cysteine and is stimulated by iron, so buffered charcoal yeast extract agar with L-cysteine is the standard medium.

Question 21Bacteriology

Gram-negative bacilli are intrinsically resistant to vancomycin because:

  1. Vancomycin binds altered D-Ala-D-Lac precursors
  2. Vancomycin cannot cross the outer membrane Correct answer.
  3. The peptidoglycan layer is too thick
  4. Beta-lactamase hydrolyzes vancomycin

Explanation

Vancomycin is a bulky glycopeptide that cannot penetrate the outer membrane of gram-negative bacteria, so it never reaches the peptidoglycan. D-Ala-D-Lac precursors and beta-lactamase are unrelated resistance mechanisms.

Question 22Bacteriology

A patient with Enterobacter cloacae bacteremia initially responds to ceftriaxone but relapses with a resistant isolate. Which mechanism best explains this?

  1. Stable AmpC derepression Correct answer.
  2. Loss of outer membrane porins
  3. Ribosomal methylation by an erm gene
  4. Acquisition of a VanA ligase

Explanation

Enterobacter species carry an inducible chromosomal ampC gene; exposure to third-generation cephalosporins can select stably derepressed mutants that hyperproduce AmpC beta-lactamase and become resistant.

Question 23Bacteriology

Bacteremia due to Streptococcus gallolyticus (Streptococcus bovis biotype I) is classically associated with:

  1. Colorectal carcinoma Correct answer.
  2. Otitis media
  3. Dental caries
  4. Rheumatic heart disease

Explanation

S. gallolyticus bacteremia and endocarditis are strongly associated with colorectal neoplasia, so isolation of this organism from blood should prompt evaluation of the colon.

Question 24Bacteriology

A gram-negative rod isolated from a wound is oxidase positive and motile, grows on Ashdown's agar, and is resistant to colistin and gentamicin. Which organism is most likely?

  1. Stenotrophomonas maltophilia
  2. Acinetobacter baumannii
  3. Pseudomonas aeruginosa
  4. Burkholderia pseudomallei Correct answer.

Explanation

Burkholderia pseudomallei is oxidase positive, motile, intrinsically resistant to colistin and gentamicin, and forms characteristic wrinkled colonies on Ashdown's medium.

Question 25Bacteriology

Which feature best distinguishes Clostridioides difficile from Clostridium perfringens on egg yolk agar?

  1. Absence of lecithinase activity Correct answer.
  2. Catalase positivity
  3. Absence of lipase activity
  4. Aerobic growth

Explanation

Clostridium perfringens produces lecithinase (phospholipase C), which forms an opaque precipitate around colonies on egg yolk agar, whereas C. difficile is lecithinase negative.

Question 26Bacteriology

A slide test is performed by mixing a colony of gram-positive cocci into a drop of 3% hydrogen peroxide; one isolate bubbles vigorously while the other does not. Which statement correctly describes this test?

  1. Enterococci bubble because they produce catalase; staphylococci do not.
  2. Streptococci bubble because they produce catalase; staphylococci do not.
  3. Staphylococci bubble because they produce catalase; streptococci do not. Correct answer.
  4. Both groups bubble, so the reaction cannot separate them.

Explanation

Catalase converts hydrogen peroxide to water and oxygen, and the released oxygen is seen as bubbling. Staphylococci and micrococci possess the enzyme, whereas streptococci and enterococci lack it. The test is therefore a first-step screen that separates the two major groups of gram-positive cocci.

Question 27Bacteriology

A gram-positive coccus in clusters is recovered from a wound and gives a positive tube coagulase test. Which organism does this identify?

  1. Staphylococcus epidermidis
  2. Streptococcus agalactiae
  3. Staphylococcus aureus Correct answer.
  4. Enterococcus faecalis

Explanation

Coagulase converts fibrinogen to fibrin and is the classic marker that separates Staphylococcus aureus from the coagulase-negative staphylococci. S. aureus is also typically DNase and mannitol positive, but coagulase alone is sufficient for species-level presumptive identification in this group.

Question 28Bacteriology

A gram-negative diplococcus from a urethral swab oxidizes glucose but not maltose or lactose. Which organism is most likely?

  1. Acinetobacter baumannii
  2. Neisseria gonorrhoeae Correct answer.
  3. Moraxella catarrhalis
  4. Neisseria meningitidis

Explanation

Neisseria gonorrhoeae ferments glucose only, while Neisseria meningitidis ferments glucose and maltose. Carbohydrate oxidation patterns among the pathogenic Neisseria are the standard means of separating these two species.

Question 29Bacteriology

A sputum culture grows a heavily mucoid, lactose-fermenting, nonmotile gram-negative rod that is urease positive and indole negative. Which organism is most likely?

  1. Escherichia coli
  2. Klebsiella pneumoniae Correct answer.
  3. Proteus mirabilis
  4. Enterobacter aerogenes

Explanation

Klebsiella pneumoniae forms a prominent polysaccharide capsule that gives colonies a mucoid, sometimes stringy appearance. It ferments lactose, is urease positive, indole negative, and characteristically nonmotile. Loss of motility separates it from other mucoid lactose fermenters such as Enterobacter species.

Question 30Bacteriology

A stool isolate from a child with bloody diarrhea is a lactose-fermenting gram-negative rod that fails to ferment sorbitol and agglutinates with O157 antiserum. Which organism is this?

  1. Salmonella enterica
  2. Escherichia coli O157:H7 Correct answer.
  3. Yersinia enterocolitica
  4. Shigella sonnei

Explanation

Most Escherichia coli ferment sorbitol, but the O157:H7 serotype is a sorbitol nonfermenter, which is the basis of sorbitol-MacConkey screening. Confirmation is by agglutination with O157 antiserum and detection of Shiga toxin. The organism is a lactose fermenter, which helps exclude the other enteric pathogens listed.

Question 31Bacteriology

A gram-positive coccus isolated from urine grows in broth containing 6.5% NaCl and hydrolyzes esculin in the presence of 40% bile. Which organism is most likely?

  1. Streptococcus pneumoniae
  2. Staphylococcus saprophyticus
  3. Enterococcus faecalis Correct answer.
  4. Streptococcus gallolyticus

Explanation

Enterococci are bile esculin positive and uniquely tolerant of 6.5% NaCl, which separates them from the viridans and bovine streptococci. Streptococcus gallolyticus is also bile esculin positive but fails to grow in 6.5% salt broth. Growth in salt broth is the definitive feature here.

Question 32Bacteriology

A nasopharyngeal swab from a child with paroxysmal cough is submitted for Bordetella pertussis culture. Which medium is appropriate for this specimen?

  1. Modified Thayer-Martin agar containing vancomycin, colistin, and nystatin
  2. Cysteine-tellurite blood agar with potassium tellurite
  3. Cefsulodin-irgasan-novobiocin (CIN) agar incubated at 25 degrees C
  4. Regan-Lowe charcoal agar with cephalexin Correct answer.

Explanation

Bordetella pertussis requires charcoal-based medium to adsorb growth-inhibiting fatty acids, and cephalexin suppresses normal nasopharyngeal flora. Regan-Lowe and Bordet-Gengou media serve this purpose. Cysteine-tellurite is selective for Corynebacterium diphtheriae, and the other listed media target different organisms.

Question 33Bacteriology

A slow-growing gram-negative rod isolated from a human bite wound pits the agar surface, has a bleach-like odor, and is oxidase positive. Which organism is most likely?

  1. Fusobacterium nucleatum
  2. Capnocytophaga canimorsus
  3. Eikenella corrodens Correct answer.
  4. Pasteurella multocida

Explanation

Eikenella corrodens is a normal oral flora organism that characteristically corrodes or pits the agar surface and produces a hypochlorite-like odor. It is oxidase positive and grows best in a carbon dioxide-enriched atmosphere. These features, together with the bite-wound source, point to this species.

Question 34Bacteriology

A blood culture from a laboratory worker with undulant fever grows small gram-negative coccobacilli after 5 days of incubation. The isolate is oxidase positive and urease positive and grows on chocolate agar but not on MacConkey agar. Which organism is most likely?

  1. Haemophilus influenzae
  2. Bartonella henselae
  3. Brucella melitensis Correct answer.
  4. Francisella tularensis

Explanation

Brucella species are slow-growing, oxidase-positive, urease-positive gram-negative coccobacilli that require enriched media and fail to grow on MacConkey agar. Undulant fever in a laboratory worker suggests occupational exposure to the organism. Cultures are handled under biosafety level 3 conditions because of the high risk of laboratory-acquired infection.

Question 35Virology

What is the primary function of the viral capsid?

  1. Synthesizing the lipid envelope
  2. Protecting the genome and aiding attachment Correct answer.
  3. Generating ATP for viral replication
  4. Providing ribosomes for protein synthesis

Explanation

The capsid is the protein shell that encloses the viral nucleic acid, shielding it from nucleases and presenting the attachment proteins that bind host cell receptors. Viruses lack the machinery for ATP generation and protein synthesis, so they must use host ribosomes and energy.

Question 36Virology

Which step of viral replication involves the virus binding to a specific host cell receptor?

  1. Penetration
  2. Assembly
  3. Uncoating
  4. Adsorption Correct answer.

Explanation

Adsorption (attachment) is the initial step in which viral surface proteins bind specific receptors on the host cell membrane, and this specificity largely determines host and tissue tropism. Penetration, uncoating, and assembly occur only after attachment has taken place.

Question 37Virology

How should a swab specimen for viral culture be transported to the laboratory?

  1. Frozen at -20 degrees C without medium
  2. At 4 degrees C in viral transport medium Correct answer.
  3. At room temperature in a dry tube
  4. Immersed in formalin fixative

Explanation

Viruses are heat labile and sensitive to drying, so specimens are kept refrigerated at 4 degrees C in a protein-containing viral transport medium that preserves infectivity. Freezing at -20 degrees C, drying, or fixation markedly reduces or destroys recovery in cell culture.

Question 38Virology

Which virus is the most common cause of bronchiolitis in infants?

  1. Influenza A virus
  2. Rhinovirus
  3. Adenovirus
  4. Respiratory syncytial virus Correct answer.

Explanation

Respiratory syncytial virus is the leading cause of lower respiratory tract infection and bronchiolitis in children under one year of age. Influenza, adenovirus, and rhinovirus cause respiratory illness but are far less frequently the cause of infant bronchiolitis.

Question 39Virology

Which virus is the leading cause of severe infantile gastroenteritis worldwide?

  1. Astrovirus
  2. Adenovirus
  3. Norovirus
  4. Rotavirus Correct answer.

Explanation

Rotavirus is the major cause of severe dehydrating diarrhea in infants and young children globally, which is why routine vaccination is recommended in early infancy. Norovirus causes outbreaks across all age groups, while astrovirus and adenovirus generally produce milder disease.

Question 40Virology

Which virus is most strongly linked to the development of cervical carcinoma?

  1. Epstein-Barr virus
  2. Human papillomavirus type 16 Correct answer.
  3. Cytomegalovirus
  4. Herpes simplex virus type 2

Explanation

High-risk human papillomavirus types, chiefly 16 and 18, encode E6 and E7 proteins that inactivate p53 and Rb, driving malignant transformation of cervical epithelium. The other viruses listed are associated with different tumors or with no consistent cervical cancer link.

Question 41Virology

An adult develops a painful vesicular rash confined to a single dermatome. Which virus is responsible?

  1. Coxsackievirus A16
  2. Herpes simplex virus type 1
  3. Molluscum contagiosum virus
  4. Varicella-zoster virus Correct answer.

Explanation

Dermatomal vesicular rash in an adult represents herpes zoster, caused by reactivation of latent varicella-zoster virus residing in dorsal root ganglia. HSV-1 causes orolabial lesions, coxsackievirus causes hand-foot-and-mouth disease, and molluscum causes umbilicated papules.

Question 42Virology

Detection of virus-specific IgM antibody in a single serum specimen most likely indicates:

  1. Successful vaccination in childhood
  2. Recent or current infection Correct answer.
  3. Remote infection acquired years earlier
  4. Passive antibody transfer from a transfusion

Explanation

IgM is the first antibody class produced after antigen exposure and generally persists for weeks to months, so its presence suggests recent or ongoing infection. IgG predominates in past infection and post-vaccination immunity, and passively transferred antibody is not virus-specific in a way that implies infection.

Question 43Virology

Which description best fits the cytopathic effect of herpes simplex virus in cell culture?

  1. Grape-like clusters of rounded cells without syncytia
  2. Enlarged cells with owl's-eye intranuclear inclusions
  3. No visible change; detected only by hemadsorption
  4. Rounding and ballooning with multinucleated giant cells Correct answer.

Explanation

HSV infects contiguous cells and fuses their membranes, producing rounded, ballooning cells and multinucleated giant cells with marginated chromatin. Grape-like clusters suggest adenovirus and owl's-eye inclusions suggest cytomegalovirus.

Question 44Virology

What is the main advantage of the shell vial centrifugation culture technique?

  1. It shortens the time needed for viral detection Correct answer.
  2. It eliminates the need for a cell monolayer
  3. It allows growth of viruses that cannot be cultured
  4. It provides quantitative viral load results

Explanation

Centrifugation enhances viral adsorption onto the monolayer, and staining with monoclonal antibody at 24 to 72 hours allows detection long before conventional tube culture shows cytopathic effect. The method still requires a viable monolayer and does not quantify viral burden.

Question 45Virology

In the CDC-recommended HIV testing algorithm, a repeatedly reactive fourth-generation HIV-1/2 antigen-antibody immunoassay is next followed by:

  1. An HIV-1 RNA viral load
  2. An HIV-1/HIV-2 antibody differentiation immunoassay Correct answer.
  3. A Western blot for HIV-1
  4. A CD4 lymphocyte count

Explanation

The current algorithm uses a supplementary HIV-1/HIV-2 antibody differentiation assay to confirm and discriminate the type; nucleic acid testing follows only when that assay is negative or indeterminate. CD4 counts and viral load are used for staging and monitoring, not for initial diagnosis.

Question 46Virology

Which serologic marker is the first to appear in acute hepatitis B infection?

  1. HBsAg Correct answer.
  2. Anti-HBc IgM
  3. Anti-HBs
  4. HBeAg

Explanation

HBsAg is the earliest detectable marker, appearing weeks before symptoms and before any antibody response. Anti-HBc IgM rises shortly afterward, HBeAg reflects active replication, and anti-HBs signals recovery and immunity.

Question 47Virology

A patient has a reactive anti-HCV antibody screen but a nonreactive HCV RNA test. What is the most likely interpretation?

  1. Active chronic hepatitis C infection
  2. Past infection that has cleared Correct answer.
  3. Acute infection before seroconversion
  4. A result that requires no further follow-up

Explanation

A positive antibody result with undetectable RNA most often reflects resolved infection with loss of viremia, though a false-positive antibody test is also possible. Active infection requires detectable RNA, and seroconversion would produce a negative antibody result rather than a positive one.

Question 48Virology

Rubella-specific IgM is detected in serum from a pregnant woman at 10 weeks' gestation. This finding suggests:

  1. Recent rubella infection Correct answer.
  2. Immunity from prior vaccination
  3. Maternal antibody of no clinical importance
  4. Remote infection during childhood

Explanation

IgM is the early antibody class and its presence in pregnancy raises concern for recent primary rubella, which carries high risk of congenital rubella syndrome in the first trimester. Past infection or vaccination is reflected by IgG, not IgM.

Question 49Virology

Which specimen is preferred for detecting influenza virus by RT-PCR in an adult?

  1. Nasopharyngeal swab Correct answer.
  2. Throat swab
  3. Sputum
  4. Serum

Explanation

Influenza virus replicates primarily in the ciliated epithelium of the nasopharynx, so a nasopharyngeal swab collects the highest viral burden and gives the best sensitivity. Serum and throat specimens are substantially less sensitive for nucleic acid detection.

Question 50Virology

Adenovirus produces which characteristic appearance in cell culture?

  1. Grape-like clusters of rounded cells Correct answer.
  2. Owl's-eye intranuclear inclusions
  3. Syncytia without inclusions
  4. Negri bodies

Explanation

Adenovirus causes rounding and aggregation of cells into grape-like clusters, often with enlarged nuclei containing basophilic inclusions. Owl's-eye inclusions indicate cytomegalovirus and Negri bodies indicate rabies virus.