Medical Bacteriology And Parasitology End Year 2024/2025 | MCQ Quiz | OmpathStudy Kenya

Question 1

Fish are second intermediate hosts of?

Accepted Answer

Echinostoma ilocaanum — Fish serve as the second intermediate host for Clonorchis sinensis (Chinese liver fluke). Humans get infected by eating raw or undercooked fish containing the parasite's metacercariae. ---

Question 2

Which of the following secretes defensive secretions to cause irritation on human skin?

Accepted Answer

Millipedes — Millipedes have defensive glands that secrete irritating chemicals (benzoquinones, hydrogen cyanide) causing skin burns and discoloration. Centipedes bite rather than secrete defensive substances. ---

Question 3

Holometabolous insects have?

Accepted Answer

2 life stages — Holometabolous insects undergo complete metamorphosis with four stages: egg → larva → pupa → adult. Examples include mosquitoes, flies, and beetles. ---

Question 4

Which of the following transmits parasites for river blindness?

Accepted Answer

Culex species — Simulium species (blackflies) are the vectors of Onchocerca volvulus, causing river blindness (onchocerciasis). They breed in fast-flowing rivers. ---

Question 5

Which insecticide targets GABA in its action?

Accepted Answer

DDT — Bendiocarb is a carbamate insecticide that inhibits acetylcholinesterase, affecting GABA neurotransmission. DDT and permethrin target sodium channels instead. ---

Question 6

Presence of triatomine bugs could predispose the population to?

Accepted Answer

Sleeping sickness — Triatomine bugs (kissing bugs) transmit Trypanosoma cruzi, which causes Chagas disease. They defecate while feeding, and parasites enter through the bite wound or mucous membranes. ---

Question 7

People living in forested areas like Arabuko Sokoke are at a risk of?

Accepted Answer

Sleeping sickness — Forested areas harbor sandflies (Phlebotomus/Lutzomyia species) that transmit Leishmania parasites. Forest ecosystems provide ideal habitats for sandfly vectors and animal reservoirs. ---

Question 8

Which of the following insects are commonly found in Latin America?

Accepted Answer

Glossina species — Triatomine bugs are endemic to Latin America where they transmit Chagas disease. Glossina species (tsetse flies) are found only in sub-Saharan Africa. ---

Question 9

Pruritus can be best diagnosed for?

Accepted Answer

Sarcoptes scabiei — Sarcoptes scabiei (scabies mite) burrows into skin causing intense pruritus (itching), especially at night due to mite activity and allergic reaction to mite proteins. ---

Question 10

If you found lice eggs (nits) in someone's clothing, what species would they most likely be from?

Accepted Answer

Crab lice — Pediculus humanus (body lice) live and lay eggs in clothing seams, not on the body. Pediculus capitis (head lice) attach eggs to hair shafts, not clothing. ---

Question 11

Which of the following is odd one out in terms of transmission?

Accepted Answer

Vibrio cholerae — Thelazia species (eye worm) is transmitted by flies (mechanical vectors), while the others are transmitted via fecal-oral route through contaminated water/food. ---

Question 12

Which one of the following is larviparous?

Accepted Answer

Phlebotomus species — Glossina species (tsetse flies) are larviparous - they give birth to live larvae rather than laying eggs. The larva immediately pupates after birth. ---

Question 13

Argasid ticks have?

Accepted Answer

One host — Argasid (soft) ticks are multi-host ticks that feed quickly (minutes to hours) on different hosts throughout their life stages, unlike ixodid ticks. ---

Question 14

Ixodid ticks have nymphal stages.

Accepted Answer

One — Ixodid (hard) ticks have a single nymphal stage in their life cycle: egg → larva → nymph → adult. This is standard for hard ticks. ---

Question 15

Traps for Aedes mosquitoes are composed of?

Accepted Answer

Black and white colors — Aedes mosquitoes are attracted to contrasting black and white patterns. Ovitraps and BG-Sentinel traps use this color combination for effective Aedes surveillance and control. ---

Question 16

Traps for Glossina species are composed of?

Accepted Answer

Black and white colors — Tsetse flies (Glossina species) are attracted to black and blue colors. Biconical traps and targets use these colors for effective tsetse fly control. ---

Question 17

Black water disease is due to presence of in the environment.

Accepted Answer

Simulium species — Blackwater fever is a severe complication of falciparum malaria (transmitted by Anopheles mosquitoes), characterized by massive intravascular hemolysis causing dark urine. ---

Question 18

Hepatitis B virus has been associated with?

Accepted Answer

Cimex species — Cimex species (bed bugs) have been studied for potential mechanical transmission of Hepatitis B virus, though their role remains controversial and not definitively proven. ---

Question 19

Which of the following statements regarding vaccination for Bacillus anthracis is correct?

Accepted Answer

It is routinely available for all citizens of the United States — Newer recombinant protective antigen vaccines have demonstrated good safety and efficacy in trials. The current AVA vaccine requires multiple doses and has tolerability issues. ---

Question 20

Lowenstein Jensen media is used to isolate?

Accepted Answer

Streptococcus species — Lowenstein-Jensen medium is an egg-based selective medium specifically designed for culturing Mycobacterium tuberculosis and other mycobacteria, which grow slowly and require special nutrients. ---

Question 21

All of the following statements regarding Clostridium perfringens are correct EXCEPT

Accepted Answer

It produces an enterotoxin — Clostridioides difficile (not C. perfringens) is the most common cause of antibiotic-associated diarrhea. C. perfringens causes food poisoning and gas gangrene. ---

Question 22

Motility of the bacteria can be observed by

Accepted Answer

Hanging drop method — Bacterial motility is observed using hanging drop method (direct microscopic visualization) and soft agar method (growth pattern spreading from stab line). Pour plate is for colony counting. ---

Question 23

Three months ago, a 53-year-old woman had surgery and chemotherapy for breast cancer. Four weeks ago, she developed a cough occasionally productive of purulent sputum. About 2 weeks ago, she noted a slight but progressive weakness of her left arm and leg. On chest examination, rales were heard over the left upper back when the patient breathed deeply. Neurologic examination confirmed weakness of the left arm and leg. Chest radiography showed a left upper lobe infiltrate. Contrast enhanced computed tomography showed two lesions in the right hemisphere. Gram stain of a purulent sputum specimen showed branching gram-positive rods that were partially acid fast. Which of the following organisms is the cause of this patient's current illness?

Accepted Answer

Actinomyces israelii — The patient is immunocompromised (chemotherapy), has pulmonary infection with brain abscesses, and shows branching gram-positive rods that are partially acid-fast - all classic for Nocardia species, which disseminate to the brain. ---

Question 24

The drug of choice to treat this patient's infection (Question 23) is

Accepted Answer

Penicillin G — Trimethoprim-sulfamethoxazole (TMP-SMX) is the first-line treatment for Nocardia infections. Treatment duration is prolonged (6-12 months) due to tendency for relapse. ---

Question 25

can cause food INTOXICATION?

Accepted Answer

Staphylococcus aureus — Staphylococcus aureus produces preformed enterotoxins in food, causing food intoxication (rapid onset 1-6 hours). Salmonella and E. coli cause food infection (longer incubation, bacteria must multiply). ---

Question 26

Helicobacter pylori possesses that helps to neutralize stomach acid (HCl).

Accepted Answer

Coagulase — H. pylori produces large amounts of urease enzyme, which converts urea to ammonia and CO2. The ammonia neutralizes gastric acid, creating a protective alkaline microenvironment around the bacterium. ---

Question 27

An 8-year-old boy develops a severe sore throat. On examination, a grayish exudate (pseudomembrane) is seen over the tonsils and pharynx. The differential diagnosis of severe pharyngitis such as this includes group A streptococcal infection, Epstein-Barr virus (EBV) infection, Neisseria gonorrhoeae pharyngitis, and diphtheria. The cause of the boy's pharyngitis is most likely

Accepted Answer

A gram-negative bacillus — The grayish pseudomembrane is pathognomonic for diphtheria caused by Corynebacterium diphtheriae, which is a club-shaped (coryneform) gram-positive bacillus. ---

Question 28

The primary mechanism in the pathogenesis of the boy's disease (Question 27) is

Accepted Answer

A net increase in intracellular cyclic adenosine monophosphate — Diphtheria toxin inhibits elongation factor 2 (EF-2), blocking protein synthesis in host cells. This causes local tissue necrosis (pseudomembrane) and systemic effects on heart and nerves. ---

Question 29

Which of the following aerobic gram-positive bacilli is modified acid-fast positive?

Accepted Answer

Nocardia brasiliensis — Nocardia species are weakly (modified) acid-fast positive due to mycolic acids in their cell walls. This helps differentiate them from other gram-positive bacilli. ---

Question 30

A 45-year-old fisherman embedded a fishhook into his right forefinger. He removed it and did not seek immediate medical therapy. Five days later, he noted fever, severe pain, and nodular-type swelling of the finger. He sought medical therapy. The violaceous nodule was aspirated, and after 48 hours of incubation, colonies of a gram-positive bacillus that caused greenish discoloration of the agar and formed long filaments in the broth culture were noted. The most likely cause of this infection is

Accepted Answer

Lactobacillus acidophilus — Erysipelothrix rhusiopathiae causes erysipeloid in fishermen/meat handlers. Key features: violaceous lesions, greenish α-hemolysis on blood agar, and long filamentous forms in broth. Exposure history is characteristic. ---

Question 31

A biochemical reaction that is useful in the identification of the causative agent of the infection in question 30 is

Accepted Answer

Catalase positivity — Erysipelothrix rhusiopathiae produces H2S (hydrogen sulfide), which is a key identifying biochemical test. It is catalase-negative, differentiating it from other gram-positive bacilli. ---

Question 32

A hospitalized patient who had an indwelling urinary catheter develops fever, chills, suprapubic pain and difficulty voiding 48 hours after the catheter is removed. His bladder appears obstructed, and he has white blood cells and bacteria on a urinalysis. Cystoscopy reveals a large bladder stone, and the urine culture grows greater than 10,000 CFU/ml of a short, irregular gram-positive rod. The most likely organism causing this infection is

Accepted Answer

Corynebacterium urealyticum — Corynebacterium urealyticum is a urease-producing organism that causes alkaline-encrusted cystitis and bladder stone formation in catheterized patients. It's a fastidious, slow-growing coryneform bacterium. ---

Question 33

Drug of choice for treatment of mycoplasma infection are

Accepted Answer

Tetracycline — Mycoplasma lacks a cell wall, making penicillin ineffective. Tetracyclines and macrolides (erythromycin, azithromycin) are effective as they target ribosomes and protein synthesis. ---

Question 34

The mode of spread of tetanus neurotoxin from blood to brain is via

Accepted Answer

Lymphatics — Tetanus neurotoxin spreads via retrograde axonal transport through peripheral motor neurons to the spinal cord/brainstem, not through blood, lymphatics, or cranial nerves primarily. ---

Question 35

Patient with presence of penile chancre should be advised by physician to

Accepted Answer

Take rest at home — Primary syphilis chancre requires dark-field microscopy to visualize motile Treponema pallidum spirochetes. Treponema cannot be cultured on routine media or Gram-stained effectively. --- ## SECTION B: SHORT ANSWER QUESTIONS (25 MARKS) Instructions: Answer ALL questions ---

Question 36

Outline differences between toxic shock syndrome and staphylococcal scalded skin syndrome. (5 Marks) ANSWER: TOXIC SHOCK SYNDROME (TSS): Causative Agent: - Staphylococcus aureus producing TSST-1 (toxic shock syndrome toxin-1) or other enterotoxins Mechanism: - Superantigen-mediated massive T-cell activation - Systemic inflammatory response Clinical Features: - High fever ( 38.9°

Accepted Answer

- Hypotension/shock - Diffuse erythematous rash (resembles sunburn) - Desquamation (especially palms/soles) 1-2 weeks later - Multi-organ involvement (≥3 systems) - Vomiting, diarrhea, myalgia Age Group: - Primarily menstruating women (tampon-associate

Question 37

##### A 33-year-old indigent man comes to the emergency room of the county hospital. The emergency room nurse immediately notices that the man cannot open his mouth because of facial muscle spasms. The physician on duty detects right-sided face pain and trismus. She is able to ascertain from the patient that he has not been able to eat for two days because of jaw pain. Examination of his body shows necrotic, blackened areas on the bottom of his left foot. ###

Accepted Answer

Based on these signs and the physical exam results, what organism has infected this man and what disease does he have? (4 Marks) ANSWER POINTS: Organism: *Clostridium tetani * - Gram-positive, spore-forming anaerobic bacillus - Produces terminal spores giving "drumstick" appearance - Found in soil, dust, animal feces Disease: Tetanus (Lockjaw) - Caused by tetanospasmin (tetanus neurotoxin) - Clinical presentation confirms diagnosis: Trismus (lockjaw) - inability to open mouth - Facial muscle spasms (risus sardonicus) - Progressive muscle rigidity - Necrotic wound on left foot (portal of entry) --- ###

Medical Bacteriology And Parasitology End Year 2024/2025 | MCQ Quiz | OmpathStudy Kenya

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