Medical Bacteriology & Entomology 2021/2022 Q&A

Question 1

Which one of the following is a complication of streptococcus pharyngitis?

Accepted Answer

Rheumatic fever — Rheumatic fever is a post-infectious autoimmune complication of Group A Streptococcus (S. pyogenes) pharyngitis. It occurs 2-4 weeks after untreated strep throat due to molecular mimicry between streptococcal M protein and cardiac myosin, leading to carditis, arthritis, and other manifestations. ---

Question 2

The presence of a pseudomembrane is a result of

Accepted Answer

Diphtheria — Diphtheria toxin produced by Corynebacterium diphtheriae causes local tissue necrosis and inflammation, leading to formation of a characteristic gray-white pseudomembrane in the throat that can obstruct airways. This fibrinous exudate is pathognomonic for diphtheria. ---

Question 3

A paroxysm is a associated with

Accepted Answer

Paroxysmal cough — Paroxysmal cough is the hallmark of pertussis (whooping cough) caused by Bordetella pertussis. The characteristic paroxysm consists of rapid-fire coughing fits followed by a high-pitched "whoop" during inspiration, often accompanied by vomiting. ---

Question 4

The Mantoux test is used to identify

Accepted Answer

Q fever — The Mantoux test (tuberculin skin test) uses purified protein derivative (PPD) injected intradermally to detect delayed-type hypersensitivity response indicating previous exposure to Mycobacterium tuberculosis or BCG vaccination. Induration ≥10mm in normal individuals suggests TB exposure. ---

Question 5

To treat patients who have ingested botulism toxin, large doses of must be administered

Accepted Answer

Antitoxin — Botulism antitoxin (equine-derived antiserum) neutralizes circulating botulinum toxin and prevents progression of paralysis. It must be administered early as it cannot reverse existing nerve damage but prevents further toxin binding to nerve terminals. ---

Question 6

The organism Clostridium perfringens multiplies in foods only under conditions

Accepted Answer

Anaerobic — Clostridium perfringens is an obligate anaerobe that multiplies rapidly in foods under anaerobic conditions. Its spores survive cooking and germinate when oxygen is excluded, leading to rapid multiplication in improperly stored cooked foods. ---

Question 7

A spore-forming, motile rod that can cause foodborne illness in a diarrheal or emetic form is Bacillus

Accepted Answer

Cereus — Bacillus cereus causes two forms of food poisoning: diarrheal syndrome (8-16 hours after ingestion, watery diarrhea) and emetic syndrome (1-6 hours, nausea and vomiting). It's commonly associated with rice dishes and forms heat-resistant spores. ---

Question 8

Woolsorter disease applies to the form of

Accepted Answer

Woolsorter disease — Woolsorter disease is pulmonary (inhalation) anthrax historically seen in workers processing contaminated wool, hair, or hides. Bacillus anthracis spores are inhaled, germinate in alveolar macrophages, and cause severe pneumonia with high mortality if untreated. ---

Question 9

Which one of the following describes the mode of action of tetanospasmin?

Accepted Answer

Tetanospasmin — Tetanospasmin cleaves synaptobrevin proteins in inhibitory neurons, preventing release of GABA and glycine neurotransmitters. This blocks muscle relaxation signals, resulting in sustained muscle contractions and spastic paralysis characteristic of tetanus. ---

Question 10

Salpingitis is associated with and can lead to

Accepted Answer

Gonorrhea; sterility — Salpingitis (fallopian tube inflammation) is commonly caused by ascending Neisseria gonorrhoeae infection. Chronic inflammation leads to scarring and tubal occlusion, resulting in infertility or increased risk of ectopic pregnancy. ---

Question 11

Ophthalmia is associated with what two STDs?

Accepted Answer

Gonorrhea and chlamydia — Neonatal ophthalmia (conjunctivitis) is primarily caused by Neisseria gonorrhoeae and Chlamydia trachomatis transmitted from infected mothers during delivery. Both can cause severe purulent conjunctivitis that may lead to blindness if untreated. ---

Question 12

Toxin-generated S. aureus diseases resulting from contact include

Accepted Answer

Scalded skin syndrome — Staphylococcus aureus produces exfoliative toxins causing staphylococcal scalded skin syndrome (SSSS) and toxic shock syndrome toxin-1 (TSST-1) causing toxic shock syndrome. Both are toxin-mediated diseases that can result from skin contact or colonization. ---

Question 13

A 22-year-old woman who works in a plant nursery presents with fever and cough for 2 months, 5 kg weight loss, bilateral upper lobe infiltrates with cavities, and acid-fast bacilli in sputum. The likely means of infection acquisition is

Accepted Answer

This presentation — This presentation is classic for pulmonary tuberculosis caused by Mycobacterium tuberculosis. TB is transmitted via airborne droplet nuclei containing viable bacteria. The patient's occupation and clinical findings suggest respiratory transmission, not soil contact. ---

Question 14

A 65-year-old woman with a central venous catheter develops fever and multiple blood cultures positive for Staphylococcus epidermidis with biofilm formation. Which statement about this infection is correct?

Accepted Answer

Extracellular polysaccharide production inhibits S. epidermidis growth — S. epidermidis biofilms on catheters are highly resistant to antimicrobials due to decreased metabolic activity, altered gene expression, and physical barrier effects of the extracellular matrix. Catheter removal is often necessary for cure. ---

Question 15

The first microorganism to satisfy Koch's postulates (in the late 19th century) was

Accepted Answer

Bacillus anthracis — Robert Koch first demonstrated his postulates using Bacillus anthracis in 1876, proving it was the causative agent of anthrax. This established the germ theory of disease and the scientific method for linking specific pathogens to specific diseases. ---

Question 16

Which of the following statements about lipopolysaccharide is correct?

Accepted Answer

The toxic component is the O side chain — Lipopolysaccharide (endotoxin) binds to CD14/TLR4 receptors on macrophages and monocytes, triggering release of inflammatory cytokines (TNF-α, IL-1, IL-6) that cause fever, hypotension, and other septic shock symptoms. The toxic component is lipid A, not the O antigen. ---

Question 17

Which of the following best describes the mechanism of action of diphtheria toxin?

Accepted Answer

Degrades lecithin in eukaryotic cell membranes — Diphtheria toxin ADP-ribosylates elongation factor 2 (eEF2), permanently inactivating it and halting protein synthesis in eukaryotic cells. This leads to cell death and the characteristic local tissue necrosis and systemic toxicity of diphtheria. ---

Question 18

Certain microorganisms are never considered members of normal flora and are always considered pathogens. Which organism fits this category?

Accepted Answer

M. tuberculosis — M. tuberculosis is a true (obligate) pathogen that always causes disease when it infects humans and is never part of normal flora. The other organisms can be found as normal flora in certain body sites and cause opportunistic infections. ---

Question 19

Which one of the following genera is the ODD one out in terms of pathogen transmission?

Accepted Answer

Musca — Bulinus is a freshwater snail that serves as an intermediate host for Schistosoma haematobium (biological vector), while Fannia, Musca, and Blatta are arthropods that primarily serve as mechanical vectors of pathogens through contamination. ---

Question 20

Which of the following diseases can be effectively controlled by the use of acaricides?

Accepted Answer

Amoebiasis — Q-fever is transmitted by ticks (Ixodes species), which are arachnids (mites and ticks) controlled by acaricides. Leishmaniasis is transmitted by sandflies, Katayama fever by snails, sleeping sickness by tsetse flies (all insects), and amoebiasis is not vector-borne. ---

Question 21

Which one of the following genera is a biological vector of scrub typhus pathogens?

Accepted Answer

Leptotrombidium — Leptotrombidium mites (chiggers) are the biological vectors of Orientia tsutsugamushi, the causative agent of scrub typhus. The mites serve as both vector and reservoir, with transovarial transmission maintaining the pathogen in mite populations. ---

Question 22

Which of the following pathogens can be transovarially transmitted by its biological vector?

Accepted Answer

Orientia tsutsugamushi — Orientia tsutsugamushi (scrub typhus) is maintained in Leptotrombidium mite populations through transovarial transmission from infected female mites to their offspring, making the mites both vector and reservoir host. ---

Question 23

Which of the following is the BEST treatment for scabies?

Accepted Answer

Amphotericin B — Benzyl benzoate is a topical scabicide effective against Sarcoptes scabiei mites causing scabies. It kills adult mites and eggs when applied to the entire body. Other options treat different parasites: metronidazole for protozoa, amphotericin B for fungi, sodium stibogluconate for leishmaniasis, praziquantel for helminths. ---

Question 24

Which of the following reagents can be used in the diagnosis of mites infection?

Accepted Answer

Liquid crystal violet — Liquid iodine can be applied to skin suspected of scabies infection to visualize burrows created by Sarcoptes scabiei mites. The iodine stains the burrows dark brown, making them more visible for diagnosis. This is a simple diagnostic technique for scabies. ---

Question 25

Indoor residual spraying is BEST effective against insect vectors of pathogens

Accepted Answer

Exophilic — Indoor residual spraying (IRS) is most effective against endophilic vectors that rest indoors after blood feeding, where they contact insecticide-treated surfaces. Exophilic vectors rest outdoors and have minimal contact with indoor-applied insecticides. ---

Question 26

Which one of the following genera belongs to the family Argasidae?

Accepted Answer

Ornithodoros — Ornithodoros belongs to the family Argasidae (soft ticks), characterized by lack of a hard scutum and mouthparts not visible from above. The other genera belong to Ixodidae (hard ticks) with visible scutum and prominent mouthparts. ---

Question 27

Which one of the following vectors utilizes one host in its life cycle and pathogen transmission?

Accepted Answer

Boophilus — Boophilus ticks are one-host ticks that complete their entire life cycle (larva, nymph, adult) on a single host animal. The other genera are either two-host or three-host ticks that drop off between life stages to molt before finding new hosts. ---

Question 28

Which one of the following vectors of pathogens is BEST controlled by using boric acid powder (e.g., borax)?

Accepted Answer

Periplaneta species — Periplaneta species (cockroaches) are effectively controlled using boric acid powder, which acts as a stomach poison when ingested during grooming. Boric acid damages the insect's digestive system and is a common cockroach control method in integrated pest management programs.

Medical Bacteriology & Entomology 2021/2022 Q&A

Questions, Answers & Explanations