Free ASCP Technologist in Microbiology Questions and Answers 1 — Questions and Answers
Question 1: Which culture media are commonly used to cultivate different species of Mycobacterium?
- Thayer-Martin agar and Lowenstein-Jensen agar
- Lowenstein-Jensen and Middlebrook agar (Correct answer)
- Cefalotin-buffered dextrin broth and Middlebrook agar
- Buffered Charcoal Yeast Extract and MacConkey Sorbitol agar
Correct answer: Lowenstein-Jensen and Middlebrook agar
Lowenstein-Jensen (LJ) agar and Middlebrook agar are specialized culture media specifically formulated for the isolation and growth of Mycobacterium species, including Mycobacterium tuberculosis. LJ agar is an egg-based medium that inhibits other bacteria, while Middlebrook agars (e.g., 7H10, 7H11) are synthetic agar-based media. Both provide the necessary nutrients and conditions for the slow-growing mycobacteria to thrive, making them essential for diagnosing mycobacterial infections.
Question 2: In the Laboratory Response Network for Biological Threats, sentinel laboratories play which of the following roles?
- Perform regular diagnostic procedures and determine if samples need to be sent somewhere else for additional testing. (Correct answer)
- Specialized handling of biological agents that are highly contagious, identification of the origin of illness outbreaks, and characterization of novel organisms and viruses.
- Obtain and process clinical or environmental samples at high risk for testing on behalf of other organizations.
- Provide other laboratories instruction and direction.
Correct answer: Perform regular diagnostic procedures and determine if samples need to be sent somewhere else for additional testing.
Sentinel laboratories are the first line of defense in the Laboratory Response Network (LRN) for biological threats. Their primary role is to perform routine diagnostic testing on clinical samples. If a sample exhibits characteristics suspicious for a high-consequence biological agent, sentinel laboratories are responsible for ruling out common pathogens and then referring the sample to a higher-level LRN laboratory for definitive identification and advanced testing.
Question 3: Which antibiotic, by binding to D-alanyl D-alanine, inhibits the formation of peptidoglycans and hence inhibits the growth of bacteria?
- Flucloxacillin
- Streptomycin
- Vancomycin (Correct answer)
- Linezolid
Correct answer: Vancomycin
Vancomycin is a glycopeptide antibiotic that inhibits bacterial cell wall synthesis, primarily in Gram-positive bacteria. It achieves this by binding specifically to the D-alanyl-D-alanine termini of peptidoglycan precursors. This binding prevents the transpeptidation and transglycosylation reactions necessary for cross-linking the peptidoglycan chains, thereby disrupting cell wall formation and inhibiting bacterial growth.
Question 4: Since hyphae exhibit _____ between the yeast cell and the hyphae or pseudohyphae, they can be identified from germ tubes.
- buds
- dilation
- hypha
- constriction or septa (Correct answer)
Correct answer: constriction or septa
Germ tubes are true outgrowths of yeast cells, typically observed in Candida albicans, and are characterized by a lack of constriction at their base where they emerge from the parent cell. In contrast, true hyphae or pseudohyphae exhibit a visible constriction or septa (cross-walls) at the point of budding from the yeast cell or other hyphal segments. This morphological difference is a key diagnostic feature for distinguishing C. albicans germ tubes.
Question 5: A throat swab was obtained from an individual who appeared to have thrush. Which of the following would make it possible to distinguish Candida albicans from other Candida species?
- Super Optimal broth with Catabolite repression
- Sabouraud dextrose agar
- Canavanine-Glycine-Bromothymol blue
- Pagano-Levin agar (Correct answer)
Correct answer: Pagano-Levin agar
Pagano-Levin agar is a differential culture medium specifically designed to distinguish Candida albicans from other Candida species. It contains tetrazolium salts that are reduced by C. albicans, resulting in the formation of distinctive pink or red colonies. Other Candida species typically produce white or cream-colored colonies, allowing for presumptive identification of C. albicans in clinical samples, such as throat swabs from thrush patients.
Question 6: A patient's aspirated joint fluid following a recent arthroplasty was placed on a blood agar plate. Under a microscope, gram-positive cocci were found. The colonies were alpha hemolytic following a 24-hour incubation period. Which test would be most helpful in determining the infection's cause?
- mannitol salt agar
- catalase test (Correct answer)
- oxidase test
- coagulase
Correct answer: catalase test
Given gram-positive cocci that are alpha-hemolytic from a joint fluid sample, common pathogens include Streptococcus pneumoniae and viridans streptococci. The catalase test is crucial for differentiation, as streptococci are catalase-negative, while staphylococci (another group of gram-positive cocci) are catalase-positive. This test helps narrow down the potential causative agent, guiding further identification and treatment.
Question 7: Which of the following describes a cutaneous contaminant that originates in the gastrointestinal tract?
- Klebsiella oxytoca (Correct answer)
- Brevibacterium casei
- Pasteurella multocida
- Propionibacterium acnes
Correct answer: Klebsiella oxytoca
Klebsiella oxytoca is a Gram-negative bacterium commonly found as a commensal in the human gastrointestinal tract. While part of the normal flora, it is also an opportunistic pathogen capable of causing various infections, including skin and soft tissue infections. Therefore, it can act as a cutaneous contaminant that originates from the gastrointestinal tract, especially in healthcare settings or immunocompromised individuals.
Question 8: A patient, age 21, exhibits symptoms of exhaustion, headache, fever, and hurting muscles. The patient visited Uganda not too long ago. The results of their blood testing are displayed below. Which substance is the cause?
- Malaria (Correct answer)
- Trypanosomiasis
- Strongyloidiasis
- Leishmania
Correct answer: Malaria
The patient's symptoms of exhaustion, headache, fever, and muscle pain, combined with recent travel to Uganda (an endemic area), are highly indicative of malaria. Malaria is caused by Plasmodium parasites transmitted by mosquitoes, and its characteristic clinical presentation often includes cyclical fevers, chills, and flu-like symptoms. Blood tests would typically reveal the presence of parasites within red blood cells, confirming the diagnosis.
Question 9: A woman with a bad-smelling discharge and pruritis had a vaginal swab taken. Microscopic analysis identified the presence of protozoa with motile flagella. What is the symptoms' most likely cause?
- Giardia duodenalis
- Chlamydia trachomatis
- Chlamydomonas coccifera
- Trichomonas vaginalis (Correct answer)
Correct answer: Trichomonas vaginalis
The clinical presentation of a woman with a bad-smelling vaginal discharge, pruritis (itching), and the microscopic finding of motile flagellated protozoa is classic for an infection with Trichomonas vaginalis. This sexually transmitted infection, known as trichomoniasis, often causes symptoms like frothy, greenish-yellow discharge and vulvovaginal irritation. The characteristic motility and flagella are key diagnostic features.
Question 10: Which sample is most likely to contain Trichinella larvae?
- brain biopsy
- nasopharyngeal
- wound
- muscle biopsy (Correct answer)
Correct answer: muscle biopsy
Trichinella species are parasitic nematodes that cause trichinellosis, an infection acquired by consuming undercooked meat containing larvae. After maturing in the intestine, new larvae migrate from the intestine to muscle tissue, where they encyst. Therefore, a muscle biopsy is the most appropriate sample for detecting Trichinella larvae in infected individuals, as this is where the parasites primarily reside.
Question 11: In tissue, what staining method can be used to identify Aspergillus fumigatus?
- potassium hydroxide staining
- Grocott's silver stain (Correct answer)
- Calcoflour
- Immunohistochemistry
Correct answer: Grocott's silver stain
Grocott's Methenamine Silver (GMS) stain is a widely used histopathological stain for visualizing fungi, including Aspergillus species, in tissue sections. The GMS stain highlights fungal cell walls in black or dark brown, making them clearly visible against a light background. This allows for the identification of fungal elements like hyphae and conidia, which are characteristic of Aspergillus infections in tissue.
Free ASCP Technologist in Microbiology Questions and Answers 1
Which culture media are commonly used to cultivate different species of Mycobacterium?