Microbiology tests with answers: 50 questions for exam preparation

The CD19 molecule is a pan-B-cell marker that appears at the pro-B-lymphocyte stage and persists throughout antigen-independent maturation in the bone marrow. The other listed markers (CD3, CD4, CD8) are characteristic of T-lymphocytes.

The antigen-binding cleft of MHC class II molecules is formed by domains of two different chains (alpha and beta) and has open ends, allowing it to bind longer peptides compared to MHC class I.

Recognition of an antigen by the T-cell receptor without simultaneous receipt of a co-stimulatory signal (signal 2) leads to the induction of apoptosis or lymphocyte anergy.

House dust mites (e.g., Dermatophagoides pteronyssinus) belong to the family Pyroglyphidae and are the main sources of indoor inhalant allergens.

Single-stranded viral RNA is recognized by endosomal receptors TLR7 and TLR8. By contrast, TLR3 binds double-stranded RNA, and TLR9 binds unmethylated DNA.

Consumption of pathogen-contaminated water from drinking troughs executes the fecal-oral mechanism of infection transmission. The main route of infection in this case is alimentary (waterborne).

Congenital listeriosis (granulomatous sepsis of newborns) is characterized by the formation of specific granulomas—listeriomas—containing necrotic masses, macrophages, and intracellular bacteria.

Infection with listeriosis through the consumption of contaminated dairy products occurs via the alimentary route through the gastrointestinal tract.

The primary route for zoonotic bacteria (e.g., leptospires or listerias) to enter soil and water bodies is through their excretion by infected rodents along with urine and feces. This ensures the maintenance of the natural focus of infection.

The gold standard and primary method for confirming the diagnosis of listeriosis remains bacteriological examination with the isolation and identification of a pure culture of Listeria monocytogenes from sterile biological fluids.

Mycoplasmas genetically lack the ability to synthesize peptidoglycan, which is why they do not have a rigid cell wall. This allows their cells to easily change shape and determines pronounced pleomorphism.

Mycoplasma pneumoniae is tropic to respiratory epithelial cells, to the surface of which it attaches, causing damage to cilia and impaired mucociliary clearance.

Urogenital mycoplasmas (Mycoplasma hominis and Ureaplasma urealyticum) are capable of being transmitted from mother to fetus intrauterinely or during childbirth, causing congenital pneumonia, meningitis, and sepsis in premature infants.

Mycoplasmas lack a cell wall and exhibit a pronounced tropism for host cell membranes, attaching tightly to them and exerting a membranetoxic and cytolytic effect through peroxides and enzymes.

Mycoplasmas lack a cell wall; therefore, sterols (cholesterol), which they are unable to synthesize independently, are necessary to stabilize their cytoplasmic membrane.

The iatrogenic transmission route is associated with medical interventions. In the case of prion diseases, infection can occur through the use of contaminated neurosurgical instruments, grafts, or products of human origin (e.g., growth hormone).

Historically, kuru spread among the tribes of Papua New Guinea via the alimentary route during ritual consumption of the brains of deceased fellow tribesmen, which contained a high concentration of prions.

Upon oral ingestion, prions are first captured by the intestinal lymphoid tissue and accumulate in the organs of the reticuloendothelial system (tonsils, spleen) prior to neuroinvasion.

Carlton Gajdusek experimentally proved the infectious nature of kuru in the 1960s by successfully infecting chimpanzees with a brain tissue suspension from deceased individuals, for which he was subsequently awarded the Nobel Prize.

Prion pathologies are classified as conformational diseases because their pathogenesis is driven by the conversion of the normal cellular protein PrPC into the pathological isoform PrPSc with an altered tertiary structure.

Old cultures of Trichophyton violaceum are characterized by the absence of micro- and macroconidia, while the mycelium becomes thin and convoluted, forming numerous chlamydospores and arthrospores. This anthropophilic fungus is one of the main causative agents of superficial trichophytosis.

The dermatophyte group traditionally includes three anamorphic fungal genera: Microsporum, Trichophyton, and Epidermophyton, which exhibit keratinolytic activity and infect the skin, hair, and nails.

Fungi of the genus Microsporum causing hair infection in vivo are characterized by an ectothrix type of sporulation, where arthrospores form a dense sheath on the outside of the hair shaft.

Sabouraud medium contains peptone, a high concentration of carbohydrates (maltose or glucose), and has a mildly acidic reaction. This creates optimal conditions for the elective cultivation of pathogenic fungi, including dermatophytes.

Since black piedra affects only the cuticle of the hair shaft without involving the hair follicle and skin, the primary treatment is hair clipping/shaving combined with topical antifungals.

Louis Pasteur was the first to apply the principle of attenuation (weakening) of microorganisms to create vaccines. His major achievements in this field included the development of vaccines against fowl cholera, anthrax, and rabies.

The study of human pathogens (bacteria, viruses, fungi, and protozoa) is the subject of medical microbiology.

Edward Jenner empirically used the natural cowpox virus for vaccination, whereas Louis Pasteur purposefully developed methods for the artificial attenuation (weakening) of pathogenic microorganisms to obtain safe vaccine strains.

In 1942, Zinaida Vissarionovna Yermolieva obtained the first domestic penicillin (krustosin) in the USSR and actively introduced antibiotic therapy into clinical practice.

The method of converting exotoxins into safe yet immunogenic toxoids by treatment with formalin at 37–40 °C was proposed by the French microbiologist Gaston Ramon in 1923.

Hepatitis D virus is a defective virus (satellite) that requires the hepatitis B surface antigen (HBsAg) to assemble complete virions and exit the cell. Therefore, hepatitis D virus infection is only possible in the presence of hepatitis B virus.

Invasiveness ensures microbial penetration through mucous membranes and connective tissue, while aggressiveness aims to counteract the host's defense mechanisms, for example, by suppressing phagocytosis.

The aggression enzyme hyaluronidase degrades hyaluronic acid in the extracellular matrix, facilitating pathogen invasion into tissues.

Antibodies are large protein molecules that are unable to penetrate inside cells. They can neutralize only freely circulating toxin, but are powerless against subunits that have already entered the cytoplasm of the target cell.

Diseases caused by animal parasites (including helminths and arthropods) are classified as invasion (parasitic) diseases.

Spongiform neuronal degeneration, glial proliferation (astrocytosis), and amyloid plaque formation in the complete absence of signs of inflammation represent the classic pathomorphological picture of prion diseases (transmissible spongiform encephalopathies).

The HIA is based on the ability of specific antibodies to bind to the surface hemagglutinins of viruses, thereby depriving them of the ability to agglutinate erythrocytes.

Secretory immunoglobulin A predominates on the mucous membranes of the respiratory tract and provides the first line of specific defense against respiratory viruses.

Most rhinovirus serotypes (the so-called major group) use intercellular adhesion molecule 1 (ICAM-1), located on the surface of respiratory epithelial cells, as a cellular receptor.

SARS-CoV and SARS-CoV-2 are representatives of the genus Betacoronavirus within the family Coronaviridae.

Deuteromycetes (imperfect fungi) bring together species with an undetermined sexual process. Upon discovery of a teleomorph (sexual stage), they are most often reclassified into the phyla Ascomycota or Basidiomycota.

Apicomplexans are parasitic and lack independent organs of movement at the adult stage, unlike flagellates, sarcodines, and ciliates.

The supercapsid of complex viruses is a lipid bilayer with embedded virus-specific glycoproteins that form spikes (peplomers) on the surface. They play a key role in recognizing host cell receptors and attaching to them.

The infectious form of chlamydia (elementary body) enters a susceptible cell via receptor-mediated endocytosis with the formation of an endosome.

The bacterial nuclear apparatus (nucleoid) is a DNA molecule that is not separated from the cytoplasm by a nuclear membrane, does not form a nucleolus, and is not associated with true histones.

Coronaviruses have a helical nucleocapsid symmetry type, in which genomic RNA is associated with the N protein, forming a helical structure inside the viral envelope.

On electron microscopy, coronaviruses have a characteristic appearance due to massive club-shaped peplomers (S proteins) on the supercapsid. They form a figure resembling a solar corona.

RT-PCR is used to detect filovirus RNA (Marburg, Ebola), while immunofluorescence assay (IFA) and ELISA are used to detect viral antigens and specific antibodies.

The spike glycoprotein S is responsible for binding the coronavirus to target cell receptors, which is why antibodies specifically directed against this protein block virus entry and possess neutralizing activity.

Coronaviruses are relatively large enveloped spherical viruses ranging in size from 80 to 220 nm.