The technique that combines freezing and drying to preserve microbes and other cells is

Correct Answer: B

Rationale: The correct answer is B: lyophilization. This technique involves freezing the sample and then removing the ice through sublimation, preserving the cells in a dry state. Desiccation (A) simply involves drying without freezing. Pasteurization (C) is a heat treatment to kill pathogens, not used for preservation. Radiation (D) can sterilize but doesn't involve freezing and drying like lyophilization.

Correct Answer: A

Rationale: The correct answer is A: 4 and 250. Coli index is calculated by dividing the number of red colonies by the volume of water analyzed, which gives 2 red colonies / 500 ml = 4. Coli titer is the reciprocal of the coli index, so it is 1 / 4 = 250. This indicates the concentration of coliform bacteria in the water sample. Choices B, C, and D are incorrect as they do not follow the correct calculation steps for determining the coli index and coli titer. B has the correct coli index but incorrect coli titer. C and D have the values reversed, leading to incorrect results.

Correct Answer: A

Rationale: The correct answer is A: Toxoplasma. The crescent-shaped protozoa with pointed ends and blue cytoplasm described in the question are characteristic of Toxoplasma gondii, the causative agent of toxoplasmosis. Toxoplasma staining with Romanovsky-Giemsa method typically shows these specific morphological features. Plasmodium causes malaria and does not exhibit the described morphology. Leishmania and Trypanosoma are both kinetoplastid parasites, but they do not typically present as crescent-shaped protozoa with blue cytoplasm. Therefore, based on the specific characteristics described in the question, the correct answer is Toxoplasma.

Correct Answer: D

Rationale: The correct answer is D: PCR. PCR (Polymerase Chain Reaction) is the most suitable method for detecting genitourinary chlamydiosis due to its high sensitivity and specificity in detecting the genetic material of Chlamydia trachomatis. PCR can detect even low levels of the pathogen, providing accurate results. A: Cultural diagnostic is not as sensitive as PCR and may take longer to produce results. B: ELISA detects antibodies, which may not be present in early stages of infection, leading to false-negative results. C: CFT (Complement Fixation Test) is an older method with lower sensitivity compared to PCR for detecting chlamydiosis.

Correct Answer: B

Rationale: The correct answer is B: EBV. Osteomyelitis is primarily caused by bacteria, not viruses like Epstein-Barr virus (EBV). The main pathogens involved in osteomyelitis are typically Staphylococcus aureus, including Methicillin-resistant Staphylococcus aureus (MRSA), Haemophilus influenzae, and Pseudomonas aeruginosa. EBV is not a causative agent of osteomyelitis. It is crucial to differentiate between bacterial and viral etiologies in infectious diseases to guide appropriate treatment.

Correct Answer: A

Rationale: The correct answer is A: Escherichia coli. E. coli typically produces red colonies on Endo agar due to its ability to ferment lactose. This results in the production of acid, causing the colonies to appear red. Salmonella and Shigella are non-lactose fermenters, so they would appear colorless or transparent on Endo agar. Proteus vulgaris is not commonly associated with red colonies on Endo agar. Therefore, based on the characteristic lactose fermentation pattern, E. coli is the most likely microorganism in this scenario.

Correct Answer: D

Rationale: The correct answer is D: All of the above. Salmonella enterica, Clostridium botulinum, and Escherichia coli are all commonly associated with food poisoning. Salmonella causes symptoms like diarrhea, vomiting, and abdominal cramps. Clostridium botulinum produces a toxin that leads to symptoms like muscle weakness and paralysis. Escherichia coli can cause symptoms like severe stomach cramps, diarrhea (often bloody), and vomiting. Therefore, all three bacteria are known to cause food poisoning. The other choices are incorrect because each of the bacteria listed is associated with food poisoning.

Correct Answer: A

Rationale: Rationale: 1. Thin, pale pink microorganisms with spiral coils suggest Treponema pallidum, the causative agent of syphilis. 2. Staining with Romanovsky-Giemsa method highlights the characteristic morphology of T. pallidum. 3. Syphilis presents with various stages and symptoms, correlating with the lymph node involvement. 4. Leptospirosis is caused by Leptospira interrogans, presenting with different clinical features. 5. Relapsing fever is caused by Borrelia species, which do not match the description. 6. Trypanosomiasis is caused by Trypanosoma species, which have distinct morphology and staining properties.

Correct Answer: C

Rationale: The correct answer is C: Binding of mast cell-fixed IgE. The Bezredka method involves introducing small amounts of the antigen to which the individual is allergic, leading to the binding of mast cell-fixed IgE. This process desensitizes the immune system and prevents anaphylactic shock by reducing the release of histamine and other mediators from mast cells. Rationale: 1. A: Stimulation of antigen-specific IgG2 is incorrect because the Bezredka method primarily targets IgE, not IgG2. 2. B: Stimulation of the immunological antigen tolerance is incorrect as this method aims to block the allergic response rather than induce tolerance. 3. D: Blocking of mast cell mediators synthesis is incorrect because the Bezredka method does not directly inhibit the synthesis of mast cell mediators, but rather blocks their release by binding IgE.