Researchers of a bacteriological laboratory examine tinned meat for botulinic toxin. For this purpose a group of mice was injected with an extract of the material under examination and antitoxic antibotulinic serum of A, B, E types. A control group of mice was injected with the same extract but without antibotulinic serum. What serological reaction was applied?

Correct Answer: A

Rationale: The correct answer is A: Neutralization. In this experiment, the researchers used antitoxic antibotulinic serum of different types to neutralize the botulinic toxin in tinned meat extract injected into mice. Neutralization is the process of rendering a toxin harmless by combining it with specific antibodies. The purpose of injecting the antitoxic serum was to neutralize the toxin and prevent it from causing harm to the mice. This serological reaction of neutralization directly aligns with the objective of the experiment. Summary of other choices: B: Precipitation - Precipitation involves the formation of a visible insoluble complex when an antigen reacts with its corresponding antibody. This process was not described in the scenario. C: Complement binding - Complement binding involves the activation of the complement system by antigen-antibody complexes. This was not the main focus of the experiment described. D: Double immune diffusion - This technique is used to detect the presence of specific antigens or antibodies

Correct Answer: D

Rationale: The correct answer is D: Salmonella typhi. Typhoid fever is caused by the bacterium Salmonella typhi. This bacterium is responsible for causing the systemic infection that leads to symptoms such as high fever, abdominal pain, and diarrhea. Yersinia pestis (choice A) causes plague, Shigella dysenteriae (choice B) causes dysentery, and Escherichia coli (choice C) can cause various gastrointestinal infections, but not typhoid fever. Salmonella typhi specifically targets the intestines and is transmitted through contaminated food or water. Therefore, choice D is the correct answer for the cause of typhoid fever.

Correct Answer: A

Rationale: Step-by-step rationale: 1. Clostridium botulinum is known for producing the neurotoxin causing botulism. 2. Botulinum toxin paralyzes muscles, leading to symptoms of botulism. 3. Clostridium tetani produces tetanus toxin causing muscle rigidity, not botulism. 4. Streptococcus pneumoniae causes pneumonia, not botulism. 5. Escherichia coli can cause food poisoning, but not botulism. Summary: Choice A is correct (Clostridium botulinum) due to its association with botulism and neurotoxin production. Choices B, C, and D are incorrect as they are associated with different diseases and toxins.

Correct Answer: A

Rationale: 1. Bordetella pertussis causes whooping cough. 2. It secretes toxins that damage the respiratory tract. 3. Symptoms include severe coughing fits and the characteristic "whoop" sound. 4. Clostridium tetani causes tetanus, not whooping cough. 5. Haemophilus influenzae causes various infections, not whooping cough. 6. Staphylococcus aureus causes skin infections, not whooping cough.

Correct Answer: C

Rationale: The correct answer is C: Lag phase. During the lag phase, bacteria adapt to the new environment before starting to grow and divide. This phase is characterized by a period of low growth as bacteria adjust their metabolism to the available nutrients. The stationary phase (A) is when growth rate equals death rate, the log phase (B) is rapid exponential growth, and the death phase (D) is when cells start to die due to nutrient depletion or accumulation of waste products. Thus, the lag phase is the initial phase where bacteria prepare for growth, making it the correct answer.

Correct Answer: D

Rationale: The correct answer is D: Cell cultures. Rotavirus diagnosis involves detecting viral antigens in stool samples using cell cultures. Cell cultures allow for the replication of the virus, facilitating its identification. A: Egg inoculation and B: Sensitive laboratory animals are not commonly used for Rotavirus diagnosis due to ethical concerns and practical limitations. C: Ascoli test is used for detecting specific proteins in serum, not for Rotavirus detection in stool samples. In summary, cell cultures are the most appropriate method for laboratory diagnosis of Rotavirus infection due to their ability to support viral replication and antigen detection.

Correct Answer: A

Rationale: Rationale for Correct Answer A (Lamblia): 1. Pyriform protozoa with twin nuclei, four pairs of flagella, and a suctorial disc match the characteristics of Giardia lamblia. 2. The presence of two supporting filaments between the nuclei is a unique feature of Giardia lamblia. 3. Giardia lamblia is known to infect the duodenum and cause symptoms such as diarrhea and abdominal pain. Summary of Incorrect Choices: B: Toxoplasma - Toxoplasma gondii is not characterized by four pairs of flagella or supporting filaments in the nuclei. C: Leishmania - Leishmania species do not typically have the described morphology or location in the duodenum. D: Intestinal trichomonad - Intestinal trichomonads do not exhibit the specific features mentioned in the question, such as twin nuclei and supporting filaments.

Correct Answer: B

Rationale: The correct answer is B, Helicobacter pylori. This bacterium is the main cause of peptic ulcers by damaging the protective lining of the stomach and duodenum. It secretes enzymes that weaken the mucosal barrier, allowing stomach acid to cause damage. Salmonella typhi (A) causes typhoid fever, not peptic ulcers. Shigella boydii (C) causes dysentery, not peptic ulcers. Salmonella enterica (D) causes food poisoning, not peptic ulcers. Therefore, the correct answer is B based on its direct association with peptic ulcer formation.

Correct Answer: D

Rationale: The correct answer is D: Blood. Normal flora refers to the microorganisms that naturally inhabit specific areas of the body. Blood is considered a sterile environment in healthy individuals, meaning it does not harbor any microorganisms under normal circumstances. In contrast, the intestine, skin, and vagina all have normal flora as they provide suitable environments for various microbial species to thrive. The presence of normal flora in these sites helps maintain a balance and protect against pathogenic invaders. Blood, being a vital and sterile fluid, is not meant to have any resident microbial populations.