Skin Infections Quiz

Staphylococcus aureus is the most common cause of skin infections. This bacterium is commonly found on the skin and can cause a range of infections, including boils, cellulitis, and impetigo. It is highly contagious and can easily spread through direct contact or contaminated objects. Staphylococcus aureus can also be resistant to antibiotics, leading to more severe infections that are difficult to treat. Therefore, it is important to practice good hygiene and take precautions to prevent the spread of this bacterium.

Vesicular skin lesions are characterized by the presence of small, fluid-filled blisters on the skin. These lesions are commonly caused by viral infections such as herpes simplex virus or varicella-zoster virus. The fluid within the blisters contains the virus, which can be easily transmitted to others through direct contact. Therefore, vesicular skin lesions are indeed sites of viral replication and are infectious.

Cellulitis is an acute spreading infection of the skin that affects the subcutaneous fat tissue. It is characterized by redness, warmth, swelling, and pain in the affected area. Unlike folliculitis, which is an infection of the hair follicles, cellulitis involves a deeper layer of the skin. Erysipelas is a type of cellulitis that affects the upper layers of the skin, while gangrene refers to tissue death caused by a lack of blood supply. Therefore, the correct answer is cellulitis.

Reactivation of VZV (Varicella-Zoster Virus) in sensory neurons is characterized by the clinical symptom of paresthesia and pain. Paresthesia refers to abnormal sensations like tingling, numbness, or burning, while pain can range from mild to severe. This symptom is commonly associated with herpes zoster, also known as shingles, which occurs when the VZV virus reactivates in individuals who have previously had chickenpox. The reactivation typically leads to a painful rash along with the paresthesia, making it a key clinical symptom of VZV reactivation.

Vancomycin is the correct answer because it is a powerful antibiotic that is effective against MRSA (methicillin-resistant Staphylococcus aureus). MRSA is a type of bacteria that is resistant to many commonly used antibiotics, including penicillin and methicillin. Vancomycin is often considered the drug of choice for treating MRSA infections due to its effectiveness in killing the bacteria. Cephalosporin is not typically used to treat MRSA infections, making it an incorrect choice.

Erysipelas presents as a well-defined, spreading erythematous rash that involves the blocking of dermal lymphatics. It is a bacterial skin infection caused by Streptococcus pyogenes. The infection usually starts with a small skin break or wound and spreads rapidly, causing redness, swelling, and pain. Erysipelas can occur on any part of the body, but commonly affects the face and legs. Prompt treatment with antibiotics is necessary to prevent complications.

Strep. pyogenes secrete toxic products, such as pyrogenic endotoxins (SPEA, B, C), which act on skin blood vessels to cause the diffuse erythematous rash seen in scarlet fever. This condition is characterized by a red rash that typically starts on the neck and chest and spreads to the rest of the body. It is caused by the Streptococcus pyogenes bacteria and is often accompanied by symptoms such as fever, sore throat, and swollen glands. Scarlet fever is most commonly seen in children and can be treated with antibiotics.

Erysipelas is a bacterial skin infection caused by Streptococcus pyogenes. It primarily affects the dermal lymphatics and presents with a distinctive "butterfly-wing" rash. This infection is characterized by red, raised, and well-defined borders, often accompanied by pain and swelling. Folliculitis is an infection of the hair follicles, impetigo is a superficial skin infection, and cellulitis is a deeper infection of the skin and underlying tissues. Therefore, the correct answer is erysipelas.

Gram-negative bacteria produce the enzyme beta-lactamase which acts by hydrolyzing lactam rings. Lactam rings are an essential part of the structure of penicillin antibiotics. By breaking these rings, beta-lactamase inactivates penicillin and renders it ineffective. This mechanism is a defense mechanism employed by gram-negative bacteria to resist the action of penicillin and other beta-lactam antibiotics.

The thoracic dermatomes are the most commonly affected sites for varicella lesions. This is because varicella, also known as chickenpox, is caused by the varicella-zoster virus, which tends to affect the trunk and back more than other areas of the body. The thoracic dermatomes cover the chest and upper back, making them the most likely areas to be affected by the viral infection.

Varicella, also known as chickenpox, is typically more severe in adults rather than children. Adults tend to experience more severe symptoms and are at a higher risk of developing complications from the infection. On the other hand, children usually have milder symptoms and are less likely to experience complications. Therefore, the statement that varicella is less severe in adults and more likely to cause complications in children is false.

VZV (varicella-zoster virus) is known to have only one serologic type. This means that there is only one specific antibody response to VZV, indicating that individuals who have been infected with VZV will have the same serologic type. In contrast, other viruses like HSV (herpes simplex virus), HPV (human papillomavirus), and hepatitis have multiple serologic types, indicating that individuals can be infected with different strains or subtypes of these viruses.

ELISA (Enzyme-Linked Immunosorbent Assay) is a laboratory technique used to detect antibodies in the blood. In the context of VZV (Varicella-Zoster Virus) infection, detecting VZV IgG (Immunoglobulin G) using ELISA can determine past infection. IgG antibodies are produced by the immune system in response to an infection, and their presence indicates previous exposure to the virus. ELISA involves binding VZV-specific antigens to a solid surface, then adding the patient's serum. If VZV-specific IgG antibodies are present, they will bind to the antigens, and the reaction can be detected using an enzyme-linked detection system. Therefore, ELISA is the appropriate laboratory technique to detect VZV IgG and determine past infection.

Ritter's disease is another name for Staphylococcal scalded syndrome. This condition is characterized by widespread blistering and peeling of the skin, caused by a toxin produced by certain strains of Staphylococcus aureus bacteria. The name "Ritter's disease" is derived from the dermatologist Alfred Ritter, who first described the syndrome in the early 20th century. Gangrene is a separate condition involving tissue death, Elsberg syndrome is a neurological disorder, and TSS (Toxic Shock Syndrome) is a different bacterial infection with distinct symptoms.

Fibrin deposits are the histological finding in folliculitis responsible for enclosing the site of infection, only allowing for the local spread of infection. Fibrin is a protein involved in blood clotting, and its presence indicates inflammation and tissue damage. In the case of folliculitis, fibrin deposits act as a barrier, preventing the infection from spreading beyond the affected hair follicle. This containment mechanism helps to limit the infection to a localized area and prevent it from spreading to surrounding tissues.

Synergistic bacterial gangrene is typically caused by microaerophilic streptococci and Staphylococcus aureus. Microaerophilic bacteria are organisms that require low levels of oxygen to survive and grow. In the case of synergistic bacterial gangrene, these bacteria thrive in an environment with reduced oxygen levels, such as deep tissue wounds. The combination of microaerophilic streptococci and Staphylococcus aureus can lead to a severe and rapidly progressing infection, causing tissue death and gangrene.