Indicate the true statements and then correct the false statements so that they are true.
a. HIV is transmitted by a parenteral route.
b. Candida albicans is an opportunistic pathogen that can cause disease in an immune-competent host if the normal microbiota are disrupted.
c. Gram-positive bacteria may produce endotoxin.
d. Siderophores help pathogens obtain calcium.
e. Emerging pathogens tend to exhibit expanded tropism.
f. The more toxic a substance is, the higher its LD₅₀.
g. Virulence is the ability of a microbe to cause disease.
h. Gram-negative bacteria may produce exotoxins.

Verified step by step guidance

1. Step 1: Evaluate statement (a): 'HIV is transmitted by a parenteral route.' Understand that parenteral transmission refers to entry through breaks in the skin or mucous membranes, such as via needles or blood transfusion. Since HIV can be transmitted through blood and other body fluids entering the bloodstream, this statement is true.
2. Step 2: Evaluate statement (b): 'Candida albicans is an opportunistic pathogen that can cause disease in an immune-competent host if the normal microbiota are disrupted.' Recognize that Candida albicans normally exists as part of the microbiota and can cause infection when the balance is disturbed, even in immune-competent individuals. This statement is true.
3. Step 3: Evaluate statement (c): 'Gram-positive bacteria may produce endotoxin.' Recall that endotoxins are lipopolysaccharides (LPS) found in the outer membrane of Gram-negative bacteria, not Gram-positive bacteria. Therefore, this statement is false. Correct it to: 'Gram-positive bacteria do not produce endotoxin; endotoxins are produced only by Gram-negative bacteria.'
4. Step 4: Evaluate statement (d): 'Siderophores help pathogens obtain calcium.' Understand that siderophores are molecules secreted by bacteria to scavenge iron, an essential nutrient, from the host environment. They do not bind calcium. This statement is false. Correct it to: 'Siderophores help pathogens obtain iron.'
5. Step 5: Evaluate statement (e): 'Emerging pathogens tend to exhibit expanded tropism.' Tropism refers to the specificity of a pathogen for a particular host tissue or cell type. Emerging pathogens often have expanded tropism, allowing them to infect new hosts or tissues. This statement is true.

Key Concepts

Routes of Transmission in Infectious Diseases

Transmission routes describe how pathogens spread between hosts. The parenteral route involves direct entry into the body through breaks in the skin or mucous membranes, such as via needles or blood transfusions. HIV is primarily transmitted parenterally, sexually, or vertically, highlighting the importance of understanding these pathways for infection control.

Microbial Toxins: Endotoxins vs. Exotoxins

Endotoxins are lipopolysaccharides found in the outer membrane of Gram-negative bacteria and trigger strong immune responses. Exotoxins are proteins secreted by both Gram-positive and Gram-negative bacteria that target specific host cells. Gram-positive bacteria do not produce endotoxins but can produce potent exotoxins.

Virulence Factors and Pathogen Adaptations

Virulence refers to a microbe's ability to cause disease, influenced by factors like toxin production, adhesion, and immune evasion. Siderophores are molecules secreted by pathogens to scavenge iron, not calcium, which is vital for their growth. Emerging pathogens often show expanded tropism, meaning they can infect new host types or tissues.