MicroBiology Fall 2025

What’s the first stage of a Fever?

Ascent Phase (Chills/Onset):

Description: The body's temperature set point in the hypothalamus is raised by pyrogens (fever-inducing substances, like bacterial endotoxins or cytokines). The body initially perceives itself as being too cold at the old set point, leading to heat generation and conservation.

Physiological Changes: Shivering/rigors (increased heat production by muscle contractions) and peripheral vasoconstriction (reduced heat loss through the skin, causing a feeling of coldness and pale skin).

What’s the second stage of a Fever?

Peak Phase (Stadium/Plateau):

Description: The body's core temperature has risen and stabilized at the new, higher set point.

Physiological Changes: Heat production and heat dissipation are in balance. The person feels hot, and shivering stops. This is the period of maximum fever benefit for the immune system.

What’s the third stage of a Fever?

Decrease Phase (Defervescence):

Description: The pyrogen concentration decreases, or the hypothalamic set point is lowered (e.g., due to fever-reducing medication or the pathogen being cleared).

Physiological Changes: The body now perceives itself as too hot at the new, lower set point, triggering heat-loss mechanisms: Vasodilation (flushed, warm skin) and increased sweating (evaporative cooling).

What’s the fourth stage of a Fever?

Normalization (Resolution):

Description: The body temperature returns to the normal range, and the thermoregulatory center establishes the pre-fever set point.

Physiological Changes: Heat-loss and heat-production mechanisms return to normal balance.

Which of the following is a difference between and Endotoxin and Exotoxin?

The source of Endotoxin is produced only by Gram-Negative Bacteria.

The source of Exotoxin is produced by both Gram-Positive and Gram-Negative Bacteria.

1) Which of the following is a difference between and Endotoxin and Exotoxin?

The composition of endotoxin is Lipopolysaccharide (LPS), specifically the Lipid A portion.

The composition of exotoxin is a secreted Protein (Polypeptide).

2) Which of the following is a difference between and Endotoxin and Exotoxin?

The location of the endotoxin is an integral part of the bacterial outer membrane, and it is released upon cell lysis.

The location of the exotoxin is that it is actively secreted/excreted by the living cell and found freely in the surrounding environment.

3) Which of the following is a difference between and Endotoxin and Exotoxin?

The toxicity of endotoxin is low; large doses are typically required to cause fatal effects.

The toxicity of exotoxin is high; it is often fatal even in minute quantities (micrograms).

4) Which of the following is a difference between and Endotoxin and Exotoxin?

The heat stability of exotoxin is labile (heat-sensitive) and is often inactivated by temperatures around 60 degrees Celsius.

The heat stability of endotoxin is stable (heat-resistant), and it can often tolerate 100 degrees Celsius for an hour.

5) Which of the following is a difference between and Endotoxin and Exotoxin?

For Endotoxins, Toxoid formation cannot be easily converted into a toxoid for vaccination.

For Exotoxins, Toxoid formation can be converted into a toxoid, which is used to make vaccines, such as those for Tetanus and Diphtheria.

6) Which of the following is a difference between and Endotoxin and Exotoxin?

The endotoxin mechanism causes general, systemic effects like fever, inflammation, and septic shock, as it is a powerful pyrogen.

The exotoxin mechanism acts with high specificity, often with enzymatic action (e.g., neurotoxins, enterotoxins), and is typically non-pyrogenic.

What’s the first step of Cholera Toxin Action?

The B-subunit (pentamer) of the toxin binds to the GM1 ganglioside receptor on the surface of intestinal epithelial cells (enterocytes).

What’s the second step of Cholera Toxin Action?

The entire toxin complex is taken into the host cell via endocytosis.

What’s the third step of Cholera Toxin Action?

The toxin travels backward through the Golgi network to the Endoplasmic Reticulum (ER) via retrograde transport

What’s the fourth step of Cholera Toxin Action?

The active A1 chain is cleaved and released into the host cell's cytosol.

What’s the fifth step of Cholera Toxin Action?

The A1 chain acts as an enzyme, catalyzing the ADP-ribosylation of the regulatory Gs protein, which locks the Gs protein in a permanently active state.

What’s the sixth step of Cholera Toxin Action?

The continuous activation of adenylate cyclase leads to a massive, persistent increase in cyclic AMP (cAMP), which triggers the active secretion of large amounts of chloride (Cl-) and water into the intestinal lumen, causing severe watery diarrhea.

What’s the first stage of a disease?

The Incubation Period is the time between the initial infection (pathogen entry) and the appearance of the first signs or symptoms. During the incubation period, the pathogen is multiplying, and the host is often unaware but potentially contagious.

What’s the second stage of a disease?

The Prodromal Period is a short period characterized by early, general, and non-specific symptoms (e.g., mild malaise, aches)

What’s the third stage of a disease?

The Period of Illness is the stage where the disease is most severe and exhibits the characteristic signs and symptoms, as the pathogen load is at its peak.

What’s the fourth stage of a disease?

The Period of Decline occurs when the signs and symptoms begin to subside (decline) as the host's immune response or medical treatment reduces the pathogen load. During the decline, the host is vulnerable to secondary infections.

What’s the fifth stage of a disease?

The Period of Convalescence is the stage where the host recovers and returns to a pre-disease state of health. Tissues are repaired in the convalescence stage, and the host may still be shedding the pathogen.

Define Antisepsis:

The process of removing or reducing pathogenic microorganisms on living tissue (e.g., skin) using a chemical (antiseptic) to prevent infection.

Define Aseptic:

The condition of being free of contamination by pathogenic microorganisms.

Define Degerming:

It is the mechanical removal of microbes from a limited area, usually skin, which is primarily achieved through scrubbing and the use of soap and water.

Define Sterilization:

It is the complete removal or destruction of all forms of microbial life, including highly resistant bacterial endospores, from an object or surface.

Define Pasteurization:

Is a heating process applied to liquids (e.g., milk) for a short time at a specific temperature to destroy most vegetative pathogens and spoilage organisms, but it is not complete sterilization.

Define Sanitization:

Sanitization is the process of reducing the number of microorganisms on inanimate objects to safe public health levels (a level deemed acceptable by health standards).

Define Stasis/Static

indicates that microbial growth or multiplication is being inhibited or stopped (e.g., bacteriostatic).

Define Cide/Cidal

Indicates that the organism is being killed (e.g., germicidal).