Microbiology Chapter on Immunity and Resistance

DPAS 5200A25 Day 3: Introduction to Bacteria and Viruses

• The class covered infectious agents and their basic introduction.
• Introductory material included an inspirational presentation for the study of infectious agents to spark interest.
• Today's focus was on bacteria and virus physiology, covering objectives for the two-day session.

Objectives for Day 2: Bacteria/Virus Physiology

• Describe the structures of bacteria and viruses.
• Translate bacteriological nomenclature.
• Classify bacteria into their subgroups.
• Understand the role of normal flora in preventing infection.
• Explain the terms and concepts of specific, nonspecific immunity, host immunity, virulence, and mutability in the context of pathogenicity.
• Understand the lytic and lysogenic cycles of viral replication.
• Explain how bacteria and viruses cause infection.

Bacterial Life Cycle

• Bacteria are prokaryotes without membrane-bound organelles such as the nucleus, ER, or Golgi.
• The bacterial life-cycle is simple, characterized by growth-DNA replication-division-and repetition.

Bacterial Reproduction

• Many bacteria replicate every 20 minutes exponentially.
• A single bacterium could theoretically cover the globe in 24 hrs if conditions permit.
• However, bacterial reproduction is limited by resource availability, environmental conditions, predators, and defense mechanisms (the immune systems).

Bacterial Classification

• Bacteria are grouped by criteria like shape and arrangement, gram stain reaction (gram-positive and gram-negative), and biochemical characteristics (aerobic and anaerobic species). There's also spore formation profile, and antigenic structure analysis like in cell bodies, capsule, and flagella.

Classification of Bacteria: Human Correlations

• Bacteria are grouped according to their likeness to humans, such as skin color differentiation or hair color/amount, language background, diet preferences (omnivore, vegetarian, vegan), tolerance to heat, and burn-related tolerance versus tanning-related tolerance.
• This is different from the more scientific classification methods mentioned previously.

Bacterial Growth Preferences

• Bacteria have varying preferences for growth media and environmental conditions, classifying as fastidious or hardy organisms based on their preference.
• Fastidious bacteria require enriched media with specialized conditions like precise temperature, and acidity to thrive.
• Hardy bacteria are resilient and thrive in a wide range of environmental conditions.
• Other key criteria for their classifications are oxygen requirements, in which there are aerobic, anaerobic and facultative anaerobic species.

Structural Features of Bacteria

• Flagella (hair-like processes) aid in bacterial motility.
• Spore formation (dormant, resilient structures) allows bacteria to survive under harsh conditions until favorable conditions return.
• Recognition of the formation of spores or flagella may give insight into identification.

Antigenic Structure

• Antigens are unique components of an invading organism that stimulate antibody production in mammals.
• These antigens are usually parts of the bacterial cell body, capsule, wall, or flagellum, triggering an immune response as 'not-you'.
• A biochemical difference between the organism and its host will make specific parts of the organism antigens.

Symbiotic Relationships Between Humans and Bacteria

• Symbiotic interactions can be categorized as mutualism (benefits both), commensalism (benefits one, no harm to the other), or opportunistic (harmless then harmful).
• Symbiotic relationships with humans, where bacteria benefit the human and/or cause no harm, can even benefit.

Normal Flora

• Normal flora are microorganisms that colonize the human body (such as the GI tract) without causing harm; rather, they aid in immune system development.
• Flora establishment in humans begins shortly post-birth.
• Normal flora perform metabolic functions and contribute to immunity.

Normal Flora and maintaining "Peri-human" health

• Normal flora create a protective layer (glycoprotein and polysaccharide molecules, the mucosal layer).
• This layer stops pathogens from entering the body.
• The presence of normal flora needs to be maintained to protect the body.

Maintaining Healthy Normal Flora

• Ensuring a healthy normal flora population is crucial for preventing bacterial overgrowth.
• Treatments for diseases like C. difficile can be illustrated using three different treatments for C diff.

Normal vs. Overpopulation

• "Normal" also encompasses the absence of overpopulation of specific bacteria.
• This applies to various areas of the body, such as the vaginal area.
• Overpopulation of normal bacterial types can be problematic.
• Example: Normal vaginal flora vs bacterial vaginosis.

Bacterial Vaginosis

• Lactobacilli produce acid that maintain a vaginal pH of 3.8-4.2.
• Decrease in lactobacilli population can shift vaginal pH to over 4.5.
• This shift can lead to overgrowth of harmful bacteria, yeast overgrowth, or environmental factors leading to more pathogenic overgrowths.

Obligate Pathogens

• Obligate pathogens are always harmful and never normal findings in a healthy person.
• Examples mentioned include Lyme disease, Toxic Shock, Food Poisoning, and Cholera.

Human Immunity

• Human immunity includes both nonspecific and specific (acquired) components.
• Nonspecific immunity involves innate defenses like skin, pH levels in organs, and compartmentalization, as well as inflammation and normal flora.
• Specific immunity involves specialized responses targeted toward particular pathogens (details in Pathophysiology).

Acquired immunity

• Passive immunity involves antibodies that are obtained from an exterior source like another organism (not produced by your body).
• This immunity is temporary and not long-term because antibodies have a limited life span.
• Active immunity occurs when the body creates its own antibodies in response to a vaccine or an encountered pathogen.

Antibiotics

• Antibiotics come from living organisms and/or lab-synthesized formulas, with resistance issues stemming from over-prescribing, inappropriate use, overuse in livestock feed, and widespread resistance propagation.
• Antibiotics work by inhibiting bacterial cell wall and membrane synthesis; inhibiting bacterial protein synthesis; inhibiting bacterial reproduction, and turning off bacterial enzymes.

Antibiotic Resistance mechanisms

• Resistant strains develop through spontaneous mutation, plasmid transfer (conjugation and transformation), and the development of enzymes (like penicillinase) that degrade antibiotics.
• Testing for antibiotic sensitivity to diagnose bacterial infections can be done using procedures like tube dilution (measuring highest inhibition) or disk diffusion (seeing the inhibition zone around placed antibiotic disks on a microbial lawn).

Plasmids and Resistance

• Plasmids are small, circular DNA molecules separate from the bacterial chromosome.
• Some plasmids carry genes (like the F-factor) facilitating conjugation (transferring genes between bacteria).
• Others (R-factors) can code for antibiotic resistance genes, also transferred via conjugation or transformation.

Bacterial Conjugation

• A process where bacteria can exchange genetic material (including plasmids, possibly containing antibiotic resistance genes).

Bacterial Transformation

• Bacteria may absorb stray DNA from their environment and integrate it into their own genetic material using endocytosis.

Viral Life Cycles

• Viruses can have lytic or lysogenic cycles.
• Viral replication depends on host cells for machinery and components.

Lytic Viral Replication

1. Attachment
2. Entry
3. Replication
4. Assembly
5. Release

Lysogenic Viral Replication

1. Attachment
2. Entry
3. Integration
4. Cell Division/Reproduction
5. Induction
6. Replication
7. Assembly
8. Release

Lytic versus Lysogenic Viral Systems Summary

• Lytic viral replication involves the release of many viral particles, destroying the host cell in the process.
• Lysogenic viral replication involves the integration of viral genetic material into the host cell genome with the viral genetic material being reproduced during the host cell's reproduction (e.g., prophage or provirus).

RNA Viruses

• RNA viruses lack a "proofreader" during replication; hence, mistakes during RNA synthesis (leading to mutations) are often left uncorrected.
• These RNA viruses often mutate rapidly and therefore evolve easily to be more pathogenic (cause more disease).
• RNA viruses, like HIV, have a specific mechanism of DNA synthesis through reverse transcriptase and may have both lytic and lysogenic life cycles.

COVID-19

• A single-stranded RNA virus that has a high mutation rate is often linked to the spike protein.

HIV: A Retrovirus

• HIV is a Retrovirus, a virus with an RNA genome that uses reverse transcriptase to synthesize DNA from its RNA genome.
• It has a lysogenic cycle. The acute phase and chronic phase of infection are characterized by different stages of viral reproduction and CD4 cell counts.

Helper T Cells

• Helper T cells are critical for coordinating the immune response.
• They activate cytotoxic T cells, B cells, and other immune cells.
• Without Helper T cells, the immune response is severely compromised.

HIV as an Emerging Virus

• HIV, like other emerging viruses, is linked to mutations, contact between species, spread from isolated populations, and spread to overcrowding areas with poor sanitation (which increases exposure and decreases the immune system's ability to defend).

Additional Viruses

• Rhinovirus, Mumps, Influenza, Measles, and Chicken Pox were mentioned as additional viruses.