Week 2: Infections & Microbiology

Learning Objectives

Students will be able to classify major groups of microorganisms and explain their structural differences
Students will be able to explain how the normal microbiota supports health and how endogenous infections arise
Students will be able to describe bacterial morphology, reproduction, and key virulence factors
Students will be able to explain viral structure, replication cycles, and mechanisms of host specificity
Students will be able to differentiate between fungal types and their clinical significance
Students will be able to identify different parasite types and their relationships with hosts
Students will be able to explain the chain of infection and apply infection control strategies to break transmission
Students will be able to define healthcare-associated infections and identify common hospital risk factors
Students will be able to distinguish endemic, epidemic, and pandemic disease patterns
Students will be able to describe the five stages of the infectious process from incubation to convalescence
Students will be able to explain antimicrobial stewardship and why careful antimicrobial use matters

Understanding Microorganisms and Infections

Microbiology studies microscopic organisms such as bacteria, fungi, protozoa, and helminths, as well as infectious acellular agents such as viruses. These tiny biological agents are found everywhere - in the environment, on our skin, and inside our bodies.

Many microbes are helpful. Your normal microbiota helps digest food, produces vitamins, trains the immune system, and makes it harder for harmful pathogens to become established. Problems occur when virulent microbes enter the body or when normal flora move to the wrong site or take advantage of weakened defenses.

Bacteria are simple single-celled organisms that come in three main shapes: spheres (cocci), rods (bacilli), and spirals (spirilla). They reproduce quickly by splitting in two (binary fission) and can form protective capsules or endospores. Viruses are much smaller acellular infectious agents that need host cells to reproduce. They consist of genetic material wrapped in a protein coat and can mutate to cross species barriers, like how SARS-CoV-2 spread from an animal source into humans.

Fungi include yeasts (single-celled) and molds (filamentous), living in moist, slightly acidic environments. Some cause infections, while others produce life-saving antibiotics like penicillin. Parasites live on or in host organisms, stealing nutrients and causing disease - either on the surface (ectoparasites like lice and ticks) or inside the body (endoparasites like worms and malaria-causing protozoa).

Infections spread through a chain involving the germ, a reservoir (where germs live), portals of exit and entry, and transmission methods. Breaking any link in this chain prevents infection. We control microbes through sterilization (killing all microbes), disinfection (killing most pathogens on objects), and antisepsis (reducing microbes on living tissue). Healthcare-associated infections, disease outbreaks, and antibiotic resistance all make infection control a major nursing responsibility.

Advanced: Microbiology and Infection Control

Microbiology encompasses the study of diverse microscopic organisms including bacteria (prokaryotes), fungi (eukaryotic heterotrophs), and parasites (protozoa and helminths), as well as viruses, which are acellular obligate intracellular parasites rather than living cells. Bacteria exhibit three primary morphologies: cocci (spherical), bacilli (rod-shaped), and spirilla/spirochetes (spiral). Key structural features include the cell wall (peptidoglycan in true bacteria), plasma membrane, capsule (glycocalyx), flagella (motility), pili (attachment), and endospores (dormant resistant forms). Binary fission enables exponential growth with generation times as short as 20 minutes under optimal conditions.

Human health depends heavily on the microbiome. Normal flora colonize the skin, gastrointestinal tract, upper airways, and other body sites, where they contribute to competitive exclusion, vitamin production, and immune maturation. Disease can result from exogenous pathogens or from endogenous flora entering normally sterile sites or proliferating when host immunity is impaired.

Viruses possess a simple acellular structure comprising a protein capsid enclosing genetic material (DNA or RNA), sometimes surrounded by a lipid envelope with glycoprotein peplomeres. Viral replication follows specific cycles: attachment, penetration, biosynthesis, maturation, and release. Viruses demonstrate host specificity determined by receptor compatibility but can undergo antigenic drift or shift, enabling cross-species transmission (zoonosis).

Fungi exist as unicellular yeasts (reproducing via budding) or multicellular molds with hyphae and mycelia; clinically significant species include Candida, Aspergillus, and Cryptococcus, causing superficial to systemic infections. Parasitology addresses protozoa (unicellular eukaryotes like Plasmodium causing malaria) and helminths (multicellular worms including nematodes, cestodes, and trematodes).

The chain of infection model identifies six links: infectious agent (pathogen), reservoir (host or environment), portal of exit, mode of transmission (contact, droplet, airborne, vector-borne), portal of entry, and susceptible host. Infection control employs sterilization (destruction of all microbial life via autoclaving, dry heat, or gas sterilization), disinfection (chemical reduction of vegetative pathogens on inanimate objects), and antisepsis (chemical reduction of microbes on living tissue). In healthcare settings this extends to HAI prevention, isolation practice, and antimicrobial stewardship to slow the emergence of resistance.

🦠 Infection Patterns & Prevention

How Infections Are Classified

Infections can be described in several practical ways. Endogenous infections come from microbes already living in or on the patient, while exogenous infections come from outside sources such as other people, equipment, food, or the environment.

A primary infection is the first infection causing illness. A secondary infection appears during or after the first one, often because normal defenses are weakened.

Localized infections stay in one area, such as an infected wound. Systemic infections spread through the body, producing wider effects such as fever, hypotension, or sepsis.

Nurses break the chain of infection by using hand hygiene, aseptic technique, cleaning shared equipment, using PPE and isolation when needed, caring for wounds and lines correctly, and reducing host risk through vaccination, nutrition, and timely treatment.

🧫 Microbiome & Normal Flora

Helpful Microbes and When They Cause Trouble

Your body is not sterile. Normal flora live on the skin, in the mouth, in the gut, and at other body sites. These microbes usually help rather than harm by making vitamins, helping digestion, occupying space that pathogens could use, and supporting immune development.

An infection can still come from your own flora. This is called an endogenous infection. It happens when microbes enter the wrong place, such as gut bacteria reaching the urinary tract or bloodstream, or when immunity is weakened and organisms like Candida overgrow.

This is why nurses pay attention to skin integrity, catheter care, wound care, nutrition, antibiotic use, and immune status. Preventing infection is not only about avoiding outside germs; it is also about preventing normal flora from becoming opportunistic pathogens.

🏥 Healthcare-Associated Infections

Hospital Care Can Reduce Infection Risk, but It Can Also Create Risk

A healthcare-associated infection (HAI), also called a nosocomial infection, is an infection linked to healthcare rather than being present before admission. Common examples include catheter-associated urinary tract infection, surgical site infection, pneumonia, and bloodstream infection from invasive lines.

Week 2 source material emphasizes that HAIs are a major burden in Australian healthcare, with about 200,000 infections each year, around 7,000 deaths, and roughly 2 million hospital bed days affected.

Risk rises with surgery, indwelling devices, poor hand hygiene, immunosuppression, antibiotic pressure, crowding, and breaks in aseptic technique. Prevention focuses on hand hygiene, line and wound care, PPE, cleaning, early device removal, and using antimicrobials carefully.

🌍 Disease Patterns & Infection Stages

How Disease Appears in Populations and in Individual Patients

Endemic means a disease is regularly present at a baseline level in a region. Epidemic means cases rise above what is expected in one place. Pandemic means an epidemic spreads across many countries or continents.

Individual infections also follow stages. The incubation period is the time between infection and symptoms. The prodromal period brings vague early symptoms such as tiredness or malaise. The acute period is when the illness is most obvious. The decline phase follows as symptoms improve, and convalescence is the recovery period.

Patients may still spread infection before, during, or after obvious illness, depending on the pathogen. That is why timing, isolation, and careful clinical observation matter.

💊 Antimicrobial Stewardship

Using Antimicrobials Carefully

Antimicrobials are drugs or substances used against bacteria, viruses, fungi, or parasites. Antibiotics only work against bacteria, so they do not treat viral infections like influenza or COVID-19.

Antimicrobial stewardship means choosing the right drug, at the right dose, for the right time, only when it is actually needed. Overuse and misuse create selection pressure that helps resistant microbes survive.

Good stewardship works together with infection prevention. Fewer preventable infections means less antibiotic use, less disruption of normal flora, and less opportunity for resistant organisms such as MRSA or other multidrug-resistant pathogens to spread.

🎥 Video Lectures

Infections Overview

Introduction to infections and microbiology fundamentals

Topic Title

Select a topic from the list to view detailed information.

📄 Lecture Notes

Key Terms

Microorganism

Microscopic organisms and infectious agents relevant to health, including bacteria, fungi, protozoa, helminths, and viruses

Prokaryote

Unicellular organism lacking membrane-bound nucleus and organelles; includes bacteria and archaea

Binary Fission

Asexual reproduction in bacteria where one cell divides into two identical daughter cells

Cocci

Spherical-shaped bacterial cells; may occur singly, in pairs (diplococci), chains (streptococci), or clusters (staphylococci)

Bacilli

Rod-shaped bacterial cells; may be single, in pairs, or in chains

Endospore

Dormant, highly resistant structure formed by some bacteria for survival in harsh conditions

Capsule

Glycocalyx layer surrounding some bacteria providing protection and aiding in virulence

Virus

Acellular infectious agent consisting of genetic material (DNA or RNA) within a protein capsid; requires host cell for replication

Capsid

Protein shell enclosing viral genetic material; provides protection and host cell recognition

Envelope

Lipid bilayer surrounding some viruses, derived from host cell membrane, containing viral glycoproteins

Peplomere

Spike-like glycoprotein projections on viral envelope that facilitate attachment to host cells

Fungi

Eukaryotic heterotrophic organisms including yeasts (unicellular) and molds/filamentous fungi (multicellular)

Mycelium

Network of branching hyphae forming the vegetative structure of filamentous fungi

Budding

Asexual reproduction in yeast where a small outgrowth forms and separates from parent cell

Ectoparasite

Parasite living on the external surface of host (e.g., lice, ticks, mites)

Endoparasite

Parasite living within the host body (e.g., helminths, Plasmodium, amoeba)

Helminths

Parasitic worms including flukes (trematodes), tapeworms (cestodes), and roundworms (nematodes)

Chain of Infection

Sequential model of infection transmission: agent, reservoir, portal of exit, transmission, portal of entry, susceptible host

Sterilization

Process destroying all microbial life including bacterial endospores using heat, pressure, or chemicals

Antimicrobial Resistance

Ability of microorganisms to survive exposure to antimicrobial agents through genetic adaptation and horizontal gene transfer

Normal Microbiota

Microbes that usually live on or in the body without causing disease and often support digestion, vitamin production, and defense against pathogens

Endogenous Infection

Infection arising from a patient's own flora when microbes move to the wrong site or host defenses are weakened

Nosocomial Infection

Healthcare-associated infection acquired in connection with hospital or clinical care, often linked to devices, procedures, or transmission failures

Endemic

Disease consistently present at an expected baseline level in a specific population or region

Epidemic

Increase in disease cases above expected levels in a defined place and time

Pandemic

Epidemic that spreads across multiple countries or continents

Incubation Period

Time between infection and the appearance of symptoms

Prodromal Period

Early phase of illness with vague, nonspecific symptoms before the full disease pattern is obvious

Convalescence

Recovery period after acute illness when the patient gradually returns toward baseline health

Antimicrobial Stewardship

Careful, evidence-based use of antimicrobials to improve treatment while reducing resistance and avoidable harm

Interactive Activity

End of Week Test

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Clinical Case Study

Apply your knowledge of Infections & Microbiology to a clinical scenario.

Open Case: The Post-Op Infection →