Infectious Diseases and Microbial Agents Adapted from http://cte.unt.edu/health/pathophysiology/

An infection is an organism’s response to disease-causing microorganisms. It forms when pathogens enter and multiply in the body

Objectives • Identify and describe the main ways that infectious disease spreads • Identify the main human bodily defenses against infectious pathogens and explain how they work • Describe the different microorganisms that cause infectious disease • Identify the main classes of pathogenic organisms and the common diseases associated with each pathogen

We Are Not Alone We are outnumbered On the average human, there are about 100 trillion microscopic beings As long as they stay in balance and where they belong, they do us no harm Many of them provide important services for human survival Many, however, are opportunists, who if given the opportunity of increasing growth or invading new territory, will cause infection

Facts Microorganisms cannot be seen without a microscope, with the exception of some intestinal parasites Some of these organisms cause infection and illness Others are “good” organisms that help keep a balance in the environment and in the body

Good vs Bad Microbes Microbes that cause disease (germs) are referred to as pathogens Microbes that are beneficial or harmless are called nonpathogens Only a small percentage of microbes are pathogenic. Most are beneficial or harmless Some cause disease only if they accidentally invade the “wrong place” at the “right time.” These organisms are referred to as opportunistic pathogens

87% – Beneficial Microbes 10% – Opportunists 03% – Potential Pathogens

Opportunistic Pathogens Opportunistic infections When is the “right time” for an opportunistic pathogenic invasion? 1. When the host’s resistance is low 2. When otherwise harmless microbes gain entry to an organ system where they can multiply and do harm

Opportunistic Pathogens Usually opportunistic pathogens live on and in the healthy human body (on skin, in mouth, in intestines) Since many of these microbes are potentially pathogenic, they can cause disease if they gain entrance to the bloodstream or internal organs, such as the bladder

What are ideal growth conditions for microorganisms? A. Most microorganisms that cause illness prefer warm temperatures (98.6° F) B. Most organisms prefer a dark area to grow and reproduce (many are killed quickly by sunlight) C. All need food to survive—some live on dead matter or tissues, and others use living matter (parasites) D. All organisms need moisture Note: the human body is the ideal supplier of all requirements of microorganisms

Main classes of pathogenic microbes Bacteria Protozoa and helminths Fungi Viruses

Bacteria Single-celled Prokaryotic

Pathogenic Bacteria Pathogenic bacteria carry cell-damaging proteins that come in 2 types: Endotoxins: released when bacterial cell wall decomposes (cause fever and are not affected by antibiotics) Exotoxins: released during cell growth

Classified by shape and arrangement Cocci (spherical) Bacilli (rod-shaped) Spirilla (spirals or corkscrew)

Pairs: Diplococci (Example Streptococcus pneumoniae) Gram positive

Pairs: Diplococci (Example Neisseria gonorrhoeae) Gram negative Coffee bean -shaped

Pairs: Diplococci (Example Neisseria meningitidis) Very similar to Neisseria gonorrhoeae in appearance Can cause meningitis

Cocci in chains: Example Streptococcus pyogenes Causing strep throat and rheumatic fever

Cocci in clusters: Example: Staphylococcus aureus Pus producing; cause infections like boils, wound infections and toxic shock

Bacilli Can occur in pairs or chains Many contain flagella for movement

Proteus mirabilis

Proteus mirabilis on agar

Bacilli Some produce spores (thick-walled capsules ) that allow them to survive when growth conditions are unfavorable In spore from bacteria are very difficult to kill Examples: Bacillus anthracis, Clostridium tetani, etc

Bacillus anthracis

Clostridium tetani

Tetanus

Mycobacterium tuberculosis (Acid fast stain)

Corynebacteria diphtheriae Notice chinese lettering and size

Spirilla Spiral or corkscrew shaped Examples: Treponema pallidum: causative agent for syphilis

Vibrio cholera

Lyme Disease Caused by Borrelia burgdorfii

Unusual types of bacteria Chlamydia and rickettsia i.They are smaller than conventional bacterial but larger than viruses ii.Chlamydia causes a variety of infections including conjunctivitis, chlamydial urethritis and cervicitis iii.Rickettsia causes forms of typhus including Rocky Mountain spotted fever iv.Spread through vectors such as mites, ticks,orlice

Chlamydia

Rickettsiae

Protozoa single-celled, animal-like Found in aquatic habitats Obtain food by ingesting bacteria, waste products of other organisms, algae, other protozoa Usually motile by flagella, cilia or amoeboid movement Some are pathogenic Cause diseases such as malaria, ameobic dysentery, trichomonas, African Sleeping Sickness, leishmaniasis, toxoplasmosis

Malaria (Plasmodium species)

Amoebic Dysentery (Entamoeba histolytica)

Entamoeba histolytica trophozoite

Trichomonas

Giardiasis

African Sleeping Sickness (Trypanosomiasis)