1. Infectious Diseases and Microbial Agents
Adapted from

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

3. 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

4. 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

5. 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

6. 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

7. 87% – Beneficial Microbes
10% – Opportunists
03% – Potential Pathogens

8. 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

9. 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

10. 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

11. Main classes of pathogenic microbes
Bacteria
Protozoa and helminths
Fungi
Viruses

12. Bacteria
Single-celled
Prokaryotic

13. 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

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

15. Pairs: Diplococci (Example Streptococcus pneumoniae)
Gram
positive

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

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

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

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

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

21. Proteus mirabilis

22. Proteus mirabilis on agar

23. 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

24. Bacillus anthracis

25. Clostridium tetani

26. Tetanus

27. Mycobacterium tuberculosis (Acid fast stain)

28. Corynebacteria diphtheriae
Notice chinese lettering and size

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

30. Vibrio cholera

31. Lyme Disease
Caused by Borrelia burgdorfii

32. 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

33. Chlamydia

34. Rickettsiae

35. 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

36. Malaria (Plasmodium species)

37. Amoebic Dysentery (Entamoeba histolytica)

38. Entamoeba histolytica trophozoite

39. Trichomonas

40. Giardiasis

41. African Sleeping Sickness (Trypanosomiasis)