Download Microbes Pt 1

Infectious Diseases and
Microbial Agents
ADAPTED FROM
HTTP://CTE.UNT.EDU/HEALTH/PATHOPHYSI
OLOGY/
 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)