The Microbial World

Dr. Shler Ghafour RaheemBSc., MSc., PhD Medical Microbiology

shler.ghafour@tis.edu.iq

Lecture No. 1

Objectives

1- Introduction to Microorganisms causing human diseases

2- Important Features of Microbes

Microbiology

Microbiology is the study of microscopic organisms.

Medical Microbiology is the study of microorganisms of medical importance:

1. Bacteria

2. Fungi (yeasts and molds)

3. Helminthes (Worms)

4. Protozoa

5. Viruses

Important Features of Microbes

There are three distinct criteria to differentiate microorganisms:

1 – Structure:

- Nucleus or nucleoid

- Cytoplasm

2 – Method of Reproduction

- Binary fission (e.g. bacteria)

- Replication (e.g. viruses disassemble and reassemble)

3 – Nature of the nucleic acids

- DNA and RNA (e.g. fungi and bacteria)

- DNA or RNA (e.g. viruses)

Viruses

Viruses are smaller than bacteria.

Most viruses cause disease (e.g. flu, chickenpox, AIDS).

• They are noncellular; that is, they do not have anucleus and cytoplasm.

• Cannot make their own energy, and are unable tosynthesize proteins.

• Obligate intracellular pathogens. They arecompletely reliant upon host cells for replication

https://microbiologysociety.org/why-microbiology-matters/what-is-microbiology/viruses.html

H3N2 influenza virus particles, coloured

transmission electron micrograph

Bacteria

• Bacteria are found in every habitat on Earth: soil, rock,and oceans. Some live in other organisms including humans.

• Increase in number via binary fission

• Some types cause food spoilage but others are incrediblyuseful in the production of fermented foods such as yoghurt

• Majority are helpful or harmless. But some cause disease

o Normal Flora: Harmless bacteria under normal condition that grow onskin, intestine, oral cavity and other organs

- They protect our body from invaders and pathogens

- Helpful in digestion

o Pathogens: They cause infection and diseases

https://microbiologysociety.org/why-microbiology-matters/what-is-microbiology/viruses.html

Fungi

• Fungi can be single celled or very complex multicellular organisms.

• They are found in just about any habitat but most live on the land, mainly in soil or on plant material rather than in sea or fresh water. • Large plant-like structures which lack chlorophyll• Fungi can be very helpful and humans have used them

in • The food industry

• Medicine: making antibiotics

• They can also be harmful to humans: • Toxins: mould on bread

• Destruction of tissues: athletes foot ( caused by dermatophytes)

https://www.google.com/search?q=pathogenic+fungi&source

Protozoa

oProtozoa are single celled organisms.

oThey live in a wide variety of moist habitats including freshwater, marine environments and the soil.

oSome are parasitic, for example, Plasmodium causes malaria.They are motile and can move by:

• Cilia - tiny hair like structures that cover the outside of the microbe.

• Flagella - long thread-like structures that extend from the cellsurface.

• Amoeboid movement - the organism moves by sending outpseudopodia.

http://microbialclassification.blogspot.com

Range in size from microscopic forms to adulttapeworms over 10 meters in length.

Many of them cause diseases, laboratoryscientists diagnose infections of parasitic wormsby finding microscopic eggs and immature stagesin blood, fecal, urine, and lymph specimens.

They are divided into three main groups:

o Tapeworms (cestodes),

o Flukes (trematodes),

o Roundworms (nematodes).

Helminthes (Worm)

Eggs of different species of parasitic worm

https://en.wikipedia.org/wiki/Parasitic_worm

References

• Richard V. Goering, Hazel M. Dockrell, Mark Zuckerman, PeterL. Chiodini. 2019. Mims' Medical Microbiology andImmunology. Sixth edition. Elsevier.

• Warren E. Levinson, Peter Chin-Hong, Elizabeth Joyce, JesseNussbaum, Brian Schwart. 2018. Review of MedicalMicrobiology & Immunology, 15th edition. McGraw-HillEducation.