CLASSIFICATION OF MICROORGANISMS

DISCLOSURE

Relevant relationships with commercial

entities – none

Potential for conflicts of interest within this

presentation – none

Steps taken to review and mitigate potential

bias – N/A

LEARNING OBJECTIVES

This lecture is designed to meet the following end-of-week learning objective:

1. Describe the broad group classification of microorganisms and the differences between bacteria, fungi, viruses, and parasites

2. Describe the classification of bacteria and fungi.

MODULE OBJECTIVES

By the end of this module, you should be able to:

1. Describe a general scheme to classifying microorganisms

2. Differentiate the major different classes of microorganisms

3. Identify where common/important microorganisms (highlighted in this lecture) fit into the classification scheme

RECOMMENDED READING

Engleberg et al (eds.) Schaechter’s Mechanisms of Microbial Disease (5th Edition), Lippincott Williams & Wilkins 2013

- Chapters 10, 31, 46, 51

GENERAL DEFINITIONS

Microorganisms – an organism (form of life) of microscopic or submicroscopic size

Microbiology – the branch of biology that deals with microorganisms and their effects on other living organisms

Medical Microbiology – the branch of medicine that deals with microorganisms and their effects on human health

GENERAL CLASSIFICATION

Microorganisms

Bacteria Viruses Fungi Parasites

(Ch. 10) (Ch. 31) (Ch. 46) (Ch. 51)

RELATIVE SIZE OF MICROORGANISMS

Limits of

Resolution:

50,000-V

electron microscope

0.003 m

Light

microscope

0.2 m

Unaided

human eye

40 m

Protozoa & Fungi

4 - 40 m

Bacteria

0.1 - 10 m Viruses

0.03 - 0.3 m

0.001 0.01 0.1 1 10 100

Size (m)

BACTERIA - DESCRIPTION

Prokaryotic, single cell organisms characterized by the presence of a strong cell wall containing peptidoglycan

– single circular chromosome

– absence of a distinct, membrane-bound nucleus

– absence of membrane-bound organelles

– divides by binary fission

Bacterial Cell

Structure

Black JG. Microbiology Principles

and Explorations 5th Edition 2002

Slide 11 Black JG. Microbiology Principles and

Explorations 5th Edition 2002

Binary Fission

BACTERIA - CLASSIFICATION

• Divided into Gram-positive and Gram-

negative

• Divide by microscopic morphology

• Divided into aerobic and anaerobic based

on whether they can tolerate environments

with oxygen

O2 Staphylococcus spp. Listeria spp. Neisseria spp. E. coli

Streptococcus spp. Corynebacterium spp. Moraxella spp. P. aeruginosa

Enterococcus spp. Bacillus spp. [Haemophilus spp. (coccobacilli)]

AnO2 Peptostrepto- Clostridium spp. Veillonella spp. Bacteroides spp.

coccus spp.

BACTERIA - EXAMPLES

O2 Staphylococcus spp. Listeria spp. Neisseria spp. E. coli

Streptococcus spp. Corynebacterium spp. Moraxella spp. P. aeruginosa

Enterococcus spp. Bacillus spp. [Haemophilus spp. (coccobacilli)]

AnO2 Peptostrepto- Clostridium spp. Veillonella spp. Bacteroides spp.

coccus spp.

BACTERIA - EXAMPLES

VIRUSES - DESCRIPTION

Acellular infectious particles consisting of a core of RNA or DNA surrounded by a protein coat (capsid), unable to replicate without a host cell

Black JG. Microbiology

Principles and Explorations 5th

Edition 2002

Viral Structures

Slide 18

Viral Replication

Black JG. Microbiology Principles

and Explorations 5th Edition 2002

Black JG. Microbiology Principles and Explorations 5th Edition 2002

VIRUSES - CLASSIFICATION

• Divided into DNA vs. RNA viruses

• Sub-divided by:

– single-stranded, double-stranded, segmented nucleic acid

– presence/absence of envelope

– shape of capsid

• icosahedral (20 faces), helical, complex

VIRUSES - EXAMPLES

Viruses

DNA RNA

Hepatitis B Hepatitis A, C, E, G

Herpesviruses Influenza A, B

Adenovirus Respiratory Syncytial Virus

Parvovirus B19 HIV

Poxviruses West Nile Virus

Rotavirus

Norovirus

VIRUSES - EXAMPLES

Viruses

DNA RNA

Hepatitis B Hepatitis A, C, E, G

Herpesviruses Influenza A, B

Adenovirus Respiratory Syncytial Virus

Parvovirus B19 HIV

Poxviruses West Nile Virus

Rotavirus

Norovirus

FUNGI - DESCRIPTION

Eukaryotic, uni- to multi-cellular organisms characterized by the presence of a rigid cell wall predominantly made of chitin, mannan, and glucan that can reproduce asexually or sexually

plasma membrane & cell wall

nucleus

mitochondria

microtubules

Fungal Cell Structure

FUNGI - CLASSIFICATION

Divided into yeast and filamentous fungi (the latter also referred to as moulds)

YEAST

• Single cells, ovoid or spherical

• Divide by budding

FILAMENTOUS FUNGI (MOULDS)

Multi-cellular

Grow as microscopic,

branching, threadlike

filaments (hyphae),

collectively known as

mycelium

Black JG. Microbiology Principles

and Explorations 5th Edition 2002

FILAMENTOUS FUNGI (MOULDS)

Multi-cellular

Grow as microscopic,

branching, threadlike

filaments (hyphae),

collectively known as

mycelium

FUNGI - EXAMPLES

Fungi

Yeast Moulds

Candida spp. Aspergillus spp.

Cryptococcus neoformans Histoplasma capsulatum

Blastomyces dermatitidis

Zygomycetes

FUNGI - EXAMPLES

Fungi

Yeast Moulds

Candida spp. Aspergillus spp.

Cryptococcus neoformans Histoplasma capsulatum

Blastomyces dermatitidis

Zygomycetes

PARASITES - CLASSIFICATION

Eukaryotic, uni- to multi-cellular organisms that live upon or within another living organism

PARASITES - CLASSIFICATION

Divided into protozoa and helminths

PROTOZOA

• One-celled eukaryotes bounded by only a cell membrane that reproduce asexually and sexually

• Divided into categories – Amoebae, ciliates, flagellates, coccidia,

microsporidia, sporozoa

• Divided by typical site of infection – Intestinal, blood, tissue, other

HELMINTHS (WORMS)

• Multicellular eukaryotic organisms that reproduce sexually

• Divided into categories

– Nematodes (round worms), cestodes (flat worms), trematodes (flukes)

• Divided by typical site of infection

– Intestinal, blood, tissue

PARASITES – EXAMPLES

Parasites

Protozoa Helminths

Intestinal Entamoeba histolytica Ascaris lumbricoides

Giardia lamblia Taenia spp.

Blood Plasmodium spp. Schistosoma spp.

Other Sites Toxoplasma gondii Echinococcus spp.

Acanthamoeba spp.

PARASITES – EXAMPLES

Parasites

Protozoa Helminths

Intestinal Entamoeba histolytica Ascaris lumbricoides

Giardia lamblia Taenia spp.

Blood Plasmodium spp. Schistosoma spp.

Other Sites Toxoplasma gondii Echinococcus spp.

Acanthamoeba spp.

QUIZ

What are the four main classes of microorganisms?

QUIZ

What are the four main classes of microorganisms?

1. Bacteria

2. Viruses

3. Fungi

4. Parasites

KEY MESSAGES

Microorganisms can be classified as follows: 1. Bacteria

– Gram-Positive vs Gram-Negative – Cocci or Bacilli – Aerobic vs. Anaerobic

2. Viruses – DNA vs RNA

3. Fungi – Yeast vs filamentous fungi (moulds)

4. Parasites – Protozoa vs. Helminths

MODULE OBJECTIVES

By now you should be able to:

1. Describe a general scheme to classifying microorganisms

2. Differentiate the major different classes of microorganisms

3. Identify where common/important microorganisms (highlighted in this lecture) fit into the classification scheme