Introduction: The microbial world, Classification,

Taxonomy, Nomenclature

Objectives To understand the broad classification

of microbes as bacteria, fungi, protozoa, helminths, viruses, and prions

To know the differences between prokaryotes and eukaryotes

To discuss the basis of bacterial taxonomy

To have an overview of the morphology,staining and lifecycles of bacteria, fungi, protozoa, and helminthes

To outline the immune response for protection against microbial invasion

Three Domains All living organisms can be

classified into one of three major groups called domains

Bacteria Archaea

Eukarya

} = Prokaryote

= Eukaryote

Bacteria & Archaea Both have same shape, size &

appearance Major differences exist in their

chemical composition Archaea

lack peptidoglycan means "ancient" because use

ancient energy mechanisms Grow in harsh environments

e.g high salt, very high temp

EukaryotesArthropods (insects, ticks & mites)Helminthes (worms)Fungi Protozoa

ProkaryotesArchaea Bacteria

Classes of infectious organisms

VirusesPrions

Prokaryotes

Vs.

Eukaryotes

Features of cells

Prokaryotic Eukaryotic

Size 0.3-2µm 2-20µmChromosome

Single, circular Multiple

Nucleus No nuclear envelope; no nucleoli

Membrane bound; nucleoli present

Membrane bound organnelles

Not present Present

Ribosomes 70S ribosomes (50S & 30S subunits)

80S ribosomes (60S & 40S subunits

Cell wall Unique chemical components, peptidoglycan

Not present (except in plant cells), no peptidoglycan

Plasma membrane

No carohydrates; most lack sterols

Carbohydrates & sterols present

Mitochodria Cytoskeleton& Chloroplasts

No YesChloroplast only in plant & algae

DomainKingdom

PhylaClass

OrderFamily

GenusSpecies

Microbial taxonomy is commonly called prokaryotic taxonomy. The widely accepted prokaryotic taxonomy is Bergey’s Manual of Systematic Bacteriology, first published in 1923 by the American Society for Microbiology.

Bacterial Naming Adopts the species and generic names Species:

basic unit of classification collection of strains with common characteristic

Genus (plural: Genera) group of bacterial organisms having in common several structural,

biochemical & physiological traits Group of species make up the genus

Every organism is identified by its genus and species The generic name is the first name and starts with a capital

letter The species name is the second name and starts with a

small letterExample: genus species

Staphylococcus aureusStaphylococcus epidermidis

Bacterial classification - mixture of characteristics

Macroscopic Colonies: color, size, shape, smell Haemolytic/ non-haemolytic Special growth requirements

Microscopic Shape: cocci, rods, curved, or spiral Staining properties

Respiration Aerobic, Anaerobic, Microaerophilic

Reproduction: Sporing, non-Sporing

Biochemical characteristics Fermentation of sugars Production of enzymes

Antigenicity

Molecular (Genotype)

Microscopic

Size, shape and configuration of the organisms cocci, rods, curved, or spiral

Ability to retain the Gram stain gram-positive or gram-negative

Gram-positive cocci

Gram-negative bacilli

Classification of Bacteria

True bacteria Spirochaetes Mycoplasmas Riickettsiae & Chlamydiae Filamentous bacteria

PROKARYOTES

Diagrammatic structure of a bacterium

Comparison of Eukaryotic microbes

Helminths

Protozoa

Fungi

Multicellular

Single celled

Single or multicellular

Cell organization

Organic compounds derived from host

Organic compounds

Organic compounds

Source of energy

Macroscopic

Microscopic

Microscopic or macroscopic

Size

Fungi Diverse group of

saphrophytic organisms getting nutrients from

dead organic matter

Two basic forms: Filamentous, mold-like:

Consist of threads(mycelia) that elongate and branch

Example: Mold & mushrooms

Yeast-like, single cells, round

Divide by budding, larger than bacteria

Example: Candida

Yeast cells e.g. Candida

Fungal mould

Parasites Classification

P ro to z o ap se u d o p o d s , sp o ro z o ite s

fla g e lla te s , c ilia te s

C e s to d a(T a p e w o rm s)

T re m a to d a(F lu k e s)

P la ty h e lm in th s(F la t w o rm s)

N e m a th e lm in th s(ro u n d w o rm s)

H e lm in th s(W o rm s)

P a ra s ite s

Protozoa Single-celled eukaryotes, larger than

bacteria Some are motile with flagella

Can have 2 forms during the lifecycle: Trophozoite- larger form, metabolically

active, motile, dividing Cyst- smaller form, metabolically

inactive, not dividing, can survive harsh conditions

Some Protozoa (unicellular) of medical importance

Amoeboids (Pseudopods)

Ciliates (cilia)

Zooflagellates (flagella)

Sporozoa (no locomotion)

Entamoeba histolytica

Entamoeba coli)

Balantidium coli

Trichomonas vaginalis

Giardia lambliaLeishmania tropica

Plasmodium

Toxoplasma gondii

Cryptosporidium

Iodine stained wet preparation Showing: Cysts of Entamoeba coli and Entamoeba histolytica

E. histolytica cyst (4 nuclei)

E. coli cyst (more than 4 nuclei)

E. coli (trophozoite) E. histolytica (trophozoite)

Protozoa: Flagellates

Giardia lamblia :Transmitted by faeco-oral routeHas a two life cycle stages: Flagellated trophozoite & Cyst

Trichomonas vaginalis : Sexually transmittedOne life cycle stage: Flagellated trophozoite

Leishmania : Amastigote form inside macrophages

Ring stage of P. falciparum (malaria parasite)

PROTOZOA

Helminths – worms Largest and

multicellular Most have 3 stages in

life-cycle: Egg Larva Adult

Helminths

Platyhelminths(flat worms

Cestodese.g. Tape

worm

Trematodes (Flukes)

e.g. Schistosoma

Nematehelminths

(Nematodes or round worms)

E.g. Ascaris

Viruses No cellular structure,

not living cells Obligate intracellular

pathogens Viruses must enter host

cells to multiply & cause disease

Genome has DNA or RNA surrounded by protein

capsid coat

Defense against microbes Innate immunity

Inborn, non-specific

Adaptive immunity Acquired, specific, Immunological

memory