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