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

} = Prokaryote Three Domains = Eukaryote 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

Classes of infectious organisms Eukaryotes Arthropods (insects, ticks & mites) Helminthes (worms) Fungi Protozoa Prokaryotes Archaea Bacteria Viruses Prions

Prokaryotes Vs. Eukaryotes

Features of cells Prokaryotic Eukaryotic Size 0.3-2µm 2-20µm Chromosome 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 Yes Chloroplast only in plant & algae

Domain Kingdom Phyla Class Order Family Genus Species 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 letter Example: genus species Staphylococcus aureus Staphylococcus 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-negative bacilli Gram-positive cocci

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 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

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 lamblia Leishmania tropica Plasmodium Toxoplasma gondii Cryptosporidium

E. histolytica (trophozoite) E. coli (trophozoite) E. histolytica (trophozoite) Iodine stained wet preparation Showing: Cysts of Entamoeba coli and Entamoeba histolytica E. coli cyst (more than 4 nuclei) E. histolytica cyst (4 nuclei) Edited by A. Qareeballa

Protozoa: Flagellates Trichomonas vaginalis : Sexually transmitted One life cycle stage: Flagellated trophozoite Giardia lamblia : Transmitted by faeco-oral route Has a two life cycle stages: Flagellated trophozoite & Cyst

PROTOZOA Ring stage of P. falciparum (malaria parasite) Leishmania : Amastigote form inside macrophages

Helminths – worms Largest and multicellular Most have 3 stages in life-cycle: Egg Larva Adult

Nematehelminths (Nematodes or round worms) Platyhelminths (flat worms Cestodes e.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