Properties of Microorganisms PDF

**Introductory Posting Lecture notes.** **Facilitator: Dr. I. Osaigbovo** **Department of Medical Microbiology, UNIBEN** **August, 2024** **PROPERTIES OF MICROORGANISMS** **Lecture Objectives** At the end of the lecture, students should a. Be able to differentiate eukaryotes from prokaryotes...

**Introductory Posting Lecture notes.** **Facilitator: Dr. I. Osaigbovo** **Department of Medical Microbiology, UNIBEN** **August, 2024** **PROPERTIES OF MICROORGANISMS** **Lecture Objectives** At the end of the lecture, students should a. Be able to differentiate eukaryotes from prokaryotes b. Be conversant with the chief properties of different classes of microorganisms c. Know the structural properties of bacteria and their function d. Identify the practical applications of some microbial properties especially Gram stain and drug action. All living cells are either prokaryotes or eukaryotes. Agents of human infectious disease belong to 4 major groups namely bacteria, fungi, parasites (protozoa and helminths) and viruses. Bacteria belong to the prokaryote kingdom; Fungi belong to the kingdom of Fungi, Protozoa are members of the kingdom Protista, while helminths are classified in the animal kingdom. Understanding the properties of microorganisms helps in their diagnosis and treatment. Viruses are a distinct group of microorganisms. They are acellular and inert while in extracellular environments. They are only capable of replication when they enter living cells. **Properties of prokaryotes and eukaryotes** The primary distinguishing characteristics of prokaryotes are their relatively small size and the absence of a nuclear membrane. Although they lack membrane-bound subcellular components, they do possess a specialised region of the cell containing DNA known as the nucleoid. The kingdom Prokaryota contains two domains: Archaebacteria and Bacteria. Bacteria are studied in medical microbiology because they are clinically relevant. Eukaryotic organisms include the protists (Protista), fungi and animals. They possess a true nucleus, i.e., they have a nuclear membrane compartmentalising their genetic material from other cellular components. They also possess organelles which are membrane-bound and they have a complex intracellular structure. The eukaryotic cell possesses multiple chromosomes surrounded by a nuclear membrane and uses a mitotic apparatus to ensure equal allocation of chromosomes to progeny. Prokaryotic cells have a nucleoid consisting of a single circular molecule of loosely organised DNA lacking nuclear membrane and mitotic apparatus. **Property** **Prokaryotic cells** **Eukaryotic cells** ------------------------------------------------------------------ ---------------------------------------- ---------------------- **DNA with a nuclear membrane** No Yes **Mitotic division** No Yes **DNA associated with histones** No Yes **Chromosome number** One More than one **Membrane-bound organelles such as mitochondria and lysosymes** No Yes **Size of ribosomes** 70 S 80 S **Cell wall containing peptidoglycan** Yes (with the exception of Mycoplasma) No **Cell membrane sterols** No (with exception of Mycoplasma) Yes **Properties of bacteria** They are unicellular prokaryotic microorganisms. Most of them range in size from 1μm to 3 μm. Mycoplasma are the smallest measuring 0.2 μm while Borrelia are quite large and measure up to 10μm in length. Bacteria may be classed into 3 basic groups based on shape- cocci, bacilli and spirochaetes. Some are however, variable in shape, i.e., pleomorphic. They may also be classified based on the structure, chemical composition and thickness of the cell wall using the Gram staining procedure into Gram positive and Gram negative. **Structural properties of bacteria** +-----------------------+-----------------------+-----------------------+ | **Structure** | **Chemical | **Function** | | | composition** | | +=======================+=======================+=======================+ | **Cell wall- | Sugar back-bone with |. Gives rigid | | peptidoglycan** | peptide side-chains | support, protects | | | that are cross-linked | against osmotic | | | | pressure | | | | | | | |. Structure, chemical | | | | composition and | | | | thickness | | | | differentiates | | | | bacteria into Gram | | | | positive and Gram | | | | negative | | | | | | | |. Site of action of | | | | beta-lactam | | | | antibiotics | | | | | | | | Degraded by lysozyme | +-----------------------+-----------------------+-----------------------+ | **Cytoplasmic | Lipoprotein bilayer | Site of oxidative and | | membrane** | without sterols | transport enzymes | +-----------------------+-----------------------+-----------------------+ | **Ribosome** | RNA and protein in |. Protein synthesis | | | 50S and 30S subunits | | | | |. Site of action of | | | | aminoglycosides, | | | | macrolides, | | | | tetracyclines and | | | | chloramphenicol | +-----------------------+-----------------------+-----------------------+ | **Nucleoid** | DNA | Genetic material | +-----------------------+-----------------------+-----------------------+ | **Mesosome** | Invagination of | Participates in cell | | | plasma membrane | division | +-----------------------+-----------------------+-----------------------+ | **Non-essential | | | | structures** | | | +-----------------------+-----------------------+-----------------------+ | **Capsule** | Polysaccharide | Protects against | | | | phagocytosis | +-----------------------+-----------------------+-----------------------+ | **Pilus or fimbria** | Glycoprotein |. Mediates attachment | | | | to cell surfaces | | | | | | | |. Sex pilus mediates | | | | attachment of two | | | | bacteria during | | | | conjugation | +-----------------------+-----------------------+-----------------------+ | **Flagellum** | Protein | Motility | +-----------------------+-----------------------+-----------------------+ | **Spores** | Keratin-like coat, | Provides resistance | | | dipicolinic acid | to dehydration, heat | | | | and chemicals | +-----------------------+-----------------------+-----------------------+ | **Plasmids** | Extrachromosomal DNA | Contains a variety of | | | | genes for antibiotic | | | | resistance and toxins | +-----------------------+-----------------------+-----------------------+ **Figure: Morphology of the bacterial cell** **Properties of fungi** 1. They are eukaryotic organisms. 2. They are obligate or facultative aerobes. 3. They are non-photosynthetic i.e., cannot synthesise food using light. 4. They are chemotrophic, i.e., they secrete enzymes that degrade a wide variety of organic substrates into soluble nutrients which are either passively absorbed or actively transported into the cell. 5. Most of them grow as a mass of branching, interlacing filaments (hyphae) known as mycelium. A few are unicellular existing as ovoid or spherical cells called yeasts. Some are dimorphic and capable of growth as yeasts or moulds depending on environmental conditions. 6. They all have an essential rigid cell wall that determines their shape. The major constituent is chitin but the cell wall also contains glucans and mannans. 7. Fungal cell membrane contains a unique sterol known as ergosterol which is an important target for antifungal drugs like polyenes and azoles. 8. Fungi produce spores to enhance their survival. These spores may be derived from asexual or sexual reproduction. Asexual spores arise via mitosis and are genetically identical. There are 2 main types- conidia and sporangiospores. Sexual spores include zygospores, ascospores and basidiospores. 9. The major subphyla of fungi are Ascomycota, Basidiomycota, Glomeromycota, and Chytridiomycota (does not contain medically relevant species). Some fungi are described as Deuteromycota (or fungi imperfecti) because their sexual forms remain unidentified. **Parasites: Made of the protozoa and helminths** **Properties of protozoa** 1. They are a large and diverse group of non-photosynthetic, unicellular, eukaryotic organisms. Those of medical importance are parasites 2. They are classified based on the type of locomotion in the mature stage: a. Sarcodina which move by means of cytoplasmic processes called pseudopodia e.g Entamoeba b. Ciliophora in which movement is carried out by hair-like projections called cilia e.g. Balantidium coli c. Mastigophora whose members move by means of long, thin whip-like structures called flagella e.g Trypanosoma d. Sporozoa which lack structures for locomotion in the mature stage e.g Plasmodium 3. Most protozoa have typical life cycles that have a vegetative trophozoite stage and a resting cyst stage. 4. They reproduce asexually by binary fission or by multiple fission (schizogony) and some also by a sexual mechanism (sporogony) **Properties of helminths** The helminths of medical importance are parasitic worms. 1. They are complex, multicellular organisms classified as metazoan within the animal kingdom 2. They contain 2 phyla namely Nematoda (round worms) and Platyhelminthes (flat worms) 3. Nematodes have the following characteristics a. Elongated and tapered at both ends b. Round in cross section c. Unsegmented d. Possess a complete digestive system e. Possess a highly developed separate-sexed reproductive system 4. Plathyhelminthes have the following features: a. Dorsoventrally flattened in cross-section b. Mostly hermaphroditic, except for Schistosoma c. Medically important classes are Trematoda and Cestoda. The trematodes have a leaf shape and a bifurcated gut. Cestodes are flat and have a ribbon-like chain of segments (called proglottids) containing male and female reproductive structures. d. They possess no mouth or gut and absorb nutrients directly from their host through their integuments e. Their life cycle of plathyhelminthes is usually indirect involving one or more intermediate hosts. **Properties of viruses** 1. They are the smallest infectious agents 2. They are, in actual fact, not cells but can only replicate within cells. 3. They contain only one kind of nucleic acid (RNA or DNA) as their genome, never both. This serves as the basis of their classification 4. The nucleic acid is encased in a protein shell called capsid which in some viruses is surrounded by a lipid containing membrane called envelope. Enveloped viruses are sensitive to ether and other organic solvents 5. Viruses are inert in the extracellular environment and are able to replicate only in living cells. i.e., they are obligate intracellular parasites. This is because they have no cytoplasm and so they depend on host cells to provide the machinery for protein synthesis and energy production. **Properties of microorganisms (Summary)** **Property** **Viruses** **Bacteria** **Fungi** **Protozoa & Helminths** ------------------------------- --------------------------------------- ------------------------------------------ ----------------------------------- -------------------------------------------------------------------- **Cells** No Yes Yes Yes **Approximate diameter (μm)** 0.02-0.2 1-5 3-10 (yeasts) 15-25 (trophozoites) **Nucleic acid** Either DNA or RNA Both DNA and RNA Both DNA and RNA Both DNA and RNA **Type of nucleus** None Prokaryotic Eukaryotic Eukaryotic **Ribosomes** Absent 70 S 80 S 80 S **Mitochondria** **Nature of outer surface** Protein capsid ± lipoprotein envelope Rigid cell wall containing peptidoglycan Rigid cell wall containing chitin Flexible membrane or cuticle **Motility** None Some (by means of flagella) None Most by means of: flagella; cilia; pseudopodia; muscle in heminths **Method of replication** Binary fission Budding; mitosis Mitosis **Assignment** Read about Gram staining procedure and learn the steps.