RESC 203 unit 2.pdf

UNIT 2: GENERAL PROPERTIES OF MICROBES Objectives ¨ Microbial Taxonomy ¨ Bacterial dimension ¨ Microscopy and staining ¨ Morphology of bacteria Taxonomy ¨ The formal system for organizing, classifying, and naming living things is taxonomy. ¨ Taxonomy consists of three s...

UNIT 2: GENERAL PROPERTIES OF MICROBES Objectives ¨ Microbial Taxonomy ¨ Bacterial dimension ¨ Microscopy and staining ¨ Morphology of bacteria Taxonomy ¨ The formal system for organizing, classifying, and naming living things is taxonomy. ¨ Taxonomy consists of three separate but interrelated areas; classification, nomenclature, and identification. ¨ Classification is the orderly arrangement of organisms into groups (taxa) on the basis of similarities or relationships. ¨ Nomenclature is the process of assigning names to the various taxonomic rankings. ¨ Identification is the process of discovering and recording the character of organisms. Taxonomy: Origin ¨ Current system of Taxonomy was developed by the Swedish botanist Carolus (Carl) Linnaeus, in 18th Century. ¨ He is considered as the 'Father of Taxonomy' ¨ His system of classification is still used today. ¨ His two most important contributions to taxonomy were: 1. A hierarchical classification system 2. The system of binomial nomenclature  The hierarchical classification system ¨ Has eight ranks from general to specific: domain, kingdom, phylum, class, order, family, genus, and species. ¨ With each step down in classification, organisms are split into more and more specific groups. ¨ A domain is the highest (most general) rank of organisms and species is the most specific taxonomic rank. Taxonomic Ranks: Most general to most specific Two-Kingdom classification ¨ Linnaeus identified living organisms according to similarities ¨ And divide them into two “kingdoms” ¨ Vegetalia (plantae) ¨ Animalia Five kingdom classification ¨ R.H Whittaker proposed the five kingdom classification in 1969 (Whittaker classification). 1. Monera (Bacteria, Archea) 2. Protista (algae, protozoa) 3. Fungi 4. Plantae 5. Animalia Domain system ¨ In the late 1970s, Carl Woese, developed the Domain system of classification ¨ based on rRNA genes. ¨ Three primary Domains: 1. Archaea 2. Bacteria 3. Eukarya ¨ Domains are placed above the kingdom level. ¨ Viruses are not part of the Domain Classification ¨ they lack ribosomes and therefore lack rRNA sequences for comparison. ¨ They are classified separately, using characteristics specific to viruses. Binomial Nomenclature ¨ Developed by Carolus Linnaeus. ¨ Until his time, the names of organisms varied from country to country and from one scientist to another. ¨ Linnaeus provided a system that standardized the naming and classification of organisms based on characteristics they have in common. Binomial Nomenclature (contd…) ¨ The method of giving the scientific name to living things is called the binomial (two-name) nomenclature and it is always a combination of the genus name followed by the species name. ¨ The source for nomenclature is usually Latin or Greek. ¨ Scientific names are unique, they ensure there is never any confusion as to which organism a scientist may be referring. Binomial Nomenclature (contd…) ¨ Important rules that must be followed to keep all binomial names standardized: ¨ The entire two-part name must be written in italics (or underlined when handwritten). ¨ The genus name is always written first. ¨ The first alphabet of genus name must be capitalized ¨ The species name is never capitilzed. Staphylococcus aureus or Staphylococcus aureus ¨ The source for nomenclature is usually Latin or Greek. ¨ An international group oversees the naming of every new organism discovered. ¨ The inspiration for names is extremely varied: 1. in honor of a microbiologist who discovered it 2. who has made outstanding contributions to the field. 3. a characteristic of the microbe (shape, color), 4. a location where it was found, 5. a disease it causes. ¨ Staphylococcus aureus: (staf-i-lo-kok’kus o-re-us).This genus owes its name to the grapelike (Gr. staphyle) appearance of the clusters. From Latin. aurum, gold. Named for the tendency of some strains to produce a golden yellow pigment. ¨ Escherichia coli Escherichia (ess-shur-eek_-ee-uh) After the German physician Theodor Escherich., coli since it is found in the colon a section of intestine ¨ Salmonella dammam (Salmonella, named after the American microbiologist-D.E. Salmon, Dammam after the city of dammam in Saudi Arabia where this organism was first isolated ¨ Campylobacter jejuni (cam-pee_-loh-bak-ter jee- joo_-neye) Gr. kampylos, curved, bakterion, little rod, and jejunum, a section of intestine. Microbial Dimensions ¨ The unit of measurement used in bacteriology is the micron/micrometer.(1000µm = 1 mm) ¨ Bacteria of medical importance generally measure 3-5µm in length and 0.2-1.5µm in diameter. ¨ The size range of most microbes extends from the smallest viruses, measuring around 20 nm, to protozoans measuring 3-4 mm and visible with the naked eye. Microscopy ¨ Microbiology is concerned with organisms so small they cannot be seen distinctly with the unaided eye. ¨ Hence, the microscope is of high importance. ¨ Thus, it is important to understand how the microscope works and the way in which specimens are prepared for examination. Types of microscopes Optical microscopes Electron Microscopes 1. Simple 1. Transmission EM 2. Brightfield 2. Scanning EM 3. Darkfield Compound microscopes 4. Phase contrast 5. Fluorescence Optical microscopes use visible light as the source of illumination. Simple Microscope ¨ It is composed of a single magnifying lens with a large field.  The Bright-Field Microscope ¨ The ordinary microscope is called a bright-field microscope because ¨ Object/image is dark ¨ Field/background is bright Dark Field Microscope ¨ the object is bright while the field appears black. ¨ Because the back ground is dark it is called dark ground microscope. Phase contrast microscope ¨ Can see organisms alive and unstained. ¨ most useful for observing intracellular (internal)structures such as bacterial spores, granules, and organelles. Comparing three versions of an image from optical microscopes. A live cell of Paramecium viewed with (a) bright-field (b) dark-field), and (c) phase-contrast Note the difference in the appearance of the field and the degree of detail shown by each method of microscopy. Only in phase-contrast are the cilia (fine hairs) on the cells noticeable.  Fluorescence microscope ¨ The specimen must first be coated with a fluorochrome (fluorescent dye) and ¨ then illuminate by UV radiation produces an intense fluorescent image against a black field.  ELECTRON MICROSCOPES ¨ Beam of electrons are employed instead of light. ¨ 1. Transmission EM ¨ 2. Scanning EM Scanning EM Transmission EM STAINING ¨ Most microorganisms are colorless and difficult to view with bright-field microscopes. ¨ Stains are used to make microorganisms more visible because stains increase contrast between structures and between a specimen and its background. Types of stains (dyes) 1. Basic dyes / Cationic dyes : Positive charge 2. Acidic dyes /Anionic dyes : Negative charge How do bacteria appear following staining with basic and acidic dyes?  Staining ¨ The common staining techniques used in diagnostic microbiology are: v Simple staining v Differential staining v Negative staining v Special staining  Simple Staining ¨ Simple stains are composed of a single basic dye, such as methylene blue. ¨ They are “simple” because they involve no more than soaking the smear in the dye for 30–60 seconds and then rinsing off with water. ¨ Used to determine size, shape, and arrangement of cells. ¨ Disadvantage: All organisms take up same color Simple stain Differential staining ¨ Most staining used in microbiology are differential staining, which use more than one dye. ¨ This type of staining imparts different colors to different bacteria ¨ Common differential stains are; Ø Gram staining Ø Acid-fast staining Ø Endospore staining.  Gram staining Ø The histologist Christian Gram originally devised this staining technique in 1884. Ø Differentiates bacteria into Gram positive and Gram Negative bacteria based on their cell wall content. Ø The Gram positive bacteria appear violet/purple. Ø The Gram negative bacteria appear reddish-pink. Ø Typically, a Gram stain is the first step performs to identify bacterial pathogens. Acid fast staining / Ziehl Neelsen staining ¨ Used in laboratories to stain ¨ Mycobacterium (cause many human diseases, including tuberculosis, leprosy) and ¨ Nocardia (causes lung and skin infections). ¨ Cells of these bacteria have large amounts of waxy lipid especially mycolic acid in their cell walls, so they do not readily stain with the Gram stain. ¨ Modern microbiological laboratories commonly use a variation of the acid-fast stain called Ziehl-Neelsen acid- fast staining. ¨ Acid fast bacilli stain bright red while the tissue cells and other organisms appear blue Endospore Stain ¨ Some bacteria—notably those of the genera Bacillus and Clostridium, that cause such diseases as anthrax, gangrene, and tetanus—produce endospores. ¨ These dormant, highly resistant cells form inside the cytoplasm of the bacteria and can survive environmental extremes such as desiccation, heat, and harmful chemicals.  Schaeffer-Fulton endospore staining ¨ Endospores cannot be stained by normal staining procedures because their walls are impermeable to chemicals. ¨ The Schaeffer-Fulton endospore staining procedure results in green- stained endospores and red-colored vegetative cells Negative staining ¨ Acidic stains are used for Negative staining. ¨ Acidic dyes are repulsed by the negative charges on the surface of cells and therefore do not stain them. ¨ Such stains are called negative stains because they stain the background and leave cells colorless. Negative Staining ¨ Negative stains are used primarily to demonstrate bacterial capsules. ¨ Therefore, they are also called capsule stains. ¨ E.g; Nigrosin, India ink, Eosin Bacterial Morphology ¨ Prokaryotic cells exist in a variety of shapes, or morphologies. ¨ The three basic shapes are coccus, bacillus and spiral. ¨ Depending on their morphology, bacteria are classified into several varieties 1. Cocci: (kokkos-berry) spherical or oval bacteria. Staphylococcus aureus 2. Bacilli: (baculus-rod) rod shaped bacteria e.g. Eschericia coli, Pseudomonas 3. Coccobacilli: Shape in between cocci and bacilli; Slightly elongated than cocci but shorter than bacilli. 4. Vibrios: comma shaped curved rods. e.g.; Vibrio cholerae 4. Spirilla: rigid (stiff) spiral forms. e.g.; Spirillum minus 5. Spirochetes: (speira-coil; chaite-hair) Flexible spiral forms. e.g.; Treponema pallidum Actinomycetes ¨ Branching filamentous bacteria resembling fungi ¨ e.g; Actinomyces Mycoplasma Cell wall deficient bacteria ¨ No stable morphology. ¨ They occur as round or oval bodies and as interlacing filaments. ¨ Variable morphology - Pleomorphism ¨ e.g. Mycoplasma, Ureaplasma Arrangement of Cocci Arrangement of Bacilli