Introduction to the Medical Microbiology :

Human Biology Lecture 8

1. University of Duhok College of Health Sciences Dep. of Medical Laboratories Sciences Human Biology/1 st Stage Lecture 8 Dr.: Shameeran S. Ismael BVM & S, M.Sc Medical Microbiology( Parasitology ), PhD Molecular Parasitology

2. Microbiology Microbiology : The study of living things too small to be seen without magnification Microorganisms or microbes - these microscopic organisms Commonly called “germs, viruses, agents…” but not all cause disease and many more are useful or essential for human life

3. Why should we study Microbiology ? Understand how microbes affect human health Understand life processes of microbes that are common to all organisms Understand how microbes can be used for our benefit (e.g. biotechnology)

4. Bacteriology : study of bacteria and Archaebacteria . Mycology : study of fungi (Yeasts and Molds ). Virology : study of viruses. Parasitology: study of Parasite (Protozoa and Helminths)

5. Classification of Microorganisms : General classification: microorganisms are classified according to international code taxonomy – Each microorganism belong to a: Kingdom Phylum Class Order Family Genus Species Some have further divisions to: Sub – order, super family, sub – species

6. Each microorganism have two names i.e. Genus and species . The former begins with an initial capital and the latter with an initial small letter The Genus and species names are in italic, If italics are not used, each name must be underlined separately Entamoeba histolytica Genus Species How to write the scientific name?

7. I. Bacteriology Bacteriology: It is a branch of microbiology that is concerned with bacteria Bacteria – single celled organism that lack a nuclear membrane and true nucleus. They are classified as prokaryotes

8. G eneral features of Bacteria Bacteria are prokaryotes, lacking well-defined nuclei and membrane-bound organelles. Bacteria usually have a cell wall. Chromosomes composed of a single closed DNA circle. They come in many shapes and sizes. Bacteria  are unicellular (single-celled) organisms and are of microscopic and invisible to the naked eye. Divide by binary fission. Temperature extremes: -20oC to 110oC.

9. Bacteria: shape The classification is done based on factors like their shape, nutrition requirement, cell wall staining, the cell appendages, etc . Spherical ( cocci ): Single cell Arranged in bunches (Staphylococcus). Arranged in chains (Streptococcus). Arranged in pairs (Neisseria). Curved or Comma shaped : vibrios . Spirillum : Campylobacter. Bacilli: (Bacillus ). Coccobacilli : (Escherichia ). Fusoform : Fusobacterium

10. Size of Bacteria : Bacteria are very small in size. The unit of measurement in bacteriology is the micron or micrometer ( mm).

11. Bacterial Cell Components: These can be divided into: A. Cell envelope The outer layer or cell envelope consists of two components: 1. Cell wall 2. Cytoplasmic or plasma membrane— beneath the cell wall B. Cellular appendages: Capsule, fimbriae, and flagella

12. 1. Cell wall The cell wall is the layer that lies just outside the plasma membrane. It is strong and relatively rigid, and openly porous. The cell wall is present in most bacteria, except some members like the genus Mycoplasma . In General the cell wall of bacteria typically have one of two types: - a Gram positive cell wall or a Gram negative cell wall . The two different cell wall types can be identified in the lab by a differential stain known as the Gram stain A. Cell envelope

13. After the gram stain technique is applied the gram positive bacteria will stain purple , while the gram negative bacteria will stain pink . Both gram positive and gram negative cell walls contain an component known as peptidoglycan.

14. Functions of the cell wall: 1. It imparts shape and rigidity to the cell. 2. It supports the weak cytoplasmic membrane against the high internal osmotic pressure. 3. It maintains the characteristic shape of the bacterium. 4. It takes part in cell division. 5. It also functions in interactions (e.g. adhesion) with other bacteria and with mammalian cells. 6. It provides specific protein and carbohydrate receptors for the attachment of some bacterial viruses.

15. 2.Plasma Membrane : Controls the transfer of substances in and out of the cell Cytoplasm : Contains enzymes that catalyse the chemical reactions of metabolism

16. Pili : Are for adhesion allowing bacteria to colonize environmental surfaces or cells and resist flushing. Flagella : A slender whip-like structure used for locomotion. Ribosomes : Protein synthesis Naked DNA (Nucleoid): circular single strand, that s tores the genetic information that controls the cell and is passed onto daughter cells Mesosome : In folding of the plasma membrane. Plays a role in cellular respiration and movement of DNA

17. Plasmids : Circular rings of naked DNA Extra genetic material Can be passed from one cell to another cell Used as vectors in genetic engineering Slime capsule: Protects the cell against chemicals and drying out Photosynthetic Membranes: Possess pigments to assist in photosynthesis

18. Bacterial Spore: A number of gram-positive bacteria, such as those of the genera Clostridium and Bacillus can form a special resistant dormant structure called an endospore or, simply, spores . Sporulation in bacteria, is not a method of reproduction but of preservation.

19. Types of Bacteria: Non-Pathogenic – Beneficial or harmless bacteria Most numerous bacteria Useful functions – decompose refuse, improve some conditions Pathogenic Bacteria: harmful and disease causing Pathogenic Bacteria (germs or microbes) are harmful microorganisms, and although in the minority, that can cause disease or infection in humans when they invade the body, plant or animal tissue .

20. Bacterial Growth and Cultivation

21. Source of Carbon (for making cellular constituents). Carbon represents 50% of the dry weight of a bacterium. A source of nitrogen (for making proteins). Nitrogen makes up 14% of the dry weight Source of energy (ATP) – for carrying out cellular functions). Three major nutritional need for growth

22. Nutrient Requirements A. Carbon Classification of organisms : 1. Autotrophs (lithotrophs) – require only water, inorganic salts, and carbon dioxide for growth; they don’t require organic nutrients for growth 2. Heterotrophs (organotrophs) – require an organic form of carbon for growth

23. B. Nitrogen Major component of proteins and nucleic acids of a typical bacterial cell. The end product of all pathways for nitrogen assimilation is the ammonium ion (NH 4 +).

24. C. Growth Factors Organic compounds needed by bacteria in order to grow. In bacterial culture, these substances are usually provided in the culture medium.   Classification: Prototrophics – do not require an exogenous source of growth factor since they synthesize their own. Auxotrophics – require the addition of growth factor to culture media for growth to occur.  

25. D. Inorganic Salts Salt in small amount stimulates the growth of some organisms. Organisms requiring high salt concentrations are called halophilic .

26. E. Oxygen Classification of organisms Aerobes – grow in the presence of atmospheric (free) oxygen Obligate aerobes – grow only in the presence of oxygen Facultative anaerobes – fundamentally aerobes, but can grow in the absence of oxygen Microaerophiles – grow best at low or reduced oxygen tensions

27. Anaerobes – grow in the absence of atmospheric oxygen Obligate anaerobes – grow only in the absence of oxygen Facultative aerobes – fundamentally anaerobes, but can grow in the presence of oxygen Aerotolerant anaerobes – do not grow well but do survive in the presence of oxygen

28. F. Carbon dioxide Some organisms such as Neisseria and Brucella require a higher concentration (3-10%) of CO 2 for growth. These organisms are called capnophiles .

29. G. Moisture This is indispensable for bacterial growth. It serves as a solvent for food and forms the major portion of the protoplasm. Organisms requiring increased moisture content are termed humidophiles.  

30. Physical Requirements A. Temperature Every bacterium has an optimal temperature , the temperature at which the organism grows best.   Classification: 1. Psychrophilic (cold loving) – grows at 1 C-20 C 2. Mesophilic – grows at 20-40 C (most pathogens grow at 37C) 3. Thermophilic (heat loving) – grows at 50-60 C  

31. B. Hydrogen Ion Concentration Most pathogenic bacteria have an optimal pH of 7.2 – 7.6. Classification: 1. Acidophiles – grows at pH 6.5 – 7.0 2. Neutrophiles – grows at pH 7.5 – 8.0 3. Alkalophiles – grows at pH 8.4 – 9.0

32.   C. Osmotic Pressure Organism requiring high osmotic pressures are called osmophiles .

33. Characteristics of Bacterial Growth:       Even on general purpose growth media, bacteria can exhibit characteristic growth patterns. On agar plates, bacteria grow in collections of cells called  colonies . Each colony arises from a single bacterium or a few bacteria. Although individual cells are too small to be viewed, masses of cells can be observed. Colonies can have different forms, margins, elevations, and colors. Observing colony characteristics is one piece of information that microbiologists can use to identify unknown bacteria. 

34. Shown below are isolated colonies of  S. aureus  on a blood agar plate.  

35. Six parameters are normally used to describe microbial colonies growing on an agar surface : a.  Size :  pinpoint, small, medium, or large; range: <  l mm  - 3cm b. Color :   absolutely white, various degrees of pigmentation c. Texture :   the texture of the colony as determined by touching the colony with a needle; smooth (buttery), dry (granular), or mucoid (slimy) and the appearance as judged by the manner in which the colony refracts light; clear, glistening, dense, opaque, or translucent.

36. d. Form:   the shape of the colony; circular, irregular, filamentous, or rhizoid e.  Elevation:   the degree to which colony growth is raised; flat, raised, convex   f.  Margin:   the shape of the edge or margin of the colon