GENERAL BACTERIOLOGY

Transcription

1 GENERAL BACTERIOLOGY Dr. Waleed Eldars Lecturer of Medical Microbiology and Immunology Faculty of Medicine Mansoura University Growth requirements of Bacteria A) Nutrition Basic elements: Carbon and Nitrogen Major elements: Phosphorus and Sulpher. Minor elements: Mg ++, K+, Ca ++ and Iron. Essential metabolites and growth factors like Nucleotides and vitamins 1

2 (B) Gases: Oxygen: 1. Obligatory aerobes: Grow only in the presence of O 2 e.g. Mycobacterium tuberculosis. 2. Facultative anaerobes: Grow well in the presence and absence of O 2 e.g. pathogenic bacteria. 3. Obligatory anaerobes: they can not grow in the presence of O 2 e.g. Clostridium. 4. Microaerophilic: They grow best in the presence of a minimal amount of O 2.(Helicobacter pylori) 2

3 CO2: The normal atmospheric CO 2 (0.03%) is usually sufficient for growth of most bacteria. Some organisms may require higher CO 2 concentration e.g.: for stimulation of growth or toxin production. (C) Temperature: The optimum temperature for growth and multiplication of most pathogenic bacteria is 37 o C. They have a minimum temperature (10 o C) below which they can not grow and a maximum temperature (42 o C) above which they can not grow. 3

4 (D) Hydrogen ion concentration (ph): Pathogenic bacteria grow at a narrow range of ph with an optimum 7.5. Some bacteria need alkaline ph e.g. Vibrio cholera. Some bacteria need acidic ph e.g. Lactobacillus acidophilus. (E) Moisture. 4

5 Bacterial Products A)Bacterial enzymes: Proteolytic enzymes: act on proteins. Saccharolytic enzymes: act on carbohydrates. Lipolytic enzymes: act on lipids. Respiratory enzymes. 5

6 (B) Bacterial pigments: Endopigment: Exopigment: Localized inside the organism and giving color to the colony. Diffuses from the organism giving color to surrounding medium. Example: Golden yellow pigment of Staphylococcus aureus. Example: the bluish green pigment of Pseudomonas aeruginosa. Staphylococcus aureus endopigment Pseudomonas aeruginosa exopigment 6

7 (C) Bacterial toxins: Exotoxin Endotoxin Diffusibility Diffusible Cell bounded Antigenicity Strong Weak Toxicity High Low Specificity Specific action on Non specific cells Nature Protein Lipopolysaccharide Source Gram positive, Cell wall of Gram some Gram negative negative Heating Labile Stable Effect of formalin Change to toxoid Not affected 7

8 Bacterial Growth and Reproduction Growth: Increase in the number of bacterial cells which result from increased in biomass of bacteria. Reproduction: Simple binary fission Steps: Increase in size. Elongation. Duplication of chromosome Transverse septum. Formation of new cells. 8

9 Bacterial Growth Curve When bacteria are cultured on fluid media, the viable bacterial number follows a course called "growth curve". The growth passes into four stages when we plot the logarithmic number of viable bacteria against time in hours. Steps: A. The lag phase. B. The logarithmic phase. C. The stationary phase. D. The decline phase. 9

10 1- Lag Phase: No increase in bacterial numbers as bacteria prepares themselves for active division. The duration of the lag phase may be few hrs to few days depending on: Type of organism: E. coli < 1hr, while T.B. bacilli: few days. Medium (suitable). It correspond to the incubation period of the disease 2- Logarithmic Phase: Division occurs at a maximum rate (active & regular division). Represented as ascending straight line. Bacteria keep dividing rapidly till a point (saturation point) which depends on type of organism and environmental factors (suitability of the medium and the growth conditions). This stage corresponds to the invasive period of diseases. 10

11 3- Stationary Phase: In this stage the rate of division = rate of death so the number of living organisms remains stationary. Growth rate decrease due to: 1- Exhaustion of food. 2- O 2 starvation. 3- Accumulation of toxic materials. This stage corresponds to the period of signs and symptoms of disease. 4- Decline phase: In this stage the rate of death > rate of growth and at end, bacteria are completely died. Increased death rate is due to: Accumulation of toxic metabolites. O 2 exhaustion. This phase corresponds to the convalescent period of the disease. 11

12 Chemostat (from Chemical environment is static) It is a bioreactor to which fresh medium is continuously added, while culture liquid is continuously removed to keep the culture volume constant. By changing the rate with which medium is added to the bioreactor the growth rate of the microorganism can be easily controlled. Mechanisms of pathogenesis Microorganisms cause disease by two basic mechanisms: 1. Invasiveness: Invasion of tissue. 2. Toxigenicity: Production of toxins. Intracellular pathogens: generally produce chronic disease; extracellular pathogens generally produce acute disease. 12

13 1) Invasiveness: The ability to invade host tissues. Capsules. Extracellular enzymes: Some bacteria produce enzymes that degrade host tissues e.g. hyaluronidase, collagenase, protease and phospholipase Attachment: fimbriae and surface proteins (adhesins). 2)Toxigenicity: The production of toxins 13

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