Lecture 4 Bacterial Growth (1) PDF

Microbiology & Immunology Unit Lecture 4 Bacterial Growth (1) Dr. Rasha Mokhtar Elnagar M.B.B.C, MSc, PhD, MD Medical Microbiology and Immunology Associate Professor of Medical Microbiology & Immunology Consultant Microbiology & Immunology Bacterial Growth Requi...

Microbiology & Immunology Unit Lecture 4 Bacterial Growth (1) Dr. Rasha Mokhtar Elnagar M.B.B.C, MSc, PhD, MD Medical Microbiology and Immunology Associate Professor of Medical Microbiology & Immunology Consultant Microbiology & Immunology Bacterial Growth Requirements: Chemical requirements: o Major elements (Carbon, nitrogen) o Minor elements Physical requirements: o PH o Temperature o Osmotic pressure o Gaseous requirements: oxygen and CO₂. o Water Chemical Growth Requirements  Physical Growth Requirements 1. PH: o Most pathogenic bacteria grow best at neutral pH (6.8 - 7.4). o Acidophilic bacteria are able to survive in acidic PH (3-5). Example: Helicobacter pylori, lactobacillus. o Alkaliphilic bacteria prefer alkaline conditions (up to 10.5). Example: Vibrio cholerae. 2. Temperature Requirements: Normal flora and most pathogens grow at or near normal human body temperature of 37 °C. Bacteria are classified into 3 groups as regard the temperature: 1- Psychrophilic: The bacteria is growing between 0 °C and 20 °C. 2- Mesophilic: The bacteria grow between 20 °C and 44 °C (bacteria producing disease). 3- Thermophilic: The bacteria can grow between 50 °C and 80 °C. 3. Osmotic Pressure: Most bacteria can grow in isotonic (0.9% NaCl) and hypotonic solutions. Hypertonic solutions: cause shrinkage and death to most bacteria. Halophilic bacteria resist high salt concentrations.  4. Gaseous Requirements: O2 & CO2 Oxygen Requirements 1. Strict or obligate aerobes: Requires oxygen to grow. Example: Mycobacterium, Pseudomonas. 2. Strict or obligate anaerobes: Die in the presence of oxygen. Example: Clostridium. 1. Facultative anaerobes: Can grow in the presence or absence of oxygen. Example: Majority of bacteria as Escherichia coli. 4. Microaerophilic: Use low concentrations of oxygen (5%). Examples: Helicobacter and campylobacter. 5. Aerotolerant anaerobes: do not use oxygen, but have mechanisms to protect themselves from oxygen (able to grow in its presence or absence). Example: Enterococcus faecalis.  CO2 Requirement: o Most bacteria need CO₂ in atmospheric concentration (0.03%). o Capnophilic bacteria: need higher concentration of CO₂ (5- 10%). Example: Streptococcus pneumoniae, Neisseria, Brucella abortus. 5- Moisture: Water is needed for the bacterial growth and metabolic reactions.  Bacterial Growth Curve  The bacterial growth curve: Bacterial growth: is the division of one bacterium into two daughter cells by simple binary fission. Bacterial growth curve represents the relationship between microbial quantity and time of incubation. Phases of growth curve: lag, exponential, stationary and decline phase.  Lag phase Exponential Stationary Decline phase (Log) phase phase Number of Fixed (not Increase with fixed at Gradual bacteria increasing) time in fixed maximum decrease at rate till reach concentration fixed rate max. concentration Condition of adapt - Dividing - Not dividing -Dying rapidly bacteria themselves to rapidly growth conditions (no division) Media Full of Gradual nutrient Complete nutrient consumption depletion and consumption of nutrients accumulation of nutrient of toxic products. In vivo Incubatory Invasive period Symptoms Convalescent correspond to period and signs of period the disease  Bacterial Metabolism According to biochemical pathway used in energy production, bacterial metabolism can be categorized into three types: Aerobic Respiration. Anaerobic Respiration. Fermentation. Fermentation  Aerobic respiration Anaerobic respiration Fermentation ATP 38 ATP 38 ATP 2 ATP produced Glucose Complete by glycolysis, Krebs Complete by glycolysis, Incomplete by glycolysis Utilization cycle & electron transport Krebs cycle & electron chain transport chain Electron O2 Nitrate or sulfate Pyruvate acceptor Examples Obligatory aerobes such Obligatory anaerobic Obligate anaerobic as: Mycobacterium bacteria such as: bacteria e.g., Clostridium Facultative anaerobic Clostridium Facultative anaerobic bacteria such as: E. coli bacteria e.g., E. coli Q: A 28 years old young man sustains major soft tissue injury and open fractures of his right leg after a motorcycle accident. One day later, he has a temperature of 38°C and increased heart rate. On examination, the leg is swollen and tense, with thin, dark fluid draining from the wound. Microscopic examination of wound swab showed Gram positive obligate anaerobic spore forming bacilli. Which of the following microorganisms is the most likely cause of this infection? A. Staphylococcus aureus B. Streptococcus pneumonia C. Clostridium tetani D. Escherichia coli Reference Lippincott Illustrated Microbiology 4th edition, Chapters: 6.