Medical Microbiology Lecture Notes PDF

Medical Microbiology 1/16/2025 1 MICROBIAL GROWTH AND NUTRITION 1/16/2025 2 Expected Student Learning Outcomes for bacterial growth and nutrition 1. Provide requirements for bacterial growth 2. Differentiate different types of microorganisms according to...

Medical Microbiology 1/16/2025 1 MICROBIAL GROWTH AND NUTRITION 1/16/2025 2 Expected Student Learning Outcomes for bacterial growth and nutrition 1. Provide requirements for bacterial growth 2. Differentiate different types of microorganisms according to growth requirements 3. Understand the different phases of bacterial growth curve 4. Explain the clinical significance of bacterial growth curve 1/16/2025 3  1. Temperature Growth Requirements I. Physical 2. pH II. Gaseous 3. Osmotic pressure III. Chemical 1/16/2025 4  1. TEMPERATURE ❑Bacteria vary in temp requirements ❑Each bacteria grow at a particular growth temp. 1.Minimum growth temp: The lowest temp at which the bacteria can grow and below it bacteria can't grow 2.Optimum growth temp: Temp at which the bacteria grow best 3.Maximum growth temp: The highest temp at which the bacteria can grow and above it bacteria can't grow ❑Temp range: Growth does not occur above maximum or below minimum temp 1/16/2025 5 1/16/2025 6  Bacteria Synonymous Temp range Optimum Temp Psychrophiles Cold-loving -10 to 20C 12C Psychrotrophs Cold-tolerant 0 to 30 C 20C Mesophiles* moderate-temp-loving 10 to 48C 37C Thermophiles Heat-loving 40 to72C 60C Hyperthermophile Extreme Heat-loving 65 to 110C 90C ❑*Normal human flora & most of medically important pathogens are mesophiles ❑Mesophilic bacteria grow best at 37°C (body temperature) 1/16/2025 7 7 Microbes Differ In Their Temperature 1/16/2025 8  2. pH (H-ion Concentration) ❑pH of an environment can greatly affect microbial growth ❑Most organisms grow best between pH 6 and 8 ❑Some organisms have evolved to grow best at low or high pH ❑The internal pH of a cell must stay relatively close to neutral adjusted with ion pumps even though the external pH is highly acidic or basic 1/16/2025 9  2. pH (H-ion Concentration) ❑According to pH bacteria can be classified into; 1.Neutophiles : ❑ Majority bacteria grow best between pH6.8-7.4 2.Acidophiles (Acidic pH) ❑Few bacterial species tolerate low pH e.g. Helicobacter pylori ❑Lactobacilli grow between pH 5-6 ❑Mycobacterium grow at pH 6.5-6.8 ❑Fungi prefer acidic pH (4.5-5.5) 3.Alkalophiles (Alkaline pH): ❑Few species (e.g. Vibrio cholorae) tolerate high pH (pH8-9) 1/16/2025 10  3. OSMOTIC PRESSURE ❑Osmotic pressure depends on the surrounding solute concentration & water activity (aw) ❑aw is the ratio of the vapor pressure of a solution to the vapor pressure of pure water ( aw 1.00) 1/16/2025 PHRM 222-MICROBIAL PHYSIOLOGY AL-AGAMY 11  3. OSMOTIC PRESSURE 1. Non-halophile: ❑Most bacteria require isotonic or hypotonic environment for optimum growth 2. Osmotolerant / halotolerant / barotolerant: ❑Bacteria don't require high osmotic pressure ❑They can tolerate it ❑grow at up to 10% Na Cl e.g. Staphylococcus 3. Obligate or extreme Halophiles/osmophiles: ❑Bacteria require relatively high salt conc. for growth ❑e.g. some Archea that require 20% Na Cl 1/16/2025 PHRM 222-MICROBIAL PHYSIOLOGY AL-AGAMY 12 1/16/2025 13  Growth Requirements I. Physical 1. Oxygen O2 II. Gaseous 2. Carbon dioxide CO2 III. Chemical 1/16/2025 14  1- Oxygen and microbial growth ❑ O2 & CO2 are very essential for bacterial growth ❑ Utilization of O2 during metabolism yields toxic molecules ❑ Toxic molecules are Reactive O2 Species (ROS; free radicals) ❑ ROS such as O2-, 1O2, H2O2, OH* ❑ ROS is converted to harmless substances by detoxifying enzymes i.e. Catalase (or peroxidase) & Superoxide dismutase (SOD) ❑ Ability of bacteria to grow in presence of O2 require two detoxifying enzymes i.e. Catalase & SOD ❑ SOD converts O2- into H2O2 and O2 ❑ Catalase breaks down H2O2 into H2O and O2 ❑ Any organism that can live in or requires O2 has SOD and catalase (peroxidase) 1/16/2025 15  Toxic Forms of Oxygen and Detoxifying Enzymes Hydrogen peroxide Superoxide 1/16/2025 16  Classification of organisms based on O2 utilization 1.Obligate aerobes ❑ Require O2 (21%) for energy production ❑ Have both SOD and Catalase (DETOXIFIYING ENZYMES) ❑ e.g. Pseudomonas and Mycobacterium 2. Facultative anaerobes: ❑ Can grow in presence or in absence of O2 ❑ Have both SOD and Catalase ❑ Most of bacteria e.g. Staphylococcus, E. coli 1/16/2025 17  Classification of organisms based on O2 utilization 3. Aerotolerant anaerobes: e.g. Clostridium perfringens ❑ Tolerate or survive in presence of O2, but do NOT utilize it ❑ Have SOD only that detoxify oxygen's poisonous forms 4. Microaerophiles e.g. Campylobacter, Helicobacter ❑ require low levels of O2 (5%) ❑ Have SOD +/-Catalase 5. Obligate anaerobes: e.g. Bacteroides ❑ can’t grow in the presence of O2 ❑ do not utilize O2 for energy production ❑ Lack both catalase and SOD 1/16/2025 18 1/16/2025 19  Test for Oxygen Requirements of Microorganisms Thioglycolate broth : contains a reducing agent and provides aerobic and anaerobic conditions a) Aerobic b) Anaerobic c) Facultative d) Microaerophil e) Aerotolerant 1/16/2025 20  2. Carbon dioxide (CO2)requirement: ❑The small amount of CO2 present in the air is enough for most bacteria to grow ❑Some aerobic bacteria require high CO2 concentration (5-10%) ❑CO2 concentration is higher than in atmosphere ❑These bacteria are called Capnophiles ❑Intestinal tract, respiratory tract & other body tissues where pathogens grow e.g. Campylobacter, Haemophilus, Streptococcus pneumoniae 1/16/2025 21  Thanks! 1/16/2025 22