Chapter 7 - Bacterial Growth PDF

Chapter 7: Fundamentals of Microbial Growth (Replication) Microbes show dynamic and complex growth in nature, and more distinct growth stages in the laboratory When nutritional requirements are met, a microbe will enlarge in size and eventually divide Microbial growth is cell divisi...

Chapter 7: Fundamentals of Microbial Growth (Replication) Microbes show dynamic and complex growth in nature, and more distinct growth stages in the laboratory When nutritional requirements are met, a microbe will enlarge in size and eventually divide Microbial growth is cell division that produces new (daughter) cells and increases the total cell population Most of our knowledge comes from studying species that can be _________ in the laboratory _______ of the bacteria species on our planet  Bacterial replication In the laboratory, bacteria are usually grown as _________________ cultures But in nature, bacteria intermingle and live side by side with archaea and eukaryotes ________________ factors play a significant role in the life, metabolism and structure of bacteria Escherichia coli converts from a motile bacillus shape to a filamentous non- motile form during urinary tract infections  Biofilms Cells living in biofilm communities communicate and collaborate to survive In healthcare settings, biofilms are a major concern ________________ Contribute to persistent infections Biofilm formation occurs when free-floating (planktonic) bacteria adhere to a surface Medical devices like ________ and heart valves are potential havens for biofilms Bacterial Replication ________________ Occurs in most prokaryotes Involves dividing a single cell into two cells Asexual process Determines the ___________ of bacteria Staph, strep, tetrads, singles, etc. Time it takes for each division is generation time Can change over time  Generation Time Generation time Time it takes for a cell to divide Times are diverse Range from about 15 minutes to 24 hours Depends on the species and _______________ The _____________ impact how fast a microbial population increases Generation time for many common bacteria is less than an hour E. coli: 20 minutes Some bacteria have fairly slow generation times Mycobacterium tuberculosis: 15–20 hours Generation Time As bacteria divide by binary fission, they exhibit ____________ growth Bacterial growth phases In the lab, bacteria are usually isolated and grown in closed pure batch cultures Bacteria undergoes distinct growth phases that can be detected by counting the number of ________ cells  Bacterial growth phases Phase One: _____ Phase Delay that occurs while cells adjust to their new environment Phase Two: Log Phase Period of rapid exponential growth Phase Three: _______ Phase Nutrients are depleted, waste accumulates Population growth rate levels off Phase Four: Death Phase At a critical point of waste buildup and decreasing nutrients, the cells begin to die Rate of cell death is exponential Small number of the cells survive by adapting to the waste and by feeding off dead cells Prokaryotic Growth Requirements Prokaryotes adapt to various growth conditions All microbes find a niche by adapting to specific conditions Temperature ______ Salt concentrations _________ needs Available nutrients Temperature Temperature is an important component of a microbe’s environment Low temperature ___________ enzymatic reactions Increased temperature Speeds up enzymatic reactions Can increase growth rate High temperatures ___________ cell proteins (kills cell) Temperature Three principal temperatures: Maximum temperature – highest temperature that supports growth Minimum temperature – lowest temperature that supports growth ___________temperature – temperature where cellular growth is highest  Temperature Can be used to classify microbes _____________ Thrive between −20°C and 10°C Psychrotrophs Grow at about 0–30°C Associated with foodborne illness _____________ Grow best around 10°–50°C Associated with most pathogens Thermophiles Grow around 40–75°C Associated with compost piles and hot springs Extreme thermophiles Grow around 65–120°C pH Every microbe has a minimum, optimum, and maximum range of pH for growth ___________ Grow at pH 1 (or less) to pH 5 Live in areas such as sulfur hot springs and volcanic vents Often maintain a fairly neutral cytoplasmic pH Proton pumps export excess protons from the cytoplasm to raise pH Neutralophiles Grow best in a pH range of 5–8 Make up _____________________ ____________ Alkaliphiles Grow in the basic pH range of 9–11 Associated with soda lakes High-Salt Conditions ____________________ Thrive in high-salt environments Tolerate up to 35% Associated with the Dead Sea and the Great Salt Lake of Utah Facultative halophiles Tolerate higher salt but may not grow well Example: Staphylococcus aureus Bacterial cytoplasm is _______ water Normal cells undergo plasmolysis Halophiles must overcome the osmotic stress of a high-salt environment Keep high concentrations of organic materials and ions in their cytoplasm Oxygen Requirements Many microbes on this planet live either without oxygen or with minimal oxygen Oxygen levels are _______ beneath the soil or within silt deposits in lakes and oceans Most pathogens thrive in ______-oxygen environments within the host Oxygen Requirements Atmospheric Oxygen (O2) easily diffuses across cell plasma membranes Inside the cell, some of the oxygen is converted into ____________ _________________ (ROS) (e.g. Hydrogen peroxide H2O2) ROS can rapidly damage proteins and DNA Many microbes have evolved ways to detoxify ROS (e.g., aerobes) Many aerobic microbes use enzymes to detoxify ROS Superoxide dismutase converts reactive superoxide ions to hydrogen peroxide _________ converts the hydrogen peroxide to water and oxygen  Oxygen Requirements Obligate ___________ Require O2 for cellular processes Obligate anaerobes Do not use O2 in their metabolic processes Can’t eliminate ROS Tend to die in aerobic environments ________________ Use only small amounts of O2 Live in low oxygen environments Limits ROS Oxygen Requirements Aerotolerant ___________ Do not use O2 in their metabolic processes but can grow in presence Can manage ROS Facultative anaerobes Grow with and without O2 Switch between using aerobic respiration and fermentation Examples of Pathogen s with Oxygen Requirem ents  Control strategies aim to reduce or eliminate microbial contamination Microbial control measures occur in every area of our lives (e.g., water sanitation to hospital and restaurant cleaning standards) Decontamination removes or reduces microbial populations to render an object safe for handling _______________ eliminates all bacteria, viruses, and endospores Required for drugs, objects used for medical procedures, and for lab media and glassware _______________ reduces microbial numbers Use for cosmetics, foods, surfaces, and external medical equipment Temperature Changes Both cold and heat have important roles in ___________ microbial growth Refrigeration (4°C) and freezing (0°C) slow the growth of microbes Slows food spoilage In the lab, used to preserve specimen isolates and increase the shelf life of media Refrigeration preserves clinical samples Temperature Changes Most microbes are sensitive to heat Heat can be used to achieve either sterilization or decontamination ___________ is a machine that applies steam heat along with pressure to sterilize Used for microbiological media and assorted medical or lab equipment Boiling Another way to reduce microbial numbers is through boiling Municipalities often issue a “boil water advisory” when drinking water is contaminated Boiling water for _____ minutes eliminates most pathogenic bacteria, protozoans, and viruses Endospores can withstand _____ of boiling therefore it is not an efficient sterilization method Pasteurization Pasteurization is used to eliminate pathogens (e.g. Listeria, Salmonella, E. coli) Application of moderate heat (below the liquid’s boiling point) Eliminates pathogens and reduces harmless microbes that cause milk spoilage Developed by _____________ Dry heat Incineration or hot-air ovens can also be used for sterilization or disinfection Common examples of dry heat sterilization: Heating an inoculating loop to red hot in a _______________ flame Incinerating waste Placing an object at 170°C (338°F) for 2 hours in a dry heat oven achieves sterilization Radiation Some physical decontamination methods involve radiation, or high- energy waves Radiation can serve as a disinfection or sterilization tool depending on the protocol ___________ Radiation Short wavelength/high frequency higher energy ___________ Radiation Longer wavelength/lower frequency lower energy Filtration Large volumes of _____ ________ can be passed through microbe- capturing filters Filter pore sizes can even be made small enough to remove viruses High-efficiency particulate air (HEPA) filters remove microbes and allergens from the air Germicides are chemical controls that limit microbes Chemical control of microbial growth involves chemicals called germicides Germicides that ________ microbes are classified as microbiocidal Germicides that only _________ microbial growth are microbiostatic Two key classes: Disinfectants – used to treat inanimate objects Antiseptics – applied to living tissue Alcohols Alcohols Intermediate-level disinfectants Denature proteins and attack lipid membranes Example: ____________ and isopropanol Optimal concentration is ____________ Used to disinfect small equipment (e.g., thermometers, scissors, stethoscopes) Peroxygens Peroxygens _______________ germicides at high concentrations Can be used as antiseptics and disinfectants Strong oxidizing properties Examples: hydrogen peroxide, peracetic acid Detergents Detergents Cleaning agent ____________ molecules having both hydrophilic and hydrophobic parts Remove water-soluble and water-insoluble substances Some detergents damage the lipid envelope of certain viruses and the lipid membrane of certain bacterial cells Many factors must be considered to select an appropriate germicide Item uses Germicide ____________ Germicide concentration and treatment times Types of infectious agents being controlled Presence of organic and inorganic matter Impact of germicide residues on equipment use Germicide _____________ Different control methods work for different microbes Mycobacterium Control Mycobacterium species cause tuberculosis and leprosy Contain cell walls rich in waxy ______________ Harder to kill, more resistant Spread by airborne droplets Therefore, control measures target reducing airborne particles from infected individuals  Different control methods work for different microbes Endospore Control Endospores are dormant structures Can revert to growing (vegetative) cells once favorable growth conditions are restored Endospores survive drying, radiation, boiling, chemicals, and heat treatments Most effective way to ensure elimination of endospores is by _________ Other methods include ____________________ vapor at high heat or sporicides Concept Questions 1. Two bacteria species were left in the incubator for 6 hours. Species A replicates 4 times during that time period, and Species B replicated 7 times during that time period. What are the generation times for each species? If these are pathogenic species, which one would be more dangerous and why? 2. What is the difference between sterilization, decontamination, and disinfection? 3. List and explain the five different oxygen requirements we’ve discussed. 4. Why is it necessary for aerobic species of bacteria to have a method to detoxify reactive oxygen species (ROS)? 5. We’ve talked about many things that affect bacterial growth. How might these factors (temp, pH, nutrients, salinity, etc.) contribute to why we’ve only classified less than 1% of bacteria?