Lecture 4: Bacterial Growth

(Bacterial Growth) Lecture 4 Toxin Review: · Endotoxin eg. Lipid A in LPS · Exotoxin eg. tetanus toxin, botulinum -part of cell wall -lipid molecule (fat) -released from cell when the cell dies and disintegrates (Always in gram -) Factors that affect bacterial growth: · Metabolism · Temperature -produced by bacterial cell (synthesized in ribosomes) >this means its a protein -released from cell in many ways, damages other cells -enterotoxin (intestines), neurotoxin (tetanus), cytotoxin (trash cells in contact with) Metabolism: the sum total of all chemical reactions happening in the body/organism ↳ catabolic: releases energy · PH · Osmotic Pressure · Gas · Chemicals (metals, nutrients... ) · Environment (intracellular vs. extracellular) Reaction Rates ↳ anabolic: stores energy Catabolism: chemical reactions that release energy, breakdown of organic compounds (releases ATP) Anabolism: chemical reactions that require energy, building of complex organic molecules from simpler compounds (stores ATP) · temperature can speed up a reaction, but temperatures above 55* denatures the proteins ↳ enzymes are used so you don't have to increase the temp · Biological catalysts Enzymes are affected by: · Temperature · may need co factors (makes them function belter) · saturation Enzymes · makes chemical reactions happen 100,000,000x faster · pH · recyclable, unchanged during reaction · salt concentration · inhibitors (mercury, silver) Energy production · most microbes use carbohydrates as main energy source · glucose is the most common nutrient source ↳ cellular respiration Respiration Aerobic: -produces more ATP (~38) -obligate aerobes NEED oxygen to grow -aerobic Anaerobic: -Less ATP produced (2-4) -anaerobic ↳ fermentation (final product is pyruvate) · NEED TO PRODUCE ATP TO RUN CELL PROCESSES Temperature -grows slower -obligate anaerobes CANNOT grow in presence of oxygen · psychrophiles(-5 to + 15* C) Energy sources: · Glucose · psychotrophs (20-30* C) -Listeria · Lipids (fats) -most pathogens · Proteins -broken down by lipases · mesophiles (25-45* C) -broken down by proteases · thermophiles (45-70* C) · hypothermophiles (70-110* C) PH · a pH of 5-8 is the usual activity zone for human pathogens (neutrophiles) · at higher or lower pH's the proteins get denatured Active sites are in the corners When stretched out they no longer can work Osmotic Pressure 1. isotonic: no osmotic flow occurs and the cell is a normal size and shape 2. hypotonic: water flows in the cell causing it to swell all big or burst (hemolysis) · more solutes in cell than outside 3. hypertonic: water flows out of the cell causing it to shrivel (crenation) · more solutes outside cell than inside ·plasmolysis: causes growth inhibition Hypertonic Environment Tolerance · Obligate halophiles: requires high salt concentrations for growth ↳ not human pathogens · faculatative halophiles: tolerates salt from 2-15% ↳ Enterococcus, vibrio, some Staphylococci Environmental Factors · intracellular vs. extracellular growth (inside or outside of cells) · intracellular organisms: -evade defense mechanisms -need for antibiotics to penetrate host cell to be treated -some cannot grow on artificial media Chemical Factors · sources of C, N, O, S, P, and trace elements · sources of organic growth factors ↳ yeast extract in artificial media ↳ cysteine or other amino acids Gas · oxygen requirement can be used to classify bacteria -may be dependent on host cells for energy ↳ chlamydia* · extracellular growth -can grow anywhere in body Strict aerobe, facultative anaerobe, strict anaerobe, aerotolerant anaerobe, microaerophile Bacterial Growth: I. Reproduction I. Bacterial Reproduction · Binary fission: splitting into two II. Generation Time III. Growth Kinetics IV. Biofilms V. Lab Growth II. Generation Time · the time it takes for one bacterium to divide into two · dependent on media and growth conditions · aerobic bacteria grow faster (more ATP) III. Bacterial Growth kinetics · Lag phase, log phase stationary phase, death/decline phase · antibiotics are best used on the log phase (exponential phase) IV. Biofilms · a community of bacteria that attaches to a surface to create a mound ↳ difficult to treat (antibiotics ineffective) ↳ can harden-WBC cannot penetrate ↳ acts as a "home base" V. Bacterial Lab Growth · need nutrient material (solid, semi-solid, or liquid) ↳ should be sterile · agar: complex polysaccharide from algae for solid culture ↳ matrix looks like gelatin ↳ often add animals blood (sheep, horse) for nutrients · Bacteria grow in colonies · You often need to know the growth requirements in order to successfully grow them hemolysis: breakdown of blood cells in agar plates ↳ used for presumptive bacterial identification of streptococcus species Alpha a: partial breakdown of RBC (greening) around and under colony Beta B: total breakdown (clearing) of RBC around and under colony Gamma y: no breakdown of RBC around or under colony complex media: often used for growing most human pathogens, they are rich in nutrients and are used to grow lots of bacteria differential media: used to see differences between different groups of bacteria ↳ eg. blood agar (hemolysis) selective media: only allows targeted bacteria to grow ↳ eg. MacConkey plate only grows G-bacteria and differentiates between them (Food pathogen) LISTERIA MONOCYTOGENES · Illness can stay hidden for long periods of time due to vague symptoms, but is often fatal · Listeria is very hardy, can survive in low temperature, high acidity, and salt concentrations · widely distributed in soil > gets on grass > cows eat grass > we eat cows · Facultatively anaerobic, Gram + bacillus, non-spore forming, psychotroph ↳ grows well on complex media (BAP) ↳ wide temp range (3-42* C) ↳ wide pH range (5.5-9.5) ↳ high salt concentrations · Transmission: fecal-oral transmission · Virulence Factors: gene Act A codes for "invasin", listerolysin, phospholipases · Pathogenecity: -invasion of bacteria through gastric epithelial cells (rearrangement of actin propels bacteria like a rocket into the next cell) -grows in macrophages (strongest WBC), destroys the phagolysome with listerolysin -other phospholipases (hemolysins) destroy cell membranes -can grow intracellularly or extracellularly - protein Act A binds to the actin cytoskeleton and builds a tail that pushes the bacteria into to adjacent cell Symptoms · in animals: -CNS infections "circling disease" -septic abortion (bacteria enters bloodstream) · in man: -food borne disease (feeling queasy or unwell) -CNS infections -abortion -meningitis, encephalitis, septicemia -death (mortality is 20-50%) · pregnant women (special case) -influenza like bacteremic illness that can result in abortion or stillbirth -baby takes the brunt of the infection Elderly and immunocomprimised > risk (Food pathogen) LISTERIA MONOCYTOGENES Epidemiology · hard to track because of long incubation period and underreporting · estimated to be responsible for ~1700 cases of invasive disease in the US yearly · Fatal in about 1/3 of cases even with appropriate antibiotic treatment Prevention/Treatment · No vaccine · Antibiotics for treatment but you have to diagnose the infection in time