Structure Of Bacteria PDF

STRUCTURE OF BACTERIA CONT………. Cytoplasm  It is a gel-like matrix composed of water, enzymes, nutrients, wastes, and gases and contains cell structures such as ribosomes, a chromosome, and plasmids.  No organelles (NO Mitochondria, No Golgi, etc.)  metabolism and replication are carried o...

STRUCTURE OF BACTERIA CONT………. Cytoplasm  It is a gel-like matrix composed of water, enzymes, nutrients, wastes, and gases and contains cell structures such as ribosomes, a chromosome, and plasmids.  No organelles (NO Mitochondria, No Golgi, etc.)  metabolism and replication are carried out in cytoplasm Ribosomes  Bacterial ribosomes are the site of protein synthesis as in eukaryotic cells, but they differ from eukaryotic ribosomes in size and chemical composition.  Bacterial ribosomes are 70S in size, with 50S and 30S subunits, whereas eukaryotic ribosomes are 80S in size, with 60S and 40S subunits.  This ribosomal differences between humane and bacteria are the basis of the selective action of several antibiotics that inhibit bacterial, but not human, protein synthesis Nucleoid  Nucleoid - The nucleoid is a region of cytoplasm where the chromosomal DNA is located.  Most bacteria have a single folded chromosome that is responsible for replication  There is no nuclear membrane Non essential components Flagella Used for Motility (movement) Flagella are long, whiplike appendages that move the bacteria toward nutrients and other attractants Swarming :Swarming motility is the movement of bacteria over a solid surface by rotating flagella. – Spread across Petri Dish Medical important of flagella  Flagella are medically important for two reasons: (1) Some species of motile bacteria (e.g., E. coli and Proteus species) are common causes of urinary tract infections. Flagella may play a role in pathogenesis by propelling the bacteria up the urethra into the bladder.  (2) Some species of bacteria (e.g., Salmonella species) are identified in the clinical laboratory by the use of specific antibodies against flagellar proteins Pilli Short protein appendages – smaller than flagella  Advantage of pilli 1 Attachment to specific receptors on the human cell surface, which is a necessary step in the initiation of infection for some organisms E.g. E. coli Pilli  2-A specialized kind of pilus, the sex pilus, forms the attachment between the male (donor) and the female (recipient) bacteria during conjugation Called F-pilus  Plasmid  Extranuclear genetic elements consisting of DNA Transmitted to daughter cells during binary fission Plasmids carry the genes for the following functions and structures of medical importance:  (1) Antibiotic resistance, which is mediated by a variety of enzymes.  (2) Resistance to heavy metals, such as mercury, the active component of some antiseptics (e.g. mercurochrome)  (3) Resistance to ultraviolet light, which is mediated by DNA repair enzymes.  (4) Exotoxins, including several enterotoxins.  Capsule ❖ Glycocalyx or slime layer: Viscous layer secreted around the cell wall. antigenic in nature Advantage: 1-Adhere bacteria to surface 2-Prevents Phagocytosis 3-Protects bacteria from lytic enzymes 4-capsular polysacharide is one of the key components for bacterial biofilm Biofilm  A biofilm is an group of interactive bacteria attached to a solid surface or to each other and encased in an exopolysaccharide matrix.  biofilm formation on indwelling medical devices is a common cause of hospital-acquired infection  Some of the bacteria within the biofilm show marked resistance to antimicrobials  Biofilm  Streptococcus mutans which causes dental caries uses the sugars in food to build its capsule is example on biofilm Endospores endospore is a dehydrated ,tough and non reproductive stage of bacteria that allows it to survive unfavorable conditions like: Low nutrient conditions Radiation High temperatures disinfectants  When growth requirement depleted  When condition was unfavorable for growth Sporulation: adaptive response that allows the organism to survive adverse conditions by formation of spores from vegetative cells  The endospore is able to survive for long periods of time until environmental conditions become favorable for growth, The endospore then germinates, producing a single vegetative bacterium.  Endospore production is usually associated with Gram Positive bacteria ❖Example : Clostridium (gangrene) Bacillus (anthrax) Endospore structure  Coat (keratin-like structure)  cortex (thick peptidoglycan)  core (bacterial chromosome).  Probiotics  Probiotics are live nonpathogenic microorganisms administered to improve microbial balance, in the gastrointestinal tract or vagina.  Probiotics, such as Lactobacillus spp., Bifidobacterium spp. and Saccharomyces boulardii, are living microorganisms or endospore like Bacillus endospore that confer health benefits on the host. They are taken with food or as capsules/tablets and powder. Probiotic benefits  Probiotics improve antibiotic therapy as they reduce microbial adhesion and growth  possess immunomodulatory properties and improve intestinal barrier integrity.  may help children get over diarrhea caused by rotavirus more quickly.  In patients treated with antibiotics, probiotics promote the recovery of microbiota and increase treatment tolerability. Spore forming probiotics  Products containing endospores of members of the genus Bacillus are used commercially as probiotics, and they offer some advantage on lactobacillus and bifidobacterial in that they have high stability to the surrounding atmospheric conditions such as :  heat  gastric conditions  moisture Spore forming probiotic Example : Bacillus clausii  Bacillus clausii strains are used as probiotics mainly because of their immune-modulatory and antimicrobial properties.  over-the-counter (OTC) B. clausii strains available as probiotics for human use in acute diarrhea BACTERIAL GROWTH  Growth of Bacteria Growth is the orderly increase in the sum of all the components of an organism Bacteria reproduce by binary fission, a process by which one parent cell divides to form two progeny cells. Because one cell gives rise to two progeny cells, bacteria undergo exponential growth (logarithmic growth) One cell becomes colony of hundred cells Generation Time Time required for cell to divide. For many "typical" bacteria under "ideal" conditions this doubling time may be as fast as 20 minutes. E. coli generation time = 20 min –20 generations (7 hours), 1 cell becomes 1 million cells!  geometric progression: 2, 2x2, 2x2x2, 2x2x2x2, etc Growth of Bacteria  The doubling (generation) time of bacteria ranges from as little as 20 minutes for Escherichia coli to as long as 18 hours for Mycobacterium tuberculosis  The doubling time varies not only with the species, but also with the amount of nutrients, the temperature, the pH, and other environmental factors  Factors affect bacterial growth  The growth of microorganisms is influenced by various factors of their environment. 1-Physical factors (Temperature ,PH ,Osmotic pressure) 2-Chemical Requirements 3-Oxygen Requirements Physical factors  Temperature  PH  Osmotic pressure  Temperature  Temperature is the most important factor that determines the rate of growth, multiplication, survival, and death of bacteria.  High temperatures damage bacteria by denaturing enzymes, transport carriers, and other proteins. Temperature  Cold temperatures are often used to slow microbial growth and thus preserve foods.  Freezing temperatures do not kill microbes but preserve them in "suspended animation."  Freeze-drying or lyophilization is often used to preserve microbial cultures  Lyophilization is a process whereby a product is dried by removing the water under low temperature and pressure  A properly freeze-dried bacterial strain can be stored for years  PH  pH refers to negative logarithm of hydrogen ion concentration.  Microbial growth is strongly affected by the pH of the medium.  pH abnormality disrupt the bacterial plasma membrane.  Optimal acidity pH values between 6 - 8.  Exception, Helicobacter pylori which inhabits the stomach with a pH approaching pH 1. Osmotic pressure (solutes and water activity)  Osmotic pressure is the minimum pressure needs to be applied to prevent the inward flow of water across cytoplasmic membrane  Osmotic pressure is of vital importance in cell growth. Osmotic pressure (solutes and water activity) If a cell is put in a solution that has a solute concentration higher than its own, then it will shrink up. If it is put in a solution with a lower solute concentration than its own, the cell will expand and burst. Osmotic pressure (solutes and water activity)  Salt and sugar are used to create hypertonic environment for microorganisms and are commonly used as food preservatives  When a cell is placed in a hypertonic solution, water actually flows out of the cell into the surrounding solution thereby causing the cells to shrink and lose its turgidity.  Hypertonic solutions are used for antimicrobial control. Chemical Requirements 1 Water 2 Elements A– Carbon (50% of cell’s dry weight) Chemical Requirements  Carbon Source: A-Organic compounds - glucose and other sugars, amino acids, sometimes complex preformed organic compounds (ie. vitamins, growth factors). B-Inorganic carbon - carbon dioxide Capnophiles Capnophiles are microorganisms that grow strongly in the presence of high concentrations of carbon dioxide. Typically, in a cell culture the CO2 concentration is around 5%.  capnophiles may require carbon dioxide in their metabolism Bacteriological incubator: Cells are grown and maintained at an appropriate temperature and gas mixture of oxygen, carbon dioxide, and nitrogen in a cell incubator. Oxygen Requirements  For most organisms, an adequate supply of oxygen enhances metabolism and growth.  Because the use of oxygen generates two toxic molecules, hydrogen peroxide (H2O2 ) and the free radical superoxide (O2 ), bacteria require two enzymes to utilize oxygen. The first is superoxide dismutase, which catalyzes the reaction 2O2 + 2H+ → H2O2 + O2  and the second is catalase, which catalyzes the reaction 2H2O2 → 2H2O + O2 Oxygen Requirements Bacteria types according to oxygen requirement: obligate aerobes – M. Tuberculosis, are obligate aerobes; that is, they require oxygen to grow facultative anaerobes – can use O2 but also can grow without it such as E. Coli, are facultative anaerobes; they utilize oxygen, if it is present, to generate energy by respiration, but they can use the fermentation pathway to synthesize ATP in the absence of sufficient oxygen. Oxygen Requirements Microaerophilic: grow best at very low levels of oxygen  Obligate anaerobes –such as Clostridium tetani, which cannot grow in the presence of oxygen because they lack either superoxide dismutase or catalase, or both. Obligate anaerobes vary in their response to oxygen exposure; some can survive but are not able to grow, whereas others are killed rapidly. Stages of bacterial growth  Stages of Growth  When an organism is inoculated into a nutrient solution Bacteria has 4 distinct growth phases  1-Lag phase – making new enzymes in response to new medium during lag phase vigorous metabolic activity occurs but cells do not divide. This can last for a few minutes up to many hours.  Stages of Growth  2-Log phase – exponential growth –Most sensitive to drugs and radiation during this period The log (logarithmic) phase is when rapid cell division occurs. β-Lactam drugs, such as penicillin, act during this phase because the drugs are effective when cells are making peptidoglycan (i.e., when they are dividing). The log phase is also known as the exponential phase.  Stages of Growth  3-Stationary phase – The stationary phase occurs when nutrient depletion or toxic products cause growth to slow until the number of new cells produced balances the number of cells that die, resulting in a steady state – death rate = division rate  4-Death phase – Rate of cell death is faster than regeneration. The final phase is the death phase, which is marked by a decline in the number of viable bacteria.