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Chapter 6 Bacteria and Archaea
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Shapes Cocci Bacilli Pleomorphic
Overall shape is spherical or nearly spherical Bacilli Rod-shaped Some endospore forming Pleomorphic e.g., Coccobacilli—bacilli that are elongated and spherical Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.
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Bacterial Cell Morphology
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Staphylococcus aureus
Shapes Staphylococcus aureus Escherichia coli Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.
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Shapes Coccobacilli Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.
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Shapes Spirals Vibrios Spirillum Spirochetes
Curved or comma-shaped rods Spirillum Thick, rigid, spiral organisms Spirochetes Thin, flexible spirals Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.
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Shapes: Spirals Spirillum Spirochete Vibrio
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Arrangements In addition to their shape, bacteria can also be categorized according to their arrangement and their style of grouping after cell division Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.
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Cocci Diplococci Streptococci Tetrads
Typically appear in pairs—one plane only e.g., Streptococcus pneumoniae Streptococci Beadlike chains e.g., Streptococcus pyogenes Tetrads Produced by division within two planes—cocci arranged in squares of four Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.
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Cocci Sarcina Staphylococci
Cocci arranged in cubes of eight as a result of division in three planes Staphylococci Grapelike clusters formed by cell division in random planes Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.
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Arrangements of Cocci Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.
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Bacilli Diplobacilli Streptobacilli
Paired rods that remain in pairs after division Streptobacilli Fail to separate after they divide and remain in chains Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.
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Arrangements of Bacilli
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Coccobacilli Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.
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Binary Fission Results in two identical daughter cells
Sufficient metabolites necessary to divide A cascade of regulatory events must occur to initiate replication Once replication is started, DNA synthesis must run to completion When metabolites are depleted—cessation Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.
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Binary Fission Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.
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Population Growth Curve
Lag phase Bacteria have to adapt to medium before cell division Cells are metabolically active Logarithmic or exponential growth phase The rate of growth increases with time Each cell introduced to medium divides by binary fission Each subsequent binary fission doubles the bacterial cells Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.
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Population Growth Curve
Stationary phase Occurs when essential nutrients are depleted or byproducts of metabolism accumulate Death phase Begins when growth stops and the number of dead cells is larger than the number of viable cells Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.
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Bacterial Growth Curve
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Measuring Growth Measurement of cell mass Dry weight
More accurate estimation More time-consuming Cells need to be washed and then dried Turbidity (cloudiness) Measured with spectrophotometer In optical density units The greater the cell mass—the less light will pass through Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.
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Measuring Growth Measurement of cell number Direct cell count
Microscopically in counting chambers (Petroff-Hauser chambers)—slide with a grid of 25 small squares Viable counts Only viable cells are counted Pour plating Spread plating Most probable number method Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.
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Slide Counting Chamber
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Factors Influencing Bacterial Growth
Nutritional requirements Temperature Osmotic pressure Other atmospheric conditions Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.
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Nutritional Requirements
Phototrophs Acquire energy from light Chemotrophs Acquire energy from chemical compounds Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.
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Nutritional Requirements
Carbon Provides the backbone for all organic compounds—essential for all life forms Autotrophs Obtain carbon from atmospheric carbon dioxide Heterotrophs Use carbon from organic compounds Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.
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Nutritional Requirements
Photoautotrophs Use sunlight as the energy source Use carbon dioxide as their carbon source Photosynthetic bacteria, algae, green plants Chemoautotrophs Use chemical compounds as the source of energy and carbon dioxide Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.
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Nutritional Requirements
Photoheterotrophs Use sunlight for energy Use organic compounds as carbon source Chemoheterotrophs Use organic compounds for both the source of energy and a carbon source Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.
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Nutritional Requirements
Nitrogen Some bacteria can obtain nitrogen from inorganic compounds such as nitrates Sulfur and phosphorus Can be met by organic compounds or inorganic salts of sulfates, sulfides, and thiosulfates Minerals Required in trace amounts Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.
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Temperature Mesophiles Thermophiles
Optimal growth in moderate temperatures Generally between 25° C and 40° C Habitat: soil, human body, animals Most bacteria fall into this classification Thermophiles Heat-loving organisms Grow best at temperatures of 45° C or higher Hot springs, deep sea hydrothermal vents, tropical soil composts (rotting), hay stacks Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.
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Temperature Psychrophiles (cryophiles) Psychrotrophs
Cold-loving—can grow at 0° C or lower Optimal growth around 15° C Arctic and Antarctic regions Psychrotrophs Grow very slow at 0° C but have an optimal growth range of 25° C to 30° C Abundant in nature and can cause food spoilage at refrigerator temperatures Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.
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Osmotic Pressure Microorganisms with cell walls can withstand some osmotic pressure— osmotolerant Osmophiles—require high solute concentration in the environment for optimal growth Most microbes do not tolerate hypertonic environments Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.
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Tonicity Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.
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Hydrostatic Pressure Pressure that a fluid exerts in a confined space
Barotolerant Microbes that can survive in increased hydrostatic pressures Basophiles Grow best under high hydrostatic pressure Occur only in the deepest part of oceans Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.
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Atmospheric Conditions
Obligate aerobes Grow only in the presence of oxygen Aerobic cellular respiration Obligate anaerobes Grow only in the absence of oxygen Inhibited or killed by the presence of oxygen Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.
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Atmospheric Conditions
Aerotolerant anaerobes Can grow in the presence of oxygen but cannot use oxygen for energy requirements Fermentation only (obligate fermenters) Facultative anaerobes Grow either in the absence or presence of oxygen Aerobic respiration with oxygen—fermentation in the absence of oxygen Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.
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Atmospheric Conditions
Microaerophiles Require a low concentration of oxygen Approximately 2% to 10% less than atmospheric oxygen Capneic Require more carbon dioxide than present in regular atmosphere Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.
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pH pH of natural environments ranges from approximately 0.5 in acidic soils and approximately10.5 in alkaline lakes Optimal pH range varies for microbes Neutrophils—range: 5–8 Acidophils—best pH below 5.5 Alkaliphiles—best pH above 8.5 Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.
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pH Scale Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.
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Genetics Genome Gene The sum of genetic material in an organism
In form of chromosome Nonchromosomal plasmid—bacteria Gene Unit that codes for particular information on a DNA molecule Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.
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Genetics Chromosome Single DNA molecule
Includes proteins (histones) in eukaryotes Prokaryotes do not have proteins associated with their DNA Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.
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Genetics Plasmid Independent from chromosomal DNA Generally circular
Self-replicating Between 5 and 100 genes Not essential for normal bacterial growth Bacteria can gain or loose plasmids Antibiotic resistance Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.
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Genetics Episome A unit of genetic material
Composed of a series of genes (i.e., plasmid) Can integrate itself into the chromosomal DNA of the organism and therefore can stay intact and is duplicated with every cell division It becomes part of the genetic makeup Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.
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Genetics Genotype Phenotype Exact genetic makeup of an organism
Bacterial strains—slightly altered genome Phenotype Observable characteristics of an organism Environmental factors can somewhat alter the appearance = phenotypic plasticity Genotype + environment = phenotype Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.
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Mutations Changes to the base pair sequence of DNA or RNA
Passed on by cell division Random events that are unpredictable Spontaneous Occur naturally—no known cause Induced mutations Due to exposure to radiation or chemicals Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.
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Mutations Mutations may be neutral, beneficial, or harmful
Mutagen is an agent that causes mutations Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.
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Mutations Microlesion Macrolesion
Injury to the DNA that involves only one base pair Macrolesion More than one base pair or several genes are affected Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.
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Mutations Point mutation (base substitution)
A single base is altered; involves the replacement of one base pair with another Most frequent type of mutation Transition—purine or pyrimidine replaces another purine or pyrimidine Transversion—purine replaces pyrimidine and vice versa Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.
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Mutations Frameshift mutation
Insertion or deletion of one or more nucleotide pairs Results in misreading of the genetic code Different product results Nonsense mutation Results in nonsense codon Missense mutation Results in change of amino acid sequence Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.
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Mutations Transposons (jumping genes) Reversions
Genes that move from one segment of DNA to another On chromosomes, plasmids, or within viruses Reversions Are mutants that can revert back to the wild-type phenotypes Restore the original phenotype Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.
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Mutations Inversions Are macrolesions where the order of bases are switched or inverted Produce nonsense codons Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.
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Genetic Transfer in Prokaryotes
Transformation Transfer of free DNA from one cell to another Occurs naturally in many bacterial species Transduction Transfer of bacterial DNA from a bacteriophage into another cell Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.
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Genetic Transfer in Prokaryotes
Conjugation Transfer of genetic material during cell-to-cell contact Between mating cells of the same species or between closely related species Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.
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Classification Prokaryotes are divided into bacteria and archaea
According to Bergey’s Manual of Systematic Bacteriology Much more is known about bacteria than archaea Archaea are a group of bacteria that have different features than other bacteria Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.
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Binomial System of Nomenclature
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Spirochetes Group of helical, motile bacteria
Twisting motions of their axial fibrils Found in various aqueous environments and in association with human or animal hosts Pathogens: Treponema pallidum—syphilis Borrelia burgdorferi—Lyme disease Leptospira interrogans—Leptospirosis Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.
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Leptospira Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.
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Aerobic/Microaerophilic Helical Viroid Gram-Negative Bacteria
They are either slightly curved or have multiple helical turns Motile with help of flagella Live in fresh or coastal waters Some cause disease in humans or animals: Campylobacter, Helicobacter, Bdellovibrio, Vampirovibrio Helicobacter pylori—peptic ulcers, gastritis, duodenitis Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.
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Gram-Negative Aerobic Rods and Cocci
Diverse group—extensively investigated Widely distributed in nature Many are human and animal pathogens Respiratory metabolism—not fermentation Rhizobium, Legionella, Neisseria, Bordetella, Francisella Rhizobia are soil bacteria—nitrogen fixation Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.
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Gram-Negative Rods and Cocci
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Facultative Anaerobic Gram-Negative Rods
Large group of bacteria with simple nutritional requirements Present in soil, water, intestinal tract of animals and humans Enterics: Escherichia, Salmonella, Shigella, Enterobacter, Proteus, Providencia E. coli—“workhorse” in molecular biology Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.
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Facultative Anaerobic Gram-Negative Rods
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Anaerobic Gram-Negative Rods
Can be straight, curved, helical, motile, or nonmotile Present in the GI tract of humans and animals Leptotrichia buccalis and Fusobacterium species are often found along the gum line and tooth surfaces Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.
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Anaerobic Gram-Negative Cocci
Often occur in pairs Found in mouth, intestines, vagina Veillonella causes rare opportunistic infections Often associated with long-standing gingivitis in dental patients Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.
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Rickettsias and Chlamydias
Very small gram-negative bacteria Majority require host for replication Generally rod-shaped but also may look coccoidal Often cause disease Rickettsiae need a vertebrate and an arthropod host Chlamydiae do not infect invertebrates Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.
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Rickettsias and Chlamydias
Rickettsiae rickettsii—Rocky Mountain spotted fever Chlamydiae trachomatis—urogenital infections Picture of pap smear with the organism Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.
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Rickettsia (From Murray PR, Rosenthal KS, Pfaller MA: Medical microbiology, ed 5, St. Louis, 2005, Mosby.) Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.
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Mycoplasmas and Ureaplasma
Smallest of the free-living bacteria Do not have cell walls Pleomorphic Resistant to penicillin, cephalosporins, vancomycin, and other antibiotics that interfere with cell wall synthesis Special growth requirements Can cause disease in humans, animals, and plants Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.
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Gram-Positive Cocci Include aerobic and anaerobic bacteria
Range from harmless to very virulent forms Micrococcus, Staphylococcus, Streptococcus, Peptococcus Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.
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Staphylococcus epidermidis
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Endospore-Forming Gram-Positive Rods and Cocci
Include Bacillus and Clostridium Important in medicine and food industry Spores are resistant to heat and disinfectants Widespread in the soil Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.
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Bacillus Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.
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Endospore-Forming Gram-Positive Rods and Cocci
Clostridium perfringens is widely distributed in the environment Decaying matter, marine sediment, intestinal tract of humans and other animals (cont'd…) Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.
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Endospore-Forming Gram-Positive Rods and Cocci
(…cont'd.) Common cause of food poisoning Bacilli are either obligate aerobes or facultative anaerobes Include free-living and pathogenic species Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.
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Regular Nonsporing Gram-Positive Rods
Obligate or facultative anaerobes Complex nutritional requirements Include Carnobacterium, Lactobacillus, and Listeria Lactobacillus—vaginal smear Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.
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Regular Nonsporing Gram-Positive Rods
Lactobacilli convert lactose and other sugars to lactic acid Most are harmless Some species used in industry Yogurt, cheese, sauerkraut, pickles, etc. Listeria monocytogenes—causative agent of Listeriosis Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.
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Irregular Nonsporing Gram-Positive Rods
Unusual shape—pleomorphic Mostly facultative anaerobes, few obligate aerobes Medically important species: Actinomyces—opportunistic Corynebacterium diphtheria—diphtheria Propionibacterium acnes—acne Actinomyces israelii—periodontal disease, lung infections Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.
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Mycobacteria Gram-positive, aerobic, acid-fast rods
Tend to form filaments Widespread in water, soil, and food sources Some are obligate intracellular parasites in humans and animals Difficult to grow in culture Can colonize in host without symptoms Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.
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Mycobacteria Infections are difficult to treat
Neither truly gram-negative or gram-positive Difficult to treat—naturally resistant to many antibiotics Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.
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Mycobacterium smegmatis
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Nocardioforms Aerobic, gram-positive, catalase-positive rods—form branching filaments Widespread in the environment Opportunistic Infection generally rare Originate in lungs and spread to other organ systems Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.
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Streptomycetes Gram-positive
Predominantly in soil and decaying vegetation Most are spore forming Generally not pathogenic—infrequently cause disease Important source for antibiotics Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.
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Methanogens Are archaea
Grow in anaerobic environments— swamps, marshes, marine sediments, sludge, hydrothermal vents Produce methane as metabolic byproduct Rapidly killed by oxygen Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.
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