Intro to Bacteria Flashcards
Differences between Euk cells and Prok cells? significance?
Euk- membrane bound organelles
- diploid
- multiple chromosomes
- have sterols in membrane
- energy synthesis done in mitochondria
- has nucleus
Prok- no membrane bound organelles
- energy synthesis done in cytoplasm
- peptidoglycan cell wall- antibiotic target
- smaller ribosomes, different components
- smaller cells
- circular, haploid chromosomes
- no nucleus
- reproduction binary fission (asexual) significant: many distinctions provide basis for antimicrobial action
Macroscopic distinction of bacteria? what things to we observe in colonies of bacteria?
Growth characteristics on nutrient and selective media
Colony:
- color, size, shape, smell
- antibiotic resistance
- fermentation of sugars
- lysis of RBCs (hemolysis)
What are the 3 basic shapes of bacteria?
- round- cocci
- rods- bacilli
- spirals - spirillium
- each bacteria has characteristic arrangements, some make chains, some have flagella
What is the gram staining technique?
allows clinicians to separate bacteria into 2 major classes of bacteria, develop an initial diagnosis, and initiate therapy based on differences in cell wall structure
-ex. staf vs strep
gram negative color? gram positive?
negative- red
positive- purple
T/F All bacteria can be classified by gram staining.
False
- Mycobacterium (waxy outer coat)
- Mycoplasma (no peptidoglycan)
- Chylamydia trachoma’s (atypical cell wall)
What are the step of the gram staining technique?
- Crystal violet - both are purple
- Gram’s Iodine - both purple
- Decolorizer (alcohol or acetone)- gram positive stays purple, gram negative becomes colorless
- Safranin Red– gram positive stays purple, gram negative turns red
What are metabolic distinctions of bacteria?
- oxygen requirements: aerobic or anaerobic growth
- substrate utilization: lactose or non lactose fermenter (acid or gas end products)
- production of specific enzymes (catalase)
- automated procedures have been developed for distinguishing members of certain groups of bacteria based on these properties
What are antigenic distinctions of bacteria?
- strains of bacteria can be distinguished using antibodies to detect characteristic antigens expressed by the bacteria, this is called serotyping
- this method is important for identifying bacteria difficult or dangerous to grow
What are genetic distinctions of bacteria?
- most precise method for classifying bacteria
- specific DNA sequence detected using DNA hybridization, PCR, and DNA sequencing
- doesnt require living bacteria and can be used for rapid detection
- highly conserved sequences identify genus
- highly variable sequences identify species of subspecies for epidemiological investigations
- methods: analysis of DNA fragments, plasmid analysis, ribotyping
What are 5 methods used to differentiate or classify bacteria?
- colony morphology media
- gram staining morphology
- metabolic signature
- detection of characteristic surface antigens
- genetic makeup
Describe the cytoplasmic structure of a prokaryotic cell?
Contains:
- DNA chromosome
- mRNA, ribosomes
- proteins
- plasmids
- storage granules
- transcription and translation can occur at the same time
Functions of the cytoplasmic membrane in bacteria? Different from Euk?
- responsible for many functions that occur in Euk organelles (e- transport, ATP synthesis, DNA synthesis)
- structurally resembles Euk cytoplasmic membrane but no sterols
Characteristics of the Cell Wall of bacteria?
- outermost component common to all bacteria (except mycoplasma)
- structural components and functions distinguish Gram + from Gram -
- prevent osmotic lysis of cytoplasmic membrane, determines and maintains cell shape
- consists of components unique to bacteria and repetitive structures elicit innate immune response
- contain peptidoglycan
Structure of peptidoglycan?
- mesh (exoskeleton) that cover whole bacteria
- alternating sugars of N-acetylmuramic acid (NAM) and N-acetylglucosamine (NAG)
- off of each NAM component there are four peptides (tetra peptide) that are involved in cross linking with adjacent sugar chains, makes it rigid
- unique to bacteria
What does lysozyme do to bacteria cell wall?
it cleaves the beta 1,4 bond between NAM and NAG, kills cell
What bond is broken and used for cross linking in bacteria cell walls? penicillin?
- bond between D-alanine and D-alanine
- penicillin looks like D-alanine so the enzyme involved in cross linking binds it, so no cross linking, cell lyses
What are transpeptidases?
- mediate cross linking
- enzyme that binds penicillin instead of D-alanine
Describe the gram positive cell wall?
- thick layer of peptidoglycan protects from drying and desiccation
- contains techoic and lipotechoic acid
- pentaglycine bridge expands the cross linking in staph
What are the two types of teichoic acids? characteristics?
- wall teichoic acids (WTA, TA)- polymer of glycerol or ribitol phosphate covalently attached to peptidoglycan
- lipoteichoic acid (LTA)- polyglycerol phosphates covalently linked to glycolipids in the cytoplasmic membrane
Characteristics:
- very antigenic, different serotypes exist
- promote adherence between bacteria and to mammalian cells
- can induce inflammation and septic shock
Describe the gram negative cell wall?
- more complex
- periplasmic space with thin layer of peptidoglycan
- outer membrane with lipopolysaccharides
- cross linking different and much less than Gram +
Describe the periplasmic space in gram - bacteria? what does it contain?
- space between cytoplasmic membrane and outer membrane of gram - bacteria
- contains gel like peptidoglycan with little to no cross linking
Contains:
- hydrolytic enzymes to break down large macromolecules for metabolism
- binding proteins for uptakes of metabolites
- collagenases, proteases, hyalaudinases, and antibiotic inactivating enzymes (Beta-lactamases)
Describe the outer membrane in Gram - bacteria?
- assymetrical bilayer structure (outer and inner leaflet)
- outer layer consists of lipopolysaccharides (LPS) -barrier to large hydrophobic molecules (lysozyme, antibiotics-vancomycin), and protection from adverse environments
- small hydrophilic molecules pass through transmembrane proteins called Porins
- has proteins that mediate interactions with host cells
Describe the structure of lipopolysaccharides?
- glycolipid only in the outer leaflet of Gram - outer membrane
- aka endotoxin- major mediator of fever and inflammation caused by infections with Gram - bacteria
- in large doses, can cause systemic shock and even death
- O antigen portion can change
What are the components of LPS?
Lipid A -mediates endotoxic activity
-phosphorylated glucosamine disaccharide backbone with fatty acids, that link lipid A in the outer membrane
Core polysaccharide -linked to Lipid A
-short series of sugars nearly the same in most Gram -
O antigen -outer most portion
- long hydrophilic carbohydrate chain up to 40 sugars in length, extends away from bacteria
- covers bacterial surface and excludes hydrophobic compounds and antibiotics
- highly antigenic and variable, this is the reason for different antigenic specificities of Gram - (E coli O 157)
What are specialized external structures of bacteria? does every bacteria have them?
- not all bacteria have them
- structures are dispensable, needed by bacteria under certain circumstances
- capsule
- biofilm
- flagella
- fimbriae
- spores
Function of the capsule?
- gelatinous covering entire bacterium
- composed of polysaccharide (sometimes peptide)
- serotypes distinguished by antigenic differences in sugars
- protects bacteria from phagocytosis (anti phagocytic)
- promotes non specific adherence to tissues, prosthetic devices, and protects from drying
- makes organism sticky
What is biofilm?
- aggregate of bacteria that bind to each other on a surface within a slime layer
- slime layer- bacteria embedded in an extracellular polymeric substance (EPS) composed of extracellular DNA, protein and polysaccharide
- dental plaque is an example
Flagella? Function?
- long helical protein filaments that endow bacteria with motility (tumbling or swimming)
- antigenic, recognized toll like receptors
- number of flagella varies with species
- located at one end, both ends, or completely surrounding bacteria
Fimbriae? Function?
- hair like structures composed of pilin (protein subunits), cover entire surface of bacteria
- can mediate specific binding to host cells, often required for infection
- F-pili (sex pili) are involved in genetic exchange between bacteria (conjugation)
Spores? Function?Location?
- endospores
- dormant structures formed by Gram + bacteria in response to environmental stress (nutrient depletion)
- resistant to heat, drying, freezing, disinfectants, for months or years
- vegetative state returns when good conditions return
- location in a cell is characteristic of bacteria and can assist in identification
How do bacteria grow?
- microbial cells grow by doubling cell constituents and dividing into two cells
- asexual division (binary fission) and continues exponentially
- time required is called doubling time or generation time
Phases of bacteria growth?
- Lag phase-acclimate to environment
- little change in cell number
- high metabolic activity
- DNA and enzyme synthesis - Log or exponential growth phase- this phase is necessary for some antibiotics (penicillin) to be effective
- multiplication at fastest possible rate - stationary phase
- equilibrium between cell division and cell death
- nutrients exhausted, waste builds, pH increases - Death phase
- number of death exceeds number of newly formed cells
Factors that affect bacterial growth?
- Availability of major and minor essential elements
- carbon source
- nitrogen- protein synthesis
- iron - electron transport
- some pathogens require very little growth (pseudomonas aeruginosa can grow in distilled water or detergent) - Hydrogen
- most bacteria grow best at pH 6-8 -some can grow and sometimes prefer lower pH conditions (lactobacillus) - Temperature
- most grow at 37 C
- some can grow at extremely hot or cold temperatures - Oxygen concentrations
- aerobic metabolism- produces hydrogen peroxide (H2O2) and superoxide anion (O2-) which are toxic
- necessary to have superoxide dismutase to grow aerobically
Obligate aerobes?
- require O2 for growth, cannot ferment sugars
- produce superoxide dismutase
Obligate anaerobes?
- killed by O2
- are fermenters
- lack superoxide dismutase
- cannot use O2 as terminal electron acceptor
Facultative anaerobes?
- can grow in presence or absence of O2
- most bacteria that cause disease
Microaerophilic organisms?
grow only in the presence of low O2 levels
What type of distinction is the classification by response to O2?
metabolic distinction
