2-Bacterial Classification Flashcards
What is serotyping?
can distinguish a particular strain of bacteria with the use of Ab’s which detect characteristic antigens on the bacteria.
When is serotyping used?
Typically used to identify organisms that are either to dangerous or to difficult to grow in the lab, associated with specific disease syndromes, or need to be identified rapidly.
What is biotyping?
Biochemical testing, certain tests go with certain organisms. Connect what tests go with what organism. Catalase, coagulase, indole, etc.
What is DNA hybridization?
When DNA is heated to denaturation temperatures to form single strands and then cooled double helices will re-form (renaturation) at regions of sequence complementarity. This technique is useful for determining sequence similarity among DNAs of different origin and the amount of sequence repetition within one DNA.
When is DNA hybridization used?
Most commonly used for the analysis of sequences of ribosomal DNA to detect the highly conserved sequences of ribosomal DNA (identify a family or genus) and highly variable sequences (identify a family or genus)
What is the gram staining process?
Process: Bacteria Heat Fixed –> Stained with Crystal Violet –> Stained with Iodine –> Unbound and excess stain with washed away with Decolorizer (acetone based) and Water –> Stain with Safranin (Red Counterstain; added to stain any decolorized cells)
What bacterial cannot be classified by gram staining?
• Mycobacteria and mycoplasms cannot be classified by gram stain
What is the coccus shape?
a spherical-shaped bacterium. Many species of bacteria have characteristic arrangements that are useful in identification. Pairs of cocci are called diplococci; rows or chains of such cells are called streptococci; grapelike clusters of cells, staphylococci; packets of eight or more cells, sarcinae; and groups of four cells in a square arrangement, tetrads. These characteristic groupings occur as a result of variations in the reproduction process in bacteria
What is an example of a coccus bacteria?
staphylococcus aureus
What is the bacillus shape?
cylindrical or rodlike bacteria
What is an example of a bacillus bacteria?
B. anthracis
What is the spirillum shape?
Curved shaped bacteria
What is an example of a spirillum bacteria?
spirillum minus
What is the branched filamentous shape?
look like little filaments; often appear beaded when staining
What is an example of the branched filamentous shape?
candidatus savagella
What is the diplococcus shape?
paired spherical bacteria, including those of the genus Diplococcus, some of which are pathogenic
What is an example of a diplococcus bacteria?
neisseria meningitidis
What is the pleomorphic shape?
Different morphological forms of same species or strain. Changes within natural environment
What is an example of a pleomorphic bacteria?
diphtheroids, Corynebacterium sp
What is the cell wall of the gram + bacteria look like?
thick, multilayered cell wall consisting mainly of peptidoglycan surrounding the cell membrane. There is not outer membrane and therefore no hydrophobic barrier.
What are the 2 layers of the gram (-) bacteria?
1) Thin Peptidoglycan layer- makes up 5-10% of the cell wall by weight, no teichoic or lipoteichoic acids. 2) Outer membrane has lipopolysaccharides, access through this outer membrane is through porins. It maintains the bacterial structure and is a permeability barrier to large molecules and hydrophobic molecules. It also provides protection.
What is teichoic acid?
water-soluble polymers, containing a ribitol or glycerol residue linked by phosphodiester bonds; found in cell walls and is chemically bonded to peptidoglycan. Essential to cell viability and important factor in virulence.
What is lipoteichoic acid?
found in cell membrane and is chemically bonded to membrane glycolipid (fatty acid), particularly in mesosome. Anchored into the cytoplasmic membrane, these surface antigens are used to distinguish bacterial serotypes and promote attachment to other bacteria and to specific receptors on mammalian cell surfaces (adherence). When these antigens are shed initiate innate protective responses similar to endotoxin.
Where is teichoic and lipoteichoic acid found?
Gram + bacteria
What cells have the periplasmic space?
Gram (-) cells
What is the periplasmic space?
an area between the external surface of the cytoplasmic membrane and the internal surface of the outer membrane is referred to as the periplasmic space, this is where many of the virulence factors (collagenases, hyaluronidases, proteases, and β-lactamases) are located.
What cells have the LPS endotoxin?
Gram (-) cells
What is the LPS endotoxin?
found on the out leaflet of the outer membrane of Gram- negative cells. Consists of lipid A and a polysaccharide composed of a core and terminal repeating units. The LPS is negatively charged and non-covalently cross-bridged by divalent cations. The LPS serves as an endotoxin (powerful stimulator of the immune system); it is shed from the bacteria into the media and host. The toxicity is associated with the lipid A. It also contains major surface antigenic determinants, including O antigen found in the polysaccharide component.
What type of cells have porins?
Gram (-) cells
What are porins?
In Gram – there are proteins that traverse the lipid bilayer and thus they are transmembrane proteins, they allow the diffusion of hydrophilic molecules (metabolites and hydrophilic antibiotics)
What is the structure of the peptidoglycan layer in gram + bacteria?
highly cross-linked, multilayered (usually thick) peptidoglycan cell wall that traps large crystal violet-iodine complex
What is the structure of the peptidoglycan layer in gram (-) bacteria?
thin (1-3 layers) of peptidoglycan layer linked to an outer membrane; the peptidoglycan is not highly cross-linked, so it easily loses the gram crystal violet/iodine dye complex on decolorization with alcohol
What are pili?
rigid hairlike surface appendages composed mainly of a protein called pilin; typically are small and not coiled in structure. Promotes adherence (adhesins) to other bacteria or to the host and are involved in attachment of donor and recipient bacteria in G- cell conjugation (sex pili; F pili)
What are capsules?
a loose polysaccharide (sticky) or protein layer found in G+ and G- bacteria. The capsule is very important for survival in the host, it is poorly antigenic and antiphagocytic and is a major virulence factor. It also has several other functions: Adherence , Prevent dehydration, Nutrient source, Avoid phagocytosis. Some bacteria will produce a polysaccharide biofilm which establishes a community of microorganisms and protects them from antibiotics and host defenses (ex: tooth plaque).
What are flagella?
one or more ropelike protein appendages for locomotion and contain prominent antigenic determination. Composed of helically coiled protein subunits (flagellin) that are anchored in bacterial membranes through hook and basal body structures and are driven by membrane potential. Provides motility so the bacteria can follow chemotaxis.
What are plasmids?
pieces of DNA that replicate independently of chromosomal replication. They may exist in an episomeform that can integrate into the bacterial chromosome and replicate with it. Plasmids tend to carry antibiotic resistance genes, toxic genes, and transposons (moveable genetic elements).
What is the 1st step in peptidoglycan synthesis?
Synthesis in the Cytosol
UDP-NAG and UDP-NAM polymers formed
Peptides added to UDP-NAM
What is the 2nd step in peptidoglycan synthesis?
Synthesis in the Cell membrane
UDP-NAM transferred to a lipid carrier (bactoprenol)
Bactoprenol is a carrier for NAG-NAM to take it across the membrane, then the carrier gets recycled
UDP displaced
NAG added to NAM
Bactoprenol transports to a cell wall growth point
What is the 3rd step in peptidoglycan synthesis?
Synthesis in the Periplasm or exterior
Autolytic enzymes cut NAG-NAM loose from bactoprenol
New NAG-NAM polymer is added to the cell wall
Cross-linking of peptides occurs
Penicillin Binding Proteins (PBP’s) are enzymes that cross-link amino acids
What is the mechanism of action of penicillin?
Penicillin- inhibit the transpeptidation enzymes involved in cell wall synthesis
Active against G+ and G- Bacteria
React with Penicillin-Binding Proteins
The transpeptidase binds penicillin (which inhibits it) thereby preventing the cell wall from properly forming and causing it to fall apart, as a result killing the cell (bacteriocidal)
Have a β-lactam ring structure that is inactivated by β-lactamases (penicillinases), which are genetically coded in some bacterial DNA or some R plasmids.
What is the mechanism of action of cephalosporins?
What genera form spores?
• Some G+ (but never G-) bacteria such as members of the genera Bacillus and Clostridium are spore formers
o Bacillus antrhacis (anthrax) & Clostridium tetani (tetanus; lock jaw)
What is the importance of spore formation?
• Under harsh environmental conditions, such as loss of a nutritional requirement, sporulating bacteria can convert from a vegetative state to a dormant state, spore. Location of spore may be used in identification of bacterium. The spore is a dehydrated, multishelled structure that protects and allows the bacteria to exist in “suspended animation”, it is the most resistive state of bacterium (difficult to decontaminate with standard disinfectants). However once the bacteria is in a favorable environment it may start back up the germination process essentially coming back to life.
