01 Basic Bacteriology Flashcards
What is Peptidoglycan?
Single covalently linked macromolecule (peptides, sugars). Provides rigid support for the cell. Maintains shape of cell and allows cell to withstand media of low osmotic pressure, such as water
What is the cell wall like for Gram (+) bacteria?
Thick peptidoglycan layer
What is the cell wall like for Gram (-) bacteria?
Complex outer layer consists of lipopolysaccharide (endotoxin), lipoprotein, and phospholipid. Periplasmic space b/w outer membrane layer and the cytoplasmic membrane. Thin peptidoglycan layer
What is unique about Mycobacteria?
“acid-fast” - inability to be gram-stained due to high concentration of mycolic acids. Classified as Gram (+)
What is a bacterial Capsule?
Gelatinous layer covering the entire bacterium. Composed of polysaccharide, sugar components vary among bacteria species
What are the functions of bacterial Capsules?
Determines virulence: limits ability of phagocytes to engulf the bacteria. Adherence of bacteria to human tissues
What do bacterial Capsules allow us to do?
Lab identification (use of antiserum against the capsular polysaccharide). Capsular polysaccharides used as antigen in vaccines (capable of eliciting protective antibodies)
How can Flagella help E.coli, Proteus sp.?
Propell the bacteria up the urethra into the bladder –> UTIs
What is an example of Flagella being used for lab identification?
Salmonella sp. - identified by use of specific antibodies against flagellar proteins
What are Pili?
Hairlike filaments that extend from the cell surface. Found mainly on Gram (-)
What are the Functions of Pili?
Mediate the ATTACHMENT of bacteria to specific receptors on the human cell surface –> initiates infection. Forms attachment between donor and recipient bacteria during CONJUGATION and allow genetic exchange
What is Glycocalyx?
Polysaccharide coating that is secreted by many bacteria. Covers surfaces like a film allowing bacteria to ADHERE firmly to various structures (skin, heart valves, catheters). Mediates adherence Strep mutans to surface of teeth –> forms plaque, precursor of dental carries
Which gram stain correlates with positive/negative?
Positive (Blue). Negative (Red)
What are the steps in gram staining?
Crystal violet dye stains cells blue. Iodine solution forms complex with violet. Solvent (acetone or EtOH) extracts blue (easier from lipid-rich, thin walled Gram (-)). Red dye safranin stains decolorized Gram (-) red; Gram (+) remains blue
Why are Mycobacteria NOT seen on Gram-Stain?
Acid-fast. Too much lipids in cell wall
Why are Treponema pallidum NOT seen on Gram-Stain?
Too thin to see
WHy are Mycoplasma pneumoniae NOT seen on Gram-Stain?
No cell wall; very small. This causes “walking pneumonia”
Why are Legionella pneumophila NOT seen on Gram-Stain?
Poor uptake of red counterstain
Why are Chlamydiae, Rickettsiae NOT seen on Gram-Stain?
Intracellular; very small
What is the common morphology of Gram-Positive Cocci?
Clusters. Chains
What are some common Gram-Positive Cocci found in CLUSTERS?
Usually characteristic of Staphylococcus spp., such as S. aureus
What are some common Gram-Positive Cocci found in CHAINS?
Usually characteristic of Streptococcus spp., such as S. pneumoniae, Group B streptococci (GBS)
What are some common Gram-Positive Bacilli that are THICK?
Usually characteristic of Clostridium spp., (i.e. C. perfringens, C. tetani)
What are some common Gram-Positive Bacilli that are THIN?
Usually characteristic of Listeria spp.