Bacterial Structure and Physiology Flashcards
What is the basic structure of peptidoglycan?
Long polymers of N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM) w/ alternating L-and D- amino acids
The polymers are crosslinked to each other to form 3D sheets
What kinds of bacteria contain teichoic acid in their cell walls?
Gram positive
Which enzymes are responsible for proper crosslinking of NAG/NAM chains?
Penicillin-binding proteins (PBPs)
Which types bacteria are poorly visualized by Gram staining?
Mycobacteria, some spirochetes, and mycoplasma
Mycobacteria: cause TB, leprosy, other diseases
Spirochetes: Treponema pallidum causes syphilis
How do capsules prevent engulfment by phagocytes?
Prevent complement activation via the alternate pathway on the cell surface
What diseases are encapsulated bacteria important in causing?
- Meningitis
- Bacteremia in people without a functional spleen
What are K antigens?
Capsules of certain bacteria used for serological typing
What are flagella designated for serotyping?
H antigens
The presence of flagella can be used to serologically distinguish and classify which bacteria?
Gram-negative enteric bacteria
Ex: Escherichia coli O157:H7 has type 7 flagella and type 157 O antigen
What causes bacterial running?
Counterclockwise rotation of flagella
What causes tumbling of bacteria?
Clockwise rotation of flagella
Describe bacterial ribosomes
What subunits do they include?
70S ribonucleoprotein structures
50S subunit (includes 23S, 5S, 34 proteins)
30S subunit (includes 16S and 21 proteins)
The gene sequence of which portion of bacterial ribosomes can be used to identify bacteria?
Which subunit is it found in?
Why can this be done?
16s rRNA gene sequence
Found in 30S subunit
The sequences of some regions of 16S rRNA gene are unique to various bacterial genera and species
In what ways does bacterial transcription differ from eukaryotic transcription?
- Bacterial RNA polymerase is different
- Genes may be organized into operons (clusters of genes all transcribed from a single promoter onto a single mRNA molecule)
- Occurs in cytoplasm
- Performed concurrently w/ translation
What is an operon?
A cluster of genes that are all transcribed from a single promoter onto a single mRNA molecule
What stage do the Gram-positive bacilli have to be in for spores to develop?
Vegetative (dividing cells)
Which sorts of bacteria can form spores?
Which bacteria specifically?
Some Gram-positive bacilli
Clostridium and Bacillus
How do many bacteria acquire iron from host molecules?
Secrete siderophopres (low molecular weight molecules) that remove iron from host molecules and allow it to be taken up by bacterial cells
(Exceptions: Neisseria meningitidis and Neisseria gonorrhoeae produce surface receptors that bind to lactoferrin and transferrin, then remove and internalize iron)
Which bacteria contain cytochrome c?
What test can detect cytochrome c? What does it measure?
Pseudomonas aueroginosa and Neisseria spp.
Oxidase test: measures ability of bacteria to oxidize and change color of N,N-dimethyl-p-phenylenediamine
What are oxidase positive bacteria?
Bacteria containing cytochrome C
Why would you use MacConkey agar?
MacConkey agar is selective for gram (-) rods
It is also differential for lactose fermentation
What is the difference between an insertion sequence and a transposon?
Insertion sequences (IS) only contain genes for tranposases
Transposons contain genes for transposase AND other genes that may encode antibiotic resistance or virulence determinants.
Note: Transposons may contain IS at each end
What virulence determinants of Escherichia coli are encoded by plasmids?
Enterotoxins (LT and ST)
What virulence determinants of Clostridium tetani are encoded by plasmids?
Tetanus toxin
What is transformation?
Pieces of naked DNA from lysed bacterial cells are taken up by other bacterial cells and incorporated into their chromosomes
What are “naturally competent bacteria?”
Bacteria that are naturally able to take up DNA in transformation
What is transduction?
The mechanism that bacteriophages use for DNA transfer
2 types of transduction:
- Generalized
- Specialized
Can lytic bacteriophages every be useful to humans? How?
Lytic phages can be useful in treating certain bacterial infections in humans
The lytic phage infects the bacterium and causes it to lyse, thus killing the bacteria and potentially eradicating the bacterial infection
Would a beta-lactam antibiotic be useful against gram-positive or gram-negative bacteria?
Both; Both types of bacteria can be treated by beta-lactam antibiotics because both have peptidoglycan in their cell walls (although the layer is thinner in gram (-) bacteria)
What kinds of bacteria contain superoxide dismutase and catalase?
Obligate aerobes, facultative anerobes, aerotolerant anaerobe
What kinds of bacteria (in general) would not contain superoxide dismutase and catalase?
Obligate anaerobes
Which genetic exchange mechanism utilizes a sex pilus?
Conjugation
