Microbiology Flashcards
What are the different cocci shapes?
Diplococci - pairs (pneumococci,meningococci, gonococci)
Chains (streptococci)
Grape like clusters (staphylococcus)
What is a spheroplast?
Gram negative bacterium that has retained some or all of its outer membrane components following lysozyme hydrolysis or inhibition of cell wall synthesis by anti microbial agents
What are the different types of rod shapes?
Square or rounded ends
Short, rounded
Tapered ends - fusiform
Curved rods - helical or spiral shaped, hook shaped
What are the different ribosomes in prokaryotes vs. eukaryotes?
P - 70s
E - 80s
Which are two genera of bacteria that can produce spores and are medically significant?
Genus bacillus - obligate aerobe
Genus clostridium - obligate anaerobe
Both gram positive rods
What do spores do?
Germinate - produce a single vegetative cell which then divides further when nutritional conditions are favorable
What is a big difference in the cytoplasmic membranes of bacteria as opposed to eukaryotes?
No cholesterol or sterols except for mycoplasmas that cause primary atypical pneumonia
What are the orders of the dyes added in the gram stain?
Crystal violet
Iodine
Ethanol or acetone - decolorization
Safranin
What is the structure of peptidoglycan?
N-acetylglucosamine and N-acetylmuramic acid held together by strong beta 1,4 linkage - cleaved by lysozyme found in bacteria, tears, and WBCs - first host cell line of defense
Penicillin inhibits pentaglycine bridges between chains
What are teichoic acids?
Only in gram positive
Wall teichoic acids anchored covalently to n-acetylmuramic acids in peptidoglycan
Membrane teichoic acids covalently attached to membrane glycolipids
Major surface antigens - antibody accessible
Also bacteriophage receptors
What is the structure of the outer membrane in gram negative bacteria?
LPS containing o antigens is anchored - major antigenic determinants - also called endotoxin
Lipoprotein linked to peptidoglycan through protein portion and lipid portion anchored to outer membrane
What are the three regions that form the typical LPS?
Lipid A - endotoxic activity - virtually constant
Core polysaccharide
O antigen - may or may not be present - most that have it are virulent and called smooth and vice versa, often receptors for bacteriophages, imp. for serological typing
What are protoplasts vs spheroplasts?
Upon treatment with lysozyme:
Proto - from gram positive
Sphero - from gram negative, don’t completely shed peptidoglycan due to outer membrane
How are mycoplasmas protoplast-like?
Devoid of peptidoglycan layer
What is a capsule’s role in bacteria?
Protects from phagocytosis
Most are polysaccharides
K antigens
Can be a pathogenic determinant
What are flagellas role in bacteria?
Carry H antigens
Not virulence factor but useful diagnostically
Composed of flagellin
Differences due to amino acid primary structure
Are PAMPs recognized by TLR
What are the different routes of bacteria entry into the body?
Skin - usually only penetrate broken skin
Body cavities - protected by mucus, ciliates epithelium, and antibacterial secretions
Ingestion
Inhalation
Trauma
Arthropod bite
Sexual transmission
How can bacteria penetrate the mucin layer of body cavities?
Lack mucin receptors and avoid being trapped
Production of mucin degrading enzymes
Can move through viscous mucin material
Entry through m cells
How do pili and fimbriae mediate attachment of bacteria?
Tips attach to receptors on host cells
Allow initial contact which is loose and may circumvent negative charges of both membranes
What are aim rial adhesions?
Bacterial cell surface proteins that don’t form pili
Mediate tighter binding of bacteria to host
Ma bind proteins rather than carbs
What are biofilms?
Bacteria binding to each other and surfaces within polysaccharide slime
Bacteria surrounded by wager channels that allow nutrients to reach bacteria and toxic metabolites to diffuse out
Very resistant
Can form on body surfaces and on plastic tubing or plastic implants
What are four methods bacteria use to acquire iron?
- Siderophores - secreted by bacteria and chelate iron, then complex taken up by siderophore receptors and cleaved
- Binding of transferrin, lactoferrin, etc. - sequester iron from them
- Toxins to kill host cells
- Iron abstinence - some bacteria don’t require iron - use manganese instead
What are three ways that bacteria fight phagocytosis?
- Prevent phagosome lysosome fusion
- Escape from phagosome by degrading membrane lipids or forming pores in membrane - more nutrients and protection in cytoplasm
- Adapt to live in phagolysosome - produce enzymes that detoxify ROS or prevent oxidative burst
What are the only effective host defenses to bacteria that survive phagocytosis?
NK cells and cytotoxic T cell response
What can bacteria do to host cytoskeleton?
Bacteria that grow in cytoplasm interact with actin promoting its condensation on one end to propel bacteria through cytoplasm to adjacent cells
What are pathogenicity islands?
Majority of genes encoding virulence factors tend to be clustered together in bacterial chromosome
Usually within or close to tRNA genes
Have been acquired by bacteria through horizontal gene transfer through bacteriophages or transposons
Unstable
Presence of mobility genes
Flanked by direct repeats
What is a type 1 secretory system?
Spans both inner and outer membranes with one channel
No periplasmic intermediate step
Usually one protein
What is a type 2 secretory system?
Several proteins
Inner membrane step
Periplasmic intermediate step
Proteins that use this have a signal sequence
Secretes both virulence and non virulence factors
What is a type 3 secretory system?
Most important one - specialized to secrete virulence factors
Several proteins spanning both membranes that form single channel
Forms needle type structure permitting bacteria to inject factors directly from bacterial cytoplasm to eukaryotic cytoplasm
What is a type 4 secretory system?
Several proteins form channel that span inner and outer membranes
Transfers either bacterial DNA or bacterial effector proteins to mammalian cells
Form pili-like structure (as opposed to needle) between cytoplasms
How can bacteria circumvent complement and phagocytes?
Capsules - can resemble host polysaccharides to avoid antibodies from host binding, can prevent c3 convertase, protect against complement activation and phagocyte mediated killing
LPS modifications - attachment of sialic acid to LPS o antigen prevent c3 convertase, changes in length of LPS o antigen prevents MAC killing
What are exotoxins?
Found in both gram positive and negative
Toxic to mammalian cells
Majority of bacterial toxins encoded on mobile genetic elements such as bacteriophages and plasmids
What are type 1 toxins?
Super antigens
What are type 2 toxins?
Proteins that forms channels in membranes - trigger water rush into cell which will rupture
Enzyme (phospholipase) that degrades phospholipids in membrane
What are type 3 toxins?
AB toxins (evolution favors 5b:1a arrangement) - remain connected through disulfide bond
B unit - binds to host cell receptor and provides specificity
A unit - enzyme activity - removes ADP-ribosyl group from NAD and attach it covalently to host cell protein - effects depend on which protein has been ADP-ribosylated
What are the products of respiratory metabolism and which organisms do it?
Carbon dioxide and water
High amounts of energy per molecule
Strict aerobes and facultative anaerobes
What are the products of anaerobic metabolism and which organisms do it?
Large amounts of organic compounds with or without concomitant gas production
Low levels of energy per molecule
Facultative anaerobes, strict anaerobes, and microaerophiles
Which enzymes detoxify hydrogen peroxide, and superoxide ion?
Catalase
Superoxide dismutase
What are the four classes of microorganisms and which have superoxide dismutase and catalase?
Aerobes - both
Anaerobes - neither
Facultative anaerobes - both
Microaerophiles - SOD and sometimes catalase
What are autotrophs?
Bacteria which derive energy from oxidation of inorganic substrates, or sunlight, and use it to fix and convert CO2 into bacterial mass
What are heterotrophs?
Include all bacteria of medical importance
Require one or more organic carbon components as new sources for bio synthetic precursors
What are the three groups of bacteria with respect to temperature relationships?
Psychrophiles - range 0-25 degrees c, optimum 10-15
Mesophiles - range 15-45, optimum 30-37
Thermophiles - range 35-70, optimum about 55
Most invasive human pathogens are mesophilic
How does osmotic pressure influence bacterial growth?
Conditions of high osmotic pressures inhibit bacterial growth
Medically imp. bacteria grow best at physiological saline pressure
What are indirect measures of bacterial growth?
On liquid culture
Use parameters related to cell mass like changes in turbidity, bacterial dry weight or bacterial nitrogen
What are the four growth phases of bacteria?
- Lag phase - low cellular activity and small cell size, little or no increase in numbers
- Logarithmic phase - very high cellular activity, balanced growth, steady state, large cell size, most susceptible to antibiotics that target cell division
- Stationary phase - low cell activity, birth rate = death rate, small cell size, more resistant to toxic agents
- Death or decline phase
What controls the changes in protein synthesis and expression patterns that occur during different phases of bacterial growth?
Sigma factors of the RNA polymerase - different sigma factor associations target different sets of genes
What is the difference between disinfection and sterilization?
Sterilization - complete absence of life
Disinfection - killing or removal of potentially pathogenic microorganisms, may be achieved without complete sterilization
What are temperature dependent methods of disinfection?
Moist heat more effective than dry, longer the better
Autoclave - treat materials in pressure chamber with steam at 15 lbs pressure (equivalent to 121 d cel.) for at least 15 min
Dry heat - in an oven, 2 hours at 160-180 deg cel is adequate
How does radiation work in disinfection and sterilization?
Ultraviolet or germicidal lamps effective because of sensitivity of DNA to uv radiation
How does filtration work for disinfection and sterilization?
Filters of cellulose ester type are most convenient and available in broad range of pore sizes
What is asepsis?
Technique for maintaining sterility of material already sterilized by providing barrier impervious to bacteria
What are some chemical methods of disinfectants?
Alcohols, detergents, phenols - disrupt cell membrane
Halogens - oxidizing agents
Heavy metals - bind to sulfhydryl groups and block enzyme activity
Hydrogen peroxide
Formaldehyde and gluteraldehyde - alkylating agents
Ethylene oxide - alkylating agent in gaseous form
What is the start codon and the stop codons?
ATG
TAA TAG TGA
How does haploid nature of bacteria allow it to adapt faster?
Don’t have to worry about dominance of a second or diploid allele
How does generation of spontaneous mutations occur in regards to antibiotic resistance?
They arise randomly in the absence of anti microbial agents and may just happen to provide resistance to the antibiotic you give
What are different fates of a missense mutation?
Second spontaneous mutation can rescue original mutation either back to original codon or redundant codon (reversion) or altered codon that doesn’t affect function of translated protein (suppression)
What are the four main forms of recombination?
Homologous
Site-specific
Insertion sequences and transposons
Illegitimate
What is homologous recombination?
Large regions of homology
Requires recA to align homologous sequences
Two crossovers required for linear DNA, one for circular DNA
What is illegitimate recombination?
Nonhomologous
Require enzymes that recognize specific Regions in the DNA
No recA required
What is site specific recombination?
Sites don’t share enough for homologous recombination
Requires site specific recombinase that recognizes site and performs crossover
No recA necessary
What are transposons?
Insertions sequences that can hop from one location in the DNA to another
Requires site specific transposase
Element usually requires all genes necessary to allow it to transpose
Inverted repeats at their ends
Often carry antibiotic resistance genes
What are the three main types of genetic exchange in bacteria?
Transformation
Transduction
Conjugation
What is transformation and what are the two types?
Introduction of naked DNA into a recipient bacterial cell followed by its intro into chromosome or existence as extra chromosomal element (plasmid)
Sensitive to enzymes that degrade DNA (DNAases)
Natural (genetic) - certain bacteria possess ability to take up DNA naturally, then homologous recombination
Induced - high salt concentrations or electroporation in lab make bacteria competent
What is conjugation?
Direct contact between donor and recipient bacteria using pilus
Almost exclusively mediated by plasmids
Conjugative plasmids possess gene to allow transfer and low in copy number, non-conjugative high in copy number
What is a replicon?
Any DNA molecule that contains all genes to duplicate or replicate themselves
NOT a transposon - cannot replicate itself, must jump into something else to be replicated
What are the three independent genetic elements capable of replicating within bacteria? (Replicons)
Chromosome
Plasmids
Bacteriophages (bacterial viruses)
What are the four types of conjugation?
Sexduction - F and F’
Hfr chromosome transfer
Nonconjugative plasmid mobilization
Conjugative transposons
What is sexduction?
F+ donor cells with plasmid encode f pilus and all proteins involved in transferring plasmid to a recipient F- bacteria, which will now express f pilus
What is Hfr chromosome transfer?
High frequency recombination donor strains formed when f plasmid can integrate into bacterial chromosome at various locations using site specific recombination
Part of chromosomal replicon but can still conjugate
What are the two options for an Hfr?
- Can excise to form f plasmid again - can result in F’ element that carries small piece of adjacent chromosomal DNA and leaves behind small element of f in chromosome
- Hfr can conjugate into recipient f cell directly from chromosome in a specific direction, results in time dependent transfer of genome based on its original insertion point
What are mobilizable plasmids?
Lack genes necessary for transfer but do have origin of transfer
Transfer factors can be provided by helper plasmid in same cell
Increases number of plasmids that can be conjugated
What are conjugative transposons?
In addition to hopping into new DNA contain ability to transfer themselves to recipient strain via conjugation
Self transfer or mobilization can occur
What are R or resistance plasmids?
Carry antibiotic resistance markers, often several genes on same plasmid
Others produce small proteins that kill other bacteria and an immunity system to prevent self killing
What is transduction?
Ability of phage to carry chromosomal DNA from an infected donor cell to a newly infected recipient cell
What nucleic acids can a phage carry?
Can package either DNA or RNA but transducing phage must package DNA
What is the lytic phage infection cycle?
Interaction of T4 phage with its receptor on E. coli is very specific lock and key - limited host range of bacteriophage
Phage binds to surface things like pili, flagella, or teichoic acid, then contracts and injects DNA into bacteria
What is generalized transduction?
Normal - packaging and transfer of genetic material in phage particle
Sometimes - aberrant packaging with large fragments of donor chromosomal DNA instead of phage genome - not lytic and can inject recombinant DNA into new host without lysis since phage doesn’t have it’s own genetic material
What is the lysogenic cycle?
Integration of phage genome (prophage) into bacterial chromosome to form lysogen
When cell is stressed, lysogen converted to lytic cycle by production of protease that degrades repressor molecules
Lysogen immune to second or superinfection with another similar phage
What’s a specialized transducing phage?
Rare recombinant formed during excision of prophage upon stress that contain small region of chromosome adjacent to prophage attachment site
What is phage conversion?
If phage carries genes encoding virulence factor, can transform nonpathogenic recipient to pathogenic
How can E. coli be differentiated from salmonella?
E. coli is Lacoste fermenting
Salmonella is non-lactose fermenting
Can cultivate on plates
What are the different types of agar?
Trypticase soy and luria - non selective
Blood - rich medium
Chocolate - blood agar heated to release internal contents of red cell
MacConkey - isolation of gram negative
Colistin-nalidixic acid - isolation of gram positive
What is the oxidase test?
Used to determine if organism produces cytochrome c oxidase - indicates use of ETC
converts colorless solution to purple
What are Koch’s postulates?
- microorganism or other pathogen must be present in all cases of disease
- pathogen can be isolated from diseased host and grown in pure culture
- pathogen from pure culture must cause disease when inoculated into healthy, susceptible host
- pathogen must be reisolated from new host and shown to be the same as originally inoculated pathogen
