Basic Concepts Flashcards
- Identify the 5 major groups of disease-producing microorganisms an their salient features from Table 1.
Prokaryotic: 1. viruses: replicate only within host cells, no nucleus Eukaryotic: 2. bacteria- peptidoglycan cell wall, double stranded DNA 3. fungi- glucans, chitin, mannas in cellular wall (molds are multi-celluar and yeasts are unicellular), sexual or asexual reproduction, can be superficial or deep 4. protozoa: sporozoa, flagellates, amoebae and ciliates 5. helminths- nematodes, tapeworms and flukes;sexual reproduction
- List and describe the bacterial cellular morphology types-shapes and groupings.
coccus(round): diplococci, streptococci (chains), staphylococci (clusters) bacillus(rod-shaped): cocobacilli, fusiform, vibrio (curved); can line up side by side (palisading) helical (spirochete)
- Explain how the Gram stain is used in clinical microbiology.
cell wall structure of the organism that determines gram reaction, gram-positive retain the Gram stain after wash, Gram-negaive will take up safranin counter stain after Gram stain is washed out used to classify organisms and aid in diagnosing infection and determining initial antibiotic tx.
- List the common, medically significant bacterial according to Gram stain reactions.
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- Describe the 4 phases of bacterial growth curve and the relationship of the log phase to antimicrobial therapy and susceptibility testing.
** growth curve described in a closed system
lag phase: inital growth, maturation but not multiplication
exponential phase (log phase): logarithmic multiplication; bacteria must be actively growing for most antimicrobials to work (inhibit cell wall sythesis or protein synthesis); susceptibility test read 18-24hrs of incubation
stationary phase: depletion fo nutrients and byproduct build-up results in longer generation time, number of viable bacteria remain constant
death/decline phase: death of culture
- Describe the temperature requirements of bacteria; define and discuss the clinical relevance of the following terms: psychrophile, meosphile and thermophile.
mesophiles grow between 20-45 deg. C, optimal range body temperature, clinically significant
psychorophiles (cold-lovers) grow below 20 deg C important for food and blood products
thermophiles: optimal between 45 and 60 deg C, significant for some food processing
- Define and discuss the clinical relevance of the following terms: aerobe, anaerobe, facultative anaerobe, microaerophile and aeortolerant.
aerobe: replicate in oxygen and pocess reducing enzymes (ie. TB)
anaerobe: do not replicate in oxygen
facultative anaerobe: can replicate in the presence or absence of oxygen (majority of medically significant bacteria)
microaerophile: (low O2) aerobe which possess low levels of reducing enzymes
aeortolerant: anerobes that can tolerate being exposed to air but cannot initaite growth if O2 is present
- Describe how bacterial genetic material is transferred through transformation and the clinical relevance of each.
transformation: taking up of DNA fragments from related species across their cell wall (internalized and integrated into the recipient’s chromosome (used in genetic engineering, limited number of bacterial species are “naturally copentent”) Strep pneumoniae, Haemophilus influenzae and Neisseria
- Discuss the clinical implications of lysogenic conversion.
lysogenic conversion is a specialized type of transduction that has clinical relevance, it is a process whereby nonvirulent bacterial strains become virulent due to acquisition of virulence genes carried by transducing phage
Contrast the cell wall structure of Gram positive v. Gram negative bacteria.
positive: peptidoglycan is thick, highly cross-linked and woven over the cytoplasmic membrane, teichoic acid negative: outer membrane, petioglycan, open and netlike structure, OM with endotoxin and LPS
Name 3 bacterial enzymes that are used to break down oxidants.
Superoxide dismutase
catalase
peroxidase
(some organisms possess these enzymes and can handle oxygen, others cannot)
What are plasmids and transposons?
plasmid: extrachromosomal circular pieces of DNA in cytoplasm (can be passed to daughter or between bacteria), usually include genes for their replicationand transmission
transposons: fragments of DNA that can excise and transfer themselves from one bacterial chromosome to a recipient without DNA homology (must be incorporated into plasmid or chromosome)
- Describe how bacterial genetic material is transferred through transaction and the clinical relevance of each.
transduction: bacterial DNA can be carried by phages in generalized tranduction wen fragments of degraded bacterial DNA are assembled into phages; specialized transduction, teh injected viral DNA incorportates into specific insertion sites int eh bacterial genome, once activated is spliced out and can take some bacterial DNA with it (lysogenic conversion causes virulance by transduction ie. C. diphtheriae, S. pyogenes and Vibro choleae
- Describe how bacterial genetic material is transferred conjugation and the clinical relevance of each.
DNA is passed directly from one bacterium to another by cell-to cell contact (between related or not related bacteria)
Gram-negative: conjugation requires a fertility factor that carries the genes required to carry out the process of producing a sex pilus for transmission of genes
Gram-positive: donor and recipient cells clump by adhering to each other via adhesins and plasmid DNA is transferred across conjugation bridges into the recipient cells (can include genes called R factors that incode fo antbiotic resistance
