Structure, Reproduction & Classification Flashcards
Commensalism
A symbiotic association in which the commensal organism benefits from the host’s food and shelter, and the host is not harmed nor does it benefit
Ex. Saprophytic cells eat dead cells in our ear and external genitals and do not cause us any harm
Mutualism
A symbiotic association in which both members benefit; obligatory and dependent
Ex. E.coli lives in our gut and produces vitamin K
Parasitism
A symbiotic association in which a parasitic microbe is dependent on host and benefits; host is harmed and disease may result (not to be confused with “parasites”)
What are bacteria?
- Prokaryotic; no nuclei, single-called organisms, which live singly, in pairs, chains or clusters
- most common type of microbial infection in Canada
What are viruses?
- Acellular microbes (not alive); not visible by light microscopy
- Obligatory microbes composed of genetic material surrounded by a protein coat
What are fungi?
- Eukaryotic; possess a nuclei and cell wall, organelles, obtain nutrients from other organisms
- Yeasts (unicellular) and molds (multicellular)
What are protozoa?
- Eukaryotic, single-called organisms, possess a nucleus
What are helminths?
- Eukaryotic, multicellular, possess a nuclei, visible with the naked eye
- Infections often diagnosed via microscopic examination of eggs or larvae in clinical specimens
Which type of infection is more serious - viral or bacterial?
Bacterial infections are generally more serious and are more likely to cause an emergency - viruses are very small, not alive and are usually self-limiting
How do antibiotics work?
- Antibiotics work by exploiting the differences between eukaryotes and prokaryotes; thus are own cells go unharmed
- Target cell wall components (i.e. Penicillin) or the smaller ribosomal subunits (i.e. Erythromycin)
Which microbe is the smallest?
Viruses
What are some key characteristics of bacteria?
1) single called organism
2) no nucleus
3) possess smaller separate circles of DNA called “plasmids,” which often contain information related to resistance mechanisms
4) ribosomes are smaller than those of eukaryotes
5) cell wall (composition can vary) and cell membrane
6) external cellular structures such as flagella or pili
What are 5 ways in which bacteria is classified?
1) Cell morphology - shape, arrangement, colony morphology, external structures, capsules, spore formation
2) Cell wall structure - staining and microscopy; Gram and acid fast stains
3) Growth characteristics - oxygen and energy requirements
4) Metabolism - carbohydrate utilization, fermentation end-products, etc.
5) Molecular techniques - DNA sequencing
Bacteria Cell Morphology
- diplococci
- streptococci - chains of round cells
- staphylococci - clusters of round cells
- bacilli - rod shaped
- coccobacilli - oval shaped
- sarcina- tetrad of round cells
- neisseria - diplococci
Bacteria Colony Morphology
- characteristics of colonies grown on agar plates allows for tentative identification
- shape of colony, margin/edge, elevation, surface texture, no pigmentation are all important to identification and there are various possibilities
What are flagella?
- external protein filaments that extend from cell membranes
- motile (rotate 360), allowing microbe to move in a series of tumbles and runs in response to stimuli (light, nutrients, etc.)
- number and location of flagella can be used for classification
- Polar; Vibrio spp. (single), Spirillium spp. (double)
- Peritrichous; E. coli spp. (several hairs)
What are fimbriae?
- straight filaments arising from bacterial cell wall - facilitate formation of biofilms
- shorter than flagella, not used for propulsion but can be used to “pull” the bacterium across a substrate
- allows for adherence, binding to specific host cell receptors - critical step in infection (ex. E. coli binds to intestinal epithelial cells causing GI infection)
What is a conjugation pili?
An external structure on bacterial cell wall which transfers DNA from one bacteria to another and allows for plasmid sharing
What is glycocalyx?
- a protective substance surrounding some bacteria, normally made of polysaccharides
- presence/absence can be used for classification
- slime layer OR capsule
What is a slime layer?
- type of glycocalyx on bacteria
- sticky and loose - prevents dehydration, allows bacteria to bind to surfaces and inorganic material and to form a protective layer encapsulating colonies of bacteria
What is a capsule?
- type of glycocalyx that is firmly attached to the cell surface
- virulence factor that facilitates adherence and impairs phagocytosis - allows the bacterium to remain “hidden” from the immune system until infection ensues
What are endospores?
- defensive strategy against hostile or unfavorable environmental conditions (driven by nutrient supply)
- metabolically dormant and resistance to heat, cold, drying, chemicals and radiation
- germinate when conditions improve
- formed by two genera: Clostridium spp. and Bacillus spp.
- requires special environmental controls to kill spores - cleaning and disinfecting is not sufficient - sterilization required (steam, under pressure, chemical sterilants, etc.)
- can be found in water
What is the function of the bacterial cell wall?
- possess unique characteristics that differentiate it from other microbes (peptidoglycan layer)
- used to classify species - probably most important feature
- provides structure and maintains microbe’s shape
- counters the effects of osmotic pressure - protect from fluid
- provides rigid platform for external appendages
- facilitates adherence to host cells and evasion of host defenses
- target for antibodies
What is the Gram stain?
Identifies two types of bacterial cell wall:
1) Gram-Positive; bacteria that retain primary crystal violet dyes due to thick, dense and relatively non-porous walls become a purple color post Gram stain
2) Gram-Negative; bacteria that are easily discolored due to thin cells walls surrounded by an outer membrane take on a pink red color post Gram stain
- starting point for bacterial identification
- difference in dye retention depends on thickness, density, porosity, integrity , and chemical composition of cells wall
- very quick process (30 min) in comparison to growing a culture
- also reveals where the person likely got sick and makes morphology more distinct
- very important as Gram negative and Gram positive bacteria have different susceptibility profiles to antibiotics
What is LPS?
- LPS (or Lipid A) is a potent endotoxin found in the outer membrane of most Gram negative bacteria
- causes fever, vasodilation, and inflammation
- can induce shock and blood clot formation
- makes Gram negative harder to manage than Gram positive
What are some considerations for the Gram stain?
- some non-bacterial organisms with thick cells wall (some yeasts) may also stain Gram positive
- Gram positive bacteria that have lost cell wall integrity through aging or damage may stain Gram negative; thus, specimen collection is very important
- not all bacteria Gram stain; specialized stains are required for some species