5. Bugs in the System Flashcards
Define obligate.
Another organism relies on it.
Why can’t the bacteria in stomach epithelial surface stained with H&E be seen?
They stain poorly with H&E, the tissue preparation removes lots of the bacteria and there is often insufficient magnification.
How can bacteria be seen?
By using gram staining or acid fast stains.
What is the process of gram staining?
Positively charged crystal violet binds it the negative cell components. Iodine forms large molecular complexes with the crystal violet. Acetone or methanol extract the complexes through the gram-negative but not through gram-positive cell walls. A red dye is used to stain the unstained gram-negative cells.
What is the difference between gram positive and gram negative bacteria in terms of their cell envelopes?
Gram positive cell envelopes have a thick peptidoglycan layer whereas gram negative cell envelopes have a thinner peptidoglycan layer and instead have a small outer membrane too.
Briefly state the four stages of a gram stain.
Add crystal violet, add iodine, de-colourise, add red stain.
What colour do gram positive bacteria present after gram staining?
Purple/ violet.
What colour do gram negative bacteria present after gram staining?
Pink.
What are the three categories of bacterial shape?
Cocci, rods/bacilli or coccobaccilli.
What are the three categories of bacterial variations?
Curved, spiral or filamentous.
What internal structures can bacteria have?
Spores and inclusion granules.
What external structures can bacteria have?
Pili, flagellae and capsules.
What is used to stain mycobacteria?
Acid fast stains.
Why is the cell wall of bacteria clinically important?
It can be used for detection and diagnosis through the two staining methods and is the target for antibiotics as human cells don’t have cell walls so antibiotics can destroy cell walls but not harm human cells.
What are three growth environments of bacteria?
Broth turbidity, colonies and biofilms.
