General Microbiology Flashcards
What are the four key differences between prokaryotes and eukaryotes?
- Prokaryotes have no membrane-bound organelles.
- Eukaryote DNA is double-stranded linear DNA, while prokaryotes have double-stranded circular DNA.
- Eukaryotic cells have a membrane-bound nucleus, and prokaryotic cells do not.
- Eukaryotes store their genetic information in the nucleus, while prokaryotes store it in a nucleoid region.
What is a facultative aerobe?
An organism that can grow with or without oxygen, but will grow better in the presence of oxygen.
What is an aerotolerant anaerobe?
Aerotolerant organisms cannot use oxygen but tolerate its presence.
What is a facultative anaerobe?
An organism that can grow with or without oxygen, but will grow better with no oxygen present.
Describe the cell wall of a Gram-positive bacteria.
Gram-positive bacteria have a thick layer of peptidoglycan in their cell wall, which retains the crystal violet stain during the Gram staining process.
Describe the cell wall of a Gram-negative bacteria.
Gram-negative bacteria have a thinner layer of peptidoglycan in their cell wall, which is sandwiched between an outer membrane and an inner membrane. The outer membrane contains lipopolysaccharides (LPS) and lipoproteins.
What are the two major differences between Gram-positive and Gram-negative bacterial cell walls?
- Gram-negative bacteria have an outer membrane, while Gram-positive bacteria do not.
- Gram-negative bacteria have a thin layer of peptidoglycan, whereas Gram-positive bacteria have a very thick layer.
How does the Gram-positive bacteria uptake gram stain?
- A violet coloured stain is added which penetrates the cell wall, and the Gram stain’s iodine forms a complex with it.
- The alcohol dehydrates the peptidoglycans in the cell wall, but because the peptidoglycan layer is so thick, the violet stain gets trapped there in Gram-positive organisms. The alcohol washes away the colour in Gram-negative organisms.
- A pink/red coloured safranin counter stain is applied and absorbed, but its pink colour is not visible over the dark purple of the retained crystal violet. This makes Gram-positive bacteria appear purple.
How does the Gram-negative bacteria uptake gram stain?
- A violet coloured stain is added which penetrates the cell wall, and the Gram stain’s iodine forms a complex with it.
- The alcohol washes away the stain in Gram-negative organisms since they have a thinner layer of peptidoglycan than Gram-positive organisms.
- A pink/red coloured safranin counter stain is applied and absorbed. This makes Gram-negative bacteria appear pink.
What are the layers of the Gram-positive bacterial cell wall (outside to inside)?
- Capsule
- Cell wall (thick peptidoglycan layer)
- Cytoplasmic membrane
- Cytoplasm
What are the layers of the Gram-negative bacterial cell wall (outside to inside)?
- Capsule
- Outer membrane
- Cell wall (thin peptidoglycan layer)
- Cytoplasmic membrane
- Cytoplasm
What colour do Gram-positive bacteria appear under a gram stain and why?
Gram-positive bacteria retain the crystal violet stain and appear purple or blue under a microscope after Gram staining.
What colour do Gram-negative bacteria appear under a gram stain and why?
Gram-negative bacteria lose the crystal violet stain during the decolorization step and take up the safranin counterstain, appearing pink or red under a microscope.
What is the cell envelope composed of?
- Capsule
- Cell wall (peptidoglycan layer)
- Cell membrane
What is the bacterial capsule?
An extracellular polymeric material that covers the bacteria. It is variable between species and can be a capsule, glycocalyx, or slime layer.
What is the function of the bacterial capsule?
- Protection from the environment
- Adhesion
What does a slimy/mucoid appearance of a bacterial colony usually indicate?
The presence of capsules.
What are the functions of the bacterial cell wall?
- Prevents osmotic rupture
- Peptidoglycan in the cell wall provides strength.
What are two disadvantages of the cell wall (for the bacteria)?
- The cell wall contains adherence ligands and receptors for drugs and viruses.
- Allows quick and easy classification of bacteria.
True or False: The cell wall is essential for bacterial structure.
True.
What are the eight classification groups of bacteria?
- Gram-positive cocci
- Gram-positive bacilli
- Gram-negative cocci
- Gram-negative bacilli
- Acid fast
- Mycoplasma
- Spirochaetes
- Rickettsia
What are the two characteristics of mycoplasma?
- Very small
- Lack a cell wall.
What are the two characteristics of spirochaetes?
- Gram-negative but stain poorly
- Can be seen with dark field microscopy.
What are the three characteristics of Rickettsia?
- Gram-negative but stain poorly
- Small
- Intracellular.
Why can’t acid-fast bacteria be gram stained?
Acid-fast bacteria lack the peptidoglycans necessary to retain Gram stain.
What occurs in acid fast staining?
In acid-fast staining, when the primary stain (carbofuschin) is applied, all cells are stained red at first. However, only the acid-fast bacteria will retain the stain afterwards.
What type of bacteria can release endotoxins and why?
Gram-negative bacteria because they have lipopolysaccharides (LPS) in their cell wall that are released when the bacteria ruptures.
What type of bacteria can release exotoxins and why?
Gram-positive bacteria because they have lipoteichoic acid that can be released from the cell membrane.
How is the cell wall of a bacteria an important site for antibiotic attack?
Many antibiotics specifically target enzymes involved in peptidoglycan synthesis or disrupt the integrity of the peptidoglycan layer.
What is the cytoplasmic membrane?
A bacteria’s lipid bilayer with embedded proteins. It is selectively permeable.
What is the function of the cytoplasmic membrane?
It is the site of respiration, secretion, and photosynthesis.
What does the cytoplasmic membrane contain?
It contains sensing proteins, enzymes, and transport proteins.
What are flagellae?
Structures present in mobile bacteria.
What bacteria commonly have flagellae?
Gram-negatives.
What are fimbriae?
A structure that plays a role in adhesion and conjugation.
What bacteria commonly have fimbriae?
Gram-negatives.
Why does it matter that prokaryotes and eukaryotes have different ribosome structures?
Many antibiotics work by inhibiting protein synthesis at the ribosome.
What is the function of bacterial granules?
They are the storage site for nutrients/energy.
How do bacteria replicate?
Via binary fission (asexual reproduction).
What are the characteristics of binary fission?
- Increase in cell mass and number of ribosomes 2. Duplication of chromosome 3. Synthesis of new cell wall and cytoplasmic membrane 4. Partitioning of chromosomes 5. Septum formation 6. Cell division.
How do you assess bacterial growth in culture?
- Measurement of cell mass 2. Measurement of cell number.
Describe the bacterial growth curve (in a closed system).
- Lag phase: Cell numbers don’t increase. 2. Exponential growth phase: Generation time can be calculated. 3. Stationary phase: Population stabilizes. 4. Death phase: Bacteria die as nutrients are used up.
What is bacterial generation time?
The time it takes for the bacterial population to double.
What are endospores?
Structures on bacteria that are tough, and long-lasting in the environment.
Name two examples of endospore forming bacteria.
Bacillus and Clostridium.
What happens to endospores if the conditions become more favourable for the bacteria?
They can unactivate themselves and turn back into vegetative cells.
Describe the six steps of sporulation.
- Initiation of endospore occurs when bacteria encounter adverse conditions. 2. A spore septum forms. 3. Plasma membrane surrounds isolated DNA and cytoplasm. 4. Spore septum surrounds the ‘mini-spore’. 5. Peptidoglycan layer forms. 6. A spore ‘coat’ forms. 7. The endospore is released.
What is sporulation?
The process of a bacteria making endospores.
Describe the bacterial genome.
Bacteria have a single chromosome that contains all essential genetic information for survival.
What are plasmids?
Small, circular pieces of DNA that exist separately from the bacterium’s own chromosomal DNA.
True or False: Plasmids can be transferred from one bacteria to another.
True.
True or False: Binary fission is what leads to the great variability we see in bacteria.
False.
What accounts for the great variation in bacterial genetics?
- Recombination 2. Transposition.
What type of bacterial genetic process encodes antibiotic resistance?
Transposition.
What is transduction?
The transfer of genetic information between bacteria by bacteriophages.
What is bacterial conjugation?
Bacterial ‘sex’ that requires an F plasmid.
True or False: Conjugation occurs in both Gram-negative and Gram-positive bacteria.
True.
True or False: Pilus formation occurs in both Gram-negative and Gram-positive bacteria.
False.
What is transformation?
The uptake of a naked segment of DNA from a lysed ‘donor’ bacterium.
True or False: Bacterial transformation does not often happen in nature.
True.
What are the four main classifying categories of bacteria we use in veterinary medicine?
- Gram-positive aerobes 2. Gram-positive anaerobes 3. Gram-negative aerobes 4. Gram-negative anaerobes.
What are the six requirements for bacterial growth?
- Energy source 2. Carbon source 3. Major elements 4. Trace elements 5. Growth factors 6. Permissive conditions.
True or False: Bacteria are more tolerant of osmotic variation than eukaryotic cells because of their cell wall.
True.
Bacteria are generally ______osmotic relative to their normal environments.
Hyper.
What is the limiting requirement of sterilization?
The destruction of the bacterial spore.
True or False: Boiling is equal to sterilization.
False.
What is pasteurization?
The process of heating food to a degree that kills all potential human pathogens.
What are some pros and cons of using ethanol as a disinfectant?
Pros: Denatures proteins and dissolves lipids. Cons: Not effective against spores.
What is the difference between using ethanol and isopropyl alcohol as a disinfectant?
Isopropyl alcohol is less prone to dehydrating living tissue.
True or False: The activity of disinfectants is inhibited by organic matter.
True.
How does povidone-iodine kill bacteria?
Free iodine dissociates from the compound and interacts with bacterial proteins, nucleotides, and fatty acids to cause cell death.
How does chlorhexidine gluconate kill bacteria?
It interferes with bacterial cell membrane function causing cell death.
What is the name for bacteria that do not require an animal host to survive?
Facultative pathogens.
Which four bacteria can live and reproduce in the environment?
- Pseudomonas 2. Listeria 3. Clostridia 4. Bacillus anthracis.
What is an opportunistic pathogen?
A bacteria that is normally benign but can act as a pathogen under certain circumstances.
What are the six portals of entry for microbial disease?
- Alimentary system 2. Respiratory system 3. Urogenital system 4. Integumentary system 5. Eyes 6. Ears.
What are the four initial host defenses against bacterial access?
- Physical barrier 2. Chemical barrier 3. Transport systems 4. Immune system.
What are five methods used to diagnose bacterial infection?
- Cytology 2. PCR 3. Culture and isolation 4. Antibody detection 5. Cellular immune response.
What are the four commonly used types of selective media for bacteria?
- Blood agar 2. MacConkey agar.
What is the ucocilliary apparatus in the respiratory tract?
It is a structure involved in the respiratory system.
What does MALT stand for?
Mucosal associated lymphoid tissue.
What are five methods used to diagnose bacterial infection?
- Cytology
- PCR
- Culture and isolation
- Antibody detection (ELISA)
- Cellular immune response
What are the four commonly used types of selective media for bacteria?
- Blood agar (detects presence of hemolysins)
- MacConkey agar (selective for Gram-negatives and detects ability to ferment lactose)
- Hematin/chocolate agar (used to culture Hemophilus sp. and Taylorella equigenitalis)
- Xylose lysine deoxycholate (XLD) agar (contains pH indicator)
Which two plates are used for identifying mastitis?
SELMA and SELMA+ plates.
What is the coagulase test?
A test that measures the ability of bacteria to convert fibrinogen to fibrin.
What does the coagulase test allow you to differentiate between?
It allows differentiation between coagulase positive Staphylococcus aureus and coagulase negative Staphylococci.
True or False: The presence of antibodies indicates bacterial infection.
False. Since many bacteria are present normally within the host or in the environment, the presence of antibodies does not necessarily indicate infection.
What type of antibody response is indicative of bacterial infection?
Two serum samples collected two weeks apart and showing a 4X increase in antibody titer, combined with clinical signs, are considered indicative of infection.
What is the caudal fold/tuberculin test in cattle?
A test that detects a specific cellular immune response to the animal.
What is the gamma interferon test?
A test used to confirm results of a caudal fold/tuberculin test. T-lymphocytes will release IFN-γ when exposed to specific antigens and we can use ELISA to detect IFN-γ.
