Week 3 Diebel - Microbial Structure & Bacterial Growth & Physiology Flashcards
What are three ways bacteria cause disease?
- Toxin production: release toxins > cause illness
- Host immune response: response of host > cause illness
- Bacterial proliferation and invasion: growth and spread of bacteria > cause damage > lead to illness
What are three ways viruses cause disease?
- Cytopathic effect: infection disrupts cell physiology > cell disease & death
- Host immune response: host responds > illness
- Tumorigenesis: infection promotes uncontrolled proliferation of infected cells (oncogenic viruses)
Who is Antonie Van Leeuwenhoek?
1632-1723
“Father of Microbiology”
came up with first simple microscope
What is Louis Pasteur (1822-1895) famous for?
His work on spontaneous generation.
He disproved the theory 200 years after Leeuwenhoek and Hooke.
Led to the development of methods for controlling the growth of microorganisms.
What is the Spontaneous Generation Hypothesis?
The hypothesis that living organisms can originate from nonliving matter.
How did Louis Pasteur disprove the spontaneous generation hypothesis?
“Swan Neck Experiment”
compared the growth of microorganisms in one flask containing sterile broth that was exposed to the air and one containing sterile broth that was not exposed to the air.
***Proved that all life came from pre-existing life forms.
What did Robert Koch (1843-1910) demonstrate in his studies on infectious disease?
The link between microbes and infectious diseases, i.e. the “Germ Theory of Disease”
What are the four modes of transmission of infectious diseases?
- Person-to-person
- Zonotic
- Soil-born
- Common source
What are three types of person-to-person transmission of infectious disease?
- Air-born
- Direct contact or contact with a product of another person
- Sexually transmitted infections
What is Zonotic transmission of infectious disease?
Vector-born disease
i.e. animals, arthropods, etc.
What is common source transmission of infectious disease?
Diseases transmitted through water sources, food born illnesses.
ex. cholera
What two conditions did Robert Koch identify the the causative agents of?
Anthrax and Tuberculosis
What are Koch’s postulates?
- The suspected pathogen must be present in ALL cases of the disease and absent from healthy animals.
- The suspected pathogen must be grown in pure culture.
- Cells from a pure culture of the suspected pathogen must cause disease in a healthy animal.
- The suspected pathogen must be reisolated and shown to be the same as the original.
What are the pro’s and con’s of Koch’s Postulates?
Pro’s:
-Link certain diseases with specific pathological organism.
Con’s:
- Requires small animal model system to test pathogen in.
- Not all pathogens have an animal model (e.g. HIV).
- Some pathogens act differently in carrier than host (e.g. malaria and misquito).
What is the “Gene Theory of Disease”?
- Microbial infections that lead to disease can be viewed as an arms race for replication that in the purest sense is related to the survival of one set of genetic information at the expense of another.
- Microbiology and disease = a war for resources
- who is best at replicating their genetic information over others
What is a virulence factor?
- Any molecule of a microorganism that aides in its ability to establish and maintain a pathogenic infection.
- Help to acheive: invasion, colonization, immunosuppression, obtain nutrition, exit
Describe the Pathway of Infection (7 steps)
- EXPOSURE to pathogens
- ADHERENCE to skin or mucosa
- INVASION through epithelium
- COLONIZATION and GROWTH production of virulence factors
- INVASIVENESS: further growth at original and distant sites
- TOXICITY: toxin effects are local or systemic
- TISSUE DAMAGE & DISEASE when you finally know you are sick
Describe Frederick Griffith’s experiment with bacteria and transformation.
- Rough strain (nonvirulent) bacteria > mouse LIVES
- Smooth strain (virulent) bacteria > mouse DIES
- Heat-killed smooth strain > mouse LIVES
- Rough strain (nonvirulent) + Heat-killed smooth strain >>> MOUSE DIES!!!!
What did Frederick Griffith’s experiment suggest about bacteria?
Bacteria are capable of transferring genetic information.
***Transformation***
What are the five classifications of microorganisms that can cause disease?
- Viruses
- Bacteria
- Helmnets (worms)
- Fungus
- Protozoa
(plus prions)
What is a disease fact sheet?
Gives the following about a disease:
- Disease Name
- System(s) affected
- Most likely causative microorganism
- General disease information
- Differential diagnosis
- Treatment
Why do we stain bacteria?
- Most bacteria are colorless
- Helps to classify bacteria
- Improves contrast
- Staining dyes are positively charged organic compounds that are attracted to the negative charge under bacterial plasma membrane
- It’s easy!
How do you prepare a gram stain?
- Prepair a Smear: spread culture in thin film over slide and air dry
- Heat Fixing: Pass slide through flame to heat fix
- Staining: flood slide with crystal violet stain for 1 minute
- Add iodine solution for one minute
- Decolorize with alcohol rinse for 20 seconds
- Counterstain with safranin for 1-2 minutes
Describe the six bacterial morphologies.
- Coccus (sphere)
- Bacilli (rod)
- Spirillium (rigid, gm (-), helical/spiral)
- Spirochete (thin, spiral shape)
- Budding and Appendaged Bacteria (stalk+hypha)
- Filamentous bacteria
What are four features of a Gram Positive (+) Cell wall?
Purple!
- Inner cytoplasmic membrane
- Thick peptidoglycan cell wall
- Teichoic acids
- Smooth outer appearance
What are six features of Gram Negative (-) cell wall?
Pink!
- Lipopolysaccharide
- Outer membrane
- Thin peptidoglycan cell wall
- Periplasm
- Inner cytoplasmic membrane
- Appears bumpy
What are five differences between prokaryotic cells and eukaryotic cells?
- Nucleoid with aggregated mass of DNA in proks, and membrane-enclosed nucleus in euks
- Circular DNA in proks, linear DNA in euks
- Naked DNA in proks, chromosome/histone proteinated DNA in euks
- Plasmid in proks
- Membrane bound organelles in euks
What are common structures in prokaryotic and eukaryotic microbial cells? (four)
- Cytoplasm
- Cytoplasmic Membrane
- Ribosomes
- Usually a cell wall…
What is a plasmid?
Circular extrachromosomal genetic elements (DNA), nonessential for growth, found in prokaryotes.
** Contains virulence factors **
How is the peptidoglycan in the cell wall arranged?
Peptide cross-links bonded to sugar groups with glycosidid bonds.
(built in two different directions with two different molecules)
Polysaccharide backbone with branching peptides and various interbridge connections.
X-axis: glycosidic bonds
Y-axis: peptide bonds
What is binary fission?
Method in which microbial growth and replication occurs:
- Cell elongation
- Septum formation
- Completion of septum, formation of cell wall, cell separation.
What type of growth patterns do microbial populations show?
Exponential growth
What step of peptidoglycan synthesis and cell division does Penicillin block?
Penicillin binds to and blocks the activity of the enzyme required for the transpeptidation reaction (DD-transpeptidase).
**Thus Selectively Toxic!
What are three mechanisms by which bacteria can cause disease?
- Toxicity
- Host Immune Respones
- Colonization & Proliferation
(Gray area between the last two)
How do you measure a microorganism’s virulence?
By determining its lethal dose in a model organism.
(ex. highly virulent organisms need a smaller numer of cells to kill 50% of model organism)
How is virulence determined according to Dr. Diebel?
Determined by the “Gene Theory of Disease”.
“Determined by the genes available to aid in the steps of pathogenesis, including mechanisms such as invasiveness, immune evasion, and toxicity.”
What are some basic properties of Exotoxins?
- proteins secreted out of bacterial cell
- generally heat liable
- bind to specific cell receptors or structures
- often highly toxic, sometimes fatal
- highly immunogenic, body can neutralize toxin with antitoxin
- does not produce fever
What are some basic properties of endotoxins?
- Structural component of the cell, usually Lipopolysaccharide-lipoprotein complexes
- extremely heat-stable
- non-specific binding or action
- cause fever, diarrhea, & vomiting
- weakly toxic, rarely fatal
- immune response not sufficient to neutralize toxin
What are some of the examples of exotoxins discussed in class?
- Cytolytic exotoxins - protein secreted from bacterial cell that forms holes in a cell membrane exposing contents >> cells die!
- Hemolysins (alpha, beta, & gamma)
- AB Toxins - B toxin binds to membrane and release A toxin into the cell to hurt cell
- Neurotoxins - blocks release of neurotransmitter or release of glycine to allow muscle relaxation
- Superantigen - activates any local T-cells by binding MHC class II to SEH receptor
What was the example of endotoxins discussed in class?
- LPS - released on cell lysis and Lipid A causes toxic effect > fever
What were some of the virulence factors discussed in the Salmonella example in class?
- Toxins - enterotoxin, endotoxin, & cytotoxin
- Adherence - cell surface polysaccharide O antigen, flagellar H antigen, & fimbriae
- Plasmid - drug resistance genes
- Host-immune evasion - pathogenicity islands that integrate info into host cell
What are the three layers of the immune system?
- Physical barriers (ex. skin)
- Innate Immune Response (“built-in” immunity)
- Adaptive Immune Response (“memory” immunity)
What is the innate immune system?
- non-inducible, pre-existing ability to recognize and destroy pathogens and their associated products
- responds by phagocytosis (facilitated by complements)
- recognizes PAMPs (pathogen-associated molecular patterns)
- interferons mediate an early response to viral infection