40 Questions
What is the term for bacteria that require a higher amount of CO2 for their growth?
Capnophilic bacteria
Which type of bacteria grows at acidic pH (below 4.0)?
Acidophile
What is the term for bacteria that derive energy from sunlight?
Phototrophs
Which type of bacteria grows at temperatures between 25-40°C?
Mesophiles
What is the term for bacteria that can survive at high salt concentrations?
Halophiles
Which type of bacteria obtains its food from other living organisms?
Heterotrophs
What is the term for bacteria that grow at alkaline pH (8.2-8.9)?
Alkaliphile
Which type of bacteria reduces inorganic carbon into organic compounds?
Autotrophs
What is the characteristic of symbiotic bacteria?
They obtain nutrition from the host organism by offering something in return
Which type of bacteria obtain nutrition from dead and decaying matter?
Saprophytic bacteria
What is the characteristic of monotrichous bacteria?
They have a single polar flagellum
Which of the following bacteria is an example of a peritrichous bacterium?
Salmonella
What is an obligate intracellular organism?
An organism that cannot reproduce outside the cell
Which of the following is an example of an obligate intracellular organism?
Chlamydia
What is a pathogenic microorganism?
One that causes or is capable of causing disease
Why are people with T-cell deficiencies susceptible to intracellular pathogens?
Because they are immunocompromised
What is the general structure of exotoxin proteins?
Two polypeptide components
What is the target of diphtheria toxin?
Human protein elongation factor EF-2
What is the effect of moderate heating on most exotoxins?
Toxins are inactivated
What is the effect of dilute formaldehyde on exotoxins?
Toxins are inactivated, but antigenicity is retained
What is the term for formaldehyde-inactivated toxins?
Toxoids
What is the location of the gene that encodes the diphtheria exotoxin?
Temperate bacteriophage
What is a characteristic of endotoxins?
Heat-stable
What is the main physiologic effect of LPS endotoxins?
Fever, shock, hypotension, and thrombosis
What is the primary defense mechanism of the host that bacteria must overcome after entering the host?
Phagocytosis
What is the term for the dose of a pathogen required to cause disease in 50% of those exposed?
ID50
Which of the following is NOT a port of entry for bacteria into the host?
Brain
What is the purpose of an outer polysaccharide capsule in bacteria such as Streptococcus pneumoniae?
To resist host defenses
Which stage of the infectious process involves the propagation of the organism?
Propagation of the organism
What is the term for the ability of a bacterium to cause disease?
Pathogenicity
Which bacterium uses pili to adhere to host cells?
Escherichia coli
What is the term for the dose of a pathogen required to kill 50% of test animals?
LD50
What is the possible consequence of eliminating the causative bacteria by antibiotics?
Sudden massive release of endotoxin into the circulation
Why can gram-positive bacteria cause a shock syndrome similar to that caused by LPS?
Because their cell wall peptidoglycan can elicit a shock syndrome
What is the mechanism by which certain bacteria can turn off and turn on the expression of genes coding for surface antigens?
Phase variation
What is the result of antigenic variation in bacteria?
The expressed surface antigen can assume many different antigenic structures
What can be concluded if a particular microorganism is isolated from infected tissue?
Nothing can be concluded about the isolated organism
Why are peptidoglycan fragments of gram-positive bacteria not considered to be endotoxins?
Because they are less potent than LPS
What is the purpose of antigenic switching and variation in bacteria?
To evade the host's immune system
What can be a consequence of multiple organ failure?
Death
Study Notes
Morphology of Bacteria
- Bacilli: rod-shaped, can appear as coccobacilli, streptobacilli, comma-shaped, or spirella
- Spirochetes: slender, flexuous, spiral-shaped
- Actinomyces: branching filamentous
Growth and Nutrition
Oxygen Requirements
- Aerobic bacteria:
- Obligate aerobes (e.g., P. aeruginosa)
- Facultative aerobes (e.g., E. coli)
- Microaerophilic bacteria (e.g., Campylobacter jejuni)
- Anaerobic bacteria:
- Obligate anaerobes (e.g., Clostridium tetani, Bacteroids)
- Aerotolerant anaerobes (indifferent to O2)
Carbon Dioxide Requirement
- Capnophilic bacteria: require higher CO2 levels (5-10% CO2 and 15% O2) for growth (e.g., H. influenzae, Brucella abortus)
Temperature
- Psychrophiles: grow at 0-20°C
- Mesophiles: grow at 25-40°C
- Thermophiles: grow at 55-80°C (e.g., B. stearothermophilus)
pH
- Acidophiles: grow at acidic pH (below 4.0) (e.g., Lactobacillus)
- Alkaliphiles: grow at alkaline pH (8.2-8.9) (e.g., V. cholerae)
- Neutrophiles: grow at neutral pH (7.2-7.6) (most pathogenic bacteria)
Light
- Phototrophs: derive energy from sunlight
- Chemotrophs: derive energy from chemical sources
Osmotic Pressure
- Halophiles: survive at high salt concentrations
- Osmophiles: survive at high sugar concentrations
Carbon Source
- Autotrophs: reduce inorganic carbon into organic compounds (e.g., through photosynthesis)
- Heterotrophs: obtain carbon from other sources (e.g., host organisms)
Method of Obtaining Nutrition
- Heterotrophic bacteria: obtain food from other living organisms
- Symbiotic bacteria: obtain nutrition from host organisms by offering something in return
- Pathogenic bacteria: obtain food from host but harm the host, causing disease
- Saprophytic bacteria: obtain nutrition from dead and decaying matter
Flagella
- Monotrichous: single polar flagellum (e.g., Vibrio cholerae)
- Lophotrichous: multiple polar flagella (e.g., Spirilla)
- Peritrichous: flagella distributed over the entire cell (e.g., Salmonella, E. coli)
- Amphitrichous: single flagellum at both ends (e.g., Spirillum minus)
- Atrichous: no flagella (e.g., Staphylococcus, Shigella)
Motility
- Motile: able to move (e.g., Salmonella, Vibrio cholerae, Pseudomonas)
- Non-motile: unable to move (e.g., Staphylococcus, Shigella)
Obligate Intracellular Organisms
- Viruses
- Bacteria: Chlamydia, Rickettsia, Coxiella, Mycobacterium leprae
- Protozoa: Plasmodium spp., Toxoplasma gondii, Leishmania spp., Trypanosoma cruzi
- Fungi: Pneumocystis jirovecii
Pathogenicity of Bacteria
- Factors influencing pathogenicity:
- Entry into the host
- Adhesion to host cells
- Propagation of the organism
- Damage to host cells by bacterial toxins or inflammatory response
- Evasion of host secondary defenses
- Virulence factors: characteristics of a bacterium that enhance its pathogenicity
Virulence Factors
- Entry into the host:
- Respiratory tract
- Gastrointestinal tract
- Urogenital tract
- Skin
- Adherence to host cells:
- Pili (e.g., Escherichia coli)
- Fimbriae (e.g., Group A streptococci)
- Toxins:
- Exotoxins:
- Proteins with two polypeptide components (binding and toxic effect)
- Examples: diphtheria toxin, staphylococcal enterotoxin
- Endotoxins:
- Lipopolysaccharide (LPS) components of gram-negative bacteria
- Releases into circulation after bacterial cell lysis
- Causes fever, shock, hypotension, and thrombosis (septic shock)
- Exotoxins:
Antigenic Switching
- Mechanisms to evade host immune system:
- Phase variation: reversible expression of surface antigens
- Antigenic variation: modification of expressed surface antigen genes by genetic recombination
This quiz covers the different shapes and arrangements of bacteria, such as bacilli, spirochetes, and actinomyces, as well as their oxygen requirements and growth patterns.
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