Microbial Oxygen Requirements

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Questions and Answers

What is the maximum temperature that psychrophiles can grow at?

45C

20C (correct)

37C

At what temperature do mesophiles thrive best?

60C

37C (correct)

20C

45C

Which of the following examples is a psychrophile?

Thermus aquatica

Geobacillus stearothermophilus

Listeria monocytogenes (correct)

Bacillus infernus

What type of organism grows best at pH levels between 5.5 and 8.0?

Neutrophiles Signup and view all the answers

Which method is used for obtaining a pure culture?

Streak/spread plate method Signup and view all the answers

What is the thermal death time?

The minimum time to kill organisms at a constant temperature Signup and view all the answers

Which organism is classified as an alkalophile?

Vibrio Signup and view all the answers

Which of the following is NOT a characteristic of liquid culture media?

Contains agar for solidification Signup and view all the answers

Which type of media would be used for the growth of fastidious organisms?

Enriched media Signup and view all the answers

What does Blood Agar Plate (BAP) help to distinguish?

Hemolytic patterns Signup and view all the answers

Which medium differentiates E.coli from other lactose fermenting bacteria?

EMB agar Signup and view all the answers

What type of media incorporates antibiotics to inhibit the growth of unwanted organisms?

Selective media Signup and view all the answers

Which medium is specifically selective for Vibrio?

TCBS medium Signup and view all the answers

What does HEA identify?

Salmonella and Shigella Signup and view all the answers

Which component can be added to a selective medium to inhibit swarming bacteria?

Alcohol Signup and view all the answers

What is the function of the Antimicrobial Removal Device in blood culture systems?

To absorb absorbed antibiotics Signup and view all the answers

What does the automated BACTEC system detect to indicate microbial growth?

Carbon dioxide production Signup and view all the answers

What are the possible appearances of colonies on agar plates?

Mucoid, slimy, or swarming Signup and view all the answers

How do some bacteria exhibit chromogenesis?

By retaining pigment within the cell or coloring the medium Signup and view all the answers

What characteristic is NOT observed in colony margins?

Expansive or flat Signup and view all the answers

What does turbid growth in a nutrient broth indicate?

Presence of 106 CFU/mL or more Signup and view all the answers

Which feature is observed in the optical characteristics of colonies?

Colonies can appear opaque, translucent, shiny, or opalescent Signup and view all the answers

In gelatin slants, how does bacterial growth usually appear?

Confined within the zone of inoculation Signup and view all the answers

What kind of odors may bacteria produce during growth?

Putrid, fruity, ammoniacal, or aromatic Signup and view all the answers

What characterizes obligate aerobes?

They require oxygen and grow well in normal air. Signup and view all the answers

Which organism is an example of an obligate anaerobe?

Clostridium Signup and view all the answers

Facultative anaerobes are significant in which way?

They can grow in both presence and absence of oxygen. Signup and view all the answers

Microaerophiles require which concentration of oxygen for optimal growth?

2%-10% Signup and view all the answers

Capnophiles prefer an environment with increased levels of which gas?

Carbon dioxide Signup and view all the answers

Which statement is true about phototrophs?

They use light as their energy source. Signup and view all the answers

What is the optimal temperature range for most clinically significant bacteria?

35C to 37C Signup and view all the answers

Heterotrophs differ from autotrophs in that they:

Utilize organic material from other organisms. Signup and view all the answers

What is the primary use of semi-solid medium?

To observe bacterial motility and detect indole and sulfide production Signup and view all the answers

Which of the following is NOT a characteristic of solid medium?

Is used for bacterial motility studies Signup and view all the answers

Which type of medium has known components and is designed for research purposes?

Synthetic or defined medium Signup and view all the answers

What is the function of enrichment media?

To enhance the growth of specific bacteria from a mixture Signup and view all the answers

What type of medium is Hela 229 cells grown in?

Tissue culture medium Signup and view all the answers

Which example is associated with solid medium?

MacConkey agar Signup and view all the answers

What characterizes synthetic or defined medium?

The components are fully known Signup and view all the answers

Alkaline Peptone Water is best known for its use with which species?

Vibrio Signup and view all the answers

Study Notes

Oxygen Requirement

Obligate aerobes require oxygen for growth and thrive in room air (15-20% oxygen, 1% carbon dioxide).
Examples: Bordetella, Brucella, Mycobacterium, Neisseria, and Pseudomonas
Obligate anaerobes cannot survive in the presence of oxygen and die after prolonged exposure.
Examples: Clostridium and Bacteriodes
Facultative anaerobes grow in both the presence and absence of oxygen, but thrive better with oxygen.
Examples: Enterobacteriaceae, Staphylococcus, Streptococcus
Aerotolerant anaerobes can survive in the presence of oxygen but cannot use it for metabolism.
Examples: Lactobacillus, Clostridium perfringes, and Cutibacterium
Microaerophiles require low oxygen concentrations (2-10%) and can be grown in special jars or bags.
Examples: Campylobacter, Helicobacter, and Treponema
Capnophiles require increased carbon dioxide concentration (5-10%) and 15% oxygen.
Examples: Neisseria, HACEK

Carbon Dioxide Requirement

Capnophiles require increased carbon dioxide (5-10%).
Most aerobic and facultative aerobic bacteria need 0.03% carbon dioxide.
Example: Haemophilus influenza

Carbon Source

Autotrophs utilize carbon as their sole carbon source.
Heterotrophs obtain reduced organic material from other organisms.

Energy Source

Phototrophs use light as their energy source.
Chemotrophs obtain energy from the oxidation of organic or inorganic compounds.

Electron Source

Lithotrophs obtain electrons from inorganic molecules.
Organotrophs require organic substances like carbohydrates and lipids for growth and multiplication.

Temperature Requirement

Optimum temperature for most clinically significant bacteria: 35°C to 37°C.
Psychrophiles/Cryophiles: Grow well at 0°C to 20°C.
Examples: Listeria monocytogenes, Yersinia enterocolitica
Mesophiles: Grow between 20°C to 45°C, with an optimum of 37°C.
Most commonly encountered pathogenic bacteria in clinical labs.
Thermophiles/Hyperthermophiles: Grow between 50°C to 60°C.
Examples: Geobacillus stearothermophilus, Thermus aquaticus, Sulfolobus, Pyrococcus, Pyrodictum
Extremophiles: Prokaryotes that thrive in unusual conditions, like low oxygen, high temperatures, or underground environments.
Example: Bacillus infernus
Thermal death time: The minimum time required to kill organisms at a constant temperature.
Thermal death point: The lowest temperature required to kill organisms in a constant time.

pH Tolerance

pH scale: Measures hydrogen ion concentration.
Acidophiles: Grow between pH 0 to 5.5.
Example: Lactobacillus acidophilus
Neutrophiles: Grow between pH 5.5 to 8.0.
Most clinically significant bacteria.
Alkalophiles: Grow between pH 8.5 to 11.5.
Example: Vibrio

Culture and Culture Media

Pure culture: Contains a single species.
Used for identification and antimicrobial susceptibility testing.
Methods: Streak/spread plate, pour plate, selective medium, animal inoculation.
Mixed culture: Contains more than one species.
Stock culture: Contains several species in separate culture media (one species per medium).
Cultivated in large volumes of broth, divided into small vials for long shelf life (up to 1 year).

Classification of Culture Media by Consistency

Liquid media: No agar; for rapid culture; supports growth of aerobes, anaerobes, and facultative anaerobes.
Examples: Brain heart infusion, trypticase soy broth, thioglycolate broth
Semi-solid media: Contains 0.5% to 1% agar; used to observe bacterial motility and detect indole and sulfide production.
Example: Sulfide Indole Motility (SIM) medium
Solid media:
- Liquefiable: Contains 2% to 3% agar, liquefies when heated.
- Non-liquefiable: Doesn't contain agar.
- Biphasic: Contains both liquid and solid components.
Examples: Triple Sugar Iron (TSI) agar, MacConkey agar, Blood agar plate (BAP), chocolate agar plate (CAP).

Classification of Culture Media by Composition

Synthetic/Defined media: Components are known; used for research purposes; can be liquid or solid.
Non-synthetic media: Some components are unknown (peptones, meat, yeast extracts).
Tissue culture media:
- HELA 229 cells: Human cervical tissue cells.
- McCoy cells (W138 cells): Fibroblasts.
- Used for isolating Chlamydia.
Embryonated cells: Used for propagating Rickettsia.

Classification of Culture Media by Dispensing/Distribution

Tube media: Prepared as liquid, slant, butt and slant, or butt.
Plated media: Distributed in dishes or plates.

Classification of Culture Media by Use

Simple/General purpose/Supportive media: Support growth of most non-fastidious bacteria; routine in laboratory.
Examples: Blood agar, nutrient broth, trypticase soy agar
Enrichment media (Liquid types): Enhance growth of specific bacteria while inhibiting others.
Alkaline Peptone Water: Used for Vibrio species.
Thioglycolate broth: General purpose enrichment medium, supports growth of many non-fastidious organisms.
Gram-negative broth: Enhances growth of Salmonella and Shigella.
Enriched media and non-selective media (Solid types): Provide additional supplements for fastidious organisms.
Examples: BAP, CAP (Blood agar plate and chocolate agar plate).
Blood agar plate (BAP): 5% defibrinated sheep's blood (horse and rabbit blood are second and third choices, respectively).
Human BAP: Used for Gardnerella.
Buffered Charcoal Yeast Extract (BCYE): Another enriched medium.
Differential media: Allow visualization of metabolic differences between bacterial groups.
Examples:
- MacConkey agar (MAC): Separates lactose fermenters from non-lactose fermenters.
- BAP: Differentiates hemolytic patterns.
- Eosin Methylene Blue (EMB) agar: Differentiates E. coli from other lactose fermenting bacteria.
- Hektoen Enteric (HEA) agar: Identifies Salmonella from Shigella.
Selective media: Inhibit growth of unwanted bacteria while promoting growth of desired bacteria.
Examples:
- Gentamicin blood agar: For Streptococcus.
- Bacitracin chocolate agar: For Haemophilus.
- Blood agar plate with ampicillin: For Aeromonas.
- Phenylethyl alcohol agar: For Gram-positive bacteria.
Inhibitory substances for selective media:
- To inhibit Gram-positive bacteria: Crystal violet/Gentian violet/carbon fuchsin, bile salt
- To inhibit Gram-negative bacteria: Potassium tellurite, sodium azide
- To inhibit swarming of bacteria: Alcohol, chloral hydrate
Special media: Used to isolate bacteria with specific growth requirements.
Examples:
- Lowenstein-Jensen (LJ) medium: Protein-rich, composed of whole eggs and malachite green.
- Thiosulfate-citrate-bile-salts-sucrose (TCBS) agar: Selective for Vibrio; sterilized by boiling, not autoclaving.

Blood Culture System

Blood culture bottles: Used to isolate aerobic and anaerobic bacteria.
Antimicrobial Removal Devices (ARDs) or resins: Added to the medium to absorb antibiotics present in the blood sample.
Manually: Biphasic medium containing MacConkey agar (MAC) and Blood agar plate (BAP).
Automated system (BACTEC): Detects carbon dioxide production by bacteria as an indicator of growth.

Quality Control of Culture Media

After preparing media, an uninoculated sample should be incubated overnight at 35°C to check for bacterial contamination.

Cultural Characteristics

Appearance of bacteria on various media: Color of colonies and media, abundance of growth, odor.

Reporting Cultural Characteristics

Agar plate colonies:
- Size: Pinpoint to large, mucoid, slimy.
- Margin and elevation: Smooth, entire, filiform, lobate, undulate.
- Chromogenesis (Pigmentation): Colored or unpigmented.
- Optical features: Opaque, translucent, shiny, opalescent.
- Odor: Putrid, fruity, ammoniacal, aromatic.
Growth on slant:
- Amount: Scanty, moderate, abundant.
- Margin or edge: Same as agar plate descriptions.
- Consistency: Butyrous, viscous, dry, brittle.
- Chromogenesis: Pigmented.
- Odor.
Growth in nutrient broth:
- Turbid: Indicates bacterial growth.
- Viscous: Thick, sticky appearance.
Growth in gelatin slant:
- Thread-like or beaded-like string pearl pattern: Growth confined to the inoculation zone.
- Liquefaction: Starts evenly from the top of the agar slant, creating a funnel-like appearance.

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Description

This quiz explores the different types of microbial oxygen requirements, including obligate aerobes, obligate anaerobes, facultative anaerobes, aerotolerant anaerobes, microaerophiles, and capnophiles. Learn about the examples of bacteria that fall into each category and their respective oxygen needs for growth. Test your understanding of these essential microbiological concepts.