Microbiology Lecture 12: Antimicrobial Susceptibility Testing

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Questions and Answers

What is the primary purpose of the Epsilometer test (E test)?

To provide a direct quantification of antimicrobial susceptibility of microorganisms.

How does the E-test quantify antimicrobial susceptibility?

By combining a disk diffusion pattern with the determination of Minimum Inhibitory Concentration (MIC).

What is meant by cultivation in the context of bacterial growth?

To nurture and help grow bacteria.

What is the difference between aerobic and anaerobic cultures?

Aerobic cultures grow in the presence of oxygen, while anaerobic cultures grow in the absence of oxygen. Signup and view all the answers

What type of culture would be suitable for bacteria found on the skin surface?

Aerobic culture. Signup and view all the answers

What is the purpose of a culture medium in bacterial cultivation?

To provide a controlled laboratory environment for bacterial growth. Signup and view all the answers

What is the significance of Minimum Inhibitory Concentration (MIC) in antimicrobial susceptibility testing?

It is the lowest concentration of an antimicrobial that inhibits the visible growth of a microorganism. Signup and view all the answers

How do the rectangular plastic strips used in the E-test provide a gradient of antibiotic concentration?

One side of the strip contains the antimicrobial agent concentration gradient, and the other side contains a numeric scale that indicates the drug concentration. Signup and view all the answers

Which type of bacteria can grow in either aerobic or anaerobic conditions, switching from aerobic respiration to fermentation or anaerobic respiration if oxygen is absent?

Facultative anaerobes, e.g. E. coli, Salmonella, Listeria, and Staphylococci Signup and view all the answers

What type of microorganism is typically found in the nasopharynx of healthy individuals?

Streptococcus pneumoniae, Haemophilus influenza, and Moraxella catarrhalis Signup and view all the answers

Which type of bacteria requires oxygen for survival and is present in aerated moist soil containing organic carbon sources?

Aerobic bacteria Signup and view all the answers

What is the term for an organism that does not require oxygen for growth but can tolerate its presence?

Aerotolerant Signup and view all the answers

Which type of bacteria cannot grow in the presence of oxygen?

Obligate anaerobes, e.g. Fusobacterium and Bacteroides Signup and view all the answers

What is the term for an organism that achieves optimal growth at low oxygen concentrations, but not in the complete absence of oxygen?

Microaerophilic Signup and view all the answers

Which type of bacteria is classified as an anaerobe, but can tolerate oxygen?

Aerotolerant, e.g. Strep. pyogenes and Lactobacillus Signup and view all the answers

What are the two main types of aerobic bacteria?

Obligate aerobes and facultative anaerobes Signup and view all the answers

What is the characteristic behavior of facultative bacteria?

They can behave both aerobically and anaerobically, depending on the prevailing conditions. Signup and view all the answers

What do microaerophilic bacteria require for growth?

Low concentrations of oxygen. Signup and view all the answers

What are the three main methods of cultivating anaerobic bacteria?

An atmosphere free of oxygen, an anaerobic indicator, and an anaerobic jar with a catalyst. Signup and view all the answers

What is the purpose of the glove-like sleeves in an anaerobic box?

To allow for the handling of cultures inside the box without compromising the anaerobic environment. Signup and view all the answers

How does an anaerobic jar create anaerobic conditions?

By adding water to a gas generator envelope (GasPak) that is placed in the jar before sealing. Signup and view all the answers

What is the purpose of a candle in a candle jar?

To consume oxygen and create a carbon dioxide-rich, oxygen-poor atmosphere. Signup and view all the answers

Why is an anaerobic jar used to culture anaerobic bacteria?

To provide an environment with minimal oxygen, ideal for anaerobic bacterial growth. Signup and view all the answers

How do facultative bacteria respond to changes in their environment?

They adapt by switching between aerobic and anaerobic metabolic pathways. Signup and view all the answers

What is the result of adding water to a gas generator envelope in an anaerobic jar?

The creation of anaerobic conditions by consuming oxygen and producing carbon dioxide. Signup and view all the answers

Study Notes

Antimicrobial Susceptibility Testing

Epsilometer test (E-test) is a quantitative method that provides direct quantification of antimicrobial susceptibility of microorganisms.
It combines disk diffusion pattern with the determination of Minimum Inhibitory Concentration (MIC).
MIC is the lowest concentration of an antimicrobial that inhibits the visible growth of a microorganism.
E-test uses rectangular plastic strips with a predefined, continuous, and exponential gradient of antibiotic concentration.

Bacteria Culture and Cultivation

Cultivation of bacteria is a biological activity where microorganisms multiply themselves in a predetermined culture media under laboratory conditions.
Most bacteria can grow to some extent in the presence of oxygen, known as aerobic culture.
Species that are naturally found in low oxygen environments, such as in deep wounds or abscesses, will typically grow best in the absence of oxygen – anaerobic culture.
Examples of bacteria that can grow in aerobic culture include Staph. epidermidis, Staph. aureus, Streptococcus pneumoniae, Haemophilus influenza, and Moraxella catarrhalis.

Oxygen Requirements for Bacterial Growth

Microorganisms can be found as normal flora in the nasopharynx of healthy individuals.
Some bacteria cannot grow in the presence of oxygen at all, e.g. Fusobacterium and Bacteroides.
Some bacteria cannot grow in the absence of oxygen, e.g. Pseudomonas and Mycobacterium tuberculosis.
Some bacteria can grow in either aerobic or anaerobic conditions, switching from aerobic respiration to fermentation or anaerobic respiration if oxygen is absent, e.g. E. coli, Salmonella, Listeria, and Staphylococci.

Aerotolerant Organisms

Aerotolerant organisms are those that do not require oxygen for growth but can tolerate its presence.
An aerotolerant organism is classified as an anaerobe.
Examples of aerotolerant organisms include Strept. pyogenes (harmful) and Lactobacillus (beneficial).

Cultivation of Aerobic and Anaerobic Bacteria

Aerobic bacteria require oxygen for survival and are present in aerated moist soil containing organic carbon sources.
There are two main types of aerobic bacteria: obligate aerobes and facultative and microaerophile aerobes.
Obligate aerobes compulsorily require oxygen for energy, growth, and cellular respiration.
Facultative bacteria can behave both aerobically and anaerobically, depending on the prevailing conditions.
Microaerophilic bacteria require oxygen but in very low concentrations.
Anaerobic bacteria can be cultivated using an atmosphere free of oxygen, an anaerobic indicator, and an anaerobic jar with a catalyst.

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Description

Understand the principle of Epsilometer test (E test) for antimicrobial susceptibility of microorganisms, including Minimum Inhibitory Concentration (MIC) and disk diffusion pattern. Learn about cultivation of bacteria at atmospheric conditions.