Unit 1.2 - Antibiotic Treatment
Antibiotic Resistance
The mass use of antibiotics has resulted in new strains of bacteria that are
resistant to antibiotics
Over the last decade, almost every type of bacteria known to cause disease
has become stronger and less responsive to antibiotic treatment
Increasing number of antibiotic resistant bacteria: Tuberculosis, gonorrhea,
malaria, skin infections, pneumonia, & ear infections
Antibiotic resistance has been called one of the world’s most pressing
public health problems and is one of the Centers for Disease Control’s top
concerns.
Unit 1.2 - Antibiotic Treatment
Mechanism of Action
Specific antibiotics are effective at preventing the growth of certain
strains of bacteria
The effectiveness of antibiotics is dependent on the mechanism of
action of the drug and the structure of the bacteria
Unit 1.2 - Antibiotic Treatment
KEY TERMS
Crossword Puzzle
Unit 1.2 - Antibiotic Treatment
Unit 1.2 - Antibiotic Treatment
Activity 1.2.3
Introduction
The purpose of this activity is for you to review and build upon your
knowledge of bacterial cells.
In the last lesson, you were introduced to 18-year-old Sue Smith, who was
diagnosed with bacterial meningitis.
In this activity, you will learn about the structure of a bacterial cell in order
to understand how different classes of antibiotics work.
Your goal is to put all the information together to determine the best type
of antibiotic to use to treat Sue Smith.
Unit 1.2 - Antibiotic Treatment
What is a bacterium?
What are the types of bacteria?
How do antibiotics kill bacteria?
Unit 1.2 - Antibiotic Treatment
What is a bacterium?
• Bacteria are a large group of unicellular, prokaryote, microorganisms
• Typically a few micrometers in length
• A wide range of shapes (ranging from spheres to rods and spirals)
• 40 million bacterial cells in a gram of soil
• A million bacterial cells in a milliliter of fresh water
• Approximately five nonillion (5×1030) bacteria on Earth
Unit 1.2 - Antibiotic Treatment
A Typical Bacterium
Unit 1.2 - Antibiotic Treatment
Bacterial DNA
Chromosomal: bacteria possess a single chromosome composed of
double‐stranded DNA in a closed loop. The DNA is located in the nucleoid of
the cell and is not associated with protein. Transfer of chromosomal DNA is
accomplished through replication then division to daughter cells.
Plasmid: A small circular double-stranded DNA molecule that carries
accessory genes separate from those of the bacterial chromosome. They
carry a small number of genes. Easily transferred between bacteria in
cellular contact.
Unit 1.2 - Antibiotic Treatment
Bacterial Gene Transfer
Three primary types of gene transfer between bacterial cells
1) Bacterial conjugation is the transfer of genetic material (plasmid)
between bacterial cells by direct cell-to-cell contact or by a bridge-like
connection between two cells
2) Transduction is the process by which DNA is transferred from one
bacterium to another by a virus. It also refers to the process whereby
foreign DNA is introduced into another cell via a viral vector.
3) Transformation is the genetic alteration of a cell resulting from the direct
uptake and incorporation of exogenous genetic material (exogenous
DNA) from its surroundings and taken up through the cell membrane(s).
Unit 1.2 - Antibiotic Treatment
Gram Staining
Gram-negative bacteria
• Thin cell wall consisting of a few layers of peptidoglycan surrounded by a second
lipid membrane containing lipopolysaccharides and lipoproteins
• Do not retain crystal violet dye in the Gram staining protocol due to their
lipopolysaccharide outer layer
• In a Gram stain test, a counterstain (commonly safranin) is added after the crystal
violet, coloring all Gram-negative bacteria with a red or pink color.
Gram-positive bacteria
• Do not have an outer membrane BUT they have a thickened peptidoglycan layer
• Will retain the crystal violet dye when washed in a decolorizing solution
Unit 1.2 - Antibiotic Treatment
Gram Staining
The higher lipid content of the gram-negative bacteria cell walls allows the alcohol
destain to wash the purple colored stain out of the cells.
Gram positive bacteria will retain the purple color because the alcohol is not able
to destain the purple color from the cells.
Gram negative bacteria stain reddish-pink
Gram positive bacteria stain purple
“Positively Purple”
Unit 1.2 Antibiotic Treatment
Gram Staining
Gram Negative
Gram Positive
Unit 1.2 Antibiotic Treatment
Gram Staining
Unit 1.2 - Antibiotic Treatment
Mechanism of Action
Specific antibiotics are effective at preventing the growth of certain
strains of bacteria
The effectiveness of antibiotics is dependent on the mechanism of
action of the drug and the structure of the bacteria
Unit 1.2 - Antibiotic Treatment
How do antibiotics work?
A number of bacterial processes, including the synthesis of bacterial cell walls,
proteins, metabolic pathways, and the integrity of the cytoplasmic membrane, are
the targets of most antibacterial drugs.
4 Main Classes of Antibiotics:
1) β-Lactam Antibiotics
2) Tetracyclines
3) Fluoroquinolones
4) Sulfonamides
Unit 1.2 - Antibiotic Treatment
β-Lactam Antibiotics
“Blocks cell wall synthesis”
Irreversibly inhibit enzymes involved in the final steps of cell wall synthesis. These
drugs vary in their spectrum of activity; some are more active against Gram positive
bacteria; whereas, others are more active against Gram negative bacteria.
Tetracyclines
“Blocks protein synthesis”
Reversibly bind to the 30S ribosomal subunit, blocking the attachment of tRNA to
the ribosome and preventing the continuation of protein synthesis. They are
effective against certain Gram positive and Gram negative bacteria.
Unit 1.2 - Antibiotic Treatment
Fluoroquinolones
“Disrupts bacterial DNA organization”
Inhibit one or more of a group of enzymes called topoisomerases, which maintain
the supercoiling of the chromosomal DNA within the bacterial cells. The inhibition
of these enzymes prevents essential cell processes. The fluoroquinolones are active
against a wide variety of bacteria, including both Gram positive and Gram negative.
Sulfonamides
“Disrupts metabolic pathways”
Inhibit the growth of many Gram positive and Gram negative bacteria. They are
structurally similar to paraminobenzoic acid (PABA), a substrate in the pathway for
folic acid biosynthesis. Because of this similarity, the enzyme that normally binds
with PABA preferentially binds with the sulfonamide drugs, resulting in its
competitive inhibition. Human cells are not affected by these drugs because they
lack this enzyme.
Unit 1.2 Antibiotic Treatment
Antibiotic Resistance
It may take the form of a spontaneous or induced genetic mutation, or the
acquisition of resistance genes from other bacterial species by horizontal
gene transfer via conjugation, transduction, or transformation.
Many antibiotic resistance genes reside on transmissible plasmids,
facilitating their transfer via conjugation.
Unit 1.2 Antibiotic Treatment
Unit 1.2.4.A – When Antibiotics Fail
Exposure to an antibiotic naturally selects for the survival of the
organisms with the genes for resistance. In this way, a gene for
antibiotic resistance may readily spread through an ecosystem of
bacteria. Antibiotic-resistance plasmids frequently contain genes
conferring resistance to several different antibiotics.
What does it mean by select?
After completing the conclusion questions please address
this in the form of a paragraph in your notebook
(diagrams welcomed)
Begin
Unit 1.2.4.A – When Antibiotics Fail
Unit 1.2 - Antibiotic Treatment
Mechanism of Action
Specific antibiotics are effective at preventing the growth of certain strains of bacteria. The
effectiveness of antibiotics is dependent on the mechanism of action of the drug and the structure
of the bacteria. In the last lesson, students were introduced to 18-year-old Sue Smith, who was
diagnosed with bacterial meningitis. In this lesson, students will review bacterial structure,
investigate various types of antibiotics and their mode of action against the bacteria they target,
and suggest an antibiotic treatment for Sue Smith. Students will then investigate the mechanisms
by which DNA from one bacterial cell is transferred to another bacterial cell and explore antibiotic
resistance.
Review
Unit 1.2 –Antibiotics
Quiz Review
1) The one-way transfer of DNA between bacteria in cellular contact (1 pt)
a) Transformation
b) Replication
c) Conjugation
d) Transduction
2) The gel-like region within the cytoplasm containing the single, circular,
double-stranded DNA molecule? (1pt)
a) Nucleoid
b) Pili
c) Plasma Membrane
d) Organelle
Quiz Review
3) True or False: Gram negative bacteria will stain purple? (1 pt)
Positively Purple!!!
4) Match the correct term to the structure shown below. (3 pts)
_______
B
E
_______
_______
A
D
_______
_______
F
C
_______
Cell Wall
Flagellum
Cell membrane
Nucleoid
Pilus
Ribosome
Quiz Review
5) For Project 1.2.3.P ("Superbugs") we have been working with 2 strains of
bacteria. The first strain, E. coli Strain I, contains a gene found on the
chromosomal DNA coding for streptomycin resistance. The second strain, E. coli
Strain II, contains a gene found on the plasmid DNA coding for ampicillin
resistance. On the back of this page, answer the following question based on
the what you have learned about gene transfer and bacterial resistance. If your
results indicate that you did create a superbug with both streptomycin and
ampicillin resistance, was the streptomycin resistant gene transferred from
Strain I to Strain II, or was the ampicillin resistant gene transferred from Strain
II to Strain I? You must explain in detail your reasoning for full credit. (4 pts)
The ampicillin resistant gene on the plasmid DNA is
transferred from Strain II to Strain I. The mechanism
leading to this gene transfer is conjugation.
Quiz Review
b
β-Lactam Antibiotics ______
Fluoroquinolones ______
d
c
Sulfonamides _______
Tetracyclines _______
a
a)
b)
c)
d)
“Blocks protein synthesis”
“Blocks cell wall synthesis”
“Disrupts metabolic pathways”
“Disrupts bacterial DNA organization”
Unit 1.2 - Antibiotic Treatment
Understandings
• Antibiotics disrupt the pathways that bacteria use to survive.
• Bacterial cells use multiple pathways to gain resistance to antibiotics.
• Overuse and misuse of antibiotics promotes the selection of resistant bacteria.
Knowledge and Skills
It is expected that you will:
• Label the structures of a bacterial cell.
• Explain the method of action for different classes of antibiotics.
• Describe the pathways through which bacterial cells transfer genes.
• Explain the importance of taking antibiotics as prescribed.
• Use proper laboratory techniques to “mate” a streptomycin resistant strain of E.
coli with an ampicillin resistant strain of E. coli.
• Simulate the effects of antibiotics on a bacterial population during an infection.
• Simulate the effect of a missed dose of antibiotics on a bacterial population
during an infection.
Unit 1.2 - Antibiotic Treatment
Unit 1.2 - Essential Questions
1) How do antibiotics work to fight bacterial infections?
2) What methods do bacteria use to share antibiotic resistant genes?
3) What actions are humans taking that are contributing to bacteria
becoming resistant to commonly used antibiotics?