Manoj Mahato

1. CLINICAL MICROBIOLOGIST MR. MANOJ MAHATO
ANTIMICROBIAL AGENTS

2. Antimicrobial therapy refers to the use of antimicrobial agents that kill or inhibit
the growth of these microorganisms such as bacteria, fungi, or parasites.
Antimicrobial agents, also known as antibiotics, are drugs that kill or inhibit the
growth of microorganisms such as bacteria, fungi, or viruses.
They are used to treat infections caused by these microorganisms.
Antimicrobial agents work by interfering with the essential processes of the
microorganisms, such as cell wall synthesis, protein synthesis, or DNA
replication.
CLINICAL MICROBIOLOGIST MR. MANOJ MAHATO
ANTIMICROBIAL THERAPY

3. Antimicrobial agents are used to preventing infections and diseases caused by
pathogens. Different types of antimicrobial drugs are commonly available. These are as
follows:
Antibacterial drug: A drug that is used to inhibit the pathogenic activity of bacteria is
called an antibacterial drug. Example: Zithromax.
Antifungal drug: A drug that is used to prevent fungal activity in the host is called an
antifungal drug. Example: Miconazole
Antiviral agent: A drug which is used to stop the pathogenic action of a virus is called
antiviral agents. Example: Tamiflu.
Antiparasitic drug: A drug that is used to prevent the growth of pathogenic parasites.
Example: Anthelmintics
CLINICAL MICROBIOLOGIST MR. MANOJ MAHATO
ANTIMICROBIAL AGENTS

4. MODE OF ACTION OF ANTIMICROBIAL AGENTS

5. The mode of action of antimicrobial agents varies depending on the type of agent and the target
microorganism. Some common modes of action include:
Inhibition of cell wall synthesis: Some antimicrobial agents, such as penicillin and
cephalosporins, inhibit the synthesis of the bacterial cell wall, which is essential for the survival
of the bacteria.
Disruption of the cell membrane: Other antimicrobial agents, such as polymyxins and
amphotericin B, disrupt the cell membrane of the microorganism, causing leakage of cell contents
and ultimately cell death.
Inhibition of protein synthesis: Some antimicrobial agents, such as tetracycline and
erythromycin, inhibit protein synthesis in the microorganism, which is essential for the growth
and reproduction of the microorganism.
Inhibition of nucleic acid synthesis: Some antimicrobial agents, such as rifampin and
fluoroquinolones, inhibit the synthesis of nucleic acids (DNA and RNA) in the microorganism,
which is essential for the replication of the microorganism
CLINICAL MICROBIOLOGIST MR. MANOJ MAHATO
MODE OF ACTION OF ANTIMICROBIAL AGENTS

6. Antimicrobial agents have various properties that make them effective in combating
microorganisms. Some key properties include:
Spectrum of activity: Antimicrobial agents can be broad-spectrum, effective against a wide
range of microorganisms, or narrow-spectrum, targeting specific types of microorganisms.
Mechanism of action: Antimicrobial agents work through different mechanisms such as
inhibiting cell wall synthesis, disrupting cell membranes, inhibiting protein synthesis, or
interfering with nucleic acid synthesis.
Efficacy: The effectiveness of an antimicrobial agent is crucial in treating infections. Factors
like concentration, duration of exposure, and susceptibility of the microorganism can impact
efficacy.
CLINICAL MICROBIOLOGIST MR. MANOJ MAHATO
MODE OF ACTION OF ANTIMICROBIAL AGENTS

7. Selectivity: Ideally, antimicrobial agents should target microorganisms while sparing host cells
to minimize side effects.
Resistance: Microorganisms can develop resistance to antimicrobial agents through various
mechanisms, posing a significant challenge in treating infections.
Pharmacokinetics: Properties such as absorption, distribution, metabolism, and excretion
determine the concentration of the antimicrobial agent at the site of infection.
Toxicity: Antimicrobial agents can have adverse effects on the host, ranging from mild reactions
to severe toxicity. Balancing efficacy with safety is essential in antimicrobial therapy.
CLINICAL MICROBIOLOGIST MR. MANOJ MAHATO
MODE OF ACTION OF ANTIMICROBIAL AGENTS

8. Classification of Antimicrobial Agents
Antimicrobial agents, also known as antibiotics, are drugs that kill or inhibit the growth of
microorganisms such as bacteria, fungi, or parasites. They are used to treat infections caused by
these microorganisms. Antimicrobial agents are classified into several groups based on their
chemical structure, mechanism of action, and spectrum of activity.
1. Classification by Chemical Structure
Beta-lactams: This group includes penicillin's, cephalosporins, carbapenems, and
monobactams. Beta-lactams work by inhibiting the synthesis of the bacterial cell wall.
Glycopeptides: This group includes vancomycin and teicoplanin. Glycopeptides work by
inhibiting the synthesis of the bacterial cell wall.
Aminoglycosides: This group includes gentamicin, tobramycin, and amikacin. Aminoglycosides
work by damaging the bacterial cell membrane and inhibiting protein synthesis.
Tetracyclines: This group includes tetracycline, doxycycline, and minocycline. Tetracyclines
work by inhibiting protein synthesis.
CLINICAL MICROBIOLOGIST MR. MANOJ MAHATO
CLASSIFICATION OF ANTIMICROBIAL AGENTS

9. Macrolides: This group includes erythromycin, azithromycin, and clarithromycin. Macrolides
work by inhibiting protein synthesis.
Quinolones: This group includes ciprofloxacin, levofloxacin, and moxifloxacin. Quinolones
work by inhibiting the synthesis of DNA.
2. Classification by Mechanism of Action
Bactericidal agents: These agents kill bacteria. Examples include penicillin's, cephalosporins,
carbapenems, aminoglycosides, and quinolones.
Bacteriostatic agents: These agents inhibit the growth of bacteria. Examples include
tetracyclines, macrolides, and sulfonamides.
CLINICAL MICROBIOLOGIST MR. MANOJ MAHATO
CLASSIFICATION OF ANTIMICROBIAL AGENTS

10. 3. Classification by Spectrum of Activity
Narrow-spectrum agents: These agents are effective against a limited range of bacteria.
Examples include penicillin G and erythromycin.
Broad-spectrum agents: These agents are effective against a wide range of bacteria. Examples
include amoxicillin, cephalosporins, and fluoroquinolones.
CLASSIFICATION OF ANTIMICROBIAL AGENTS

11. DRUG RESISTANCE

12. Drug resistance is a phenomenon in which a disease-causing organism (such as a
bacterium or virus) develops the ability to resist the effects of a drug that was previously
effective in treating it.
This can occur through various mechanisms, including genetic mutations, changes in
gene expression, or the acquisition of new genes.
Drug resistance is a major public health concern as it can lead to treatment failure,
increased healthcare costs, and even death.
 It is a particular challenge in the treatment of infectious diseases, such as tuberculosis,
malaria, and HIV/AIDS, where drug resistance can render existing treatments
ineffective.
CLINICAL MICROBIOLOGIST MR. MANOJ MAHATO
DRUG RESISTANCE

13. To combat drug resistance, various strategies are employed, including:
Developing new drugs with novel mechanisms of action
Using combination therapies to target multiple pathways
Implementing prudent antibiotic use practices to reduce the selective pressure
for resistance
Conducting surveillance and research to understand the mechanisms and spread
of drug resistance
CLINICAL MICROBIOLOGIST MR. MANOJ MAHATO
DRUG RESISTANCE

14. MECHANISM OF DRUG RESISTANCE

15. Drug resistance is a serious problem in public health, occurring when microorganisms such as
bacteria, viruses, and fungi develop the ability to resist the effects of antimicrobial drugs.
There are several types of drug resistance:
Efflux pumps: These pumps actively transport drugs out of the cell, reducing intracellular drug
concentrations.
Enzymes that modify or destroy drugs: These enzymes can alter the structure of drugs,
making them less effective or completely inactive.
Alteration of drug targets: Mutations in the target sites of drugs can reduce the binding affinity
of the drug, making it less effective.
Reduced drug uptake: Some microorganisms can reduce the uptake of drugs, making them less
effective.
CLINICAL MICROBIOLOGIST MR. MANOJ MAHATO
DRUG RESISTANCE

16. Biofilm formation: Biofilms are communities of microorganisms that form a
protective matrix around themselves, making it difficult for drugs to penetrate and
reach the microorganisms.
Drug resistance can have serious consequences, including:
Increased healthcare costs
Longer hospital stays
Increased risk of death
Reduced effectiveness of antimicrobial drugs
CLINICAL MICROBIOLOGIST MR. MANOJ MAHATO
DRUG RESISTANCE

17. To combat drug resistance, it is important to:
Use antimicrobial drugs only when necessary
Take antimicrobial drugs exactly as prescribed
Do not share antimicrobial drugs with others
Practice good hygiene
Support research into new antimicrobial drugs
DRUG RESISTANCE

18. There are several mechanisms by which microorganisms can develop drug
resistance.
One common mechanism is the production of enzymes that break down or
modify the antimicrobial agent, rendering it ineffective.
 Another mechanism is the alteration of the target site of the antimicrobial
agent, preventing it from binding and exerting its effect.
Microorganisms can also develop efflux pumps that actively pump the
antimicrobial agent out of the cell, reducing its intracellular concentration.
CLINICAL MICROBIOLOGIST MR. MANOJ MAHATO
DRUG RESISTANCE

19. Mechanisms of Drug Resistance:
•Enzymatic Modification or Inactivation:
• Resistance genes code for enzymes that chemically modify antimicrobials,
rendering them inactive.
• For example:
• Aminoglycoside resistance: Enzymatic transfer of chemical groups impairs
drug binding to its bacterial target.
• β-lactam resistance: Enzymatic hydrolysis of the β-lactam bond within the
drug molecule, mediated by β-lactamases.
• Rifampin resistance: Inactivation through glycosylation, phosphorylation,
or ADP ribosylation.
• Macrolides and lincosamides resistance: Enzymatic inactivation or
modification
•.
CLINICAL MICROBIOLOGIST MR. MANOJ MAHATO
MECHANISMS OF DRUG RESISTANCE

20. Mechanisms of Drug Resistance:
•Modification of Antimicrobial Target:
• Some microbes alter the target site of antimicrobials, reducing their effectiveness.
• For instance, mutations in bacterial ribosomal RNA can lead to resistance against
specific antibiotics.
CLINICAL MICROBIOLOGIST MR. MANOJ MAHATO
MECHANISMS OF DRUG RESISTANCE

21. Antibiotic sensitivity tests, also known
as antimicrobial susceptibility tests, are
laboratory procedures used to determine
the effectiveness of different antibiotics
against specific bacteria or fungi.
These tests help guide physicians in
selecting the most appropriate antibiotics
to treat infections, ensuring targeted and
effective therapy.
CLINICAL MICROBIOLOGIST MR. MANOJ MAHATO
ANTIBIOTIC SENSITIVITY
TESTS

22. 1.Purpose: The primary goal of this testing is to determine which antibiotic(s) will be most
effective in treating a bacterial infection. It helps clinicians make informed decisions about
antibiotic therapy.
2.Why It Matters: Bacteria can develop resistance to antibiotics, making some drugs ineffective.
By understanding bacterial susceptibility, we can choose the right antibiotic to combat the
infection.
3.How It Works:
1. Culture Methods: In a medical laboratory, bacteria are exposed to various antibiotics. One
common method involves placing paper discs containing antibiotics on agar culture dishes
inoculated with bacteria. The “zone of inhibition”—the area where bacteria cannot grow
around sensitive antibiotics—is measured. The minimum inhibitory
concentration (MIC), which is the lowest antibiotic concentration that stops bacterial
growth, can be estimated from the zone size.
CLINICAL MICROBIOLOGIST MR. MANOJ MAHATO
ANTIBIOTIC SENSITIVITY TESTS

23. CLINICAL MICROBIOLOGIST MR. MANOJ MAHATO