Definition and Purpose

Antimicrobial medications are drugs used to treat or prevent infections caused by pathogenic organisms, including bacteria, fungi, viruses, and parasites. They are essential when the body's natural defense mechanisms are insufficient to eliminate infectious agents.

• Antimicrobials are not effective against all microorganisms; they specifically target pathogens.

• They are necessary when host defenses are compromised or overwhelmed.

Microorganisms and Infections

Pathogenesis of Infection

Microorganisms initiate infection by attaching to host cell receptors, invading tissues, multiplying, and evading host defenses. Biological adaptations allow microbes to resist both immune responses and antimicrobial drugs.

• Attachment to host cells is the first step in infection.

• Microbes multiply and produce infection if not eliminated.

• Adaptations include resistance to immune mechanisms and drugs.

Classification of Microorganisms

• Bacteria

• Viruses

• Fungi

• Parasites

Normal Microbial Flora

Role and Disruption

Normal microbial flora are non-pathogenic microorganisms that colonize various body sites, providing protection against pathogenic invasion. Disruption of normal flora, such as by antimicrobial therapy, can allow potential pathogens to proliferate.

• Common sites: Skin, upper respiratory tract, colon.

• Suppression of normal flora may lead to overgrowth of pathogens.

• Normal flora can cause disease in immunocompromised or debilitated individuals.

Infectious Diseases

Transmission and Clinical Features

An infectious disease is characterized by the presence of a pathogen and clinical signs and symptoms. Transmission commonly occurs via direct contact with infected individuals or contaminated objects, food, or water.

• Direct contact: person-to-person, contaminated hands, objects.

• Clinical signs: fever, inflammation, organ dysfunction, etc.

Opportunistic Pathogens

Definition and Risk Factors

Opportunistic pathogens are typically non-pathogenic organisms that become pathogenic under certain conditions, such as immunosuppression or disruption of normal barriers.

• Risk factors: severe burns, cancer, HIV infection, indwelling catheters, antibiotic or corticosteroid therapy.

• Infections are often serious and may be caused by drug-resistant organisms.

Laboratory Identification of Pathogens

Diagnostic Methods

Laboratory tests are essential for identifying causative pathogens and guiding therapy.

• Gram stain: Identifies microscopic appearance of bacteria.

• Culture: Grows microbes in the laboratory for identification and sensitivity testing.

• Serology: Detects antibodies to identify infectious agents.

• Polymerase Chain Reaction (PCR): Detects microbial DNA in clinical samples.

Antibiotic-Resistant Microorganisms

Prevalence and Consequences

Antibiotic resistance is increasingly common among human pathogens, leading to infections that are more difficult and costly to treat, with higher morbidity and mortality rates.

• Resistant organisms proliferate when susceptible organisms are suppressed by antimicrobials.

• Impaired host defenses (e.g., immunosuppression) facilitate the emergence of resistant strains.

• Resistance often emerges during or after antimicrobial therapy.

Mechanisms of Resistance

• Production of enzymes that inactivate drugs (e.g., beta-lactamases).

• Modification of antibiotic target sites.

• Production of alternative enzymes to bypass drug action.

• Altered cell wall permeability.

• Efflux pumps that expel drugs from the cell.

Host Defense Mechanisms

Components of Host Defense

The body employs multiple defense mechanisms to prevent infection:

• Intact skin and mucous membranes

• Anti-infective secretions (e.g., saliva, gastric acid)

• Mechanical movements (coughing, swallowing, peristalsis)

• Phagocytic cells (e.g., neutrophils, macrophages)

• Immune and inflammatory processes

Impairments of Host Defense

• Breaks in skin/mucosa (trauma, inflammation, lesions, devices)

• Impaired blood supply

• Blood disorders (e.g., neutropenia)

• Malnutrition

• Poor hygiene

• Suppression of normal flora or immune response

• Chronic diseases (e.g., diabetes), advanced age

Characteristics of Antimicrobial Drugs

Terminology

• Anti-infective/antimicrobial: General terms for drugs against infections.

• Antibacterial/antibiotic (ATB): Drugs specifically for bacterial infections.

• Antiviral: Drugs for viral infections.

• Antifungal: Drugs for fungal infections.

Spectrum and Activity

• Broad-spectrum: Active against a wide range of organisms.

• Narrow-spectrum: Active against specific organisms.

• Bactericidal: Kills bacteria.

• Bacteriostatic: Inhibits bacterial growth.

Antimicrobial Mechanisms of Action

How Antimicrobials Work

• Inhibition of bacterial cell wall synthesis

• Inhibition of protein synthesis or production of abnormal proteins

• Disruption of microbial cell membranes

• Inhibition of nucleic acid synthesis or replication

• Inhibition of cell metabolism and growth

Principles of Antimicrobial Therapy

Goals and Rational Use

The primary goal is to eradicate the causative microorganism and restore the host to normal function. Rational use is essential to minimize adverse effects, costs, and the development of resistance.

• Antimicrobials are among the most frequently used drugs worldwide.

• Overuse and misuse contribute to resistance and increased healthcare costs.

Antimicrobial Therapy Use Guidelines

Selection and Administration

• Use older, cost-effective drugs if appropriate.

• Combination therapy may be needed for mixed or hospital-acquired infections.

• Route (oral or IV) depends on infection severity, location, and patient factors.

Duration of Therapy

• Prophylactic: single dose

• Acute infection: 7–10 days or until afebrile/asymptomatic for 48–72 hours

Special Populations

• Perioperative patients

• Children and older adults

• Patients with renal or hepatic impairment

• Critically ill or home care patients

Guidelines to Promote Appropriate Antimicrobial Drug Use

• Avoid antibacterial drugs for viral infections.

• Use narrow-spectrum drugs when possible.

• Collect specimens for culture before starting antibiotics.

• Minimize therapy for fever unless infection is confirmed.

• Follow CDC recommendations for infection prevention and treatment.

• Consult specialists for complicated or resistant infections.

Sample Table: Comparison of Antimicrobial Drug Types

Key Equations and Concepts

• Minimum Inhibitory Concentration (MIC): The lowest concentration of an antimicrobial that inhibits visible growth of a microorganism.

• Therapeutic Index (TI): Where is the toxic dose for 50% of the population, and is the effective dose for 50% of the population.

Examples and Applications

• Example: Lower respiratory tract infections and infections in cystic fibrosis patients are often associated with high rates of antimicrobial resistance and may require specialized therapy.

• Application: Collecting cultures before starting antibiotics ensures accurate identification and susceptibility testing, guiding effective treatment.

Additional info: This summary expands on the original slides by providing definitions, examples, and a sample table for clarity and exam preparation.