Antimicrobial sensitivity testing is a critical procedure in applied biology, particularly in clinical diagnostics and pharmaceutical research. This chapter focuses on understanding antibiotics and their modes of action, which underpin the selection and interpretation of sensitivity tests. Professionals working in Kenyan hospitals, research laboratories, and pharmaceutical companies use this knowledge to guide effective treatment of infections and to combat antibiotic resistance, a growing public health challenge in Kenya and globally.

3.1 Definition of Antibiotics

In the context of applied biology, antibiotics are substances used to inhibit or kill microorganisms, primarily bacteria, to treat infections. Their discovery revolutionized medicine and remains central to controlling infectious diseases in Kenya’s healthcare system. Understanding what antibiotics are, their origin, and their relevance helps professionals conduct meaningful antimicrobial sensitivity testing.

3.1.1 Origin and Nature of Antibiotics

Antibiotics are natural or synthetic compounds that target pathogenic microorganisms. Originally, many antibiotics were derived from microorganisms such as fungi and bacteria. For example, penicillin, discovered from the fungus Penicillium notatum, is a classic natural antibiotic. In Kenya, pharmaceutical companies like Universal Corporation Limited manufacture antibiotics both from natural sources and synthetic processes to meet local demand.

3.1.2 Definition and Scope of Antibiotics in Applied Biology

Antibiotics are chemical agents capable of selectively inhibiting or killing bacteria without harming the host. This selectivity is crucial for their therapeutic use. Antibiotics do not include antiviral or antifungal agents, which are classified separately. In microbiological techniques, antibiotics are used to test bacterial susceptibility, guiding clinical decisions and research on resistance patterns.

3.1.3 Therapeutic and Non-Therapeutic Uses

While antibiotics are mainly used therapeutically to treat bacterial infections, they also serve non-therapeutic roles such as in agriculture to promote livestock health and growth. In Kenya, misuse in agriculture has contributed to antibiotic resistance, complicating treatment in human health. Applied biologists must understand these uses to interpret sensitivity testing results accurately.

3.1.4 Importance of Antibiotics in Kenyan Healthcare

Antibiotics remain essential in treating common bacterial infections in Kenyan hospitals, such as urinary tract infections and respiratory diseases. The rise of resistant bacteria like Escherichia coli and Staphylococcus aureus in county hospitals underscores the importance of proper antimicrobial sensitivity testing. This ensures that treatments are effective and resistance is minimized.

Chapter Summary

This chapter explored the concept of antibiotics, defining them as substances used to inhibit or kill microorganisms causing infections. It examined various classes of antibiotics and their modes of action, highlighting how they target different microbial processes. The discussion then covered antimicrobial samples, including crude plant extracts, commercial antibiotics, and commercial antifungals, each serving as sources for testing antimicrobial activity. Attention was given to the challenge of antibiotic resistance, which threatens effective treatment of infections. The chapter detailed several antibiotic sensitivity testing methods such as the Kirby Bauer disk diffusion, automated systems, PCR, and broth dilution, explaining their principles and applications. It also addressed microbial culture isolation and enumeration techniques, including the plate count method, most probable number, direct count, and the use of flow cytometry, which are essential for assessing microbial populations in samples. Overall, the chapter provided a comprehensive understanding of how antimicrobial sensitivity testing is conducted and its critical role in microbiology.