Essay On An Overview Of Antimicrobial Typology

An overview of antimicrobial typology

Introduction
The term antimicrobial is an umbrella term referring to a wide array of pharmaceutical agents that are active against different micro organisms including, bacteria, fungi, viruses and parasites. The name has its origin in the three Greek words, anti (against), mikros (little) and bios (life).
There are several ways by which antimicrobial agents may be classified. This work provides a brief overview of various categories of antimicrobial agents in use and underlines the importance of appropriate antimicrobial treatment.

Antibiotics

The name antibiotic is often used synonymously with antimicrobial. However, the term antibiotic refers to drugs which are sourced from living organisms like bacteria and fungi. There are several ways of categorizing antimicrobials, e.g., according to their source, chemical structure, mechanism of action and spectrum, etc. ("Overview of antibacterial drugs: Bacteria and antibacterial drugs: Merck Manual Professional," 2009)

Categorization of antimicrobials

Antimicrobials can be sourced from living organisms or synthesized in the laboratory. Most antimicrobials belong to one of the three main sources: Bacteria (e.g., Bacillus spp.), fungi (e.g., Penicillium spp., Streptomyces spp.) and synthetic or semisynthetic (e.g., Sulphonamides)

According to chemical structure

This is the most commonly used means of classifying antimicrobial agents. (Leekha et al. 2011) Generally, members of one group have a common basic chemical structure which lends them specific pharmacokinetic properties. Most members within a particular group have certain peripheral alterations in molecular composition but retain the same core basic structure.

Beta lactam antibiotics: include Penicillins and Cephalosporins

Lincosamides: e.g., Lincomycin

Aminoglycosides: Gentamycin, Amikacin

Fluoroquinolones: Ciprofloxacin, Ofloxacin
Tetracyclines: Doxycycline
Miscellaneous: Chloramphenicol, certain anti tubercular drugs like Isoniazid
According to mechanism of action
At the cellular level, antimicrobials act on the target cells by one or more of the following mechanisms-
Inhibition of cell wall synthesis (Penicillins)
Inhibition of protein synthesis (Gentamycin)
Affecting integrity of cytoplasmic membrane (e.g., by increasing permeability-Polymixin B)

Inhibiting nucleic acid synthesis (Ciprofloxacin)

Affecting metabolic pathway of the target organism (Sulphonamides)
Viral infections
The classification of viruses relies primarily on their genomic structure and their mode of reproduction. DNA viruses and RNA viruses are the two principle viral categories. They can be further classified as single-stranded and double-stranded based on their chromatin structure. Viruses differentiate themselves from bacteria by their mode of replication. With few exceptions, DNA viruses tend to multiply within the host cell nucleus while RNA viruses typically multiply in the cytoplasm. At the time of infection, viral particles invade the host cell by binding to receptors on the cell surface. This is followed by uncoating of the viral particle and entry of DNA or RNA material inside the host cell. The next step is replication of viral genetic material, a complex process mediated by specific enzymes at different steps. The new viral genetic material produced is transformed into complete virus particles, often concurrently with the host cell death followed by release of multiple viral agents. Most antiviral agents act by blocking at one or more level, the enzymatically mediated cascade of steps leading to viral replication. Host cells respond to viral invasion by producing interferons which inhibit replication of viral RNA. Interferons are increasingly being used for antiviral treatment. ("Overview of viruses: Viruses: Merck Manual Professional," 2013)

Bacterial versus viral infection

Clinically, bacterial and viral infection may be virtually indistinguishable from each other owing to similar signs and symptoms. (Leekha et al. 2011) Both may cause similar diseases, e.g., pneumonia is caused both by streptococcal bacteria and haemophilus influenza virus. Further, both viral and bacterial infections often coexist. Indeed, many viral infections reduce immunity thereby increasing vulnerability to bacterial infections. e.g., HIV infected patients frequently suffer from opportunistic bacterial infections. However, there are several important differences between the two. Bacteria are unicellular organisms with ubiquitous presence in environment. Viruses on other hand are generally labile to environmental agents and require living host cells for their survival and multiplication. ("Overview of viruses: Viruses: Merck Manual Professional," 2013)
Many viral infections are easily preventable by the use of live or attenuated vaccines (active immunity) as well as immunoglobulins (passive immunity). Some bacterial infections like cholera may also be prevented by use of vaccines.

Clinical features

The manifestation of both bacterial and viral infections ranges from asymptomatic infection to acute illness and chronic latent infections. While many viral infections are successfully thwarted by the host immunity, some viruses tend to persist inside host cells in a dormant stage. These latent infections manifest themselves at a later stage, often triggered by exacerbating influences like immune suppression caused by drugs or due to coexisting morbidity. Chronic viral infections are marked by persistent shedding of viral particles, e.g., in Cytomegalovirus disease and Hepatitis B. Both viral and bacterial infections may transmit through air, food, water, vectors and through the parenteral route. The commonest portal of entry is respiratory and alimentary system. Some of the bacterial and viral infections are sexually transmitted or may be iatrogenic (blood infection through contaminated blood, mucous or needle injury). Several other animals (like rodents, bats) often are carriers of viral infections. ("Overview of viruses: Viruses: Merck Manual Professional," 2013)

Therapeutic principles

Antimicrobial agents are indispensable in modern clinical practice. Based on clinical presentation alone, both bacterial and viral infections may be virtually indistinguishable from each other. Thus laboratory testing is often the only way to definitively establish the nature of infection. As far as is possible, therefore, laboratory diagnosis should precede institution of anti microbial therapy. Indiscriminate (blanket) antimicrobial therapy, treatment with suboptimal dosage or inadequate duration of treatment leads to rapid emergence of drug-resistant pathogens. Indeed, the phenomenon of antibiotic resistance has rendered many of the commonly used antibiotics as redundant. Resistance to first generation anti tubercular drugs like Isoniazid is a prominent example. Similarly, use of antibiotics to treat common viral infections like common cold has contributed to this phenomenon. (Leekha et al. 2011)
Antimicrobial treatment is one of the most important and commonly used therapeutic modality in modern clinical practice. Development of newer and better antimicrobial drugs has helped cure diseases that were once considered untreatable. However, indiscriminate and inappropriate use of antimicrobials should be avoided. The basic principle of antimicrobial therapy is timely institution of the right agent at an optimal dosage and for an optimal duration of time. Often, combination of synergistically acting antibiotics is administered in order to target multiple co-existing infections. Wherever possible, lab culture and antibiotic sensitivity testing should guide appropriate antimicrobial therapy.

References

Leekha, Surbhi, Christine L. Terrell, and Randall S. Edson. “General Principles of Antimicrobial Therapy.” Mayo Clinic Proceedings 86.2 (2011): 156–167. PMC. Web. 18 Jan. 2015.
Overview of antibacterial drugs: Bacteria and antibacterial drugs: Merck Manual Professional. (2009, July). Retrieved January 19, 2015, from http://www.merckmanuals.com/professional/infectious_diseases/bacteria_and_antibacterial_drugs/overview_of_antibacterial_drugs.html?qt=antiviral%20drugs%20mechanism%20of%20action&alt=sh#v1000083
Overview of viruses: Viruses: Merck Manual Professional. (2013, August). Retrieved January 18, 2015, from http://www.merckmanuals.com/professional/infectious_diseases/viruses/overview_of_viruses.html