PHARMACOLO NURS 251 MODULE 6

Module 6 6.1: Introduction to Infectious Diseases Infectious diseases are caused by pathogenic (disease-causing) organisms such as bacteria, fungi, and parasites as well as by viruses. Bacteria are defined as single-celled microorganisms. They can be found virtually everywhere and can either be harmless or very dangerous. This module will focus on the role of antibiotics to eliminate the pathogenic effects brought on by bacteria within a human host. Antibiotics are drugs that have the ability to destroy or interfere with the development of a living organism, typically bacteria. Bacteria Bacteria can be classified as either Gram-positive or Gram-negative. This classification refers to how they respond to the Gram stain procedure. Gram-positive bacteria stain purple, and Gram-negative stain pink. Interestingly, the results of a Gram stain actually play a significant role in selecting an appropriate antibiotic therapy. Due to differences in the composition of the cell membrane, some drugs cannot effectively penetrate the membrane which is often required to elicit the desired effects. Generally, Gram-negative bacterial infections are harder to treat because Gram-negative bacteria have a more complex cell wall structure. Another way bacteria are classified is by whether they are an aerobe or anaerobe. An aerobe is defined as a bacterium that grows in the presence of air or requires oxygen for growth. An anaerobe is defined as a bacterium that does not require oxygen in order to grow. Anaerobes, for instance, are most commonly found in the GI tract. Although there are many different kinds of bacteria and strategies for classifying them, this goes beyond the scope of this introductory module. Instead, it is important to understand generally that bacteria do not simply cause a single disease: rather, multiple disorders are possible depending on where in the body the bacteria accumulate. For example, the bacteria streptococcus pyogenes is the specific bacteria responsible for the common throat infection known as strep throat. This bacterium is spread through airborne droplets when someone with the bacteria coughs or sneezes. It can also be spread by sharing food or drinks. When the bacteria spread through the air or even food, the throat is one of the first contact points in the body, which makes strep throat a common result. However, if it happened to be transferred via contact with a contaminated surface and the person had an open sore, the very same bacteria could cause an entirely different infection, in this case, a skin infection. There are also common infections associated with certain bacteria based on where they are found naturally or how the pathogen is acquired. Take for instance, the bacteria E.coli. Although typically found within the intestines of a healthy individual, when someone becomes exposed to a pathogenic strain of E.coli, often via contaminated food, it often presents as diarrhea because of where the bacteria naturally end up by way of the digestive tract. One last factor is related to where the person contracts the infection—different types of bacteria are found in the environmental community compared to a healthcare setting. Generally, healthcare-associated infections are much more difficult to treat because the microorganisms have been exposed to strong antibiotics in the past; therefore, they are resistant to many treatments. Healthcare-associated infections are defined as an infection acquired during the course of receiving treatment for another condition in a health care institution. Examples of common Gram-positive bacteria and Gram-negative bacteria can be found in Table 5.1 below. This study source was downloaded by from CourseH on :04:14 GMT -06:00 Important terminology to be familiar with regarding antibiotics and bacteria: Antibiotic spectrum- bacteria that are susceptible to the antibacterial actions of a particular drug. Broad Spectrum is defined as an antibiotic that is effective against a wide variety of both Gram-positive and Gramnegative bacteria. Bacteria Resistance is defined as the ability of some bacteria to resist the actions of antibiotics. MRSA stands for methicillin-resistance Staphylococcus aureus. Methicillin is a penicillin-related antibiotic that was previously effective against resistant staph infections. However, over time, an even more drug-resistant strain developed and was termed MRSA. MRSA infections have become a major problem because none of the penicillin-class drugs are effective against it. In fact, only a few antibiotics, such as Vancomycin, have demonstrated effectiveness. 6.2: Antibiotics Similar to other types of medications, antibiotics are classified into broad categories or classes. These classifications are most often based on their chemical structure; however, these classes vary in more ways than just their chemical structure. Distinguishing characteristics include antibacterial spectrum, mechanism of action, potency, toxicity, and pharmacokinetic properties. Antibiotics are different than most other drugs in that their targeted site of action is not a part of the body but is actually the foreign bacteria that is causing an infection. The ultimate goal of the drug treatment is to kill or destroy the bacteria causing harm. There are four common mechanisms of action associated with antibiotics: 1. Interference with bacterial cell wall synthesis. This causes the formation of defective cell walls within the bacteria that are unstable and easily broken down. This generally causes the bacteria cell to rupture and ultimately die. 2. Interference with protein synthesis. Without the ability to make proteins, the bacteria can no longer function. 3. Interference with replication of DNA and RNA. DNA and RNA replication are how bacteria cells multiply. If they are not able to multiply, then the infection cannot survive. 4. Antimetabolite action that disrupts important metabolic reactions within the bacterial cell. By inhibiting important metabolic activities, the bacteria are no longer able to grow and function properly. Antibiotics are either considered bactericidal or bacteriostatic. Bactericidal antibiotics work by killing the bacteria.