Pathogens_and_Infection

Pathogens Pathogens are microorganisms that cause disease and include various species of bacteria, viruses, protozoa and fungi, although not all microorganisms cause disease. Pathogens can cause disease in animals and plants, although the human body has some natural defences that can protect against some of these pathogens. Infection is nothing but disease acquired by a healthy human being through any means (by touching an object or infected person, through inhaling air containing germs or bacteria of diseases or through body fluid that contains such germs, viruses, parasites or bacteria which cause disease in a healthy human being). We're all exposed to micro-organisms, and we all get infections from time to time, but that doesn't explain why some people in a certain place develop an infection, while others in the same place at the same time don't. Bacteria Bacteria can be classed a living cells as they have the characteristics required to be classed as life form. The cell structure of bacteria is a single celled prokaryote (meaning no nucleus in its cell) and its size can range from 0.2 to 2 micrometres. Most bacteria have an outer, rigid cell wall. This provides shape and support. In the cytoplasm are ribosomes and nuclear material which carry genes that control resistance to drugs. Some bacteria have long, whip-like structures called flagella and its main function is movement. Bacterial cells can multiply successfully and transfer genetic information from an old cell to a new cell. Bacteria can be found everywhere, in animals and plants, inside and outside of the body. Most bacteria found are harmless and useful for making yogurts and cheese. Gut bacteria found inside of the human body helps with the digestion process by destroying harmful bacteria that enters the human body. Helpful bacteria are also used to purify water at sewage treatment plants. It is estimated that only 1 % of bacteria is harmful. Cholera, Tuberculosis, and Tetanus are all pathogenic bacteria. Antibiotics have been useful in treating bacterial infections, but bacteria can become resilient to medicines. Viruses Viruses are parasitic microorganisms that survive and spread by multiplying in the host cells. They can be species specific, so can only infect certain plants and animals. They are the smallest organisms and consist of two basic components; a very strand which contains the genetic coding in the DNA (deoxyribonucleic acid) or RNA (ribonucleic acid) (RNA). The genetic material has the information for determining the structure and behavior of a cell. In a virus, a protein coat called a "capsid" surrounds the nucleic acid. This coat serves to protect the nucleic acid and aid in its transmission between host cells. The capsid is made of many small protein particles called capsomeres. The shape of a virus varies and range from being simple to more complex. Viruses are thought to be one hundredth the size of bacteria, ranging from 0.02 micrometres to 0.3 micrometres. Figure 2 The image shows a flu virus. The Virus strains are characterised by the nature of the two proteins found on their surface, namely Neuraminidase and Hemagglutinin. Approximately 80 percent of the spikes are hemagglutinin, a trimeric protein that functions in the attachment of the virus to a host cell. The remaining 20 percent of the glycoprotein spikes consist of neuraminidase, which is thought to be predominantly involved in facilitating the release of newly produced virus particles from the host cell. The inner of the cell contains the RNA nucleotides which are the genetic code for the virus replication. Other virus include the HIV virus, chicken pox, measles. Antiviral drugs have been made to help with preventing certain viruses from spreading, but once a virus enters a host it is difficult to treat it as viruses seem to have no effect from medication. Fungi Fungi is a microorganism from a large group of eukaryotic organisms. They are large, plant-like organisms that lack chlorophyll (the substance that makes plants green and converts sunlight into energy) hence they have to absorb food from whatever they are growing on. Fungi can be very helpful if used correctly in various tasks:- brewing beer, making bread rise, decomposing trash – but they can also be harmful if they steal nutrients from another living organism. Mushrooms are important fungi, but there are other forms such as molds and yeasts. The main identifying characteristic of fungi is the makeup of their cell walls. Many contain a nitrogenous substance known as chitin, which is not found in the cell walls of plants, but can be found in the outer shells of some crabs and molluscs. Most fungi are multicellular (made up of many cells), with the exception of the yeasts. The cells make up a network of branching tubes known as hyphae, and a mass of hyphae is called a mycelium, which is permeable allowing nutrients to be absorbed. The genetic material is gathered together and enclosed by the membrane in the nucleus. Also, there are other structures called organelles in the cell that help the cell to function, such as mitochondria which converts energy, endoplasmic reticulum which makes complex proteins, and other organelles. The Golgi apparatus forms many types of proteins and enzymes. Lysosomes contain enzymes and help digest nutrients. Centrioles are necessary for proper division of the cell. Both bacteria and fungi have ribosomes, but those of the bacteria are smaller in size and also reproduce differently. They have extracellular digestion by secreting enzymes into environment and absorbing the nutrients produced. This can be a problem if fungi start absorbing nutrients from a living organism, because once they start to reproduce it can cause disease, such as athletes foot (which is a fungal infection). Protozoa Figure 4 Protozoa are single celled eukaryotes that commonly show characteristics usually associated with animals, most notably mobility and heterotrophy (the use of organic carbon for growth). They are the cause of more sickness and death than any other group of disease-causing organisms. As eukaryotes, protozoa have a membrane-bound nucleus with well-defined chromosomes. They also have other cellular organelles that are characteristic of eukaryotes. The various forms have in common a unicellular structure consisting of a mass of cytoplasm with one or more nuclei. Like all cells, they are bounded by a thin cell membrane; in addition, most have a tough outer membrane called a pellicle, which maintains their form. Despite their small size and lack of organization into multicellular systems, protozoans carry on all the metabolic functions of animals. Organelles, or intracellular structures, carry out a variety of functions, such as digestion, excretion, respiration, and coordination of movement; some protozoans are much more complex in their internal structure than are the cells of multicellular animals. Some protozoans have complex digestive systems and feed on large food particles, such as other microorganisms. The food is digested by means of enzymes and the wastes transported to the cell surface or stored in vacuoles (bubblelike spaces in the cytoplasm). Others have no digestive system and absorb dissolved organic matter through the cell membrane. Toxoplasmosis is caused by ingesting infective cysts of the parasite Toxoplasma gondii. Toxoplasmosis is acquired by eating raw or undercooked meat and through contact with an infected animal, mainly cats. Amoebic dysentery is caused by the protozoan Entamoeba histolytic and tourists often find they have picked up amoebic dysentery whilst travelling. It is found throughout the world, is transmitted by faecal cysts in contaminated food or water. Once ingested, the organism secretes enzymes that digest in the intestinal lining. This leads to a perforated colon, and complications can be fatal. The liver and the lungs may also become hosts to the parasites, causing death. Infection in Hospitals With technology, there has been an improvement in techniques and precautions used to avoid infections during hospital stay of a patient. However, it is not possible to avoid or eliminate hospital infections completely. A hospital acquired infection is considered to be one of the most serious concerns throughout the medical history. In most of the countries (including developed and developing), doctors and hospital staff are educated to avoid any kind of possibility of infection during hospitalisation of a patient. However, it is also very important to make patients and people visiting hospitals aware of such situations and educate them to avoid such infections. Every patient who is admitted to the hospital stands a chance of being infected. What matters is how susceptible an individual is and how well their immune system can defend them. People who have a weakened immune system (people suffering from immune system related disease such as AIDS or other diseases that weakens their immune system) are most vulnerable for such infections. Not only people who are admitted to hospital, but also those who visit hospitals are under the risk of acquiring infections in hospitals. The other factors that contribute to such conditions are: longer stay of a patient in a hospital, use of unhygienic procedures and instruments during operation or any such treatment, improper use of medicines such over or under use of antibiotics which may lead to development of resistance to such medicines in bacteria, failure to maintain hygiene, age of the patient and also genetics. Despite sanitation protocol, patients cannot be entirely isolated from infectious agents. Furthermore, patients are often prescribed antibiotics and other antimicrobial drugs to help treat illness; this may increase the selection pressure for the emergence of resistant strains. Invasive devices, for instance intubation tubes, catheters, surgical drains, and tracheostomy tubes all bypass the body’s natural lines of defence against pathogens and provide an easy route for infection. Infections caught at hospital mainly involve infections of lungs, blood, skin, urinary tract etc. Patients having weakened immune system are most vulnerable to such infections. Some of the most common hospital infections are: MRSA (Methicillin-Resistant Staphylococcus Aureus): This is a common bacterium which spreads through infection. This bacterium is found on the skin and other parts of body such as nose of people. MRSA bacterium finds its way into a person’s body through a wound or cut and infects him/her. MRSA bacterium has become resistant to most of the antibiotics which makes it very hard to treat infection caused by these bacteria. MRSA is one of the most commonly spread infections during a person’s stay in hospital. Clostridium difficile or ‘C. diff’: another infection which has made headlines recently as nearly 80 per cent of sufferers are over 65 years old and can be triggered by antibiotics for urinary or chest infections and is more prevalent in hospital in-patients. Symptoms may be mild in most cases but in severe infections, C. diff can cause a serious illness or even death. Pneumonia: Half of all pneumonia cases are caused by bacteria. The bacteria, known as streptococcus pneumonia is the main cause of the most typical pneumonia. Pneumonia is still a common disease affecting around 1 per cent of the adult UK population each year. Many people die from it every year, most commonly women and especially people over the age of 70. The overall death rate due to pneumonia is currently 5 per cent. Infection Control To help prevent hospital associated infection from spreading, it is important that everyone in the hospital environment follows the stringent procedure of sanitisation and cleanliness. These procedures do not apply to the wider society, as the risk of spread of infection in a care environment is higher compared to non-health care environment. Some health care settings, especially hospitals, are more likely to harbour dangerous micro-organisms. Patients are particularly vulnerable to infection because their immune systems tend to have been weakened by disease. The organisms that tend to survive in hospitals are those which have developed resistance to antibiotics. One example that has caused a lot of concern in recent years is MRSA. This type of bacteria is easily spread and healthy people can live with it on their skin or in their noses without becoming ill thus being a carrier of the bacteria. Health care staff and visitors carry the bacteria around and unwittingly spread MRSA to patients to whom it can cause potentially life-threatening infections. Therefore it is necessary to wash hands and sanitise before and after every visit to the hospital is made, to stop the spread of the bacteria. If a person does become infected or has a contagious disease, then they may be isolated or put in a room with others who have the same infection or contagious disease in order to quarantine the illness. Isolation precautions are designed to prevent transmission of microorganisms by common routes in hospitals. If anyone of the visitors is already suffering from any disease which can lead to infection in patients in the hospital, in such case they should be requested not to visit unless they are not contagious any more. It is also vital that all medical equipment and protective clothing are cleaned correctly. Equipment used during treatment must be sterilised properly, as well as the person treating must wash their hands and wear gloves whilst treatment is in progress. Gloves must always be changed every time a new patient is seen. Hand washing frequently is the single most important measure to reduce the risks of transmitting skin microorganisms from one person to another or from one site to another on the same patient. Washing hands as promptly and thoroughly as possible between patient contacts and after contact with blood, body fluids, secretions, excretions, and equipment or articles contaminated by them is an important component of infection control and isolation precautions. Although hand washing may seem like a simple process, it is often performed incorrectly. Healthcare settings must continuously remind practitioners and visitors on the proper procedure in washing their hands to comply with responsible hand washing and hand sanitisation. Simple reminders such as the use of hand washing signals can assist healthcare facilities in the prevention of nosocomial infections. Hospitals have sanitation protocols regarding uniforms, equipment sterilisation, washing, and other preventative measures. Thorough hand washing and use of alcohol rubs before and after each patient contact is one of the most effective ways to combat nosocomial infections. All visitors must follow the same procedures as hospital staff to adequately control the spread of infections. Visitors and healthcare personnel are equally to blame in transmitting infections. Figure 1 Accessed 1/05/2011 http://www.nrccnrc.gc.ca/eng/education/biology/basics_bacteria.html Figure 2 Accessed 7/5/2011 http://www.chm.bris.ac.uk/webprojects2006/Kelly/fluv.htm Figure 3 Accessed 7/5/2011 http://www.peteducation.com/article.cfm'c=16+2160&aid=2956 Figure 4 Accessed 8/5/2011 http://homeschoolersresources.blogspot.com/2010/09/biology-module-3-kingdom-protista.html http://www.netdoctor.co.uk/health_advice/facts/virusbacteria.htm (internet) accessed 6/5/2011 http://en.wikipedia.org/wiki/Protozoa (internet) accessed 7/5/2011 http://www.naturegrid.org.uk/biodiversity/crypfungi.html (internet) accessed 7/5/2011 http://en.wikipedia.org/wiki/Fungus (internet) accessed 6/5/2011 http://en.wikipedia.org/wiki/Pathogen (internet) accessed 1/5/2011 http://en.wikipedia.org/wiki/Bacteria (internet) accessed 1/5/2011, 5/5/2011 http://www.mcwdn.org/Animals/PROTOZOA.html (internet)accessed 5/5/2011,6/5/2011 http://www.biology-online.org/articles/fungi/characteristics_fungi.html (internet) accessed 6/05/2011,7/05/2011 http://www.bbc.co.uk/health/physical_health/conditions/infections1.shtml (internet) accessed 9/5/2011,10/05/2011 http://en.wikipedia.org/wiki/Nosocomial_infection (internet) accessed 10/05/2011, 9/5/2011