Medical Microbiology - Research Paper Example

Medical Microbiology Difference between Gram-positive and Gram-negative bacteria A number of structural differences that are evident between Gram-positive and Gram-negative bacteria. The primary structural difference between gram negative and gram-positive bacteria relates to the arrangement of their outer portions. Gram negative bacteria has a Peptidoglycan layer that is thin and single layered while gram positive bacteria have Peptidoglycan layer that is thick and multilayered (Golan 2008, p. 66). Most gram-positive bacteria have teichoic acids while gram-negative bacteria do not have teichoic acids at all. Gram-negative bacteria have Periplasmic space while gram-positive bacteria do not have. Another difference is that gram-negative bacteria have an outer membrane while gram-positive bacteria do not. Gram-positive bacteria have 2 rings in basal body while gram negative bacteria have 4 rings in basal body (Harvey, Champe, & Fisher 2007, p. 110). Despite the fact that gram positive bacteria have a thick Peptidoglycan layer, the lack of an outer membrane makes it easier for there to be easy penetration of stains that’s why they take the initial stain and turns purple. On the other hand, the presence of an outer membrane of gram-negative bacteria has the outer membrane that makes it impossible for the initial stain to penetrate (Murray, Rosenthal & Pfaller 2013, p. 189). The gram-negative bacteria that have medical relevance because of their capability to cause primarily respiratory problems include Hemophilus influenzae, Legionella pneumophila, and Klebsiella pneumoniae. Others that cause primarily urinary problems include Escherichia coli and Serratia marcescens. Those that cause primarily gastrointestinal problems include Helicobacter pylori and Salmonella enteritidis. Applications of other staining techniques for identification purposes Staining techniques can be used for identification purposes. The simple staining technique can be used by using basic dyes that are positively charged can be used in the identification of the negatively charged material of microbial cytoplasm. This is because the opposite charges will obviously lead to attraction. The vice-versa would apply for negatively charged dyes. The acid-fast technique can be used in differentiating species of Mycobacterium from other types of bacteria. In this technique heat or in some situations liquid solvent is used in carrying out the initial stain, carbolfuchsin, into cells. The cells are then supposed to be washed using a dilute acid-alcohol solution. The identification will be done because Mycobacterium species have the ability of resisting the effect brought about by the acid-alcohol solution thus retaining the bright red colour of the carbolfuchsin stain (Tucker & Hargreaves, 2004, p. 223). The other bacteria losses the stain and turn into blue. Special stains technique can be used in highlighting the flagella of bacteria by a coat of dyes or metals around the bacteria, resulting in an increase in the width of the bacteria. The staining will lead to identification of flagella (Zourob, Elwary & Turner 2008, p. 231). Selective and differential media are in many instances, uses in diagnostic bacteriology. Some media have both selective and differential properties. Clinical history can always affect the choice of selective and differential media to be used. For instance, hereditary hemochromatosis (HH) and other conditions of Iron Overload can be one of the conditions whereby clinical history is important. Clinical history helps in distinguishing between the primary and the secondary causes of iron overload. Bacterial Group Species Disease Caused Gram positive cocci Staphylococcus pneumonia Pneumonia Streptococcus cellulites Cellulites Micrococcus luteus Septic shock Gram positive bacilli (rods) Bacillus anthracis Cutaneous anthrax Gastrointestinal anthrax0 Bacillus cereus Abdominal cramps Clostridium Perringens Myonecrosis Gram negative cocci Neisseria maningitidis Meningitis Neisseria gonorrhoeae Gonorrhoea Bordetella pertussis Whooping cough Gram negative bacilli Haemophilus Influenza Influenza Salmonella typhi Typhoid Pseudomonas aeruginosa Mycobacteria Mycobacterium tuberculosis Tuberculosis Mycobacterium leprae Leprosy Mode of action of antibiotics Aminoglycosides act by initially penetrating the cell walls of the target bacteria to reach the periplasmic space through the porin channels by the mechanism of diffusion. There is movement through the cytoplasmic membrane through an active transport mechanism of the proton pump. This process is dependent on the availability of oxygen. The antibiotics, then bind 30S sub-units of ribosomes and interfere with the initiation complex. This induces a misreading of the genetic code on the MRNA thereby leading to a breakup of the polysomes into monosomes (Gantz 2006, p. 121). This inhibits the activity of the bacteria. Aminoglycosides also exhibit the concentration dependent killing. They possess a great post-action effect. Tetracycline is a broad-spectrum antibiotic, which acts through binding on the 30S subunits of microbial ribosomes. They act by inhibiting the synthesis of proteins through blocking the attachment of the charged aminoacyl-tRNA. This therefore prevents the introduction of new amino acids in the chain of nascent peptides. This action usually is inhibitory and could be reversed by withdrawal from the usage of the said drug. Resistance to the antibiotic results from changes in the microbial cell envelope that affects its permeability (Wilson, M 2005, p. 217). In susceptible cells, the drug is usually concentrated within and not allowed to readily leave the cell. In the cells that are resistant, the drug is never actively transported into the cell and leaves rapidly thereby interfering with inhibitory actions. The actions are therefore never maintained. It is usually plasmid-controlled. Tetracyclines, however, are not actively concentrated by mammalian cells. Trimethoprim acts by interfering with the functionality of bacterial dihydrofolate reductase, thereby inhibiting the synthesis of tetrahydrofolic acid, which is an essential precursor in the synthesis of the intermediate Thymidine monophosphate, which is the precursor of DNA metabolite, Thymidine triphosphate. Bacteria are normally unable to absorb folic acid from their environment and are usually dependent on their own de novo synthesis of the acid (De Filippis, & Mckee 2013, p.88). When the enzyme is inhibited, the bacterium is starved of nucleotides, which are necessary for the replication of DNA, therefore causing cell lethality due to thymineless death. Rifampicin acts by inhibiting bacterial RNA polymerase. This enzyme is responsible for the transcription of DNA, through the formation of a drug-enzyme complex that is stable with a binding constant of 10 at 37degrees Celsius. Corresponding mammalian enzymes are, however, not affected by the actions of the antibiotic. Mutations cause resistance to these antibiotics which lead to a change in the beta subunit of the polymerase RNA. A large number of polymerases, however, develop different degrees of resistance to the antibiotic and it is therefore not a case of all or nothing (Greenwood 2012, p. 192). Sulfonamides; several microbes need p-aminobenzoic acid to synthesize dihydrofolic acid that is required to produce purines leading to the formation of nucleic acids. Sulfonamides are competitive inhibitors of dihydropteroate synthetase. These antibiotics are therefore reversible inhibitors of the folic acid synthesis process and are bacteriostatic (Lennette, Lennette & Lennette 1995, 201). Methods of identification and classification of pathogenic bacteria GDS™ This is a salmonella genetic detection system, and a computerized nucleic-acid amplification system that is used in detecting the salmonella bacteria in food products. It detects the presence of salmonella in levels that are very low (Ogunseitan 2007, p. 197). BAX® Thus an accurate and yet fast method for detecting the presence of pathogens and other organisms in food samples and in environmental samples too. It breaks down the samples at the genetic levels using the power produced by the polymerase chain reaction to detect the presence of bacteria and other pathogens with high levels of occurrence. ELISA This stands for an enzyme-linked immunosorbent assay. The tests use components of the immune system of a body and other chemicals in the detection of immune responses within the body. The test involves an enzyme, antigen, and antibody. It is widely used in the detection of foreign substances that have antigenic properties. The microbiologists culture method has been/ is being used in the determination of the type of organism present by allowing the sample collected to multiply. The method, however slow, is used in determining the presence and amount of an organism, and to what state it has reached within its host. Serological methods include EIA, RIA, immunofluorescent tests, and ELISA amongst others. These methods involve the use of serum as the sample in the test. These methods are the most used due the quick responses that are attached to them (Murray, Rosenthal & Pfaller 2009, p. 199). Uniqueness of Rickettsia and Chlamydia Rickettsia is a non-motile, non-spore-forming, highly pleomorphic bacteria and can therefore take a round shape, rod-like or thread shape. They are intracellular parasites and are highly dependent on entry, growth, and replication in the eukaryotic host cells’ cytoplasm. They cannot live in nutrient environments and are grown in either embryo or tissue cultures (NATO Advanced Research Workshop On Detection Of Bacteria, Viruses, Parasites And Fungi & Magni 2010, p. 246). They are highly susceptible to antibiotics of the tetracycline class. Chlamydia is a major cause of human genital and eye infections. It is also obligate intracellular. Due to their lack of a cell wall, they take into distinctive shapes. They are rarely found as rods. They also have a peptidoglycan cell wall. Rifampicin Viruses, parasites, and Fungi Viruses are microscopic infectious agents, which replicate only inside living cells of organisms. Viruses are comprised of their genetic material, DNA or RNA, a lipid envelope that covers and protects the whole cell, and the protein coat of the genetic material. They are spread through cellular contact. They are much smaller than bacteria. Their replication cycle is comprised of the stages of attachment, penetration, uncoating, and replication. Viruses are classified through two major broad classification systems that are the Baltimore and ICTV classification systems. Examples of common diseases that are caused by viruses include AIDS, Common cold, Chickenpox, SARS, and the Avian Influenza. AIDS is caused by HIV, which is the human immunodeficiency virus, whereas chicken pox is caused by varicella. Fungi include eukaryotic organisms that include moulds, yeasts, and mushrooms. Most fungi grow as cylindrical, threadlike structures know as hyphae. Haephae grow from tips and new ones are formed through branching. Fungal mycelia may become visible on surfaces such as damp walls and on spoilt food where they are commonly called molds. They are referred to as colonies when grown in petri dishes in laboratories. Several fungi produce toxins that are poisonous to humans and other organisms too. Amatoxins and aflatoxins are examples of the same. Parasites are classified into four major groups. They majorly live in the digestive systems, whereas there are those, which live in other parts of the body including blood, brain, eye, and sinus cavities. These parasites include protozoa, which are single cellular and can attack any single cell in a body. They replicate and multiply by duplication just like viruses and bacteria. Another category of parasites is the nematodes. They are the roundworms and are introduced into the body in the form of microscopic eggs, which hatch within the body. They include the pinworms, whipworms, and hookworms. Trematodes are the hardest parasites to get rid of. They are the flukes and can stay within the human body for up to 20years without removal. Each fluke lives for a year and the reproduction process is continuous. The last category of parasites is the cestodes. They are greyish white in colour and are about half an inch in length. They can lay up to 1million eggs a day. They hook their heads on the intestinal walls. They are commonly referred to as tapeworms. Conventionally, fungi are usually identified and isolated based on their microscopic and macroscopic features. Colour and spore content are also observed. After their genera are determined, their samples are transferred into a medium of selected genus monographs for species identification. Viruses are, however, identified through serological methods, cytopathic effect and molecular methods. Most commonly used serological method is western blotting. PCR and RFLPs are the common molecular methods used. Intestinal parasites are majorly isolated and identified from faecal samples. After the samples are collected, the eggs are separated from the sample. The eggs are examined microscopically and a faecal culture prepared for the identification process. The physical features of the infective larvae are observed, recorded and identified and to determine its nature and type. After this is when diagnosis is possible. If the features are unknown to the researcher, the worm is isolated. Bibliography De Filippis, I & Mckee, ML 2013, Molecular typing in bacterial infections. Gantz, NM 2006, Manual of clinical problems in infectious disease, Lippincott Williams & Wilkins, Philadephia. Goering, RV 2012, Mims' medical microbiology, Saunders, Edinburgh. Golan, DE 2008, Principles of pharmacology: the pathophysiologic basis of drug therapy, Lippincott Williams & Wilkins, Philadelphia, Pa., [etc.]. Greenwood, D 2012, Medical microbiology, Churchill Livingstone, Edinburgh. Harvey, RA, Champe, PC & Fisher, BD 2007, Microbiology, Lippincott Williams & Wilkins, Philadelphia, Pa. Hassan, RM, Scholes, R & Ash, N 2005, Ecosystems and human well-being: current state and trends : findings of the Condition and Trends Working Group, Island Press, Washington, DC. Lennette, EH, Lennette, DA & Lennette, ET 1995, Diagnostic procedures for viral, rickettsial, and chlamydial infections. Washington, DC, American Public Health Association. Murray, PR, Rosenthal, KS & Pfaller, MA 2009, Medical microbiology, Mosby/Elsevier, Philadelphia, Murray, PR, Rosenthal, KS, & Pfaller, MA 2013, Medical microbiology. Nato Advanced Research Workshop On Detection Of Bacteria, Viruses, Parasites And Fungi, & Magni, MV 2010, Detection of bacteria, viruses, parasites, and fungi: bioterrorism prevention, Springe, Dordrecht. Ogunseitan, O 2007, Microbial Diversity, John Wiley & Sons, Oxford. http://public.eblib.com/EBLPublic/PublicView.do?ptiID=233100. Tucker, CS & Hargreaves, JA 2004, Biology and culture of channel catfish, Elsevier, Amsterdam. http://www.engineeringvillage.com/controller/servlet/OpenURL?genre=book&isbn=9780444505767. Wilson, M 2005, Microbial inhabitants of humans: their ecology and role in health and disease, Cambridge University Press, Cambridge, UK. Zourob, M, Elwary, S & Turner, APF 2008, Principles of bacterial detection: biosensors, recognition receptors, and Microsystems, Springer, New York. Read More