District Laboratory Practice in Tropical Countries - Essay Example

District laboratory practice in tropical countries Culture and sensitivity is a microbiological diagnostic technique. Microbiologists rely on the culture principles and techniques in order to establish organisms present in a sample. The sample in this case may be urine, blood, vaginal swab, fluid from wounds and pimples. A microbiologist identifies the most appropriate culture technique for the sample. The technique of culturing denotes the process of providing an organism with appropriate growth conditions and allowing it to reproduce. After growth of the organism on the selected media occurs, an identification process takes place. After successful identification, a sensitivity test follows to determine the most effective antibiotic. This paper will highlight the micro biological principles that govern culture and sensitivity. Different microorganisms thrive in different systems of the body due to the varying environmental conditions. Microbiologists have described a vast range of microorganisms that thrive in the digestive tract, urinary tract, and blood (Baker, & Swain, 2002). Moreover, more elaborate studies have sought to establish the microorganisms that are responsible for causing different infections. Other critical studies focus on describing the conditions under which different organisms thrive. The understanding of these basic fundamental aspects in microbiology led to the development of cultures. The main purpose of culture is to foster the growth and multiplication of the microbes in a sample. After intensive growth in the appropriate media, identification and analysis follow. Bacterial Classifications The microbiologist should have vast knowledge concerning the classification of bacteria. Gram’s classification of bacteria into the renowned categories of gram positive and gram negative strains remained very essential. Moreover, depending on the need for oxygen as a growth factor is an additional criterion for classifying bacteria. Some are aerobic and oxygen must be present for any form of growth to occur while others do not need it. A good mastery of the bacterial classification criterion is critical in choosing the most appropriate culture conditions (Baker, & Swain, 2002). Media Composition and Classification Media denotes any substance prepared for the growth, transport and storage of microbes. Consistency of media varies from liquid to solid. The composition of media varies depending on the microbe of interest (Rao, 2010). The media contains all the necessary growth requirements. Microorganisms have different metabolic pathways. The basic nutritional requirements include a carbon source, nitrogen source, salts, and minerals in different quantities. However, different species of bacteria may require additional nutritional elements, a factor that helps in identification of microbes (Wilson, & Walker, 2010). Liquid media is critical for transport of microbes. Solid media contains a percentage of agars as a solidifying agent. Media preparation is a critical step prior to culturing any microbes. The quality of the media prepared determines whether growth of pure cultures can occur. Therefore, a microbiologist thrives to operate in sterile conditions as well as sterilizing all equipment and materials before use. Sterility is essential because contamination will translate to growth of microbes that are not present in the sample. When the purpose of a culture is obtaining a pure culture for diagnostic analysis, then contamination hinders any accuracy in the identification compelling the researcher to start all over again (Wilson, & Walker, 2010). There are different classifications of bacteria according to their nutritional characteristics. A clear understanding of this classification is very crucial because it serves as a guideline in the choice of the most appropriate media. Autotrophs are microbes that have the capacity to utilize inorganic carbon dioxide in the synthesis of macromolecules (Widdel, 2010). Depending on the source of inorganic carbon, autotrophs belong to two different categories namely photoautotrophs and chemoautotrophs, On the other hand, heterotrophs require organic carbon for biosynthesis. However, there is great diversity in the nutritional requirements of bacteria, and the microbiologist needs to understand the needs of the specific species. Types of Media Media can either be defined or complex. Complex media comprises of plant, animal or yeast extracts. Since the exact amount of the nutritional requirements in complex media surpasses the minimal growth requirements, microbiologists consider it undefined. Complex media has the capacity to support the growth of a vast range of microbes. On the other hand, defined media consist of known amounts of the nutritional requirements (Cheesbrough, 2005). Since defined media has a limited amount of nutritional requirements, it serves to support the growth of a few microbes. There are certain types of media designed for differentiating different microbes. Sometimes the microbiologist needs to provide specific requirements to ease the identification of microbes. Special media are essential during bacterial characterization. Selective media may prove very useful when the researcher intends to inhibit some microorganisms from growing. The design of selective media and its purpose takes advantage of the nutritional differences between microbes (Lindh, 2010). Moreover, other forms of selective media have their basis on the fact that some organisations can metabolize a certain element while others in the sample cannot. In DNA recombination techniques, selective media prove to be very efficient in selection of the organism of interest (Vaz-moreira et al., 2010). On the other hand, a scientist may opt to use a differential media in differentiating organisms during culture. Although differential media encourages the growth of a variety of micro organisms, it provides a unique aspect that can aid in differentiation of the growing microbes. In other cultures, the researcher can choose to combine the selective and differential media principles as an avenue towards easier identification of bacteria. Inoculation The choice of the most appropriate media forms the initial step towards the growth of a culture. Different samples such as urine, blood and stool have special media designated for the growth of all the organisms that can thrive in each sample. After preparation, dispensation of eth media into sterile petri dishes follows. Solid media settles to form a gel-like appearance in the petri-dish. Inoculation of the microbes from the sample onto the surface of the medium occurs. As mentioned previously, maintenance of high sterility levels is mandatory in microbiology. In cases where precision is desirable, contamination may alter the results completely, confusing the researcher (Lindh, 2010). Therefore, inoculation must occur in safety hood, coupled with flaming techniques to enhance sterility. There are different procedures of inoculation. One of them involves different streaking techniques (Andersen2005). Irrespective of the streaking technique used, a researcher anticipates to observe the growth of distinct colonies. Poor inoculation will lead to overcrowded colonies that prove difficult to characterize and analyze. There are multiple guidelines to help a microbiologist perfect the skill of streaking. Incubation After inoculation, the organism needs time to grow on the media in the petri dish. In diagnostic cultures, human samples provide the inoculums used in the culture. This translates to the fact that most of the organisms need a temperature that matches the normal body temperatures of 37 degree Celsius (Joint, Muhling, and Querellou, 2010). Therefore, incubation in a sterile incubator with temperatures adjusted to 37 degree Celsius. 24 hours is the duration that many organisms will take to form a culture. In these hours, the organism inoculated can demonstrates its ability to metabolize the available nutrients. Positive growth becomes evident when colonies form on the surface of the medium. Identification and Characterization It is important to analyze the organism growing on a single plate in order to gain evidence of drawing conclusions about the sample (Lindh, 2010). The initial step in identification involves a description of the colony morphology. Different bacteria exhibit various colony morphologies. Analyzing the size, color and shape of colonies can give the microbiologist a hint of the organisms growing on the plate. If multiple colonies grow on the plate, then it becomes necessary to carry out a sub-culture. This will involve setting up a new culture plate for each of the colonies. Allowing colonies to grow distinctly can help in easier identification. After colony description, gram staining becomes the second step that helps to differentiate gram positive and gram negative rods. Moreover, the distinction of gram positive and negative bacterial is an important criterion in sensitivity tests. Depending on the purpose of the culture, the microbiologist may indulge in further tests of identifications (Engelkirk at al., 2011). There are numerous test of distinguishing both gram positive and gram negative microbes. In diagnostic tests, a microbiologist may need to identify the exact organism in the sample. In this case, he or she must commit to running an array of tests after the gram staining. The gram difference is very crucial because it determines the steps that follow. For gram negative bacteria, there are numerous biochemical tests such as methyl red, motility, urease, indole production, citrate utilization and vogesproskauer. For gram positive bacteria, catalase test proves useful in identification. Although it is essential to master the difference between both a positive and negative result in all identification tests, there is a guideline that provides insights into the expected results for both gram positive and gram negative bacteria. Sensitivity Tests Sensitivity testing forms the last step in microbiological diagnostic tests. A researcher cannot afford to disregard this step. After successful culture and identification of a pathogenic microbe from a sample, a microbiologist needs to establish the best antibiotic for the patient. The structural difference of the cell wall evident in both gram positive and gram negative bacteria, translates to different antibiotics for the two categories of microorganisms. There are sensitivity discs designed for the sensitivity test (Pommerville, & Alcamo, 2007). The test requires a pure sample from the identified bacteria. Procedure Carrying out an effective sensitivity test requires the availability of the unique sensitivity test media. Through a spreading technique, application of the organism from the sample occurs. After spreading, the microbiologist places the sensitivity discs on the surface of the inoculated medium (Microbiology Laboratories, 2012). The sensitivity disc has different antibiotics attached to different places. Incubation provides growth conditions for the bacteria. However, the presence of the antibiotics on the disc alters the rate of growth. Any drug possessing the capacity to inhibit the growth of the organism leads to minimized growth in the areas of close proximity to the drug. However, drugs that are resistant do not exhibit any inhibition, and colonies are evident. Interpretation Antibiotics have different mechanisms of limiting the growth of microorganisms. However, they do so at markedly different rates. While some can inhibit the growth at a markedly high rate, some drugs lack the capacity to alter normal cell function inhibiting microbial growth. Antibiotics that have the potential to interfere with cell growth, exhibit a large zone of inhibition. On the other hand, weaker antibiotics exhibit minimal inhibition to microbial growth. A microbiologist should record the size of the zones of inhibition as evident on the plate after incubation (American Society for Microbiology, 2005). The sensitivity test should serve to influence the choice made in prescription. The best drug through proven efficiency in the test should be first choice. However, other factors are of significant contribution in determining the final choice of an antibiotic. One of these factors surrounds the side effects presented by a certain drug. Any drug that presents numerous adverse reactions ceases to become a first choice in prescription despite its efficiency as evident from the sensitivity test. In such cases, a specialist should search for a drug with considerable capacity and a high level of safety. Conclusion As described above, the choice of the most appropriate medium forms the initial step towards the growth of a culture. Different samples such as urine, blood and stool have special media designated for the growth of all the organisms that can thrive in each sample. The technique of culturing denotes the process of providing an organism with appropriate growth conditions and allowing it to reproduce. After growth of the organism on the selected media occurs, an identification process takes place. After successful identification, a sensitivity test becomes a critical tool in guiding a specialist in choice of the best drug for prescription. References American Society for Microbiology. (2005). Manual of Antimicrobial susceptibility test. Retrieved on 2nd March from http://forms.asm.org/ASM/files/ccLibraryFiles/Filename/000000002484/Manual%20of%20Antimicrobial%20Susceptibility%20Testing.pdf Andersen, R. A. (2005). Algal culturing techniques. Amsterdam [u.a.: Elsevier, Academic Press [u.a.. Baker, C., & Swain, H. L. (2002). Principles of science for nurses. Osney Mead, Oxford: Blackwell Science. Cheesbrough, M. (2005). District laboratory practice in tropical countries. Cambridge: Cambridge University Press. Engelkirk, P. G., Duben-Engelkirk, J. L., & Burton, G. R. W. (2011). Burton's microbiology for the health sciences. Philadelphia: Wolters Kluwer Health/Lippincott Williams & Wilkins. Joint, I., Muhling, M., and Querellou, J. (2010). Culturing marine bacteria-an essential prerequisite for biodicsovery. Jounal for Applied Microbiology and Blackwell Publishing Lrd, 3(5), p. 564-575. Lindh, W. Q. (2010). Delmar's comprehensive medical assisting: Administrative and clinical competencies. Clifton Park, NY: Delmar Cengage Learning. Microbiology Laboratories. (2012). The Antibiotic disc sensitivity test. Retrieved on 2nd March 2012 from http://inst.bact.wisc.edu/inst/index.php?module=book&func=displayarticle&art_id=135 Pommerville, J. C., & Alcamo, I. Edward. (2007). Alcamo's laboratory fundamentals of microbiology. Sudbury, Mass: Jones and Bartlett. Rao, S. (2010). Bacterial culture media. Retrieved on 2nd March 2013 from http://www.microrao.com/micronotes/culture_media.pdf Repositorio (n. d.). Surveys target different bacteria: A case study in a freshwater sample. Retrieved on 2nd march 2013 from http://repositorio.ucp.pt/bitstream/10400.14/7457/1/Culture-dependent%20and%20culture-independent%20diversity%20surveys%20target%20different%20bacteria%20%20a%20case%20study%20in%20a%20freshwater%20sample.pdf Vaz-Moreira et al. (2010). Culture-dependent and culture-independent diversity. Widdel, F. (2010). Theory and measurement of bacterial growth. Retrieved on 2nd March 2013 from http://www.mpi-bremen.de/Binaries/Binary13037/Wachstumsversuch.pdf Wilson, K., & Walker, J. M. (2010). Principles and techniques of biochemistry and molecular biology. Cambridge, UK: Cambridge University Press. Read More