DNA contains the cell’s genes and its genetic code and is integral to the proper functioning of the cell (Engelkirk and Duben-Engelkirk, 2011). The information that makes up the genetic code
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consists of four nucleotides, or bases – A (adenosine), T (thymine), G (guanine) and C (cytosine) – that are strung together in a long sequence, resembling two entwined ribbons, which is made up of thousands of millions of individual letters. The sequence in which these letters appear is different in all organisms, and because of this it is possible to determine the specific, unique sequence of these four bases in an organism. If the order in which these letters or bases appear within the sequence changes, this indicates that a mutation has occurred.
Fact Box 7.5 Genome Sequencing
In 1999, the Human Genome Sequencing Project began (completed in 2003) in which the sequence of three billion DNA subunits was undertaken and all of the human genes were identi- fied (http://www.genome.gov/10001772; Venter, Adams, Myers et al., 2001). In 2005, genome sequencing enabled the Spanish flu virus to be re-created (Taubenberger et al., 2005). In 2001, Parkhill et al. reported that genome sequencing of a strain of Yersinia pestis, the organism known to have caused the Black Death (plague), had identified the presence of virulence genes acquired from other bacteria and viruses (Parkhill et al., 2001), and more recently, in 2011, approximately 99% of the genome was recovered from the 600-year-old skeletal remains of plague victims buried in the fourteenth century (Bos et al., 2011). (See Fact Sheet 1.8 on the companion website.)
•
Bacterial growth involves an increase in both the size and number of organisms, resulting in an increase in its total mass.•
An adequate supply of nutrients is essential for bacteria’s survival.•
All organisms have an optimum growth temperature, where they will be growing at their optimum rate.•
The majority of bacteria will die without an adequate moisture supply, although some bacteria form spores which protect them when the moisture or nutrient supply is low.•
Some bacteria can grow and replicate only in an environment that is either rich or deficient in oxygen. The ability to grow in both is the most advantageous.•
The amount of time that it takes for one single bacterial cell to divide varies amongst bacterial species.•
Bacteria can be artificially grown in the laboratory using culture media and nutrient broths, and various techniques are employed in order to aid bacterial and viral identification.Chapter summary: key points
108 References
Barer M. (2007).Bacterial growth, physiology and death. In: Greenwood D., Slack R., Peutherer J., Barer M. (Eds.), A Guide to Microbial Infections: Pathogenesis, Immunity, Laboratory Diagno- sis and Control. 17th ed. Churchill Livingston Elsevier, London: 38–51.
Bos K.I., Schuenemann V.J., Golding G.B., Burbano H.A., Waglechner N. (2011). A draft genome of Yersinia pestis from victims of the Black Death. Nature. 478 (27 October): 506–510.
Department of Health (2012). Updated Guidance on the Diagnosis and Reporting of Clostridium difficile. Department of Health, London.
Engelkirk P.G., Duben-Engelkirk J. (2011). Biochemistry: the chemistry of life. In: Engelkirk P.G., Duben-Engelkirk J. (Eds.), Burton’s Microbiology for the Health Sciences. 9th ed. Lippincott Williams and Wilkins, Philadelphia: 84–101.
Fitzgerald D.W., Sterling T.R., Haas D.W. (2010). Mycobacterium tuberculosis. In: Mandell G.L., Bennett J.E., Dolin R.D. (Eds.), Mandell’s Principles and Practices of Infectious Diseases. 6th ed. Churchill Livingstone Elsevier, London. Expert Consult online: http://expertconsult.com (12 December 2012)
Harwood J. (2010). Serology. In: Ford M. (Ed.), Medical Microbiology. Oxford University Press, Oxford: 322–327.
Health Protection Agency (2010). Coagulase Test. BSOPTP 10, Issue 4. Health Protection Agency, London.
Health Protection Agency (2011a). Standards for Microbiological Investigations: Inoculation of Culture Media for Bacteriology. Health Protection Agency, London.
Health Protection Agency (HPA) (2011b). UK Standards for Microbiology Investigations: Staining Procedures. Bacteriology TP39, Issue 1. Health Protection Agency, London.
Health Protection Agency (2012a). UK Standards for Microbiology Investigations: Investigation of Specimens for Screening for MRSA. Bacteriology B29, Issue 5.2. Health Protection Agency, London.
Health Protection Agency (2012b). UK Standards for Microbiology Investigations. Investigation of Specimens for Mycobacterium species. Bacteriology. B40, Issue 6. Health Protection Agency, London.
Levinson W. (2010). Growth. In: Review of Medical Microbiology, 11th ed. McGraw-Hill Lange:
New York, 4–13.
National Clostridium difficile Standards Group (2003). Report to the Department of Health. Depart- ment of Health, London.
Parkhill J., Wren B.W., Thomson N.R., Titball R.W., Holden M.T., et al. (2001). Genome sequence of Yersinia pestis, the causative agent of plague. Nature. 413 (68555): 523–527.
Pratt R.J., Grange J.M., Williams V.G. (2005). Diagnosis of tuberculosis and other mycobacterial diseases. In: Pratt R.J., Grange J.M., Williams V.G. (Eds.), Tuberculosis: A Foundation for Nursing and Healthcare Practice. Hodder Arnold, London: 95–108.
Further resources are available for this book, including interactive multiple choice questions. Visit the companion website at:
www.wiley.com/go/fundamentalsofinfectionprevention
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Strohl W.A., Rouse H., Fisher B.D. (2001). Bacterial growth, structure and metabolism. In: Harvey R.A., Champe P.A. (Eds.), Lippincott’s Illustrated Reviews. Microbiology. Lippincott, Williams and Wilkins, Philadelphia: 101–114.
Taubenberger J.K., Reid A.H., Laurens R.M., Wang R., Guozhong J., et al. (2005). Characterisation of the 1918 Influenza virus polymerase genes. Nature. 437 (6 October): 889–893.
Venter J.C., Adams M.D., Myers E.W., Li P.W., Mural R.J., et al. (2001). The sequence of the human genome. Science. 291 (5507): 1304–1351.
Willey J.M., Sherwood J.M., Woolverton C.J. (2011). The evolution of microorganisms and micro- biology. In: Willey J.M., Sherwood J.M., Woolverton C.J. (Eds.), Prescott’s Microbiology. 8th ed. McGraw-Hill International Edition, New York: 1–24.
Contents
Fundamentals of Infection Prevention and Control: Theory and Practice, Second Edition. Debbie Weston.
© 2013 John Wiley & Sons, Ltd. Published 2013 by John Wiley & Sons, Ltd. Companion Website: www.wiley.com/go/fundamentalsofinfectionprevention
Understanding the immune system and the nature and pathogenesis of infection
8
The innate, or natural,
immune response 111
The adaptive, or acquired,
immune response 115
The immune response and allergy 118
Understanding the chain of infection 120 Colonisation, infection and
the inflammatory response 123
Chapter summary: key points 126
References 127
111
Introduction
In order to care for patients with an infection or infectious disease, a basic understanding of the workings of the immune system and the pathogenesis (development) of infection is advantageous.
This is particularly important given that many of the clinical features of infection are a result of the defence mechanisms employed by the immune system. In order to destroy invading pathogens and protect the host from infection, the immune system has to be able to differentiate between self and non-self – what is foreign to the body and what is not. There are two branches of the immune system which work both independently of each other and together: the innate or natural immune response, and the adaptive or acquired immune response. Since immunology is a complex subject and requires more than just one chapter to do it justice (which is beyond the scope of this book), this chapter aims to provide a broad and brief overview of the disease process, linking together the immune response, the chain of infection and the pathogenesis of infection – common themes which will tie in with Chapters 20–24 in Section 4 of this book. Sepsis and neutropenic sepsis are covered in Chapter 9.
Learning outcomes
After reading this chapter, the reader will be able to: