Medical microbiology

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A microbiologist examining cultures under a Stereoscope.


A medical microbiologist studies the characteristics of pathogens, their modes of transmission, mechanisms of infection and growth. Using this information a treatment can be devised. Medical microbiologists often serve as consultants for physicians, providing identification of pathogens and suggesting treatment options. Other tasks may include the identification of potential health risks to the community or monitoring the evolution of potentially virulent or resistant strains of microbes, educating the community and assisting in the design of health practices. They may also assist in preventing or controlling epidemics and outbreaks of disease. Not all medical microbiologists study microbial pathology; some study common, non-pathogenic species to determine whether their properties can be used to develop antibiotics or other treatment methods.


History of Medical Microbiology[edit]









DNA sequencing, a method developed by Walter Gilbert and Frederick Sanger in 1977,[4] caused a rapid change the development of vaccines, medical treatments and diagnostic methods. Some of these include synthetic insulin which was produced in 1979 using recombinant DNA and the first genetically engineered vaccine was created in 1986 for Hepatitis B.

In 1995 a team at The Institute for Genomic Research sequenced the first bacterial genome; Haemophilus influenzae.[5] A few months later, the first eukaryotic genome was completed. This would prove invaluable for diagnostic techniques.[6]

Commonly Treated Infectious Diseases[edit]





Causes and Transmission of Infectious Disease[edit]


The site at which a microbe enters the body is referred to as the portal of entry.[19] These include the respiratory tract, gastrointestinal tract, genitourinary tract, skin, and mucous membranes.[20] The portal of entry for a specific microbe is normally dependent on how it travels from its natural habitat to the host.[19]

There are various ways in which disease can be transmitted between individuals. These include:[19]



Diagnostic Tests[edit]



Microbial Culture[edit]

Four nutrient agar plates growing colonies of common Gram negative bacteria.


The 3 main types of media used for testing are:[24]



The previously mentioned culture techniques will often rely on microscopic examination for identification of the microbe. Instruments such as compound light microscopes can be used to assess critical aspects of the organism. This can be performed immediately after the sample is taken from the patient and is used in conjunction with biochemical staining techniques, allowing for resolution of cellular features. Electron microscopes and fluorescence microscopes are also used for observing microbes in greater detail.[26]

Biochemical Tests[edit]


Serological methods are highly sensitive, specific and often extremely rapid tests used to identify different types of microorganisms. The tests are based upon the ability of an antibody to bind specifically to an antigen. The antigen (usually a protein or carbohydrate made by an infectious agent) is bound by the antibody, allowing this type of test to be used for organisms other than bacteria. This binding then sets off a chain of events that can be easily and definitively observed, depending on the test. More complex serological techniques are known as immunoassays. Using a similar basis as described above, immunoassays can detect or measure antigens from either infectious agents or the proteins generated by an infected host in response to the infection. [27]

Polymerase chain reaction[edit]

PCR assays are the most commonly used molecular technique to detect and study microbes,[28] as compared to other methods, sequencing and analysis is definitive, reliable, accurate and fast.[29] Today, quantitative PCR is the primary technique used, as this method provides faster data compared to a standard PCR assay. For instance, traditional PCR techniques require the use of gel electrophoresis to visualize amplified DNA molecules after the reaction has finished. quantitative PCR does not require this, as the detection system uses fluorescence and probes to detect the DNA molecules as they are being amplified.[30] In addition to this, quantitative PCR also removes the risk of contamination that can occur during standard PCR procedures (carrying over PCR product into subsequent PCRs).[28] Another advantage of using PCR to detect and study microbes is that the DNA sequences of newly discovered infectious microbes or strains can be compared to those already listed in databases, which in turn helps to increase understanding of which organism is causing the infectious disease and thus what possible methods of treatment could be used.[29] This technique is the current standard for detecting viral infections such as AIDS and Hepatitis.





In addition to drugs being specific to a certain kind of organism (bacteria, fungi, etc.), some drugs are specific to a certain genus or species of organism, and will not work on other organisms (for example, many antibacterial drugs only work on certain kinds of bacteria). Because of this specificity, medical microbiologists must consider the effectiveness of certain antimicrobial drugs when making recommendations. Additionally, strains of an organism may be resistant to a certain drug or class of drug, even when it is typically effective against the species. These strains, termed resistant strains, present a serious public health concern of growing importance to the medical industry as the spread of antibiotic resistance worsens.


Medical microbiology is not only about diagnosing and treating disease, it also involves the study of beneficial microbes. Microbes have been shown to be helpful in combating infectious disease and promoting health. Treatments can be developed from microbes, as demonstrated by Alexander Fleming's discovery of penicillin as well as the development of new antibiotics from the bacterial genus Streptomyces among many others.[33] Not only are microorganisms a source of antibiotics but some may also act as probiotics to provide health benefits to the host, such as providing better gastrointestinal health or inhibiting pathogens.[34]

See also[edit]

Notes and references[edit]

  3. ^ Brock TD (1999). Robert Koch: a life in medicine and bacteriology. Washington DC: American Society of Microbiology Press. ISBN 1-55581-143-4. 
  7. ^ Shaikh N, Leonard E, Martin JM (September 2010). "Prevalence of streptococcal pharyngitis and streptococcal carriage in children: a meta-analysis". Pediatrics 126 (3): 557–564. doi:10.1542/peds.2009-2648. PMID 20696723. 
  8. ^ Vos T et al. (December 2012). "Years lived with disability (YLDs) for 1160 sequelae of 289 diseases and injuries 1990-2010: a systematic analysis for the Global Burden of Disease Study 2010". Lancet 380: 2163–96. doi:10.1016/S0140-6736(12)61729-2. PMID 23245607. 
  11. ^ Dennehy PH (2012). "Rotavirus infection: an update on management and prevention". Advances in Pediatrics 59 (1): 47–74. doi:10.1016/j.yapd.2012.04.002. PMID 22789574. 
  13. ^ Dunne EF, Unger ER, Sternberg, M (February 2007). "Prevalence of HPV infection among females in the United States.". Journal of the American Medical Association 297 (8): 813–9. doi:10.1001/jama.297.8.813. PMID 17327523. 
  14. ^ Kappus KD, Lundgren RG, Jr., Juranek DD, Roberts JM, Spencer HC (June 1994). "Intestinal parasitism in the United States: update on a continuing problem.". American Society of Tropical Medicine and Hygiene 50 (6): 705–13. PMID 8024063. 
  18. ^ Washington, JA (1996). "10 Principles of Diagnosis". In Baron, S. Medical Microbiology. (4th ed.). University of Texas Medical Branch at Galveston. ISBN 0-9631172-1-1. 
  19. ^ a b c Siebeling, RJ (1998). "Chapter 7 Principles of bacterial pathogenesis". In Bittar, Neville, E, B. Microbiology. Elsevier. p. 87. ISBN 1-55938-814-5. 
  20. ^ Rhinehart E, Friedman M (1999). Infection control in home care. Jones & Bartlett Learning. p. 11. ISBN 0-8342-1143-2. 
  22. ^ Hilleman M (October 2004). "Strategies and mechanisms for host and pathogen survival in acute and persistent viral infections". Proceedings of the National Academy of Sciences of the United States of America 101: 14560–14566. doi:10.1073/pnas.0404758101. PMC 521982. PMID 15297608. 
  23. ^ Greggs WM, Clouser CL, Patterson SE, Manksy LM (April 2012). "Discovery of drugs that possess activity against feline leukemia virus". Journal of General Virology 93 (4): 900–905. doi:10.1099/vir.0.039909-0. 
  24. ^ Nester E, Anderson D, Evans Roberts, C, Nester M (2009). Microbiology: A human perspective. McGraw Hill. pp. 336–337. ISBN 1-55938-814-5. 
  25. ^ Møller M, El Maghrabi R, Olesen N, Thomsen VØ (November 2004). "Safe inoculation of blood and bone marrow for liquid culture detection of mycobacteria". Occupational Medicine (London) 54 (8): 530–3. doi:10.1093/occmed/kqh106. PMID 15520021. 
  29. ^ a b Viljoen GJ, Nel LH, Crowther JR (editors) (2005). Molecular Diagnostic PCR Handbook. Springer. p. 58. ISBN 978-1-4020-3404-6. 
  30. ^ Tang YW, Persing DH (2009). Encyclopedia of Microbiology. Oxford Academic Press. pp. 308–320. ISBN 978-0-12-373944-5. 