Medical microbiology


Medical microbiology, the large subset of microbiology that is applied to medicine, is a branch of medical science concerned with the prevention, diagnosis and treatment of infectious diseases. In addition, this field of science studies various clinical applications of microbes for the improvement of health. There are four kinds of microorganisms that cause infectious disease: bacteria, fungi, parasites and viruses, and one type of infectious protein called prion.
A medical microbiologist studies the characteristics of pathogens, their modes of transmission, mechanisms of infection and growth. The academic qualification as a clinical/Medical Microbiologist in a hospital or medical research centre generally requires a Bachelors degree while in some countries a Masters in Microbiology along with Ph.D. in any of the life-sciences. Medical microbiologists often serve as consultants for physicians, providing identification of pathogens and suggesting treatment options. Using this information, a treatment can be devised.
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.
Epidemiology, the study of the patterns, causes, and effects of health and disease conditions in populations, is an important part of medical microbiology, although the clinical aspect of the field primarily focuses on the presence and growth of microbial infections in individuals, their effects on the human body, and the methods of treating those infections. In this respect the entire field, as an applied science, can be conceptually subdivided into academic and clinical sub-specialties, although in reality there is a fluid continuum between public health microbiology and clinical microbiology, just as the state of the art in clinical laboratories depends on continual improvements in academic medicine and research laboratories.

History

In 1676, Anton van Leeuwenhoek observed bacteria and other microorganisms, using a single-lens microscope of his own design.
In 1796, Edward Jenner developed a method using cowpox to successfully immunize a child against smallpox. The same principles are used for developing vaccines today.
Following on from this, in 1857 Louis Pasteur also designed vaccines against several diseases such as anthrax, fowl cholera and rabies as well as pasteurization for food preservation.
In 1867 Joseph Lister is considered to be the father of antiseptic surgery. By sterilizing the instruments with diluted carbolic acid and using it to clean wounds, post-operative infections were reduced, making surgery safer for patients.
In the years between 1876 and 1884 Robert Koch provided much insight into infectious diseases. He was one of the first scientists to focus on the isolation of bacteria in pure culture. This gave rise to the germ theory, a certain microorganism being responsible for a certain disease. He developed a series of criteria around this that have become known as the Koch's postulates.
A major milestone in medical microbiology is the Gram stain. In 1884 Hans Christian Gram developed the method of staining bacteria to make them more visible and differentiated under a microscope. This technique is widely used today.
In 1910 Paul Ehrlich tested multiple combinations of arsenic based chemicals on infected rabbits with syphilis. Ehrlich then found that arsphenamine was found effective against syphilis spirochetes. The arsphenamines was then made available in 1910, known as Salvarsan.
In 1929 Alexander Fleming developed one of the most commonly used antibiotic substances both at the time and now: penicillin.
In 1939 Gerhard Domagk found Prontosil red protected mice from pathogenic streptococci and staphylococci without toxicity. Domagk received the Nobel Prize in physiology, or medicine, for the discovery of the sulfa drug.
DNA sequencing, a method developed by Walter Gilbert and Frederick Sanger in 1977, 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. A few months later, the first eukaryotic genome was completed. This would prove invaluable for diagnostic techniques.
In 2007, a team at the Danish food company Danisco, were able to identify the purpose of the CRIPR-Cas systems as adaptive immunity to phages. The system was then quickly found to be able to help in genome editing through its ability to generate double strand breaks. A patient with sickle cell disease was the first person to be treated for a genetic disorder with CRISPR in July 2019.

Commonly treated infectious diseases

Viral
Parasitic
  • Malaria
  • Giardia lamblia
  • Toxoplasma gondii
Fungal
Prion - Misfolded proteins that usually occur in the brain and trigger other normal proteins to misfold. They are extremely rare, and these built-up proteins lead to complications.
Infections may be caused by bacteria, viruses, fungi, prions, and parasites. The pathogen that causes the disease may be exogenous or endogenous.
The site at which a microbe enters the body is referred to as the portal of entry. These include the respiratory tract, gastrointestinal tract, genitourinary tract, skin, parenteral, blood transfusion, congenital, optic, and mucous membranes. The portal of entry for a specific microbe is normally dependent on how it travels from its natural habitat to the host.
There are various ways in which disease can be transmitted between individuals.
These include:
Like other pathogens, viruses use these methods of transmission to enter the body, but viruses differ in that they must also enter into the host's actual cells. Once the virus has gained access to the host's cells, the virus' genetic material must be introduced to the cell. Replication between viruses is greatly varied and depends on the type of genes involved in them. Most DNA viruses assemble in the nucleus while most RNA viruses develop solely in cytoplasm.
The mechanisms for infection, proliferation, and persistence of a virus in cells of the host are crucial for its survival. For example, some diseases such as measles employ a strategy whereby it must spread to a series of hosts. In these forms of viral infection, the illness is often treated by the body's own immune response, and therefore the virus is required to disperse to new hosts before it is destroyed by immunological resistance or host death. In contrast, some infectious agents such as the Feline leukemia virus, are able to withstand immune responses and are capable of achieving long-term residence within an individual host, whilst also retaining the ability to spread into successive hosts.
Virulence refers to the ability of an organism to invade a host and cause disease. Virulence factors are molecules that enable bacteria to attach to and invade the host's cells. These factors can be secreted, featured on the membrane, or located inside the cell. Cytosolic factors help bacteria rapidly adapt their metabolic, physical, and structural characteristics. Membrane-bound factors help bacteria adhere to the host and avoid detection by the host's immune system. Secreted factors assist bacteria to overcome the body's innate and adaptive immune defenses. In extracellular threats, secreted factors work together to destroy host cells.

Diagnostic tests

Identification of an infectious agent for a minor illness can be as simple as clinical presentation; such as gastrointestinal disease and skin infections. In order to make an educated estimate as to which microbe could be causing the disease, epidemiological factors need to be considered; such as the patient's likelihood of exposure to the suspected organism and the presence and prevalence of a microbial strain in a community.
Diagnosis of infectious disease is nearly always initiated by consulting the patient's medical history and conducting a physical examination. More detailed identification techniques involve microbial culture, microscopy, biochemical tests and genotyping. Other less common techniques are used to produce images of internal abnormalities resulting from the growth of an infectious agent.

Microbial culture

is the primary method used for isolating infectious disease for study in the laboratory. Tissue or fluid samples are tested for the presence of a specific pathogen, which is determined by growth in a selective or differential medium.
The 3 main types of media used for testing are:
  • Solid culture: A solid surface is created using a mixture of nutrients, salts and agar. A single microbe on an agar plate can then grow into colonies containing thousands of cells. These are primarily used to culture bacteria and fungi.
  • Liquid culture: Cells are grown inside a liquid media. Microbial growth is determined by the time taken for the liquid to form a colloidal suspension. This technique is used for diagnosing parasites and detecting mycobacteria.
  • Cell culture: Human or animal cell cultures are infected with the microbe of interest. These cultures are then observed to determine the effect the microbe has on the cells. This technique is used for identifying viruses.