Medical brain notes 33

  MICROBIOLOGY   Introduction:   The world of microorganisms includes various species of bacteria, viruses, fungi and protozoan parasites. The discovery of microscope and the ingenius techniques of isolation and identification of these microbial organisms opened up a new field of study named  Microbiology . This study deals with the form, structure, reproduction, physiology, metabolism and classification of micro organisms. The area of microbiological studies include various aspects of their distribution in nature, their relationship to each other and to other organisms, their effects on plants, animals and human beings, their roles in the sustainability of environmental habitats such as soil, air and water and also their beneficial aspects to biotechnology.   History of Medical microbiology:   The medical microbiology had its origin in the year 1888 when the Pasteur Institute in Paris (France) was established. Robert Koch became the Director of the Institu...

  Structure of Viruses:   Animal and plant viruses are composed of a central core of nucleic acids surrounded by a protein covering called capsid. The capsid is made up of units called capsomeres. Viruses exhibit a characteristic symmetry, 1. Spherical viruses are isohedral, 2. Rod shaped viruses are helical in symmetry. Certain group of viruses are complex in symmetry. Some animal viruses, in addition to the nucleocapsid structure contain an outer membrane like structure called the envelope. The envelope is made up of lipoproteins. The envelope conceals the symmetry of viruses. Virions with envelopes are sensitive to lipid solvents such as ether and chloroform. On the other hand, the naked virions are not affected by the lipid solvents.   Isohedral viruses such as adeno viruses, SV15, polio viruses and blue tongued viruses are spherical in shape and their surface is a lattice with identical triangular units.   Helical surface symmetry and structure are characteristi...

  Viral Diseases: A. Cancer and Viruses:   Viruses have been identified as one of the causative agents for cancer or tumour. Such tumour inducing viruses are called oncogenic viruses. Adenoviruses, polioma virus, simian virus 40 (SV 40), Epstein-Barr virus (EBV) ( a herpes virus) are oncogenic DNA viruses. The RNA sar-coma viruses are oncogenic RNA viruses (eg., Rous sarcoma).   B. Rabies Virus and Rabies disease:   Rabies virus belongs to the rhabdovirus family. It is a parasite of domestic and wild mammals. The transmission to humans occurs through the bite of an infected animal. Dogs, cats, bats, are the mammalian animal sources for the rabies virus.   In humans, the symptoms of rabies are severe headache, high fever, alternating excitement and depression, muscular spasms in throat and chest, hydrophobia etc. The incubation time in humans is usually about 3 to 8 weeks but it may also vary. If untreated the mortality rate from rabies is 100 percent.   The...

  Cultivation (culture) of Animal viruses:   Viruses can grow only in living cells. However the culture of viruses is possible nowadays. The most economical and convenient method of cultivating a wide variety of animal viruses is the 'chicken embryo technique'. In this technique, fertile chicken eggs incubated for 5 to 12 days are inoculated with the virus particles through the shell, aseptically. The opening may be sealed with paraffin wax. The eggs incubated at 36 o C are ideal sources for the growth of viruses.   Chick embryos contain several different types of cells in which various viruses will undergo replication. The yolk sac is a general ideal medium for the growth of viruses.   Viral cultures are of three types viz., Primary cell cultures, diploid cell strains and continuous cell lines.   1. Primary culture:   Primary cell culture are derived from normal tissue of an animal such as mouse, hamster, chicken and monkey or a human being. When cells fro...

  Bacteria - structure   The structure, size and arrangement of bacterial cells consitute their morphology. The various morphological features are   1.                    They are spherical or rod like or spiral shaped.   2.                  The arrangement of cells in pairs, clusters, chains, trichomes and filaments etc.   3.                  The appendages are visible by special staining techniques or by electron microscopy.   The above three features represent the gross morphological characteristics, which are of taxonomic importance in bacterial species identification. In addition, the bacterial cells possess elaborate internal structures, which constitute microbial cytology and bacterial anatomy.   Bacterial Culture   All bacteria need ...

  Bacterial Genetics :   In bacteria the cells have a single circular strand of DNA. It is not associated with proteins as are eukaryotic chromosomes. The bacterial genes, like the eukaryotic genes possess the features of replication, phenotype expression, mutation and genetic recombination etc. In bacteria the genetic recombination results from three types of gene transfer viz., conjugation, transduction and transformation.   Conjugation involves the transfer of some DNA from one bacterial cell to another followed by the separation of the mating pair of cells. In this, large segments of the chromosomes and in special cases the entire chromosome may be transferred. Bacterial transformation is a process in which cell free or naked DNA containing the genetic information is transferred from one bacterial cell to another. It was discovered by an English health officer, Griffith in 1928. The transforming principle was identified as DNA by Avery Macleod and Mc Carthy in 1944. ...

  Bacterial Diseases   A. Salmonella and Human Diseases:   Salmonella are pathogenic bacilli which cause three kinds of infection to humans viz., enteric fever (Typhoid or Paratyphoid), Gastroenteritis and Septicemia.   Typhoid fever is caused by  S.typhi.  It is transmitted via Pathogen contained food and water. The disease is characterized by a continued fever, inflammation of the intestine, formation of intestinal ulcers and enlargement of the spleen.   Gastroenteritis is caused by Salmonella, but most commonly by S.choleraesuis. The bacteria reach the blood stream from the intestinal tract, where it multiplies. It causes recurring high fever, chills, loss of appetite and weight loss. When the bacteria infect the organs from blood they can cause meningitis, pneumonia, abscesses, nephritis, osteomyelitis, or endocarditis, etc.   B. Cholera :   Cholera is caused by  Vibrio cholere.  It is a disease of antiquity and has been the cau...

  Protozoan microbiology   Protozoans are eukaryotic, single celled organisms, which are predominantly microscopic in size. The majority are between 5 to 250 microns in diameter. Protozoan microbiology is mostly concerned with the disease aspects in humans. Some well known protozoan diseases in human beings are the intestinal amoebiasis, African sleeping sickness, and malaria. Several flagellate protozoans are responsible for diseases in both children and adults.  Giardia intestinalis  is associated with diarrhoea in children. Trichomonads are found in the mouth and cause gingivitis.   A. Plasmodium and Malaria:   Malaria is a mosquito borne disease caused by the protozoan, Plasmodium. The life cycle of malarial parasite comprises two phases namely the asexual phase in man and the sexual phase in the female Anopheles mosquito (Definitive host).   Four different types of Malaria are recognized on the basis of period of recurrence of fever. They are 1. T...

  Larval microbiology   Larval microbiology deals with human diseases caused by parasitic larvae. Parasitic infections which man acquires from animals are known as zoonotic infections or  zoonoses . In the zoonoses, human infections are only accidental events and the parasite is not benefited since the chain of transmission is usually broken with human infection. The term  anthroponoses  means infections with parasites species that are maintained in man alone. Malaria and filaria are examples. The term  Zooanthroponoses  refers to infections in which man is not merely an incidental host but an essential link in the life cycle of the parasite (eg., Beef and pork tapeworm.   Schistosomes or blood flukes   Pathogenecity of Microorganisms:   Pathogenecity refers to the ability of microorganism to cause the disease in animals and humans. Infectious diseases more often result due to the interactions between the disease producing pathogenic mic...