Category Archives: Microbiology for Beginners

General and differential characteristics of Gram positive and Gram Negative bacteria

The cell wall of Gram negative bacteria is more complex than those of Gram Positive bacteria. Gram negative bacteria contain an extra layer of cells called outer membrane or LPS layer which surrounds the thin peptidoglycan layer. LPS layer is absent in Gram positive bacteria.

Difference between Gram positive and Gram Negative bacterial cell wall

Difference between Gram positive and Gram Negative bacterial cell wall

Some of the main differences between Gram Positive bacteria and Gram Negative bacteria are:

Types of Staining techniques used in Microbiology and their applications

Acid fast stain (Ziehl-Neelsen technique):  It distinguishes acid fast bacteria such as Mycobacterium spp from non-acid fast bacteria; which do not stain well by the Gram Staining.  It is used to stain Mycobacterium species  (Mycobacterium tuberculosis, M. ulcerans and M. leprae)

Acridine Orange Stain: This staining method is used to confirm the presence of bacteria  in blood cultures when Gram stain  results are difficult to interpret or when presence of bacteria is highly suspected but none are detected using light microscopy. Acridine orange binds to nucleic acid and stains them. It is also used for the detection of Mycoplasmas (cell wall deficient bacteria)

Auramine-Rhodamine technique: This fluorochrome staining  method is used to enhance the detection of mycobacteria directly in patient specimens and initial characterization of cells grown in culture.

List of interesting infectious diseases and reason behind their funny name

Common name of some of the infectious diseases are really funny and dont bear any relationship with their scientific names or etiology. But some of these names are derived from the mode of transmission of diseases and in which group of people, the disease is more prevalent.

Here i have tried to list some of those funny names. If you know any such other names, please write it in the comment.

  1. Darling disease: Histoplasma capsulatum causes Histoplasmosis which is also called “Darling’s disease”.
  2. Kissing disease: Infectious mononucleosis is also called Kissing disease which is caused by Epstein-Barr Virus (EBV) . EBV is commonly transmitted by infected saliva and initiates infection in the oropharynx.
  3. Farmer’s lung disease:  Farmer’s lung disease (FLD) is a hypersensitivity pneumonitis  which is caused by the inhalation of moldy hay spores. Farmers are at high risk of developing this disease compared with other occupations.
  4. Rose Gardner’s disease: Sporotrichosis also called as rose gardner’s disease,  is caused by Sporothrix schenckiii
    Rationale behind common name: 
    Sporotrichosis  is occupational hazards for farmers, nursery workers, gardeners and florists.

Primary Biosafety Levels and Agents of Disease

Biosafety level designations are based on a composite of the design features, construction, containment facilities, equipment, practices and operational procedures required for working with agents from the various risk groups.

Laboratory facilities are designated as: 

  • basic – Biosafety Level 1,
  • basic – Biosafety Level 2,
  • containment – Biosafety Level 3, and
  • maximum containment – Biosafety Level 4.

Bio-safety Level One:

  1. Facilities and Practices
    Standard, open bench, no special facilities needed; typical of most microbiology teaching labs; access may be restricted.
  2. Risk of Infection and Class of Pathogens
    Low infection hazard; microbes not generally considered pathogens and will not colonize the bodies of healthy persons; Micrococcus luteus, Bacillus megaterium, Lactobacillus, Saccharomyces.

    Classification of infective microorganisms by risk group

    Classification of infective microorganisms by risk group

Bio-safety Level Two:

Most common cause of bacteremia and fungemia

Pathogens of all four major groups of microbes- bacteria, fungi, viruses and parasites may be found circulating in blood during the course of many diseases.

Presence of bacteria in the blood is called Bacteremia. Bacteria may reach to bloodstream via trauma or from focus on infection. On the basis of duration of presence of bacteria in the blood it is classified as-

  1. Transient bacteremia,
  2. Continuous bacteremia and
  3. Intermittent bacteremia.

The presence of fungi in blood is termed as fungemia.