Category Archives: Microbiology for Beginners

Microbiology Laboratory Safety Rules and Procedure

You will find some of these rules and procedures listed in the beginning material of your laboratory manual. If you find any safety rules or procedures listed here appears to be in conflict with those given  in your laboratory manual, please resolve it by asking your course instructor or teaching assistant (TA) for clarification.

Safety in a microbiology laboratory is important in the prevention of infection as Microbiology laboratory cultures, manipulates, and uses virulent and/or potentially pathogenic microorganisms.  In addition to microorganisms, there are some chemicals used in this laboratory that are potentially harmful. Many procedures involve glassware, open flames, and sharp objects that can cause trauma/ damage if used improperly.

General Safety Rules and Procedures

  1. The laboratory procedures must be read prior to attending that laboratory session.
  2. Smoking, eating, and drinking in the laboratory are absolutely prohibited in the laboratory at any time.

Robert Koch and Koch’s postulates

Robert Koch (1843-1910) was a German physician and scientist and the first person to prove that Bacterium are the cause of animal disease. Robert Koch was born on December 11, 1843 at Clausthal in the Upper Harz Mountains in the northwestern region of Germany.Dr. Koch died on the 27th of May 1910 of a heart-attack in Baden-Baden at the age of 66.

Robert Koch

He has given the famous Koch’s postulates . Robert Koch is also known as Father of Clinical Microbiology.

Robert Koch and his discoveries
He worked on Anthrax and in 1877, discovered typical Bacilli (Bacillus anthracis) with squarish ends in the blood of cattle that had died of anthrax.

Other bacteria discovered by Robert Koch are Mycobacterium tuberculosis (1882), Vibrio cholerae (1883), Staphylococcus (1878).

He also developed a technique for isolating bacteria on a culture plate.Robert Koch was the first person to grow bacteria on solid culture media. He employed gelatin as a solidifying agent. 

Catalase test: principle, uses, procedure and results

catase test

Catalase Test: Positive and Negative results

Catalase is an enzyme, which is produced by microorganisms that live in oxygenated environments to neutralize toxic forms of oxygen metabolites; H2O2.  The catalase enzyme neutralizes the bactericidal effects of hydrogen peroxide and protects them. Anaerobes generally lack the catalase enzyme.

Catalase mediates the breakdown of hydrogen peroxide H2O2 into oxygen and water.  To find out if a particular bacterial isolate is able to produce catalase enzyme, small inoculums of bacterial isolate is mixed into hydrogen peroxide solution (3%) and the rapid elaboration of oxygen bubbles occurs.  The lack of catalase is evident by a lack of or weak bubble production.

Seven common characteristics of family Enterobacteriaceae

Enterobacteriaceae family contains a large number of genera that are biochemically and genetically related to one another. Many of the traditional or familiar bacteria are found in this family e.g. Escherichia, Shigella, Salmonella, Enterobacter, Proteus, Yersinia etc.

Seven common characteristics of family Enterobacteriaceae are:

  1. They are gram negative, short rods
  2. They are non-sporulating, facultative anaerobes
  3. These organism have simple nutritional requirements and MacConkey agar is used to isolate and differentiate  organisms of Enterobacteriaceae family (Pink colored colonies of lactose fermenter-coliforms and pale colored colonies of Non lactose fermenter)

What are the roles of Medical Microbiologist?

Microbiologists work in public health laboratories, hospital laboratories, reference or independent laboratories, and physician office laboratories.

Microbiologist must be aware of what the physician needs and as well as what the laboratory needs.

At an elementary level, the physician needs answers to three basic questions from the microbiology laboratory:


Role of Microbiologist: Cartoon by Czichos

  1. Is my patient’s illness caused by a microbe?
  2. If so, what is it?
  3. What is the antibiotic susceptibility profile of that organism so that therapy can be targeted?