INTRODUCTION TO BACTERIOLOGY
Microbiology
– A branch of biology which deals with the study of living
organisms that are too small to be seen by naked eye.
1. Two main threads in the history of bacteriology:
a) the natural history of bacteria and
b) the contagious nature of infectious diseases, were united in the
latter half of the 19th century. During that period many of the Medical Microbiology
bacteria that cause human disease were identified and – A branch of medical science that deals with the study
characterized. of medically important microorganisms, specifically their
role in human disease which includes diagnosis,
2. Individual bacteria were first observed microscopically by treatment, and prevent of infectious diseases.
Antony van Leeuwenhoek at the end of the 17th century.
3. Bacteria are readily visible when present in large numbers Diagnostic Bacteriology
because they make a turbid suspension. The controversy over
spontaneous generation of bacterial life in liquid cultures led to the – A branch of medical microbiology that focuses on the
development of two important bacteriological procedures. laboratory identification of medically important bacteria
a. Sterilization: the preparation of medium or instruments such
by phenotypical and genotypical characterization
that no living bacteria are present. including antibiotic susceptibility testing.
b. Aseptic technique: laboratory technique that allows the
manipulation of sterilized material without bacteriological
contamination.
4. Bacteria are most easily studied in pure cultures in which only a Microbiology
single species is present. Pure cultures were originally produced
by limiting dilution in liquid medium. Today pure cultures are
• study of living organisms / microbes
usually prepared on medium solidified with agar, a gelling agent
derived from seaweed. A mixed bacterial suspension is • study of certain nonliving entities as well as certain
mechanically spread on the agar surface to yield isolated
individual bacterial cells. These grow to yield macroscopic living organisms.
colonies (clones) that can be used to prepare pure cultures.
• Microbes are said to be ubiquitous, meaning they
are virtually everywhere.
5. The ability to prepare pure cultures led to the study of bacterial
classification and taxonomy.
a. The first basis for classification was shape. Round bacteria are
called cocci (singular coccus).
Rod shaped bacteria are called bacilli (singular bacillus). Other
shapes will be considered later
in the course.
b. Bacteria are very difficult to study microscopically unless
stained. The staining characteristics of bacteria in the Gram stain
are very useful in classification. Gram positives are violet, while
gram negatives are red.
c. Bacterial taxonomy today depends upon the extent of DNA
sequence homology. An important laboratory technique for the
amplification and detection of specific DNA sequences (as, for
example, in a bacterium or a virus) is the polymerase chain
reaction (PCR). Examples of when PCR is used for clinical
diagnostics will be considered later in this course. However, for
routine laboratory diagnosis the most important bacterial
characteristics are:
1) The morphology of colonies on appropriate agar medium.
2) Microscopic morphology and staining of individual bacteria.
3) Simple biochemical characteristics such as the ability to
ferment a given carbohydrate.
4) Specific antigens detected by known antisera.
Microbiology
– A branch of biology which deals with the study of living
organisms that are too small to be seen by naked eye.
1. Two main threads in the history of bacteriology:
a) the natural history of bacteria and
b) the contagious nature of infectious diseases, were united in the
latter half of the 19th century. During that period many of the Medical Microbiology
bacteria that cause human disease were identified and – A branch of medical science that deals with the study
characterized. of medically important microorganisms, specifically their
role in human disease which includes diagnosis,
2. Individual bacteria were first observed microscopically by treatment, and prevent of infectious diseases.
Antony van Leeuwenhoek at the end of the 17th century.
3. Bacteria are readily visible when present in large numbers Diagnostic Bacteriology
because they make a turbid suspension. The controversy over
spontaneous generation of bacterial life in liquid cultures led to the – A branch of medical microbiology that focuses on the
development of two important bacteriological procedures. laboratory identification of medically important bacteria
a. Sterilization: the preparation of medium or instruments such
by phenotypical and genotypical characterization
that no living bacteria are present. including antibiotic susceptibility testing.
b. Aseptic technique: laboratory technique that allows the
manipulation of sterilized material without bacteriological
contamination.
4. Bacteria are most easily studied in pure cultures in which only a Microbiology
single species is present. Pure cultures were originally produced
by limiting dilution in liquid medium. Today pure cultures are
• study of living organisms / microbes
usually prepared on medium solidified with agar, a gelling agent
derived from seaweed. A mixed bacterial suspension is • study of certain nonliving entities as well as certain
mechanically spread on the agar surface to yield isolated
individual bacterial cells. These grow to yield macroscopic living organisms.
colonies (clones) that can be used to prepare pure cultures.
• Microbes are said to be ubiquitous, meaning they
are virtually everywhere.
5. The ability to prepare pure cultures led to the study of bacterial
classification and taxonomy.
a. The first basis for classification was shape. Round bacteria are
called cocci (singular coccus).
Rod shaped bacteria are called bacilli (singular bacillus). Other
shapes will be considered later
in the course.
b. Bacteria are very difficult to study microscopically unless
stained. The staining characteristics of bacteria in the Gram stain
are very useful in classification. Gram positives are violet, while
gram negatives are red.
c. Bacterial taxonomy today depends upon the extent of DNA
sequence homology. An important laboratory technique for the
amplification and detection of specific DNA sequences (as, for
example, in a bacterium or a virus) is the polymerase chain
reaction (PCR). Examples of when PCR is used for clinical
diagnostics will be considered later in this course. However, for
routine laboratory diagnosis the most important bacterial
characteristics are:
1) The morphology of colonies on appropriate agar medium.
2) Microscopic morphology and staining of individual bacteria.
3) Simple biochemical characteristics such as the ability to
ferment a given carbohydrate.
4) Specific antigens detected by known antisera.
