Microorganisms are ubiquitous. They are found in soil, air, water, food,
sewage and body surfaces. In short, every area of our environment is replete
with them. When grown on a variety of media, microorganisms will exhibit
differences in the microscopic appearance of their growth.
These differences,
called cultural characteristics, are used as basis for separating microorganisms
into taxonomic groups. The cultural characteristics for all non-microorganisms
are contained in Bergy’s Manual of Systemic Bacteriology with their
morphological characteristics.
Objectives
After studying and performing this experiment, you should be able to:
• differentiate microorganisms into bacteria, yeasts and moulds; and
• know the different forms / shapes of microorganisms.
EXPERIMENT
The microorganisms can be divided into bacteria, yeasts and moulds on basis
of the difference in their morphological, cultural and physiological
characteristics.
of the difference in their morphological, cultural and physiological
characteristics.
Bacteria
Among the major characteristics of bacterial cells are their size, shape,
structure and arrangement. These characteristics constitute the morphology of
the cell. Bacteria are very small, most being approximately 0.5 to 1.0
micrometers in diameter.
structure and arrangement. These characteristics constitute the morphology of
the cell. Bacteria are very small, most being approximately 0.5 to 1.0
micrometers in diameter.
They are unicellular, have cell wall and cytoplasm
but the nucleous is not well developed. The shape of a bacterium is governed
by its rigid cell wall. Typical bacterial cells are spherical (cocci), straight rods
(bacilli) or rods that are helically covered (spirilla).
but the nucleous is not well developed. The shape of a bacterium is governed
by its rigid cell wall. Typical bacterial cells are spherical (cocci), straight rods
(bacilli) or rods that are helically covered (spirilla).
Different patterns for arrangement for identification purposes are monococci,
diplococci, streptococci, tetrads, staphylococci and sarcinae (Figure 3.1). Cocci
generally reproduce by binary fission.
diplococci, streptococci, tetrads, staphylococci and sarcinae (Figure 3.1). Cocci
generally reproduce by binary fission.
Rod shaped bacteria may be sporulating
type like Bacillus species and Clostridium species which produce endospores
or they are non-sporulating like Lactobacillus species (Figure 3.2). Bacteria
may be both motile (having flagella) or non-motile (no flagella).
type like Bacillus species and Clostridium species which produce endospores
or they are non-sporulating like Lactobacillus species (Figure 3.2). Bacteria
may be both motile (having flagella) or non-motile (no flagella).
Fungi
Fungi is a group of eukaryotic organisms. They comprise of yeasts and
moulds. Whereas moulds are filamentous and multicellular, yeasts are
unicellular.
moulds. Whereas moulds are filamentous and multicellular, yeasts are
unicellular.
Yeasts
In general yeast cells are larger than most bacteria. Yeasts vary considerably in
size ranging from 1-5 micrometer in width and from 5-30 micrometer in
length. They are commonly egg-shaped, but some are elongated and some
spherical.
size ranging from 1-5 micrometer in width and from 5-30 micrometer in
length. They are commonly egg-shaped, but some are elongated and some
spherical.
Moulds
The thallus of moulds consist essentially of two parts: the mycelium and the
spores. The mycelium is a complex of several filaments called hyphae.
Filaments are made up of cells arranged end to end, branched and intertwined.
spores. The mycelium is a complex of several filaments called hyphae.
Filaments are made up of cells arranged end to end, branched and intertwined.
Cells are like cells of higher plants in that they have visible nuclei, cell wall of
varying thickness and cytoplasm. Mycelia in some fungi are divided into
individual cells separated by cross walls and each cell containing a nucleus.
varying thickness and cytoplasm. Mycelia in some fungi are divided into
individual cells separated by cross walls and each cell containing a nucleus.
Requirements (Equipment/ Machinery/ Instrument and Chemicals/
Material)
• Compound microscope
• Bunsen burner
• Immersion oil
• Glass slides
• Inoculating needle
• Cover slips
• Tissue paper
• Microbial culture
• Distilled water
Procedure
1. Prepare the required media (broth or agar) for culturing the
microorganisms
microorganisms
2. Place a small amount of media into test tubes, plug and sterilize them in an
autoclave.
autoclave.
3. In case of solid media tubes, cool them in an incline position (slants)
4. When the medium is cold and solid, inoculate the surface of the medium
using pre-sterilized needle. Move the needle gently on the agar surface in a
snakelike motion from the butt to the top. In case of broth tubes, inoculate
in the liquid media
using pre-sterilized needle. Move the needle gently on the agar surface in a
snakelike motion from the butt to the top. In case of broth tubes, inoculate
in the liquid media
5. Incubate both culture tubes at 30°C for few days.
6. In case of solid media, scoop out the mass of surface growth in which
organism grows and put on clean, dry slide. From liquid broth, place a drop
of culture on slide.
organism grows and put on clean, dry slide. From liquid broth, place a drop
of culture on slide.
7. Observe under microscope.
Observations
In the chart provided:
1. Draw several cells from a typical microscopic field as viewed under each
magnification.
magnification.
2. Give the total magnification for each objective.
3. Observe spores or conidia and their arrangement.
Results
Different types of spoilage have been encountered caused by various
microorganisms. The type of microorganism proliferating depends on the
composition of the material.
microorganisms. The type of microorganism proliferating depends on the
composition of the material.
The different spoilage microorganisms include
bacteria, yeasts and moulds that can be observed and identified under a
microscope by studying the morphological characteristics. These organisms
vary in size, shape, colour, growth habit and mode of reproduction.
bacteria, yeasts and moulds that can be observed and identified under a
microscope by studying the morphological characteristics. These organisms
vary in size, shape, colour, growth habit and mode of reproduction.