introduction to bacteriology

An introductionMARX P. CATALAN, RMT

It is a branch of microbiology that is concerned with bacteria

Bacteria – single celled organism that multiply by binary fission Larger and more complex than viruses Viable under light microscope Prokaryotic, has both DNA and RNA

Generally belong to the Kingdom Monera.

Minute, unicellular organisms that reproduce through binary fission.

Considered prokaryotes due to the absence of a nuclear membrane. They possess both DNA and RNA.

There are two domains of Bacteria

I. Eubacteria▪ Proteobacteria▪ Thin gram negative cell wall▪ Includes photosynthetic, anaerobic photosynthetic bacteria and cyanobacteria

▪ Firmicutes▪ Thick gram positive cell wall▪ Includes rods, cocci, Actinomycetes, Mycoplasma (wall-less bacteria

II. Archae Bacteria Methanogenes▪ Strict Anaerobes▪ Produce Methane (CH4), CO2 and Hyroden

Extreme Halophiles▪ Require High Salt concentration

Thermoacidophiles▪ Grow on Hot and acidic environment

SIZE Unit of microbial measurement is the

micrometer (m), formerly micron () which is equal to: 1m = 1/1000 of a millimeter (mm) 1m = 1/25,000 of an inch.

Average size of the bacteria generally varies from 0.5 – 2m in diameter and 2 – 8m in length.

FUNDAMENTAL SHAPES

Bacilli (bacillus, singular) – rod shaped organisms

Cocci (coccus, singular) – spherical or round organisms

Spirilla (spirillum, singular) – spiralled or comma-shaped organisms

Bacilli

Cocci

SPIRILLUM

Two factors that affect bacterial arrangements:

Plane of division

Position taken after cell division

Pairs – diplococci (e.g., N. gonorrheae) – diplobacilli (e.g.,)

DIPLOCOCCI DIPLOBACILLI

Chains – streptococci, – streptobacilli

STREPTOCOCCI STREPTOCBACILLI

Grapelike clusters – staphylococci

STAPHYLOCOCCI

Groups of four – tetrads (e.g., Peptococcus)

TETRADS

Packets of eight – cuboidal (e.g., Sarcinae)

PACKETS OF EIGHT

Palisades (slipping) – organisms tend to place themselves side by side (e.g., Corynebacterium)

PALISADES

Chinese character (snapping) – organisms tend to bend at the point of division

CHINESE CHARACTERS

Greek words “taxes” – arrangement, “nomos” – law

It is an orderly classification and grouping of organisms into taxa (categories)

Involves three structured, interrelated categories:

Classification/Taxonomy

Nomenclature

Identification

Based on the is based on similarities and differences in genotypes and phenotypes

Microbiologist traditionally emphasize placement and naming of bacterial species into three categories Family (similar to Human clans) Genus (equivalent to human last name) Species (equivalent to human 1st name)

The plural of genus is genera and there are many genera in the family Enterobacteriaceae

Ex: Famliy: Enterobacteriaceae▪ Genus: Escherichia▪ Species: coli

Nomenclature provides naming assignments for each organism

Standard rules for bacterial names: The name of the family is CAPITALIZED

and has an aceae ending (ex:Enterobacteriaceae)

Source of Carbon (for making cellular constituents). Carbon represents 50% of the dry weight of a bacterium.

A source of nitrogen (for making proteins). Nitrogen makes up 14% of the dry weight

Source of energy (ATP) – for carrying out cellular functions).

orderly increase of all chemical constituents of the cell.

A process which entails the replication of all cellular structures, organelles and protoplasmic components from the nutrients present in the surrounding environment.

Under favorable conditions almost all bacteria are able to produce very rapidly.

The average time required for an organism to double its number is referred to as the generation time or doubling time. (e.g., E. coli – 20 minutes)

A. CARBON

Classification of organisms:1. Autotrophs (lithotrophs) – require only

water, inorganic salts, and carbon dioxide for growth; they don’t require organic nutrients for growth

2.Heterotrophs (organotrophs) – require an organic form of carbon for growth

B. NITROGEN

Major component of proteins and nucleic acids of a typical bacterial cell.

The end product of all pathways for nitrogen assimilation is the ammonium ion (NH4+).

Most microorganisms use NH4+ as a sole nitrogen source, and many organisms possess the ability to produce it from amines.

C. GROWTH FACTORS

Organic compounds needed by bacteria in order to grow. In bacterial culture, these substances are usually provided in the culture medium.

 Classification: Prototrophics – do not require an exogenous source of

growth factor since they synthesize their own.

Auxotrophics – require the addition of growth factor to culture media for growth to occur.

Examples of growth factors:

1. B-complex vitamins 4. pyrimidines

2. amino acids 5. pentoses3. purines 6. fatty acids

D. INORGANIC SALTS

Salt in small amount stimulates the growth of some organisms. Organisms requiring high salt concentrations are called halophilic.

E. OXYGEN

Classification of organisms

Aerobes – grow in the presence of atmospheric (free) oxygen Obligate aerobes – grow only in the presence of

oxygen Facultative anaerobes – fundamentally aerobes,

but can grow in the absence of oxygen Microaerophiles – grow best at low or reduced

oxygen tensions

Anaerobes – grow in the absence of atmospheric oxygen Obligate anaerobes – grow only in the

absence of oxygen Facultative aerobes – fundamentally

anaerobes, but can grow in the presence of oxygen

Aerotolerant anaerobes – do not grow well but do survive in the presence of oxygen

F. CARBON DIOXIDE

Some organisms such as Neisseria and Brucella require a higher concentration (3-10%) of CO2 for growth. These organisms are called capnophiles.

G. MOISTURE

This is indispensable for bacterial growth. It serves as a solvent for food and forms the major portion of the protoplasm. Organisms requiring increased moisture content are termed humidophiles.

A. TEMPERATURE

Every bacterium has an optimal temperature, the temperature at which the organism grows best.

 Classification:

1.Psychrophilic (cold loving) – grows at 10C-200C2.Mesophilic – grows at 20-400C (most pathogens

grow at 37C)3.Thermophilic (heat loving) – grows at 50-600C 

B. HYDROGEN ION CONCENTRATION

Most pathogenic bacteria have an optimal pH of 7.2 – 7.6.

Classification:

1.Acidophiles – grows at pH 6.5 – 7.02.Neutrophiles – grows at pH 7.5 – 8.03.Alkalophiles – grows at pH 8.4 – 9.0

 C. OSMOTIC PRESSURE

Organism requiring high osmotic pressures are called osmophiles.

Refers to the increase in number of organisms

is obtained by plotting the logarithm of the number of cells against the time of growth.

A. LAG PHASE (PHASE OF REJUVENATION OR PHASE OF PHYSIOLOGIC YOUTH)

The period of adaptation of the organisms to their new environment characterized by little or no multiplication.

The cells in this phase are very active metabolically. Active synthesis of enzymes and other essential constituents occurs.

B. EXPONENTIAL PHASE (LOGARITHMIC PHASE)

The period at which the cells are in a state of balanced growth characterized by maximal rates of cell division and mass increase. It is during this phase that the generation time is constant.

C. STATIONARY PHASE (PHASE OF EQUILIBRIUM OR PLATEAU PHASE)

The period at which the rate of cell production equals the rate of cell death. Growth ceases due to:

1. accumulation of waste products2. exhaustion of nutrients3. change in pH and other factors

D. DEATH PHASE (PHASE OF DECLINE)

The period at which complete cessation of multiplication occurs such that the death rate in the medium increase rapidly.

ASSIGNMENT: (5 points each)

1. ENUMERATE METHODS OF MICROBIAL CONTROL AND STERILIZATION

2. ENUMERATE METHODS OF MICROSCOPIC IDENTIFICATION OF BACTERIA

3. ENUMERATE THE DIFFERENT TYPES OF BACTERIAL CULTURE

4. ENUMERATE THE CLASSIFICATION OF CULTURE MEDIA

Study in advance BACTERIAL CULTURE AND IDENTIFICATION, and METHODS OF MICROBIAL CONTROL and STERILIZATION