Bacteriology

THE CAPSULE Many bacteria are surrounded by a covering layer of gelatinous material that lies outside and immediately in contact with the cell wall. Capsules of most bacteria are polysaccharides but those of a few bacteria are polypeptides. A capsule is not essential to the life of the bacterium but is protective, mainly against phagocytosis. It is also used for attachment to surfaces. It therefore plays part in pathogenicity. Its presence is best demonstrated by negative stains.

CAPSULE Enterobacter aerogenes Klebsiella pneumoniae

THE FLAGELLA Motile strains of bacteria possess filamentous appendages known as flagella which act as organs of locomotion. Flagella are protein in nature. There may be one or several flagella per cell. The arrangement of the flagella may be (a)Atrichous(b)monotrichous (c)lophotrichous(d)amphitrichous (e)kophotrichous (f)peritrichous

Types of flagella

FLAGELLA Electron Micrograph of Bacteria with Flagella

THE FIMBRIAE Certain Gram-negative bacilli possess filamentous or hair-like appendages known as fimbriae or pili. There are two types of fimbriae: common and sex pili. They are shorter and more numerous than flagella. The common pili are organs of adhesion. Adhesion may be of value to the bacteria in holding on to nutritionally favourable areas. The sex pili are involved in reproduction.

THE NUCLEOID The genetic information of a bacterial cell is contained in a single molecule of double stranded DNA that occurs in the form of a closed circle. This single molecule is referred to as the chromosome. It is about 1000 m (1 mm) long. There is no nuclear membrane or nucleolus. It replicates by growth and simple binary fission. The DNA can be transferred between bacteria in several different ways: Transformation Transduction Conjugation

Transformation involves the uptake of naked bacterial DNA across the cell wall. In transduction, DNA fragments are transferred from one bacterial cell to another by viruses called bacteriophages. Conjugation occurs when bacteria transfer DNA along a specialized hollow tube (‘sex pilus’) connecting the two cells.

BACTERIAL SPORES Certain bacterial spp., especially Bacillus and Clostridium spp., develope a highly resistant resting phase or endospore, when subjected to harsh conditions like starvation or high temperatures.

The process of forming a spore is called sporulation or sporogenesis and does not involve multiplication. Before a bacterial cell has formed a spore it is called a vegetative cell. Reversion back to vegetative form is called germination, and is not a means of reproduction, since one spore germinates into one cell. The medical importance of spores lies in their extraordinary resistance to heat and chemicals.

1. Central. 2. Terminal 3. Sub-terminal Types of Spores 1. Central. 2. Terminal 3. Sub-terminal

SPORE Bacillus anthracis Bacillus megaterium

Bacterial Nutrition As a group, bacteria are nutritionally quite diverse. Autotrophic:  is an organism that produces complex organic compounds (such as carbohydrates, fats, and proteins) from simple substances present in its surroundings, generally using energy from light or inorganic chemical reactions. Photoautotrophs: autotrophs that obtain their energy from sunlight. Chemoautotrophs: those that harvest energy from inorganic chemicals. Heterotrophs: is an organism that uses organic carbon for growth. Photoheterotrophs: heterotrophs that obtain their energy from sunlight. Chemoheterotrophs: those that harvest energy from organic molecules.

Bacterial Respiration Bacterial Respiration Bacteria can be classified based on oxygen requirements into: Obligate aerobes. a constant supply of oxygen in order to live Obligate anaerobes. so they must live in the absence of oxygen. Facultative anaerobes This kind of bacteria can survive with or without oxygen Bacterial Respiration Bacterial Respiration

Bacterial reproduction Binary fission  The method by which bacteria reproduce. The circular DNA molecule is replicated; then the cell splits into two identical cells, each containing an exact copy of the original cell's DNA.

Types of Bacterial reproduction: Sexual. Asexual.

Sexual Reproduction of Bacteria: It involves transfer of a portion of genetic material (DNA) from a donor cell to a recipient cell and then proceeds as in asexual reproduction. This process is called as genetic recombination or parasexuality. It is known to occur in the following three ways: 1. Transformation. 2. Transduction. 3. Conjugation.

Bacterial reproduction Asexual Reproduction of Bacteria: in which the bacterial cell divides into two identical daughter cells in a process called Binary fission.

Bacterial Growth Curve