Assessing Microbial Growth: Methods and Techniques

Medical Questions

Table of Contents
1. The structure and function of bacterial pili and flagella..............................................................3
2. Life cycle of Leishmaniasis and its range of mammalian hosts make it a particularly difficult
pathogen to control. .......................................................................................................................5
3. Salmonella chromogenic agar plates used to distinguish enteric pathogens and normal floral...6
4. The growth of the microbes can be assessed in many ways ......................................................7
Metabolic Activity.......................................................................................................................8
5.. The life cycle of Schistosomiasis and ways they cause disease in the humans .........................9
REFERENCES..............................................................................................................................12

1. The structure and function of bacterial pili and flagella.
Pili
The cell surfaces of the prokaryotic cells have short, hair-like structures on them, these
structures are called pili. They are attached to the surface which cause infections and have the
ability to overcome host defences. Pili are commonly attached to Gram-negative bacteria.
(Jacobsen, Bardiaux and et.al, 2020).
Depending on the assembly pathway pili are divided into four groups in Garm-negative bacteria:
i) Usher pathway pili
ii) Type IV pili(Drame, Lafforgue and et.al, 2021)
iii) Curli pili
iv) CS1 pilus family
They are divided into two types of groups:
 Short and Thin Pili – These type of pili are found in normal body of flora streptococcus
species.
 Longer and Flexible Pili- These types of pili are found on Corynebacterium species and
pathogenic streptococci.
Functions
 Pili help the bacterial cells to avoid the attack from the white blood cells.
Pili are called sex pilus or F pilus because they recognize the recipient cell to receive the donors
genetic material and stabilize the bacteria during DNA transfer which is done by conjugation.
 Pili is used for the movement in Pseudomonas aeruginosa and Myxococcus xanthus.
Flagella
The word flagellum means whip. The bacterial flagella is a microscopic-hair like
structure and are used for the locomotion of a cell (Poghosyan, Iacovache and et.al, 2020). Types
of flagella:
• Monotrichous
• Peritrichous
• Lophotrichous
• Amphitrichous
Structure

The structure of flagella is divided into three parts:
 Basal body- Pair of proteins called MotB surrounds the ring(L-ring, P-ring, C-ring, M-S
ring ) in basal body and is attached to the cell membrane and cytoplasmic membrane.
 Hook- The base of the filament consist of a broader area which is called hook. Hook
connects the motor protein in the base to the filament.
 Filament- The thin hair -like structure coming out from the hook is called filament.
Functions
• Flagella help in the movement.
• In some organisms, flagella are used as sensory organs..
• flagellum is used to increase the reproductive rates in some eukaryotes
Comparison
Both bacterial pili and flagella have thread like structures to them, attached to some
bigger organism, are made from proteins, have tube like structures and have a specific number of
them in bacterial cells.
Contrast
Flagella Pili
Flagella is attached to both Gram positive and
Gram-negative bacteria. Flagella are
originated from cytoplasmic membrane which
is an interior origin
Pili are attached to only Gram-negative
bacteria.
Flagella are originated from cytoplasmic
membrane which is an interior origin
Pili is originated from bacterial cell wall
which is an exterior origin.
Gene present in the nucleoid region of
bacteria is responsible for the formation of
flagella.
Gene present in plasmids is responsible for
the formation of pili.
Flagella are helical. Pili are straight.
Flagella are very long, thick and rigid. Pili are short, thin and soft in comparison to
flagella.
The pattern of distribution in flagella can be
polar and lateral.
The pattern of distribution in pili is random
on the surface of bacteria.
Flagella's main function is locomotion and
sometimes act as sensory organ.
The main function of pili is transfer of gene
and attachment and mobility.
Flagella, at base is associated with a complex
motor for propulsion.
There is no motor system in pili.