This document discusses two microbes - Lactobacillus and Rhinovirus. Lactobacillus is a rod-shaped, Gram-positive bacteria that produces lactic acid and inhabits the gastrointestinal tract of humans and animals. It reproduces through binary fission and has several useful effects like inhibiting harmful bacteria and producing enzymes to aid in digestion. Rhinovirus is a small, non-enveloped virus that causes the common cold. It inhabits the nasal passages of humans, reproduces within 8-12 hours, and spreads through respiratory droplets. Infection leads to cold symptoms like runny nose, cough and sore throat that typically last 2-14 days.

1. Lactobacillus – Useful Bacteria
Structure-Lactobacilli are rod-shaped, Gram-positive,
fermentative, organotrophs. They are usually straight, although
they can form spiral or coccobacillary forms under certain
conditions. They are often found in pairs or chains of varying
length. Lactobacilli are classified as lactic acid bacteria, and
derive almost all of their energy from the conversion of glucose
to lactate during homolactic fermentation.
Lactobacilli are commonly associated with plant herbage.
althoughthermophilic strains can be comfortable at
temperatures as high as 60 degrees Celsius.
Habitat-the habitat of L. acidophilus can be found in many
places. This bacterium can be found in animal and human
intestinal tracts (for humans it is found in the gastrointestinal
tract), soil, water, milk and milk products, plants, silage, and
manure. This bacteria is found in yogurt and other fermented
milk products and is partially responsible for their sour taste.
Mode of Reproduction-They have a generation
time ranging from 25 minutes to several hundred minutes, and
grow optimally between the temperatures of 30 and 40
degrees Celsius. Lactobacillus acidophilus reproduces by binary
fission, a type of asexual reproduction. Binary fission is when

2. the bacterium doubles its contents and divides into two. It is
the primary form of reproduction for all bacteria, and can grow
the colonies very quickly because each generation increases
two fold.
Useful Effects –
1. Lactobacillus acidophilus is the most commonly used
probiotic.
2. Lactobacillus acidophilus inhibits the growth of harmful
bacteria.
3. It helps in breaking down of food particles and helps in
production of lactic acid and hydrogen peroxide and other
byproducts.
4. lactobacillus prevents the growth of harmful bacteria in
the digestive tract.
5. Lactobacillus acidophilus produces lactase breaking down
lactic acid which helps in intolerance of lactose.
6. It is also used in the treatment of urinary tract infections.
7. Lactobacillus bacteria can be used to treat specific
outbreaks of diarrhea and other problems, to prevent
digestive problems, or to supplement the diet after taking
antibiotics.

3. Rhinovirus- Harmful Microbe
Structure-they are among the smallest viruses, with
diameters of about 30 nanometers only.It is lytic in nature.
There are over a 100 recognized types of rhinovira that differ
based on their varying surface proteins.Rhinovira are among
the smallest vira, with diameters of about only 30 nanometers
They are small, icosahedral, non-enveloped viruses containing
one positive RNA strandof between 7.2 and 8.5 kb in
length.Rhinovira are composed of a capsid, that contains four
viral proteins VP1, VP2, VP3 and VP4. VP1, VP2, and VP3 form
the major part of the protein capsid. Rhinovirus attaches to the
folds in the mucous membranes of the nose (hence the name
rhinovirus).
Habitat -HRV survives for many hours on environmental
surfaces. Rhinovirus types are most active in early fall, spring,
and summer. Rhinoviruses can live up to 3 hours on your skin.
They also can survive up to 3 hours on objects such as
telephones and doorknobs. Rhinoviruses grow best at
temperatures of about 91 degrees Fahrenheit, the temperature
inside the human nose. Transmission of the rhinovirus occurs in
one of two ways:

4. Touching your skin or environmental surfaces, such as
telephones and stair rails, that have the rhinovirus on
them and then touching your eyes or nose.
Inhaling drops of mucus full of rhinovirus from the air
when a contagious person coughs or sneezes.
Mode of reproduction -The RV is inhaled directly
or finds its way to the nassal passage through hands that are
contaminated with the virus. The virus is then transported to
the back of the nose by the regular functioning of the nose
itself. Here, the RV attaches itself to the receptors at the
surface of the nasal cells, where it reproduces. These receptors
are called Intercellular Adhesion Molecule- 1(ICAM- 1). The
reproductive cycle of the RV is 8-12 hours long. Once the cells
have been attacked, in the infected cells, the virus replicates as
rapidly as possible, and continually sheds progeny viruses.
These progeny viruses can propagate the infection by invading
neighboring cells. The infection remains localized in the upper
respiratory tract.
Harmful Effects-When someone becomes infected
with a rhinovirus, he or she will experience what is commonly
known as the common cold. The symptoms usually begin 2 to 3
days after infection. The symptoms of infection with this type
of virus often include:

5. Mucus buildup in your nose
Difficulty breathing through your nose
Swelling of your sinuses
Sneezing
Sore throat
Cough
Headache.
With a rhinovirus infection, fever is usually slight, but can
climb to 102 degrees Fahrenheit in infants and young
children.
Symptoms can last from 2 to 14 days, but like most people,
you'll probably recover in about a week. An infection rarely
causes serious problems.