Bacterial
Growth &
Reproduction
Types of Reproduction
ƒ Asexual
ƒ Sexual
ƒ Spore Formation
Asexual Reproduction
ƒ a.k.a. Binary Fission
ƒ Bacteria reproduce by splitting in two
ƒ NO genetic diversity
ƒ Rapid massive reproduction possible
Binary Fission
Sexual Reproduction
ƒ a.k.a. Conjugation
ƒ Pili form bridge between different
bacteria
ƒ Genetic material is transferred
ƒ Genetic diversity RESULTS
ƒ Allows bacteria to transfer resistance
to antibiotics to other species
(contained in genes)
Conjugation
Figure 8.25
Bacterial conjugation.
The sex pilus connecting
these cells undergoing
conjugation allows the
transfer of genetic
information. At the actual
time of genetic exchange,
the cells’ connecting bridge
contracts and the cells are
much closer together.
Notice that one cell has
numerous fimbriae.
QUESTION??
ƒ Why is sexual reproduction of
bacteria bad for Humans?
ƒ Bacteria can pass on resistance
to antibiotics , even between
species!!!!!!
Spore Formation
ƒ Endospores
ƒ Formed under conditions of environmental
stress
ƒ Spores are thick walled & contain genetic
information
ƒ Extremely resistant to heat, desiccation
(drought), cold, UV light, and toxic chemicals
Spore Formation
ƒ Spores that survive such conditions
go on to become typical cells
ƒ By being exposed to heat or chemicals =
the spore takes on water, swells, and
releases a vegetative (metabolically
active/growing) cell
Sporulation
Nutrient & Energy Sources for
Bacterial Growth
† Organic matter
† Carbon (from CO2)
† Sunlight
† Chemicals
Environmental Factors That
Influence Growth
„
Temperature
„
„
Oxygen
„
„
Most pathogens grow between 41-140 oF (20-50 oC)
Some require O2 and others do not
pH
Most bacteria grow in a range of pH 6.5-7.5
„ Few can survive below ~pH 4
„ Serious food contamination @ pH above ~5
„
„
Water Availability
„
Bacteria need moisture
Limits to Growth
• pH <4.6 (acidic)
• HOT and DRY environment
• NO FOOD source
• NO SPACE for growth
How Do Bacteria Cause
Disease?
1. Metabolize Host
– Secretion of enzymes to “eat” host
tissue
2. Produce Toxins
– Bacterial waste can be toxic to host
cells
Controlling Growth
& Prevention from Infection
„
Sterilization = destruction/removal of all
microorganisms (including endospores)
„
„
Disinfection = removal of most
(the harmful) microbes
„
„
Used for surgical instruments
Lysol wipes, etc.
Pasteurization = mild heat treatment to rid
consumables of spoilage microorganisms
(not sterile)
„
Milk
Controlling Growth &
Prevention from Infection
„
Sanitization = microbes removed to a safe
public health standard/level
„
„
Restaurants
Preservation = process to delay spoilage of
consumable goods
„
Cheese
Controlling Growth
& Prevention from Infection
„
Antibiotics = a substance produced by
microorganisms that in small amounts
inhibits another microorganism
Usually produced naturally by a bacteria or
fungus
„ Some are used to control bacterial growth in the
body
„ Others are put into foods to inhibit growth of
food spoiling bacteria
„