food microbiology bacterial contamination

food safety

1. Food Microbiology
PGDC-1005
1
st
Lecture
Prof. Dr. Tahir Zahoor
1

2. Bacteria
Bacteria constitute a large domain of prokaryotic
microorganisms
Typically a few micrometres in length
Bacterial cells are about 10 times smaller than eukaryotic
cells and are typically 0.5–5.0 micrometers in length
Have a number of shapes, ranging from spheres to rods and
spirals
Bacteria were among the first life forms to appear on Earth
and are present in most of its habitats
2

3. Cont..
The study of bacteria is bacteriology - a branch of
microbiology
Bacteria are ubiquitous (in every habitat on Earth)
Bacteria inhabit soil, water, acidic hot springs,
radioactive waste land the deep portions of Earth's crust
Some bacteria can even survive in the extreme cold and
vacuum of outer space
Live in symbiotic and parasitic relationships with plants
and animals
3

4. Cont…
There are typically 40 million bacterial cells in a gram of
soil and a million bacterial cells in a milliliter of fresh
water
Bacteria are vital in recycling nutrients, and many
important steps in nutrient cycles depend on bacteria,
such as the fixation of nitrogen from the atmosphere.
There are approximately 10 times as many bacterial cells
as human cells in the human body, with large numbers of
bacteria on the skin and in the digestive tract
4

5. Cont...
Pathogenic bacteria cause infectious diseases, including
cholera, tuberculosis, anthrax and bubonic plague.
 The most common fatal bacterial diseases are
respiratory infections, with tuberculosis alone killing
about 2 million people a year, mostly in sub-Saharan
Africa
5

6. Parts of a Cell
 Cell envelope
Cell wall- murein sacculus
Outer
Cell membrane-plasma membrane, cytoplasmic membrane
 Cytoplasm
Nucleiod
Ribosomes
Spores
plasmids
 Appendages
Capsule
pili
flagella
6

7. Cont…
Bacterial cell is surrounded by a lipid
membrane or cell membrane
They lack:
Mitochondria,
Chloroplasts and
Other organelles present in eukaryotic
cells, such as the Golgi apparatus and
endoplasmic reticulum
7

8. Cytoplasmic membrane
Lipid bilayer
Similar to eukaryotic membranes
But no sterols (cholesterol)
Responsible for many functions
Attributable to organelles in eukaryotes:
-electron transport
-energy production (mitokondria in eukaryotes)
Transport proteins: uptake of metabolites release of
other substances
Ion pumps: to maintain a membrane potential
8

9. Cell wall
 Around the outside of the cell membrane is bacterial
cell wall
Except: Archaebacteria (pseudoglycan and
pseudomurein) and mycoplasmas (no cell wall)
Peptidoglycan:
N acetyl glucosamine & N acetyl Muramic acid
Protect the cell from osmotic changes
Provides rigidity and
Determines the shape of a bacteria
Multilayered in Gram positive
Teichoic acid
Mono to bi layered in Gram negative
9

10. Two different types of cell wall in bacteria, called
Gram-positive and Gram-negative
The names originate from the reaction of cells to the
Gram stain, a test used for observing bacteria
Gram positive bacteria have a thick cell wall and stain
purple
Gram negative bacteria have a thin cell wall with an
outer lipid layer and stain pink.
.
10
Cont…

11. Cytoplasm
Nucleoid
Chromosomal DNA
Plasmids
Inclusion bodies
Storage of excess food and energy
○Metachromatic granules/ Babes Ernst granules
○Much granule
Spores
Resist adverse condition
11

12. Ribosomes
Like all living organisms, bacteria contain
ribosomes for the production of proteins, but the
structure of the bacterial ribosome is different
from those of eukaryotes
Unlike the eukaryotic 80S(40S+60S)ribosome
Bacterial ribosome – 70S – (30S & 50S)
Proteins and RNA of the ribosome are
significantly different
Major targets for antibacterial drugs
12

13. Bacterial chromosome
Bacterial DNA is circular and is attached at a point to
the plasma membrane
Unlike eukaryotes
A single, double stranded circle
Not in a membrane bound nucleus
No histons
In a discrete area called nucleoid
13

14. Plasmids
Smaller
Circular
Extrachromosomal DNAs
Not usually essential for cellular survival
Most commonly found in gram-negative bacteria
Often provide a selective advantage: resistance to
antibiotics
14

15. Capsules
Some bacteria (gram-positive and gram-negative)
Loose polysaccaride or proteinlayer
Slime layer: loosely adherent and nonuniform in
density and thickness
Glycocalyx: capsule and slime layer are also called.
Polypeptide capsule:
Bacillus anthracis (polyglutamic acid)
Poorly antigenic
Antiphagocytic and a major virulence factor
(Streptococcus pneumoniae)
Barrier to toxic hydrophobic molecules such as
detergents
Promote adherence (Streptococcus mutants: stick the
tooth)
15

16. Thanks
16