Factors affecting microbial growth in food

1. Introduction toIntroduction to
Microbiology and MycologyMicrobiology and Mycology

2. Introduction
Microbiology - the study of microorganisms
Organisms too small to be seen with the naked eye
Study of microscopic (living ) things
E.g
Viruses
Bacteria
Fungi
Protozoa
Microscopic Algae

3. Branches of Microbiology
Bacteriology: study of bacteria
Mycology: study of fungi
Virology: study of viruses
Parasitology: study of protozoa and
parasitic worms

4. Branches of Microbiology
Recombinant DNA Technology
– Recombinant DNA
– Genetic engineering
– Microbial genetics – mechanism by which
microbes inherit genes
– Molecular biology – structure and function
(expression) of genes

5. Branches of Microbiology
Biotechnology
– GMOs/GEMs for industrial, pharmaceutical and
agricultural applications
– Improvements of agriculture (plants and
animals)

6. Benefits
Maintain balance of environment (microbial
ecology)
Basis of food chain
Nitrogen fixation
mycorrhizae
Photosynthesis
Digestion, synthesis of vitamins
Manufacture of food and drink

7. Benefits
Genetic engineering
Synthesis of chemical products
Recycling sewage
Bioremediation: use microbes to remove
toxins (oil spills)
Use of microbes to control crop pests
Normal microbiota

8. Harmful Effects
Cause disease (basis for bioterrorism)
Food spoilage

9. History of Microbiology
-Pioneers of Microbiology
1590 – First compound light microscope
Zacharias Janssen

10. Pioneers of Microbiology
1676 –first observation of bacteria
“animalcules”
Anton Von Leeuwenhoek

11. Pioneers of Microbiology
Louis Pasteur (1822-1895), Chemist

12. Pioneers….
Louis Pasteur
– Fermentation (1857)
– Pasteurization: heat liquid enough to kill
spoilage bacteria (1864)
– Proposed aseptic techniques (prevent
contamination by unwanted microbes)
– Director of Pasteur Institute, Paris (1894)

13. Pioneers of Microbiology
Joseph Lister, UK (1867)
Used phenol (carbolic acid) to disinfect
wounds
First aseptic technique in surgery

14. Pioneers of Microbiology
Robert Koch, DE (1876)
– Identified microbes that caused anthrax
(1876), tuberculosis (1882) and cholera
(1883)
– Developed microbiological media &
streak plates for pure culture (1881)

15. Pioneers….
Robert Koch

16. Pioneers….
1929 Discovery of Penicillin
(first antibiotic)
Alexander Fleming

17. Pioneers….
1953 Structure of DNA Revealed by Watson & Crick

19. Tools of Microbiology
Compound light Microscope
Electron Microscope
Digital microscope-connected to the
computer
Incubator – keep microbes warm for
growth
Water bath
Autoclave-Uses temperature above boiling
water

20. Techniques of Microbiology
Staining – to better see structures of the microbes –
-Stains and dyes are frequently used in microbiology and
parasitology to highlight structures in biological tissues for
viewing, often with the aid of different microscopes.
-In some cases, staining is unnecessary, for example when
microorganisms are very large or when motility is to be
studied, and a drop of the microorganisms can be placed
directly on the slide and observed
Microbial Culture – for growing the microbes
-Container for microbe culture is usually Petri dish
Culture media
- Food for the microbes
- E.g. Agar – (from red algae)

21. Agar

24. Microbial Taxonomy
Classification Systems
Levels of Classification
Definition of “Species”
Nomenclature
Useful Properties in Microbial
Classification
Microbial Phylogeny

25. Microbial Taxonomy
-Classification Systems
Taxonomy: hierarchical placement of living
organisms into groups
Phylogenetic Classification System:
– Groups reflect genetic similarity and
evolutionary relatedness
Phenetic Classification System:
– Groups do not necessarily reflect genetic
similarity or evolutionary relatedness. Instead,
groups are based on convenient, observable
characteristics.

26. Definition of “Species”
The “basic unit” of taxonomy, representing
a specific, recognized type of organism
For sexually reproducing organisms, a
fundamental definition of “species” has
been reproductive compatibility
This definition fails for many microbial
species because they do not reproduce
sexually

27. Definition of “Species”
Definition of “species” in microbiology:
– Classic definition: A collection of microbial
strains that share many properties and differ
significantly from other groups of strains
– Species are identified by comparison with
known “type strains”: well-characterized pure
cultures; references for the identification of
unknowns
– There are several collections of type strains,
including the American Type Culture
Collection (ATCC)

28. Definition of “Species”
Definition of “species” in microbiology
(cont.):
– Strain:
• A population of microbes descended from a single
individual or pure culture
• Different strains represent genetic variability within
a species
• Biovars: Strains that differ in biochemical or
physiological differences
• Morphovars: Strains that vary in morphology
• Serovars: Strains that vary in their antigenic
properties

29. Nomenclature
Scientific name (Systematic Name)
Binomial System of Nomenclature
– Genus name + species name
• Italicized or underlined
• Genus name is capitalized and may be abbreviated
• Species name is never abbreviated
• eg: Escherichia coli
E.coli
• A genus name may be used alone to indicate a genus
group; a species name is never used alone

30. Nomenclature
Common or descriptive names
(trivial names)
– Names for organisms that may be in common
usage, but are not taxonomic names
• eg: tubercle bacillus
(Mycobacterium tuberculosis)
• meningococcus
(Neiserria meningitidis)
• Group A streptococcus
(Streptococcus pyogenes)

31. Useful Properties in microbial
classification
Colony morphology
Cell shape & arrangement
Cell wall structure (Gram staining)
Special cellular structures
Biochemical characteristics
Molecular characterization

32. Useful Properties in Classification
Nucleic acid hybridization
– By mixing ssDNA from two different species
and determining the percentage of the DNA that
can form dsDNA hybrids
– The greater the percent hybridization, the closer
the species

33. Useful Properties in Classification
Nucleic acid sequencing
– The nucleic acid sequence for the complete
genome of several species is now available
– 5S and 16S rRNA (ribosomal RNA) sequences;
comparison of these sequences has been
extensively used to determine the phylogenetic
relationships of microbial groups from the gene
bank

34. Microbial Phylogeny
Bergey’s Manual of Systematic Bacteriology
– In 1927, David Bergey & colleagues published
Bergey’s Manual of Determinative
Bacteriology, a manual that grouped bacteria
into phenetic groups, used in identification of
unknowns.
– In 1984, a more detailed work entitled Bergey’s
Manual of Systematic Bacteriology was
published, still primarily phenetic in its
classification.

35. Microbial Phylogeny
Bergey’s Manual of Systematic Bacteriology
– Publication of the second edition of Bergey’s
Manual of Systematic Bacteriology was begun in
2001.
– The 2nd edition gives the most up-to-date
phylogenic classification of prokaryotic
organisms, including both eubacteria and
archaea.
– The classification in Bergey’s Manual is accepted
by most microbiologists as the best consensus for
prokaryotic taxonomy.

36. Microbial Phylogeny
Phylogeny of domain Bacteria
– The 2nd edition of Bergey’s Manual of
Systematic Bacteriology divides domain
Bacteria into 23 phyla. 12 of the more notable
phyla are described here.

37. The Bacteria Domain:
Approximately 12 distinct groups

38. Group 1:
Aquifex-Hydrogenobacter
Mainly thermophilic Bacteria found
in deep sea vents, geyser etc.
Aquifex pyrophilus (85-95o
C)
Thermophillus furiosus (103o
C)
among the most thermophilic bacteria
known.

39. Group 2: Thermotoga
•Thermotoga and relatives are
all thermophillic, anaerobic,
fermentative rods
•Cells enclosed in a sheath.

40. Group 3: Green Non-Sulfur
Bacteria.
Also thermophilic.
Includes Chloroflexus,
Thermomicrobium,
Thermoleophilum,
Herpetosiphon. These organisms
are filamentous and move by
gliding.

41. Chloroflexus

42. Group 1-3 environments

43. Leptothrix:
Iron oxide accumulating bacteria

44. Group 4: Deinococcus,
Thermus group
•Deinococci are resistant to
radiation: gamma rays, X-rays,
and UV. (20x E. coli).
•Cells have efficient DNA repair
systems
•Thermus aquaticus (Taq -PCR)

45. PCR Taq DNA Polymerase
Taq stands for Thermus aquaticus, which is a
microbe found in 176°F hot springs in Yellow
Stone National Forest
Yellowstone National Park established in 1872
It is America's first national park. Located in
Wyoming, Montana and Idaho, it is home to a large
variety of wildlife
Taq produces an enzyme called DNA polymerase,
that amplifies the DNA from the primers by the
polymerase chain reaction

46. Group 5: Spirochaetes
Only 9 genera, including Borrelia
(cause of Lyme disease) and
Treponema (cause of syphillis).

47. Lyme disease, Lyme borreliosis
is an infectious disease caused by at least three species of
bacteria belonging to the genus Borrelia.Borrelia
burgdorferi
Borrelia is transmitted to humans by the bite of infected
ticks
Early symptoms may include fever, headache, fatigue,
depression, and a characteristic circular skin rash called
erythema migrans (EM).
Left untreated, later symptoms may involve the joints,
heart, and central nervous system. In most cases, the
infection and its symptoms are eliminated by antibiotics,
especially if the illness is treated early.
Delayed or inadequate treatment can lead to more serious
symptoms, which can be disabling and difficult to treat.

48. Ixodes scapularis, the primary vector
of Lyme disease in eastern North
America

49. Borrelia bacteria, the causative agent
of Lyme disease

50. rash pattern associated with Lyme
disease

51. Spirochaetes….
Helicobacter pylori- a causative agent for
peptic ulcers (80%) belongs to this group.
A peptic ulcer, also known as PUD or peptic ulcer
disease is the most common ulcer of an area of the
gastrointestinal tract that is usually acidic and thus
extremely painful.
It is defined as mucosal erosions equal to or greater
than 0.5 cm.
As many as 70–90% of such ulcers are associated with
Helicobacter pylori, a spiral-shaped bacterium that lives
in the acidic environment of the stomach;
However, only 40% of those cases go to a doctor.WHY?
Ulcers can also be worsened by drugs such as aspirin

52. Deep gastric ulcer

53. Spirochaetes……–Characterized by flexible, helical cells
with a modified outer membrane (the
outer sheath) and modified flagella (axial
filaments) located within the outer sheath
–Important pathogenic genera include
Treponema, Borrelia, and Leptospira

54. Spirochaetes