Bacterial cell structure and normal flora in human body.

2. Bacterial Cell Structure
A. L. Samer Faisal

3. 3
Microbiology
• Agents of human infection:
– Bacteria Prokaryotes
– Helminthes Eukaryotes
– Protozoa Eukaryotes
– Fungi Eukaryotes
– Viruses Non-cellular

4. • Difference between Eukaryotes and
Prokaryotes
• Structure
• Replication
• Nucleic acid

5. 5
Earliest
Prokaryotes
• Most numerous
organisms on Earth
• Include all bacteria
• Earliest fossils date 2.5
billion years old

6. BACTERIA
• Bacteria are large group of single celled
prokaryotic microorganisms
• 10 times as many bacteria cells in the human
flora as there are human cell in the body

7. Shape of Bacteria
Three basic shapes
• Cocci:streptococci, Staphylococci, Diplococci
• Bacilli: E.coli, Klebsiella, Bacillus.
• Spirochetes: Treponema, Borrelia

9. Bacterial Size
• Bacteria range in size from about 0.2 to 5 µm.
• The smallest bacteria (Mycoplasma) are about the
same size as the largest viruses (poxviruses) and are
the smallest organisms capable of existing outside
the host.
• The longest bacteria rods approach the size of some
yeasts and human R.B.Cs

10. 10

11. According to staining
• Gram positive Thick peptidoglycan layer
and teichoic acid
• Gram negative Thin peptidoglycan layer and
lipopolysaccharide- endotoxin
• Acid fast bacilli Mycolic acid (lipids)

12. • Some bacteria are variable in shape
• PLEOMORPHIC----many shaped
• Shape of the bacteria is determined by its rigid
cell wall
• The microscopic appearance of bacterium is most
important criteria for its identification

13. 13
pH requirements
• Most grow best at pH of 6.5 to 7.0
• Many act as decomposers
recycling nutrients
• Some cause disease (Pathogenic)

14. The Prokaryote
• Structural Components
MACROMOLECULE SUBUNIT POSITION IN CELL
PROTEIN Amino Acid Flagella, pili, cell wall,
cytoplasmic membrane,
ribosomes, cytoplasm
POLYSACCHARIDE Sugar/Carbohydrate Capsule, Inclusions, Cell wall
PHOPHOLIPID Fatty Acid Membranes
NUCLEIC ACID
(DNA/RNA)
Nucleotide DNA, Nucleoid, Plasmids,
Ribosomes,

15. Structural Components
Prokaryotes have 5 essential components
• Nucleoid (DNA)
• Ribosomes
• Cell membrane
• Cell wall
• Surface layer (Capsule)
• Appendages

16. Structural Components

17. BACTERIAL STRUCTURE
COVERING LAYERS
• Cell wall
• Peptidoglycan
Sugar back bone
with peptide side
chains,which are
cross linked
Rigidity osmotic
protection , site of
action of antibiotic,
lysozyme degrade.
Outer membrane
Gram Negative
bacteria
Lipid A
Polysaccharide
Toxic component
of endotoxin.
Surface antigen.
Surface fiber on
Gram Positive
bacteria
Teichoic acid Surface antigen

19. 19
Protection
• Cell Wall made of Peptidoglycan
• May have a sticky coating called
the Capsule for attachment to
host or other bacteria

20. FUNCTION OF CELL WALL
• Maintaining the cell's characteristic shape
• Countering the effects of osmotic pressure
• Providing attachment sites for
bacteriophages-teichoic acids
• Providing a rigid platform for surface
appendages- flagella, fimbriae

21. Peptidoglycan

23. COMPARISON
Property Gram Positive Gram Negative
Thickness of wall 20-80 nm 10 nm
Number of layers in wall 1 2
Peptidoglycan content >50% 10-20%
Teichoic acid in wall + -
Lipid and lipoprotein content 0-3% 58%
Protein content 0% 9%
Lipopolysaccharide 0 13%
Sensitive to penicliiin + - (not as much)
Digested by lysozyme + - (not as much)

24. Properties of cell wall
• Gram negative bacteria contains endotoxin---
lipopolysaccharide
• Polysaccharides and proteins are antigens
• Porin proteins helps entry of hydrophilic
molecules
• Teichoic acid are fibers on outer surface of
gram positive ---ability to induces septic shock

25. Cell Membrane
• Composed of phospholipid bilayer
• FUNCTIONS
• Active transport
• Energy generation---oxidative phosphorylation
• Synthesis of precursors of cell wall
• Secretion of enzymes and toxins

26. 26
• Infoldings of cell membrane carry
on photosynthesis & cellular
respiration
• Infoldings called Mesosomes

27. 27
Mesosomes
MESOSOME

28. 28
Sticky Bacterial Capsule

29. Plasmids
• Molecules of DNA that are found in bacteria
separate from the bacterial chromosome.
• A circular molecule only much SMALLER than the
genomic DNA
• REPLICATE AUTONOMOUSLY from the genomic
chromosome. Often there are MANY PLASMID
COPIES present in one cell. Further, a cell may
contain SEVERAL DIFFERENT PLASMIDS or it may
contain NO PLASMIDS at all. Plasmids generally carry
genes that are NOT ESSENTIAL for a cell's survival
• May carry genes for ANTIBIOTIC RESISTANCE

30. Transposons
• Transposons are pieces of DNA move from one
site to another ---- within or between the
DNAs of bacteria plasmid or bacteriophage.
• Nick name as Jumping genes
• Genes for one or more (usually more) proteins
imparting resistance to antibiotics. When such
a transposon is incorporated in plasmid, it can
leave the host cell and move to another. This
is the way that the alarming phenomenon of
multidrug antibiotic resistance spreads so
rapidly.

31. Appendages
Flagella: Flagellin
Function: Motility/chemotaxis

32. 32
Flagella
• Bacteria that are
motile have
appendages called
flagella
• Attached by Basal
Body
• A bacteria can have
one or many
flagella

33. 33
Flagella
• Made of Flagellin
• Used for Classification
• Monotrichous: 1
flagella
• Lophotrichous: tuft at
one end
• Amphitrichous: tuft at
both ends
• Peritrichous: all around
bacteria

34. 34
Pili
• Short protein appendages PILIN
• Smaller than flagella
• Adhere bacteria to surfaces
• Used in conjugation for Exchange of
genetic information
• Aid Flotation by increasing buoyancy

35. 35
Pili in Conjugation

36. 36
Bacterial Shapes

37. 37
Shapes Are Used to Classify
• Bacillus: Rod shaped
• Coccus: Spherical (round)
• Vibrio: Comma shaped with flagella
• Spirillum: Spiral shape
• Spirochete: wormlike spiral shape

38. 38
Grouping of Bacteria
• Diplo- Groups of two
• Strepto- chains
• Staphylo- Grapelike clusters

40. 40

41. 41
Bacillus and E. coli

42. Spirochetes

43. ACCORDING TO STAINING
GRAM STAINING

45. Crystal
violet
Gram's
iodine
Decolorise with
acetone
Counterstain with
e.g. methyl red
Gram-positives
appear purple
Gram-negatives
appear pink
The Gram Stain

46. Gram-positive rods
Gram-negative rods
Gram-positive cocci
Gram-negative cocci

50. FORMATION OF BACTERIAL SPORE

52. • Found in Gram positive bacteria
• Tough, heat resistant
• Peptidoglycan > Picolinic acid

54. Normal Flora
• Definition
Normal flora is the
mixture of
microorganisms
(bacteria and fungi) that
are regularly found at
any anatomical site of
human body.

56. Symbiotic Relationship
• 1. Mutualistic
– Both organisms benefit – “mutually benefical”
• 2. Commensalistic
– One organism benefits, the other is neither helped
nor harmed
• 3. Opportunistic
– Under normal conditions, microbe does not cause
disease, but if conditions become conducive , it
can cause disease

57. Mutualistic
• Escherichia coli
– Synthesizes Vitamin K & B complex Vitamins
– In return, we provide a warm, moist nutrient rich
environment for E. coli

58. Commensalistic
• We have no Commensalistic relationships with
Bacteria
• If Bacteria are in or on our body, they are either
helping us (Microbial Antagonism) or harming
us.

59. Opportunistic
• Escherichia coli - normally in our digestive
tract where it causes no problems, but if it
gets into the urinary tract it can become
pathogenic.
• Staphylococcus aureus – commonly found in
the upper respiratory tract, but if it gets into a
wound or a burn it can become pathogenic

60. The Three Types of Symbiotic
Relationships
Table 14.1

61. Normal Microbial Flora
• 1. Resident Flora
– Microbes that are always present
• 2. Transient Flora
– Microbes that live in or on your body for a period
of time (hours, days, weeks, months) then move on
or die off

62. Transient Microbiota
• Remain in the body for only hours to
months before disappearing
• Found in the same regions as resident
microbiota
• Cannot persist in the body…because…
– Competition from other microorganisms
– Elimination by the body’s defenses cells
– Chemical or physical changes in the body

63. Sterile tissues
In a healthy human, the
internal tissues such as:
• blood
• brain
• muscle
• cerbrospinal fluid (csf.)
are normally free of
microorganisms.
Normal Flora

64. Normal Flora
• Skin
• Eyes (i.e.Cunjunctiva)
• Nose (i.e. Respiratory tract)
• Mouth (i.e Human Oral
Cavity)
• Ears
• Urogenetal tract
• Elementry tract

65. Normal Flora
• Resident flora
– Acquired rapidly during
& after birth

66. Normal Flora
• Resident flora
– Reflects age of person
– Changes continuously
through out life
– Reflects nutrition of
person
– Reflects genetics of
person
– Reflects environment of
person
– Reflects sex of person

67. 1. They constitute a
protective host
defense mechanism
by occupying
ecological niches.
Importance of The Normal
Flora (Advantages)

68. Importance of The Normal Flora
(Advantages)
2. They produce vitamin B
and vitamin K in
intestine.

69. Importance of The Normal Flora
(Advantages)
3. The oral flora
contribute to
immunity by inducing
low levels of
circulating and
secretory antibodies
that may cross react
with pathogens.

70. Importance of The Normal Flora
(Advantages)
4. The oral bacteria flora
exert microbial
antagonism against
nonindigenous species by
production of inhibitory
fatty acids, peroxides,
bacteriocins, etc.

71. Importance of The Normal Flora
(Advantages)
5. The normal flora may
antagonize other bacteria
through the production
of substances which
inhibit or kill
nonindigenous species.

72. Importance of The Normal Flora
(Disadvantages)
1. They can cause disease in
the following:
a) When individuals become
immunocompromised.
b) When they change their
usual anatomic location.

73. Contamination vs. Infection
• Contamination – the mere presence of microbes in
or on the body
• Infection – results when the organism has evaded
the body’s external defenses, multiplied, and
become established in the body

74. Portals of Entry
• Sites through which pathogens enter the body
• Four major types
– Skin
– Mucous membranes
– Placenta
– Parenteral route

75. Skin
• Outer layer of packed, dead, skin cells
usually acts as a barrier to pathogens
• Some pathogens can enter through
openings or cuts
• Others enter by burrowing into or
digesting the outer layers of skin…flesh-
eating bacteria

76. Mucous Membranes
• Line the body cavities that are open to
the environment
• Provides a moist, warm environment that
is hospitable to pathogens
• Respiratory tract is the most commonly
used site of entry – entry is through the
nose, mouth or eyes
• Pathogens able to survive the acidic pH
of the stomach may use the
gastrointestinal tract as a route of entry

77. Some Pathogens that Cross the
Placenta
Table 14.3

78. Parenteral Route
• Pathogens deposited directly into tissues
beneath the skin or mucous membranes

79. Infection vs. Disease
• Infection is the invasion of the host by a pathogen
• Disease results only if the invading pathogen alters
the normal functions of the body
• Disease is also referred to as morbidity

80. Manifestations of Disease
• Symptoms – subjective characteristics of disease
felt only by the patient
• Signs – objective manifestations of disease that can
be observed or measured by others
• Syndrome – group of symptoms and signs that
characterize a disease or abnormal condition
• Asymptomatic, or subclinical, infections lack
symptoms but may still have signs of infection

81. Etiology
• Study of the cause of disease
• Germ theory of disease – disease caused by
infections of pathogenic microorganisms
• Robert Koch developed a set of postulates one
must satisfy to prove a particular pathogen causes
a particular disease