1
Q
Six cell shapes (Morphology)
A
- Coccus (Spherical)
- Bacillus (Rod-Saped)
- Coccbacillus (Short oval rods)
- Vibrio (Curved/comma-shaped)
- Sprillium (Rigid spirals)
- Spirochete (Flexible corkscrew)
2
Q
Seven cell arrangements
A
- Coccus
- Diplococcus
- Tetra
- Strepto (chain of cocci)
- Staphylococcus (cluster of cocci)
- Bacillus (single rod)
- Streptobacillus (chain of rods)
3
Q
Monotrichous
A
Single flagellum
4
Q
Lophotrichous
A
Tuft at one pole
5
Q
Amphitrichous
A
One or more at both ends
6
Q
Peritichouso
A
All over surface
7
Q
Atrichous
A
None
8
Q
Colony Morphology
A
- Size
- Shape (circular, irregular, filamentous)
- Margin (entire, undulate, lobate)
- Elevation (flat, raised, convex, umbonate)
- Texture (Smooth/Rough)
- Pigmentation (colour)
9
Q
Cell
A
One microscopic organism
10
Q
Colony
A
A visible cluster of genetically identical cells that grew from one cell
11
Q
Structure of peptidoglycan
A
Repeating chains of NAG and NAM
Linked by tetrapeptide cross bridges
12
Q
Gram stain procedure
A
- Crystal violet (primary stain) all cells become purple
- Iodine - mordant (fixes dye)
- Alcohol - decolourizer (gram + retain purple; gram - lose colour)
- Safranin - counterstain
13
Q
Differentiating step
A
Alcohol because it removes dye only from gram - cells
14
Q
Obligate aerobe
A
Needs Oxygen
Growth in tube: top only
15
Q
Facultative anaerobe
A
Grows with or without oxygen
Growth on tube: mostly top, some throughout
16
Q
Obligate anaerobe
A
Killed by oxygen
Growth in tube: bottom only
17
Q
Aerotolerant anaerobe
A
Doesnt use oxygen but tolerates it
Growth in tube: evenly throughout
18
Q
Microaerophile
A
Low oxygen only
Growth in tube: grows just below surface
19
Q
Fermentation test
A
Detects acid and/or gas from carbohydrate fermentation using pH indicator
Colour change = acid production
Bubble = gas
20
Q
Gelatinase test
A
Tests for enzymes that liquifies gelatin
Positive = medium remain liquid after chilling
21
Q
Urease test
A
Detects urease that breaks urea
pH indicator turns pink = positive
22
Q
Amino acid/Deamination Test
A
Detects amino acid break down, positive result = phenol red
23
Q
Principle of serology test
A
Based on antigen-antibody reactions specific to bacterial surface antigens
24
Q
Slide agglutination test
A
Mix bacteria with on slide
Clumping = positive
25
Direct ELISA
Antibody on plate binds antigen --> enzyme substrate --> colour change
Detects Antigen
26
Indirect Elisa
Detects Antibody
Antigen on plate -> patient antibody -> enzyme linked --> colour
27
Main categories of growth requirements
1. Physical requirments: temperature, pH, osmotic pressure
2. Chemical requirements: water, nutrients, CHONPs, organic growthg factors1
28
Psychrophile
-10°C to 20°C
Arctic/deep ocean
29
Psychrotroph
0–30°C
Cause food spoilage in fridge
30
Mesophile
25–40°C
Most pathogens; human body temp ~37°C.
31
Thermophile
40–80°C
Hot springs, compost piles.
32
Main problem with thermophiles
Heat resistant, can survive pasteurization
33
Acidophile
<5.5pH
34
Neutrophile
5.5-8.0
35
Alkaphile
>8.0
36
Acidophilic Organisms and Locations
Lactobacillus acidophilus – vagina; lowers pH, prevents infection.
Helicobacter pylori – stomach; tolerates acid (not protective).
37
Osmosis
movement of water across membrane.
38
Isotonic
equal solutes → no net water movement.
39
Hypotonic
fewer solutes outside → water enters cell.
40
Hypertonic
more solutes outside → water leaves cell.
41
Crenation
Cell shrinks (in animal cells)
42
Plasmolysis
Bacterial cell membrane pulls away from cell wall
43
Toxic By Products of oxygen Metabolism
1. Superoxide anion
2. Hydrogen peroxide
44
Detoxifying enzymes
1. Superoxide dimutase
2. Catalase (breaks hydrogen peroxide)
3. Peroxidase
45
Why can Obligate aerobe use O2?
Has SOD and Catalase
46
Facultative anaerobe can use oxygen because
It has SOD and Catalase
47
Aerotolerant anaerobe tolerates oxygen because
It has SOD only
48
Olbigate anaerobes is killed by O2 because
Lacks detox enzymes
49
Biofilm
In nature, bacteria live on surfaces in complex, slime-encased communities not as single cells (planktonic)
50
Formation of Biofilms
1. Attach: Microbes stick to a surface with nutrients.
2. Protect: They make a sticky layer (EPS).
3. Grow: The microbes multiply.
4. Build: The sticky layer traps more microbes → forms a slimy community with water channels for nutrient flow.
5. Spread: Some microbes break off and move to new spots.
51
Advantages of Biofilms
Nutrient/waste exchange
* DNA exchange (remember HGT!)
* Protection (in numbers and also the whole community
is encased for further protection)
52
Problems with biofilms
Resists antibiotics and cleaning agents
Difficult to remove
53
Biofilm example
Dental plaque, contact lens
54
Indirect methods
Turbidity
55
Direct methods
Direct microscope count
Plate count
56
Liquid media
Use to grow up large amounts of bacteria
57
Solid media
Used to isolate colonies in mixed samples
58
Agar is used as a solidifying agent because
* A complex polysaccharide
* Not metabolized by microbes
* Liquid at 100°C and solid at 40
59
Chemically defined media type
Exact ingredients known; for specific microbes (autotrophs); slow to make. Example: EZ medium
60
What is complex media?
Mix of plant/meat/yeast extracts; amounts unknown; easy and common; for chemoheterotrophs.
Examples: Nutrient broth, TSB
61
Selective media
Inhibits unwanted microbes; lets desired ones grow.
62
Differential media
Uses a chemical to visually distinguish between
one species versus another species
63
Mannitol Salt Agar (MSA)
Selective: High salt → only Staphylococcus (halotolerant) grows
Differential: Mannitol fermentation → acid → color change (helps tell S. aureus from S. epidermidis)
64
Blood agar (Differential medium)
Not selective
Shows hemolysis ability
β (beta): complete → clear zone
α (alpha): partial → green zone
γ (gamma): none → no change
65
Other lab requirements for microbial growth
Temp: incubator or fridge
pH/osmotic pressure: use buffers & proper nutrients
Oxygen:
Aerobes – easy to grow
Anaerobes – need reducing media, anaerobe jars, or chambers
66
Preserving bacterial cultures
Short-term: Refrigeration (2–4 weeks)
Long-term:
Deep-freezing: –50°C to –95°C (6–12 months)
Lyophilization: freeze-dry into powder (lasts years)
67
Growing bacteria vs. viruses
Bacteria - grow on media (agar/broth)
Viruses - need living host cells
68
Growing Bacteriophages
Start with bacterial lawn
Add phage → infects & lyses susceptible bacteria
Clear spots = lysis zones
Phages are specific to certain species/strains
69
Where viruses are grown
Bacteriophages: bacteria cultures
Animal viruses: living animals, cell cultures, embryonated eggs
70
When is antibiotics most effecitve
Log phase
71
What phase is the production of endospores
Stationary phase
72
Lag phase
Enzymes made
73
Log
Rapid division: more susceptible to antibiotics
74
Stationary
Endospores form
75
Death phase
Nutrients gone, waste toxic
76
Fomite
Non-living objects that can carry microbes
77
Sterilization
Destruction/removal of all living microorganisms, including endospores.
78
Sterile
Free of all life forms and viruses including endospores
79
Commericially sterile
Kills C. botulinum endospores in canned food, may have other harmless microbes
80
Disinfection
Destruction of vegetative pathogens on inanimate surfaces.
81
Disinfectant
Chemical used on non-living surfaces.
82
Bactericide
Bactericide
Kills bacteria (not necessarily spores).
83
Bacteriostatic
Inhibits bacterial growth (reversible).
84
Sanitization
Reduces microbial counts to safe public health levels.
85
Antiseptic
Used on living tissue (e.g., iodine on skin).
86
Aseptic
Free from contamination; sterile technique.
87
Degerming
Mechanical removal of microbes (e.g., hand washing).
88
D-VALUE
Decimal reduction time: time required to kill 90% of a population at a given temperature.
89
Factors that affect AMA (antimicrobial agent) effectiveness
of microbes – more = takes longer to kill
Time of exposure – longer = more killed
Environment – temp & organic matter can block action
Microbe type – Gram+ vs Gram–, enveloped vs non-enveloped viruses
90
Why are biocides more effective against Gram-positive than Gram-negative bacteria?
Gram+: No outer membrane → easier for chemicals to enter
Gram–: Has outer membrane (LPS layer) → blocks many biocides
91
How do antimicrobial agents kill microbes?
Damage cell wall/membrane → leaks → cell lysis
Disrupt proteins or DNA/RNA → stops metabolism & reproduction
92
Physical methods of microbial control
1. Heat
2. Cold
3. Dessication
4. Pressure
5. Filtration
6. Radiation
93
Heat – Moist heat
Boiling kills most microbes (not endospores)
Autoclave: steam + pressure (121°C, 15 psi, 15+ min) → sterilization
Used for agar, media, syringes
94
Heat – Dry heat
Direct flaming/incineration: burns to ash
Hot-air sterilization: >170°C for 2h (glassware)
95
Heat – Pasteurization
Mild heat kills pathogens but keeps taste
Milk: 72°C 15s (HTST) or 140°C 1s (UHT)
96
Cold
Refrigeration (0–7°C): slows growth (bacteriostatic)
Freezing (<–2°C): ice crystals rupture cells; kills parasites (e.g., Trichinella)
97
Dessication
Removes water (freeze-drying) → stops growth (bacteriostatic)
Not effective for viruses
Some bacteria survive on dried fluids (e.g., N. gonorrhoeae)
98
Pressure (Osmotic)
High salt/sugar → plasmolysis (water leaves cell)
Preserves food; fungi more resistant
99
Filtration
Traps microbes using small pores
HEPA filters: air
Membrane filters: liquids (e.g., vitamins, antibiotics)
100
Radiation – Ionizing
Gamma/X-rays form toxic radicals → destroy DNA
Sterilizes gloves, tubing, tissue, spices
101
Radiation – Non-ionizing (UV)
Damages DNA (thymine dimers)
Surface-only; used for water & surface disinfection
102
3 main chemical agent types
1. Antiseptics – skin/mucous membranes
2. Disinfectants – on surfaces
3. Antibiotics – treat infections in the body
103
8 Major categories of chemical agents
Phenols
Heavy metal
Halogens
Alcohols
Surfactants
Alkylating agents
Gaseous alkylating agents
Oxidizing agents
💡Mnemonic: Please Make Hot And Spicy Alligator Gumbo – Ouch!
104
Phenols & Phenolics
Disrupt membranes & denature proteins
Effective vs Gram+ & yeast
Disinfectant: Lysol
Antiseptic: Triclosan (soap, toothpaste)
105
Heavy metals
Denature proteins
Silver: disinfectant, antiseptic (bandages, eye drops)
Copper: kills algae/fungi
Zinc: in mouthwash, dandruff shampoo
106
Halogens (I, Cl, F)
Oxidize proteins & membranes
Iodine/betadine: antiseptic
Chlorine/bleach: disinfectant for water & surfaces
107
Alcohols (ethanol, isopropanol)
Denature proteins & damage membranes
Work best at 70–90%
Used for skin & surface cleaning
Fast-acting, evaporates quickly
108
Surfactants – soaps & detergents
Lower surface tension → remove microbes (degerming)
Soaps: mechanical removal
109
Alkylating agents
Damage DNA & proteins
Glutaraldehyde: disinfects hospital tools
Formaldehyde: preserves specimens, kills microbes
Toxic → not for skin use
110
Gaseous alkylating agents
Ethylene oxide, propylene oxide
Sterilize heat-sensitive items (plastics, mattresses)
Used in closed chambers; carcinogenic & explosive
111
Oxidizing agents
Oxidize proteins & membranes
Hydrogen peroxide: disinfects surfaces (not ideal for wounds)
112
Can chemicals destroy endospores?
Few chemicals can
Most are ineffective
Best to prevent endospore formation
Must use physical methods (e.g., autoclaving) to destroy them
113
What is the disc-diffusion (Kirby-Bauer) test?
Swab plate with bacteria → place AMA-soaked disc
Zone of inhibition = AMA effectiveness
Used for antibiotic susceptibility testing
⚠️ Limitations: depends on AMA solubility; can’t tell if cidal or static
114
Antibiotic
Substance made by microbes (or synthetic) that inhibits or kills other microbes.
115
Narrow-spectrum antibiotics
Target specific microbes (e.g., only Gram+)
Example: Penicillin G
Less harm to normal flora
116
Broad-spectrum antibiotics
Kill many types (Gram+ & Gram–)
Example: Tetracycline
Useful right away or for mixed infections
117
Bactericidal
Kills microbes
For life-threatening infections.
118
Bacteriostatic
Inhibits growth
Lets immune system finish job.
119
How do antibiotics kill or stop bacteria?
Inhibit cell wall synthesis
Damage plasma membrane
Block protein synthesis
Inhibit nucleic acid (DNA/RNA) synthesis
Block essential metabolite production
120
Inhibit cell wall synthesis
Weakens wall → cell lysis (bactericidal)
Human cells lack walls → safe
Example: Penicillin (β-lactam ring)
Blocks peptidoglycan crosslinks
Narrow spectrum → mostly Gram+ (Strep, Staph, Clostridium)
121
Interacts with lipoproteins in G- membranes
Alters permeability → leaks metabolites → cell death (bactericidal)
Not selective
Example: Polymyxin B
Broad spectrum, but mainly Gram–
Topical only (toxic if internal)
122
Stops tRNA from binding to ribosome
Targets 30S/50S ribosomal subunits → stops protein formation
Example: Tetracycline
Broad spectrum (Gram+, Gram–, others)
Bacteriostatic
123
Inhibit nucleic acid synthesis
Blocks DNA/RNA replication → stops reproduction
Example: Rifamycin (Rifampin)
Broad spectrum
Bactericidal
Used for tuberculosis
124
Competes with PABA, decreasing folic acid production
Stops folic acid production → halts growth
Example: Sulfonamides
Broad spectrum
Bacteriostatic
Mimic PABA → block enzyme for folic acid
125
What are superbugs?
Bacteria resistant to many antibiotics
126
How do bacteria resist antibiotics?
Block entry – modify porins (esp. Gram–) to stop drug entry
Inactivate drug – make enzymes like β-lactamase (breaks penicillin)
Alter target – change binding site (e.g., MRSA modifies enzyme for cell wall)
Efflux pumps – pump out antibiotics before they act
127
What is phage therapy?
Uses bacteriophages to kill bacteria (cell lysis)
Fewer side effects
128
Why are eukaryotic infections harder to treat?
Eukaryotes ≈ human cells → less selective toxicity
More side effects, fewer drug options
129
Antifungal drugs
Target ergosterol in fungal membranes (different from animal sterols)
Example: Miconazole → blocks ergosterol synthesis → weakens membrane
Treats Candida infections
130
Anti-protozoan drugs
Example: Atovaquone
Blocks electron transport chain in protozoa
Used with Proguanil (Malarone) to treat malaria
131
Anti-helminthic drugs
Example: Ivermectin
Interferes with helminth neurons
132
Antiviral drugs – 3 main actions
1. Inhibit DNA synthesis: Acyclovir → herpes
2. Block viral enzymes:
Protease inhibitors (Ritonavir) – stop virion maturation
Reverse transcriptase inhibitors (AZT) – stop DNA/RNA synthesis
Integrase inhibitors (Raltegravir) – stop viral DNA insertion
3. Release inhibitors: Tamiflu, Relenza → block neuraminidase → stop flu virus release
