Basics of bacteriology Flashcards
Capsule (found in some species)?
Assist with adhesion
Prevents phagocytosis
Reservoir for polysaccharides
Helps the cell not to dry out
Cell-wall?
Provides structural support
Protects against physical and chemical effects
Cell-membrane (plasma-membrane)?
Separates inside from outside (selective barrier)
Regulates transport in and out of the cell
DNA?
Present in a region called nucleoid
Usually a single circular chromosome
Plasmids?
Extrachromosomal DNA (usually contains 5-100 genes)
Often encodes advantageous properties (antibiotic-resistance)
Are moved by pili via conjugation
Pili (f-pili and p-pili)?
Some pili (fertility-pili) are used to transfer plasmids
Others are used by the bacterium to attach (p-pili)
Shorter than fimbriae
Fimbriae?
Attachment
Flagella?
Movement
Cell-wall?
Provides structural support
Protects against physical and chemical effects
Gram-staining?
Primary system of classification
The bacteria are exposed to different dyes
Gram-positive: blue-purple
Gram-negative: pink-red
Gram positive?
Thick cell-wall
• 35-40 layers of peptidoglycan
Quite large quantities of teichoic acid (TA)
• Unique sort of polysaccahride
• Maintains structure of the cell-wall
o Attract cations such as Mg2+ och Na+
Lipoteichoic acid (LTA)
• Teichoic acid with a ”lipid-tail” that is
anchored within the cell-membrane
Gram negative?
Thin cell-wall • 1-2 layers of peptidoglycan Has two membranes • Inner cytoplasmic membrane • Bacterial outer-membrane Structures ”unique” for Gram-negatives • Porins • Lipopolysaccharides (LPS)
Porins?
Crosses the bacterial outer-membrane Acts as a pore • Molecules can diffuse through • Concentration-gradient is required Other protein-systems then transport the molecules further
The genes encoding the porin-proteins can mutate
• The permeability changes
LPS?
Present in most Gram-negative bacteria
Has a very complex lipid-structure
• Uncommon sugar and fetty-acids
Function
• Increases the negative charge of the cell-membrane
• Stabilizing the membrane-structure
Lipid A (endotoxin)
• Has fatty-acids associated that ”anchor” LPS to the cell-membrane
• Strongly immunogenic
Structure cell-wall?
Mainly consists of peptidoglycan
• Polysaccharide that consists of two sugar-derivatives
o N-acetylmuramic acid (NAM)
o N-acetylglucosamine (NAG)
NAMs are ”linked” by short polypeptides
Lysozyme?
An enzyme found in e.g. tears, saliva och intestines
• Prevents bacterial infections
• Break glycosidic bonds between
NAG and NAM (hydrolysis)
Gram-negatives often less sensitive than -positives
• Protected by the bacterial outer-membrane
Coccus?
(Lat. cocci ≈ ”berry”)
• E.g. Staphylococcus spp. and Streptococcus spp.
Bacillus?
(Lat. bacilli ≈ small rod)
• E.g. Bacillus spp.
Vibrion?
(spiral, slightly bent)
• E.g. Vibrio cholerae
Spirillum?
(spiral, twisted - one or several turns)
• E.g. Campylobacter jejuni
Spirochaete?
(spiral, very thin, long and twisted)
• E.g. Borrelia spp.
And pleomorphic (change shape)
Diplococcus?
(two and two)
• E.g. Streptococcus pneumoniae
Tetrad?
(four and four)
• E.g. Micrococcus luteus
Sarcinae?
(eight and eight)
• E.g. Sarcina spp
Streptococcus?
(chains)
• E.g. Streptococcus pyogenes
Staphylococcus?
(bunches)
• E.g. Staphylococcus aureus
Single bacillus?
(one and one)
• E.g. Bacillus cereus
Diplobacilli?
(two and two)
• E.g. Moraxella bovis
Streptobacilli?
(chains)
• E.g. Streptobacillus moniliformis
Palisades?
(picked-fence)
• E.g. Corynebacterium diphtheriae
Capsule?
The capsule is glycoproteins firmly attached to cell-wall
• Assist with adhesion to surfaces
• Prevents phagocytosis from different immune-cells
Examples of encapsulated bacteria
• Streptococcus pneumoniae
• Haemophilus influenzae typ B
Slime-layer?
Slime is glycoproteins loosely attached to cell-wall
• Assist with adhesion to surfaces
• The slime-layer prevents the bacteria from drying out
Examples of slime-producing bacteria
• Streptococcus spp.
o The slime-layer of S. mutans helps the bacteria to adhere the tooth-enamel
• Staphylococcus spp.
o The slime-layer of S. epidermidis helps the bacteria to survive on the
salty hypertonic skin
Biofilm?
A natural way for different bacteria to grow
Consists of
• Bacterial-cells
• Polysaccharides
• Proteins and nucleic acid
Formation • Bacteria adhere to a surface (colonization) • Growth • Production of exopolymers such as EPS • Formation of a biofilm • Other organisms attend • Spread
Surfaces?
Important microbiological habitats • Physical forces • Nutrient-access • Protection • Toxic molecules
Endospores?
Some Gram-positive bacilli can form endospores
Very robust structure • Radiation • Dehydration • Temperature • Starvation • Chemical disinfectants
Spore-formation?
- The chromosome is replicated
• Aligns alongside the cell - The cytoplasmic membrane invaginates
• A ”pre-spore” is formed - The cytoplasmic membrane grows and engulfs the ”pre-spore”
• The DNA of the vegetative cell is dissolved - A cortex of calcium and dipicolinic acid is formed between the membranes
• Most of the water is removed from the cell - A spore-coat is formed around the endospore
• Consists for instance of keratin that makes the endospore extremely rough - Finally an outer spore-coat is formed
• Increases its resistance to heat and different chemicals - The endospore is released
• The vegetative cells goes through lysis
