MOD2 Bacterial Anatomy

what is a tetrad

cocci arrangement group of four

what are sarcinae

cocci arrangement cube of eight

what is a palisade

bacilli arrangement stacks

involution forms

dead, degenerating, or old/dying bacteria

what causes involution forms

• poor growth conditions

• lack of nutrients

• abx treatment

flagella

long filamentous appendages for movement

what is the outer part of a flagellum

hollow core surrounded by strands of protein called flagellin

how are flagella connected to bacteria

anchored to the cell wall and cytoplasmic membrane by a basal body

what flagellum arrg is this and what type of movement

monotrichous; rapid and directional movement

what flagellum arrg is this and what type of movement

amphitrichous; spin/flip end to end/tumbling

what flagellum arrg is this and what type of movement

lophotrichous'; rapid, directional movement

what flagellum arrg is this and what type of movement

peritrichous; slow, non-directional, spinning, circular

which type of bacteria are flagella found

some rods and spirals. NOT cocci

how does flagella work

spinning actions of filaments around each access

requires continuous generation of energy

how can we detect flagella

• flagella stains — tar and feather

• electron microscope

what movement might be observed with wet preps

• brownian motion

• drifting/streaming

• true motility

what are the advantages of motility

• move to areas with better nutrition/atmosphere

• colonize another area of host

• allows pathogenic bact to spread infection

brownian motion

caused by molecular bombardment by sale against bacteria

appears to vibrate or jiggle

drifting/streaming

everything moves in direction with the flow of the liquid

true motility

movement of bacteria against flow of liquid

slide motility

liquid culture under the microscope, see if the bacteria move

motility media

inoculate a semisolid medium and observe for growth spreading

what growth phase is best for org

log phase

what temperature should plates be incubated in

room temp

what is observed if bacteria is nonmotile using the test tube method

stab line, clear medium

what does a positive motility tube look like

medium is cloudy

what is umbrella motility

cloudy at the top of the tube, stab line and clear medium in the rest

seen w aerobic org — grows with oxygen

what are capsules

organized glycocalyx, firmly attached to cell wall

what is the viscous layer that surrounds cells

glycocalyx

what is glycocalyx +composition

viscous layer excreted by SOME cells

polymer — usually polysaccharide, sometimes polypeptide or combo of both

what are slime layers

unorganized glycocalyx, loosely attached to cell wall

functions of capsules

• protection

• interferes with phagocytosis

• allows bacteria to adhere to host — inc virulence

• maintains colonization — forms biofilms

what is a biofilm

community of mono/polymicrobial bac living tgh on surface

what do colonies of capsulated bacteria look like

mucoid and slimy

how are capsules identified on stained slides

clear halo surrounding bacterium

how many genes are in bacterial chsomes

1000-5000

what are plasmids

extrachromosomal elements

nonessential genetic material — can be gained or lost without affecting cell

size: 1-2kilobases to >1megabase

what are the functions of plasmids

• encode for Abx resistance

• decomp of organics

• production of toxins harmful to host

• allow bacteria to mate and exchange genetic info

what are fimbriae

non-flagellar, short, hair-like projections — many

on both GP and GN cells

facilitates in adhesion of org to host cell surface

what are pili

longer than fimbriae

only 1 or 2 on cell

aka “sex pili”

exchange of genetic info

ONLY GN

what type of soln is used for bacterial growth and suspensions in the lab

isotonic saline — 85% NaCl

what is in the cytoplasm

• 80% water

• ribosomes

• volutin/metachromatic granules —phos. storage

• polysaccharide granules —glycogen/starch/food storage

• lipids (few bact)

• sulfur granules (sulfur bact)

whats a bacterial colony

single bacterium that divides and all daughter bact stay together — forms visible cluster on plates

what is observed when hemolysis occurs on a plate

clearing around colonies

degree of clearing depends on extent of hemolysis

complete RBC lysis = beta-hemolysis

what does the cell wall do

rigid structure outside of plasma membrane

f’n:

• cell shape

• strength to withstand changes in environmental pressure

• protect against mechanical stress

• barrier of passage to larger molecules

cell wall composition

peptidoglycan aka murein layer

• NAG and NAM sugars = backbone

• NAG/NAM polymers cross link to form polypeptide sheets

• sheets cross link w each other to form multilayer

whats the difference between the cell walls of GPO and GNO

• GPO has thicker peptidoglycan layer (up to 10x)

• GNO have outer phospholipid/lipopolysaccharide layer

• GPO has teichoic acid

penicillin inhibits cell wall synthesis by binding enzymes in peptidoglycan production, why is it not usually used for GNO

outer lipid layer on GNO protects peptidoglycan layer

abx would be ineffective

GPO doesnt have lipid layer, more exposed peptidoglycan

why do we use gram stains

• rapid assessment of level of infection prior to having culture

• allows physician to decide what abx to use

what happens if a direct smear is too thick

• cellular detail unclear

• may interfere with staining

• bacteria may be hard to find

what happens if a direct smear is too thin

• cellular and bacterial populations not accurately represented

• difficult to locate cells

• inaccurate staining results

what is the first step of gram staining

fixation

what is fixation —gram staining

process of adhering specimen to glass slide

• kills bacteria — NOT spores

• fixes morphology of the cells

• makes cells more permeable to stain

• prevents autolysis

what happens if the specimen is not fixed to the slide

• specimen may wash off slide

• cells may float in oil under scope

what happens if the specimen is overfixed

poor staining results

• odd shapes

• pale staining

what four reagents are used in gram staining

1. primary stain of crystal violet CV

2. iodine I

3. decolourizer

4. counterstain of safranin

crystal violet

• first reagent used in gram staining

• cationic/basic stain

• positively charged stain molecule

• bonds with negatively charged proteins in cell

• all cells/bact stain DARK BLUE

iodine

• mordanting effect — enhances staining effect

• forms crystal violet-iodine complex

• traps CV dye into cells/bact

mordant

molecule that enhances the staining effect

decolourization

• most important step

• uses acetone-alcohol

• makes peptidoglycan layer more porous

• allows CV-I to escape

• GPO: thick peptidoglycan layer retains CV-I — still dark blue

• GNO: thin layer, CV-I leaves cell — colourless

what happens if a slide is over decolourized

• affects cell wall integrity

• GPO appear pink instead of blue

• excess CV-I taken out

• false GN

what happens if a slide is under decolourized

• GNO appear blue

• not enough CV-I taken out

• false GP

safranin

• last step

• counterstain

• colourless GNO take up counterstain

• appear pink/red

what objective lens should gram slides be examined under

100x oil immersion lens

what colour should the background of the slide be

pink bcs last stain was pink

factors affecting gram stain

• lysozyme in human fluids

• rough handling of bact during processing, freezing, drying, heat, ect

• cells in death phase/ old

• patient alr on abx

• *expired reagents*

what bacteria type are spores found in

only gram positive bacilli

when are bacterial spores formed

when nutrients are low/depleted or environmental conditions are poor

• survival mechanism

when is the best time to see spores

death phase of bacterial growth

what do spores look like under the scope

• resistant to staining

• hollow cavity in cell

  • endospore — middle of cell

  • terminal spore — end of cell

qualities of spores

• heat resistant — autoclave to destroy (121C)

• not killed by moderate heat or disinfectants

• can survive in environment for years

• survival factor, not virulence factor