Microbiology II

Question 1

how are bacteria organized?

Answer 1

shape, arrangement, and staining

Question 2

what shape are coccus (cocci)?

Answer 2

spherical

Question 3

what shape are bacillus (bacilli)?

Answer 3

rod or cylinder

Question 4

what shape are spiral bacteria (spirilla)?

Answer 4

twist like a spiral (motile)

Question 5

what shape are pleomorphic bacteria?

Answer 5

range from cocci to rod
ex: cocobacilli

Question 6

single bacterial arrangement

Answer 6

single spirilla
most spirillum and bacilli are single arrangement

Question 7

pairs bacterial arrangement

Answer 7

diplococci

Question 8

short or long chain bacterial arrangements

Answer 8

ex: streptococcus

Question 9

clusters, branches, or group bacterial arrangements example

Answer 9

ex: staphylococcus

Question 10

palisade bacterial arrangement example

Answer 10

ex: corynebacterium

Question 11

endospores

Answer 11

non-reproductive structure that allows the bacteria to survive environmental stress
intracellular refractile bodies
can help ID the bacteria
might need a special stain to see them but can often see on a gram stain

Question 12

what are endospores resistant to?

Answer 12

heat, desiccation, chemicals, radiation

Question 13

which bacterium have central endospores?

Answer 13

Bacillus anthracis

Question 14

which bacterium have subterminal endospores?

Answer 14

Clostridium chauvoei, Clostridium tetani

Question 15

which bacterium have terminal endospores?

Answer 15

Clostridium botulinum, C. difficile
C. difficile causes supra-infections

Question 16

supra-infection

Answer 16

an infection on top of another infection

Question 17

how do stains help ID bacteria?

Answer 17

determines predominate organism in a mixed specimen, determines culture medium, determines appropriate anti-bacterial meds for sensitivity testing

Question 18

gram stain

Answer 18

differential stain: differentiates gram positive from gram negative bacteria
gram positive stains purple, gram negative stains pink

Question 19

gram positive bacteria in a gram stain

Answer 19

have thick complex cell wall which prevents leaching of the dye from the cytoplasm

Question 20

gram negative bacteria in a gram stain

Answer 20

have thinner cell walls that contain lipids which can be freed allowing the cytoplasm to be decolorized

Question 21

process of gram staining

Answer 21

1. crystal violet (cells stain purple)
2. iodine solution (cells remain purple)
3. decolorizer (gram positive remain purple, gram negative become colorless)
4. safranin (counterstain): gram negative become pink

Question 22

common errors in gram staining

Answer 22

too thick, excessive heat fixing, under and over decolorization

Question 23

under-decolorization

Answer 23

neutrophils that should stain pink are under-decolorized at decolorizer step and stained purple

Question 24

over-decolorization

Answer 24

gives a false impression of gram negative rods being present

Question 25

how can antibiotics change how organisms appear under the microscope?

Answer 25

can render organisms with a bizarre appearance
ex: can have gram variable or gram negative that normally stain positive because the cell wall is more permeable to the stain

Question 26

what can make gram stain challenging?

Answer 26

Nocardia and actinomyces are weak gram positive and are small, frail, branching rods
we can further identify with acid fast stain if suspected

Question 27

looking at a gram stain under the microscope

Answer 27

low power: can see signs of acute bacterial infection (segs) unless it’s a bacterial infection that destroys WBCs, see epithelial cells
oil: see bacteria
look at multiple areas of smear, make multiple smears

Question 28

how to save a slide that stained badly

Answer 28

use xylol to remove the immersion oil
if under-decolorized: decolorize further and follow steps 3 and 4 (counterstaining)
if over-decolorized: do all 4 steps again

Question 29

reporting gram stain results

Answer 29

use systematic, descriptive terminology
1. quantify entire smear
2. quantify individual bacteria
3. describe background (inflammatory: neutrophils, proteinaceous background: yeast)

Question 30

fecal smear

Answer 30

normal psittacine stool consists of 95% gram positive rods and cocci and up to 5% gram negative rods with occasional yeast

Question 31

KOH test for gram variable reaction

Answer 31

drop of potassium hydroxide is mixed with the sample
dissolves wall of gram-negative bacteria releasing DNA
gram negative: after 30secs-2 min of stirring a mucoid strand develops
gram positive: mixture will remain homogenous

Question 32

simple stains used for microbiology

Answer 32

crystal violet: yeast, methylene blue: yeast, lactophenol blue: confirm and ID fungi

Question 33

acid fast stain

Answer 33

penetrates resistant cells: these bacteria have a thick, waxy wall which makes them resistant and difficult to detect with gram stain
acid fast bacteria (bacteria that retain stain) stain red/pink
non-acid fast stain blue/green
used for Mycobacterium, Nocardia, and Crytosporidia

Question 34

biochemical testing

Answer 34

media or chemical reagents that assist in identifying bacteria at a species level
basic approach: follow a predetermined step by step method of rule outs until you narrow the possibilities down to 1 species
usually done through flowcharts: different flowcharts for different species

Question 35

catalase test

Answer 35

performed on gram positive cocci
catalase used is hydrogen peroxide which produces gas bubbles
catalase positive: staphylococcus
catalase negative: streptococcus, do CAMP test for S. agalactiae

Question 36

coagulase test

Answer 36

performed on catalase-positive, gram positive cocci
coagulase positive: pathogenic Staph. aureus
coagulase negative: non-pathogenic Staph. epidermidis

Question 37

CAMP test

Answer 37

performed on gram positive, catalase negative cocci
CAMP positive: Streptococcus agalactiae
CAMP negative: Streptococcus pyogenes
strep agalactiae is the only beta-hemolytic strep that hemolyzes RBCs on a CAMP test

Question 38

oxidase test

Answer 38

performed on gram negative bacilli
oxidase positive: non-enterics, pseudomonas
oxidase negative: enterics (ex: E. coli, Salmonella, Shigella, Proteus)
oxidase reagent is added to a piece of filter paper with bacteria
a positive test will turn purple within 60sec, if it takes longer it’s negative

Question 39

Indole test

Answer 39

identifies enterobacteria
2 methods: Kovac’s reagent broth and spot test
Kovac’s reagent broth: Indole positive will turn it red
spot test: Indole positive will turn it blue to blue-green

Question 40

TSI test

Answer 40

triple sugar iron: lactose, sucrose, glucose, plus iron
distinguishes between enteric organisms: E. coli, Salmonella, Shigella, Proteus, Pseudomonas
multiple results that differ based on whether sugars are fermenting and whether gas is produced or not

Question 41

bile esculin test

Answer 41

esculin: product from horse chestnut bark
selects organisms 1st on the basis of their ability to grow in a medium with 4% bile salts followed by selection based on their ability to hydrolyze esculin
identifies enterbacter organisms

Question 42

what are examples of bacterium that test positive and negative on a bile esculin test?

Answer 42

positive: enterococcus faecalis
negative: escherichia coli

Question 43

sulfur, indole, motility (SIM) test

Answer 43

tests for the reduction of sulfur to sulfide, the production of Indole, and motility
sulfur positive organism form black precipitate
Indole positive create a red reaction
motile organisms will make the entire culture turbid

Question 44

what are some other tests we can use to test bacteria cultures?

Answer 44

commercially prepared kits:
enterotubes (enterics): gram negative
API: most commonly used for enterics, gram negative

immunology tests: ELISA, PCR