26 terms

Microbiology Lab

Lab test
What are the four main reasons for learning about the normal flora
a: to gain understanding of the different bacteria at specific body sites which provide greater insite to possible infections that result from injury

b: to gain knowlege of the source and significance of bacteria isolated from clinical infections

c: to gain knowlege of the consequences of overgrowth of those bacteria normally absent from a specific body site

d: to be aware of bacterias play in stimulating the host's immune system
what organisms are most commonly isolated from the throat?
corynebacteria, Nisseria, staph epi, strep pneumonia, strep veridians, group a strep, staph aureus
what bacteria are commonly isolated from the rectum
e coli, citrobacter, enterobacter species, proteus species, psudomonas
why is a wet swab used on the skin?
allows more bacteria to be picked up
what four organisms are commonly isolated from the skin?
staph epe, corynebacteria, staph aureus, strep viridians, yeast, baccillus species, microcuccus species
what is the importance of catalase to certain bacteria
catalase protects against toxic oxidizing agents such as hydrogen peroxide, super oxidate which destroys bacteria cellular constituents
do most strict anaerobes produce catalase?
no most cannot tolerate O2 which is a biproduct of catalase reactions
explain the reaction how bacteria with 2O2 (superoxide end up with water and free oxygen
2O2+2H+ superoxide/disimutase 02+H2O2 , positive reaction is bubbles
what can cause a false positive catalase reaction? why?
red blood cells from blood agar can be picked up when picking up a colony RBC's have catalase + and would give false positive reaction
what bacteria produce coagulase and how does the enzxyme function to help the bacteria survive? what constitutes a positive reaction?
staph aureus, it produces a fibrin clot around istself and avoiding the attack of the host defences....formation of a clot in the bottom of the tube is a positive result
what is being looked for in the indole reaction? what constitutes at positive reaction?
production of indole from tryptophane, developement of a pink color constitutes a positive reaction
what is being looked for in the oxidase reaction? what constitutes a positive reaction?
indophenal oxidase oxidizes redox reagent resulting in a change of color from yellow to dark purple for a psitive reaction
what are the three different types of motility?
gliding, flagellar, corckscrew/bending
what is Brownian movement and how does it differ form true motility?
movement results from random motion of H2O molecules n=bombarding the bacteria and causing them to move whereas true motility is self propotion and involves one of the three modes of motility
why would it be hard to focus the microscope in the hang drop procedure?
a: bacteria are harder to see because of the reflection of light in unstained prep

b: emmersion oil cannot be used because it causes the cover slip to move

c: the thicker special slide and the cover slip with grease makes it difficult to focus with the change and the working distance
describe how to perform the tube motility procedure including materials needed
materials: stock culture, enoculating needle, motility medium

1: using needle pick up culture, stab down center of the media but not all the way down carefully remove the needle straight out w/o disturbing the stab line
2: incubate overnight at 37 degrees C observe for diffused growth of red color area growing away from the stab line for a positive test. A negative test has red color only in the stab line
what are the key ingredients in TSI media that produce various reactions? why is one sugar lower in % concentration than the other sugars?
dextrose, lactose, sucrose, sodium thiosulfate, ferric amonia citrate,.. to detect bacteria that fements only dextrose the concentration is 1/10 the concentration of the other sugars, small acid produced in the slant oxidizes quickly to revert back to alkaline PH or color low oxygen
describe the reactions and processes involved to produce the reactions in a TSI tube
tension in the butt of the tube keeps an acid ph or yellow color if hydrogen sulfide is produced from thiosulfate it reacts citrate to form balck precipitate
describe the reactions and processes involved to produce the reactions in a A/A gas tube
glucose and or sucrose and or lactose is fermented producing a yellow slant yellow butt, gas produced causes bubbles, splitting of agar causes bubbles and or displacement of agar in the tube
describe the reactions and processes involved to produce the reactions in a 2Alk/A H2S tube
glucose only is fermented producing a red slant and a yellow butt H2S production is indicated by a black color precipitate that spreads throughout the butt
describe the reactions and processes involved to produce the reactions in a Alk/Alk tube
none of the sugars are fermented no change of color or PH and or red slant and red butt
what is the purpose of the OF procedure
to determine the oxidative and fermintation metabolism of carbs or sugars by gram- bacilli
list and explain the three reactions that can occur in OF procedure
1: oxidation- air tube is yellow and and oil tube is green, bacteria can only use the sugar in the presence of O2 so the air tube turns yellow from the acid biproducts of oxidation and the oil tube without O2 cannot utilize the sugar so it remains green
2: fermentation, both tubes are yellow and the bacteria do not need O2 to utilize the sugar both turn yellow because of acid biproducts
3: non utilization air and oil tubes are green bacteria does not utilize the sugars so no PH change in any tube
desribe materials and how to perform OF procedure
materials: 2 OF tubes, needles, stock culture, mineral oil
using needles inoculate both tubes with the stock culture by stabbing each tube 4-5 times but not all the way to the bottom, overlay one tube with mineral oil. leave both caps loose incubate overnight
why should a control tube with no sugars be used
because some bacteria might use other substances than sugars producing biproducts and producing a yello color or false positive
what sugar does a control tube contain
no sugars