Microbiology Lab Final Exam

How do you use a hematocrit reader?

Top of plasma should be at the top of the reader, and read RBC at the level between RBC and plasma layers

What is a hematocrit? What is Hct:Hgb ratio?

Hematocrit: percentage of RBCs in the blood

3 HCT:1 Hgb

What do neutrophils look like, their functions, normal values in blood? Another name for neutrophils?

Segmented nucleus, pinkish granules

Phagocytize infectious agents (bacteria, viruses, germs)

Most numerous, 40-60%

Also “segs”

What are banded neutrophils? Their appearance, function, and normal levels in the blood?

Banded neutrophils are immature neutrophils

Have a banded nucleus (hasn’t segmented yet) with purple granules

Same function as neutrophils

0-5%

What do lymphocytes look like, their functions, normal values in blood?

Agranular with a large purple nucleus that fills most space leaving a thin gray-blue cytoplasm ring

Includes B and T cells that fight invaders, cancerous, and infected cells

20-40%

What do monocytes look like, their functions, normal values in blood?

Bean- or C-shaped nucleus, agranular gray-blue cytoplasm

Function in infections to boost immune response and clear dead cells

3-8%

What do eosinophils look like, their functions, normal values in blood?

Bilobed with red-pink granules

Parasites, allergies, inflammatory response

1-3%

What do basophils look like, their functions, normal values in blood?

Bilobed nucleus, lost of dark-purple granules

Allergic reactions, asthma attacks

0-1%

Overview of WBCs

Never Let Monkeys Eat Bananas

40-60%, (Bands 0-5%), 20-40%, 3-8%, 1-3%, 0-1%

Pinkish segmented, (Purple banded), Large purple nucleus blue ring cytoplasm, bean- or c-shaped nucleus agranular gray-blue cytoplasm, Bilobed red pink granules, Bilobed dark purple granules

What is the normal range for Hct? Normal range for Hgb?

Hct: 36-54%

Hgb: 12-18%

What changes are seen in WBC amounts in bacterial, viral, parasitic, and allergic infections/responses?

Bacterial: Segs and Bands increase

Viral: Lymphocytes increase and Segs decrease

Parasitic: Eosinophils increase

Allergic: Eosinophils and Basophils increase

What is S. Viridians and its growth on BAP?

Normal flora in throat; alpha-hemolytic on BAP

Why does H. influenza grow on chocolate agar but not BAP?

It requires both growth factors X and V, and BAP doesn’t have factor X

What color do acid-fast bacteria stain, and which bacteria are acid-fast/positive?

Acid-fast bacteria stain red, and negative bacteria stain blue.

Mycobacterium are acid-fast.

What are normal flora of the intestinal tract?

G- rods: E. coli, Enterobacter, Proteus, Psuedomonas, Bacteroides

G+ cocci: E. faecalis

What are the common pathogens of the intestinal tract?

G- rods: E. coli, Salmonella, Shigella, Y. enterocolita

G- spiral rods: Campylobacter, Vibrio cholera

G+ rods: C. diff.

How do bacteria + or - for lactose fermentation grow on MAC?

+ → pink

- → colorless

How do bacteria + or - for H2S production grow on XLD and HE?

XLD: + yellow, - red

HE: + orange, - blue/green

What are the selective and differential characteristics of MAC, BE, XLD, and HE agars?

MAC: Selective because it grows only G- (bile salts and crystal violet) and differential because it tests for lactose fermentation through a pH indicator

BE: Selective because grows only G+ and differential because it tests for esculin hydrolysis, which turns black if positive

XLD: Selective because it grows only G- and differential because it tests for xylose and lactose fermentation, H2S production, and lysine decarboxylation

HE: Selective because it only grows G- and differential because it tests for lactose fermentation and H2S production

How is a TSI agar tube selective and differential?

Selective: G- only

Differential: tests for glucose and lactose fermentation and H2S production

How does TSI agar display differential results?

Tube slant: lactose and/or sucrose (+ yellow, - red)

Tube butt: glucose (+ yellow, - red)

Agar breaks or bubbles: yes is H2S production, no means no gas production

What does a urea test evaluate? + / -? Key organisms?

Evaluates urease enzyme presence, which converts urea to ammonia and water.

+ is fuschia, and - is yellow

Proteus is positive, and Salmonella is -

What does an indole test evaluate? + / -?

Tests for conversion of tryptophan to indole

+ is red, - is yellow

What does a methyl red test evaluate? + / -?

Tests for glucose fermentation pathway

+ red, mixed acid pathway

- yellow, other pathway

What does an oxidase test evaluate? + / -? Key organisms?

Evaluates presence of oxidase cytochrome enzyme that reduces O2 in the ETC

+ is blue, example: Psuedomonadaceae

- is colorless, example: Enterobacteriaceae

What are the common pathogens of the urinary tract?

Normal flora of the intestinal tract: Proteus, Enterobacter, E. faecalis, E. coli, S. saprophyticus

Urine dipstick: what would an abnormal specific gravity indicate? High pH? Protein? Glucose and ketones? Nitrites? Blood? Bilirubin? Urobilirubin?

Specific gravity: dehydration or kidney dysfunction

High pH: UTI from Proteus

Protein: infection

Glucose and ketones: diabetes

Nitrites: bacteria present

Blood: kidney dysfunction

Bilirubin: liver issue

Urobilirubin: liver issues

How would you count bacteria on agar using a 1/1000 calibrated loop and a qualitative streak method?

Count each colony as 1 CFU (colony forming unit)

If more than 100 per plate, indicates infection

What does Treponema pallidum look like in dark-field microscopy? What disease does it cause?

White spirochetes

Syphilis

How are early- and late-stage syphilis diagnosed?

Early: chancre at site of entry

Late: gummas and cardiovascular damage

RPR looks for Abs against the substances excreted by damaged cells, and confirmed with Ab test for Treponema

What disease does N. meningitis cause?

Most serious form of acute meningitis

What disease does S. pneumonia cause?

Most common form of acute meningitis

What disease does H. influenzae cause?

Acute meningitis

What would change in CSF regarding protein, glucose, and WBCs influenced by bacterial, viral, and fungal meningitis?

Bacterial: Protein increases, glucose decreases, WBCs increase (segs and bands)

Viral: Protein increases, glucose stays the same, WBCs increase slightly (lymphocytes)

Fungal: Protein increases, glucose stays the same or decreases, WBCs moderate increase (lymphocytes)

What does a catalase test evaluate? + / - results?

Evaluates presence of catalase, which breaks down H2O2 into water and CO2

+ bubbles

- no bubbles

What does a coagulase test test for? + / - results?

Tests for presence of coagulase, which breaks down fibrinogen into fibrin

+ agglutination

- no agglutination

What is Clostridium tetani and Clostridium perfringens? What disease do they cause?

Both are anaerobic bacteria and spore-formers

Tetani causes tetanus, and perfringens causes gas gangrene

How is MIC measured between tubes? (How does the amount change?)

Each concentration in the tube is doubled from the previous tube