Module #10

Give two reasons why bacterial cells may grow only at the bottom of a broth tube, growth known as sediment or pellet.

Organism is anaerobicl; nutrients or conditions more favorable at the bottom of the tube

What does th eterm Hydrophilicity mean 

The tendency of a molecule or surface to repel water; non-polar molecules are hydrophobic.

How are cell morphology and cultural morphology differentiated from each other?

Cell morphology describes microscopic shape, size, and arrangement of individual cells; cultural morphology describes macroscopic appearance of colonies on media

Would you expect the same organism, grown for the same amount of time on the same agar plate medium to produce colonies of approximately the same size?

Well-isolated colonies are about the same size colonies close together may be smaller due to nutrient competition

When many colonies grow closely together, what gets ‘used up’ and what ‘builds up’ in the microenvironment around the bacteria?

Nutrients get used up; metabolic waste products build up

Define morphology.

The study or description of the form and structure of an organism

Distinguish between cultural morphology and cellular morphology.

Cultural morphology

cellular morphology

microscopic cell characteristics

What is a pellicle and what type of microorganism would grow as a pellicle?

A film of growth on the surface of liquid media often formed by aerobic bacteria or fungi

What would spreading growth on an agar slant signify about the organism?

Indicates the organism is motile or capable of spreading over surfaces

Give two examples of pigmented organisms (Genus & species).

Serratia marcescens (red), Micrococcus luteus (yellow)

On a slant, Bacillus subtilis often exhibits what type of growth?

Spreading, filamentous growth

Pinpoint (punctiform) colonies often are indicative of what type of bacteria?

Very small or slow-growing bacterial species

If you have a pure culture growing on an agar plate, which of the following would you expect to be true?

Well-isolated colonies should be larger than colonies growing very close together because they have more nutrients and less metabolic waste buildup

The two pathogenic bacteria that cause the most disease in humans

Streptococcus pyogenes and Staphylococcus aureus

Pseudomonas aeruginosa

Opportunistic bacterium that often causes infections in healthcare settings

Streptococcus pyogenes is better known as

Group A strep

Diseases caused by Streptococcus pyogenes

Streptococcal pharyngitis, acute rheumatic fever, rheumatic heart disease, boils and other cutaneous/soft tissue infections, acute glomerulonephritis, scarlet fever, necrotizing fasciitis, toxic shock syndrome and other systemic diseases

Staphylococcus aureus is better known as

Staph

Diseases caused by Staphylococcus aureus

Foodborne intoxication, cutaneous infections (impetigo, boils, wound infections), systemic toxin-mediated diseases (toxic shock syndrome, scalded skin syndrome), bacteremia and metastatic infections

Characteristics of Pseudomonas aeruginosa

Opportunistic pathogen, grows in moist environments, distinctive grape-like odor, diffuse blue-green pigmentation

Diseases caused by Pseudomonas aeruginosa

Infection of burn victims, infection in cystic fibrosis patients, blue-green pus or abscesses in wound

Obligate Aerobe

Grows only at the surface

• Grows on the surface because it needs air

Microaerophile

Grows just below the surface

• Little air not a lot

Facultative Anaerobe

Grows throughout the medium, but greatest growth at the surface

• grows a little more with air

Aerotolerant Anaerobe

Grows with or without oxygen, dispersed equally throughout the medium

• Doesnt care if there is air

Obligate Anaerobe

Grows only at the bottom of the medium

• it has no air so it goes to the bottom and die

Distinguishing Growth Characteristics

Microorganisms can be distinguished by microscopy, staining characteristics, cellular morphology, and biochemical tests

Cultural characteristics

Distinctive growth patterns, pigments, or odors useful for preliminary identification of pathogens

Growth characteristics in broth

Observations can reveal oxygen requirements, hydrophobicity, and motility

Turbid growth

Evenly dispersed, homogeneous growth throughout the broth

Sediment/pellets

Cells grow or sink to the bottom of the tube

Pellicle

Growth forms at the broth-air interface at the top of the tub

What are some ways bacterial colonies on agar plates can differ?

Color, size, texture, shape, elevation, and cellular morphology

How can molds and yeasts be distinguished from bacteria on agar plates?

Based on cellular morphology

may contaminate cultures on bacteriological media

Why is aseptic technique important when handling agar plates?

To prevent contamination, always keep plate and tube tops on except when inoculating

What should you do if you suspect mold growth on a plate?

Do not remove the top

spores can travel long distances and contaminate the lab

How can pigment production help identify bacteria?

Pigments may indicate potential pathogens

most bacterial colonies are non-pigmented

What is the difference between diffusible and non-diffusible pigments?

Diffusible pigments spread into surrounding agar

non-diffusible pigments remain within the colony

Give an example of a bacterium that produces a distinctive pigment.

Pseudomonas aeruginosa produces bluish-green, diffusible pigment

How can odor production help identify microorganisms?

Microorganisms produce distinctive metabolic odors that can be characteristic

What microorganism produces a grape-like odor?

Pseudomonas aeruginosa

What causes the rotten egg smell (H2S) in bacterial growth?

Produced when sulfate serves as the final electron acceptor during anaerobic respiration

Which microorganism produces a sour odor like sour milk or a kitchen dish rag?

Staphylococcus