Microbiology Exam 1 (Study Guide 1)

Ch 1-13

What is a prokaryote?

a simple, single-celled organism that lacks a nucleus and membrane-bound organelles

What is peptidoglycan?

substance forms many bacterial walls and consists of glycosaminoglycan chains interlinked with short peptides

What structure does penicillin target?

the peptide cross links are targeted to disrupt the integrity of the bacterial cell wall

What is a bacterial chromosome?

single, large, circular, double-stranded DNA molecule that contains all the genetic information required by a cell

What is a plasmid?

Small, circular, double stranded DNA that is duplicated and passed to offspring. It may encode antibiotic resistance, tolerance to toxic metals, enzymes & toxins.

Where are bacterial chromosomes and plasmids located?

within the cytoplasm of the cell, the chromosome is more specifically within the nucleoid

What is transcription?

synthesis of mRNA from DNA

What is translation?

synthesis of proteins from mRNA

Why can transcription and translation occur at the same time?

The prokaryotic cell lacks a membrane bound nucleus, so all components needed for synthesis are located in the cytoplasm. This allows the cell to make proteins very quickly

Explain the endospore lifecycle.

2 phase life cycle between vegetative and endospore. It begins as a vegetative cell and begins undergoing a process in which the cell is separated into a sporangium and forespore, spore layers are synthesized around the forespore, and the spore matures causing the sporangium to disintegrate. The free spore is then released and during germination the spore swells and releases a vegetative cell causing the cycle to begin again.

What bacteria produces endospores?

Bacillus and Clostridium

Which bacteria is known to cause outbreaks of diarrhea in hospitals and nursing homes?

Clostridium difficile

Will bleach-free disinfectants kill endospores?

No - they are resistant

What is the structure of gram+ bacteria?

has a thick layer of peptidoglycan that forms a single layer around the cell

Explain the gram staining process.

1. Add crystal violet (purple) - 10 sec - rinse w/ water

2. Add Gram’s iodine - 10 sec - rinse w/ water

3. Decolorize w/ 95% ethanol - until colorless - rinse w/ water**

4. Add Safranin (pink) - 10 sec - rinse w/ water

5. Air dry or blot w/ absorbent paper

What is the most important step of the gram staining process?

The third step - most affected by technical variations in timing and reagents

What color will a gram+ bacteria stain?

Purple - due to thick peptidoglycan layer

What color will gram - bacteria stain?

Pink - due to thin peptidoglycan layer

How will staphylococcus be viewed under a microscope?

gram-positive bacteria appear as cocci in clusters “bunches of grapes”

How will streptococcus look under the microscope?

gram-positive bacteria appear as cocci in pairs or chains

How would Listeria look under the microscope?

gram positive and would appear purple and rod shaped

Does Listeria produce spores?

No it does not

What is pleomorphism?

The cells are irregular in shape and size due to variations in cell wall structure or lack of cell wall caused by nutritional or slightly hereditary differences (usually rod shaped)

Why is pleomorphism extreme in the Mycoplasma genus of bacteria?

due to the absence of cell wall these organisms can change their shape

What is inoculation?

Introduction of a sample into a container of sterile media. (Collecting a sample)

What is incubation?

Provides conditions for optimal growth. (Making sure you have enough microbes in your sample)

What is isolation?

Getting a pure culture of the microbe (Selecting only the microbe you’re interested in)

What is inspection?

Looking at colonies and microscopic characteristics (cell type and morphology, Gram stain, special stains, etc, used to identify the genus of the microbe)

What is information gathering?

Biochemical, immunologic, and genetic testing (oxygen requirements, special metabolic enzymes specific to the bacteria, PCR, etc, used to confirm the genus of the microbe and identify the species)

What is identification?

Assigning a specific name to the microbe

What are the 6 I’s of culturing microbes?

Inoculation

Incubation

Isolation

Inspection

Information Gathering

Identification

What is synthetic media?

contains pure organic & inorganic compounds in an exact chemical formula

What is non-synthetic media?

contains at least one ingredient that is not chemically definable- organic extracts

What is general purpose media?

grows a broad range of microbes, usually non-synthetic, nutrient agar and broth, peptone water, ect.

What is enriched media?

contains complex organic substances such as blood, serum, hemoglobin or special growth factors required by fastidious microbes

What is selective media?

contains one or more agents that inhibit growth of some microbes and encourage growth of the desired microbes

What is differential media?

allows growth of several types of microbes and displays visible differences among desired and undesired microbes

Which specific medium would be best to isolate pathogenic staphylococci?

Mannitol salt agar which is both selective and differential.

The mannitol salt agar turns yellow if the organism metabolizes mannitol, helping to differentiate between S. aureus (yellow) and S. epidermis (red).

Why is the growth curve in a bacterial culture closed?

they are placed in a system with finite nutrients and space without the ability to remove waste products

What are the four phases of microbial growth?

Lag Phase

Exponential Growth (Log) Phase

Stationary Phase

Death Phase

Explain the lag phase.

flat period of adjustment, enlargement, and synthesis of DNA, enzymes, ribosomes; little growth 

Explain the exponential growth (log) phase.

a period of maximum growth will continue as long as cells have adequate nutrients & a favorable environment

Explain the stationary phase.

rate of cell growth equals rate of cell death – caused by depleted nutrients & O2, excretion of organic acids & pollutants

Explain the death phase.

as limiting factors intensify, cells die exponentially in their own wastes

What is the average period of time it takes to complete the microbial growth curve?

About 4 days in any given culture

Which gram+ bacteria stain like gram- bacteria and why does this occur?

Actinomyces, corynebacterium, mycobacterium and Propionibacterium These have walls that are sensitive to breakage during cell division resulting in gram-negative staining.

Bacillus and clostridium also stain gram negative when they are growing because of decreased peptidoglycan

Which bacteria responds best to acid-fast staining?

Mycobacteria

Which groups of bacteria are considered obligate intracellular parasites?

Rickettsias and Chlamydias

What are the key factors of obligate intracellular parasites?

cannot survive or multiply outside of a host cell

cannot carry out metabolism on their own

What are the 4 main fungal divisions?

Zygomycota - rhizopus (bread mold)

Ascomyota - yeast in beer and bread, ringworm, black mold

Basidiomycota - Crytopcoccus neformans (organ infections)

Chytridomycota - not known to cause human disease

What are the two morphologies in which microscopic fungi exist?

Yeast - unicellular round/oval budding cells; asexual production

Hyphae - molds; long filamentous cells

What are primary fungal pathogens?

Yeasts or molds (dimorphic)

blastomyces, histoplasma, coccidioides, paracoccidioides, and sporothrix

What are opportunistic fungal pathogens?

Happen secondary to a weakened immune system

cryptococcus, candida, aspergillus, penicillium, zygomycetes, trichosporon, and fusarium

What are the two protozoan stages?

Trophozoite - motile feeding stage

Cyst - a dormant resistant stage

Explain the structure of flatworms.

flat (thin, segmented body plan), no definite body cavity; digestive tract a blind pouch; simple excretory & nervous systems

What are the two types of flatworms?

cestodes (tapeworms) – long, ribbon-like

trematodes (flukes) – flat, ovoid

Explain the structure of roundworms.

Nematodes

round (elongate, cylindrical, unsegmented body plan), a complete digestive tract; a protective surface cuticle; spines & hooks on mouth; excretory & nervous systems poorly developed

What type of helminth is the pinworm?

Roundworm (nematode)

What is the difference between an enveloped and naked virus?

Naked viruses do not contain a viral envelope

What are the 6 stages of viral replication?

Adsorption: Attachment to cell surface

Penetration: Fusion or endocytosis to enter the cell. Nucleic acid is then released

Uncoating: Release of viral capsid and RNA into the cytoplasm

Duplication: Using the metabolism and machinery to synthesize the basic components of new viruses

Assembly: Nucleocapsid and envelope are formed

Release: Viruses bud of the membrane; virion is ready to infect other cells

What are cytoplasmic effects caused by viruses?

virus-induced damage to host cells that alters their microscopic appearance

Ex. Changes in size/shape, inclusion bodies, cell fusion, cell lysis, altered DNA

What microbes have the highest resistance to control?

Prions and bacterial endospores

What is microbicide?

(germicide) any chemical agent that kills pathogenic orgnanisms

What is microbiostatic?

any process that temporarily prevents microbes from multiplying (bacteriostatic, fungistatic)

What is sanitization?

any cleansing technique that mechanically removes microbes (dishwashing)

What is determination?

any process that reduces the number of microbes on the human skin (surgical hand scrub)

What is antisepsis?

a process that uses chemical agents on the skin to destroy or inhibit vegetative pathogens (antibacterial soap or using iodine preoperatively

What is disinfection?

any process that destroys vegetative pathogens, but not endospores (5% bleach or boiling water)

What is microbial death?

permanent loss of reproductive capability, even under optimal growth conditions

What factors affect an antimicrobial agent’s mechanism of action?

Number of microbes

Nature of microbes in population

Temperature and pH of the environment

Concentration of agent

Mode of action

Prescience of solvents, organic matter, or inhibitors

What are the four cellular targets that antimicrobial agents aim to destroy and what agents are most effective?

Cell wall - detergents and alcohols

Cell membrane - surfactants

Cellular synthetic processes of proteins and nucleic acids - antibiotics, chemicals, radiation

Protein structure and function - heat, aids

What type of heat is more effective or microbial control?

Moist heat - using hot water or steam.

Ex. Autoclave is commonly used in hospitals

What is desiccation?

the gradual removal of water from cells, leads to metabolic inhibition

(Not an effective microbial control - many cells will regrow when reintroduced to water)

Explain ionizing vs. non-ionizing radiation.

Ionizing - deep penetrating power, breaks DNA (sterilization)

Non-ionizing - little penetrating power, causes DNA mutations by formation of abnormal bonds (disinfection)

What is filtration?

Mechanical removal of microbes by passing a gas or liquid through a filter

Used for heat sensitive liquids and in hospital isolation units

What agents are sporicidal?

Halogens - denatures proteins and enzymes

Hydrogen Peroxide (in high concentration) - damages protein and DNA

Aldehydes - alkylate proteins in the cell & disrupt enzymatic activities

What heavy metals are used for antimicrobial control?

Solutions of silver and mercury are used for antimicrobial control (on burn dressings and weak antiseptics)

What are narrow antimicrobial drugs? Explain advantages and disadvantages.

effective on a small range of microbes and target a specific cell component that is only found in certain microbes

advantages: will causes less resistance of the bacteria

disadvantages: causative organism must be identified 

What are broad-spectrum antimicrobial drugs? Explain the advantages and disadvantages.

greatest range of activity, target components common to most pathogens

advantages: less need to identify the infectious agent before starting treatment

disadvantages: increase rise due to drug resistance

What is the mechanism of action of beta-lactam antimicrobials?

Interfere with cell wall synthesis by blocking the synthesis of peptidoglycan, causing the cell wall to lyse

Explain the function of natural penicillins.

Interfere with cell wall synthesis by blocking the synthesis of peptidoglycan, causing the cell wall to lyse - narrow spectrum

Pen G and Pen V

Explain the function of semisynthetic penicillins.

Can cross the cell walls of Gram (-) bacteria - broad spectrum

Ampicillin, Carbenicillin, Amoxicillin

Are Carbapenems and Monobactams broad or narrow spectrum?

Carbapenems - broad-spectrum (Imipenem & Meropenem)

Monobactams - narrow-spectrum (Aztreonam)

What are cephalosporins?

Family of bacterial antibiotics structurally related to PCN and have a synthetically altered beta-lactam structure

What are the root names associated with generic cephalosporins?

cef, ceph, or kef

What types of bacteria are cephalosporins most effective against?

gram positive and gram negative bacteria (more gram - coverage the higher the class)

Which antimicrobials disrupt cell membrane function?

Polymyxins - cell membrane of gram - bacteria

Daptomycin - cell membrane in gram + positive (including MRSA)

Amphotericin B/Nystatin - antifungals that form complexes on fungal membranes

Which antimicrobials affect nucleic acid synthesis?

Fluoroquinolones and Antiviral drugs

How do fluoroquinolones stop DNA replication and repair?

Bind and inhibit DNA gyrase and topoisomerase – stops DNA replication and repair

What should you warn your patient about if you prescribe fluoroquinolone?

Risk of tendinosis and cardiac conduction issues

Which ribosomal subunit do aminoglycosides target to disrupt protein synthesis?

30S ribosomal subunit

Are aminoglycosides broad or narrow spectrum?

Broad spectrum - useful against aerobic gram - rods and certain gram + bacteria

streptomycin, gentamicin, tobramycin

Which antibiotics target the 30S ribosomal subunit?

Aminoglycosides

Doxycycline

Tetracycline

Minocycline

Which antimicrobials interfere with protein synthesis by targeting the 50s ribosomal unit?

Chloramphenicol - broad spectrum (rarely used)

Erythromycin - broad spectrum macrolide

Azithromycin and Clarithromycin - broad-spectrum, second generation macrolides

Which antimicrobials interfere with protein synthesis by targeting both the 30s and 50s ribosomal units?

Oxazolidinones

Which medications have a mechanism of action that affects a microbe’s metabolic pathway?

Sulfamethoxazole and trimethoprim - they block enzymes required for folate synthesis and folate is needed for DNA and RNA synthesis

What is synergistic effect?

effects of a combination of antibiotics are greater than the sum of the effects of the individual antibiotic

What is the mechanism of action of antifungal medications?

inhibition of ergosterol and cell membrane synthesis

What are macrolide polyenes?

Antifungal used to treat cryptococcus meningitis

Amphotericin B: can be given oral, topical, or IV

Nystatin: can be given oral and topical

What is griseofulvin used to treat?

Athlete’s foot - given orally