Taxonomy, the Microbial Cell, Metabolism, & Genetics

The role of the clinical microbiology lab is to assist healthcare providers with diagnosis and management of infectious diseases with information from…

• microscope stains

• cultures

• phenotype characteristics

• immunochemical testing

• molecular analysis

• antimicrobial susceptibility testing

What are some examples of microbiological point-of-care tests?

• group A streptococcus screens

• rapid influenza A and B tests

• rapid COVID-19 tests

List 8 phenotypic characteristics of bacteria used for microbial identification

• colony morphology

• microscope morphology

• staining characteristics

• environmental requirements

• nutritional requirements

• biochemical characteristics

• antigenic properties

• antibiotic resistance profiles

species

the lowest taxonomic group that encompasses bacterial strains with common genetic, physiologic, and phenotypic characteristics

What 3 groups of classification are most important in microbiology?

family, genus, and species

• bacteria are classified as “Genus species”

What 4 microorganisms are considered eukaryotic?

fungi, algae, protozoa, and parasites

• they contain many membrane-bound organelles (nucleus, mitochondria, ER, etc.)

Where can DNA be found in bacterial cells?

• in the free-floating DNA chromosome

• OR in plasmids

  • extrachromosomal DNA

  • plays a role in the development of antibiotic resistance

What components can be found in bacterial cells?

• ribosomes

• DNA chromosome (nucleoid)

• mRNA

• proteins

• metabolites

• plasmids

• ALL LOCATED in the cytosol

What 2 parts make up the cellular membrane?

• plasma membrane

• and cell wall

• Gram negative bacteria have an additional outer membrane

What does the Gram positive cell wall consist of?

• a thick layer of cross-linked peptidoglycan

  • provides stability and strength, and can also block some macromolecules

• techoic acids

  • essential for cell viability and virulence

• lipotechoic acid

  • important as surface antigens to differentiate bacterial serotypes and to help the organism attach to the host

What does the Gram negative cell wall consist of?

• a thin peptidoglycan layer

• an outer lipopolysaccharide (LPS) layer

  • consists of lipid A (endotoxin), core polysaccharides, and O antigens

  • acts as a barrier and a site of attachment to host cells

___ are bacteria that have waxy cell walls, and are known as acid fast.

mycobacteria

Which 2 types of bacteria do not have a cell wall?

mycoplasma and ureaplasma

The cellular envelope of bacteria may also have a capsule and/or slime layer. What is a capsule and slime layer?

• capsule

  • acts as a barrier, allows adherence to host surfaces, and helps the bacterium evade the immune system (antiphagocytic)

• slime layer

  • loosely arranged polysaccharides

  • allows adherence to prosthetic devices/implants and the creation of biofilms

List and describe 2 external appendages on bacteria

• pili

  • hair-like extensions that provide attachment to host cells or other bacteria

  • sex pili are involved in conjugation and exchange of DNA between bacteria

• flagella

  • not present on all bacteria, used for movement

How are nutrients needed for metabolism enter the cell?

• diffusion (water, oxygen, CO2)

• or by active transport (organic acids, amino acids, inorganic ions)

What is the difference between aerobic and anaerobic respiration in microbial metabolism?

• aerobic

  • oxygen is the terminal electron acceptor

  • bacteria grows in the presence of oxygen

• anaerobic

  • the terminal electron acceptor is another organic molecule

  • oxygen is not required for bacterial growth

What are the 3 pathways in which glucose is converted to pyruvic acid?

• Embden-Meyerhof-Parnas pathway (EMP)

• pentose phosphate pathway

• Entner-Doudoroff (ED) pathway

facultative anaerobe

organisms that prefer to grow in the presence of oxygen, but do not require it for growth

What is the electron acceptor, efficiency of, and organisms that undergo fermentation (for metabolism)?

• electron acceptor

  • not oxygen (process does NOT require oxygen)

• efficiency

  • less energy efficient

• organisms

  • obligate and facultative anaerobes

What is the electron acceptor, efficiency of, and organisms that undergo respiration (for metabolism)?

• electron acceptor

  • oxygen (requires oxygen to occur)

• efficiency

  • more energy efficient

• organisms

  • obligate aerobes and facultative anaerobes

exotoxins

• substances secreted by living bacterial cells

• produced by both gram + and - bacteria

• not associated with fever

• usually species specific

  • example: C. tetani produces the potent neurotoxin tetanospasmin, which produces muscular paralysis

endotoxins

• substances released upon cell lysis or death

  • consists of LPS, a component of gram - cell walls

• associated with gram - bacteria

• not species specific

• can induce fever and shock, or even DIC

• activates B lymphs and complement

What are the applications of PCR and hybridization in the microbiology lab?

• to identify small amounts of bacteria in specimens

• to examine antimicrobial resistance

What characteristics do plasmids encode for?

• virulence, toxins, and antibiotic resistance

• plasmids can be released and taken up by other bacteria

What are transposons?

• “jumping genes”

• DNA segments that can insert pieces of DNA into other bacteria, even if no homology exists

Describe the following form of genetic change in bacteria: recombination

• foreign DNA combines with an identical portion of a bacteria’s chromosome

• this forms a partially hybrid chromosome with segments originating from the donor and recipient

List and describe 3 types of genetic exchange in bacteria

• transformation

  • bacterium dies and releases genetic information into the environment

  • free-floating genetic material is incorporated into a living bacterium’s genome (recombination)

• transduction

  • bacteriophages attach to bacteria and injects genetic information into the cell, which is incorporated into the genome

• conjugation

  • two bacteria connect by sex pili and genetic information is transferred

What are mutations and what causes them to happen?

• changes to the genetic code that can alter the organism’s phenotype

• causes:

  • insertion or deletion of base pairs in DNA

  • physical or chemical environmental factors

  • biological factors associated with the insertion of foreign DNA

What are restriction enzymes used for?

• to protect bacteria from bacteriophages

• these enzymes snip DNA at specific sequences and new DNA can be created with the segments

• example: A bacteriophage infects a bacterial cell. The restriction enzyme prevents replication by cutting up the phage DNA into pieces. The bacterium can then form new DNA that protects itself from other bacteriophages.