General Microbiology Flashcards
What is an infectious agent?
Something that invades another living thing
What are the 6 classes of infectious agents in humans?
Bacteria (prokaryote, single cell)
Viruses (sub cellular, nonliving)
Fungi (eukaryote, single or multi cell)
Parasites (eukaryotes, single or multicellular)
Prions (transmissible, abnormally folded protein)
Algae (eukaryote, single cell)
What are the key differences between eukaryotes and prokaryotes?
Eukaryotes have true nucleus - genetic material inside a membrane and organelles are membrane bound
Prokaryotes don’t have this
This part of the light microscope focuses light onto the specimen
Condenser
Where is the light source located for a light microscope?
At the base
What structure on the light microscope first magnifies the image of the specimen?
Objective lense
What type of light is used in fluorescence microscopy?
UV light
What type of dye is used to fluorescent microscopy?
Fluorescent dye
This tool is useful for looking at organisms that are hard to grown in culture, detect organisms, or antibodies to organisms
Fluorescent microscopy
What is the difference between a scanning electron microscope and transmission electron microscope?
SEM low res 3D image of surface
TEM high res 2D image showing detailed internal structure
What are the similarities between SEM and TEM?
Both use electrons to create an image
What is the difference between colonization and infection?
Colonization bacteria present w/o causing harm to the host
Infection host tissue invasion by disease causing organisms
Are bacteria always harmful?
No; Flora/Colonizer
Don’t cause disease
Cooperate with host
What are some benefits of bacteria?
Outcompete pathogens
Help host metabolism
Keep host immune system vigilant
What are the 3 types of host-bacteria relationships?
Flora/colonizer
Opportunist
Pathogen
Are colonizers always harmless?
Can become harmful if host is compromised
What determines the pathogenicity of an organism?
Virulence factors
What are the 5 virulence factors?
Motility
Adhesion
Protection (capsule or biofilm)
Toxin production
Spore formation
What are the 3 types of toxins made by bacteria?
-Neurotoxin
-Enterotoxin impact GI tract —> infectious diarrhea or food poisoning
-Endotoxin bound to surface of bacteria but are release by normal shedding or cell lysis
Why are spores so dangerous?
Formed by some bacteria when they’re in unfavourable conditions that are difficult to kill
Spores remain dormant until favourable conditions
Difficult to kill
What are 7 ways (morphology/metabolic activity) of identifying bacteria in the lab?
- Microscopic (shape, size, gram stain)
- Macroscopic
- Colony size, colour, shape, odour
- Colony resistance, substrate use, ability to lyse blood
- Metabolic (aerobic/anaerobic, growth needs, enzyme production)
- Serotyping (using antibodies to identify bacteria by antigens)
- Molecular sequencing
What are obligate aerobes?
Absolutely need oxygen to live
Make protective enzymes to break down radicals made r/t respiration
What are obligate anaerobes?
Have no enzymes to deal with radicals
Use fermentation to make energy
What is a facultative anaerobe?
Pref O2 but don’t need it to survive
Can use respiration or fermentation for energy depending on O2 availability
What type of bacteria (aerobic/anaerobic) grows for longer?
Anaerobes - can be incubated for up to 2wks
What colour do gram positive bacteria stain?
Deep blue or purple
What causes bacteria to have a gram positive stain?
Gram (+) bacteria have a thick peptidoglycan wall causing it to retain the violet dye used even after alcohol treatment
What causes bacteria to have a gram negative stain?
Gram (-) bacteria have a thin peptidoglycan wall that doesn’t hold on to the violet dye after alcohol treatment
What colour do gram negative bacteria stain?
Pink
What are the 4 steps for gram staining?
Crystal violet: primary stain
Iodine: helps dye adhere to cell wall
Alcohol: washes away stain from gram (-) cell walls
Safranin or carbol fuchsin: counterstain allowing adherence to gram (-) cell walls
What are the 3 types of grouping for cocci bacteria?
Diplococci (pairs)
Chains
Clusters
What are the 6 types of arrangement of bacilli?
Singles
Curved
Pallisade
Streptobacilli
Fusoform
Coccobacilli
What 6 characteristics are used to describe colony morphology on a plate?
Shape (form, elevation, margin)
Size (pin-point vs large)
Pigment or sheen
Ability to break down blood cells
Mucoid (presence of capsule)
Odour
What differences are there between molds and yeasts? (cells, reproduction, temp preference)
Molds - Multicellular, filamentous (hyphae); likes colder env (25-30C)
Yeasts - Unicellular, produced by budding; likes growing in warmer env (35-37C)
What similarities are there between molds and yeasts?
Both are fungi
What are dimorphic fungi?
Can become mold or yeast depending on env temp
Do fungi always need lab testing for diagnosis?
No; some can be dx empirically
What 5 factors can fungi identification be based on?
Microscopic characteristics
Macroscopic characteristics
Growth rate
Metabolism
Protein structure on MALDI-TOF or DNA sequencing
What are 4 common medically important dimorphic fungi?
Blastomycosis dermatitidis
Coccidiodes immitis
Histoplasma capsulatum
Paracoccidiodes braziliensis
What action must be taken if a high risk pathogen is suspected?
Notify lab before sending specimen so it can be processed in biosafety lvl 3 space
This infectious agent forms rings on blood smear
Plasmodium; parasite responsible for malaria
What are the 2 classifications of parasites?
Protozoa (eukaryote, single cell)
Helminths/worms (eukaryote, multicellular)
What is the traditional means for identifying protozoan parasites?
Microscopy on blood, stool, or vaginal specimens
This technique is replacing microscopy and allows detection of multiple parasites in one sample
Molecular detection
Stool multiplex PCR allows for detection of multiple parasites in one sample
What are the 4 methods of identifying protozoans?
Microscopy
Molecular detection
Serology
Culture
What are the 3 methods of helminth identification?
Worm morphology
Egg or larva microscopy
Serology
Are viruses living cells?
No
Consist of DNA/RNA and a protein coat. May or may not have an envelope
Need a host to replicate
What are the 5 means of virus classification?
Genome
Capsid shape
Presence of envelope
Body site they infect
Source of transmission
What 2 types of genome can viruses have?
DNA
RNA
Can be single or double stranded
What are the 3 types of capsid shapes viruses can have?
Polyhedral
Helical/linear
Complex
What are the 6 methods of detection/identification of viruses?
Molecular (PCR)
Antigen detection (immunofluorescent assay)
Electron microscopy (expensive)
Viral culture (time consuming)
Isolating antibodies
ELISA (IgM and IgG; common in public health labs)
What 3 factors impact quality of lab results?
Collection
Storage
Transportation
These are 4 examples of non-sterile sources of culture samples
Urine
Stool
Sputum
Swabs
What is a challenge associated with non-sterile site sources?
Contain a large amount of colonizing bacteria and pathogens may or may not be present
Give examples of sterile fluids/samples
Blood
CSF
OR collected tissue
Abd or thoracic fluid
Suprapubic urine
Samples collected from ____ sites always represent infection unless poor collection or contamination of sample
Sterile
What are some things that can contribute to low quality specimens?
1/4 blood culture bottles grow skin colonizer
Large number of epithelial cells in sputum on gram stain
Small number of polymorphonuclear cells in gram stain
Mixed growth of organisms
What is the least preferred sample collection method?
Swabs because they give such a small sample; more is better
Microbiology specimens can’t be collected in this substance
Formalin or other preservatives
Why is prompt transport of a specimen important for microbiology of specimen?
Time is bacteria — desired bacteria may be dying and getting outcompeted by non-pathogenic bacteria
