1
Q
Commensalism
A
A symbiotic association in which the commensal organism benefits from the host’s food and shelter, and the host is not harmed nor does it benefit
Ex. Saprophytic cells eat dead cells in our ear and external genitals and do not cause us any harm
2
Q
Mutualism
A
A symbiotic association in which both members benefit; obligatory and dependent
Ex. E.coli lives in our gut and produces vitamin K
3
Q
Parasitism
A
A symbiotic association in which a parasitic microbe is dependent on host and benefits; host is harmed and disease may result (not to be confused with “parasites”)
4
Q
What are bacteria?
A
- Prokaryotic; no nuclei, single-called organisms, which live singly, in pairs, chains or clusters
- most common type of microbial infection in Canada
5
Q
What are viruses?
A
- Acellular microbes (not alive); not visible by light microscopy
- Obligatory microbes composed of genetic material surrounded by a protein coat
6
Q
What are fungi?
A
- Eukaryotic; possess a nuclei and cell wall, organelles, obtain nutrients from other organisms
- Yeasts (unicellular) and molds (multicellular)
7
Q
What are protozoa?
A
- Eukaryotic, single-called organisms, possess a nucleus
8
Q
What are helminths?
A
- Eukaryotic, multicellular, possess a nuclei, visible with the naked eye
- Infections often diagnosed via microscopic examination of eggs or larvae in clinical specimens
9
Q
Which type of infection is more serious - viral or bacterial?
A
Bacterial infections are generally more serious and are more likely to cause an emergency - viruses are very small, not alive and are usually self-limiting
10
Q
How do antibiotics work?
A
- Antibiotics work by exploiting the differences between eukaryotes and prokaryotes; thus are own cells go unharmed
- Target cell wall components (i.e. Penicillin) or the smaller ribosomal subunits (i.e. Erythromycin)
11
Q
Which microbe is the smallest?
A
Viruses
12
Q
What are some key characteristics of bacteria?
A
1) single called organism
2) no nucleus
3) possess smaller separate circles of DNA called “plasmids,” which often contain information related to resistance mechanisms
4) ribosomes are smaller than those of eukaryotes
5) cell wall (composition can vary) and cell membrane
6) external cellular structures such as flagella or pili
13
Q
What are 5 ways in which bacteria is classified?
A
1) Cell morphology - shape, arrangement, colony morphology, external structures, capsules, spore formation
2) Cell wall structure - staining and microscopy; Gram and acid fast stains
3) Growth characteristics - oxygen and energy requirements
4) Metabolism - carbohydrate utilization, fermentation end-products, etc.
5) Molecular techniques - DNA sequencing
14
Q
Bacteria Cell Morphology
A
- diplococci
- streptococci - chains of round cells
- staphylococci - clusters of round cells
- bacilli - rod shaped
- coccobacilli - oval shaped
- sarcina- tetrad of round cells
- neisseria - diplococci
15
Q
Bacteria Colony Morphology
A
- characteristics of colonies grown on agar plates allows for tentative identification
- shape of colony, margin/edge, elevation, surface texture, no pigmentation are all important to identification and there are various possibilities
16
Q
What are flagella?
A
- external protein filaments that extend from cell membranes
- motile (rotate 360), allowing microbe to move in a series of tumbles and runs in response to stimuli (light, nutrients, etc.)
- number and location of flagella can be used for classification
- Polar; Vibrio spp. (single), Spirillium spp. (double)
- Peritrichous; E. coli spp. (several hairs)
17
Q
What are fimbriae?
A
- straight filaments arising from bacterial cell wall - facilitate formation of biofilms
- shorter than flagella, not used for propulsion but can be used to “pull” the bacterium across a substrate
- allows for adherence, binding to specific host cell receptors - critical step in infection (ex. E. coli binds to intestinal epithelial cells causing GI infection)
18
Q
What is a conjugation pili?
A
An external structure on bacterial cell wall which transfers DNA from one bacteria to another and allows for plasmid sharing
19
Q
What is glycocalyx?
A
- a protective substance surrounding some bacteria, normally made of polysaccharides
- presence/absence can be used for classification
- slime layer OR capsule
20
Q
What is a slime layer?
A
- type of glycocalyx on bacteria
- sticky and loose - prevents dehydration, allows bacteria to bind to surfaces and inorganic material and to form a protective layer encapsulating colonies of bacteria
21
Q
What is a capsule?
A
- type of glycocalyx that is firmly attached to the cell surface
- virulence factor that facilitates adherence and impairs phagocytosis - allows the bacterium to remain “hidden” from the immune system until infection ensues
22
Q
What are endospores?
A
- defensive strategy against hostile or unfavorable environmental conditions (driven by nutrient supply)
- metabolically dormant and resistance to heat, cold, drying, chemicals and radiation
- germinate when conditions improve
- formed by two genera: Clostridium spp. and Bacillus spp.
- requires special environmental controls to kill spores - cleaning and disinfecting is not sufficient - sterilization required (steam, under pressure, chemical sterilants, etc.)
- can be found in water
23
Q
What is the function of the bacterial cell wall?
A
- possess unique characteristics that differentiate it from other microbes (peptidoglycan layer)
- used to classify species - probably most important feature
- provides structure and maintains microbe’s shape
- counters the effects of osmotic pressure - protect from fluid
- provides rigid platform for external appendages
- facilitates adherence to host cells and evasion of host defenses
- target for antibodies
24
Q
What is the Gram stain?
A
Identifies two types of bacterial cell wall:
1) Gram-Positive; bacteria that retain primary crystal violet dyes due to thick, dense and relatively non-porous walls become a purple color post Gram stain
2) Gram-Negative; bacteria that are easily discolored due to thin cells walls surrounded by an outer membrane take on a pink red color post Gram stain
- starting point for bacterial identification
- difference in dye retention depends on thickness, density, porosity, integrity , and chemical composition of cells wall
- very quick process (30 min) in comparison to growing a culture
- also reveals where the person likely got sick and makes morphology more distinct
- very important as Gram negative and Gram positive bacteria have different susceptibility profiles to antibiotics
25
What is LPS?
- LPS (or Lipid A) is a potent endotoxin found in the outer membrane of most Gram negative bacteria
- causes fever, vasodilation, and inflammation
- can induce shock and blood clot formation
- makes Gram negative harder to manage than Gram positive
26
What are some considerations for the Gram stain?
- some non-bacterial organisms with thick cells wall (some yeasts) may also stain Gram positive
- Gram positive bacteria that have lost cell wall integrity through aging or damage may stain Gram negative; thus, specimen collection is very important
- not all bacteria Gram stain; specialized stains are required for some species
27
What are acid fast stains?
- acid fast stains are used specifically when mycobacterial infections are suspected
- most bacteria do not retain the dye carbol fuchsin after treatment with acidic alcohol
- Mycobacterium species (e.g. Mycobacterium tuberculosis) contain a waxy material (mycolic acids) in their cell wall which retains the stain
28
Why is knowing bacterial oxygen requirements important?
- bacteria can be classified according to their ability to tolerate oxygen
- molecular oxygen is highly reactive, and toxic to bacteria unless it is inactivated by enzymes produced by the bacteria
29
What enzymes are used to detoxify reactive oxygen products?
- catalase
- peroxidase
- superoxide dismutase
30
What are obligate aerobes?
- require oxygen to survive
| - possess all three enzymes
31
What are facultative anaerobes?
- flexible to various environments with or without oxygen
- prefer to grow in the presence of oxygen, but can also grow without
- produce catalase and superoxide dismutase
32
What are microaerophiles?
- tolerate low amounts of oxygen (i.e. stomach)
| - produce superoxide dismutase
33
What are obligate anaerobes?
- cannot tolerate oxygen, lack enzymes to manage its toxicity
- require special growth conditions
34
What are the implications of bacterial oxygen requirements in clinical practice?
- must take two sets of two blood culture specimens from each venipuncture site - one aerobic, one anaerobic
- left and right arm sites to prevent contamination
- must sample before therapy is started
35
What is binary fission?
- asexual reproduction
- number of cells increase exponentially when nutrients are readily available - exponential growth phase
- doubling time differs by species and conditions (i.e. E. coli doubles every 20 min, Mycobacterium spp. double every few days)
36
What are the phases of bacterial growth?
- exponential growth phase
- stationary phase; nutrients are depleted and toxic wastes accumulate
- death phase; no nutrients available so bacteria begin to die
- lag phase; when transferred to a new environment, pathways required to utilize nutrients are reactivated
37
How does sexual reproduction occur?
- conjugation pili
38
What is obligate intracellular bacteria?
- require host cell to live; cannot make their own energy
- grow and reproduce inside the host cells (e.g. Chlamydia spp.)
- require cell/tissue cultures for growth in laboratory
39
What is facultative intracellular bacteria?
- able to survive phagocytosis, grow and reproduce within immune cells (macrophages, neutrophils) e.g. Neisseria spp.
- shielded from antibodies and other immune defenses; "hidden"
- employ specialized mechanisms to protect against lysosomal enzymes produced within phagocytic host cells
40
Characteristics of viruses
- obligate intracellular pathogen
- cannot replicate (multiply) independently, must replicate inside host cells, using enzymes, organelles and energy from the host cell to increase in number
- acellular; lack cell membrane, composed of only a few organic molecules
- possess DNA or RNA, supported by a protein capsule or "capsid" that provides both protection and recognition sites that bind to receptors on host cells
- some viruses also possess an "envelope" derived from host cells which facilitates entry into host cells, in such cases cellular membrane proteins are replaced with virus-derived proteins
41
How are viruses classified?
- virion structure (difficult to access)
- nature of genome
- mechanism of replication
- host and tissue range, cytopathic effect on host cell
- nature of disease
- serological reactions
- amino acids sequences of viral proteins, nucleic acid sequences
- HIV and Influenza are the only viruses we track; usually signs and symptoms are used to classify virus
42
What is viral replication?
- since viruses cannot reproduce independently (they lack enzymes and ribosomes), they "hack" the host cells reproduction mechanisms, forcing it to replicate viral genetic material and translate viral proteins
43
What are the steps of the viral replication cycle?
1. Attachment - specific molecular interaction with a host cell receptor
2. Entry - via direct penetration, membrane fusion, or endocytosis
- Uncoating; required for viruses that enter the host cell with their capsid intact
3. Synthesis - strategy varies depending on nucleic acid (DNA, RNA, ds, ss); DNA synthesis occurs in nucleus, RNA synthesis in cytoplasm
4. Assembly - once components are synthesized, assembled into virions
5. Release from host cells
- Budding; enveloped viruses are released via budding - virions are extruded through cell membranes, forming the viral envelope ("gentle")
- Lysis/Exocytosis; naked virus released via host cell lysis, destroying the host cell, or via exocytosis in which virion is extruded without acquisition of an envelope
44
Aborted viral infection
- little or no detectable effect of virus on host cell
45
Persistent infection
- alteration of antigenic specificity of cell surface due to presence of virus glycoproteins; host cell function is intact leading to gradual, prolonged release of progeny viral particles
46
Latent infection
- persistence of viral genome in cell with no virus progeny produced; the latent virus can be reactivated months to years later resulting in a productive infection
47
Transformation
- integration of viral genome into host cell chromosome may result in disruption of host cell metabolic functions including cell growth and replication resulting in the induction of tumors (ex. HPV is related to cervical cancer)
48
Cell death
- rapid lysis of host cell and release of progeny
| - most common
49
Characteristics of fungi
- grow as single cells (yeast) or as multicellular filamentous colonies (molds)
- most are not pathogenic, rather saprophytic, meaning they obtain food from dead organic matter
- classified and identified based on their structures, colors, habitats, carbohydrate utilization, modes of growth and reproduction
- in the laboratory, fungi are identified by direct examination or cultured to examine their characteristic structures
50
Fungal structure
- yeast; single cells
- molds; multicellular filamentous colonies, called hyphae (a mat of overlapping hyphae are called mycelia)
- dimorphic fungi; capable of growing in both forms (yeast & mold)
- yeasts reproduce via budding
- molds and dimorphic fungi form asexual spores as a mechanism for reproduction and transmission
- spores germinate to generate new organisms once an ideal environment is found
51
How does fungi differ from bacteria and other eukaryotes?
- fungal cell walls composed of chitin vs. peptidoglycans found in bacterial cell walls
- consequently, antimicrobial drugs that target the bacterial cell wall will have no effect on fungi
- fungal cell membrane contains ergosterol vs. cholesterol found in mammalian cell membranes
- limited number of drugs that target the differences between fungi and mammals
- many antifungals cause difficult to tolerate adverse effects
52
Mycoses
- chronic fungal infections; pathogens grow very slowly
| - classified into 5 groups depending on tissue involved and mode of entry
53
Superficial infections
- outermost layer of skin, nails and hair; treated topically
54
Cutaneous infections
- ringworm and tinea
- keratinized layers of skin, hair and nails; caused by dermatophytes, host immune response may be stimulated
- itchy, scaling skin that may become inflamed
- transmission human to human via infected skin
- topical therapy may not be sufficient, especially in later stages or when nails are involved
55
Subcutaneous infections
- involve the dermis, subcutaneous tissues, muscle and fascia
- most infections are chronic, expressed clinically as lesions on the skin surface, initiated by trauma to the skin
- difficult to treat, surgical excision or amputation often required
- more common in developing countries
56
Systemic infections (primary infections)
- originate primarily in the lungs, travel to distal sites
| - fungi found in soil and feces of birds and bats - geographically defined, associated with inhaled spores
57
Opportunistic infections
- observed in individuals with impaired host defenses
- alteration of normal flora, AIDs, DM, immunosuppressive therapy, cancer
- get sick from fungi that would normally not affect a person if they were healthy
58
Parasitic infections
- most common in developing countries or tropical regions
- no longer confined to particular geographical regions due to world travel
- 70% of humans infected
- at some point in life, parasites have a microscopic phase
- parasitic infections are long and chronic, although sometimes they are very serious (especially if immunocompromised)
59
Characteristics of protozoa
- eukaryotic, unicellular, and lack a cell wall
- all protozoa exist in a motile, feeding "trophozoite" stage
- many revert to a hardy, dormant "cyst" stage, characterized by a thick capsule and a low metabolic rate - protects parasitic form from poor environmental factors - INFECTIVE form
- common in Canada
60
How are protozoa classified?
- site of infection; GI and UG tracts, blood and tissues
- mode of locomotion:
- amoebas; move by extending cytoplasmic projections outward from main body
- flagellates; whip-like projections rotate and propel the organism
- ciliates; hair-like projections cover cell surface and beat in unison to move cell forward
- sporozoa; generally non-motile, although adult males sometimes have flagella
- nucleotide sequencing
61
How do protozoa reproduce?
- typically asexual (binary fission) and some reproduce by meiotic (sexual) division
- many have a complex life-cycle that includes a vector (i.e. mosquito, tsetse fly, rats) or intermediate hosts (i.e. snails, pigs, beef, fish)
62
How do protozoa gain access to a human host?
- via ingestion or penetration of anatomical barrier (i.e. insect bite), followed by attachment, replication, and host damage as organism is released from host tissues
63
What are flatworms?
- thin, soft body that is flattened dorsoventrally
- Trematoda: flukes (such as liver, blood and lung flukes), all are parasitic
- Cestoidea: tapeworms (beef, pork, and fish tapeworms), all are parasitic
64
What are roundworms?
- cylindrical shaped body, tapered at end, unsegmented
- intestinal (e.g. pinworm)
- blood and tissue (e.g. filarial and dog worm)
65
Characteristics of tapeworms
- Taenia solium, commonly known as the pork tapeworm, is acquired by ingesting the larvae present in muscle tissue of a pig
- adult tapeworms live in the small intestine of humans by attaching to the intestinal wall by the scolex, which consists of hooks and up to four suckers
- a tapeworm grows by the addition of body segments; up to 3-5 meters long, living up to 25 years
- symptoms of infection include diarrhea, increased appetite, intestinal obstruction
- detected by the presence of ova (eggs) or proglottids (segments) in feces
66
Characteristics of roundworms
- enterobius vermicularis commonly known as the pin worm
- ingestion of ova present on hands, fomites or linens
- symptoms include nocturnal itching of the anus
- detected by collecting ova or female worms from perianal region using tape
- parasite is attracted to light, females most active in the evening
- worms visible in stool
67
How do helminths reproduce?
- life cycles are highly complex; can include a definitive host (sexual cycle takes place), an intermediate host (asexual cycle takes place), and a paratenic host (no change in stage or development)
- specific to each pathogen
- plasmodium falciparum; the Anopheles mosquito is the definitive host, humans are the intermediate host
- taenia solium; humans are both the definitive and intermediate host
- transmission to humans varies with species; ingestion of larvae in raw undercooked pig, beef, fish, ingestion of helminth eggs (feces), insect bites or direct penetration through skins
- life cycle is key to understanding the infectious process, time course of the disease, and symptomology
Introductory Microbiology
flashcards
Decks in class (11)
# Cards
-
Structure, Reproduction & Classification67
-
Microbiology of Pathogenic Factors45
-
Respiratory Tract Infections58
-
Central Nervous System Infections55
-
Specimen Collection & Laboratory Diagnosis76
-
Infection Prevention & Control47
-
Cardiovascular System Infections40
-
Gastrointestinal System Infections59
-
Skin and Soft Tissue Infections56
-
Sexually Transmitted Infections76
-
Antimicrobials39
