Bacteriology Flashcards
What two shapes are common major pathogens
Coccus and rod/bacilli
Name 2 examples of cocci pathogens
Streptococcus and staphylococcus
Name 2 examples of rod/bacilli pathogens
E. coli and Mycobacterium
Name 2 examples of spiral pathogens
Borrelia and campylobacter
What are the 3 major functions of the cytoplasmic membrane
Permeability barrier, protein anchor and energy conservation
List the steps of a gram stain
Crystal violet dye
Iodine as a fixative
Alcohol to de-stain
Fuchsin or safranin stain to counter
Describe the difference between a gram-positive and gram-negative cell
Gram positive has a thicker peptidoglycan layer with LTA and TA and gram negative has an outer membrane with LPS
Gram positive is physically stronger and a bit more permeable
What is the role of LPS in gram-negative bacterial infections
LPS protects the bacteria from phagocytosis and the lipid A part stuck in the outer membrane is a pro-inflammatory endotoxin
What type of cell wall is mycobacteria’s cell wall
Acid fast
How do you stain an acid fast cell wall and what part of the cell wall gets stained
Using a Ziehl-Nielsen stain
The mycolic acid retains the pink carbol fuschin stain
What are the 3 different flagellar arrangements
Peritrichous, polar and lophotrichous
What can happen to a bacterium that can cause its flagellum to mutate and reduce virulence
Failing to reach its desired niche, failing to attach, and failing to spread
What is an endospore
A highly differentiated cell resistant to heat, chemicals and radiation
It is a dormant stage some gram POSITIVE bacterial life cycles
TLR2 recognizes bacterial….
Lipoprotein and peptidoglycan
TLR4 recognizes bacterial…
LPS and LTA
TLR5 recognizes bacterial…
Flagellin
E. coli: Gram
Negative
Where is E. coli commonly found
In the intestines of warm-blooded animals
What are the 4 antigens of E. coli
O (LPS), K (Capsule), H (Flagella) and F (Fimbriae)
Which pathotype of E. coli is shown to cause diarrhea in new born animals (calves, lambs and piglets)
Enterotoxigenic e. coli
Which pathotype of E. coli is shown to cause diarrhea in older animals
Enteropathogenic e. coli and some verotoxigenic e. coli
Which pathotype of E. coli is shown to cause urinary tract infections
Uropathogenic e. coli
Which e. coli pathotype can progress to systemic colibacillosis
enterotoxigenic e. coli
What are the 2 key enterotoxins of ETEC to cause severe diarrhea
Heat-labile toxin (LT) and heat-stable toxin (ST)
What is different about how LT and ST toxin of e. coli cause diarrhea
LT activates adenylate cyclase activity, ST activates guanylate cyclase activity
How do bacterial cells multiply
By binary fission (cell elongation, septum formation, formation and separation of cell walls)
Define exponential growth
Growth in which cell numbers double at a constant time interval
Why do microscopic cell counts always reveal more cells than the plate method
Microscopic measure both alive and dead cells, and the growth medium of a plate cannot support the growth of every bacteria in a sample
Define VBNC
A state of low metabolic activity where cells do not divide, but can become culturable if resuscitated under the right conditions
List 3 methods used to measure bacterial growth
Microscopic counts, viable cell counts and turbidimetric methods
Optimal growth temperature: psychrophile
4C
Optimal growth temperature: mesophile
39C (e. coli)
Optimal growth temperature: thermophile
60C
Optimal growth temperature: hyperthermophile
88C-106C
Neutrophile: pH
6-8
Acidophiles: pH
Less than 6
Alkaliphiles: pH
More than 9
Obligate aerobes
Need oxygen
Microaerophiles
Need oxygen but at reduced levels from what is in atmosphere
Facultative anaerobes
Can live with or without oxygen
Aerotolerant anaerobes
Can tolerate oxygen but cannot use it
Obligate anaerobes
Do not need oxygen and are killed by exposure
Selective media
Contains compounds that selectively inhibit growth
Differential media
Contains indicator (dye) that detect specific chemical reactions
Enrichment cultures
Selected for desired organisms, encourages growth and recovery
What is a bacterial plasmid
Closed circular DNA structures (like mini-chromosome) that are sometimes present in multiple copies
What are some characteristics associated with bacterial plasmids
Antibiotic resistance, toxins, adhesins, growth condition requirements
Core genome
Present in all strains
Accessory genome
Present in a subset of strains
Pangenome
Gene pool of a species
Briefly define transformation
Uptake of naked extracellular DNA
Briefly define transduction
Bacterial genome is transferred via bacteriophages
Briefly describe conjugation
Transfer of genetic material through cell to cell contact (expression of F sex pilus)
List 4 mechanisms responsible for antibiotic resistance in bacteria
- drug inactivation
- target modification
- drug efflux
- reduced drug uptake
List 3 ways bacteria can respond to environmental change at the gene expression level
- Activation/repression of gene expression
- 2 component signal transduction systems
- quorum sensing
Define infection
Presence of a micro-organism in/on host tissue
Define disease
Pathological and clinical consequence of infection
Define opportunistic pathogen
Usually commensal or environmental
Define a true pathogen
Initiate disease as a consequence of their presence on/in tissue
Define pathogenesis
The mechanisms by which an agent induce symptoms or pathology
What are koch’s postulates used for?
To define the capacity of an organism to cause disease (NOT used in routine diagnosis)
What is the function of molecular koch’s postulates?
Examination of specific virulence factors or genes in disease
What is an endogenous source of infection
Infection originating from within the animal
What is epizootic/epidemic
Disease spreading within a short time span to a large number of animals
What is enzootic/endemic
The habitual presence in a certain geographical area
Horizontal transmission
Transmission of an infection from another animal or the environment
Vertical transmission
Transmission of an infection from parent to offspring via germ-line, in utero or milk
What is Iatrogenic transmission
Infections transmitted from human interference
What is nosocomial transmission
Infections acquired during hospitalization
What is the challenge dose
The number of micro-organisms that is inoculated
What is the infective dose
The number of micro-organisms required to produce disease
List three sites of bacterial entry
Inhalation, uro-genital, mucous membranes
List five functions of cell-wall associated proteins in bacterial pathogenesis
- Adhere to matrix proteins (like fibrinogen)
- Help with biofilm formation
- Evasion of host immune defenses
- Nutrient acquisition
- Invasion
What is acquired/induced tolerance
Where tolerance to external antigens can be created by manipulation of the immune system
Give one example of low-antigenicity
Pasteurella - have a thick layer of HA on their capsule so the host won’t recognize it
Give one example of inhibition of phagocytosis
Long O antigen on gram-negative bacteria - when phagocyte binds its really far away from the cell surface
Give one example of inhibition of inflammation
IL-10 secreted by mycobacterial infected macrophage
Immunosuppressive cytokine that inhibits further macrophage activation
Give one example of inhibition of chemotaxis
CHIPS - produced by staphylococcus
Blocks action of C5a
Give one example of phagocyte killing
Salmonella (using SPI1) induces programmed cell death
Give one example of intracellular survival
M. tuberculosis prevents phagolysosome fusion by release bacterial cell wall components to modify the lysosomal membrane
Give one exampleof concealment
Staph and strep bind IgG the wrong way so that phagocytes cannot bind
Give one example of antigenic variation
Salmonella switches its surface antigens (especially the flagellin, H antigen)
Give one example of extracellular products for immune evasion
Secreted antigens - staphylococcal teichoic acid bind opsonin’s so that it prevents their interaction with the actual bacteria
List 3 forms of direct damage
Metabolic, cytolytic, extracellular enzymes
List 2 subclasses of exotoxins
Membrane damaging and cellular modifying
List 2 examples of cellular modifying exotoxins (AB toxin)
E. coli LT toxin and C. diphtheria
How does LPS act as an endotoxin
A lysed gram negative cell will release LPS which will bind to LPS binding protein, this complex will bind to a macrophage which causes it to release inflammatory cytokines and initiating blood clotting factors
What function does the mycolic acid in mycobacteria cell wall provide for pathogenicity
Resists phagocytic digestion
What is a key feature of mycobacteria pathogenesis
They can survive inside macrophages and dendritic cells
How does IFN-gamma participate in granuloma formation to mycobacteria
It helps activated macrophages and stimulates phagolysosome fusion so it kills the bacterial cells - this causes caseous necrosis inside the granuloma
Define sensitivity
The probability that a truly infected animal will test positive
Define specificity
The probability that an uninfected animal will test negative
Which strep bacteria is a causative agent of summer mastitis
Strep dysgalactiae
Which strep bacteria is a causative agent of environmental mastitis
Strep uberis
Define the three forms of haemolysis seen by strep species
Alpha - incomplete, green zone
Beta - complete clear zone
Gamma - no haemolysis
Classification of strep species is generally based on what?
Haemolysis, cell wall antigens and sugar fermentation
Which virulence factor is likely responsible for antigenic variation in S. equi supsp equi
M protein
Which streptolysin is oxygen stable?
SLS
Which streptococcal virulence factor is a superantigen
Streptococcal pyrogenic exotoxin
What is a major clinical sign of later infection with strangles
Lymphadenopathy
What is an elementary body
Extracellular infective stage of Chlamyidae
What is a reticulate body
Non-infective intracellular replicative stage of Chlamydiae
What does the T3SS of chlyamdia do
Injects the effector protein TARP to induce host cell actin remodeling and get inside the cell
List 2 chlamyidae species with proven zoonotic transmission
C. abortus and C. psittaci
Is chlamydia intracellular or extracellular?
Intracellular
What are two major clinical presentations of chlamydia infection
Pneumonia and conjunctivitis (ocular infection)
What is the most common chlamydial infection in sheep/which species is associated with koalas
Chlamydia pecorum
What is protective immunity
Host immune response stops the disease from occurring but the infectious agent is still there
What is sterile immunity
The host immune system eradicates the pathogen from the body
Name three species of clostridia to cause histiotoxic infections and the name of their disease
- C. novyi - black’s disease of sheep
- C. chauvoei - black leg
- C. perfringens - gangrene
Name two species of clostridia to cause enteropathogenic disease
- C. botulinum
- C. perfringens
What is characteristic of C. tetani spores
Drumstick shape
What are two major groups of histotoxic clostridia toxins
Lecithinase and necrotising
What is different about C. tetani infection and C. botulinum infection (in terms of clinical presentation)
C. tetani prevents the release of inhibitory neurotransmitters so there is an overstimulation of the motor neurons in the CNS
C. botulinum prevents the fusion of synapse vesicles at the neuromuscular junction preventing the release of ACh so there is a lack of stimulation
Which type of C. perfringens causes enterotoxaemia
Type D
Which type of C. perfringens causes dysentery
Type B/C
Which type(s) of C. botulinum primarily affects animals
Types C and D
Salmonella: LF or NLF
Non-lactose fermenting
What do salmonella use as their TEA
Tetrathionate
What are two non-host adapted strains of salmonella
S. typhimurium and S. enteriditis
What is the most common salmonella serovar isolated from pigs
S. typhimurium
What is are primary functions of the T3SSs of salmonella
T3SS-1 : inject effectors to induce cytoskeletal rearrangement
T3SS-2 : secretes proteins to prevent assembly of the phagolysosome
Name 3 disease syndromes causes by salmonella
Enteritis, septicemia, abortion
