FINAL General REVIEW Flashcards
Which of the following statements is false for Histophilius somenei?
a. It is an obligate pathogen
b. can cause neurological symptoms
c. colonizes urogential tract
d. causes intravasuclar cogaulation
A
Histophilius somenei is normally seen in the respiratory track of animals. THEREFORE, it is NOT an obligate pathogen. It’s an opporuntisitic pathogen
VTEC infections do NOT cause…
diarrhea.
VTECH causes edema disease
STa is a highly immunogenic toxin of ETEC. True or False
FALSE
You can use it in exams
A dog presents to your clinic with febrile illness and lameness. You are in an endemic area for Amblyomma americanum ticks and suspect a tick-borne disease. Examination of a blood smear reveals a small number of infected neutrophils that include a bacterial morulae. Which of the following etiologic agents may be the cause?
A. Anaplasma phagocytophilum
B. Ehrlichia canis
C. Ehrilicha ewingii
D. A or C
E. any of the above
C
Bacteria do not have
Nucleus, histones, membrane bound organelles(mitochrondia, lysomes, etc)
HAVE: complex cell wall, peptiodgylcan, chrosomes, ribosomes,
Choose the correct statements:
A. All bacteria have a cell membrane
B. Mycobacteria have lipopolysaccharide
C. Peptiodoglycan is present only in Gram positive Bacteria
D. Mycobacteria are the only acid fast positive bacteria
E. Teichoic acid is unique to gram positive bacteria
E.
What is present and what is absent in bacteria?
Prokaryotes (No nucleus)
Complex cell wall
A single circular chromosome (exceptions ?)
Asexual reproduction (binary fission)
Absent:
No sterol
Membrane bound organelles are absent
and no histones
Ribosomes (smaller) 70s
No cytoskeleton
Identify the mismatched pair
A. Flagella- motility
B. Fimbriae- adherence
C. Capsule- protect from phagocytosis
D. spores- survivial
E. Endoflagella- Campylobacter
E. because Camplyobacter is not a spirocte and only spirocytes have endoflagella
Size of the bacteria are critical to the virulence of a bacterial species
T/F
FALSE
Bacterial cell wall Summary
All bacteria contains peptidoglycan (exceptions?)
Gram positive bacteria have a thick peptidoglycan layer
Only Gram negative bacteria has an outer membrane which contain lipopolysaccharide(LPS)
Lipid A /endotoxin is harmful
Limulus amebocyte test is used to detect endotoxin(Lipid A) Gram Positive bacteria contain Teichoic acid on their cell walls
Mycobacteria contain mycolic acid and contribute to acid fast positive staining
Choose the incorrect statement:
A. All fungi are eukaryotes
B. Yeasts are unicellular
C. Hyphae are multicelluar
D. Dimorphic fungi exist in yeast and mold form
E. Fungal cell membrane contains sterols
F. Fungal cell wall contain petidogylcan
F- petidoglycan is only in bacteria
Which of the following is not a dimorphic yeast?
A. Blastomyces
B. Histoplasma
C. Coccidiodies
D. Cryptococcus
D- Cryptococcus is not a dimorphic yeast
The other dimorphic yeast is sporthrix
Animal A Brucella titer= 1:256
Animal B Brucella titer 1:16
who has the higher antibodies in the serum?
Animal A
Choose the incorrect statement regarding antibody titer:
A. A positive antibody titer is always diganostic
B. False positive repsonse can be due to previous exposure or vaccination
C. Flase negatives responses can occur ue to early infecgion
D. False negative result can occur due to anergy in the late stages of the disease
E. Four fold increase in the convalescent titer is suggestive of an active infectin.
A- you have to have a PAIRED titer to say that an animal is positive
Does Mycobacteria have lipopolysaccharide?
NO!!!
Bacterial structures can enhance the
Bacterial structures can enhance the virulence of bacteria
How do we identify bacteria?
Presence or absence of these structures are used in the
identification of bacteria
Flagella:
Locomotion or motility
Fimbriae or pili:
Fimbriae or pili: Adherence
Endoflagella/axial filaments
Endoflagella/axial filaments are present in spirochetes
What is the purpose of the capsule?
Capsule helps to evade phagocytosis
What is the purpose of the spores?
Spores helps in bacterial survival
Pathogenicity
Pathogenicity is the ability of a pathogen to produce a disease by overcoming the defense mechanisms of the host.
Virulence
Virulence is the degree of pathogenicity
What is imporant for the pathogenitiy of a bacteria?
- Number of organisms
- Virulence factors
- Status of host immune response
What are bacterical virulence factors?
Fimbriae, flagella, Capsule, Toxins: (exotoxins and endotoxins) Superantigens.
Transfer of virulence factors can be mediated through Plasmids, and bacteriophages by processes such as conjugation, transformation, and transduction
Quorum sensing
Biofilms
quorum sensing
Quorum sensing is a system of stimulae and response correlated to population density. Many species of bacteria use quorum sensing to coordinate gene expression according to the density of their local population.
Biofilm
A biofilm is any group of microorganisms in which cells stick to each other on a surface. These adherent cells are frequently embedded within a self-produced matrix of extracellular polymeric substance (EPS)
Exotoxins are seen in
gram positive
Endotoxins are in
gram negative
Damage caused by bacteria
Damage caused by bacteria
Using the host’s nutrients
Direct damage to the host cell (Toxins) Hypersensitivity reactions
(Type IV Hypersensitivity- Tuberculosis)
Obligate pathogen means that
if the pathogen is present, then there is a disease present
What is the morphology of Rhodococcus?
It’s a rod!
Are gram negative cocci common?
NO!!! They are very, very rare.
Fungus summary
Fungus: Summary
Eukaryotes
Eukaryotic
Sterols present (ergosterol)in the cell membrane
Contains glucans, mannans, chitin (No peptidoglycan)
Unicellular-Yeast
Multicellular –Molds (hyphae)
Dimorphic Fungus
Sexual and asexual reproduction
Polyphasic approach is necessary for accurate identification(morphology and DNA sequencing)
Seroconversion
Antibody development after exposure to a pathogen or an antigen
Antibody Titer
Antibody Titer
Measurement of antibody level (quantity),usually expressed as the reciprocal of the highest dilution of serum that positively reacts in a specific test
eg. a titer of 256 in a test means that the serum sample remains positive when diluted 1:256.
It is the highest dilution of the serum sample which give a positive result in a particular test
Interpretation of tests that measure immune response to an agent
- Generation of an immune response requires time 2. Immune response may persist
“Compare acute and convalescent phase samples”-
Paired serology titers: Four fold increase in serum titers are indicative of infection
(IgM to IgG conversion for T cell dependent responses)
False positives:
prior antigen exposure, vaccination, cross-reactions
False negatives:
Early stages of infection,Late in infection due to anergy, immunosuppression
Can any bacteria can opportunistically infect any of the body systems?
YES!
When can false positives occur?
Understand that False positive and False negative results can occur due to sampling, transport, storage issues, antimicrobial therapy, presence of fastidious organisms or when specific procedures are needed
What is a Susceptibility break point?
A drug concentration above which an organism is considered resistant and at or below this value organism is susceptible to that drug.
Generally for AST testing purposes, three break point values are set at Susceptible, Intermediate, or Resistant
What is Minimum inhibitory concentration (MIC)?
Minimum amount of drug required to inhibit bacterial growth Drugs with lower MIC values are better choices
Disk Diffusion (‘Kirby Bauer’)
Must use a bacterial isolate in pure culture
QUALATATIVE TEST- THEREFORE NO MIC VALUES
Standardized bacterial inoculum spread on an agar
plate
Single-concentration antimicrobial disks are used
Growth inhibition zone diameter measured
Published reference breakpoints (zone size) to interpret results
Different drugs will have different zone sizes based on the published data
Broth Dilution
• Multiple dilutions of antimicrobial agents (usually 2-fold serial dilutions)
Use published reference breakpoints to interpret
• Measure AND report growth inhibition
endpoint (MIC) (MIC reported in micrograms per milliliter)
Will you get full range or partial range(breakpoint) from a normal diagnostic laboratory?
partial range
Gradient diffusion test
E-Test (Diffusion and Dilution)
strip test
gives MIC
Example of a Broad spectrum antibiotics
Broad spectrum antibiotics are active against a wide variety of bacteria Eg. Tetracycline
Example of a narrow spectrum antibiotic
Narrow spectrum antibiotics affect only a narrow range of bacteria
Eg. Penicillin
Time dependant killing:
Length of time bacteria are exposed to these antibiotic at a concentration above MIC
( Need frequent dosing or constant infusions)
Beta-lactams, macrolides, tetracyclines, lincosamides, chloramphenicol potentiated sulfonmides(Cefovecin exception protein binding above MIC for 7 days)
Concentration dependant killing
Rate of killing increases as the drug concentration in plasma increases above MIC High dosing at long intervals (once daily dose)
Prolonged post antibiotic effect
Fluoroquinolones, Aminoglycosides, Metronidazole
Antifungal drugs act at the
cell membrance/sterols
Innate resistance
(preexisting genomic property)
Acquired resistance
(by mutation or horizontal gene transfer)
