This site is 100% ad supported. Please add an exception to adblock for this site.

3rd year Open questions for Micro 1st SCT


undefined, object
copy deck
Describe the color of Gram positive and gram negative bacteria respectively
Gram Positive : Dark Blue
Gram Negative : Red/PinkC
Describe the structure of the bacteriall LPS
Lipid A + core polysaccharide + O-Specific (polysaccharide) side chain
What role is attributed to bacterial Pilli(Fimbriae)?
Adhesion, Conjugation(sex fimbriae)
Mention a bacterium and its virulence factor that is encodd by a lysogenic bacteriophage
Corynebacterium diphteriae - diphteria toxin; Streptococcus Pyogenes - erythrogenic toxin
Specify the bacterial genera containing obligate intracellular pathogens
Chlamydia, Rickettsia (Coxiella, Ehrlichia)
Mention at least 5 possible tranmission ways of infections
1. Respiratory droplets (infectious aerosol)
2. Faecal-oral
3. Direct contact (such as sexual)
4. Fomites (inanimate objects)
5. Blood
6. Vectors (blood-sucking arthropods)
List the possible shapes of bacteria. Write one example per category
Coccus(spherical): Staphylococcus, Streptococcus;
Rod : Clostridium
Curved rod : Vibrio;
Spiral : Spirochetes
What are the essential components of bacterial cells?
Cytoplasm, nucleoid(genome), cell membrane,(cell wall)
What is a vector? write an example.
Vector is an arthropod that transmits infection from human to humanm, or from animal to human. Example - ticks - lyme disease
What is a reservoir ? Write an example.
The normal host of a pathogen (human or animal) serving as a continous source of inection to other hosts. Example - Salmonella typhi - human
Mention 3 reliable methods of sterilization
Autoclaving, Hot air oven(dry heat), filtration(fluids)
Mention 5 groups of disinfectants
Alcohols, Aldehydes, Phenol derivatives, detergents, Chlorine+Iodine = oxidising agents
Mention a group of antimicrobial drugs that act on the bacterial ribosome and usually
has bactericidal effect!
Describe precisely what toxoid means!
Inactivated bacterial exotoxin that is not toxic but immunogenic
Mention 3 broad-spectrum (effective against both Gram positive and Gram negative
bacteria) penicillin derivatives.
ampicillin, amoxicillin, piperacillin,
Mention an antifungal and an antibacterial drug that alter the function of the cell
antifungal: Amphotericin B, azoles; antibacterial: polymyxins
What are the possible mechanisms of acquired penicillin resistance of bacteria? Mention
at least 3 mechanisms!
1. beta-lactamase production
2. PBP (target) alteration
3. active efflux
Mention a drug belonging to macrolides!
erythromycin, spiramycin
Mention 2 drugs belonging to aminoglycosides
streptomycin, gentamycin
Mention 2 groups of antimicrobial drugs that act on the 30 S subunit of the bacterial
aminoglycosides, tetracyclines
Mention 2 groups of antibacterial drugs inhibiting the cell wall synthesis!
penicillins, cephalosporins
Which part of the bacterial cell carries the endotoxin?
Outer membrane of Gram negative bacteria
What role is attributed to the bacterial capsule in the infectious process?
antiphagocytic effect, adhesion
Mention 2 infectious diseases that are transmitted to humans by tick bites!
tick-borne encephalitis; Lyme-disease
Which type of hypersensitivity is involved in the tuberculin test?
late type (type IV)
Mention 2 bacterial infectious diseases that can be prevented or treated by passive
transfer of specific immunoglobulins!
prevention: tetanus
treatment: diphtheria, botulism, tetanus
What is (are) the nature(s) of antigen(s) in the combined vaccine against diphtheria,
pertussis and tetanus (DPT)?
Diphtheria and tetanus toxoid
Pertussis: killed bacteria or acellular vaccine (toxoid + other purified proteins)
What is (are) the nature(s) of antigen(s) in the vaccine against tuberculosis (BCG)?
live attenuated Mycobacterium bovis (Bacille Calmette-Guerin)
What is the nature of antigen in the vaccines used to prevent infections by Streptococcus
pneumoniae, Haemophilus influenzae and Neisseria meningitidis?
capsular polysaccharide
Mention 2 bacterial exotoxins that are neurotoxic!
tetanus toxin, botulinum toxin
Categorize the bacterial vaccines used in active immunisation according to the nature
of antigen!
a., live, attenuated vaccines
b., killed bacterial vaccines
c., toxoid vaccines
d., subunit vaccines (capsular polysaccharide or purified protein)
What is the mechanism of action of lysozyme? Where is lysozyme found in the host?
It destroys bacterial cell wall peptidoglycan by hydrolysing the peptide bonds
between NAM (N-acetylmuramicacid) and NAG (N-acetylglucosamine). Occurs in
tear, saliva, respiratory secretions
Which Gram negative organelles are associated with the O, H and K antigens,
O- LPS, H-flagella, K-capsule
Mention 2 bacterial exotoxins that act by ADP ribosylation!
Diphtheria toxin, cholera toxin
Describe the rules of collecting native urine for culturing bacteria! Describe also the
conditions for keeping the specimen before sending it to the laboratory
A midstream specimen, taken preferably in the morning, after thorough cleaning of
the external genital area. Keep it up to 1 h at room temperature or up to 24 h at +4
Describe the rules of collecting hemoculture specimens?
It is important to obtain at least 3 specimens (with at least 30 min. between the
specimens). The specimens should be preferably taken during fever spikes. If possible,
both aerobic and anaerobic bottles should be used (3 x 2 bottles altogether). The site of
venipuncture and the plug of the bottle containing the medium must be properly
disinfected. The amount of blood injected to the bottle should be about 10 % of the liquid
medium. Keep the specimen under conditions recommended by the manufacturer of the
medium (room temperature or 37 C degree).
Mention two clinical specimens that are heavily contaminated with bacteria belonging
to the normal body flora!
throat and nasal secretions, faeces, vaginal secretions.
Mention at least three of the physiological effects of septic shock (characterized by the
presence of large amount of bacterial endotoxin in the blood)!
fever, hypotension, disseminated intravascular coagulation (DIC)
What pathogenic role is attributed to lysogenic conversion?
Lysogenic conversion: transfer of genes from one bacterium to another by lysogenic
bacteriophages. The bacteria may gain exotoxins (diphtheria toxin, Streptococcus
pyogenes erythrogenic toxin), or the structure of LPS epitopes may be altered (Shigella,
Mention 3 mechanisms by which bacteria can evade the host's immune defences!
Capsule, fimbria, M protein: inhibit phagocytosis
leucocidin (S. aureus): destroy phagocytic cells
inhibition of phagosome-lysosome fusion (mycobac
Describe the principle of acid fast staining procedures!
Mycobacteria contain a high amount of special lipids called mycolic acids. They can be
stained by hot carbol-fuchsin, but they resist decolourisation with acid-alcohol, so they
remain red. All other cells are stained blue by the counter stain (methylene blue).
Mention 2 non-essential bacterial organelles that enhance bacterial virulence! Describe
how their function contributes to pathogenicity!
Capsule: antiphagocyter effect, adhesion to tissues
Fimbriae: binding to tissues
Mention a differentiating culture medium and describe which groups of bacteria are
distinguished on the mentioned medium!
Eosin-methylene blue (EMB) agar: Inhibits Gram positive bacteria and inhibits the
swarming of Proteus. Differentiates between lactose fermenters and non-fermenters.
Lactose fermenters produce high amounts of acids, which is indicated as dark blue
colonies by eosin and methylene blue.
McConkey agar: Inhibits Gram positive bacteria by bile salts and crystal violet.
Differentiates between lactose fermenters and non-fermenters. Lactose fermentation is
indicated by neutral red. Lactose fermenters form pink to red colonies, while nonfermenters
form colourless colonies.
Describe the definition for facultative anaerobic bacteria!
They are able to grow and metabolize both in the presence and in the absence of
oxygen. In aerobic conditions they perform respiration, in anaerobic condition, they
perform fermentation.
Mention 4 extracellular enzymes of bacterial origin functioning as virulence factors!
protease, collagenase, elastase
What is the difference between prevalence and incidence of an infectious disease?
It can be differentiated in chronical diseases. Prevalence: total number of diseases (per
100,000 people). Incidence: number of new cases in a year (per 100,000 people).
What is the difference between mortality and lethality of a disease?
Mortality: total number of deaths caused by that disease in a population (usually 100,000
people). Lethality: rate of death (in percent) among patients suffering from that disease.
Mention 2 groups of disinfectants acting on the microbial membrane structures!
a., (cationic) detergents (quaternary ammonium-compounds);c., alcohol (ethanol, isopropanol)
Describe the principals of the Kirby-Bauer (disk diffusion) method of determining
antibiotic sensitivity!
Disks impregnated with different antibiotics are placed on the surface of appropriate agar
media that has been inoculated with the bacterium isolated from the patient. After
overnight incubation, the antibiotics diffusing from the discs may cause zones of
inhibition around the discs. The size of the zone should be compared to standards to
determine antibiotic sensitivity
Explain the purpose for using beta-lactamase inhibitors in the antibacterial therapy!
Combination of beta-lactamase inhibitors (such as clavulanic acid or sulbactam) with
beta-lactamase sensitive penicillins (such as amoxicillin or ampicillin) can overcome
resistance mediated by many but not all beta-lactamases.
What are the advantages and disadvantages of live attenuated vaccines?
Advantages: induce not only serum antibodies but also cellular immunity and local IgA
antibodies. Some may be applied orally. Usually fewer doses are needed.
Disadvantages: Attenuated strains may revert to virulent in rare cases. They may cause disease in immunosuppressed patients. Live attenuated microbes are usually heat
sensitive and must be refrigerated.
Mention 4 groups of antibiotics which have bactericidal effects!
penicillins, cephalosporins, aminoglycosides, fluoroquinolons
Which antibiotics inhibit the enzyme DNA gyrase?
nalidixic acids, fluoroquinolons
What is the mode of action of the antibiotics sulfonamides and thrimethoprim,
They inhibit the synthesis of folic acid. Sulfonamides: inhibit the synthesis of dihidrofolate
(they are PABA analogues). Trimethoprim: inhibition of dihidrofolate-reductase.
What is the mode of action of the antibiotic vancomycin?
Inhibits cell wall synthesis in Gram positive bacteria by blocking transpeptidation.
Which groups of antibiotics inhibit protein synthesis?
Aminoglycosides, tetracyclines, chloramphenicol, macrolides (erythromycin ...),
(clindamycin, linezolid)
Regarding the joint effects of 2 antibiotics, what does synergism mean?
The effect of the two drugs together is significantly higher than the sum of the effects of
the two drugs acting separately.
Regarding the joint effects of 2 antibiotics, what does antagonism mean?
The effect of the two drugs together is significantly lower than the effect of the more
effective drug alone.
What does selective toxicity mean?
Selective inhibition of the growth of the microorganism without damage to the host. In
other words: the drug is highly toxic to the bacteria, but not toxic (or have very low
toxicity) to the human host.
How can one determine the different surface antigens of Gram negative bacteria?
with slide agglutination tests using antibodies of known specificity
What is the mechanism of action of diphtheria toxin?
Inhibition of protein synthesis in eukaryotic cells by ADP-ribosylation of ribosomal
EF-2 (elongation factor-2)
What is the mechanism of action of tetanus toxin?
It causes spastic paralysis by blocking the release of inhibitory neurotransmitters
(glycine) in synapses
What roles can be attributed to specific antibodies in antibacterial immunity?
a. neutralisation of exotoxins and enzymes
b. complement-dependent bacteriolysis (Gram-negatives)
c. opsonisation (helping phagocytosis)
d. interfering with attachment of bacteria to mucosal surfaces
Specify the main steps of Gram stain in the appropriate order!
Starting from a fixed smear:
1. Crystal violet
2. Lugol solution (iodine)
3. Differentiation: ethanol wash
4. Counterstaining: safranin or fuchsin
(wash with tap water after each step)
Specify the main steps of the acid-fast stain (Ziehl-Neelsen) in the appropriate order!
Starting from a fixed smear:
1. Stain with carbol-fuchsin (with heating)
2. Differentiation: wash with acid-ethanol
3. Counterstaining: methylene-blue
(wash with tap water after each step)
What is the difference between agglutination and precipitation?
Both are serological reactions where specific binding of the antigen with the antibody
directly results in a reaction visible by the naked eye. The difference is in the nature of the
antigen. Agglutination: particulate antigen (RBC, bacteria, latex particles).
Precipitation: antigen is in solution before the reaction.
What does titer mean in serological tests?
The highest dilution of the serum sample that gives a positive reaction in the test.
How can one differentiate between past and current infections in serological tests?
Current infections are indicated by: either IgM class specific antibodies or, in the case of
paired serum specimens, a significant (at least 4-fold) rise in the titer of specific
Specify the main steps of an ELISA test in which we detect antibodies from patients’
serum samples using known antigens!
1. Binding antigen to plastic surface (in wells of a 96-well plate)
2. Adding diluted serum sample (specific antibodies bind to the antigen)
3.Adding conjugate (secondary antibody conjugated with an enzyme)
4. Adding the substrate of the enzyme, reading the colour reaction.
(wash with buffer after steps 1-3.)
How can one determine the minimal inhibitory concentration of an antibiotic to a
bacterial isolate?
Inoculate the bacterial isolate into a series of test tubes containing 2-fold dilutions of the
drug. After overnight incubation, the lowest concentration of drug that prevents visible
growth of the organism is the MIC.

Deck Info