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70 Cards in this Set
- Front
- Back
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Describe the colour (in a Gram stained specimen) of Gram pos and Gram neg bacteria.
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<b> Gram pos: dark blue/purple
Gram neg: red/pink </b> |
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Describe 3 important parts of the bacterial liposaccharide!
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<b> lipid A </b>
<b> core polysaccharide <b/> O-specific (polysaccharide) <b> side chain </b> |
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Which 2 roles are attributed to bacterial pili (fimbriae)?
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<b> Adhesion
Conjugation </b> (sex fimbriae) |
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Mention a bacterium and its virulence factor that is encoded by lysogenic bacteriophage?
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<b> Cornybacterium diptheriae - diptheria toxin </b>
Streptococcus pyogenes - erthrogenic toxin |
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Specify 2 genera containing obligate intracellular pathogens!
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<b> Chlamydia
Rickettsia </b> |
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Mention at least 5 possible transmission ways of infections!
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<b> Respiratory droplets </b> (infectious aerosol)
<b> Faecal-oral </b> <b> Direct contact </b> (sexual) <b> Fomites </b> (inanimate objects) <b> Blood </b> <b> Vectors </b>(blood sucking anthropods) |
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List the possible shapes of bacteria and give one example per category
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<b> Coccus </b> (spherical) - Straphlococcus, Streptococcus
<b> Rod </b> - Clostridium, Cornyebacterium, Gram neg rods <b> Curved rod </b> - Vibrio <b> Helical </b> - Spirochetes (Treponema, Borrelia, Leptospira) |
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What are the essential components of bacterial cells?
At least 3 |
<b> Cytoplasm
Nucleoid (genome) Cell Membrane </b> (cell wall) |
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What is a vector? Give an example
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Vector is an <b> arthropod </b> that <b> transmits infection </b> from human to human, or from animal to human
eg: tick + Lyme disease; louse + epidemic typhus; mosquito + malaria |
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What is a reservoir? Write an example
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<b> Normal host </b> of a pathogen (human or animal) serving as a continuous <b> source of infection </b> to other hosts (such as humans)
Salmonella typhi - human Yersinia pestis - rodents |
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3 reliable methods of sterilization.
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<b> Autoclaving
Hot air oven Gamma radiation Filtration Gas sterilisation </b> |
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Mention 5 groups of disinfectants
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<b> Alcohols
Aldehydes Phenol derivatives Chlorine + Iodine </b> (Oxidising agents) <b> Detergents </b> |
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Mention a group of antimicrobial drugs that act on bacterial ribosome and usually has bactericidal effect
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<b> Aminoglycosides </b>
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Describe precisely what a toxoid is
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<b> An inactivated bacterial exotoxin that has an immunogenic effect but is not toxic </b>
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Mention 2 broad spectrum (Gram+ and Gram- bacteria) penicillin derivitives
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<b> Ampicillin
Amoxicillin Piperacillin </b> Azlocillin Mezlocillin |
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Mention an antifungal and antibacterial drug that alter the function of the cell membrane
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Antifungal: Azoles, Amphotericin B
Antibacterial: Polymixins |
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At least 3 possible mechanisms of acquired penicillin resistance of bacteria?
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<b> Beta lactamase production
PBP alteration </b> (target) <b> Active efflux Reduced permiability </b> |
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Mention a drug belonging to the Macrolides ?
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<b> Erythromycin </b>
Spiramycin Roxithyromicin Clarithromycin Azithromycin |
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Mention 2 drugs belonging to the Aminoglycosides
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<b> Streptomycin
Gentomycin </b> Tobramycin Amikacin |
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Mention 2 groups of antimicrobial drugs that act on the 30S subunit of bacterial ribosome
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<b>Aminoglycide
Tetracyclines </b> |
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Mention 3 groups of antibacterial drugs that inhibit bacterial cell wall synthesis.
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<b> Penicillin
Cephalosporins Glycopeptides </b> Carbapenems Monobactams |
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Which part of the cell wall contains the endotoxin?
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<b> Outer membrane </b> of Gram- bacteria
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What role is attributed to the bacterial capsule in the infectious process?
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<b> Antiphagocytic </b> effect
Adhesion |
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Mention 2 infectious diseases transmitted by tick bites
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<b> Tick borne encephalitis
Lyme disease Tularemia </b> Rocky Mountain spotted fever Recurrent fever (Borelia recurrentis) |
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Which type of hypersensitivity is involved in tubercilin test?
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<b>Late </b> type (Type IV)
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Mention 2 bacterial infectious diseases that can be prevented or treated by passive transfer of specific immunoglobins.
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Prevention: <b> Tetanus </b>
Treatment: <b> Diptheria, Botulism, Tetanus </b> |
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What do the vaccines against diphtheria and tetanus contain?
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Diphtheria and Tetanus <b> toxoid </b>
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What does the vaccine against pertussis contain?
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<u> Previously </u> <b> killed </b> bacteria
<u> Currently <u/> <b> acellular </b> vaccine (toxoid and other purified proteins) |
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What does the vaccine against tuberculosis (BCG) contain?
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<b> Live attentuated Mycobacterium bovis </b>
(Bacille Calmette-Guerin) |
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What is the nature of the antigen in the vaccines used to prevent infections by <i> Streptococcus pneumoniae, Haemophilus influenza </i> and <i> Neisseria meningitidis </i>
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<b> Capsular polysaccharide </b>
(either alone or conjugated to a carrier protein) |
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Mention 2 bacterial exotoxins that are neurotoxic!
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<b> Tetanus toxic
Botulinum toxin </b> |
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Specify the 4 groups of bacterial vaccines according to the nature of the antigen
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(a) <b> Live attenuated vaccines </b>
(b) <b> killed bacterial vaccines </b> (c) toxoid vaccines </b> (d) subunit vaccines </b> |
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What is the mechanism of lysosome? Where is lysosome located in the host?
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<b> It destroys the cell wall peptidoglycan by hydrolysing the glycosol bonds between the NAM (N-acetylmuramacid) and the NAG (N-acetylglucosamine).
It occurs in tears, saliva, respiratory secretions </b> |
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Which Gram- organelles or structures are associated with the O, H and K antigens respectively?
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O <b> LPS </b>
H <b> Flagella </b> K <b> Capsule </b> |
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Mention 2 bacterial exotoxins that act by ADP ribosylation?
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<b> Diptheria toxin
Cholera toxin Pertussis toxin </b> |
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Describe the rules for collecting <u> native </u> urine for culturing bacteria? Describe the conditions for keeping the specimen before sending it to the lab.
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<b> A midstream specimen, taken preferably in the morning, after a thorough cleaning of the external genital area.
Keep up to 1 hour at room temp or up to 24 hours at +4C </b> |
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Describe the rules for collecting hemoculture specimens
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Rxd to collect <b> 3 specimens </b> (with at least 30mins btw specimens)
Specimens should be preferably taken <b> before fever spikes (ie during rising fever) from fresh peripheral venipuncture sites </b> If possible <b> both anaerobic and aerobic </b> bottles should used (3x2 bottles altogether). The site of the <b> venipuncture and plug of the bottle </b> containing the sample must be <b> disinfected </b> . The amount of blood injected should be 10% of the collected medium. |
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Mention two clinical specimens that are heavily contaminated with bacteria belonging to the normal body fauna.
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<b> Throat and nasal secretions
Faeces Vaginal secretions |
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Mention at least 3 of the physiological effects of septic shock (characterized by the presence of large amount of bacterial endotoxin in the blood)
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<b> Fever
Hypotension Disseminated Intravascular Coagulation (DIC) Complement activation </b> impaired organ perfusion hypoglycemia |
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What pathogenic role is attributed to lysogenic conversion.
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Lysogenic conversions: transfer of genes from one bacterium to another lysogenic bacteriophages.
The bacteria may <b> gain exotoxins </b> (diptheria toxin, Streptococcus pyogenes erythrogenic toxin) The structure of <b> LPS epitopes may be altered </b> (Shigella, Salmonella) |
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Describe the principle of acid fast staining procedures
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Mycobacteria contain a high number of special lipids called <b> mycolic acids </b> . They can be stained by hot carbol-fuschin, but they <b> resist decolourisation with acid-alcohol </b> , so they remain red. All other cells are stained blue by the counter stain (methylene blue).
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Mention 2 non essential bacterial organelles that enhance bacterial virulance. Describe how they function contributes to pathogenicity
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<b> Capsule: antiphagocytic effect, adhesion to tissue
Fimbriae: binding to tissues Flagellae: spreading the bacteria </b> |
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Mention a differentiating culture medium and describe which groups of bacteria are distinguished on the mentioned medium
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<u> Eosin-Methylene blue (EMB) agar </u>: <b> Inhibits Gram+ </b> bacteria and inhibits swarming of Proteus. Differentiates <b> between lactose fermenters and non-fermenters </b>. Lactose fermenters produce high amounts of acids, which is indicated as dark blue colonies by Eo & Me Blue
<u> McConkey Blue </u> : <b> Inhibits Gram+ bacteria </b> by bile salts and crystal violet. It differentiates between <b> between lactose fermenters and non-fermenters </b> . Lactose production indicated by neutral red. Lactose fermenters form pink to red colonies, while non-fermenters form colourless colonies. |
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Describe the definition for facultative anaerobic bacteria
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They are able to grow and metabolize <b> both in the presence and absence of oxygen </b> .
In aerobic conditions they perform respiration. In anaerobic conditions they perform fermentation. |
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Mention 4 extracellular enzymes of bacterial origin functioning as virulance factors.
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<b> Coagulase
Streptokinase (fibrinolysine) Streptodornase (DNase) Hyaluronidase IgA protease Collagenase Elastase Urease</b> |
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What is the difference between prevalence and incidence of infectious disease?
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It can be differentiated in <b> chronic diseases </b>
<b> Prevalence: Total number </b> of diseases (per 100,000 people <b> Incidence: Number of new cases </b> in a year (per 100,000) |
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What is the difference between mortality and lethality of a disease?
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<b> Mortality: total number of deaths </b> caused by the disease in a population
<b> Lethality: rate of death (%) </b> among patients suffering from the disease |
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Mention 2 groups of disinfectants acting on the microbial membrane structures
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<b> (cationic) detergents </b> (quaternary ammonium-compounds)
<b> phenol compounds </b> (cresol, hexochlorophene, chlorohexidine) <b> alcohols </b> (ethanol, isopropanol) |
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Describe the Kirby-Bauer (disk diffusion) method to determine antibiotic sensitivity
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<b> disk impregnated </b> with different antibiotics are placed on the surface of appropriate agar media that has been innoculated with the bacteria isolated from the patient. After overnight incubation the <b> antibiotics diffusing from the disks </b> may cause zones of inhibition around the disks. The <b> size of the zone </b> should be compared to standards to determine antibiotic sensitivity.
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Explain the purpose for using beta-lactamase inhibitors in antibacterial therapy
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Combination of beta-lactamase inhibitors (such as <b> clavulanic acid or sulbactam </b> with beta-lactamase sensitive penicillins (such as <b> amoxicillin or ampicillin) can overcome resistance mediated by many but not all beta lactamases </b>
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What are the main advantages and disadvantages of live attenuated vaccines as
compared to killed vaccines? |
<b> Advantages: </b> induce not only serum antibodies but also <b> cellular immunity and local IgA </b>. Some may be applied orally. Usually <b> fewer doses </b> are needed
<b> Disadvantages: </b> Attenuated strains may <b> revert to virulent </b> in rare cases. This may <b> lead to disease in the immuonsuppressed </b> patients. Live attentuated microbes are usually heat sensitive and must be refrigerated. |
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Mention 4 groups of antibiotics which have bactericidal effects!
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<b> Penicillins
Cephalosporins Aminoglycosides Fluoroquinolons </b> |
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Which antibiotics inhibit bacterial DNA gyrase enzyme?
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<b> Nalidixic acids
Fluoroquinolons </b> |
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What is the mode of action of the antibiotics sulfonamides and thrimethoprim,
respectively? |
They inhibit the synthesis of folic acid.
Sulfonamides inhibit the synthesis of dihydrofolate (PABA analogues) Thrimetethoprim: inhibit the dihrofolate redcutase |
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What is the mode of action of the antibiotic vancomycin?
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Inhibit cell wall synthesis in Gram+ bacteria by <b> blocking transpeptidation </b>
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Mention 4 groups of antibiotics inhibiting protein synthesis of bacteria!
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<b> Aminoglycosides
Tetracyclines Chloramphenicol Macrolides Lincosamides </b> |
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Regarding the joint effects of 2 antibiotics, what does synergism mean?
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<b> The effect of the two drugs together is significantly higher than the sum of the effects of the two drugs acting seperately </b>
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Regarding the joint effects of 2 antibiotics, what does antagonism mean?
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<b> The effect of the two drugs working together is significantly lower than the effect of the more effective drug alone </b>
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What does selective toxicity mean?
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<b> Selective inhibition of the growth of the microorganism without damage to the host </b>
In other words the drug is highly toxic to the bacteria but not toxic (or have very low toxicity to the human host |
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How can one identify the different surface antigens of Gram negative bacteria?
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<b> With slide agglutination tests using antibodies of known specificity </b>
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What is the mechanism of action of diphtheria toxin?
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<b> Inhibition of protein synthesis </b> in ekaryotic cells by <b> ADP ribosylation of ribosomal EF-2 </b>
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What is the mechanism of action of tetanus toxin?
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It causes <b> spastic paralysis by blocking the release of inhibitory nuerotransmittors </b> (glycine and GABA) in the synapses
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What roles can be attributed to specific antibodies in antibacterial immunity? Specify at
least 3! |
(a) <b> Neutralisation of the exotoxins and enzymes
(b) complement dependent <b> bacteriolysis </b> (Gram-) (c) <b> opsonisation </b> (helping phagocytosis) (d) <b> interfering with attachment </b> of bacteria to mucosal surfaces |
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Starting from a fixed smear, specify the main steps of Gram stain in the appropriate
order! |
1. Crystal violet
2. Lugol solution (iodine) 3. Differentiation: ethanol wash 4. Counterstaining: safaranin or fuchsin (wash with water after each step) |
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Starting from a fixed smear, specify the main steps of the acid-fast stain (Ziehl-Neelsen)
in the appropriate order! |
1. Stain with carbol-fuchsin (with heating)
2. Differentiation: wash with acid-ethanol 3. Counterstaining with methylene-blue (wash with tap water after each step) |
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What is the difference between agglutination and precipitation?
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Both are serological reactions where the specific binding of the antigen with the antibody directly results in a reaction visible to the naked eye. The difference is in the nature of the antigen.
<b> Agglutination: particulate antigen </b> (RBC, bacteria, latex particles <b> Precipitation: antigen is in the solution </b> before the reaction |
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What does titer mean in serological tests?
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The <b> highest dilution </b> of the serum sample that gives a <b> positive </b> reaction to the test
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How can one differentiate between past and current infections in serological tests?
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Current infections are indicated by either <b> IgM class </b> specific antibodies or in the case of paired serum specimens (taken from the same patient at least 7-10 days apart), <b> a significant (at least 4-fold) rise in the titer </b> of specific antibodies
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Specify the main steps of an ELISA test in which we detect antibodies from patients’
serum samples using known antigens! |
1. <b> Binding antigen </b> to plastic surface (in wells of a 96-well plate)
2. Adding <b> diluted serum <b/> sample (specific antibodies bind to the antigen) 3.Adding <b> conjugate </b> (secondary antibody conjugated with an enzyme) 4. Adding the <b> substrate </b> of the enzyme, reading the colour reaction. (wash with buffer after steps 1-3.) |
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How can one determine the minimal inhibitory concentration (MIC) of an antibiotic to a
bacterial isolate? |
Inoculate the bacterial isolate into a series of test tubes containing 2-fold dilution series of the drug (prepared in appropriate liquid culture medium). After overnight incubation the <b> lowest concentration of the drug that prevents visible growth </b> of the organism is the MIC
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