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 passivetransfer of specific immunoglobulins!
treatment: diphtheria, botulism, tetanus
What do the vaccine(s) against diphtheria and tetanus contain?
Diphtheria and tetanus toxoid
What does the vaccine against pertussis contain?
Previously: killed bacteria
Currently: acellular vaccine (toxoid + other purified proteins)
What does the vaccine against tuberculosis (BCG) contain?
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 (either alone or conjugated to a carrier protein)
Mention 2 bacterial exotoxins that are neurotoxic!
tetanus toxin, botulinum toxin
Specify the 4 groups of bacterial vaccines according to the nature of the 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 glycosyl bonds between NAM (N-acetylmuramicacid) and NAG (N-acetylglucosamine). It occurs in tear, saliva, respiratory secretions.
Which Gram negative organelles or structures are associated with the O, H and K antigens, respectively?
O- LPS, H-flagella, K-capsule
Mention 2 bacterial exotoxins that act by ADP ribosylation!
Diphtheria toxin, cholera toxin, pertussis 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°C.
Describe the rules of collecting hemoculture specimens!
It is recommended to obtain 3 specimens (with at least 30 min. between the specimens). The specimens should be preferably taken before fever spikes (during rising fever), from fresh peripheral venipuncture sites. 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.
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)!
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, Salmonella).
Describe the principle of acid fast staining procedures!
Mycobacteria contain a high amount of special lipids called mycolic acids. They can bestained 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: antiphagocytic effect, adhesion to tissues
Fimbriae: binding to tissues
Flagellae: spreading the bacteria
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 theswarming 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. It
differentiates between lactose fermenters
and non-fermenters. Lactose fermentation is
indicated by neutral red. Lactose fermenters form pink to red colonies, while
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!
Describe the principle of the Kirby-Bauer (disk diffusion) method used to determine 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 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 main advantages and disadvantages of live attenuated vaccines as compered to killed 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 etc.
Which antibiotics inhibit bacterial DNA gyrase enzyme?
nalidixic acids, fluoroquinolons
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 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.
Mention 4 groups of antibiotics inhibiting protein synthesis of bacteria!
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 identify 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 and GABA) in synapses
What roles can be attributed to specific antibodies in antibacterial immunity? Specify at least 3!
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
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: safranin or fuchsin
(wash with tap water after each step)
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)
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.
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 (taken from the same patient at least 7-10 days apart), a significant (at least 4-fold) rise in the titer of specific antibodies.
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 dilution series of the drug (prepared in appropriate liquid culture medium). After overnight incubation, the lowest concentration of drug that prevents visible growth of the organism is the MIC.
Mention 5 diseases that can be caused by Staphylococcus aureus!
Impetigo, furunculus, pneumonia, osteomyelitis, food poisoning etc.
Which bacteria cause most frequently typhoid fever and enteric fever, respectively?
Salmonella typhi (typhoid)
Salmonella paratyphi A, B, C (enteric fever)
When typhoid fever is suspected, what kinds of clinical samples should be used to isolate the causative agent in the first 2 weeks of the disease?
Blood, (bone marrow)
What is the route of infection in Salmonella gastroenteritis?
Ingestion of contaminated food (such as eggs, cream, mayonnaise, creamed foods, etc.)containing a sufficient number of Salmonella.
Which antibacterial drugs should be administered in gastroenteritis caused by Salmonella?
Antibiotics are not usually necessary unless the infection is generalised. In case of extraintestinal infection (very young, very old or immunosuppressed patients):ampicillin, gentamicin, trimethoprim/sulfamethoxazole, or ciprofloxacin.
List the 4 Shigella species causing human disease!
Shigella dysenteriae, S. flexneri, S. boydii, S. sonnei
Mention 2 bacterial species belonging to different genera that cause bacillary dysentery
Mention 2 bacteria causing intestinal infections which have animal reservoirs
Salmonella (not Typhi and Paratyphi!), Campylobacter jejuni, Yersinia enterocolitica, Listeria monocytogenes, E. coli O157
What are the modes of transmission for the 2 different epidemiologic forms of plague?
- Bubonic plague is transmitted by the bite of infected rat fleas from rats to humans.
- Primary pneumonic plague spreads directly from human to human via respiratory droplets.
What are the possible portals of entry of Francisella tularensis? Specify at least 4!
tick bite, mucous membranes, skin abrasions, resp. tract, gastroint. tract
How do humans acquire brucellosis? Where do the bacteria replicate in the human body?
Via contaminated milk products or through skin abrasions (contact with animals).Organisms spread to the mononuclear phagocytes of the reticuloendothelial system(lymph nodes, liver, spleen, bone marrow).
What are the reservoirs of the different Brucella species, respectively?
B. abortus: cattle
B. melitensis: goat, sheep
B. suis: swine
What is the mechanism of action of cholera toxin?
Cholera toxin activates the adenylate cyclase enzyme in cells of the intestinal mucosa leading to increased levels of intracellular cAMP, and the secretion of large amount of water, Na+, K+, Cl-, and HCO3- into the lumen of the small intestine.
What is the principle of the treatment for cholera?
Rapid intravenous or oral replacement of the lost fluid and ions. (Administration of isotonic maintenance solution should continue until the diarrhea ceases.) In severe cases:administration of tetracycline (in addition to rehydration).
Mention 4 diseases caused by Haemophilus influenzae!
epiglottitis (obstructive laryngitis)
otitis media and sinusitis
Which disease is caused by Haemophilus ducreyi?
Chancroid (soft chancre or ulcus molle)
What can serve as source of infections caused by Pseudomonas aeruginosa?
Pseudomonas species are normally present in the environment and can be isolated from the skin, throat, and stool of some healthy persons. They often colonize hospital food,sinks, taps, mops, and respiratory equipment.
Mention 4 diseases that are frequently caused by Pseudomonas aeruginosa!
urinary tract infections
wound infections (burns)
pneumonia, sepsis (immunosupression)
Mention at least 3 drugs which may be effective to treat infections caused by Pseudomonas aeruginosa!
certain penicillins: piperacillin/tazobactam combination
a 3rd generation cephalosporin: ceftazidim
a 4th generation cephalosporin: cefepime
certain aminoglycosides: gentamycin, tobramycin, amikacin
carbapenems: imipenem, meropenem
Which 2 diseases are caused by Legionella pneumophila?
Which is the most important gas gangrene Clostridium? What is its main virulence factor?
Mention 3 Clostridium species causing gas gangrene! How are they acquired?
Clostridium perfringens, C. novyi, C. septicum, C. histolyticum, C. tertium, C.bifermentans, C. sporogenes
The site of infection is usually a wound that comes into contact with Clostridium spores that germinate in an anaerobic environment.
How can be tetanus prevented in patients who have wounds possibly contaminated with C.tetani spores?
Wound should be cleaned and debrided; tetanus toxoid booster injection given;tetanus immunoglobulin (TETIG) in previously unvaccinated patients and in case of heavy contamination of wound; penicillin may be added prophylactically
What are the main symptoms of tetanus infection? Specify at least 3!
Spastic paralysis: muscle spasms; lockjaw(trismus), rhisus sardonicus (grimace of theface), opisthotonus (spasm of the back); respiratory paralysis
What is the mechanism of action of the botulinus toxin?
Blocks release of acetylcholine in peripheral nerve synapses;
What are the main symptoms of botulism? Specify at least 3!
Treatment: respiratory support + trivalent antitoxin
Explain whether or not antibiotic treatment is useful in botulism!
Not, because antibiotics are not effective against preformed toxins.
What diseases may be associated with Helicobacter pylori? Specify at least 3!
Gastritis, peptic and duodenal ulcers, gastric carcinoma, MALT lymphoma
What is the most important virulence factor of Corynebacterium diphtheriae?
What is the mechanism of action of the diphtheria toxin
Inhibits protein synthesis. Inhibits peptide elongation in eukaryotic ribosomes by ADP ribosylation of EF-2 (elongation factor-2)
How long does immunity against diphtheria exist? Which immune effector mechanism is involved?
Antitoxic antibodies, long lasting immunity
Which assays should be done in the lab in order to prove diphtheria?
Smears of the throat swab should be stained with methylene blue or Neisser stain;bacteria are cultured on Löffler’s or tellurite (Clauberg) medium; toxin production must be demonstrated by agar precipitation ( ELEK-test)
What feature of Mycobacteria make them acid fast?
The cell envelope contains a high amount (60 – 70 %) of complex lipids: mycolic acid,cord factor. Once the cells are stained (by carbol-fuchsin) they resist decolorisation by acid-ethanol.
Mention 2 atypical Mycobacterium species!
M. kansasii, M. marinum, M. avium-intracellulare complex, M. fortuitum-chelonei complex
How can one demonstrate the presence of Mycobacterium tuberculosis in clinical samples?
Acid-fast staining (Ziehl-Neelsen)
Culture on selective media (Löwenstein-Jensen agar, liquid BACTEC medium)
PCR amplification of bacterial DNA
Why is multi-drug therapy used for tuberculosis?
To prevent the overgrowth of drug-resistant mutants during the long treatment period (if bacteria resistant to one drug emerge, they are most probably inhibited by the other drugs).
What is the main immune defense mechanism against Mycobacterium tuberculosis?
Mention 3 antituberculotic drugs that are of first choice against Mycobacterium tuberculosis!
What is the causative agent of febris undulans (undulant fever)?
What is the precise definition of bacterial food poisoning?
Acute disease, usually with vomiting and diarrhea, caused by preformed toxins produced by bacteria contaminating the food. The period between consumption of food and the appearance of symptoms is short (< 4-6 hours).
What are the main symptoms in the different stages of syphilis?
Primary syphilis: nontender ulcer (hard chancre)
Secondary lesions: maculopapular rash on skin, and condylomata lata on mucous membranes
Tertiary stage: granulomas (gummas), central nervous system involvement (tabesdorsalis, paralysis progressiva), cardiovascular lesions (aortitis, aortic aneurysm)
When syphilis is diagnosed in the lab, which antigens are used in the non-treponemal and in the specific treponemal antibody tests, respectively?
Non-treponemal antibody tests: cardiolipin
Specific treponemal antibody tests: Treponema pallidum
Which are the two different kinds of antibodies used in the diagnosis of syphilis? Give examples for tests demonstrating them!
Immobilisin (specific antibody) – TPHA (T. pallidum hemagglutination), FTA-ABS (fluorescent treponemal assay – with antibody absorption), TPI (T. pallidum immobilisation test).
What is the advantage and disadvantage of the FTA-ABS syphilis serologic test compared to the VDRL test?
Specific (treponemal) tests such as FTA-ABS are more specific, but they can not be used to follow the efficacy of treatment (because the specific antibodies persist even after effective eradication of bacteria)
What is the drug of first choice in the treatment of syphilis?
What is the reservoir and what is the vector for Borrelia recurrentis?
Reservoir: human; vector: louse
What is used for the laboratory diagnosis of relapsing fever?
Direct demonstration of bacteria from peripheral blood smear by microscopy (Giemsa stain or dark field illumination)
What is the causative agent of Lyme disease?
Mention 2 antibacterial drugs that are of first choice in early stage Lyme disease?
Tetracyclines, amoxicillin, cefuroxim
What is the first characteristic manifestation in the early phase of Lyme disease?
Erythema (chronicum) migrans
Which manifestations are characteristic for the late phases of Lyme disease?
Mention an antibacterial drug effective against Mycoplasma pneumoniae infections!
Erythromycin, azythromycin, tetracycline
Why are penicillins not effective against Mycoplasma pneumoniae infections?
Because of the absence of a cell wall, penicillins are ineffective (penicillins inhibit cell wall synthesis)
What is the Weil-Felix reaction?
It is based on the cross-reaction of an antigen present in many rickettsiae with the Oantigen polysaccharide found in certain Proteus vulgaris strains (OX19 OX2, OXK).The test is a tube agglutination test in which these Proteus strains are used as antigens to demonstrate antibodies from the patient’s serum sample.