General Microbiology Flashcards
Describe the colour (in a Gram stained smear) of Gram positive and Gram negative bacteria, respectively!
Gram positives: dark blue (purple)
Gram negatives: red (pink)
Describe the 3 important parts of the bacterial lipopolysaccharide!
lipid A + core polysaccharide + O-specific (polysaccharide) side chain
Which 2 roles are attributed to bacterial pili (fimbriae)?
adhesion; conjugation (sex fimbriae)
Mention a bacterium and its virulence factor that is encoded by a lysogenic bacteriophage!
Corynebacterium diphtheriae – diphtheria toxin
Streptococcus pyogenes – erythrogenic toxin
Escherichia coli – verotoxin Clostridium botulinum- botulinus toxin
List the possible shapes of bacteria. Write one example for each category!
coccus (spherical): Staphylococcus, Streptococcus
rod: Clostridium, Corynebacterium, E. coli
curved rod: Vibrio
helical: Treponema, Borrelia, Leptospira
What are the essential components of bacterial cells? Specify at least 3!
cytoplasm, nucleoid (genome), cell membrane, (cell wall)
Which part of the bacterial cell carries the endotoxin?
Outer membrane of Gram negative bacteria
What roles are attributed to the bacterial capsule in the infectious process?
antiphagocytic effect, adhesion
Describe the definition for obligate anaerobic bacteria!
They are able to replicate only in the absence of oxygen (under anaerobic conditions). Some of them are quickly killed by oxygen, some are able to survive but do not grow while oxygen is present.
Describe the definition for facultative anaerobic bacteria!
They are able to replicate both in the presence and in the absence of oxygen. In aerobic conditions, they perform respiration, in anaerobic condition, they perform fermentation.
What does sterilisation mean?
Sterilisation means the killing or removal of all microorganisms (including bacterial spores).
Mention 3 reliable methods of sterilization!
autoclaving, hot air oven, gamma-radiation, filtration (fluids), gas sterilisation
(not acceptable: boiling, pasteurisation, UV!)
Specify an exact set of parameters (temperature and time) necessary for effective sterilization by autoclaving!
121 °C for 20 - 30 min. (at 1 bar overpressure)
Specify an exact set of parameters (temperature and time) necessary for effective sterilization using a hot air oven (with circulation)!
160 °C for 60 min. (dry heat)
What does disinfection mean?
The purpose of disinfection is the killing of pathogenic microbes and to decrease the number of viable microbial cells. Resistant microbes and spores may survive, so disinfection does not the kill all microbes.
Mention 5 groups of disinfectants!
alcohols, phenol derivatives, detergents, chlorine, iodine, aldehydes
Mention 2 groups of disinfectants acting on the microbial membrane structures!
a. , (cationic) detergents (quaternary ammonium compounds)
b. , phenol compounds (cresol, hexachlorophene, chlorohexidine)
c. , alcohols (ethanol, isopropanol)
What does active immunisation mean?
It means the transfer of microbes or microbial products (vaccines) to the human body to induce long-lasting immunity against a specific infectious disease
What does passive immunisation mean?
It means the administration of preformed antibody (immune globulins produced in animals or humans) to the human body resulting in short-term protection against a specific infectious disease
Mention 2 bacterial infectious diseases that can be prevented or treated by passive immunisation!
prevention: tetanus
treatment: diphtheria, botulism, tetanus
Describe precisely what toxoid means!
Inactivated bacterial exotoxin that is not toxic but immunogenic
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)
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 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 2 bacterial exotoxins that act by ADP ribosylation!
Diphtheria toxin, cholera toxin, pertussis toxin
Mention 2 bacterial exotoxins that are neurotoxic!
tetanus toxin, botulinum toxin
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)