Week 5 formative quiz Flashcards
Streptococcus pyogenes is an example of a Gram-negative bacillus
False. It is a gram positive coccus
Colonies of bacteria will grow on artificial media (e.g. agar plates) after overnight incubation and are visible to the naked eye
True. However individual bacterial cells can only be seen using a light microscope and a stain such as Gram stain shows them up best
Viruses can only be cultured inside other cells
True - viruses require a host cell’s nucleic acids and organelles in order to replicate
The use of two antibiotics is always more effective than mono-therapy
False - while some infections are effectively treated by two antibiotics working synergistically, generally speaking infections should be treated using as narrow-spectrum an antibiotic regimen as possible, to prevent resistance. When treating a known pathogen with demonstrated sensitivity from a culture, a single antibiotic agent should be adequate
Bacterial exotoxins are produced by all members of a pathogenic species
False - the genetic variation within species of bacteria means not all members will produce the same exotoxins.
A prominent example is Escherichia coli, where the majority of strains are found as part of normal gut flora, while the O157:H7 strain produces an exotoxin which causes haemorrhagic colitis
Dimorphic fungi can exist as both a yeast and a mould
True - dimorphic fungi can exist as a yeast or a mould, and this is usually determined by temperature. An example is candida albicans, which causes candidiasis (thrush)
Genetic variation in bacteria only occurs by spontaneous mutation in the chromosome
False. Genetic variation also happens by transfer of plasmids between bacteria
Fimbriae are filaments on the bacterial cell surface that give it motility
False. Flagella give bacterial cells motility. Fimbriae have a role in the adhesion of bacteria to host cells
An organism which is sensitive to an antibiotic will always be killed by it
False - antibiotics can be bacteriocidal (and kill bacteria) or bacteriostatic (preventing their replication)
Escherichia coli is an example of a Gram-positive coccus
False. E. coli is an example of a gram negative bacillus
The complement fixation test detects live virus in the patient’s blood
False - the complement fixation test is used to detect whether a patient has antibodies to a specific antigen, which may be derived from a virus. A serum sample is exposed to complement and the antigen of interest. As complement will only bind to antigen-antibody complexes, the test will only show a positive result if the antibody is present in the serum
Aminoglycosides act on DNA synthesis
False - aminoglycosides bind to bacterial ribosomes, inhibiting protein synthesis
Gram negative organisms are always resistant to vancomycin
True - Vancomycin is unable to penetrate the bacterial cell wall of gram-negative bacteria
Carbapanems are members of the β-lactam class of antibiotics.
True. Penicillin, cephalosporins and carbapenems are all β-lactam antibiotics. They all possess the typical chemical structure: the β-lactam ring
All bacteria have lipopolysaccharide (endotoxin) in their cell walls
False - only gram negative bacteria have endotoxin in their cell walls
Peptidoglycan is the component of the bacterial cell wall that gives it its shape
True. Peptidoglycan is a relatively rigid layer that gives the bacterial cell its shape
Antibiotic therapy should never be started before the results of laboratory sensitivity tests are available
False - while it is desirable to know sensitivity results, there are many clinical situations where to withhold antibiotic treatment while awaiting results would cause unacceptable (and potentially fatal) delay to a patient’s care. In these cases broad-spectrum antibiotic treatment should be started based on likely infection source and common pathogens, and adjusted once sensitivities are known
The genetic component of viruses may consist of DNA or RNA
True. Viral DNA or RNA can be single or double-stranded. An example of a DNA virus is varicella zoster (chickenpox). An example of an RNA virus is Covid-19.
Staphylococcus epidermidis is an example of a Gram-positive coccus
True - all Staphylococci are gram positive cocci. Another clinically significant example is Staphylococcus aureus
All penicillins are inactivated by beta-lactamase
False - some penicillins are resistant to beta-lactamase, for example flucloxacillin
The bacterial cell has a nucleus which contains the chromosomes
False. Unlike eukaryotic cells, the bacterial cell does not have a nucleus and has just a single chromosome
Viruses may replicate in soil and water
False - viruses require a host cell in order to replicate