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
Bacterial DNA is found only in the chromosome
False - as well as chromosomal DNA, bacteria contain small loops of DNA called plasmids
Diagnosis of malaria is made by visualisation of parasites in a peripheral blood film
True - this is usually done using “thick and thin” smears. The “thick” smear examines a larger volume of blood and is better for detecting the presence of the parasite, while the “thin” smear allows identification of the species
Malaria is never passed from human to human
False- while the vast majority of malaria transmission is through mosquito vectors, it can rarely be spread human to human through blood transfusion, needle-sharing or organ transplantation
Chlorination of drinking water prevents infections with all intestinal parasites
False - an example of a parasite not killed by chlorination is Cryptosporidium
Light microscopy can be used in the routine laboratory to screen faeces for the presence of viruses
False - routine viral screening of faeces is through Polymerase Chain Reaction (PCR), looking for viral nucleic acids. Light microscopy can be used to detect larger pathogens, such as parasites
Live vaccines should not be given to pregnant or immunocompromised patients
True - live vaccines carry a theoretical risk of infection to the foetus or immunosuppressed patient
Vancomycin and penicillin act on a different stage of cell wall synthesis
True - Penicillin kills bacteria through binding of the beta-lactam ring to DD-transpeptidase, inhibiting its cross-linking activity, while vancomycin binds to the D-Ala-D-Ala terminal of the growing peptide chain during cell wall synthesis, resulting in inhibition of the transpeptidase.
Amphotericin B is the treatment of choice for all fungal infections
False - as for bacterial infections and antibiotics, treatment of fungal infections will depend on the site, pathogen and severity
All antibiotic resistance is caused by genes carried on plasmids.
False- spontaneous mutations can arise in bacterial chromosomal DNA which result in antibiotic resistance
Concerning diagnostic methods: A single elevated IgM titre is generally acceptable as serological proof of infection
True - elevated IgM titre is indicative of acute infection
Vancomycin is only active against anaerobes
False - Vancomycin is active against aerobic and anaerobic gram positive bacteria, and can be used to treat Methicillin-Resistant Staphylococcus aureus (MRSA). It is not effective against gram negative bacteria
Co-trimoxazole is combination of Teicoplanin and sulphamethoxazole
False, it is a combination of trimethoprim and sulphamethoxazole
Penicillin G (benzylpenicillin) interferes with peptidoglycan synthesis in the bacterial cell wall
True - benzylpenicillin is most commonly used for its activity against gram positive aerobes
All antiviral drugs act by inhibiting viral nucleic acid synthesis
False - many do. However antiviral drugs can act on any stage of the viral replication cycle, e.g. attachment, penetration, protein synthesis, viral budding, etc
Pasteurisation results in sterilisation of milk
False - pasteurisation involves heating milk at a moderate temperature (around 60-70 degrees celsius) for a short length of time. This greatly reduces the number of pathogens, such that they are unlikely to cause disease, and increases shelf-life.
Sterilisation completely eliminates organisms, occurs at a much higher temperature (>100 degrees), and allows milk to be stored unrefrigerated (UHT milk)
Flucloxacillin can be used to treat MRSA infection
False. Flucloxacillin, which is β-lactamase resistant, can be used to treat β-lactamase producing S. aureus, but not MRSA (methicillin resistant S. aureus)
Genetically engineered components of some pathogens have been successfully used as vaccines
True. An example is the hepatitis B vaccine
Antiviral drugs are virucidal agents
False, Antiviral drugs are all virustatic, they inhibit growth and/or replication of viruses
Resistance of a known bacterial species to a known antibiotic can always be predicted on theoretical grounds
False - while we can often predict which bacteria will be sensitive to an antibiotic based on our knowledge of the antibiotic mechanism of action, bacterial resistance can develop in a previously sensitive species through e.g. plasmid transfer during bacterial conjugation
Topical antifungal preparations can be used to treat fungal skin infections
True - an example would be topical clotrimazole for thrush
Capsulate organisms (eg, the pneumococcus) are particularly resistant to phagocytosis
True. The capsule enables the organism to evade phagpcytosis
All infections can be spread by the airborne route
False - only infections which have an affinity for the respiratory tract and are present in dust particles or aerosolised respiratory droplets will spread by the airborne route. An example is influenza.
Other examples of possible routes of transmission include faeco-oral (e.g. E coli), contact (e.g. the common cold) and fomite (e.g.Tetanus)
Bacterial exotoxins act only at the site of infection
False - bacterial exotoxins are secreted by the organism or released during cell lysis, and can enter the bloodstream and cause systemic effects
Prophylaxis should be given before every operation
False - excessive use of antibiotic prophylaxis will contribute to emergence of antibiotic resistance. Antibiotic prophylaxis is only indicated in operations with a high risk of bacteraemia (e.g. colorectal surgery, or operations involving infected tissue) or where the consequences of bacteraemia would be very serious (e.g. joint replacement, where innoculation with bacteria could cause a septic arthritis)
Light microscopy can be used in the routine laboratory as a more sensitive detection method for bacteria than culture
False - culture is a more sensitive detection method, as a much lower concentration of bacteria is required for a positive result
Aciclovir is used to treat infection with all herpes viruses
False - aciclovir is used to treat herpes simplex and varicella zoster infections, however there are many other herpes viruses, and many other antiviral agents that are used to treat these infections
An antiseptic is a disinfectant that is safe enough to use on human skin
True. Examples of antiseptics used in clinical practice include iodine, chlorhexidine and isopropyl alcohol
Concerning diagnostic methods: a single elevated IgG titre is generally acceptable as serological proof of infection
False - An elevated IgG titre can indicate previous infection, chronic infection or immunisation, and should be interpreted in the context of IgM titre and other serological markers of infection and inflammation
All antiviral drugs act by inhibiting viral nucleic acid synthesis
False - many do. However antiviral drugs can act on any stage of the viral replication cycle, e.g. attachment, penetration, protein synthesis, viral budding, etc
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
Light microscopy can be used in the routine laboratory to screen faeces for the presence of viruses
False - routine viral screening of faeces is through Polymerase Chain Reaction (PCR), looking for viral nucleic acids. Light microscopy can be used to detect larger pathogens, such as parasites
All bacteria have lipopolysaccharide (endotoxin) in their cell walls.
False - only gram negative bacteria have endotoxin in their cell walls.
Bacterial DNA is found only in the chromosome
False - as well as chromosomal DNA, bacteria contain small loops of DNA called plasmids
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
