Week 5 formative quiz

Question 1

Streptococcus pyogenes is an example of a Gram-negative bacillus

Answer 1

False. It is a gram positive coccus

Question 2

Colonies of bacteria will grow on artificial media (e.g. agar plates) after overnight incubation and are visible to the naked eye

Answer 2

True. However individual bacterial cells can only be seen using a light microscope and a stain such as Gram stain shows them up best

Question 3

Viruses can only be cultured inside other cells

Answer 3

True - viruses require a host cell’s nucleic acids and organelles in order to replicate

Question 4

The use of two antibiotics is always more effective than mono-therapy

Answer 4

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

Question 5

Bacterial exotoxins are produced by all members of a pathogenic species

Answer 5

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

Question 6

Dimorphic fungi can exist as both a yeast and a mould

Answer 6

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)

Question 7

Genetic variation in bacteria only occurs by spontaneous mutation in the chromosome

Answer 7

False. Genetic variation also happens by transfer of plasmids between bacteria

Question 8

Fimbriae are filaments on the bacterial cell surface that give it motility

Answer 8

False. Flagella give bacterial cells motility. Fimbriae have a role in the adhesion of bacteria to host cells

Question 9

An organism which is sensitive to an antibiotic will always be killed by it

Answer 9

False - antibiotics can be bacteriocidal (and kill bacteria) or bacteriostatic (preventing their replication)

Question 10

Escherichia coli is an example of a Gram-positive coccus

Answer 10

False. E. coli is an example of a gram negative bacillus

Question 11

The complement fixation test detects live virus in the patient’s blood

Answer 11

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

Question 12

Aminoglycosides act on DNA synthesis

Answer 12

False - aminoglycosides bind to bacterial ribosomes, inhibiting protein synthesis

Question 13

Gram negative organisms are always resistant to vancomycin

Answer 13

True - Vancomycin is unable to penetrate the bacterial cell wall of gram-negative bacteria

Question 14

Carbapanems are members of the β-lactam class of antibiotics.

Answer 14

True. Penicillin, cephalosporins and carbapenems are all β-lactam antibiotics. They all possess the typical chemical structure: the β-lactam ring

Question 15

All bacteria have lipopolysaccharide (endotoxin) in their cell walls

Answer 15

False - only gram negative bacteria have endotoxin in their cell walls

Question 16

Peptidoglycan is the component of the bacterial cell wall that gives it its shape

Answer 16

True. Peptidoglycan is a relatively rigid layer that gives the bacterial cell its shape

Question 17

Antibiotic therapy should never be started before the results of laboratory sensitivity tests are available

Answer 17

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

Question 18

The genetic component of viruses may consist of DNA or RNA

Answer 18

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.

Question 19

Staphylococcus epidermidis is an example of a Gram-positive coccus

Answer 19

True - all Staphylococci are gram positive cocci. Another clinically significant example is Staphylococcus aureus

Question 20

All penicillins are inactivated by beta-lactamase

Answer 20

False - some penicillins are resistant to beta-lactamase, for example flucloxacillin

Question 21

The bacterial cell has a nucleus which contains the chromosomes

Answer 21

False. Unlike eukaryotic cells, the bacterial cell does not have a nucleus and has just a single chromosome

Question 22

Viruses may replicate in soil and water

Answer 22

False - viruses require a host cell in order to replicate

Question 23

Bacterial DNA is found only in the chromosome

Answer 23

False - as well as chromosomal DNA, bacteria contain small loops of DNA called plasmids

Question 24

Diagnosis of malaria is made by visualisation of parasites in a peripheral blood film

Answer 24

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

Question 25

Malaria is never passed from human to human

Answer 25

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

Question 26

Chlorination of drinking water prevents infections with all intestinal parasites

Answer 26

False - an example of a parasite not killed by chlorination is Cryptosporidium

Question 27

Light microscopy can be used in the routine laboratory to screen faeces for the presence of viruses

Answer 27

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

Question 28

Live vaccines should not be given to pregnant or immunocompromised patients

Answer 28

True - live vaccines carry a theoretical risk of infection to the foetus or immunosuppressed patient

Question 29

Vancomycin and penicillin act on a different stage of cell wall synthesis

Answer 29

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.

Question 30

Amphotericin B is the treatment of choice for all fungal infections

Answer 30

False - as for bacterial infections and antibiotics, treatment of fungal infections will depend on the site, pathogen and severity

Question 31

All antibiotic resistance is caused by genes carried on plasmids.

Answer 31

False- spontaneous mutations can arise in bacterial chromosomal DNA which result in antibiotic resistance

Question 32

Concerning diagnostic methods: A single elevated IgM titre is generally acceptable as serological proof of infection

Answer 32

True - elevated IgM titre is indicative of acute infection

Question 33

Vancomycin is only active against anaerobes

Answer 33

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

Question 34

Co-trimoxazole is combination of Teicoplanin and sulphamethoxazole

Answer 34

False, it is a combination of trimethoprim and sulphamethoxazole

Question 35

Penicillin G (benzylpenicillin) interferes with peptidoglycan synthesis in the bacterial cell wall

Answer 35

True - benzylpenicillin is most commonly used for its activity against gram positive aerobes

Question 36

All antiviral drugs act by inhibiting viral nucleic acid synthesis

Answer 36

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

Question 37

Pasteurisation results in sterilisation of milk

Answer 37

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)

Question 38

Flucloxacillin can be used to treat MRSA infection

Answer 38

False. Flucloxacillin, which is β-lactamase resistant, can be used to treat β-lactamase producing S. aureus, but not MRSA (methicillin resistant S. aureus)

Question 39

Genetically engineered components of some pathogens have been successfully used as vaccines

Answer 39

True. An example is the hepatitis B vaccine

Question 40

Antiviral drugs are virucidal agents

Answer 40

False, Antiviral drugs are all virustatic, they inhibit growth and/or replication of viruses

Question 41

Resistance of a known bacterial species to a known antibiotic can always be predicted on theoretical grounds

Answer 41

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

Question 42

Topical antifungal preparations can be used to treat fungal skin infections

Answer 42

True - an example would be topical clotrimazole for thrush

Question 43

Capsulate organisms (eg, the pneumococcus) are particularly resistant to phagocytosis

Answer 43

True. The capsule enables the organism to evade phagpcytosis

Question 44

All infections can be spread by the airborne route

Answer 44

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)

Question 45

Bacterial exotoxins act only at the site of infection

Answer 45

False - bacterial exotoxins are secreted by the organism or released during cell lysis, and can enter the bloodstream and cause systemic effects

Question 46

Prophylaxis should be given before every operation

Answer 46

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)

Question 47

Light microscopy can be used in the routine laboratory as a more sensitive detection method for bacteria than culture

Answer 47

False - culture is a more sensitive detection method, as a much lower concentration of bacteria is required for a positive result

Question 48

Aciclovir is used to treat infection with all herpes viruses

Answer 48

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

Question 49

An antiseptic is a disinfectant that is safe enough to use on human skin

Answer 49

True. Examples of antiseptics used in clinical practice include iodine, chlorhexidine and isopropyl alcohol

Question 50

Concerning diagnostic methods: a single elevated IgG titre is generally acceptable as serological proof of infection

Answer 50

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

Question 51

All antiviral drugs act by inhibiting viral nucleic acid synthesis

Answer 51

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

Question 52

The use of two antibiotics is always more effective than mono-therapy

Answer 52

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

Question 53

Light microscopy can be used in the routine laboratory to screen faeces for the presence of viruses

Answer 53

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

Question 54

All bacteria have lipopolysaccharide (endotoxin) in their cell walls.

Answer 54

False - only gram negative bacteria have endotoxin in their cell walls.

Question 55

Bacterial DNA is found only in the chromosome

Answer 55

False - as well as chromosomal DNA, bacteria contain small loops of DNA called plasmids

Question 56

Fimbriae are filaments on the bacterial cell surface that give it motility

Answer 56

False. Flagella give bacterial cells motility. Fimbriae have a role in the adhesion of bacteria to host cells