9th lecture - antibiotics

Question 1

Antibiotics are substances produced by

Answer 1

microbes, fungi, animal-based and plant-based organisms that have a powerful antibacterial, antimycotic, partially also antiviral and anti-tumour activity.

Question 2

Chemotherapy is the systematic administration of

Answer 2

substances with an antimicrobial effect and/or cytotoxic effect.

Question 3

MIC means

Answer 3

minimum inhibitory concentration

which is the lowest concentration of antibiotics that inhibits the growth of microorganisms.

It is measured in micrograms per ml.

Question 4

Explain Hospital-acquired infection

Answer 4

An infection caused by the microbes existing in the hospital environment.

The parallel in veterinary medicine – stable infection.

hospital aquired infections are also known as nosocomial.

Question 5

Explain Infection recurrence

Answer 5

Relapse is the recurrence of a past medical condition with the same microbial strain.

Reinfection is infection following recovery from a previous infection with new agents or of another serotype of the same agent.

Question 6

explain superinfection

Answer 6

a second infection superimposed on an earlier one especially by a different microbial agent of exogenous or endogenous origin that is resistant to the treatment used against the first infection.

Question 7

Mechanism of action of antibiotics can be (2)

Answer 7

bactericidal
bacteriostatic

Question 8

Substances that inhibit cell wall synthesis are

Answer 8

bactericidal.

Beta-lactam antibiotics such as (penicillins, cephalosporins), aztreonam, imipenem, vancomycin, bacitracin.

Question 9

Beta-lactam antibiotics act how

Answer 9

bactericidal.

inhibit bacterial cell wall synthesis

Question 10

2 examples of Beta-lactam antibiotics

Answer 10

penicillins, cephalosporins

Question 11

Substances that inhibit the functions of the bacterial cell membrane are

Answer 11

bactericidal.

Polymyxins, colistin, aminoglycosides, nitrofurans.

Question 12

Substances that inhibit microbial protein synthesis are

Answer 12

bacteriostatic.

Chloramphenicol, tetracyclines, macrolides, clindamycin, lincomycin, etc.

Question 13

Substances that impact the microbial nucleic acid metabolism are

Answer 13

bacteriostatic.

Rifampicin, quinolones.

Question 14

Antimicrobial resistance is

Answer 14

The adaptation of microbes to the substances that are harmful to them.

It is caused as a result of selection or adaptation.

The resistant population of microbes will remain after each antibiotic treatment.

Resistance is capable of passing from one generation of bacteria to the next and from one type of bacteria to another.

Question 15

Main reasons for failures in antimicrobial treatment

Answer 15

Infection is caused by resistant strain – antibiotics are not effective.

Transfer of resistant gene from one bacteria to another (including normal microflora!), from one bacterial generation to another.

Treatment without specific bacterial diagnosis, disease can be caused by virus or there is no infection at all.

Question 16

Lot of gram-negative microbes are resistant to ?
How?

Answer 16

beta lactams.

Some microbes evolve to have too few binding points for the AB molecule to bind to and thus it cannot enter the bacterial cell.

Some microbes produce betalactamases which break down the AB.

Question 17

PBPs are

Answer 17

Penicillin-binding proteins (PBPs) are membrane-associated proteins involved in the biosynthesis of peptidoglycan (PG), the main component of bacterial cell walls.

These proteins were discovered and named for their affinity to bind the β-lactam antibiotic penicillin.

When bactria begin to grow resistant to beta lactams - one mechanism of this resistance is they evolve to have less AB binding points.

Question 18

Streptococci are not susceptible to what type of AB?

Answer 18

aminoglycosides

Some microbes have natural barriers to AB such as streptococci to aminoglycosides.

Question 19

Aquired resistance examples (2)

Answer 19

Mutations in bacterial chromosome.

Plasmids – genetic material, exists concurrently with the bacterial chromosomal DNA, carries resistance information.

E.g. plasmids mediate information that induces production of betalactamases in Staphylococcus aureus and some intestinal bacteria. Resistant bacteria survive after exposure to AB and are then spread.

Question 20

Bacterial cross‐resistance can be defined as

Answer 20

resistance to multiple distinct antimicrobial agents conferred by a single molecular mechanism.

Or

resistance to all the antibiotics belonging to the same class due to a single mechanism.

Question 21

Name 3 Structures responsible for transmissioon of resistance

Answer 21

Plasmids (small circular DNA molecule found in bacteria)

Transposons (class of genetic elements that can “jump” to different locations within a genome)

Integrons
(are genetic elements that contain a site-specific recombination system able to integrate, express and exchange specific DNA elements)

Question 22

Describe Plasmids

Answer 22

Extrachromosomal self-replicating small, circular genetic elements.

Not necessary for the survival of the bacteria, but they carry genes that support some selective advantages to the host bacterium, e.g. antimicrobial resistance genes.

Can be transferred both vertically and horizontally between commensal and pathogenic bacteria and can lead to massive establishment of resistant pathogens in an individual animal within days.

Question 23

Describe transposons

Answer 23

„jumping genes“ - specific DNA fragments, genetic elements.

They can not replicate themselves, but can move from one location to another in the chromosome.

Resistance genes can also move within the genome of a bacterial cell.

They can hop from the chromosome to a plasmid, between different plasmids and back to the chromosome, allowing development of different resistance gene combinations.

Question 24

Describe integrons

Answer 24

They are usually part of composite transposons (jumping genetic elements).

They are not able to move themselves but encode mechanisms that can capture new resistance genes and to excise them, thereby increasing the horizontal mobility of resistance genes.

Question 25

list mechanisms for Transmission of Resistant Genes (3+3)

Answer 25

Transformation, transduction, conjugation.

Plasmids
Transposons
Integrons

Question 26

MECHANISM OF ACTION of
β-Lactam antibiotics

Answer 26

are bactericidal agents that interrupt bacterial cell-wall formation as a result of covalent binding to essential penicillin-binding proteins (PBPs), enzymes that are involved in the terminal steps of peptidoglycan cross-linking in both Gram-negative and Gram-positive bacteria.