Macrolides, Clindamycin & Ketolides Polymyxins

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1 Macrolides, Clindamycin & Ketolides Polymyxins Kwan Soo Ko

2 Macrolides - Erythromycin - Azithromycin - Clarithromycin Lincosamides - Lincomycin - Clindamycin Unrelated chemically But, many similar biological properties

3 Ketolides - derivative of erythromycin - Telithromycin

4 Macrolides Erythromycin Clarithromycin Azithromycin 14-membered 15-membered

5 Erythromycin - in from a strain of Saccharopolyspora erythra (Streptomyces erythreus) (soil from the Philippines) - Active component, erythromycin A 14-member macrocyclic lactone ring, attached to two sugar moieties

6 Erythromycin Inhibits RNA-dependent protein synthesis at the step of chain elongation Several functional groups binds to sequences on domain V of 23S rrna (a component of 50S subunit of ribosome)

7 Binding site near peptidyltrasnferase center Prevention of peptide chain elongation by blocking of polypeptide exit tunnel Dissociation of peptidyltrna from ribosome

8 Studies of E. coli and S. aureus Erythromycin also inhibits formation of 50S ribosomal subunit

9 Erythromycin resistance Decreased microbial entry or increased export of drug Target site alterations Drug inactivation

10 Target site alteration by erm Efflux by mef Ribosomes Cytoplasm Macrolide Weisblum B. In: Gram-Positive Pathogens. 2000: Hyde TB et al. JAMA. 2001;286:

11 Intrinsic decreased permeability of outer membrane to macrolides - Enterobacteriaceae - Pseudomonas spp. - Acinetobacter spp. - Cell-free systems and protoplasts of organisms are susceptible to macrolides

12 Chromosomally encoded efflux pumps - By proton active force or by hydrolysis of ATP -in S. epidermidis and S. aureus, plasmid-mediated erythromycin resistance (MLS B phenotype) by active efflux encoded by msra gene -in S. pyogenes, S. pneumoniae & enterococci, M phenotype (14- and 15-member macrolides, but not 16- member macrolides, lincosamides, and streptogramin B) : encoded by mefa gene - Low-level resistance

13 Target site alterations - Mutations in genes for 50S ribosomal proteins or bases or critical domains of the 23S rrna receptor site - Be associated with a decreased binding affinity - High-level resistance - In some strains of S. pneumoniae, H. pylori, M. avium, B. subtilis, S. pyogenes, Campylobacter spp., M. pneumoniae, E. coli & S. aureus

14 Alterations in the 23S rrna of the 50S ribosomal subunit by dimethylation of adenine at a defined position (A2058 residue of domain V) - be associated with resistance to erythromycin and most other macrolides (M), and sometimes to the lincosamides (lincomycin & clindamycin)(l), and streptogramin B (S B ) MLS B phenotype - be mediated by the erm (erythromycin ribosome methylation)

15 Drug inactivation - By phosphotransferases In strains of S. aureus, E. coli & Nocardia spp. mpha, mphb & mphc - By esterase genes (erea & ereb) on plasmids Hydrolysis of macrocyclic lactone of erythromycin In strains of E. coli, Klebsiella spp., Citrobacter spp., Proteus spp. & Enterobacter spp.

16 Azithromycin & Clarithromycin To improve the qualities of erythromycin - better oral absorption, a longer half-life, fewer gastrointestinal side effect & a greater antimicrobial spectrum of activity

17 Erythromycin methyl-substituted nitrogen methoxy group Azithromycin Clarithromycin increase of stability in gastric acid, improving absorption by oral route

18 Azithromycin, clarithromycin & erythromycin - bind to the same receptor on 50S ribosomal subunit & inhibit RNA-dependent protein synthesis by the same mechanism Azithromycin (15-member macrolides) - greater activity than the 14-member macrolides against gram-negative bacteria (especially for M. catarrhalis and H. influenzae) due to better penetration the outer envelope Resistance mechanisms to azithromycin & clarithromycin - the same as or similar to those for erythromycin

19 Ketolides New class of semisynthetic agents derived from erythromycin Increased acid stability Increased antibacterial potency against many bacteria resistant to macrolides Unability to induce the MLS B phenotype

20 Telithromycin Be approved for clinical use in the US in April 2004 in Europe in 2001 Serious and fatal hepatotoxicity in 2006

21 Action mechanism essentially similar to that of erythromycin By interacting closely to peptidyl transferase site of 50S ribosomal subunit & by interfering with the formation of 50S ribosomal subunit

22 Different nature of their interaction with the ribosome between telithromycin and erythromycin Higher binding affinity of telithromycin due to the dual interaction with domains V and II of 23S rrna Direct interference with elongation polypeptide chain + Inhibition of formation of the 50S ribosomal subunit Inhibition of the 30S ribosomal subunit (at higher conc.)

23 Uncommon resistance to telithromycin - Poor inducer or poor substrate for bacterial strains expressing efflux mechanisms of resistance - Poor inducer of the MLS B methylase genes ; potent against S. pneumoniae isoaltes with the consitutive erm gene Rare bacterial strains with increased MICs to telithromycin - by mutations in the bases of 23S rrna of the 50S ribosomal subunit or in ribosomal proteins - most, laboratory isolates

24 Lincomycin In 1962, From Streptomyces lincolnensis (soil near Lincoln, Nebraska) Biological properties similar to those of erythromycin, but chemically unrelated (an amino acid linked to an amino sugar) Clindamycin Chemical modification

25 Clindamycin Increased antibacterial potency & absorption after oral administration

26 The same or overlapping 50S ribosomal binding sites - as those for macrolides and chloramphenicol Inhibition of protein synthesis in early chain elongation by interference with the transpeptidation reaction, possibly through blockade of the P site Also stimulate the dissocation of peptidyl-trna from ribosomes (like macrolides)

27 Resistance mechanisms Alteration in the 23S rrna of 50S ribosomal subunit by methylation of adenine (as in macrolides) - usually plasmid-mediated -MLS B type of resistance -In S. aureus, macrolide-inducible variety by positive erythromycin-clindamycin D-test

28 Exposure to clindamycin in vitro or in vivo may result in clindamycin resistance due to selection of preexisting constitutive erm mutants, especially if the organism is at high innoculum

29 Resistance mechanisms Mutations in the bacterial rrna - in some strains of Mycobacterium smegmatis Alteration in particular 50S ribosomal proteins of the receptor site (as in macrolides)

30 Resistance mechanisms Inactivation of lincomycin and clindamycin - by a few isolates staphylococci and Bacteroides spp. - plasmid-mediated 3-lincomycin 4-clindamycin 0- nucleotidyltransferase - catalyze the nucleotidylation of the hydroxyl group in position 4 of clindamycin Enterobacteriaceae, Pseudomonas & Acinetobacter - intrisically resistance to clindamycin - due to poor permeability of the cellular outer envelop

31 Polymyxins Polymyxin B & polymyxin E (colistin) Old drug, discovered in 1947 (Bacillus polymyxa) Colistin became available for clinical use in the 1960s but has been abandoned sine 1970s because of neurotoxicity and nephrotoxicity Re-introduction because of remarkable increase in resistance to antimicrobial agents currently available - Polymyxins are sometimes the only available active antibiotics

32 Polymyxin B Colistin (polymyxin E)

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34 Action mechanism of colistin Polycationic and with both hydrophilic and lipophilic moieties - bactericidal drug binding to LPS and phospholipids in the outer cell membrane of gram-negative bacteria - competitively displaces divalent cations from the phosphate groups of membrane lipids, leading to disruption of the outer cell membrane, leakage of intracellular contents, and bacterial death Colistin can bind and neutralize LPS and prevent the pathophysiologic effects of endotoxin

35 Colistin Resistance Antibiotics MIC (mg/l) 50% 90% Range % S / R Polymyxin B > / 2.1 Ceftazidime 16 > > / 48.3 Cefepime 16 > > / 37.3 Ampicillin/sulbactam 8 > > / 31.6 Imipenem 0.5 > > / 15.8 Meropenem 1 > > / 17.0 Ciprofloxacin >2 > > / 55.0 Amikacin 4 > > / 35.8 SENTRY Data (Gales et al., 2006)

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37 Extensive emergence of colistin-resistant A. baumannii subpopulations provoked by exposure to colistin Li et al. AAC 50:2946 (2006) Tan et al. AAC 51:3413 (2007)

38 Colistin resistance Specific modification of the lipid A component of the outer membrane lipopolysaccharide, resulting in a reduction of the net negative charge of the outer membrane Proteolytic cleavage of the drug Activation of a broad-spectrum efflux pump Two-component signaling systems PmrAB and PhoPQ - be involved in sensing environmental ph, Fe 3+, and Mg 2+ levels, leading to altered expression of a set of genes involved in lipid A modification

39 Mutational analysis of the pmr operon Adams et al. AAC (2009)