High-level telithromycin resistance in a clinical isolate of Streptococcus pneumoniae

A rare clinical isolate of Streptococcus pneumoniae, highly resistant to telithromycin, contained erm(B) with a truncated leader peptide and a mutant ribosomal protein L4. By transformation of susceptible strains, this study shows that high-level telithromycin resistance is conferred by erm(B), wild type or mutant, in combination with a (69)GTG(71)-to-TPS mutation in ribosomal protein L4.     

Mechanisms of resistance to telithromycin in Streptococcus pneumoniae

Reports of ketolide resistance remain scarce, however, a few laboratory-derived and clinical isolates of resistant Streptococcus pneumoniae have been documented. Mutations in key telithromycin-binding sites such as domains II and V of the 23S rRNA and ribosomal proteins L4 and L22, as well as mutations of the resistance determinant erm(B) are associated with elevated telithromycin MICs. Mutations in the secondary binding site of domain II coupled with ribosomal methylation may have serious resistance consequences should the domain II binding site be lost. Although ketolides are purported to maintain excellent activity against efflux-positive isolates, laboratory-derived telithromycin-resistant strains have been generated. As telithromycin usage increases, ketolide-resistant isolates of S. pneumoniae may well increase.     

Streptococcus pneumoniae isolates resistant to telithromycin

The telithromycin susceptibility of 210 erythromycin-resistant pneumococci was tested with the agar diffusion method. Twenty-six erm(B)-positive isolates showed heterogeneous resistance to telithromycin, which was manifested by the presence of colonies inside the inhibition zone. When these cells were cultured and tested, they showed stable, homogeneous, and high-level resistance to telithromycin.     

肺炎链球菌对泰利霉素等抗菌药物的体外抗菌活性

目的了解本院分离的肺炎链球菌对泰利霉素等抗菌药物的体外抗菌活性。方法对本院2005--2007年从各种临床标本收集的97株肺炎链球菌，用K—B纸片法进行药敏试验，测定这些菌株对泰利霉素等3种新近上市和其他7种临床常用抗菌药物的耐药性。结果97株肺炎链球菌对泰利霉素和利奈唑胺的敏感率均为100％，对喹奴普丁-达福普汀也未发现耐药菌株，只是有18．8％的菌株表现为中介。其他抗菌药物的耐药情况如下：对红霉素、克林霉素、万古霉素、左氧氟沙星、氯霉素和四环素的耐药率分别为60．8%、58．8％、0％、2．1％、12．8%和64．5％，对青霉素的敏感率为85．6％。结论本院尚未用于临床的3种新近上市的抗菌药物泰利霉素、利奈唑胺和喹奴普丁-达福普汀，对本院分离的肺炎链球菌有良好的体外抗菌活性。而上述细菌对红霉素、林可霉素以及四环素有较高的耐药性。     

High-level fluoroquinolone resistance in Streptococcus pneumoniae requires mutations in parC and gyrA.

The mechanism of high-level fluoroquinolone resistance was studied in strains of Streptococcus pneumoniae, either selected in vitro or isolated from clinical samples. By using DNA from these high-level-resistant strains, low-level-resistant transformants (MIC of pefloxacin, > or = 32 micrograms/ml; MIC of ciprofloxacin, 4 micrograms/ml; MIC of sparfloxacin, 0.50 micrograms/ml) were obtained at high frequencies (ca.10(-2)), while high-level-resistant transformants (MIC of pefloxacin, > or = 64 micrograms/ml; MIC of ciprofloxacin, 16 to 64 micrograms/ml; MIC of sparfloxacin, > or = 8 micrograms/ml) were obtained only at low frequencies (ca.10(-4)). This suggested that mutations in at least two unlinked genes were necessary to obtain high-level resistance. Low-level resistance was associated with ParC mutations (change from Ser to Tyr at position 79 [Ser79Tyr], Ser79Phe, or Asp83Gly). ParC mutations were associated, in high-level-resistant strains and transformants, with alterations in the quinolone resistance-determining region of GyrA (Ser84Tyr, Ser84Phe, and/or Glu88Lys). Low-level resistance was shown to be necessary for expression of the gyrA mutations. No mutation in the region corresponding to the quinolone resistance-determining region of GyrB and no alteration of drug accumulation were found.     

In vitro activity of telithromycin against Spanish Streptococcus pneumoniae isolates with characterized macrolide resistance mechanisms

The susceptibilities to telithromycin of 203 Streptococcus pneumoniae isolates prospectively collected during 1999 and 2000 from 14 different geographical areas in Spain were tested and compared with those to erythromycin A, clindamycin, quinupristin-dalfopristin, penicillin G, cefotaxime, and levofloxacin. Telithromycin was active against 98.9% of isolates (MICs, < or =0.5 microg/ml), with MICs at which 90% of isolates are inhibited being 0.06 microg/ml, irrespective of the resistance genotype. The corresponding values for erythromycin were 61.0% (MICs, < or =0.25 microg/ml) and >64 microg/ml. The erm(B) gene (macrolide-lincosamide-streptogramin B resistance phenotype) was detected in 36.4% (n = 74) of the isolates, which corresponded to 93.6% of erythromycin-intermediate and -resistant isolates, whereas the mef(A) gene (M phenotype [resistance to erythromycin and susceptibility to clindamycin and spiramycin without blunting]) was present in only 2.4% (n = 5) of the isolates. One of the latter isolates also carried erm(B). Interestingly, in one isolate for which the erythromycin MIC was 2 microg/ml, none of these resistance genes could be detected. Erythromycin MICs for S. pneumoniae erm(B)-positive isolates were higher (range, 0.5 to >64 microg/ml) than those for erm(B)- and mef(A)-negative isolates (range, 0.008 to 2 microg/ml). The corresponding values for telithromycin were lower for both groups, with ranges of 0.004 to 1 and 0.002 to 0.06 microg/ml, respectively. The erythromycin MIC was high for a large number of erm(B)-positive isolates, but the telithromycin MIC was low for these isolates. These results indicate the potential usefulness of telithromycin for the treatment of infections caused by erythromycin-susceptible and -resistant S. pneumoniae isolates when macrolides are indicated.     

Stability of fluoroquinolone resistance in Streptococcus pneumoniae clinical isolates and laboratory-derived mutants

The stability of fluoroquinolone resistance in Streptococcus pneumoniae was evaluated in laboratory-derived mutants and clinical isolates. Isolates with various genotypes and phenotypes were subcultured for 20 days on antibiotic-free media and were monitored by E-tests to identify any alterations in resistance. Fluoroquinolone resistance mechanisms, whether efflux or chromosomally mediated, remained stable in both clinical and laboratory-derived mutants.     

Erythromycin and clindamycin resistance and telithromycin susceptibility in Streptococcus agalactiae

The rates of resistance to erythromycin and clindamycin among Streptococcus agalactiae strains isolated in our hospital increased from 4.2 and 0.8% in 1993 to 17.4 and 12.1%, respectively, in 2001. Erythromycin resistance was mainly due to the presence of an Erm(B) methylase, while the M phenotype was detected in 3.8% of the strains. Telithromycin was very active against erythromycin-resistant strains, irrespective of their mechanisms of macrolide resistance.     

Macrolide resistance in Belgian Streptococcus pneumoniae

The genetic basis of macrolide resistance was characterized in 59 Streptococcus pneumoniae isolates. All isolates were collected in 1995 and 1997 and were from invasive infections. The majority of the isolates (54 of 59 isolates) were erythromycin and clindamycin resistant (MLS(B)-phenotype) and carried the ermAM gene. Five isolates were erythromycin resistant but clindamycin susceptible (M-phenotype). Using PCR the mefE gene was detected in these five isolates. Contrary to the situation found in Canada and the USA, mefE-mediated erythromycin resistance in S. pneumoniae is uncommon in Belgium.     

Non-PmrA-mediated multidrug resistance in Streptococcus pneumoniae

The PmrA multidrug transporter protein gene was inactivated in Streptococcus pneumoniae strains CP1000 (wild-type) and EBR (mutant with enhanced active multidrug efflux). While the resistance to fluoroquinolones and ethidium bromide shown by EBR was reduced to the wild-type level, neither the susceptibility to reserpine in the presence of ethidium bromide and selected fluoroquinolones, nor the ability to produce ethidium bromide-resistant mutants was eliminated in the CP1000 pmrA mutant, indicating the presence of an additional multidrug export protein(s).     

Activities of cethromycin and telithromycin against recent North American isolates of Streptococcus pneumoniae

The in vitro activities of two investigational ketolides, cethromycin (formerly ABT-773) and telithromycin, were determined for a selected group of 312 Streptococcus pneumoniae isolates from a national surveillance program. The MIC of cethromycin at which 50% of the isolates were inhibited was 0.008 micro g/ml, and the MIC at which 90% of the isolates were inhibited was 0.06 micro g/ml; the corresponding values for telithromycin were 相似文献   

Detection of macrolide resistance in Streptococcus pneumoniae

We determined the susceptibilities of recent clinical isolates of Streptococcus pneumoniae to 19 antibiotics. The frequency of erythromycin nonsusceptibility was high, i.e. 8/13 (61.5%), 10/14 (71.4%) and 11/11 isolates (100%) from 13 penicillin-susceptible, 14 penicillin-intermediate and 11 penicillin-resistant S. pneumoniae, respectively. Macrolide resistance was detected by polymerase chain reaction (PCR) and disk diffusion methods. Of these erythromycin-nonsusceptible pneumococcal isolates, 13/29 (44.8%) isolates contained genomic copies of MEFA and showed non-'D'-shaped zones of inhibition observed around rokitamycin and/or clindamycin disks. Sixteen out of 29 isolates (55.2%) contained copies of ERMB and showed typical 'D'-shaped zones of inhibition, except one isolate. Although the macrolide resistance determinants, MEFA and ERMB, could be identified by PCR and disk diffusion methods, PCR methods were more reliable in elucidating these determinants. The susceptibility pattern to 14-, 15- and 16-membered macrolides and clindamycin differed between the MEFA+ and ERMB+ isolates. All isolates were susceptible to levofloxacin, sparfloxacin and vancomycin. The MICs of sitafloxacin were lowest among the fluoroquinolones examined for 38 isolates.     

Activities of telithromycin against 13,874 Streptococcus pneumoniae isolates collected between 1999 and 2003

Telithromycin MICs for 13,874 Streptococcus pneumoniae isolates collected in the first 3 years of the global PROTEKT study (1999 to 2003) were studied. There was no change in the distribution of telithromycin MICs over this period, even in countries where telithromycin is in use. The telithromycin MICs for 10 isolates (0.07%) were >/=4 micro g/ml, and these 10 isolates contained erm(B); there was no evidence of reproducible clonal spread between centers.     

Low-level resistance to rifampin in Streptococcus pneumoniae

Rifampin is recommended for combination therapy of meningitis due to beta-lactam-resistant Streptococcus pneumoniae. High-level rifampin resistance (MIC, > or =4 mg/liter) has been mapped to point mutations in clusters I and III of rpoB of the pneumococcus. The molecular basis of low-level resistance (MICs, > or =0.5 and <4 mg/liter) was analyzed. Spontaneous mutants of clinical pneumococcal isolates were selected on Columbia sheep blood agar plates containing rifampin at 0.5, 4, 10, or 50 mg/liter. Low-level resistance could be assigned to mutations in cluster II (I(545)N, I(545)L). Sensitive (MIC, <0.048 mg/liter) wild-type strains acquired low-level resistance at a rate approximately 10 times higher than that at which they acquired high-level resistance (average mutation frequencies, 2.4 x 10(-7) for low-level resistance versus 2.9 x 10(-8) for high-level resistance [P < 0.0001]). In second-step experiments, the frequencies of mutations from low- to high-level resistance were over 10 times higher than the frequencies of mutations from susceptibility to high-level resistance (average mutation frequencies, 7.2 x 10(-7) versus 5.0 x 10(-8) [P < 0.001]). Mutants with low-level resistance were stable upon passage. Sequencing of a clinical isolate with low-level resistance (MIC, 0.5 mg/liter) revealed a Q(150)R mutation upstream of cluster I. The frequencies of mutations to high-level resistance for this strain were even higher than the rates observed for the in vitro mutants. Therefore, a resistance-mediating mutation located outside clusters I, II, and III has been described for the first time in the pneumococcus. In vitro low-level rifampin resistance in S. pneumoniae could be mapped to cluster II of rpoB. Mutants of pneumococcus with low-level resistance may be selected in vivo during therapy in tissue compartments with low antibiotic concentrations and play a role in the development of resistance.     

Beta-lactam and macrolide resistance in Streptococcus pneumoniae

The resistance of beta-lactam antibiotics in penicillin-resistant Streptococcus pneumoniae (PRSP) is due to alterations in penicillin-binding proteins(PBPs). Recently, highly beta-lactam-resistant strains(MIC: > or = 4 micrograms/ml for penicillin, > or = 8 micrograms/ml for ampicillin, and > or = 4 micrograms/ml for cefotaxime) have been isolated. High resistance of these strains is caused by further alterations in pbp2x and pbp2b genes adjacent to conserved amino acid motifs, in addition to that detected in common PRSP. The resistant mechanisms of macrolides in S. pneumoniae is recognized as production of a 23s rRNA methylase encoded by ermB and efflux system mediated by mefA gene. We detected these genes by PCR in clinical isolates, and showed the relationship between the presence of each gene and the susceptibilities of 14-, 15-, 16-membered macrolides.