Activity of telithromycin compared with seven other agents against 1039 Streptococcus pyogenes pediatric isolates from ten centers in central and eastern Europe

In total, 1039 pediatric Streptococcus pyogenes isolates from Bulgaria, Croatia, the Czech Republic, Hungary, Latvia, Lithuania, Poland, Romania, Slovakia and Slovenia were studied. All strains were susceptible to penicillin G, levofloxacin, and quinupristin–dalfopristin, 91–100% to telithromycin, and 82–100% to erythromycin, azithromycin, and clarithromycin, and 90–100% to clindamycin. Macrolide resistance occurred mainly in Slovakia (25%), the Czech Republic (17.3%), and Croatia (15.8%). Overall, 9.7% of S. pyogenes isolates were erythromycin resistant due to erm(B) - or erm(A) -encoded methylases (72.3%) or to a mef(A) -encoded efflux pump (25.7%). One strain had alterations of both 23S rRNA (A2058G Escherichia coli numbering) and ribosomal protein L22 (G95D).     

Activity of quinupristin–dalfopristin in invasive isolates of Streptococcus pneumoniae from Italy

Eighty-five recent isolates of Streptococcus pneumoniae from patients with invasive disease were examined for their susceptibility to erythromycin, clindamycin, penicillin and quinupristin-dalfopristin by E test. A novel duplex PCR assay was used to detect the presence of the erm (B) or mef (A) genes in all of the erythromycin-resistant isolates. All of the strains tested were susceptible to the combination quinupristin–dalfopristin, regardless of their susceptibility to penicillin or to erythromycin. By duplex PCR, two-thirds of the erythromycin-resistant strains harbored erm , and one-third harbored mef . The activity of quinupristin–dalfopristin was not influenced by the genetic determinant of erythromycin resistance. The in vitro susceptibility of S. pneumoniae to quinupristin–dalfopristin is promising for future use; however, it is important to monitor the possible emergence of resistance.     

Comparative in vitro activity of penicillin G, levofloxacin, moxifloxacin, telithromycin, pristinamycin, quinupristin–dalfopristin and linezolid against ofloxacin-intermediate and -resistant Streptococcus pneumoniae

Screening by ofloxacin disk was carried out on 1158 strains of Streptococcus pneumoniae in order to investigate the in vitro bacteriostatic activity of penicillin G, levofloxacin, moxifloxacin, telithromycin, linezolid, pristinamycin and quinupristin–dalfopristin against ofloxacin-intermediate and -resistant S. pneumoniae strains. It was concluded that these new antimicrobial agents could be useful for the treatment of pneumococcal infections caused by penicillin-sensitive and -resistant S. pneumoniae , and would represent a valid therapeutic option for patients allergic to β -lactams, should they prove to be potent in vivo.     

In vitro activity of levofloxacin against contemporary clinical isolates of Legionella pneumophila, Mycoplasma pneumoniae and Chlamydia pneumoniae from North America and Europe

Objective   To assess the activities of levofloxacin and the comparator agents erythromycin, clarithromycin, azithromycin and doxycycline against atypical respiratory pathogens.
Methods   One hundred and forty-six Legionella pneumophila , 41 Mycoplasma pneumoniae and nine Chlamydia pneumoniae isolates were procured from various culture collections in North America and Europe and tested for susceptibility to the above agents by broth microdilution. The isolates came primarily from clinical sources and were collected from patients between 1995 and 1999.
Results   Against L. pneumophila , levofloxacin was the most active agent, with an MIC₉₀ of 0.03 mg/L, twofold more active than clarithromycin (0.06 mg/L), 16-fold more active than erythromycin and azithromycin (0.5 mg/L) and 64-fold more active than doxycycline. Against M. pneumoniae , azithromycin (MIC₉₀ ≤ 0.0005 mg/L) was the most active agent. However, two isolates of M. pneumoniae , one from the USA and one from Finland, were macrolide resistant (MIC ≥ 4 mg/L), but levofloxacin susceptible (MIC 0.25 mg/L). The geographic origin of L. pneumophila and M. pneumoniae did not affect the MIC range for any antimicrobial agent tested. Against C. pneumoniae , clarithromycin was the most active agent, with an MIC range of ≤0.008–0.03 mg/L.
Conclusions   Levofloxacin had comparable activity to the other agents tested against the atypical respiratory pathogens, confirming its potential as an alternative for empirical therapy of community-acquired pneumonia.     

Activity of telithromycin against 26 quinolone-resistant pneumococci with known quinolone-resistance mechanisms

NCCLS agar dilution was used to test activity of telithromycin compared to clarithromycin, penicillin G, ciprofloxacin, levofloxacin, sparfloxacin and moxifloxacin against 26 pneumococci with defined quinolone resistance (type II topoisomerase and efflux) mechanisms. Thirteen strains were penicillin susceptible, six intermediate and seven resistant. Clarithromycin resistance ( mef and/or erm ) was seen in eight strains. Ciprofloxacin MICs (mg/L) were 8–64 compared to 1–32 (levofloxacin), 0.5 ≥ 32 (sparfloxacin) and 0.125–4 (moxifloxacin). Telithromycin MIC₅₀ and MIC₉₀ values (mg/L) were 0.016 and 0.25, with only one strain having an MIC of 2 mg/L.     

Analysis of the macrolide resistance gene in penicillin-resistant Streptococcus pneumoniae

We examined the penicillin and macrolide resistance of 496 strains of Streptococcus pneumoniae (S. pneumoniae) isolated at Showa University Hospital from November 2004 to May 2005. According to the classification established by the Clinical and Laboratory Standards Institute, the ratio of penicillin susceptible S. pneumoniae (PSSP) was 25.8%, penicillin intermediate S. pneumoniae was 35.9% and penicillin resistant S. pneumoniae (PRSP) was 38.3%. The ratios of macrolide resistant S. pneumoniae were 85.3% for erythromycin and 76.2% for clarithromycin. S. pneumoniae strains were isolated mainly from pediatric patients, and the ratios of PRSP were similar between outpatients (39.8%) and inpatients (45.6%). We screened for mutations in pbp1a, pbp2b and pbp2x, and the retention rate of the macrolide resistance genes, ermB and mefA in 90 strains isolated in the same period. Seventy two strains had at least one mutation in the pbp genes. Interestingly, some of the penicillin susceptible strains had one or two pbp mutations, suggesting a progressive genetic acquirement of penicillin resistance. In screening for retention of the macrolide resistance genes, we found that 42 strains(46.7%) had ermB, 19 strains (21.1%) had mefA and 13 strains (14.4%) had both ermB and mefA. The possession of resistance genes and the minimal inhibitory concentration indicate that the resistance to erythromycin and clarithromycin were induced by ermB or mefA, and the resistance to clindamycin was induced only by ermB. Among the 72 strains with pbps mutations, 65 strains (90.3%) had ermB or mefA or both. Together, these results show that the strains with pbp mutations were being selected and, after acquiring the macrolide resistance gene, transform to multidrug resistant S. pneumoniae.     

Development of interpretive criteria and quality control limits for macrolide and clindamycin susceptibility testing of Streptococcus pneumoniae.

A six-laboratory collaborative study was conducted to develop MIC and zone diameter quality control limits and interpretive criteria for antimicrobial susceptibility testing of Streptococcus pneumoniae with azithromycin, clarithromycin, dirithromycin, and clindamycin. The MICs of all of the agents plus erythromycin for 302 clinical isolates of pneumococci that had been selected with an emphasis on resistant strains were determined by use of the National Committee for Clinical Laboratory Standards (NCCLS)-recommended broth microdilution procedure. The zone diameters of the isolates were also determined for the same agents except erythromycin by the NCCLS disk diffusion test procedure. Repeated testing of S. pneumoniae ATCC 49619 with different sources and lots of media and disks allowed development of MIC and zone diameter quality control ranges for these agents. Interpretive criteria for the MIC of azithromycin were established and were as follows: susceptible, < or = 0.5 microgram/ml; intermediate, 1 microgram/ml; and resistant, > or = 2 micrograms/ml. The interpretive criteria advocated for the MICs of clarithromycin and clindamycin were as follows: susceptible, < or = 0.25 microgram/ml; intermediate, 0.5 microgram/ml; and resistant, > or = 1 microgram/ml. Comparison of MICs and disk diffusion zone diameters led to the development of interpretive criteria for the zone diameters for azithromycin, clarithromycin, and clindamycin that correlated well with these MIC breakpoints. Testing of this organism collection also led to the reestablishment of the erythromycin MIC breakpoints as being identical to those of clarithromycin, which resulted in equivalent cross-susceptibility and cross-resistance for the three macrolides that are currently marketed in the United States. Thus, the susceptibility of pneumococci to azithromycin and clarithromycin can be predicted accurately by testing only erythromycin in clinical laboratories. This recommendation, as well as the interpretive and quality control criteria that are described, have been accepted by NCCLS and are included in the latest NCCLS susceptibility testing guidelines.     

Erythromycin susceptibility of viridans streptococci from the normal throat flora of patients treated with azithromycin or clarithromycin

Objective   To study the emergence of macrolide resistance in throat flora following treatment with clarithromycin or azithromycin.
Methods   Throat samples were collected before and after treatment and plated as a lawn on Columbia blood agar with an erythromycin E test strip. Minimum inhibitory concentrations (MICs) of erythromycin, clarithromycin and azithromycin were determined against isolates of distinct morphology with erythromycin E test MIC results equal to or greater than 2 mg/L. Polymerase chain reaction techniques were used to determine the genetic mechanisms of resistance.
Results   There were 749 resistant isolates of which 474 (63%) were streptococci. Only a quarter of the patients had no resistant streptococci before treatment started. There were increases in the numbers of resistant isolates and in the number of patients carrying a resistant flora during and after treatment. The most common genes identified were mef A/E in isolates with low-level resistance and erm A/M in isolates with high-level resistance.
Conclusions   There is a pool of streptococci carrying genes associated with macrolide resistance in the normal respiratory flora of generally healthy adults. Differences between the patients treated with clarithromycin and those treated with azithromycin were difficult to assess because of the large number of patients in each group with macrolide-resistant streptococci before treatment. Although there were some differences these were not statistically significant.     

Susceptibility of strains of Streptococcus agalactiae to macrolides and lincosamides, phenotype patterns and resistance genes

The Group B streptococcus ( Streptococcus agalactiae ) is a pathogen of increasing importance in human disease. We therefore studied the susceptibility of clinical isolates of S. agalactiae to penicillin G, erythromycin, azithromycin and clindamycin using National Committee for Clinical Laboratory Standards methodology, and we also determined the phenotypes of macrolide-lincosamide susceptibility and the resistance genes implicated in a group of selected isolates of the different phenotypes. We used 221 isolates collected between 1997 and 1999 in two Health Authority Areas in Móstoles and Granada, Spain. The minimal concentration for 90% inhibition (MIC₉₀) for penicillin G was 0.12 mg/L and all the isolates tested were susceptible. One hundred and eighty-five (83.7%) were susceptible to erythromycin and azithromycin and 191 (86.4%) were susceptible to miocamycin and clindamycin. Twenty-three isolates (10.4%) had a constitutive MLS_B phenotype, seven (3.2%) an inducible phenotype, and six (2.7%) an M phenotype. All except one of the MLS_B phenotype isolates tested ( n  = 23) carried erm genes; in two strains with the mef (A) gene, all the M phenotype ( n  = 6) isolates tested carried mef genes, while erm and mef (A) genes were absent in all the macrolide-lincosamide-susceptible ( n  = 12) isolates tested. In our environment, resistance to macrolide and lincosamide in S. agalactiae was present in 10–16% of the isolates. The majority of resistant strains had the MLS_B phenotype.     

Antimicrobial susceptibility of Streptococcus pneumoniae from children attending day-care centers in a central Italian city

Objective: To undertake a survey of nasopharyngeal carriage of Streptococcus pneumoniae , which reflects strains causing infection, in 100 children under 3 years of age attending day-care centers in Frosinone, a city near Rome.
Methods: Fifty-three unique isolates of S. pneumoniae , isolated from 41 of the children tested, were tested for antimicrobial susceptibility to penicillin, cefotaxime, erythromycin, clindamycin, tetracycline, chloramphenicol and trimethoprim-sulfamethoxazole.
Results: Resistance rates were as follows: penicillin, 20.7% (15% intermediate; 5.7% resistant); trimethoprim-sulfamethoxazole, 64.2%; erythromycin, 64.2%; clindamycin, 30.2%; tetracycline, 32.1%; and chloramphenicol, 3.8%. Except for three intermediate strains, all strains were susceptible to cefotaxime. Only five strains were susceptible to all of the antibiotics tested. An unusual finding of this study was that 23 of the 34 erythromycin-resistant strains were penicillin susceptible, whereas erythromycin-resistant strains found in other countries are predominantly penicillin resistant as well. In addition, 18 of the 34 erythromycin-resistant strains were susceptible to clindamycin. Serogroups 6, 14, 19 and 23 accounted for 84.9% of the isolates.
Conclusions: These data show that carriage of antibiotic-resistant pneumococci in children under 3 years of age is high in Frosinone, Italy. Information on resistance rates in pneumococcal disease in different age groups and on prevalence of drug resistance in other parts of the country is urgently needed.     

The effect of carbon dioxide on susceptibility testing of azithromycin, clarithromycin and roxithromycin against clinical isolates of Streptococcus pneumoniae and Streptococcus pyogenes by broth microdilution and the Etest: Artemis Project—first-phase study

Objective: To evaluate the effect of carbon dioxide on the susceptibility testing, using broth microdilution and the Etest (AB Biodisk, Solna, Sweden), of azithromycin, clarithromycin and roxithromycin against Streptococcus pneumoniae and Streptococcus pyogenes .
Methods: Fresh clinical isolates collected from 36 hospital laboratories in 12 countries were evaluated using the Etest in the presence of carbon dioxide. The isolates were retested under ambient conditions (absence of carbon dioxide) using broth microdilution and/or the Etest.
Results: Carbon dioxide falsely elevated azithromycin, clarithromycin and roxithromycin MIC₉₀S for S. pneumoniae , determined by the Etest, approximately 12-fold. Also, the azithromycin MIC₉₀ for S. pyogenes was increased fourfold; the effect was less marked for clarithromycin and roxithromycin. When isolates were retested in the absence of carbon dioxide, using the Etest or microdilution, susceptibilities to azithroymycin were comparable to those to clarithromycin ( S. pneumoniae , 93.4% versus 91.3%; S. pyogenes , 96.4% versus 95.8%). Both organisms were less susceptible to roxithromycin ( S. pneumoniae , 71.3%; S. pyogenes , 85.7%). An internal standard control, consisting of 50 isolates each of S. pneumoniae, S. pyogenes and Haemophilus influenzae , confirmed that azithromycin susceptibility testing resulted in falsely elevated MICs.
Conclusions: Carbon dioxide falsely elevated azithromycin MICs for S. pneumoniae and S. pyogenes , with an apparent reduction in susceptibility. When the in vitro activity of azithromycin and other macrolides against S. pneumoniae and S. pyogenes is being evaluated, awareness of the pH effect is essential.     

Pharyngeal colonization prevalence rates for Streptococcus pyogenes and Streptococcus pneumoniae in a respiratory chemoprophylaxis intervention study using azithromycin

Objectives   A prospective assessment of the pharyngeal colonization prevalence rates for Streptococcus pyogenes and Streptococcus pneumoniae before and after an azithromycin chemoprophylaxis intervention clinical trial in a cohort of US Marine Corps trainees. In addition, the minimum inhibitory concentrations (MICs) for all streptococcal isolates, for azithromycin, penicillin, erythromycin and cefotaxime are reported.
Methods   Between November 1994 and March 1995, 1108 asymptomatic male US Marine Corps trainees, located in Southern California, were randomly assigned to one of three intervention groups: (1) weekly oral azithromycin, 500 mg ( n  = 362); (2) 1.2 MU benzathine penicillin G, intramuscularly once ( n  = 374); or (3) no chemoprophylaxis ( n  = 372). Subjects provided both a pre- and post-training pharyngeal culture and microbial analysis was conducted to determine the colonization status of each study subject.
Results   The pretraining colonization prevalence was 1.2% for S. pneumoniae and 2.4% for S. pyogenes . There was no statistical difference in pretraining prevalence between the three treatment groups for either organism. Post-training pharyngeal cultures revealed an overall prevalence of 1.1% with no difference between treatment arms. However, the overall post-training prevalence of S. pyogenes colonization increased to 4.8%, with the azithromycin group having significant evidence of protection (0.7%) in comparison with the no-treatment group (8.2%). The Etest method demonstrated no significant difference in the MIC₅₀, MIC₉₀, and MIC ranges between pre- and post-training isolates for any of the tested drugs.
Conclusion The use of azithromycin as a chemoprophylactic agent to reduce the colonization and subsequent infection of streptococcal respiratory disease among healthy adult male military recruits may be beneficial.     

Comparison of the in vitro activity of pristinamycin and quinupristin/dalfopristin against Streptococcus pneumoniae

The in vitro activity of quinupristin/dalfopristin, a new injectable streptogramin, and pristinamycin was evaluated against 200 recently isolated clinical Streptococcus pneumoniae strains expressing various degrees of susceptibility to penicillin G and erythromycin. MICs were determined by the agar dilution method. All strains were susceptible to pristinamycin irrespective of their susceptibility to penicillin G or erythromycin (MIC90: 0.25 mg/L for each phenotype). The activity of quinupristin/dalfopristin was slightly lower than that of pristinamycin against 42 penicillin G-susceptible/erythromycin-susceptible strains (MIC90: 0.5 mg/L), 13 penicillin G-susceptible/erythromycin-resistant strains (MIC90: 1 mg/L), 25 penicillin G-intermediate or -resistant/erythromycin-susceptible strains (MIC90: 0.5 mg/L) and 120 penicillin G-intermediate or -resistant/erythromycin-resistant strains (MIC90: 0.5 mg/L). The activity of both streptogramins was not significantly altered in case of erythromycin resistance. Thus, both streptogramins might be useful for the treatment of penumococcal infections, especially in cases of multiresistant strains.     

National surveillance programme on susceptibility patterns of respiratory pathogens in South Africa: moxifloxacin compared with eight other antimicrobial agents

AIMS: The susceptibility patterns of Streptococcus pneumoniae, Haemophilus influenzae, Moraxella catarrhalis, Klebsiella pneumoniae, and Streptococcus pyogenes isolated from specimens submitted to 12 private laboratories in South Africa were determined. METHODS: Minimum inhibitory concentration (MIC) determinations were performed on the isolates in the microbiology laboratory at Tygerberg Hospital according to the recommendations of the National Committee for Clinical Laboratory Standards (NCCLS). RESULTS: According to the NCCLS breakpoints, 24% of 729 S pneumoniae isolates were sensitive, 30% intermediate, and 46% resistant to penicillin. Rates of macrolide resistance were high, with 61% of the pneumococci being resistant to clarithromycin and azithromycin. Co-trimoxazole resistance was also high, with 28% of pneumococcal strains being sensitive, 21% intermediate, and 51% resistant. beta Lactamase was produced by 7% of 736 H influenzae isolates and 91% of 256 M catarrhalis isolates. The quinolones, moxifloxacin and levofloxacin, were universally active against all isolates tested, which included S pneumoniae, H influenzae, M catarrhalis, K pneumoniae, and S pyogenes. CONCLUSIONS: Haemophilus influenzae and S pneumoniae were the most commonly isolated organisms. Resistance to penicillin was one of the highest reported in the world (76%) in S pneumoniae, as was macrolide resistance in pneumonocci, although surprisingly, only 14% of S pyogenes were resistant. The quinolones, moxifloxacin and levofloxacin, were active against all organisms tested, including the penicillin and macrolide resistant strains and moxifloxacin was more active than levofloxacin against pneumococci.     

Macrolide-resistance mechanisms in Streptococcus pneumoniae isolates from Chinese children in association with genes of tetM and integrase of conjugative transposons 1545

This study investigated macrolide-resistant Streptococcus pneumoniae carried by Beijing children presenting with respiratory tract infections. Nasopharyngeal S. pneumoniae strains were tested for sensitivity with 15 antibiotics and further analyzed for phenotypes of macrolide-resistant strains and by PCR for the macrolide-resistant genes ermB, mefA, tetM, and integrase of conjugative transposon (Tn1545) intTn. We found 185 strains of S. pneumoniae relatively highly resistant to erythromycin (78.9%), clindamycin (76.2%), tetracycline (86%), and SMZ-TMP (78.7%) but with relatively low resistance to amoxicillin (2.2%), cefaclor (15.5%), ceftriaxone (2.8%), and cefuroxime (14.1%). The 146 strains of erythromycin-resistant S. pneumoniae showed extensive cross-resistance to other macrolides like azithromycin (100%), clarithromycin (100%), acetylspiramycin (95.2%), and clindamycin (95.9%). Genes ermB and mefA were detected in all erythromycin-resistant strains, with ermB(+) 79.5%, ermB + mefA(+) 17.8%, and mefA(+) 2.7%. About 96.9% of tetracycline-resistant isolates were positive for tetM, compared to 26.9% of sensitive strains. Ninety percent of tetracycline-resistant strains were also erythromycin-resistant versus 11.5% of tetracycline-sensitive strains. The intTn gene was present in 87.6% of S. pneumoniae strains and correlated with erythromycin and tetracycline resistance. The close relationship between the conjugative transposon Tn1545 and the genes ermB and tetM is probably one of the important mechanisms explaining the multiple drug resistance of S. pneumoniae.     

In vitro antibacterial activity of beta-lactams and non-beta-lactams against Streptococcus pneumoniae isolates from Sydney, Australia

AIMS: This study was undertaken to determine the antimicrobial resistance patterns of strains of Streptococcus pneumoniae from Sydney, Australia, comparing penicillin-susceptible, -intermediate and -resistant isolates. METHODS: Non-duplicate cultures of S. pneumoniae were collected from 1 January to 31 December 2002 in the three penicillin-susceptibility categories. Minimum inhibitory concentrations (MICs) of 19 antibacterial agents were determined by agar dilution based on the National Committee for Clinical Laboratory Standards (NCCLS) methodology. Overall for 2002, 687 non-duplicate isolates were obtained, of which 190 (28%) were intermediate or resistant to penicillin. From this set, 183 isolates were selected for study: 88 (48%) in the penicillin-susceptible group (MIC or= 2.0 mg/L). RESULTS: Resistance to non-beta-lactams was more common in penicillin-intermediate or -resistant strains. Multidrug resistance (resistance to >or= 2 non-beta-lactams) was found in 3% of penicillin-susceptible, 52% of penicillin-intermediate and 87% of penicillin-resistant isolates. Erythromycin resistance was seen in 22% of the penicillin-susceptible strains but increased significantly to 60% and 89% in the penicillin-intermediate and resistant strains, respectively. Clindamycin, tetracycline and trimethoprim/sulfamethoxazole showed similar diminished activity in penicillin-intermediate and -resistant strains; 64, 84 and 91% of the penicillin-resistant isolates were resistant to clindamycin, tetracycline and to trimethoprim/sulfamethoxazole, respectively. Chloramphenicol resistance was comparatively low level except 19% of the penicillin-resistant strains were resistant. Ciprofloxacin MICs for 14 strains were raised (MICs 4-16 mg/L); three of these were penicillin-susceptible, one penicillin-intermediate and 10 penicillin-resistant. Only one isolate was resistant to moxifloxacin and to gatifloxacin. Resistance to rifampicin, vancomycin, oritavancin, or linezolid was not detected. Twenty-three isolates were intermediate and one resistant to quinupristin/dalfopristin - 22 of these were penicillin resistant. CONCLUSIONS: Streptococcus pneumoniae isolates from Sydney are commonly resistant to beta-lactams and available non-beta-lactam agents, especially if they are penicillin non-susceptible. Resistance to moxifloxacin and gatifloxacin is still rare, but some isolates were non-susceptible to quinupristin/dalfopristin. It is important to continue to survey resistance patterns to recognise emerging resistances which affect the selection of empirical antimicrobials to treat infections with S. pneumoniae.     

Changing antimicrobial susceptibility patterns among Streptococcus pneumoniae and Haemophilus influenzae from Brazil: Report from the SENTRY Antimicrobial Surveillance Program (1998-2004)

Although antimicrobial resistance rates among Streptococcus pneumoniae and Haemophilus influenzae have increased significantly in most countries in the last years, most studies from Brazil report relatively low resistance rates among these pathogens. In this study, we analyzed the susceptibility patterns of S. pneumoniae and H. influenzae from Brazil during a 7-year period. A total of 829 S. pneumoniae and 718 H. influenzae consecutively collected from 1998 to 2004, mainly from respiratory tract and bloodstream infections, were susceptibility tested by broth microdilution methods against >30 drugs and the results were analyzed by year. Overall, 77.8% of S. pneumoniae strains were considered susceptible (MIC, < or =0.06 microg/ml) to penicillin. Resistance to penicillin (MIC, > or =2 microg/ml) and ceftriaxone (MIC, > or =4 microg/ml) were detected in 7.5 and 0.5% of strains, respectively. The fluoroquinolones, levofloxacin (MIC90) 1 microg/ml) and gatifloxacin (MIC90, 0.5 microg/ml), were active against 99.8% of the isolates tested. Among the other non-beta-lactam drugs tested, the rank order of susceptibility rates was chloramphenicol (98.9%) > clindamycin (96.4%) > erythromycin (90.6%) > tetracycline (69.8%) > trimethoprim/sulfamethoxazole (36.7%). Resistance to penicillin has increased markedly among S. pneumoniae isolates over 7 years (from 2.9 to 11.0%). Additionally, resistance rates against erythromycin, clindamycin, and tetracycline decreased among pneumococcal strains during the same period. S. pneumoniae recovered from pediatric patients (< or =5 years) showed increased penicillin and trimethoprim/sulfametroxazole resistance rates compared to older populations. The rate of ampicillin resistance among H. influenzae was 14.0%, which also corresponds with the beta -lactamase production rate. All H. influenzae isolates were susceptible to amoxicillin/clavulanate (MIC90, 1 microg/ml), ceftriaxone (MIC90, < or =0.008 microg/ml), cefepime (MIC90, 0.12 microg/ml), ciprofloxacin (MIC90, < or = 0.12microg/ml), levofloxacin (MIC90, < or =0.5 microg/ml), and gatifloxacin (MIC90, < or =0.03 microg/ml). Resistance to the antimicrobials tested remained very stable among H. influenzae isolates during the 7-year study period. The continued emerging antimicrobial resistances found in these pathogens (mainly S. pneumoniae) highlight the need for alternative agents for the treatment of infections caused by these species.     

Macrolide resistance in Streptococcus pneumoniae isolated from patients with community-acquired lower respiratory tract infections in Portugal: results of a 3-year (1999-2001) multicenter surveillance study

A nationwide multicenter study (including 31 laboratories) of the antimicrobial susceptibility of 1210 Streptococcus pneumoniae isolates from patients with community-acquired lower respiratory tract infections (LRTI) was carried out over 3 years (1999-2001) in Portugal. Testing of all isolates was undertaken in a central laboratory. Overall macrolide resistance was 13.1%. Decreased susceptibility to penicillin was 24.5% (15.5% low-level and 9.0% high-level resistance). Taken into consideration, the resistance rates reported in a previous surveillance study of 1989-1993, a six-fold increase of erythromycin resistance in the last decade was documented. Resistance to erythromycin, clarithromycin, and azithromycin was higher in pediatric patients than in adults. The overwhelming majority (82.3%) of macrolide-resistant isolates were multidrug resistant, although 44.9% were fully susceptible to penicillin. Most macrolide-resistant isolates (80.4%) showed the MLSB phenotype (76.6% MLSB-constitutive resistance, and 3.8% MLSB-inducible resistance) and were also resistant to clindamycin, tetracycline, and co-trimoxazole. The M phenotype was seen in 19.6% isolates and these had MIC90 values of 8 mg/L for erythromycin and clarithromycin, and of 12 mg/L for azithromycin. The clinical significance of macrolide resistance in the management of LRTI is discussed. Because of the specific situation concerning macrolide resistance described in S. pneumoniae, careful use of macrolide antibiotics in therapy and cautious monitoring of macrolide resistance should be continued in Portugal.     

Evolution of Streptococcus pneumoniae serotypes and antibiotic resistance in Belgium—update (1994–98)

Objective To follow the evolution of capsular types and resistance of Streptococcus pneumoniae , isolated from deep sites.
Methods More than 100 Belgian laboratories permanently collect S. pneumoniae strains isolated from puncture specimens (blood, cerebrospinal fluid, middle ear fluid, etc.) and forward them to the reference center in Leuven, in order to determine the capsular serogroups and types (SGTs) and their resistance.
Results From 1994 to 1998, the 5486 S. pneumoniae strains examined belonged to 39 of the 46 currently identified SGTs. The 10 most frequent SGTs accounted for 78.9% of the isolates, and 97% of all isolates belonged to SGTs included in the 23-valent vaccine. Overall mortality of patients with pneumococcal bacteremia or meningitis was 9.7%, and 23.8% in patients over 80 years. From 1994 to 1998, resistance to penicillin (P) increased from 7.6% to 14.2%, to tetracycline (T) from 14.9% to 28.0%, and to erythromycin (E) from 22.9% to 31%. Triple resistance (PTE) increased from 0.9% in 1994 to 6.6% in 1998. Five SGTs (6, 9, 14, 19 and 23) accounted for 50% of the isolates, but for > 90% of the penicillin-resistant or erythromycin-resistant isolates.
Conclusions Resistance of S. pneumoniae to penicillin, erythromycin and tetracycline is steadily increasing and is concentrated in five serotypes included in the 23-valent pneumococcal vaccine. Increasing resistance and high mortality of invasive infections are an incentive to vaccinate vulnerable groups.     

Induction of ribosome methylation in MLS-resistant Streptococcus pneumoniae by macrolides and ketolides

One major mechanism for resistance to macrolide antibiotics in Streptococcus pneumoniae is MLS (macrolide, lincosamide, and streptogramin B) resistance, manifested when the 23S rRNA is methylated by the product of an erm gene. This modification results in the decreased binding of all known macrolide, lincosamide, and streptogramin B antibiotics to the ribosome. More than 30 ermAM-containing clinical isolates of S. pneumoniae were examined in our lab and showed high-level resistance (MIC > or =128 microg/ml) to erythromycin, azithromycin, tylosin, clindamycin, and ketolide (macrolides that lack the cladinose sugar) TE-802. We found that the new generation of ketolides A965 and A088 displayed variable activity against the same group of resistant S. pneumoniae strains. To understand the basis of variability of the minimal inhibitory concentration (MIC) values of A965 and A088, we examined the effects of a series of macrolides and ketolides on the level of 23S rRNA methylation in five ermAM-containing resistant S. pneumoniae isolates. We show here that the basal levels of ribosomal methylation vary from strain to strain. The level of rRNA methylation can be strongly induced by erythromycin, azithromycin, and TE-802, resulting in high-level of resistance to these compounds. Ketolide A965 and A088, however, are weak inducers at sub-MIC drug concentrations, therefore showing variable activities in strains with differential methylation levels.