Streptococcus pneumoniae isolates with reduced susceptibility to ciprofloxacin in Spain: clonal diversity and appearance of ciprofloxacin-resistant epidemic clones

Fluoroquinolone resistance in Streptococcus dysgalactiae subsp. equisimilis and evidence for a shared global gene pool with Streptococcus pyogenes

Quinolone resistance is an emerging problem in Streptococcus pyogenes, and recombination with Streptococcus dysgalactiae DNA has been implicated as a frequent mechanism leading to resistance. We have characterized a collection of S. dysgalactiae subsp. equisimilis isolates responsible for infections in humans (n = 314) and found a high proportion of levofloxacin-resistant isolates (12%). Resistance was associated with multiple emm types and genetic lineages, as determined by pulsed-field gel electrophoretic profiling. Since we could not find evidence for a role of efflux pumps in resistance, we sequenced the quinolone resistance-determining regions of the gyrA and parC genes of representative resistant and susceptible isolates. We found much greater diversity among the parC genes (19 alleles) than among the gyrA genes (5 alleles). While single mutations in either GyrA or ParC were sufficient to raise the MIC so that the strains were classified as intermediately resistant, higher-level resistance was associated with mutations in both GyrA and ParC. Evidence for recombination with S. pyogenes DNA was found in some parC alleles, but this was not exclusively associated with resistance. Our data support the existence of a common reservoir of genes conferring quinolone resistance shared between S. dysgalactiae subsp. equisimilis and S. pyogenes, while no recombination with the animal pathogen S. dysgalactiae subsp. dysgalactiae could be found.

Increasing genetic relatedness of ciprofloxacin-resistant Streptococcus pneumoniae isolated in Canada from 1997 to 2005

The genetic relatedness of ciprofloxacin-resistant Streptococcus pneumoniae isolates collected from 1997 to 2002 (n = 82) and 2003 to 2005 (n = 123) was compared by pulsed-field gel electrophoresis (PFGE). Increased genetic homogeneity among the isolates from 2003 to 2005 (cluster analysis; P < 0.001) appeared to be due to expansion of existing clonal groups and to introduction of new PFGE types.

Resistance patterns of selected respiratory tract pathogens in Poland

This study presents the results of a survey of the in-vitro susceptibility to antimicrobial agents of major pathogens responsible for community-acquired respiratory tract infections in Poland during 2002-2004. The collection of 1184 bacterial isolates comprised 398 Streptococcus pneumoniae, 344 Haemophilus influenzae, 302 Streptococcus pyogenes and 140 Moraxella catarrhalis. Among the pneumococcal isolates, 16.8% were penicillin-non-susceptible (PNSP), of which 80.6% were identified as multidrug-resistant. Overall, 9.0% of H. influenzae isolates were beta-lactamase-positive, although this percentage increased noticeably in the third year of the study. Based on PCR results, 12.8% of H. influenzae isolates were identified as low-level beta-lactamase-negative, ampicillin-resistant (BLNAR), and one isolate as low-level beta-lactamase-positive, amoxycillin-clavulanic acid-resistant (BLPACR). Pulsed-field gel electrophoresis (PFGE) classified 45 H. influenzae isolates with altered penicillin-binding proteins into 15 PFGE types, including two predominant types (with four and six sub-types) containing 15 and ten isolates, respectively. Resistance to tetracycline, erythromycin and clindamycin was found in 20.9%, 8.9% and 4.6% of S. pyogenes isolates, respectively. The production of beta-lactamase characterised 91.4% of M. catarrhalis isolates. In summary, the overall occurrence of PNSP in Poland remains stable, although there was a noticeable increase in the proportion of fully-resistant isolates. A rising trend in the prevalence of beta-lactamase producers and low-level BLNAR isolates was observed among Polish isolates of H. influenzae.

In vitro activities of ertapenem against drug-resistant Streptococcus pneumoniae and other respiratory pathogens from 12 Asian countries

In vitro activities of ertapenem and 11 other comparator agents were tested against 1025 isolates of respiratory pathogens collected from 12 Asian countries. Resistance rate to ertapenem was 1.2% in 602 isolates of Streptococcus pneumoniae (MIC(50), 0.06/MIC(90), 1 microg/mL). Ertapenem was also very active against penicillin-, ciprofloxacin-, erythromycin-, and multidrug-resistant pneumococcal isolates (resistance rate: 3.5%, 2.7%, 1.9%, and 2.7%, respectively). Ertapenem-resistant pneumococcal isolates were found only in Vietnam and Korea. Ertapenem resistance was not found in methicillin-susceptible Staphylococcus aureus, Haemophilus influenzae, Moraxella catarrhalis, and Klebsiella pneumoniae, including extended-spectrum beta-lactamase producers. In vitro data suggest that ertapenem could be a useful treatment option for community-acquired pneumonia.

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= 0.06 mg/L), 25 (14%) in the penicillin-intermediate group (MIC 0.125-1.0 mg/L) and 70 (38%) in the penicillin-resistant 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.

Antibiotic consumption and generation of resistance in Streptococcus pneumoniae: the paradoxical impact of quinolones in a complex selective landscape

The development of resistance to the different antibiotics by the majority of bacterial species of clinical importance seems unavoidable. However, not all drugs have the same efficiency to select for resistance. Large differences in the qualitative and quantitative consumption of antibiotics among countries are known to exist and several authors have consistently reported the direct relationship between consumption and selection of resistance for Streptococcus pneumoniae, Streptococcus pyogenes, Haemophilus influenzae and Escherichia coli and beta-lactams and macrolides use. In Spain, extensive surveillance started in 1996, and the Willow (SAUCE) Project, to monitor and update resistance in respiratory pathogens and to couple those data with data concerning national antibiotic consumption (IMS) from both a temporal and geographical approach. Temporally, despite a continuous increase of 16% in quinolone consumption from 1997 to 2001, basically due to the arrival of respiratory quinolones, levofloxacin and moxifloxacin, a continuous linear increase in the resistance rates to ciprofloxacin in S. pneumoniae was not observed. There also was an inverse correlation between provincial consumption of quinolones and resistance to ciprofloxacin. Several hypotheses are proposed and discussed to explain these apparent paradoxical observations, such as the replacement of ciprofloxacin by more potent antipneumococcal quinolones, the possibility of an antibiotic pressure threshold, the influence of other nonquinolone drugs on the expression of ciprofloxacin-resistance biological costs, and the influence of changes in temporal or spatial prevalence of particular clones.

Relative fitness of fluoroquinolone-resistant Streptococcus pneumoniae

Fluoroquinolone resistance in Streptococcus pneumoniae is primarily mediated by point mutations in the quinolone resistance–determining regions of gyrA and parC. Antimicrobial resistance mutations in housekeeping genes often decrease fitness of microorganisms. To investigate the fitness of quinolone-resistant S. pneumoniae (QRSP), the relative growth efficiencies of 2 isogenic QRSP double mutants were compared with that of their fluoroquinolone-susceptible parent, EF3030, by using murine nasopharyngeal colonization and pneumonia models. Strains containing the GyrA: Ser81Phe, ParC: Ser79Phe double mutations, which are frequently seen in clinical QRSP, competed poorly with EF3030 in competitive colonization or competitive lung infections. However, they efficiently produced lung infection even in the absence of EF3030. The strain containing the GyrA: Ser81Phe, ParC: Ser79Tyr double mutations, which is seen more frequently in laboratory-derived QRSP than in clinical QRSP, demonstrated reduced nasal colonization in competitive or noncompetitive lung infections. However, the strain was equally able to cause competitive or noncompetitive lung infections as well as EF3030.

High genetic diversity of ciprofloxacin-nonsusceptible isolates of Streptococcus pneumoniae in Poland

We have analyzed the susceptibility to ciprofloxacin of 697 pneumococcal isolates collected in 1998-2002 in Poland from patients with respiratory tract diseases. Thirty-one ciprofloxacin-nonsusceptible isolates (MICs, > or =4 microg/ml) were identified, of which two were resistant to levofloxacin (MIC, 8 microg/ml). Serotyping, pulsed-field gel electrophoresis, multilocus sequence typing, and the analysis of resistance determinants showed their great genetic diversity.

Fluoroquinolone resistance in penicillin-resistant Streptococcus pneumoniae clones, Spain

Among 2,882 Streptococcus pneumoniae sent to the Spanish Reference Laboratory during 2002, 75 (2.6%) were ciprofloxacin-resistant. Resistance was associated with older patients (3.9% in adults and 7.2% in patients > or =65 years of age), with isolation from noninvasive sites (4.3% vs. 1.0%), and with penicillin and macrolide resistance. Among 14 low-level resistant (MIC 4-8 microg/mL) strains, 1 had a fluoroquinolone efflux phenotype, and 13 showed single ParC changes. The 61 high-level ciprofloxacin-resistant (MIC > or =16 microg/mL) strains showed either two or three changes at ParC, ParE, and GyrA. Resistance was acquired either by point mutation (70 strains) or by recombination with viridans streptococci (4 strains) at the topoisomerase II genes. Although 36 pulsed-field gel electrophoresis patterns were observed, 5 international multiresistant clones (Spain23F-1, Spain6B-2, Spain9V-3, Spain14-5 and Sweden15A-25) accounted for 35 (46.7%) of the ciprofloxacin-resistant strains. Continuous surveillance is needed to prevent the dissemination of these clones.

Fluoroquinolone and other antimicrobial resistance in invasive pneumococci, Hong Kong, 1995-2001

Fluoroquinolone resistance among invasive pneumococci in Hong Kong was high and a result of clonal expansion and spread.

We determined the susceptibilities of 265 invasive isolates of pneumococci obtained during 1995 to 2001 in Hong Kong to 11 antimicrobial agents and their serotypes. Overall, 62.6% isolates were susceptible to penicillin, 20% were intermediately resistant, and 17.4% were resistant. The overall prevalence of levofloxacin resistance (MIC >8 µg/mL) was 3.8% but increased to 15.2% among the penicillin-resistant isolates. All levofloxacin-resistant isolates were clonally related; had reduced susceptibility to penicillin, cefotaxime, and clarithromycin; and were derived from adults >50 years of age. Of the penicillin-nonsusceptible pneumococci, 90% from children <5 years of age and 54.8% from persons of all ages were of serotypes that are included in the 7-valent pneumococcal conjugate vaccine; 93.5% from children <5 years of age and 93% from persons of all ages were of serotypes that are included in the 23-valent polysaccharide vaccine.

Molecular Characterization of Clinical Streptococcus pneumoniae Isolates with Reduced Susceptibility to Fluoroquinolones Emerging in Italy

Fifteen Streptococcus pneumoniae clinical isolates with reduced fluoroquinolone susceptibility (defined as a ciprofloxacin MIC of > or = 4 microg/ml), all collected in Italy in 2000-2003, were typed and subjected to extensive molecular characterization to define the contribution of drug target alterations and efflux mechanisms to their resistance. Serotyping and pulsed-field gel electrophoresis analysis indicated substantial genetic unrelatedness among the 15 isolates, suggesting that the new resistance traits arise in multiple indigenous strains rather than through clonal dissemination. Sequencing of the quinolone resistance-determining regions of gyrA, gyrB, parC, and parE demonstrated that point mutations producing single amino acid changes were more frequent in topoisomerase IV (parC mutations in 14 isolates and parE mutations in 13) than in DNA gyrase subunits (gyrA mutations in 7 isolates and no gyrB mutations observed). No isolate displayed a quinolone efflux system susceptible to carbonyl cyanide m-chlorophenylhydrazone; conversely, four-fold or greater MIC reductions in the presence of reserpine were observed in all 15 isolates with ethidium bromide, in 13 with ulifloxacin, in 9 with ciprofloxacin, in 5 with norfloxacin, and in none with five other fluoroquinolones. The effect of efflux pump activity on the level and profile of fluoroquinolone resistance in our strains was minor compared with that of target site modifications. DNA mutations and/or efflux systems other than those established so far might contribute to the fluoroquinolone resistance expressed by our strains. Susceptibility profiles to nonquinolone class antibiotics and resistance-associated phenotypic and genotypic characteristics were also determined and correlated with fluoroquinolone resistance. A unique penicillin-binding protein profile was observed in all five penicillin-resistant isolates, whereas the same PBP profile as S. pneumoniae R6 was exhibited by all six penicillin-susceptible isolates. This is the first attempt to molecularly characterize clinical isolates of S. pneumoniae with reduced susceptibility to fluoroquinolones emerging in Italy.

Quinolone Resistance among Pneumococci: Therapeutic and Diagnostic Implications

Fluoroquinolones are widely recommended as empirical monotherapy for community-acquired pneumonia. Since 1999, case reports of failure of levofloxacin therapy due to levofloxacin-resistant strains of Streptococcus pneumoniae have started to appear. Most worrying is that, in some cases, levofloxacin resistance has been acquired by pneumococci within days of the initiation of therapy. Because use of current clinical antimicrobial resistance breakpoints fail to identify the majority of S. pneumoniae isolates with only first-step mutations, current treatment guidelines not only may have implications with regard to the ability of surveillance programs to detect emerging resistance but may have therapeutic implications as well.

Fluoroquinolone Resistance in Clinical Isolates ofStreptococcus pneumoniaefrom Asian Countries: ANSORP Study

Seventeen clinical isolates of Streptococcus pneumoniae showing reduced susceptibility to ciprofloxacin (MIC >/= 4 micro g/ml) collected from eight different Asian countries were analyzed by antimicrobial susceptibility, serotyping, pulsed-field gel electrophoresis (PFGE), and DNA sequencing of the quinolone resistance-determining regions (QRDRs) in gyrA, gyrB, parC, and parE. All isolates but one showed more than one amino acid alteration in QRDRs of four responsible genes. Ile460 --> Val in parE was the most common mutation. Data suggest that Lys137 --> Asn in parC may be a primary step in the development of high-level and multiple FQ resistance. An additional mutation of Ser81 --> Phe in gyrA resulted in high-level resistance to ciprofloxacin, levofloxacin, and gatifloxacin, whereas Ser79 --> Phe in parC may exert an important role in the development of moxifloxacin resistance. Two novel amino acid changes in gyrB, Ala390 --> Val and Asn423 --> Thr, were found. Data from PFGE suggest an introduction and local spread of multiple resistant Spain(23F)-1 clone in Hong Kong, but isolates from other Asian countries were not related to this clone.

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.

Fluoroquinolone-resistant Streptococcus pneumoniae in Spain: activities of garenoxacin against clinical isolates including strains with altered topoisomerases

The activity of garenoxacin was assessed against 412 Streptococcus pneumoniae isolates (49.3% from the adult population). Overall penicillin, erythromycin, and ciprofloxacin (MIC, >/=4 micro g/ml) resistance was 51.7, 35.4, and 1.5%, respectively. For all isolates, the garenoxacin MIC was </=1 micro g/ml. Amino acid replacements in GryA (Ser81-->Phe or Tyr), ParC (Ser79-->Phe or Tyr; Asp83-->Gly; Lys137-->Asn), and ParE (Ile460-->Val; Asp435-->Asn), alone or in combination, were ascribed to the reduced garenoxacin susceptibility (MIC range, 0.5 to 1 micro g/ml) found in four isolates. The low impact of these mutations on garenoxacin activity envisages the possible coverage of S. pneumoniae populations resistant to preexisting quinolones.

Genetic relatedness of levofloxacin-nonsusceptible Streptococcus pneumoniae isolates from North America

We characterized 32 levofloxacin-nonsusceptible Streptococcus pneumoniae (LNSP) isolates obtained from a broad geographic region of North America over a 5-year period by using capsular serotypes, antimicrobial susceptibility profiles, BOX-PCR, multilocus sequence typing (MLST), and pulsed-field gel electrophoresis (PFGE). Sixteen international clones identified by the Pneumococcal Molecular Epidemiology Network also were included for comparison. Fifteen serotypes were represented, with serogroups 6, 9, 14, 19, and 23 accounting for 63% of isolates. Among isolates whose quinolone resistance-determining regions were sequenced, all contained gyrA and parC point mutations. Sixty-three percent were penicillin susceptible, and 84% were erythromycin susceptible. BOX-PCR analysis identified 39 different band patterns among 32 LNSP and 16 international clones and grouped 16 isolates, including 2 international clones, into seven unrelated groups of 2 to 4 isolates each. PFGE analysis identified 35 different band patterns among 32 LNSP and 16 international clones and grouped 21 isolates, including 3 international clones, into eight unrelated groups of 2 to 6 isolates each. MLST performed on 10 isolates identified five allelic profiles and separated 9 isolates into four groups of 2 to 3 isolates each. Overall, each typing method indicated that the LNSP were heterogeneous and that resistance to fluoroquinolones was not closely associated with a particular serotype or with coresistance to other antimicrobial classes and suggests that LNSP have likely arisen through independent mutational events as a result of selective pressure. However, seven LNSP were found to be related to three international clones by PFGE.

Factors associated with relative rates of antimicrobial resistance among Streptococcus pneumoniae in the United States: results from the TRUST Surveillance Program (1998-2002)

To identify factors associated with antimicrobial resistance, data were analyzed from 27,828 isolates of Streptococcus pneumoniae submitted to the Tracking Resistance in the United States Today (TRUST) surveillance program during 4 consecutive respiratory seasons. From the 1998-1999 season to the 2001-2002 season, the prevalence of azithromycin resistance increased by 4.8% to 27.5%, the prevalence of penicillin resistance increased by 3.7% to 18.4%, the prevalence of ceftriaxone resistance increased by 0.5% to 1.7%, and the prevalence of levofloxacin resistance increased by 0.3% to 0.9%. Isolates recovered from patients <18 years of age and lower respiratory tract specimens had elevated rates of penicillin, azithromycin, and trimethoprim-sulfamethoxazole resistance (P<.00001); penicillin resistance correlated with coresistance to trimethoprim-sulfamethoxazole (87.3%), azithromycin (76.3%), ceftriaxone (9.1%), and levofloxacin (1.3%) (P<.00001). Only 62 (0.2%) of 27,828 isolates were concurrently resistant to penicillin and levofloxacin. Minimum inhibitory concentrations (MICs) of penicillin correlated strongly with MICs of ceftriaxone (R2=0.90), trimethoprim-sulfamethoxazole (R2=0.53), and azithromycin (R2=0.41). Patient age, specimen source, and penicillin resistance were factors associated with antimicrobial resistance, particularly for nonfluoroquinolone antimicrobial agents.

Genetic characterization of fluoroquinolone-resistant Streptococcus pneumoniae strains isolated during ciprofloxacin therapy from a patient with bronchiectasis

Five Spain(9V-3) Streptococcus pneumoniae strains were isolated from a patient with bronchiectasis who had received long-term ciprofloxacin therapy. One ciprofloxacin-susceptible strain was isolated before treatment, and four ciprofloxacin-resistant strains were isolated during treatment. The resistant strains were derived from the susceptible strain either by a parC mutation (low-level resistance) or by parC and gyrA mutations (high-level resistance). This study shows that ciprofloxacin therapy in a patient colonized by susceptible S. pneumoniae may select fluoroquinolone-resistant mutants.

Molecular epidemiology of penicillin-resistant and ciprofloxacin-resistant Streptococcus pneumoniae in Canada

Eighty-nine penicillin- and ciprofloxacin-resistant Streptococcus pneumoniae isolates were evaluated by serotyping and pulsed-field gel electrophoresis. Although penicillin-resistant isolates demonstrated considerable homogeneity, resistance to ciprofloxacin did not correlate with a reduction in genotypic variability. These results suggest that, unlike that of penicillin resistance, the spread of S. pneumoniae ciprofloxacin resistance in Canada is currently not attributable to clonal dissemination.

Fluoroquinolone resistance among Gram-positive cocci

Resistance to fluoroquinolones among Gram-positive cocci has emerged as these antimicrobial agents have become extensively used in clinical medicine. Resistance is effected by changes in the bacterial target enzymes DNA gyrase and topoisomerase IV, which reduce drug binding, and by action of native bacterial membrane pumps that remove drug from the cell. In both cases, quinolone exposure selects for spontaneous mutants that are present in large bacterial populations, and which contain chromosomal mutations that alter the target protein or increase the level of pump expression. Resistance among clinical isolates has been greatest in Staphylococcus aureus and particularly among meticillin-resistant strains, in which both selection by quinolone exposure and transmission of clonal strains in health-care settings have contributed to high prevalence. Resistance in Streptococcus pneumoniae has also emerged in the community. Fluoroquinolone resistance has arisen in multidrug-resistant clones and its prevalence has been especially high in Hong Kong and Spain. Further spread and selection of such resistance could compromise the utility of a valuable class of antimicrobial agents, a point that emphasises the importance of the careful use of these agents in appropriate patients and doses, as well as careful infection-control practices.

Activities of six different quinolones against clinical respiratory isolates of Streptococcus pneumoniae with reduced susceptibility to ciprofloxacin in Spain

Six quinolones were tested on 817 consecutive pneumococcal isolates for which ciprofloxacin MICs were high (> or =2 microg/ml); the isolates had been collected during two recent Spanish surveillance studies. For strains for which the ciprofloxacin MIC was >or =4 microg/ml, the MICs at which 90% of the isolates tested against gemifloxacin, moxifloxacin, gatifloxacin, sparfloxacin, levofloxacin, and ofloxacin were inhibited were 0.25, 1, 1, 1, 4 and 16 microg/ml, respectively, and the corresponding prevalences of resistance were 0, 1, 4.5, 9.5, 8.4 and 23%. The proportion of isolates for which the ciprofloxacin MIC is high has increased over time.