Abstract
This study aimed to evaluate the antimicrobial susceptibility profiles of 364 Streptococcus pneumoniae isolates and studied the genotypes of S. pneumoniae with high level β-lactam resistance in Taiwan. Clonal complexes related to Spain23F-1, Taiwan19F-14, and Taiwan23F-15 were responsible for the spread of isolates with high β-lactam resistance.
Antimicrobial resistance in Streptococcus pneumoniae has been an important clinical problem for several decades. Along with the increases in penicillin-nonsusceptible S. pneumoniae, the role of penicillin in the treatment of nonmeningitis pneumococcal infection was debated (2, 17). Recently, the Clinical and Laboratory Standards Institute (CLSI) published the penicillin MIC interpretative breakpoints for nonmeninigits isolates of S. pneumoniae (5).
Taiwan is an area of high prevalence of penicillin- and macrolide-resistant S. pneumoniae (14, 15). Nevertheless, the 7-valent conjugate pneumococcal vaccine has not been widely used in Taiwan. Since 2005, an increase in ceftriaxone-nonsusceptible S. pneumoniae has been reported in tertiary hospitals in Taiwan (4), raising great concern due to its negative impact on the treatment options for pneumococcal meningitis and acute otitis media. Molecular epidemiology showed that certain international clones, including England14-9, Taiwan19F-14, and Spain23F-1 accounted for the increase in resistance to extended-spectrum cephalosporin in S. pneumoniae (4). Given the high capability of spread of these international clones worldwide, programs to monitor antimicrobial susceptibility to extended-spectrum cephalosporin in S. pneumoniae are well justified.
Ceftobiprole, a new broad-spectrum cephalosporin, exhibits excellent activities against streptococci, staphylococci, and cefotaxime- or ceftriaxone-resistant S. pneumoniae (11, 13). In this study, we examined the in vitro activities of 12 antimicrobial agents, including ceftobiprole, against S. pneumoniae isolates from different regions of Taiwan from 2003 to 2006. We also identified the genotypes of S. pneumoniae isolates with high-level β-lactam resistance (penicillin MIC of ≥4 μg/ml and cefotaxime MICs of ≥2 μg/ml) by multilocus sequencing type (MLST).
During 2003, this study prospectively collected a total of 31 invasive S. pneumomiae isolates in National Taiwan University Hospital (NTUH). From January 2004 to December 2006, a total of 333 S. pneumomiae isolates were prospectively collected in NTUH, Taipei (105 isolates); China Medical College Hospital (CMCH), Taichung (36 isolates); Buddhist Tzu Chi General Hospital (BTCG), Hualien (18 isolates); and Chang-Gung Memorial Hospital (CGMH), Kaohsiung (174 isolates). The MICs of all 364 S. pneumoniae isolates were determined by the broth dilution method, and the results were interpreted according to the guidelines established by the CLSI (5). The serotypes of isolates were determined using the capsular swelling method (Quellung reaction). MLST was determined as previously described (7). A clonal complex was defined as a group in which each isolate is identical to at least one other isolate at five or more of the seven loci (6).
The chi-square test or Fisher's exact test was used for categorical variables to test independence between groups. Logistic regression was used to test the influence of time on the nonsusceptibility rate. For assessment of the influence of time on the nonsusceptibility rate and geographic effects on nonsusceptibility, only S. pneumoniae isolates collected between 2004 and 2006 were used for analysis.
In penicillin meningitis criteria, 83.2% of the S. pneumoniae isolates were not susceptible to penicillin (Table 1). In penicillin nonmeningitis criteria, 7.7% were intermediate to penicillin and 0.5% were resistant to penicillin. A total of 91.5% (333/364) of the isolates were susceptible to both amoxicillin-clavulanate and cefotaxime (nonmeningitis criteria), and 1.9% (7/364) of the isolates were resistant to both amoxicillin-clavulanate and cefotaxime (nonmeningitis criteria). Twenty-eight percent (7/25) of the isolates that were nonsusceptible to cefotaxime (nonmeningitis criteria) were nonsusceptible to amoxicillin-clavulanate, whereas 53.8% (7/13) of isolates that were nonsusceptible to amoxicillin-clavulanate were nonsusceptible to cefotaxime (nonmeningitis criteria) (P < 0.001 by chi-square test). These results indicate that isolates that were nonsusceptible to amoxicillin-clavulanate were significantly associated with isolates that were nonsusceptible to cefotaxime in Taiwan during the study period.
TABLE 1.
In vitro susceptibility of 364 clinical S. pneumoniae isolates from 2003 to 2006 in Taiwan
| Antimicrobial agent | MIC (μg/ml)a
|
% of isolatesb
|
||||
|---|---|---|---|---|---|---|
| Range | 50% | 90% | Susceptible | Intermediate | Resistant | |
| Penicillin | ≤0.03-8 | 1.0 | 2.0 | 16.8 | 38.7 | 44.5 |
| Amoxillin-clavulanate | ≤0.03-8 | 1.0 | 2.0 | 96.4 | 1.6 | 1.9 |
| Cefotaximec | ≤0.03-8 | 0.5 | 1.0 | 58.5 (93.1) | 34.6 (5.5) | 6.9 (1.4) |
| Cefepimec | ≤0.03-4 | 0.5 | 2.0 | 50 (86) | 36 (13.5) | 14 (0.5) |
| Ceftobiprole | ≤0.03-1 | 0.25 | 0.5 | — | — | — |
| Erythromycin | ≤0.03->32 | >32 | >32 | 6.9 | 2.2 | 90.9 |
| Levofloxacin | 0.03->32 | 1.0 | 1.0 | 98.1 | 0 | 1.9 |
| Moxifloxacin | ≤0.03-8 | 0.12 | 0.25 | 99.5 | 0.3 | 0.3 |
| Gemifloxacin | ≤0.03-4 | ≤0.03 | ≤0.03 | 98.9 | 0 | 1.1 |
| Vancomycin | 0.03-0.5 | 0.25 | 0.5 | 100 | 0 | 0 |
| Tigecycline | ≤0.015-0.03 | ≤0.015 | 0.03 | — | — | — |
| Daptomycin | ≤0.03-0.25 | 0.06 | 0.06 | — | — | — |
50% and 90%, MIC50 and MIC90, respectively.
Susceptibility data for the treatment of meningitis according to the interpretive criteria recommended by CLSI (5). —, no criteria provided by CLSI (5).
Susceptibility data for the treatment of nonmeningitis according to the interpretive criteria recommended by CLSI (5) are shown in parentheses.
Among 12 cerebrospinal fluid isolates, three (25%) had a cefotaxime MIC of >0.5 μg/ml. (The MIC of these three isolates was 1 μg/ml.) All isolates were inhibited by ceftobiprole at ≤1 μg/ml, and 358 of 364 (98.4%) isolates were inhibited by ceftobiprole at ≤0.5 μg/ml. All of the 364 isolates were susceptible to vancomycin (MIC at which 90% of the isolates were inhibited [MIC90], 0.5 μg/ml), tigecycline (MIC90, 0.03 μg/ml), and daptomycin (MIC90, 0.06 μg/ml).
By using logistic regression analyses to test for time trends of nonsusceptibility to miscellaneous antibiotics, we found that nonsusceptibility to penicillin, cefotaxime (both meningitis and nonmeningitis criteria), cefepime (both meningitis and nonmeningitis criteria), and erythromycin in S. pneumoniae significantly increased from 2004 to 2006 in Taiwan (P for trend = 0.047 in penicillin, 0.007 and 0.01 in cefotaxime, 0.003 and 0.001 in cefepime, and 0.02 in erythromycin). During the study period, the proportion of isolates with a penicillin MIC of ≥4 μg/ml did not significantly increase (P = 0.3 by logistic regression). Nonsusceptibility to amoxicillin-clavulanate and levofloxacin ranged from around 96% to 98% and did not significantly change during the study period.
The distributions of penicillin and erythromycin resistances were significantly different among different geographic areas. Southern Taiwan (CGMH) and central Taiwan (CMCH and BTCG) had higher resistance rates to penicillin and erythromycin than northern Taiwan (NTUH).
The most common serotypes were 23F (n = 73; 20.1%) and 19F (n = 73; 20.1%), followed in descending order by 6B (n = 67; 18.4%), 14 (n = 61; 16.8%), 3 (n = 23; 6.3%) and others from 2003 to 2006 (Table 2). All isolates of serotype 23F were nonsusceptible to penicillin. There were 89 isolates collected in 2004, 127 isolates collected in 2005, and 117 isolates collected in 2006. Serotype 23F was significantly associated with cefotaxime resistance (meningitis criteria) (odds ratio [OR] = 3.4; 95% confidence interval [CI] = 1.9 to ∼5.9) and was also significantly associated with cefotaxime resistance (nonmeningitis criteria) (OR = 5.5; 95% CI = 2.3 to ∼12.8).
TABLE 2.
Rates of nonsusceptibility among different serotypes of S. pneumoniae isolates to different agents from 2003 to 2006
| Antibiotic and yr (total no. of isolates) | % of isolates of nonsusceptible serotype(s)a
|
|||||
|---|---|---|---|---|---|---|
| 19F (n = 73) | 23F (n = 73) | 6B (n = 67) | 14 (n = 61) | 3 (n = 23) | Others (n = 67)b | |
| Penicillin | ||||||
| 2003 (n = 31) | 100 (n = 1) | 100 (n = 5) | 100 (n = 6) | 100 (n = 6) | 0 (n = 6) | 100 (n = 7) |
| 2004 (n = 89) | 100 (n = 24) | 100 (n = 10) | 93.3 (n = 15) | 100 (n = 13) | 0 (n = 11) | 85.7 (n = 16) |
| 2005 (n = 127) | 100 (n = 23) | 100 (n = 32) | 92.9 (n = 28) | 96 (n = 25) | 20 (n = 5) | 92 (n = 14) |
| 2006 (n = 117) | 96 (n = 25) | 100 (n = 26) | 94.4 (n = 18) | 82.4 (n = 17) | 0 (n = 1) | 88.9 (n = 30) |
| Total | 98.6 | 100 | 94 | 93.4 | 4.3 | 89.6 |
| Amoxicillin-clavulanate | ||||||
| 2003 | 0 | 0 | 0 | 0 | 0 | 0 |
| 2004 | 12.5 | 0 | 0 | 7.7 | 0 | 7.1 |
| 2005 | 4.3 | 0 | 3.6 | 12 | 0 | 4 |
| 2006 | 8.0 | 0 | 0 | 0 | 0 | 7.4 |
| Total | 8.2 | 0 | 1.5 | 6.6 | 0 | 6 |
| Cefotaximec | ||||||
| 2003 | 100 (0) | 80 (20) | 50 (0) | 0 (0) | 0 (0) | 0 (0) |
| 2004 | 33.3 (4.2) | 50 (10) | 53.3 (0) | 23.1 (0) | 0 (0) | 35.7 (0) |
| 2005 | 47.8 (4.3) | 62.5 (18.8) | 57.1 (3.6) | 28 (4) | 20 (0) | 44 (4) |
| 2006 | 60 (16) | 76.9 (23.1) | 44.4 (0) | 29.4 (0) | 0 (0) | 59.3 (29.6) |
| Total | 47.9 (8.2) | 67.1 (19.2) | 52.2 (1.5) | 24.6 (1.6) | 4.3 (0) | 47.8 (13.4) |
| Cefepimec | ||||||
| 2003 | 100 (0) | 100 (20) | 66.7 (0) | 16.7 (0) | 0 (0) | 0 (0) |
| 2004 | 41.7 (8.3) | 50 (20) | 73.3 (13.3) | 46.2 (0) | 0 (0) | 42.9 (7.1) |
| 2005 | 52.2 (8.7) | 65.6 (25) | 60.7 (10.7) | 44 (8) | 20 (0) | 48 (12) |
| 2006 | 64 (16) | 76.9 (46.2) | 61.1 (16.7) | 70.6 (11.8) | 0 (0) | 63 (33.3) |
| Total | 53.4 (11) | 69.9 (31.5) | 64.2 (11.9) | 49.2 (6.6) | 4.3 (0) | 52.2 (19.4) |
| Levofloxacin | ||||||
| 2003 | 0 | 0 | 0 | 0 | 0 | 0 |
| 2004 | 0 | 0 | 0 | 0 | 0 | 0 |
| 2005 | 4.3 | 3.1 | 0 | 4 | 0 | 0 |
| 2006 | 0 | 3.8 | 11.1 | 0 | 0 | 3.7 |
| Total | 1.4 | 2.7 | 3.0 | 1.6 | 0 | 1.5 |
| Erythromycin | ||||||
| 2003 | 100 | 100 | 100 | 100 | 83.3 | 100 |
| 2004 | 100 | 90 | 93.3 | 100 | 90.9 | 85.7 |
| 2005 | 100 | 100 | 92.9 | 96 | 100 | 100 |
| 2006 | 100 | 96.2 | 100 | 94.1 | 100 | 96.3 |
| Total | 100 | 97.3 | 95.5 | 96.7 | 91.3 | 95.5 |
Susceptibility data for the treatment of meningitis according to the interpretive criteria recommended by CLSI (5).
“Others” included the following serotypes or serogroups: 4 (n = 4), 7 (n = 1), 8 (n = 1), 10 (n = 2), 11 (n = 2), 15 (n = 12), 17 (n = 1), 22 (n = 1), 33 (n = 2), 18C (n = 5), 18F(n = 1), 19A (n = 6), 19B (n = 2), 19C (n = 1), 23A (n = 10), 6A(n = 7), 9V (n = 8), and nontypeable (n = 1).
Susceptibility data for the treatment of nonmeningitis according to the interpretive criteria recommended by CLSI (5) are shown in parentheses.
Eighteen isolates had high-level β-lactam resistance with a penicillin MIC of ≥4 μg/ml and a cefotaxime MIC of ≥2 μg/ml. Five isolates (27.8%; 5/18) were recovered from invasive sites (blood). The median MICs of penicillin and cefotaxime for invasive isolates with high level β-lactam resistance were 4 and 2 μg/ml: the same as those for noninvasive isolates with high-level β-lactam resistance. Serotype distribution was not significantly different between invasive isolates with high-level β-lactam resistance and noninvasive isolates with high-level β-lactam resistance. MLST showed that CC81, related to Spain23F-1; CC236, related to Taiwan19F-14; and Taiwan23F-15 were responsible for the spread of isolates with high-level β-lactam resistance.
Taiwan has been an epicenter of macrolide-resistant and penicillin-resistant S. pneumoniae strains for many years (9). Cefotaxime has been recommended for empirical treatment of children with the diagnosis of bacterial meningitis. However, cefotaxime treatment failure in cases of pneumococcal meningitis has also been reported (1, 3, 8, 10). The cefotaxime MICs in these cases of treatment failure were mostly ≥2 μg/ml. Vancomycin and cefotaxime plus rifampin are suggested for the treatment of patients with S. pneumoniae isolates having a penicillin MIC of ≥0.1 μg/ml and a cefotaxime MIC of ≥2 μg/ml (12). In the present study, the highest cefotaxime MIC found among cerebrospinal fluid isolates was 1 μg/ml. In cases of pneumococcal meningitis with isolates having a penicillin MIC of ≥0.1 μg/ml and a cefotaxime MIC of 1 μg/ml, vancomycin (60 mg/kg of body weight/day) and cefotaxime (300 mg/kg/day) were suggested (12).
Regarding treatment of pneumococcal nonmeningitis infections, cefotaxime has been suggested for isolates with a penicillin MIC of ≥4 μg/ml and a cefotaxime MIC of <2 μg/ml (16). Scaglione et al., however, showed that cefotaxime could be adequately used in treating pneumococcal pneumonia for isolates with MICs of ≤4 μg/ml for extended-spectrum cephalosporins (18). However, clinical data on the MICs of extended-spectrum cephalosporins above which treatment failure would be expected in treating pneumococcal nonmeningitis infection remain limited. Like results from other study, ceftobiprole was demonstrated to have good activity against S. pneumoniae isolates regardless of their susceptibility to other antibiotics (13).
Given the increase of MICs to penicillin and cefotaxime in S. pneumoniae in Taiwan, choosing appropriate antibiotics, at a sufficient dosage with close clinical follow-up, is important for preventing treatment failure. From the results of this study, ceftobiprole, vancomycin, tigecycline, and daptomycin could be good choices for the treatment of β-lactam-resistant pneumococcal infection.
Acknowledgments
This work was supported by grants from National Science Council, Taiwan and Wyeth-Ayerst (Asia) Ltd., Taiwan branch.
Footnotes
Published ahead of print on 14 April 2008.
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