1. Number of S, I and R to six antibiotics
Poster at the 15th ECCMID, April , Copenhagen
Antibiotic Resistance among invasive pneumococcal Isolates from Southwest Sweden
Erik Backhaus1, Birger Trollfors2, Stefan Berg2, Berndt EB Claesson1, Rune Andersson. 1. 1Department of Infectious Diseases and Clinical Microbiology, Kärnsjukhuset, Skövde, 2Department of Paediatrics, The Queen Silvia Children's Hospital, Göteborg,SwedenCorrespondence:
The abstract has been slightly revised with addition of new data.
Objectives
Streptococcus pneumoniae is a major human pathogen. In Southwest Sweden, with a population of 1.8 million, 200 patients are diagnosed each year with invasive pneumococcal disease. The rapid emergence of isolates with decreased susceptibility to several antibiotics is an increasing problem in many parts of the world. The aim of the present study was to investigate the pattern of susceptibility among invasive isolates, in order to see if the current treatment policies are appropriate, and to see if there seems to be a trend of increasing antibiotic resistance.
Methods
All clinical isolates of S. pneumoniae from blood, cerebrospinal and joint fluid were collected at the laboratories in Göteborg, Skövde, Borås, Uddevalla and Halmstad during The MIC-values for seven commonly used antibiotics (penicillin G, erythromycin, clindamycin, tetracycline, moxifloxacin, cotrimoxazole and cefotaxime) were determined with E-test (AB Biodisk) according to standard methods.
E-test
Distribution of MIC’s
Serotype distribution
Results
827 invasive strains were tested. Of these, 766 were fully susceptible and 61 (7.4%) were classified as Indeterminate (I) or Resistant (R) for any of the tested antibiotics, according to the Swedish Reference Group for Antibiotics system of species related breakpoints. No isolate had a MIC>1.0 mg/L against penicillin (R). 22 isolates (2.7%) were classified as I to penicillin (MIC >0.06, 1.0 mg/L). 13 of them had MIC’s  0.5 mg/L. Among the 22 isolates classified as I to penicillin 12 isolates were also I against cefotaxime (MIC >0.12, 1.0 mg/L) (1.5%).
The other tested antibiotics showed the following results: Erythromycin R (MIC >0.5 mg/L) 30 isolates (3.6%), clindamycin R (MIC>2 mg/L) 6 isolates (0.7%), tetracycline R (MIC>2mg/L) 16 isolates (1,9%), and moxifloxacin R (MIC>0,5 mg/L) 1 isolate (0.1%). There were no isolates classified as I for those antibiotics. There were 21 isolates (2,5%) classified as I against cotrimoxazole (MIC >16, 32 mg/L), but no R (MIC>32 mg/L).
Conclusion
The proportion of invasive isolates of pneumococci with decreased sensitivity to commonly used antibiotics is very low.
Our results indicate that there might be a clonal spread of isolates of serotype 9V and 14 with reduced susceptibility to antibiotics.
61 isolates with elevated MIC
All isolates (827 patients)
Antibiotic agent
MIC 50
MIC 90
median
90 percentile
mg/L
Penicillin G
0.016
0.023
Erythromycin
0.190
0.250
Clindamycin
Tetracycline
0.125
Moxifloxacin
Trim /Sulfa 1/19***
0.5 1
12,5%
15,6%
7,8%
43,8%
Other 9V 6B
19F
19A 14 1
17,8%
8,6%
8,5%
14,3%
Other 9V 9N 8 7F 6B 6A 4 3
23F
19A 14
12F 1
Number of S, I and R to six antibiotics
Sensitivity pattern and serotypes
Antibiotic agent
Total
Sensitive
Indeterminate
Resistant
number
breakpoint**
Penicillin G
827
805
<
0.06 mg/L
22(2.7%)
>1.0 mg/L
Erythromycin
797
0.5 mg/L
n.r.*
30 (3.6%)
>0.5 mg/L
Clindamycin
821
2 mg/L
6 (0.7%)
>2 mg/L
Tetracycline
811
16 (1.9%)
Moxifloxacin
826
1 (0.1%)
Trim/Sulfa 1/19***
815
16 mg/L
21(2.5%)
>32 mg/L
** Species related breakpoints according to the Swedish Reference Group for Antibiotics system.
*** Values on the MIC scale refer to the first component of the combination.
*not relevant
Distribution of MIC values for 827 invasive strains of Streptococcus pneumoniae
Penicillin G
Erythromycin
Clindamycin
Tetracycline
Moxifloxacin
Trimethoprim/sulphamethoxazole
MIC (mg/L) 1
,75
,50
,380
,250
,190
,125
,094
,064
,047
,032
,023
,016
,012
,008
,006
Number
400
300
200
100 S I R
1,5 2
MIC (mg/L)
,500
,380
,250
,190
,125
,094
,064
Number
400
300
200
100
256
128 64 48 32 24 16 12 S R
MIC (mg/L)
256
,500
,380
,250
,190
,125
,094
,064
Number
400
300
200
100 S R
MIC (mg/L)
,750
,500
,380
,250
,190
,125
,094
,064
Number
500
400
300
200
100 48 32 24 16 8 4 2 6 3
1,5 S R 1 12 64
MIC (mg/L) 8
,380
,250
,190
,125
,094
,064
,047
Number
500
400
300
200
100 S R
MIC (mg/L) 32 8 6 4 3 2
1,500
1,0
,75
,50
,380
,250
,190
,125
,064
Number
400
300
200
100 S I R 48 64