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Streptococcus pneumoniae Resistance to Penicillin and Other β-lactam Antibiotics from Isolates at a University Hospital in Taiwan
J Infect Chemother 1997;3:103-106
Note
StreptococcuspneumoniaeResistance to Penicillin and Other fl-lactam Antibiotics from Isolates at a University Hospital in Taiwan Shan-Chwen Chang,* Yee-Chun Chen, Kwen-Tay Luh, and Wei-Chuan Hsieh Departments of Internal Medicine and Laboratory Medicine, National Taiwan University Hospital, Taipei, Taiwan, Republic of China
The in vitro susceptibility to 9 fl-lactam antibiotics of 65 clinical strains of Streptococcus pneumoniae collected from a teaching hospital in Taiwan during the period from 1989 to 1994 were studied. Minimum inhibitory concentrations (MIC) were determined by the agar dilution method with 5% horse blood. Intermediate resistance to penicillin G was found in 24.6% of the strains (MIC, 0.125 to 1 #g/mL) and 7.7% of the strains were fully-resistant to penicillin G (MIC, > 2/.zg/mL). Ten strains (15.4%) were fully-resistant to cefotaxime (MIC, > 2 pg/mL), whereas 3 strains (4.6%) showed intermediate resistance (MIC 1 /.tg/mL). The intermediate- and fully-resistant rates for penicillin increased from 12.5% and 0% in the period 1989 to 1991 to 27.3% and 22.7% in 1994, respectively. The rate of strains intermediately- and fully-resistant to cefotaxime increased from 0% in the period 1989 to 1991 to 9.1% and 22.7%, in 1994, respectively. There was also a high probability of resistance to cefotaxime in strains that were intermediately- or fully-resistant to penicillin G. Key words: Streptococcus pneumoniae, susceptibility, penicillin resistance, fl-lactam antibiotics
INTRODUCTION Since first r e p o r t e d in 1967,1 penicillin-resistant Streptococcus pneumoniae infections have been noted in many countries. T h e rate of resistance varies by geographic regions, with some countries having less than 5% resistance, while some demonstrate greater than 50% resistance. 2,3 However, most of the reports concerning penicillin resistance of S. pneumoniae have come from Western countries, with few reported from Asian countries. Previous reports from Japan, Malaysia, Pakistan, and Bangladesh found resistance rates of 1 to 12%, 2,3 but a recent report from Japan found a rate greater than 40%, and a report from Korea found 77.5% resistance. 4,~ In order to better understand the rate of penicillin resistance worldwide, it is necessary to perform studies and obtain data from a greater n u m b e r of countries, particularly those in which the actual rate of resistance is still unknown. In areas with a high prevalence of penicillin-resistant S. pneumoniae, third-generation cephalosporins have been used as the empirical drugs of choice to treat pneumococcal meningitis. 6 Although previous in vitro studies did not detect many cefotaxime/ceffriaxone-resistant strains, an increasing n u m b e r of cases have failed in response to treatment with cefotaxime or ceftriaxone
Received Jul. 29, 1996; accepted for publication in revised form May 16, 1997. *Correspondence and requests for reprints to: Section of Infectious Diseases, Department of Internal Medicine, National Taiwan University Hospital, No. 7, Chung-Shan South Road, Taipei, Taiwan 100, Republic of China.
1341-321X/97/O302-O103/US$3.00 9 JSC/CLJ 1997
a l o n e . 7 M a n y strains f r o m t h e s e p a t i e n t s h a d a cefotaxime/ceftriaxone m i n i m u m inhibitory concentration (MIC) of at least 2/~g/mL. Accordingly, it has been suggested that the breakpoint for judging resistance to cefotaxime/ceftriaxone for S. pneumoniae needs revision. In 1993, the National Committee for Clinical Laboratory Standards ( N C C L S ) also defined new criteria for interpretation of the in vitro susceptibility testing of cefotaxime/ceftriaxone on S. pneumoniae strains. 8 This study was undertaken to determine the prevalence of penicillin and cephalosporin resistance and their relationship to each other in S. pneumoniae infections in Taiwan. T h e S. pneurnoniae isolates were collected at the NationalTaiwan University Hospital, a major teaching hospital located in Taipei, Taiwan.
MATERIALS A N D METHODS
Bacterial strains A total of 65 strains of S.pneumoniae isolated from various clinical specimens at the National Taiwan University Hospital during the period from 1989 to 1994 were used in this study.Thirty-eight were isolated from blood, 13 from sputum, 6 from eye discharges, 5 from ear or sinus discharges, 2 from pleural effusions and 1 from cerebrospinal fluid. Identification was made according to standard criteria. 9 T h e bacteria were collected and stored at - 7 0 ~ in trypticase soy broth with 15% glycerol until the M I C test was performed. No duplicate strain from a single patient was included in this study.
103
J In fect Chemother t 997;3:103-106
a slightly poorer activity, with an MICs0 of 0.06 p g / m L and an MIC90 of 8 pg/mL. Overall, 24.6% of the strains were i n t e r m e d i a t e l y - r e s i s t a n t and 7.7% were fullyresistant to penicillin G. Cephalexin, an oral first-generation cephalosporin, showed high M I C s , with an MICs0 of I p g / m L and an MIC90 o f 32 p g / m L . I n c o n t r a s t , c e f u r o x i m e a n d cefotaxime had m u c h lower M I C s , with MICs0 of 0.06 # g / m L and < 0.03 p g / m L and MIC90 of 4 p g / m L and 2 pg/mL, respectively. However, according to antibiotic sensitivity criteria, 4.6% of the strains were in the intermediate range (1 pg/mL) and 15.4% were fully-resistant to cefotaxime ( M I C _ 2 p g / m L ) . Cefaclor and cefmime showed activity in the range between cephalexin and cefotaxime.
Antibiotics Nine different fl-lactam antibiotics were supplied as standard powder for laboratory use from the individual manufacturer. These included penicillin G, oxacillin, ampicillin, amoxicillin (Bristol-Myers Squibb, Syracuse, NY, USA), cephalexin, cefaclor (Eli Lilly, Indianapolis, IN, USA), cefuroxime (Glaxo, Greenford, UK), cefixime (Fujisawa, Osaka, Japan) and c e f o t a x i m e (Hoechst, Frankfurt, G e r m a n y ) .
Antimicrobial susceptibility testing T h e agar dilution m e t h o d was used to determine the M I C for each strain. 1~An inoculum of 104 bacteria was applied to agar plates containing Mueller-Hinton agar supplemented with 5% defibrinated horse blood and the test antibiotic in a concentration ranging from 0.03 to 128 pg/mL. T h e agar plates were examined after incubation at 35~ in ambient air for 18 hours. T h e M I C was defined as the lowest concentration of antibiotic which resulted in complete inhibition of visible growth on the agar plate. S. pneumoniae A T C C 49619 was used as the internal control. Antibiotic susceptibilities were classified as either susceptible, intermediate, or resistant, and were defined as __ 0.06, 0.125 to 1, and _> 2 / 2 g / m L for penicillin G, _< 0.5, 1, and _> 2 p g / m L for cefuroxime, and _< 0.5, 1, and -> 2 p g / m L for cefotaxime, respectively, s
Chronological changes in the susceptibility to penicillin G and cefotaxime There was a clear pattern of increased resistance to penicillin G and cefotaxime over the 6-year study period (Table 2). T h e rate of intermediate resistance to penicillin G increased from 12.5% in the period 1989 to 1991 to 27.3% in 1994, and the rate of full resistance to penicillin G increased from 0% in the period 1989 to 1991 to 22.7% in 1994. Also, the rate of intermediate resistance and full resistance to cefotaxime increased from 0% in 1989 to 1991 to 9.1% and 22.7% in 1994, respectively.
RESULTS
Relationship between resistance to penicillin G and resistance to cefotaxime
Susceptibility to fl-lactam antibiotics
F o r strains intermediately- or fully-resistant to penicillin G, there was also a high probability of intermediate or full resistance to cefotaxime (P < 0.0001, Fisher's exact test). Alternatively, all 44 strains that were sensitive to penicillin G were also sensitive to cefotaxime (Table 3).
T h e susceptibilities of 65 strains of S. pneumoniae to 9 different fl-lactam antibiotics are shown in Table 1. Ampicillin and amoxicillin exhibited activity similar to that of penicillin G, and all 3 agents had an MICs0 of -< 0.03 p g / m L and an MICgo of 1 pg/mL. Oxacillin had
T a b l e 1. In v i t r o s u s c e p t i b i l i t y o f 65 strains o f Drug
Streptococcus pneumoniae t o
M I C (pg/m L) Range
Penicillin G
_< 0 . 0 3 - 2
MIC50 _< 0.03
1
N u m b e r o f strains (%)* Susceptible Intermediate Resistant 4 4 (67.7)
16 (24.6)
5 (7.7)
Oxacillin
_< 0 . 0 3 - 6 4
0.06
8
--
--
--
Ampicillin
< 0.034
_< 0.03
1
--
--
--
Amoxicillin
< 0.03-4
< 0.03
--
Cephalexin
< 0.03-128
1
Cefaclor
_< 0 . 0 3 - 1 2 8
1
--
--
32
--
--
--
0.25
8
--
--
--
Cefuroxime
< 0.03-8
0.06
4
4 6 (70.8)
Cefixime
_< 0 . 0 3 - 6 4
0.25
8
--
Cefotaxime
-< 0 . 0 3 - 8
2
52 (80.0)
_< 0 . 0 3
*Values not presented when NCCLS--approved
t04
MIC90
fl-lactam antibiotics.
breakpoints were not available.
6 (9.2) -3 (4.6)
13 (20.0) -10 (15.4)
Streptococcuspneumoniaeresistance Table 2. Chronological change in the sensitivity to penicillin G and cefotaxime of Streptococcus pneumoniae for the period 1989 to 7994.
Year
No. of strains
Number (%) of strains with MIC* of penicillin G < 0.06
0.125-1
Number (%) of strains with MIC* of cefotaxime
>2
< 0.5
1
_>2
1989-1991
16
14 (87.5)
2 (12.5)
0
16 (100)
0
0
1992
13
10 (76.9)
3 (23.1)
0
11 (84.6)
0
2 (15.4)
1993
14
9 (64.3)
5 (35.7)
0
10 (71.4)
1 (7.1)
3 (21.4)
1994
22
11 (50.0)
6 (27.3)
5 (22.7)
15 (68.2)
2 (9.1)
5 (22.7)
TOTAL
65
44 (67.7)
16 (24.6)
5 (7.7)
52 (80.0)
3 (4.6)
10 (15.4)
*Minimum inhibitory concentration in pg/mL.
Table 3. Sensitivity of penicillin G and cefotaxime to 65 strains of Streptococcus pneumoniae. Sensitivity to penicillin G
No. of strains
Number (%) of strains with MIC* of cefotaxime <0.5
1
>7
44 (100)
0
0
Sensitive
44
Intermediate resistance
16
7 (43.8)
2 (12.5)
7 (43.8)
5
1 (20.0)
1 (20.0)
3 (60.0)
High resistance
* M i n i m u m inhibitory concentration in pg/mL.
DISCUSSION
T h e results of this study show that the rate of resistance of S. pneumoniae to both penicillin and cefotaxime has increased rapidly at our institution in the past 6 years. Since the isolation rate of S. pneumoniae in clinical specimens in Taiwan is rather low, and not all isolates were viable w h e n the susceptibility test was performed, the n u m b e r of strains tested in this study is relatively small. However, the trend is a warning for clinicians treating patients with S. pneumoniae infections. T h e increased prevalence of S. pneumoniae resistance to penicillin over time has also been noted in other countries. Geslin et al. reported that the rate of penicillin resistance in France increased from 1.8% in 1987 to 17% in 1990,11 and in Spain, Linares et al. reported an increased rate from 4.3% in 1979 to 40% in 1990.12 In the United States, the Centers for Disease Control and Prevention ( C D C ) surveillance data from 21 hospitals showed a rate increase from about 1% in 1980 to about 6% in 1992.13 Although nearly all of the resistant iso 2 lates from the United States were only intermediatelyresistant, they also d e m o n s t r a t e d that the rate of fully-resistant strains also increased. Resistance to third-generation cephalosporins is also emerging as an i m p o r t a n t issue in dealing with S. pneumoniae infections. Aside from reported cases failing to respond to the treatment with cefotaxime or ceftriaxone from the United States and Spain, Klugman and Saunders reported a 30% rate of resistance to cefotaxime/ceftriaxone (MIC _> 2 pg/mL) in penicillin
fully-resistant strains in South Africa. 14 Fortunately, these studies reported an overall cefotaxime/ceftriaxone resistance rate of less than 1% from all systemic isolates. In Spain, which has a high rate of penicillin-resistant S. pneumoniae isolates, fewer than 10% of fully perti~in-resistant strains were also resistant to cefotaxime and/or ceftriaxone,15 and reports from the United States and the United Kingdom also showed that less than 1% of S. pneumoniae isolates were resistant to cefotaxime. 13,16 This present study represents the highest prevalence of cefotaxime resistance in the world to date. S i m i l a r to p r e v i o u s s t u d i e s , 12 a m p i c i l l i n a n d amoxicillin showed similar activity against S. pneumoniae with equal or 2-fold higher M I C s as compared to penicillin G, however, oxacillin had m u c h poorer activity than penicillin G. All of the first- and second-generation cephalosporins, except cefuroxime, had poorer activity than cefotaxime. T h e isolated strains in this study had higher MIC90s to the various cephalosporins which differs from previous reports and reflects a higher rate of resistance to cephalosporins in our study population. S. pneumoniae resistance to non-fl-lactam antibiotics is also a c o m m o n p h e n o m e n o n from isolates in m a n y parts of the world. 2,3 A l t h o u g h the susceptibility to non-fi-lactam antibiotics was not d e t e r m i n e d in this study, a previous study from this institution found a very high percentage (55%) of macrolide resistance in S. pneumoniae isolates. 17 In patients who failed to respond to treatment with third-generation cephalosporins and had a very high M I C o f c e f o t a x i m e / c e f t r i a x o n e in their i s o l a t e d pneumococcal strains, all had a history of previous an-
105
J Infect Chemother 1997;3:103-106
tibiotic usage. 7 A l t h o u g h the p r e v a l e n c e rate o f p e n i c i l lin r e s i s t a n c e in S. pneumoniae is lower in T a i w a n t h a t in o t h e r c o u n t r i e s , t h e r e is an e x t r a o r d i n a r i l y h i g h rate o f cefotaxime and macrolide resistance. A possible reason for this h i g h rate is the availability a n d w i d e s p r e a d usage o f a n t i b i o t i c s in T a i w a n o n a n o n p r e s c r i p t i o n basis. Penicillin was n o t w i d e l y u s e d in t h e early years in Taiw a n b e c a u s e m a n y d o c t o r s , e s p e c i a l l y t h o s e in p r i m a r y care units, f e a r e d a n a n a p h y l a c t i c r e a c t i o n , O n t h e c o n trary, c e p h a l o s p o r i n s a n d e r y t h r o m y c i n were m u c h m o r e f r e q u e n t l y p r e s c r i b e d . H o w e v e r , f u r t h e r studies o n the p r e v a l e n c e r a t e o f a n t i m i c r o b i a l r e s i s t a n c e i n S. pneumoniae infections are n e c e s s a r y . I n a d d i t i o n , t h e results o f this p r e l i m i n a r y s t u d y i n d i c a t e t h a t a l a r g e r s t u d y t h r o u g h o u t T a i w a n is w a r r a n t e d . REFERENCES
1. Hansman D, Bullen M M . A resistant pneumococcus (letter). Lancet 1967;2:264-265. 2. Klugman KP. Pneumococcal resistance to antibiotics. Clin Microbiol Rev 1990;3:171-196. 3. Appelbaum PC. Antimicrobial resistance in Streptococcus pneumoniae: an overview. Clin Infect Dis 1992; 15:77-83. 4. Ubukata K, Asahi Y, Okuzumi K, Konno M, The Working Group for Penicillin Resistant S. pneumoniae. Incidence of penicillin-resistant Streptococcus pneurnoniae in Japan, 1993-1995. J Infect Chemother 1996;2:177-184. 5. ChongY, Lee K, Kwon OH, Henrichsen J. Capsular types and antimicrobial resistance of Streptococcus pneumoniae isolated in Korea. Eur J Clin M i c r o b i o l Infect Dis 1995;14:528-531. 6. K l u g m a n KP. M a n a g e m e n t of a n t i b i o t i c - r e s i s t a n t p n e u m o c o c c a l infections. J A n t i m i c r o b C h e m o t h e r 1994;34:191-193.
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7. Klugman KP. Pneumococcal resistance to the third-generation cephalosporins: clinical, laboratory and molecular aspects. Int J Antimicrob Agents 1994;4:63-67. 8. National Committee for Clinical Laboratory Standards. Performance standards for antimicrobial susceptibility testing; fifth i n f o r m a t i o n a l s u p p l e m e n t , M 1 0 0 - S S . Villanova, PA: N C C L S , 1994. 9. Ruoff KL. Streptococcus. In: Murray PR, Baron EJ, Pfaller MA, Tenover FC,Yolken RH (eds) Manual of Clinical Microbiology 6th ed. Washington DC: ASM Press, 1995:299-307. 10. Jacobs MR.Treatment and diagnosis of infections caused by drug-resistant Streptococcuspneumoniae. Clin Infect Dis 1992;15:119-127. 11. Geslin P, Buu-Hoi A, Fremaux A, Acar JF. Antimicrobial resistance in Streptococcuspneumoniae: an epidemiological survey in F r a n c e , 1970-1990. Clin I n f e c t Dis 1992;15:95-98. 12. Linares J, Pallares R, Alonso T, Perez JL, Ayats J, Gudiol F, et al. Trends in antimicrobial resistance of clinical isolates of Streptococcus pneumoniae in Bellvitge Hospital, B a r c e l o n a , S p a i n ( 1 9 7 9 - 1 9 9 0 ) . C l i n I n f e c t Dis 1992;15:99-105. 13. Breiman RF, Butler JC,Tenover FC, Elliott JA, Facklam RR. Emergence of drug resistant pneumococcal infections in the United States. JAMA 1994;271:1831-1835. 14. Klugman KP, Saunders J. Pneumococci resistant to extended-spectrum cephalosporins in South Africa. Lancet 1993;341:1164. 15. Linares J, Alonso T, Perez JL, Ayats J, Dominguez MA, Pallares R, et al. Decreased susceptibility of penicillinresistant pneumococci to twenty-four fl-lactam antibiotics. J Antimicrob Chemother 1992;30:279-288. 16. J o h n s o n AP, Speller D C , Patel BC. Sensitivity to c e f o t a x i m e o f p n e u m o c o c c i isolated in the U K . J Antimicrob Chemother 1995;35:443-444. 17. Chang SC, Chen YC, Luh KT, Hsieh WC. Macrolide resistance of c o m m o n bacteria isolated from Yaiwan. Diagn Microbiol Infect Dis 1995;23:147-154.
Note
StreptococcuspneumoniaeResistance to Penicillin and Other fl-lactam Antibiotics from Isolates at a University Hospital in Taiwan Shan-Chwen Chang,* Yee-Chun Chen, Kwen-Tay Luh, and Wei-Chuan Hsieh Departments of Internal Medicine and Laboratory Medicine, National Taiwan University Hospital, Taipei, Taiwan, Republic of China
The in vitro susceptibility to 9 fl-lactam antibiotics of 65 clinical strains of Streptococcus pneumoniae collected from a teaching hospital in Taiwan during the period from 1989 to 1994 were studied. Minimum inhibitory concentrations (MIC) were determined by the agar dilution method with 5% horse blood. Intermediate resistance to penicillin G was found in 24.6% of the strains (MIC, 0.125 to 1 #g/mL) and 7.7% of the strains were fully-resistant to penicillin G (MIC, > 2/.zg/mL). Ten strains (15.4%) were fully-resistant to cefotaxime (MIC, > 2 pg/mL), whereas 3 strains (4.6%) showed intermediate resistance (MIC 1 /.tg/mL). The intermediate- and fully-resistant rates for penicillin increased from 12.5% and 0% in the period 1989 to 1991 to 27.3% and 22.7% in 1994, respectively. The rate of strains intermediately- and fully-resistant to cefotaxime increased from 0% in the period 1989 to 1991 to 9.1% and 22.7%, in 1994, respectively. There was also a high probability of resistance to cefotaxime in strains that were intermediately- or fully-resistant to penicillin G. Key words: Streptococcus pneumoniae, susceptibility, penicillin resistance, fl-lactam antibiotics
INTRODUCTION Since first r e p o r t e d in 1967,1 penicillin-resistant Streptococcus pneumoniae infections have been noted in many countries. T h e rate of resistance varies by geographic regions, with some countries having less than 5% resistance, while some demonstrate greater than 50% resistance. 2,3 However, most of the reports concerning penicillin resistance of S. pneumoniae have come from Western countries, with few reported from Asian countries. Previous reports from Japan, Malaysia, Pakistan, and Bangladesh found resistance rates of 1 to 12%, 2,3 but a recent report from Japan found a rate greater than 40%, and a report from Korea found 77.5% resistance. 4,~ In order to better understand the rate of penicillin resistance worldwide, it is necessary to perform studies and obtain data from a greater n u m b e r of countries, particularly those in which the actual rate of resistance is still unknown. In areas with a high prevalence of penicillin-resistant S. pneumoniae, third-generation cephalosporins have been used as the empirical drugs of choice to treat pneumococcal meningitis. 6 Although previous in vitro studies did not detect many cefotaxime/ceffriaxone-resistant strains, an increasing n u m b e r of cases have failed in response to treatment with cefotaxime or ceftriaxone
Received Jul. 29, 1996; accepted for publication in revised form May 16, 1997. *Correspondence and requests for reprints to: Section of Infectious Diseases, Department of Internal Medicine, National Taiwan University Hospital, No. 7, Chung-Shan South Road, Taipei, Taiwan 100, Republic of China.
1341-321X/97/O302-O103/US$3.00 9 JSC/CLJ 1997
a l o n e . 7 M a n y strains f r o m t h e s e p a t i e n t s h a d a cefotaxime/ceftriaxone m i n i m u m inhibitory concentration (MIC) of at least 2/~g/mL. Accordingly, it has been suggested that the breakpoint for judging resistance to cefotaxime/ceftriaxone for S. pneumoniae needs revision. In 1993, the National Committee for Clinical Laboratory Standards ( N C C L S ) also defined new criteria for interpretation of the in vitro susceptibility testing of cefotaxime/ceftriaxone on S. pneumoniae strains. 8 This study was undertaken to determine the prevalence of penicillin and cephalosporin resistance and their relationship to each other in S. pneumoniae infections in Taiwan. T h e S. pneurnoniae isolates were collected at the NationalTaiwan University Hospital, a major teaching hospital located in Taipei, Taiwan.
MATERIALS A N D METHODS
Bacterial strains A total of 65 strains of S.pneumoniae isolated from various clinical specimens at the National Taiwan University Hospital during the period from 1989 to 1994 were used in this study.Thirty-eight were isolated from blood, 13 from sputum, 6 from eye discharges, 5 from ear or sinus discharges, 2 from pleural effusions and 1 from cerebrospinal fluid. Identification was made according to standard criteria. 9 T h e bacteria were collected and stored at - 7 0 ~ in trypticase soy broth with 15% glycerol until the M I C test was performed. No duplicate strain from a single patient was included in this study.
103
J In fect Chemother t 997;3:103-106
a slightly poorer activity, with an MICs0 of 0.06 p g / m L and an MIC90 of 8 pg/mL. Overall, 24.6% of the strains were i n t e r m e d i a t e l y - r e s i s t a n t and 7.7% were fullyresistant to penicillin G. Cephalexin, an oral first-generation cephalosporin, showed high M I C s , with an MICs0 of I p g / m L and an MIC90 o f 32 p g / m L . I n c o n t r a s t , c e f u r o x i m e a n d cefotaxime had m u c h lower M I C s , with MICs0 of 0.06 # g / m L and < 0.03 p g / m L and MIC90 of 4 p g / m L and 2 pg/mL, respectively. However, according to antibiotic sensitivity criteria, 4.6% of the strains were in the intermediate range (1 pg/mL) and 15.4% were fully-resistant to cefotaxime ( M I C _ 2 p g / m L ) . Cefaclor and cefmime showed activity in the range between cephalexin and cefotaxime.
Antibiotics Nine different fl-lactam antibiotics were supplied as standard powder for laboratory use from the individual manufacturer. These included penicillin G, oxacillin, ampicillin, amoxicillin (Bristol-Myers Squibb, Syracuse, NY, USA), cephalexin, cefaclor (Eli Lilly, Indianapolis, IN, USA), cefuroxime (Glaxo, Greenford, UK), cefixime (Fujisawa, Osaka, Japan) and c e f o t a x i m e (Hoechst, Frankfurt, G e r m a n y ) .
Antimicrobial susceptibility testing T h e agar dilution m e t h o d was used to determine the M I C for each strain. 1~An inoculum of 104 bacteria was applied to agar plates containing Mueller-Hinton agar supplemented with 5% defibrinated horse blood and the test antibiotic in a concentration ranging from 0.03 to 128 pg/mL. T h e agar plates were examined after incubation at 35~ in ambient air for 18 hours. T h e M I C was defined as the lowest concentration of antibiotic which resulted in complete inhibition of visible growth on the agar plate. S. pneumoniae A T C C 49619 was used as the internal control. Antibiotic susceptibilities were classified as either susceptible, intermediate, or resistant, and were defined as __ 0.06, 0.125 to 1, and _> 2 / 2 g / m L for penicillin G, _< 0.5, 1, and _> 2 p g / m L for cefuroxime, and _< 0.5, 1, and -> 2 p g / m L for cefotaxime, respectively, s
Chronological changes in the susceptibility to penicillin G and cefotaxime There was a clear pattern of increased resistance to penicillin G and cefotaxime over the 6-year study period (Table 2). T h e rate of intermediate resistance to penicillin G increased from 12.5% in the period 1989 to 1991 to 27.3% in 1994, and the rate of full resistance to penicillin G increased from 0% in the period 1989 to 1991 to 22.7% in 1994. Also, the rate of intermediate resistance and full resistance to cefotaxime increased from 0% in 1989 to 1991 to 9.1% and 22.7% in 1994, respectively.
RESULTS
Relationship between resistance to penicillin G and resistance to cefotaxime
Susceptibility to fl-lactam antibiotics
F o r strains intermediately- or fully-resistant to penicillin G, there was also a high probability of intermediate or full resistance to cefotaxime (P < 0.0001, Fisher's exact test). Alternatively, all 44 strains that were sensitive to penicillin G were also sensitive to cefotaxime (Table 3).
T h e susceptibilities of 65 strains of S. pneumoniae to 9 different fl-lactam antibiotics are shown in Table 1. Ampicillin and amoxicillin exhibited activity similar to that of penicillin G, and all 3 agents had an MICs0 of -< 0.03 p g / m L and an MICgo of 1 pg/mL. Oxacillin had
T a b l e 1. In v i t r o s u s c e p t i b i l i t y o f 65 strains o f Drug
Streptococcus pneumoniae t o
M I C (pg/m L) Range
Penicillin G
_< 0 . 0 3 - 2
MIC50 _< 0.03
1
N u m b e r o f strains (%)* Susceptible Intermediate Resistant 4 4 (67.7)
16 (24.6)
5 (7.7)
Oxacillin
_< 0 . 0 3 - 6 4
0.06
8
--
--
--
Ampicillin
< 0.034
_< 0.03
1
--
--
--
Amoxicillin
< 0.03-4
< 0.03
--
Cephalexin
< 0.03-128
1
Cefaclor
_< 0 . 0 3 - 1 2 8
1
--
--
32
--
--
--
0.25
8
--
--
--
Cefuroxime
< 0.03-8
0.06
4
4 6 (70.8)
Cefixime
_< 0 . 0 3 - 6 4
0.25
8
--
Cefotaxime
-< 0 . 0 3 - 8
2
52 (80.0)
_< 0 . 0 3
*Values not presented when NCCLS--approved
t04
MIC90
fl-lactam antibiotics.
breakpoints were not available.
6 (9.2) -3 (4.6)
13 (20.0) -10 (15.4)
Streptococcuspneumoniaeresistance Table 2. Chronological change in the sensitivity to penicillin G and cefotaxime of Streptococcus pneumoniae for the period 1989 to 7994.
Year
No. of strains
Number (%) of strains with MIC* of penicillin G < 0.06
0.125-1
Number (%) of strains with MIC* of cefotaxime
>2
< 0.5
1
_>2
1989-1991
16
14 (87.5)
2 (12.5)
0
16 (100)
0
0
1992
13
10 (76.9)
3 (23.1)
0
11 (84.6)
0
2 (15.4)
1993
14
9 (64.3)
5 (35.7)
0
10 (71.4)
1 (7.1)
3 (21.4)
1994
22
11 (50.0)
6 (27.3)
5 (22.7)
15 (68.2)
2 (9.1)
5 (22.7)
TOTAL
65
44 (67.7)
16 (24.6)
5 (7.7)
52 (80.0)
3 (4.6)
10 (15.4)
*Minimum inhibitory concentration in pg/mL.
Table 3. Sensitivity of penicillin G and cefotaxime to 65 strains of Streptococcus pneumoniae. Sensitivity to penicillin G
No. of strains
Number (%) of strains with MIC* of cefotaxime <0.5
1
>7
44 (100)
0
0
Sensitive
44
Intermediate resistance
16
7 (43.8)
2 (12.5)
7 (43.8)
5
1 (20.0)
1 (20.0)
3 (60.0)
High resistance
* M i n i m u m inhibitory concentration in pg/mL.
DISCUSSION
T h e results of this study show that the rate of resistance of S. pneumoniae to both penicillin and cefotaxime has increased rapidly at our institution in the past 6 years. Since the isolation rate of S. pneumoniae in clinical specimens in Taiwan is rather low, and not all isolates were viable w h e n the susceptibility test was performed, the n u m b e r of strains tested in this study is relatively small. However, the trend is a warning for clinicians treating patients with S. pneumoniae infections. T h e increased prevalence of S. pneumoniae resistance to penicillin over time has also been noted in other countries. Geslin et al. reported that the rate of penicillin resistance in France increased from 1.8% in 1987 to 17% in 1990,11 and in Spain, Linares et al. reported an increased rate from 4.3% in 1979 to 40% in 1990.12 In the United States, the Centers for Disease Control and Prevention ( C D C ) surveillance data from 21 hospitals showed a rate increase from about 1% in 1980 to about 6% in 1992.13 Although nearly all of the resistant iso 2 lates from the United States were only intermediatelyresistant, they also d e m o n s t r a t e d that the rate of fully-resistant strains also increased. Resistance to third-generation cephalosporins is also emerging as an i m p o r t a n t issue in dealing with S. pneumoniae infections. Aside from reported cases failing to respond to the treatment with cefotaxime or ceftriaxone from the United States and Spain, Klugman and Saunders reported a 30% rate of resistance to cefotaxime/ceftriaxone (MIC _> 2 pg/mL) in penicillin
fully-resistant strains in South Africa. 14 Fortunately, these studies reported an overall cefotaxime/ceftriaxone resistance rate of less than 1% from all systemic isolates. In Spain, which has a high rate of penicillin-resistant S. pneumoniae isolates, fewer than 10% of fully perti~in-resistant strains were also resistant to cefotaxime and/or ceftriaxone,15 and reports from the United States and the United Kingdom also showed that less than 1% of S. pneumoniae isolates were resistant to cefotaxime. 13,16 This present study represents the highest prevalence of cefotaxime resistance in the world to date. S i m i l a r to p r e v i o u s s t u d i e s , 12 a m p i c i l l i n a n d amoxicillin showed similar activity against S. pneumoniae with equal or 2-fold higher M I C s as compared to penicillin G, however, oxacillin had m u c h poorer activity than penicillin G. All of the first- and second-generation cephalosporins, except cefuroxime, had poorer activity than cefotaxime. T h e isolated strains in this study had higher MIC90s to the various cephalosporins which differs from previous reports and reflects a higher rate of resistance to cephalosporins in our study population. S. pneumoniae resistance to non-fl-lactam antibiotics is also a c o m m o n p h e n o m e n o n from isolates in m a n y parts of the world. 2,3 A l t h o u g h the susceptibility to non-fi-lactam antibiotics was not d e t e r m i n e d in this study, a previous study from this institution found a very high percentage (55%) of macrolide resistance in S. pneumoniae isolates. 17 In patients who failed to respond to treatment with third-generation cephalosporins and had a very high M I C o f c e f o t a x i m e / c e f t r i a x o n e in their i s o l a t e d pneumococcal strains, all had a history of previous an-
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tibiotic usage. 7 A l t h o u g h the p r e v a l e n c e rate o f p e n i c i l lin r e s i s t a n c e in S. pneumoniae is lower in T a i w a n t h a t in o t h e r c o u n t r i e s , t h e r e is an e x t r a o r d i n a r i l y h i g h rate o f cefotaxime and macrolide resistance. A possible reason for this h i g h rate is the availability a n d w i d e s p r e a d usage o f a n t i b i o t i c s in T a i w a n o n a n o n p r e s c r i p t i o n basis. Penicillin was n o t w i d e l y u s e d in t h e early years in Taiw a n b e c a u s e m a n y d o c t o r s , e s p e c i a l l y t h o s e in p r i m a r y care units, f e a r e d a n a n a p h y l a c t i c r e a c t i o n , O n t h e c o n trary, c e p h a l o s p o r i n s a n d e r y t h r o m y c i n were m u c h m o r e f r e q u e n t l y p r e s c r i b e d . H o w e v e r , f u r t h e r studies o n the p r e v a l e n c e r a t e o f a n t i m i c r o b i a l r e s i s t a n c e i n S. pneumoniae infections are n e c e s s a r y . I n a d d i t i o n , t h e results o f this p r e l i m i n a r y s t u d y i n d i c a t e t h a t a l a r g e r s t u d y t h r o u g h o u t T a i w a n is w a r r a n t e d . REFERENCES
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