J Infect Chemother (2003) 9:285–291 DOI 10.1007/s10156-003-0278-y
© Japanese Society of Chemotherapy and The Japanese Association for Infectious Diseases 2003
REVIEW ARTICLE Kimiko Ubukata
Problems associated with high prevalence of multidrug-resistant bacteria in patients with community-acquired infections
Received: August 7, 2003
Introduction Streptococcus pneumoniae and Haemophilus influenzae are major causes of community-acquired respiratory tract infections (RTIs). The increased prevalence of strains of these microorganisms resistant to multiple antibiotics is a matter of worldwide concern.1,2 This review will focus on: (i) background data with respect to the detection of antibiotic-resistant pathogens that cause RTIs; (ii) mechanisms of resistance and status of susceptibility to antibiotics in S. pneumoniae and H. influenzae; (iii) meningitis caused by resistant pathogens; and (iv) concluding recommendations. Key words Community-acquired infection · Streptococcus pneumoniae · Haemophilus influenzae · Antibiotic resistance · Meningitis
Background data concerning increased prevalence of antibiotic-resistant pathogens Year-to-year changes in frequency of resistant strains As shown in Fig. 1, molecularly identified penicillinintermediately-resistant S. pneumoniae (PISP) and penicillin-resistant S. pneumoniae (PRSP), respectively, were first
K. Ubukata (*) Laboratory of Infectious Agents Surveillance, Kitasato Institute for Life Sciences and Graduate School of Infection Control Sciences, Kitasato University, 5-9-1 Shirokane, Minato-ku, Tokyo 108-8641, Japan Tel. ⫹81-3-5791-6385; Fax ⫹81-3-5791-6386 e-mail:
[email protected] Contents of this article were presented as a plenary lecture at the International Symposium “Antibiotic Resistance in Asian Countries: Present Problem and the Prevention” held in Yokohama, Japan, on May 28, 2003.
isolated in Japan in 1987 and 1988.3 Since the early 1990s, the frequency of detection of these resistant strains has increased drastically throughout the country.4 The relative prevalences of PISP and PRSP in clinical samples from pediatric patients were 33.0% and 54.9%, respectively, in 2002. Additionally, the frequency of detection of H. influenzae resistant to β-lactam agents, referred to as β-lactamasenonproducing, ampicillin-resistant strains (BLNAR), has also increased rapidly during the past 5 years.5 Last year, the prevalences of BLNAR and low-BLNAR were 28.8% and 23.6%, respectively. The increasing isolation of these resistant strains has been associated with the introduction of oral cephalosporins in clinical practice.
Characteristics of resistance mechanisms in RTI pathogens Mechanisms of resistance in S. pneumoniae and H. influenzae that cause RTI may be characterized as follows. Resistance to β-lactams in these pathogens involves alterations of penicillin-binding proteins (PBPs) encoded by PBP genes.6–13 Macrolide resistance in S. pneumoniae is mediated by the efflux membrane protein encoded by the mefA gene,14–17 methylation of the ribosomal protein encoded by the ermB gene,18 and 23S rRNA mutation.19 Resistance of S. pneumoniae to the newer quinolones is mediated by mutations involving DNA gyrase encoded by the gyrA gene,20 topoisomerase IV encoded by the parC and parE genes,21 and efflux membrane protein encoded by the pmrA gene.22 These slight alterations enable most RTI pathogens to survive in the presence of oral antibiotics. Resistant RTI pathogens characteristically show intermediate resistance, which is not clearly demonstrable by conventional susceptibility testing. This type of resistance differs fundamentally from the high degree of resistance mediated by various β-lactamase determinants in pathogens that cause urinary tract infections.
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Factors influencing the clinical efficacy of oral antibiotics Various factors, in addition to those already mentioned, may affect the clinical efficacy of oral antibiotics. While antimicrobial activity, expressed as the minimum inhibitory concentration (MIC), minimum bactericidal action (MBC), mutant prevention concentration (MPC), and postantibiotic effect (PAE), is determined readily in vitro, good absorption, long half-life (t1/2), good transfer to tissues, and a low rate of protein binding are important for good clinical results. A particular concern is whether the oral cephalosporins commonly prescribed in Japan show such profiles. The pharmacokinetic/pharmacodynamic (PK/PD) parameter considered to correlate best with therapeutic success is the percentage of the dosing interval during which a β-lactam agent’s concentration in blood exceeds the MIC for a causative pathogen (time above MIC, or T ⬎ MIC).23,24 Generally, a T ⬎ MIC of approximately 35% for penicillins and 50% for cephalosporins has been proven necessary for clinical efficacy. Based on these principles, low concentrations (0.5– 1.5 µg/ml) of most oral cephalosporin antibiotics in blood after the usual doses approved by the Japanese Ministry of Health, Labor, and Welfare are not expected to be effective against resistant pathogens. The increasingly frequent detection of resistant strains in patients with RTIs is considered to be closely related to suboptimal antibiotic concentrations.
Mechanisms of antibiotic resistance and susceptibility status in S. pneumoniae Resistance mechanisms The main targets of β-lactam agents are the PBPs located on the cell membrane, as described above. PBP1A, PBP2X, and/or PBP2B were usually found to have low affinity for βlactams in PISP and PRSP. PBP1A is an enzyme involved in the synthesis of a peptidoglycan for the long axis of the cell wall; PBP2X is necessary for septal formation, and PBP2B is necessary for the development of the lancet form. Generally, the functions of these PBPs have been deduced from morphologic changes after β-lactam exposure and from PBP affinities of the β-lactams.25 Penicillins and carbapenems bind to PBP1A and -2B, while cephalosporins bind strongly to PBP2X. Accordingly, the efficacy of cephalosporins is affected more by PBP2X alterations than by alterations of PBP1A or PBP2B.
detected. Based on technical requirements for the construction of informative PBP primers, amino-acid substitutions detected in the area of the conserved amino-acid motif in the transpeptidase region may be responsible for increases in β-lactam MICs. In macrolide-resistant organisms, amplification of DNA in samples by PCR has identified resistance genes; additionally, the LytA gene, encoding an autolysin enzyme, has been detected in a strain of S. pneumoniae.27 All three samples shown in Fig. 2 were identified as S. pneumoniae, based on positivity for LytA. In sample 1, DNA fragments corresponding to pbp1a, 2x, and 2b were detected, indicating that this strain possessed normal PBP genes. In sample 2, the pbp2x gene was abnormal because that DNA fragment was missing. Likewise, in sample 3, all PBP genes were abnormal. The time required for analysis was 2.6 h. PCR results and penicillin G susceptibility Figure 3 presents distributions of S. pneumoniae strains according to susceptibility to penicillin G and abnormal PBP genes. The upper panel shows data for clinical isolates collected from 187 Japanese institutions participating in the Study Group for Community-Acquired Bacterial Infections between 1998 and 2000. The lower panel shows data for strains collected from many other countries by Dr. P. C. Appelbaum of the Hershey Medical Center and the University of Pennsylvania in the United States between 1996 and 2000.26 For strains having no abnormal genes, the MIC of penicillin was nearly equal to or less than 0.031 µg/ml. These strains were identified as penicillin-susceptible S. pneumoniae (PSSP) by molecular methods. For strains in which only the pbp2x gene was abnormal, the MIC slightly increased, to 0.063 µg/ml, but the strain remained susceptible to penicillin according to the recommendations of the National Committee for Clinical Laboratory Standards (NCCLS). Strains of this type account for 20% of those isolated in Japan, but their proportion is lower in countries where ampicillin and amoxicillin are the predominant antibiotics used in outpatient practice. Strains having two abnormal PBP genes – pbp1a plus pbp2x or pbp2x plus pbp2b – had an increased MIC, of 0.125 or 0.5 µg/ml, and proved to be PISP. Strains having three abnormal PBP genes formed a group in which the MIC of penicillin was equal to or greater than 1 µg/ml and showed frank resistance. In addition, highly resistant strains with an MIC of penicillin of 8 µg/ml were detected, representing a future clinical problem.
Rapid identification of resistance genes PCR results and susceptibility to oral antibiotics For the rapid identification of resistance genes, a polymerase chain reaction (PCR) system was constructed, in the author’s laboratory, for routine use with all strains. In the PBP gene analysis shown in Fig. 2, the respective PBP genes are normal when the PCR products are detected,26 while the gene is abnormal when the products are not
Figure 4 depicts S. pneumoniae strains according to their susceptibility to oral cephalosporins and the presence of abnormal PBP genes. Cefpodoxime and cefdinir were developed relatively early, and are prescribed to pediatric outpatients in Japan. The MICs of both of these agents for
287 CXM-AX CFDN CEMT-PI CFIX CPDX-PR CETB CDTR-PI CFTM-PI
AMPC/CVA
S. pneumoniae
33.0%
PISP
‘94‘95
‘98 ‘00
0
‘02
40
H. influenzae
30
40
Meningitis
30 20 10
‘77
‘80
23.6%
Low-BLNAR
TEM-1 b-lactamase
‘75
BLNAR 28.8%
‘83 ‘85 ‘86
‘90
‘94‘95 ‘96
‘98 ‘00
‘02
Fig. 1. Year-to-year changes in penicillin-resistant Streptococcus pneumoniae (PRSP) and β-lactamase-nonproducing, ampicillinresistant (BLNAR) Haemophilus influenzae in respiratory tract infections, including a time line of the development of oral β-lactam antibiotics in Japan. PISP, penicillin-intermediately-resistant S. pneumoniae; AMPC, amoxicillin; ABPC, ampicillin; CCL, cefaclor; CXD, cefroxadine; AMPC/CVA, amoxicilln-clavulanic acid; CFIX, cefixime; CFTM-PI, cefteram pivoxill; CXM-AX, cefuroxime axetil; CPDX, cefpodoxime; CFDN, cefdinir; CETB, ceftibuten; CEMT-PI, cefetamet pivoxil; CDTR-PI, cefditoren pivoxil; FRPM, faropenem; CFPN-PI, cefcapene-pivoxil
Marker (bp)
A
B
C
#1
#2
#3
489 404 331
Other countries
20 10 0 MIC (mg/ml)
Fig. 3. Penicillin G susceptibility and abnormal PBP genes in S. pneumoniae. Strains (n ⫽ 1945) shown in the upper panel were isolated from samples acquired in Japan by the Community-acquired Bacterial Infections Working Group and analyzed by molecular methods between 1998 and 2000. Strains (n ⫽ 100) shown in the lower panel were collected from many countries by Dr. P. C. Appelbaum (Hershey Medical Center and University of Pennsylvania).26 Although strains with asterisk showed minimum inhibitory concentrations (MICs) below 0.25 µg/ml, amino-acid substitutions detected in the pbp1a gene did not affect the MIC. PSSP, Penicillin-susceptible S. pneumoniae
(%) 40
pbp1a+2x+2b pbp1a+2x pbp2x+2b pbp1a+2b pbp2b pbp2x PSSP
Cefpodoxime 30
242 190 147 111
16
‘90
8
‘87
4
‘85
20
2
‘80
pbp2b pbp1a+2x
10
(0%)
‘75
pbp2x pbp2x+2b
1
10
PSSP pbp1a+2b pbp1a+2x+2b
Japan
0. 5
20
40 30
PISP
Meningitis
30
50
54.9%
PRSP
40
%
(%)
FRPM CFPN -PI
0. 25
50
CCL CXD
0. 00 8 0. 01 6 0. 03 1 0. 06 3 0. 12 5
%
AMPC ABPC (1965)
20 10
67
Cefdinir 30 20 10
32
8
16
4
2
1
0 0. 5
Fig. 2. DNA fragments amplified by polymerase chain reaction (PCR) in S. pneumoniae. DNA products present following penicillin-binding protein (PBP) gene amplification were identified as normal PBP genes, while absent DNA products were identified as abnormal PBP genes. In macrolide resistance, amplification of DNA in the sample indicates that they possess the resistant genes mefA and ermB
0
40
0. 25
Abnormal Abnormal pbp1a, 2x, 2b pbp2x + mefA
0. 00 8 0. 01 6 0. 03 1 0. 06 3 0. 12 5
Normal pbp
MIC (mg/ml)
PISP strains having two abnormal PBP genes – pbp1a plus pbp2x or pbp2x plus pbp2b – and for PRSP strains having three abnormal PBP genes exceeded 1 µg/ml, clearly beyond the blood concentration resulting from the usual doses in Japan according to the T ⬎ MIC parameter. In addition, the MICs for strains having an abnormal pbp2x gene were between those for PSSP and the MICs for PRSP; these strains clearly belonged to PISP, with MICs of 0.25 to 0.5 µg/ml. Thus, alterations of the pbp2x gene in S. pneumoniae result in intermediate resistance to cephalosporin antibiotics. Figure 5 shows the cumulative curves of seven oral βlactam antibiotics against PRSP strains identified by PCR. Among these oral antibiotics, faropenem and cefditoren are effective, showing respective MIC90s of 0.5 and 1 µg/ml, followed by amoxicillin. The MIC90s of the four remaining
Fig. 4. Cefpodoxime and cefdinir susceptibilities of oral cephalosporin antibiotics and abnormal PBP gene status in S. pneumoniae (n ⫽ 1945)
agents exceeded 1 µg/ml, the estimated serum concentrations obtained from the usual dose. Importantly, amoxicillin has particularly good absorption into the circulation, which gives it greater clinical efficacy than oral cephalosporins in terms of T ⬎ MIC. PCR results concerning macrolide susceptibility PCR results for macrolide resistance genes, together with susceptibility to erythromycin and clindamycin, are illustrated in Fig. 6. Strains having the ermB gene encoding for
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methylase were highly resistant to all macrolides and clindamycin. Strains having the mefA gene, which encodes the membrane protein involved in the efflux system, showed intermediate resistance to 14-membered ring macrolides and azithromycin at concentrations from 0.5 to 8 µg/ml, but remained susceptible to clindamycin and 16membered ring macrolides. About 70% of S. pneumoniae strains possess resistance determinants and therefore show resistance to macrolides.
Table 1. Mechanisms of β-lactam resistance in Haemophilus influenzae
Quinolone resistance
PBP, penicillin-binding protein; BLNAS, β-lactamase-nonproducing, ampicillin-susceptible H. influenzae; BLPAR, β-lactamase-producing, ampicillin-resistant H. influenzae; BLNAR, β-lactamase nonproducing ampicillin-resistant H. influenzae; BLAPCR, β-lactamaseproducing, amoxicillin/clavulanic acid-resistant H. influenzae
Three mutations are known to cause quinolone resistance in clinical isolates of S. pneumoniae. Two are single-point mutations in the quinolone resistance-determing region (QRDR), positioned at Ser79 Æ Phe in parC and at Lys422 Æ Arg in parE genes encoding topoisomerase IV. These strains show slightly decreased susceptibility to levofloxacin and ciprofloxacin, with respective MICs of 1.56 µg/ml and 6.25 µg/ml, but remain susceptible to gatifloxacin.28 In addition to these two mutations, another involves the substitution of Phe at Ser81 of gyrA, which encodes DNA gyrase. This mutation apparently decreases susceptibilities to all quinolones. Recently, strains of serotype 3 and mucoid type S. pneumoniae resistant to new quinolones have been isolated from sepsis cases in adults. Therefore, mutant prevention concentrations (MPC) should be used when new quinolones are given to treat infections caused by S. pneumoniae.
Mechanisms of β-lactam antibiotic resistance and susceptibility status in H. influenzae Designations for β-lactam resistance Table 1 shows reported mechanisms of β-lactam antibiotic resistance in H. influenzae. Strains without resistance determinants are termed β-lactamase-nonproducing, ampicillin-susceptible H. influenzae (BLNAS). TEM-1 and ROB-1 β-lactamases are well-known mechanisms of resistance in this microorganism; strains possessing either are termed β-lactamase-producing, ampicillin-resistant H. influenzae (BLPAR). Another mechanism involves the presence of an altered PBP3 enzyme with decreased affinity for β-lactam agents.29 Strains with such alterations, termed BLNAR, can be classified into two types by molecular methods. As described above in the second paragraph under “Year-to-year changes in frequency of resistant strains”, BLNAR are increasing rapidly in Japan, but are rare in Europe.30,31 To further complicate the present situation, H. influenzae strains having two mechanisms of resistance, β-lactamase and PBP3 alterations, have been detected, and are termed β-lactamase-producing, amoxicillin/clavulanic acid-resistant (BLPACR). To identify these resistance de-
β-Lactamase (TEM-1 and ROB-1)
BLNAS BLPAR Low-BLNAR BLNAR BLPACR-I BLPACR-II
⫺ ⫹ ⫺ ⫺ ⫹ ⫹
Mutation on PBP3 ( ftsI ) 1 Point
2 Points
⫺ ⫺ ⫹ ⫺ ⫹ ⫺
⫺ ⫺ ⫺ ⫹ ⫺ ⫹
terminants in H. influenzae, this laboratory has developed PCR techniques for the analysis of all clinical isolates.32 Mechanisms of BLNAR All BLNAR strains show decreased β-lactam antibiotic affinity for PBP3, which mediates septum formation.29 The ftsI gene encoding the PBP3 enzyme was sequenced in this laboratory for many H. influenzae isolates considered to be BLNAR. These resistant strains were classified into two types on the basis of amino-acid substitutions shown by sequencing. Strains having only an Arg517 Æ His or an Asn526 Æ Lys substitution near the conserved KTG (Lys-Thr-Gly) motif were considered low-BLNAR. In strains termed BLNAR, three amino acids (Met373, Ser385, and Leu389) in the area of the conserved SSN (Ser-Ser-Asn) motif were replaced by Ile, Thr, and Phe, respectively, in addition to any substitution found in low-BLNAR. Figure 7 shows the characteristic inhibitory zones observed by disc susceptibility testing for BLNAR. Inhibitory zones with oral cephalosporins, such as cefaclor (30 µg/disc), cefdinir (5 µg/disc), and cefpodoxime (10 µg/disc) cannot be seen, although one is present with cefditoren (5 µg/disc). Although inhibitory zones were observed surrounding ampicillin (10 µg/disc) and cefotaxime (30 µg/disc), these zones were clearly smaller than those in susceptible strains. Other cephalosporin antibiotics showed the same phenomenon (data not shown). PCR results and β-lactam susceptibility status To demonstrate the nature of BLNAR resistance, H. influenzae are shown, in Fig. 8, according to their susceptibility to cefotaxime (CTX; instead of ampicillin used a standard antibiotic), as well as their resistance gene status. The upper panel presents data for 1408 isolates obtained in Japan between 1998 and 2000, and the lower panel presents data for 100 isolates obtained in the United States in 1999.32 The MICs of CTX against strains with no resistance gene were 0.016 µg/ml at most. In contrast, the peak MIC of CTX
289 Indication serum conc.(1 mg/ml)
(%)
100 80 60
Ampicillin (30%)
Amoxicillin (75%)
(AMP-Susceptible Strain)
Cefaclor (0%)
40
AMP (10)
BLNAS
CFDN (5)
CCL (30)
CPDX (10)
Cefditoren (75-80%) Cefdinir ( 0%)
Faropenem (95%)
CTX (30)
Cefpodoxime (<5%)
20
CDTR (5)
ABPC (10)
64
32
16
8
4
2
1
0. 5
0. 00 8 0. 01 6 0. 03 1 0. 06 3 0. 12 5 0. 25
0 CFDN (5)
BLNAR
MIC (mg/ml)
CCL (30)
Fig. 5. Cumulative MIC curves of oral β-lactam antibiotics for PRSP identified by molecular methods (n ⫽ 954). Percentages in parentheses indicate clinical efficacy based on time above MIC (T ⬎ MIC) for each antibiotic, using standard pediatric doses
40
Negative ermB
Erythromycin 30
CPDX (10) CTX (30)
CDTR (5)
Fig. 7. Characteristics of inhibitory zones observed by disc susceptibility testing in β-lactamase-nonproducing, ampicillin-susceptible (BLNAS) H. influenzae and also in the resistant counterpart (BLNAR). AMP, ampicillin; CCL, cefaclor; CTX, cefotaxime; ABPC, ampicillin; CFDN, cefdinir; CPDX, cefpodoxime; CDTR, cefditoren
mefA mefA+ermB
20 10
(%)
5 0.
1
2
4
8
16
32
64
MIC (mg/ml)
Fig. 6. Erythromycin and clindamycin susceptibilities and resistance gene status in S. pneumoniae (n ⫽ 1945)
against BLNAR strains was 0.5 µg/ml, 32 times that for BLNAS. The MICs of CTX against low-BLNAR were between 0.031 and 0.125 µg/ml and could not be distinguished easily from the MICs for BLNAS. BLPAR strains were extremely uncommon (5%). In the United States, TEM-1 and ROB-1 β-lactamaseproducing strains were prevalent, representing 41% of isolates, low-BLNAR strains accounted for only 12%, and no BLNAR strain was detected.32 The cumulative curves of seven oral β-lactam agents against BLNAR (n ⫽ 109) identified by PCR are shown in Fig. 9. Most of these agents, excluding cefditoren, exhibited MIC90s greater than or equal to 1 µg/ml, clearly beyond the serum concentrations attained with the usual dose.
Meningitis caused by PRSP and BLNAR Meningitis caused by PRSP Figure 10 shows results from the study group of the Nationwide Surveillance for Bacterial Meningitis (NSBM)
8
25
4
0.
BLPACR- I
2
3 5 1 06 03 12 0. 0. 0.
1
6 01
TEM-1
Low- BLNAR
0. 5
0.
Low-BLNAR TEM-1
BLNAS ROB-1
0. 25
0
US
0. 12 5
10
0. 06 3
20
0. 03 1
30
BLNAS BLNAR BLPACR- I
0. 01 6
Clindamycin
40
Japan
0. 00 8
50
60 50 40 30 20 10 0 60 50 40 30 20 10 0
0. 00 4
0
MIC (mg/ml)
Fig. 8. Cefotaxime susceptibility and resistant gene status in H. influenzae. Strains (n ⫽ 1408) shown in the upper panel were isolated from samples obtained in Japan by the Community-Acquired Bacterial Infections Working Group and analyzed by molecular methods between 1998 and 2000. Strains (n ⫽ 100) shown in the lower panel were collected by Dr. P. C. Appelbaum (Hershey Medical Center and University of Pennsylvania) from United States institutions.32 BLPACR-I, β-lactamase-producing, amoxicillin/clavulanic acidresistant H. influenzae
concerning S. pneumoniae isolates sent to this laboratory between 1999 and 2002, from 226 participating medical institutions throughout Japan. Of the 219 patients, 146 (66.7%) were under 19 years old; the remaining 73 patients (33.3%) were adults. The percentages of cases caused by PISP having an abnormal pbp2x, PISP having two abnormal PBP genes, pbp1a plus pbp2x or pbp2x plus pbp2b, and PRSP having three abnormal PBP genes were 20.1%, 20.6%, and 39.2%, respectively. Only 19.2% of cases were caused by PSSP. PISP and PRSP were isolated more frequently from pediatric patients than from adult patients. Recently, meningitis cases have increased in adults aged 50 to 60 years, and their prognosis is poor. The clinical course in these patients will be considered in another article.
290 100
Children: n=138
Indication serum conc.
(%)
60
Ampicillin (15%) Cefditoren (95%)
4 3.0%
3 other 5.1% 4 7.2% 5.1%
80 Amoxicillin (20%)
Adults: n=66
23A 1.4%
23F 14.5%
other 13.6%
Cefdinir (0%)
19F 16.7%
20
9 4.5%
6B 25.4%
14 8.7%
64
32
16
8
4
2
1
0. 5
0. 25
06 3 0. 12 5
0
22 13.6%
9 5.1%
19F 7.6%
14 4.5%
18 0.7%
MIC (mg/ml)
Fig. 9. Cumulative MIC curves of oral β-lactam antibiotics for BLNAR (n ⫽ 109) identified by molecular methods. Percentages in parentheses indicate clinical efficacy based on T ⬎ MIC for each antibiotic, using standard pediatric doses
10 9.1%
23A 6.1%
Cefaclor (0%)
0. 00 8 0. 01 6 0. 03 1
6B 7.6%
23F 16.7%
40
Fig. 11. Serotypes of S. pneumoniae isolates causing meningitis (n ⫽ 204)
(%)
40 PSSP PISP(pbp2x) PISP(pbp1a+2x)
35 30
PISP(pbp2b) PISP(pbp2x+2b) PRSP(pbp1a+2x+2b)
100 BLNAS (32%) Low-BLNAR (31%)
80 No. of patients
No. of Patients
6A 4.5%
6A 10.1%
Cefpodoxime (15%) Faropenem (5%)
3 9.1%
25 20 15 10 5
BLPAR (16%) BLNAR (12%)
BLPACR I + II (10%)
60 40 20
Age
6 712 13 -1 9 20 30 40 50 60 70 80 -
5
4
3
2
1
11 M
7-
6M
0
Fig. 10. Cases of meningitis according to patient age and resistance type of causative S. pneumoniae isolates classified by PCR between 1999 and 2002 (n ⫽ 219). Strains were collected throughout Japan. M, months
Serotype data for S. pneumoniae causing meningitis are very important for formulating vaccines. As shown in Fig. 11, serotypes 6A and 6B were the types encountered most frequently in pediatric patients, followed by serotypes 23F, 19F, and 14. Data not shown here indicated that many of these serotypes were identified as PISP and PRSP. In contrast, serotypes 23F, 3, and 22 were prevalent among isolates from adults. The percentages of isolates covered by seven polyvalent pneumococcal conjugate vaccines were estimated as 76.1% in children and 43.9% in adults. Meningitis caused by H. influenzae Figure 12 shows the results of our surveillance study of meningitis with respect to H. influenzae. Most of these strains were type b (except for three cases). Isolates were classified into five resistance types by molecular methods. Approximately 90% of the total number of patients were under 4 years of age. In 12% and 31% of cases, the infection was caused by BLNAR and low-BLNAR, respectively. TEM-1 β-lactamase-producing strains, i.e., BLPAR, accounted for 16% of isolates.
0 1 - 5M 6-11M
1y
2y
3y
4y
5y
6y
>7 y
ND
Age Fig. 12. Cases of meningitis according to patient age and resistance type of H. influenzae isolates classified by PCR between 1999 and 2002 (n ⫽ 310). BLPAR, β-lactamase-producing, ABPC resistant H. influenzae
Notably, the prevalence of BLNAR increased rapidly year by year: 0% in 1999, 5.8% in 2000, 14.1% in 2001, and 21.3% in 2002. In contrast, the prevalence of BLPAR has decreased gradually, from 32% in 1999 to 13% in 2002. Of future concern is a possible increase in BLPACR II isolates. The main factors underlying the rapid increase of severe infections caused by BLNAR may include the wide spread use of oral cephalosporins having weak bactericidal activity, increased numbers of toddlers attending nursery schools, and increasing population density favoring the occurrence of community-acquired infections.
Concluding recommendations A number of conclusions may be drawn from the results of molecular epidemiologic studies of S. pneumoniae and H. influenzae. In particular, doses of oral antibiotics approved by the Japanese Ministry of Health, Labor, and Welfare are small relative to PK/PD parameters for resistant strains that cause RTI. Bacteria bearing mutations in genes encoding resistance-associated enzymes are easily selected by insufficient concentrations of oral antibiotics, which partially
291
damage the pathogen but fail to cause lysis. The proliferation of selected mutants increases the prevalence of resistance. To prevent such resistance from increasing and to lengthen the useful life of new antibiotics, the most important steps to take include: (i) vaccination against these organisms, (ii) rapid identification of causative pathogens, (iii) the proper use of antibiotics based on PK/PD parameters, and (iv) the establishment of postmarketing surveillance of antibiotics by independent organizations. Ultimately, the development of oral antibiotics that are more effective than currently used ones against PRSP and BLNAR is desirable. Acknowledgments I deeply thank the many physicians and medical technicians who participated in the study groups of the Nationwide Surveillance for Bacterial Meningitis and Community-Acquired Bacterial Infections. I also thank Dr. P. C. Appelbaum of the Hershey Medical Center and the University of Pennsylvania, who kindly allowed me to analyze strains by PCR in his laboratory. Finally, I thank Keiko Hasegawa, a student of the Graduate School of Infection Control Sciences at the Kitasato Institute for Life Sciences, Kitasato University, for her helpful assistance.
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