Streptococcus pyogenes resistance to erythromycin in relation to macrolide consumption in Spain (1986–1997)

Juan J. Granizoa, Lorenzo Aguilarb,*, Julio Casalc, Rafael Dal-Réb and Fernando Baquerod

a Research Area, Fundación Jiménez Díaz, Madrid; b Medical Department, SmithKline Beecham Pharmaceuticals, C/Valle de la Fuenfria no 3, 3° D. 28034 Madrid; c Microbiology Department, National Centre of Microbiology, Instituto de Salud Carlos III, Majadahonda (Madrid); d Microbiology Department, Ramón y Cajal Hospital, Madrid, Spain


    Abstract
 Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
The relationship between Streptococcus pyogenes resistance to erythromycin and macrolide consumption in Spain was studied. Erythromycin resistance was highly correlated with the consumption of total macrolides (r = 0.88, P < 0.01). When macrolides were grouped into posological subgroups according to their pharmacokinetic and pharmacodynamic properties and analysed separately, erythromycin resistance appeared to be related mainly to those macrolides taken twice daily (bd) (r = 0.86, P < 0.01) and those taken once daily (od) (r = 0.87, P < 0.01), but not to those taken four (qds) or three times a day (tds) (r = –0.04, P = 0.90). A progressive increase in the erythromycin resistance curve was seen after the consecutive introduction of both bd and od macrolides, which contributed to the increase in the total macrolide consumption, replacing tds macrolide prescription. Although this ecological analysis cannot establish an unequivocal causal relationship between antibiotic consumption and S. pyogenes resistance, the data are consistent with the hypothesis that widespread use of macrolides, mainly of bd and od macrolides, resulted in an increased prevalence of S. pyogenes resistant to erythromycin in Spain.


    Introduction
 Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
It is well established that the prevalence of resistance to antimicrobials depends in part on their use in the community.1 However, the use of penicillin has not resulted in the appearance of in vitro resistance in Streptococcus pyogenes,2 probably because of the absence of selectable variants carrying mechanisms of ß-lactam resistance. The relationship between macrolide consumption and monoclonal spread of resistance in S. pyogenes has already been established.3,4 High rates of macrolide resistance3,510 have been described in different countries; most instances of resistance are associated with the presence of a macrolide efflux system11 (M phenotype) coded by a mef gene, which confers cross-resistance to 14-membered (erythromycin, clarithromycin, dirithromycin, oleandomycin and roxithromycin) and 15-membered lactone ring macrolides (azithromycin), but not to 16-membered macrolides (spiramycin, acetyl-spiramycin, josamycin) or clindamycin.12 This erythromycin resistance phenotype is by far the most common in S. pyogenes isolates in Spain. The so-called constitutive phenotype is relatively uncommon in this species, in contrast to S. pneumoniae strains, in which it is the predominant phenotype. The constitutive phenotype is mediated by enzymes, encoded by erm genes, that methylate rRNA, leading to a conformational change in the ribosome that results in coresistance to macrolides, lincosamides and streptogramin B-type antibiotics (MLSB). The aims of this study were to assess whether there was an association with increased macrolide use and increasing prevalence of erythromycin resistance over a 12 year period in Spain (1986–1997) and to try to determine whether this resistance was associated with the use of particular types of macrolides.


    Materials and methods
 Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
Studies on surveillance of S. pyogenes resistance in Spain were identified by means of a Medline search from 1986 to 1998 using the keywords ‘S. pyogenes’ and ‘erythromycin resistance’. Proceedings of local and international meetings and congresses related to infectious diseases, the contents of Spanish journals related to infectious diseases, paediatrics and internal medicine, as well as the references of identified papers were also reviewed. To be included in this review, reports had to comply with the following criteria: (i) analysis of pharyngeal swabs in >=70% of cases; (ii) assessment of resistance to erythromycin; (iii) the use of a defined breakpoint for erythromycin resistance; and (iv) use of a breakpoint of >=1 mg/L to define resistance to erythromycin, following NCCLS criteria.13 Nineteen studies of resistance to macrolides in S. pyogenes 8,9,12,1429 fulfilled these criteria (TableGo).


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Table. Studies of S. pyogenes resistance to erythromycin in Spain, included in the analysis by year of data collection
 
Antibiotic consumption data were obtained from Intercontinental Marketing Services (IMS) Ibérica S.A., Madrid, Spain. The defined daily dosages (DDD) used for 14- and 15-membered macrolides were: erythromycin, 2 g/day; azithromycin, 0.5 g/day; oleandomycin, clarithromycin and dirithromycin, 1 g/day; roxithromycin, 0.3 g/day. Macrolides were grouped according to whether the usual dosage regimen was tds (erythromycin and oleandomycin), bd (clarithromycin and roxithromycin) or od (azithromycin and dirithromycin). DDD/1000 inhabitants/day were calculated; population data were taken from the yearly projections of the Spanish population obtained from official data (National Statistics Institute, Spain).

For each study identified, the year-specific prevalence of resistance was obtained. For each year, the rates of resistance from different studies were combined to obtain an overall estimate for that given year. A fixed-effects model with weights equal to the inverse of the variances of the prevalence was used to obtain the combined estimates. The prevalence of resistance was plotted against the consumption of macrolides for each year in the study period. Spearman non-parametric correlation coefficients (r) between the prevalence of resistance and the consumption of macrolides were calculated. Confidence intervals were calculated by the exact method. A multivariate model was performed analysing the bd and od models. SPSS for Windows, release 7.5, was used for statistical analysis.


    Results
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 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
The TableGo shows the studies that fulfilled the inclusion criteria and were considered in this review, together with the number of strains included and the prevalence of erythromycin resistance for each of them. The prevalence of erythromycin resistance was low between 1986 [1.1%; 95% confidence interval (CI) 0.5–2.6] and 1993 (5.8%; 95% CI 4.1–8.1), but increased progressively in 1995 (23.2%; 95% CI 19.9–26.9), 1996 (18.4%; 95% CI 16.8–20.1) and 1997 (29.3%; 95% CI 26.8–31.9) (FigureGo).



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Figure. S. pyogenes resistance to erythromycin and consumption of 14- and 15-membered lactone ring macrolides grouped by dosage regimen in the period 1986–1997 in Spain. Bars indicate erythromycin resistance. Symbols: {diamondsuit}, tds macrolides; {blacksquare}, bd macrolides; {blacktriangleup}, od macrolides; •, overall macrolide consumption. r, correlation coefficient.

 
Erythromycin consumption increased until 1991 (1.09 DDD/1000 inhabitants/day) and then decreased until 1997 (0.69 DDD/1000 inhabitants/day). The use of bd macrolides was infrequent until 1988, but then increased progressively, reaching 1.40 DDD/1000 inhabitants/day in 1997. Among the bd macrolides, 58% of DDDs were attributable to clarithromycin and 42% to roxithromycin. Macrolides suitable for od use were introduced in 1993; their use increased steadily until 1997 (0.49 DDD/1000 inhabitants/ day), with 89.8% of DDDs corresponding to azithromycin in 1997.

The total consumption of macrolides showed a good correlation with the erythromycin resistance curve (r = 0.88; P < 0.001). When specific macrolide classes were analysed separately, no association was apparent between consumption of tds macrolides and erythromycin resistance (r = –0.04; P = 0.90). However, there was a strong association between prevalence of resistant strains and consumption of bd macrolides (r = 0.86; P < 0.001), with a 1–2 year lag between the observed increase in consumption and increase in resistance. The association between consumption of od macrolides and prevalence of resistance was also high (r = 0.87; P < 0.001), but these drugs were introduced after the increase in prevalence of resistant strains in the early 1990s. The results were essentially unchanged when a multivariate model was used to assess the simultaneous correlation of the three classes of macrolides with the prevalence of resistance.


    Discussion
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 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
This analysis shows that macrolide resistance in S. pyogenes was low when erythromycin was the main macrolide in use, but that it increased with the introduction of bd macrolides and before the introduction of od macrolides. Some limitations, however, have to be considered in the interpretation of these results. First, we have relied only on published data on the prevalence of resistance. In recent years, the awareness of increased prevalence of resistance may have led to selective publication of studies showing only a high prevalence of resistance, a type of publication bias. The likelihood of this is unknown, but is probably small since the increased prevalence of resistance is widely recognized as a real phenomenon. The retrospective, literature-based nature of this study obviously precludes the inclusion of manuscripts with the ideal homogeneity of samples within the same year, or between different years. Besides, rates of resistance are known to differ from one area to another, as has been reported recently,30 although this variation is likely to be considerable only in recent years, when erythromycin resistance rates were high enough for this phenomenon to manifest itself. It was in these years when the most reliable multicentre studies were conducted, so the extent of this geographical variation is relatively well characterized. Secondly, other causes of increased resistance independent of macrolide use may also explain recent changes in prevalence of resistance, such as the clonal expansion of resistant strains. Nevertheless, under conditions of sufficient intensity of antibiotic selection, the resistant clones should have a considerable selective advantage. Since many of the isolates came from children, it would also have been most desirable to consider factors such as rate of colonization, duration and transmissibility rate both in children attending day nurseries and in those staying at home. Finally, this study cannot unequivocally establish a causal connection between the introduction of bd and od macrolides and widespread resistance, but it at least seems clear that, without the increase in consumption of these new macrolides, the overall increase in macrolide consumption might not have occurred. In Finland, high rates of macrolide resistance in S. pyogenes occurred with rates of macrolide (mainly erythromycin) consumption of >2 DDD/1000 inhabitants/day.31 Similarly, in this study, the exponential growth of erythromycin resistance began to occur in 1991–1993, when the total consumption of macrolides first exceeded 2 DDD/1000 inhabitants/ day. Once erythromycin resistance was established, minimal increases in the consumption of macrolides were followed by marked increases in the prevalence of erythromycin resistance. Erythromycin use was low, but the associated selective pressure had been of long duration (several decades) and constant pressure may have resulted in the enrichment of resistant variants. In contrast, the increase in use of bd and od macrolides strongly correlates with the emergence of high resistance rates. Hence, it may be that the introduction of the newer macrolides served to surpass a critical threshold of selective intensity, which could have been followed by an increased rate of transmission of the previously selected populations.

From a pharmacodynamic point of view, other factors may have contributed to the selective process. It has been suggested that macrolide agents with low Cmax and long half-life (like bd or od macrolides) are likely to produce a longer selective window, which means longer bacterial exposure to resistance-selective concentrations.32 Long-acting agents optimize selective effects.33 In any case, either directly or indirectly, both bd and od macrolides appear to be the main reason for the increase in erythromycin resistance.

Some reports have shown a monoclonal spread of resistance3 related to macrolide consumption4 while in other reports, resistance was polyclonal,6 including in our country.9 In Spain, as in other European countries, a new efflux phenotype is responsible for the increase in resistance.8,9,12 The high prevalence (>90%) of this resistance phenotype described in Spanish studies8,9,12 may affect the choice of empirical antibiotic therapy in clinical practice.11 This is even more relevant when considering that the prevalence of resistance is higher in younger people8,10 and that a positive relationship has been described between the reduction of macrolide use and the decline of erythromycin resistance prevalence.34 Nevertheless, formal (mathematical) population analysis suggests that the decay in antibiotic resistance after a significant decrease in consumption of particular drugs takes much longer than it does for the resistance to emerge.35

This study has gathered all the reliable evidence available for the last 12 years in Spain, and put it into relation with the global trend in antibiotic use, trying to sketch hypotheses that warrant further investigation. This study shows that the increase in overall macrolide use, caused by bd and od macrolides, has resulted in an increased prevalence of erythromycin-resistant S. pyogenes in Spain. Whether this progressive increase in erythromycin resistance has been due to an increase in total macrolide consumption or can be explained on the basis of pharmacodynamic properties that are specific for the bd and od macrolides, remains unresolved. To answer this question, active intervention studies in close populations are needed, targeting bd and/or od macrolides and then tracking what happens to the level of erythromycin resistance. The relation of antibiotic consumption and prevalence of resistance among Gram-positive cocci stresses the importance of preserving the therapeutic potential of antibiotics by taking into account the ecological consequences of the generalization of their use.4 Population biology studies should be undertaken to explain the theoretical and practical consequences of antibiotic consumption on pathogenic bacteria.36


    Acknowledgments
 
We thank César García-Rey, Richard Bax, Jerónimo Pachón and Francisco Soriano for critical review of the manuscript.


    Notes
 
* Corresponding author. Tel: +34-91-334-5275; Fax: +34-91-334-5141; E-mail: lorenzo.aguilar-alfaro{at}sb.com Back


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 Introduction
 Materials and methods
 Results
 Discussion
 References
 
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Received 4 April 2000; returned 5 July 2000; revised 17 July 2000; accepted 16 August 2000