Background
Streptococcus pneumoniae (pneumococcus) often resides asymptomatically as part of human upper respiratory tract microbiota. It is an opportunistic pathogen that causes infections leading to otitis media, pneumonia, sepsis and meningitis [
1]. The World Health Organization estimated that this agent caused476,000 deaths among children less than 5 years in 2008; most of these deaths occur in developing countries [
2]. Furthermore, antibiotic resistance which has been shown to be associated with a limited spectrum of serotypes, commonly responsible for invasive disease, may have adverse impact on the epidemiology of pneumococcal disease [
3]. Resistant pneumococci have been isolated in all continents. In several settings over 40 % of clinical isolates exhibit multidrug-resistance [
4].
The emergence of
S.pneumoniae with reduced susceptibility to penicillin has been observed in Brazil [
5] and in many parts of the world. In addition, reduced susceptibility to extended-spectrum cephalosporins such as ceftriaxone has become a serious problem because it limits the available treatment options for pneumococcal invasive diseases [
6]. Penicillin-non-susceptible isolates have been identified among 15 % of the pneumococcal meningitis isolates reported in Salvador, Bahia since 1996 [
7]. These isolates are restricted to five serotypes (14, 19A, 19 F, 23 F and 6B). Serotype 14was the main penicillin-non-susceptible serotype within this area, as it was in the U.S. prior to PCV7 implementation [
8], and has disseminated to widely separate geographic areas [
3].
Widespread use of PCV7 dramatically affect the epidemiology of invasive pneumococcal disease (IPD) and carriage reservoir [
9,
10]. The Ministry of Health incorporated PCV7in Brazil in 2001 for groups with special clinical conditions considered at high risk of IPD, as immunodeficiency, asplenia and severe cardio-pulmonary diseases, who received vaccination at special immunobiological reference center and at private clinics. In 2010, nationwide PCV10vaccination started for children less than 2 years of age through the national immunization program [
11].
Pneumococcal clones have been shown to switch their capsular serotype by exchanging genetic material with other pneumococci; such changes could affect the ability of conjugate vaccines to control disease and could alter the relationship between antimicrobial resistance and serotype [
1,
3]. Pneumococcal strain surveillance over time is essential to determine the relative importance of established and emerging antimicrobial-resistant clonal complexes [
8]. So far, few publications have addressed the distribution of pneumococcal penicillin non-susceptible clonal complexes in Latin America [
7]. Here we describe the temporal incidence, serotype distributions and genotype diversity of penicillin-nonsusceptible
S.pneumoniae (PNSSP) strains recovered from meningitis cases from 1996 through 2012.
Discussion
Since the identification of the first penicillin non-susceptible
S. pneumoniae case in Brazil in 1988 [
21], surveys have reported that up to 20 % of pneumococcal meningitis isolates with decreased penicillin susceptibility [
22,
23]. Our data indicate that the proportion of PNSSP in meningitis cases has been fairly stable, with an average of 20.3 % of pneumococcal isolates being non-susceptible to penicillin. In contrast, the pneumococcal meningitis epidemiology continuously changed during the past 17 years in Salvador Metropolitan area. One of the most important changes was the sustained decrease in the incidence rate observed from 1996 to 2012.
In Brazilian nationwide surveillance from 1993 to 2004, an increase of penicillin non-susceptibility was observed (10 % to 28 %), with 6 % of the isolates displaying a high level of resistance [
24]. According to Brandileone MCC et al (2006), there are geographic differences between PNSSP isolates in this country. Between 2000 and 2005, in the northeastern region, the proportion of PNSSP isolates was 20 %. The southern and southeastern regions had a higher percentage of PNSSP isolates (28 %) and the lowest rate in the north region was 8 %[
24].
The penicillin resistance rate in Brazil was lower than other Latin America countries, including Colombia, Bolivia, Mexico and Venezuela, which reported rates above 30 % [
25]. In contrast, Japan have reported even higher proportion of PNSSP (76.6 %) [
26].
Additionally, we observed that a high proportion of isolates were non-susceptible to antibiotics commonly used in outpatient settings for acute respiratory infection treatments in Brazil. For example, the proportion of TMP-SXZ non-susceptible isolates reached 72 % in 2006 and keep a rate around 50 % until 2012. In Asian countries invasive pneumococcal isolates remained highly resistant to macrolides, tetracycline, and TMP-SXZ each year [
27]. In this study setting, we found a lower proportion (0.6 %) of isolates resistant to erythromycin in comparison with developed countries [
28,
29] other Latin American countries [
30] and wealthier regions within Brazil [
31]. This may be due to the relatively high cost of macrolides, which limits its use in clinical practice in low income population settings.
Serotype distribution information is essential in evaluating the potential benefits of pneumococcal conjugate vaccines, particularly in developing countries where the cost of newly available polysaccharide capsule-protein conjugate vaccines is high relative to the available healthcare resources. Our findings regarding serotype distributions confirm those from national surveys that indicated that a limited spectrum of serotypes were responsible for the majority of meningitis cases due to PNSSP isolates in Brazil. In general, serotypes 14, 23 F, 6B, 19 F and 19A were the most frequent among the PNSSP isolates observed in our study. These results are similar to those reported in other regions in Brazil [
32,
33] and in other Latin American countries [
6]. Serotype 14 was the most common serotype, which accounted for 44.8 % of the total PNSSP isolates. Additionally, serotypes 23 F, 6B and 19 F are important reservoirs of PNSSP in this setting.
In 2010, PCV10 was introduced country wide for children less than 2 years of age in as part of Brazil’s national immunization program. Recently, the effectiveness of PCV10 in Brazil was evaluating by a case-control study, which demonstrated that PCV10 prevents invasive disease caused by vaccine serotypes, in agreement with our finds in this study [
34]. However, evaluation of the serotype distribution showed that serotypes 14, 6B, 23 F, 18C and 19 F remain among the most frequent serotypes causing invasive disease two years after vaccine introduction. As only two years post-vaccination was evaluated (and considering the lower vaccine uptake observed in some places), there may not have been sufficient time to observe the protection effect in all population.
The largest represented clonal group (PFGE pattern A) comprised 35 % of the penicillin non-susceptible isolates. This group mainly included serotype 14 (ST66), which is a single locus variant of the ST67, Tennessee
14-18clone. ST66 is predominant throughout Brazil and is an important factor for maintaining the penicillin resistance rate [
33]. Another important clonal group of serotype 14 is ST156, which emerged in 2001 and had an elevated MIC to penicillin and cefotaxime, this clonal group is a serotype switch variant of clone Spain
9V - 3. ST156 has been associated with a broad variety of serotypes including 6B, 9A, 11A, 14, 15B/15C, 19A, 19 F, 23 F, and 24 F, suggesting a high propensity for recombination events [
35]. This clonal complex associated with serotype 14 has been encountered in multiple countries including Norway, France, Spain, and the United States [
1,
3,
8]. It is also very important to point out the circulation of Colombia
23F-26 clone, ST338. This clonal group has also been reported in several countries [
30,
36,
37]. Apart from these three clonal groups, the specific clonal structure of the PNSSP isolates was dominated by a few other clones (Fig.
4), highlighting 24 new STs. Such a high genetic diversity seems to be a characteristic of PNSSP clonal complexes in general [
1].
Serotype and genotype prevalence fluctuations can occur naturally in pneumococcal populations in the absence of pressure exerted by conjugate vaccines. In the United States, clonal expansion (the increase in the number of previously rare clones that express non-vaccine serotypes) has been documented since the introduction of the heptavalent conjugate vaccine (PCV-7). Non-vaccine serotypes were increasingly a cause of disease in the United States in the post-PCV7 era, most frequently serotype 19A, which is associated with antimicrobial resistance [
37]. In Salvador, similar to the findings of others, a relatively small number of serotypes accounted for the majority of the PNSSP isolates, which resulted in an estimated PCV10 coverage of 94 % among those infected with PNSSP.
One of the main limitations of this study is the fact that all
S. pneumoniae were isolated from meningitis cases. Information regarding other IPD manifestations in our region is often limited or unavailable. Although all of the pneumococcal isolates included in this study originated from only one hospital, Hospital Couto Maia is the state reference hospital in the city of Salvador, with about 95 % of the meningitis reports from the region originating from that site [
12].
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Competing interests
The authors declare that they have no competing interests.
Authors’ contributions
MSS, JA and JNR conceptualized and designed the study, drafted the initial manuscript and approved the final manuscript as submitted. MSS, JA, APOM, ECE, SMC and JBTLM participated in study design, and acquired and analyzed majority of data. LCC, MGC, MGR, AIK and JNR participated in the design and coordination of the study, and helped draft and revise the manuscript. All authors have read and approved the final manuscript.