Resistance patterns of Streptococcus pneumoniae from children in central Italy

Streptococcus pneumoniae biofilm formation and dispersion during colonization and disease

Streptococcus pneumoniae (the pneumococcus) is a common colonizer of the human nasopharynx. Despite a low rate of invasive disease, the high prevalence of colonization results in millions of infections and over one million deaths per year, mostly in individuals under the age of 5 and the elderly. Colonizing pneumococci form well-organized biofilm communities in the nasopharyngeal environment, but the specific role of biofilms and their interaction with the host during colonization and disease is not yet clear. Pneumococci in biofilms are highly resistant to antimicrobial agents and this phenotype can be recapitulated when pneumococci are grown on respiratory epithelial cells under conditions found in the nasopharyngeal environment. Pneumococcal biofilms display lower levels of virulence in vivo and provide an optimal environment for increased genetic exchange both in vitro and in vivo, with increased natural transformation seen during co-colonization with multiple strains. Biofilms have also been detected on mucosal surfaces during pneumonia and middle ear infection, although the role of these biofilms in the disease process is debated. Recent studies have shown that changes in the nasopharyngeal environment caused by concomitant virus infection, changes in the microflora, inflammation, or other host assaults trigger active release of pneumococci from biofilms. These dispersed bacteria have distinct phenotypic properties and transcriptional profiles different from both biofilm and broth-grown, planktonic bacteria, resulting in a significantly increased virulence in vivo. In this review we discuss the properties of pneumococcal biofilms, the role of biofilm formation during pneumococcal colonization, including their propensity for increased ability to exchange genetic material, as well as mechanisms involved in transition from asymptomatic biofilm colonization to dissemination and disease of otherwise sterile sites. Greater understanding of pneumococcal biofilm formation and dispersion will elucidate novel avenues to interfere with the spread of antibiotic resistance and vaccine escape, as well as novel strategies to target the mechanisms involved in induction of pneumococcal disease.

High levels of genetic recombination during nasopharyngeal carriage and biofilm formation in Streptococcus pneumoniae

Transformation of genetic material between bacteria was first observed in the 1920s using Streptococcus pneumoniae as a model organism. Since then, the mechanism of competence induction and transformation has been well characterized, mainly using planktonic bacteria or septic infection models. However, epidemiological evidence suggests that genetic exchange occurs primarily during pneumococcal nasopharyngeal carriage, which we have recently shown is associated with biofilm growth, and is associated with cocolonization with multiple strains. However, no studies to date have comprehensively investigated genetic exchange during cocolonization in vitro and in vivo or the role of the nasopharyngeal environment in these processes. In this study, we show that genetic exchange during dual-strain carriage in vivo is extremely efficient (10⁻²) and approximately 10,000,000-fold higher than that measured during septic infection (10⁻⁹). This high transformation efficiency was associated with environmental conditions exclusive to the nasopharynx, including the lower temperature of the nasopharynx (32 to 34°C), limited nutrient availability, and interactions with epithelial cells, which were modeled in a novel biofilm model in vitro that showed similarly high transformation efficiencies. The nasopharyngeal environmental factors, combined, were critical for biofilm formation and induced constitutive upregulation of competence genes and downregulation of capsule that promoted transformation. In addition, we show that dual-strain carriage in vivo and biofilms formed in vitro can be transformed during colonization to increase their pneumococcal fitness and also, importantly, that bacteria with lower colonization ability can be protected by strains with higher colonization efficiency, a process unrelated to genetic exchange.

Although genetic exchange between pneumococcal strains is known to occur primarily during colonization of the nasopharynx and colonization is associated with biofilm growth, this is the first study to comprehensively investigate transformation in this environment and to analyze the role of environmental and bacterial factors in this process. We show that transformation efficiency during cocolonization by multiple strains is very high (around 10⁻²). Furthermore, we provide novel evidence that specific aspects of the nasopharyngeal environment, including lower temperature, limited nutrient availability, and epithelial cell interaction, are critical for optimal biofilm formation and transformation efficiency and result in bacterial protein expression changes that promote transformation and fitness of colonization-deficient strains. The results suggest that cocolonization in biofilm communities may have important clinical consequences by facilitating the spread of antibiotic resistance and enabling serotype switching and vaccine escape as well as protecting and retaining poorly colonizing strains in the pneumococcal strain pool.

Characterization of macrolide resistance in Gram-positive cocci from Colombian hospitals: a countrywide surveillance

OBJECTIVE

The characterization of macrolide resistance in Gram-positive cocci recovered from Colombian hospitals.

METHODS

The resistance profiles and mechanism of macrolide resistance were investigated in isolates of Streptococcus pneumoniae (1679), Staphylococcus aureus (348), coagulase-negative staphylococci (CoNS) (175), and Enterococcus spp (123). Minimum inhibitory concentrations (MICs) for erythromycin (ERY) and clindamycin (CLI), detection of macrolide resistance genes, phenotypic characterization, and pulsed field gel electrophoresis (PFGE) of macrolide-resistant pneumococci were performed.

RESULTS

Resistance to ERY and CLI was 3.3% and 2.3% for S. pneumoniae, 58% and 57% for S. aureus (94% for both compounds in methicillin-resistant Staphylococcus aureus (MRSA)), and 78.6% and 60.7% in methicillin-resistant Staphylococcus epidermidis, respectively. ERY resistance was 62% in Enterococcus faecalis and 82% in Enterococcus faecium. The MLS(B)-type accounted for 71% of S. pneumoniae and 100% of MRSA. The erm(A) gene was prevalent in MRSA, erm(B) in S. pneumoniae and enterococci, and erm(C) in CoNS isolates. Efflux pump genes (mef(A) genes) were mostly identified in S. pneumoniae (24%). The most common genotype amongst ERY-resistant pneumococci was the Spain(6B)-2 clone.

CONCLUSIONS

The prevalence of macrolide resistance is low in Colombian pneumococci and high in MRSA (cMLS(B)-type).

Meta-analysis of bacterial resistance to macrolides

OBJECTIVES

Understanding changing resistance patterns is important in determining appropriate antibiotic treatments. This meta-analysis systematically evaluated resistance of Streptococcus pneumoniae and Streptococcus pyogenes to macrolide antibiotics among patients with community-acquired respiratory tract infections.

METHODS

MEDLINE and EMBASE databases were searched and experts were consulted to identify published and unpublished literature reporting macrolide resistance rates. Identified studies were evaluated by two independent reviewers; those meeting a priori specified criteria (resistance by patient condition and strain, resistance thresholds, 1997-2003 isolates) were included. Data from included studies were abstracted by two independent reviewers using a standard review form. Discrepancies in abstracted data were resolved by the study investigator.

RESULTS

Random-effects meta-analysis was performed for outcomes present in at least four studies overall and for specified subgroups. We identified 3849 studies and performed detailed review on 407; of these 29, published between 1998-2003, met the inclusion criteria. Mean resistance of S. pneumoniae isolates to azithromycin was 27.2% [95% confidence interval (CI) 24.6-29.7]; mean resistance to erythromycin was statistically equivalent (30.4%; 95% CI 28.1-32.7). Resistance of S. pyogenes to erythromycin (30.0%; CI 18.6-41.5) was similar to that of S. pneumoniae. Too few studies of clarithromycin were included to allow evaluation of resistance. In subgroup analyses, substantial variation in resistance to erythromycin was seen by geographic area.

CONCLUSIONS

Reported macrolide resistance of S. pneumoniae varies substantially and may be a significant issue in certain regions. Use of meta-analysis to aggregate individual studies enabled determination of robust values for macrolide resistance. This information is useful for clinical and policy decision makers in developing appropriate antibiotic strategies.

A cross-sectional survey of the prevalence of Streptococcus pneumoniae nasopharyngeal carriage in Belgian infants attending day care centres

Nasopharyngeal carriage is a major factor in the transmission of pneumococcal disease. The aim of this study was to determine the prevalence of asymptomatic nasopharyngeal carriage of Streptococcus pneumoniae and the distribution of serogroups and serotypes in children aged 3-36 months attending day care centres in Belgium. A single nasopharyngeal swab was cultured from 467 children attending 30 different day care centres between December 2000 and March 2001. S. pneumoniae isolates were serotyped and their antibiotic susceptibilities assessed by disk diffusion. The overall nasopharyngeal carriage rate for S. pneumoniae was 21% in the 467 children. None of the commonly accepted risk factors studied was associated significantly with carriage. Capsular serotypes isolated were 19F (27.3%), 6B (20.2%), 23F (19.2%), 19A (10.1%), 6A (7.1%), 14 (5.1%) and others (11.0%). Theoretical coverage by the seven-valent (serotypes 4, 6B, 9V, 14, 18C, 19F and 23F) pneumococcal conjugate vaccine was 73.7%. Fourteen (14.1%) of 99 strains were non-susceptible to penicillin, 48 (48.5%) to tetracycline and 61 (61.6%) to erythromycin. Theoretical coverage by the seven-valent pneumococcal conjugate vaccine was 93% for the penicillin-resistant serotypes, 69% for the tetracycline-resistant serotypes and 75% for the erythromycin-resistant serotypes. Use of the seven-valent pneumococcal conjugate vaccine could potentially reduce nasopharyngeal carriage of the antibiotic-resistant strains.

Macrolide resistance: an increasing concern for treatment failure in children

BACKGROUND

Antimicrobial treatment of pediatric respiratory tract infections has evolved during the past 30 years as a result of antimicrobial resistance. The focus of antimicrobial therapy in these conditions has shifted from penicillins to other agents because of the dramatic increase in antimicrobial resistance among common respiratory pathogens, including Streptococcus pneumoniae, Haemophilus influenzae and Moraxella catarrhalis. It is important for clinicians to understand how resistance develops so that they can help prevent this phenomenon from occurring with other antimicrobials.

METHODS

This article reviews the published literature on resistance to macrolide antimicrobials among common pediatric respiratory tract pathogens and clinical and bacteriologic outcomes of infections with these pathogens.

RESULTS

Resistance among common pediatric respiratory tract pathogens to macrolides occurs through two main mechanisms, alteration of the target site and active efflux. Although resistance patterns vary by geographic region, the widespread use of macrolides has contributed to the emergence of both types of macrolide-resistant organisms. Conditions that favor the selection and proliferation of resistant strains include children with repeated, close contact who frequently receive antimicrobial treatment or prophylaxis, such as children who attend day care. Recent US surveillance data show that 20 to 30% of S. pneumoniae are resistant to macrolides, with approximately two-thirds of macrolide-resistant strains associated with an efflux mechanism and the remainder associated with a ribosomal methylase. Additionally, although less well-known, virtually all strains of H. influenzae have an intrinsic macrolide efflux pump. As resistance to macrolides has increased, clinical failures have resulted, and these agents are no longer considered appropriate for empiric first line antimicrobial therapy of acute otitis media and sinusitis unless patients are truly penicillin-allergic. Therefore, other antimicrobials are recommended for the empiric treatment of children with respiratory tract infections, including higher doses of amoxicillin and amoxicillin/clavulanate (90 mg/kg/day amoxicillin), cefuroxime axetil and intramuscular ceftriaxone.

CONCLUSIONS

As resistance to macrolides increases and clinical failures in children become more common with this class of antimicrobials, judicious use of antimicrobials is needed. This includes limiting antimicrobial use for viral infections and using the most effective agents when antimicrobials are clinically indicated, such as higher doses of amoxicillin and amoxicillin/clavulanate. Application of these principles may prevent proliferation and further development of resistance.

Phenotypic and genotypic characterization of two penicillin-susceptible serotype 6B Streptococcus pneumoniae clones circulating in Italy

Twenty-nine penicillin-susceptible serotype 6B strains isolated from patients with invasive diseases and from healthy carriers were examined by different genotyping methods. Ten groups were identified on the basis of the pulsed-field gel electrophoresis (PFGE) profiles, and two of these contained multiple isolates and were analyzed further. PFGE group 1 comprised 12 isolates, the majority of which had a multiresistant phenotype (resistance to erythromycin, clindamycin, tetracycline, chloramphenicol, and trimethoprim-sulfamethoxazole), corresponding to that of a clone previously described in the Mediterranean area and related to penicillin-resistant clone Spain(6B)-2. The pbp2b, pbp2x, dhf, and pspA genes of the isolates had identical restriction profiles; and the partial sequence of pspA was identical to that of clone Spain(6B)-2. In all isolates the resistance determinants erm(B) and tet(M) were inserted in a Tn1545-like element; 11 isolates carried cat as part of the integrated plasmid pC194. Multilocus sequence typing (MLST) performed with two isolates confirmed that their profiles corresponded to that of the Mediterranean clone. PFGE group 2 comprised nine strains, of which the majority showed no antibiotic resistance. Their pspA profiles were different, and the partial sequences obtained for two representative isolates indicated the presence of PspA proteins of different clades. The MLST profile of one strain was identical to that of a serotype 6B strain from the United Kingdom, while two other isolates were novel one-allele variants. This clone appears to be related (five of seven identical alleles) to two other internationally disseminated clones, Hungary(19A)-6 and Poland(23F)-16, both of which are penicillin resistant. The presence of antibiotic-susceptible isolates of this clone suggests that traits other than antibiotic resistance can make a clone successful.

Nasopharyngeal carriage of potential bacterial pathogens related to day care attendance, with special reference to the molecular epidemiology of Haemophilus influenzae

Nasopharyngeal carriage of Haemophilus influenzae, Streptococcus pneumoniae, and Moraxella catarrhalis was studied in 259 children attending day care centers (DCC) in Amsterdam, The Netherlands, and in 276 control children. The DCC children were sampled a second time after 4 weeks. Carriage rates for DCC children and controls were 58 and 37% for S. pneumoniae, 37 and 11% for H. influenzae, and 80 and 48% for M. catarrhalis, respectively. No increased antibiotic resistance rates were found in strains isolated from DCC children. All H. influenzae isolates were typed by random amplified polymorphic DNA (RAPD) analysis. Evidence for frequent transmission of H. influenzae strains within DCC was found. In the control group only two isolates (4%) displayed identical RAPD types versus 38% of strains from DCC children. Colonization with H. influenzae appeared to be short-lived in these children; more than half of the children harboring H. influenzae in the first sample were negative in the second sample, whereas most children still positive in the second sample had a different genotype than in the first sample. Of the newly acquired strains in the second sample, 40% were identical to a strain that had been found in a child in the same DCC in the first sample. DCC are to be considered epidemiological niches with a high potential for the spread of pathogenic microorganisms.

Clinical relevance of macrolide-resistant Streptococcus pneumoniae for community-acquired pneumonia

Macrolides are often the first choice for empirical treatment of community-acquired pneumonia. However, macrolide resistance among Streptococcus pneumoniae has escalated at alarming rates in North America and worldwide. Macrolide resistance among pneumococci is primarily due to genetic mutations affecting the ribosomal target site (ermAM) or active drug efflux (mefE). Prior antibiotic exposure is the major risk factor for amplification and perpetuation of resistance. Clonal spread facilitates dissemination of drug-resistant strains. Data assessing the impact of macrolide resistance on clinical outcomes are spare. Many experts believe that the clinical impact is limited. Ribosomal mutations confer high-grade resistance, whereas efflux mutations can likely be overridden in vivo. Favorable pharmacokinetics and pharmacodynamics, high concentrations at sites of infections, and additional properties of macrolides may enhance their efficacy. In this article, we discuss the prevalence of macrolide resistance among S. pneumoniae, risk factors and mechanisms responsible for resistance, therapeutic strategies, and implications for the future.

Pneumococcal resistance: the treatment challenge

OBJECTIVE

To review in vitro and in vivo information dealing with pneumococcal antibiotic resistance and provide a review of the incidence, mechanisms, and controversies surrounding this growing problem. The review is also intended to provide clinicians with relevant recommendations on treatment and prevention of this organism.

DATA SOURCES AND SELECTION

Primary and review articles were identified by MEDLINE search (1966-August 2000) and through secondary resources such as conference proceedings. All of the articles identified from the data sources were evaluated, and all information deemed relevant was included in this review.

DATA SYNTHESIS

The growing incidence and reporting of pneumococcal isolates that are resistant to one or more classes of antibiotics have become a troubling trend that has resulted in significant shifts in treatment. Although clinicians have shifted to a new generation or class of antibiotics when faced with a resistance trend, data with resistant pneumococci show that this may not be necessary. By incorporating the pharmacokinetic and pharmacodynamic data of antimicrobials into the decision-making process, many of the drugs that we have become hesitant to use due to this resistance may still be appropriate if used correctly.

CONCLUSIONS

Appropriate dosing of antimicrobials, combined with optimal use of pneumococcal vaccines, will not only prolong the longevity of some agents, but also hopefully slow resistance development.

Antibiotic susceptibility and serotype distribution of Streptococcus pneumoniae causing meningitis in Italy, 1997-1999

Because few data are available in Italy regarding antimicrobial susceptibility and serotype distribution of invasive Streptococcus pneumoniae strains, meningeal isolates collected at Italian hospitals during the years 1997-1999 were studied. The 12 most common serogroups, representing > 85% of the isolates, were 14, 23, 6, 4, 3, 9, 19, 8, 1, 12, 18, and 7 (in order of frequency). The serogroups identified in children < 5 years old were more limited in number: 80% are included in the 7-valent conjugate vaccines. Penicillin resistance was observed in 14 (9.5%) of 148 strains and increased from 5% in the first part of the study to 13% in the last part. Only 2 strains were fully penicillin resistant, and these belonged to serotype 9V. Thirty percent of the strains, mostly belonging to serogroups 14 or 6 and carrying either the ermB or the mef genes, were resistant to erythromycin.

Antimicrobial use and colonization with erythromycin-resistant Streptococcus pneumoniae in Greece during the first 2 years of life

We evaluated nasopharyngeal colonization with erythromycin-resistant Streptococcus pneumoniae during the first 2 years of life in central and southern Greece. Of 2448 children studied from February 1997 to February 1999, 766 (31%) carried 781 pneumococcal isolates. Ninety-five (3.9%) of the children attended day care centers. Eighteen percent of the pneumococci were resistant to erythromycin (minimal inhibitory concentration 1 to >128 microg/mL), with 67.9% of them carrying the erm(B) gene and 29.2% mef(A) gene products. Four strains possessed neither the erm(B) nor the mef(A) gene. Multidrug resistance occurred in 97% and 40% of isolates carrying the erm(B) and mef(A) gene, respectively. An association was found between the erm(B) gene and serotypes 6B and 23F and between the mef(A) gene and serotypes 14 and 19F. A significant relationship existed between carriage of erythromycin-resistant pneumococci and use of macrolides or beta-lactams in the previous 3 months; the association was strongest when macrolide therapy was administered during the last month (odds ratio, 5.92; P=.0001). The findings indicate the necessity of a judicious use of both macrolides and beta-lactams in young children to reduce the colonization with erythromycin-resistant pneumococci and the subsequent spread of such strains to the community.