Molecular epidemiology of erythromycin resistance in Streptococcus pneumoniae isolates from blood and noninvasive sites

Induction of the macrolide-resistance efflux pump Mega inhibits intoxication of Staphylococcus aureus strains by Streptococcus pneumoniae

Streptococcus pneumoniae (Spn) kills Staphylococcus aureus (Sau) through a contact-dependent mechanism that is catalyzed by cations, including iron, to convert hydrogen peroxide (H₂O₂) to highly toxic hydroxyl radicals (^•OH). There are two well-characterized ABC transporters that contribute to the pool of iron in Spn, named Pia and Piu. Some Spn strains have acquired genes mef(E)/mel encoding another ABC trasporter (Mega) that produces an inducible efflux pump for resistance to macrolides. In macrolide-resistant Spn clinical isolates the insertion of Mega class 1. IV and 2. IVc deleted the locus piaABCD and these strains were attenuated for intoxicating Sau. The goal of this study was to investigate if the disruption of iron acquisition, or the antimicrobial-resistance activity of Mega, contributed to inhibiting the killing mechanism. Neither depletion of iron with 2,2'-dipyridyl-d8 (DP) nor incubating with a double knockout mutant SpnΔpiaAΔpiuA, inhibited killing of Sau. Clinical Spn strains carrying Mega1. IV or Mega2. IVc showed a significant delay for killing Sau. An ex vivo recombination system was used to transfer Mega1. IV or Mega2. IVc to reference Spn strains, which was confirmed by whole genome sequencing, and recombinants TIGR4^{Mega2. IVc}, D39^{Mega2. IVc}, and D39^{Mega1. IV} were delayed for killing Sau. We then compared Sau killing of selected Mega-carrying Spn strains when incubated with sub-inhibitory erythromycin (Mega-induced) or sub-inhibitory cefuroxime. Remarkably, killing of Sau was completely inhibited under the Mega-induced condition whereas incubation with cefuroxime did not interfere with killing. Both mef(E) and mel were upregulated > 400-fold, and spxB (encoding an enzyme responsible for production of most H₂O₂) was upregulated 14.2-fold, whereas transcription of the autolysin (lytA) gene was downregulated when incubated with erythromycin. We demonstrated that erythromycin induction of Mega inhibits the ^•OH-mediated intoxication of Sau and that the inhibition occurred at the post-translational level suggesting that an imbalance of ions in the membrane inhibits these reactions.

Characterization of macrolide resistance in bacteria isolated from macrolide-polluted and unpolluted river sediments and clinical sources in Croatia

Environments polluted with excessively high levels of antibiotics released from manufacturing sites can act as a source of transferable antibiotic resistance (AR) genes to human commensal and pathogenic bacteria. The aim of this study was to evaluate AR of bacteria isolated from the Sava river sediments (Croatia) at the discharge site of effluents from azithromycin production compared to those from the upstream site and isolates collected in Croatian hospitals. A total of 228 environmental strains of azithromycin-resistant bacteria were isolated and identified, with 124 from the discharge site and 104 from the upstream site. In addition, a total of 90 clinical, azithromycin-resistant streptococcal and staphylococcal isolates obtained from the Croatian Reference Center for Antibiotic Resistance Surveillance were analyzed. PCR screening of isolates on 11 relevant macrolide-resistance genes (MRGs) showed that discharge isolates had greater detection frequencies for 4 gene targets (ermB, msrE, mphE and ermF) compared to upstream isolates. Among clinical isolates, the most frequently detected gene was ermB, followed by msrD, mefE and mefC. The discharge site demonstrated a greater abundance of isolates with co-occurrence of two different MRGs (predominantly msrE-mphE) than the upstream site, but a lower abundance than the clinical sources (most commonly msrD-mefE). The simultaneous presence of three or even four MRGs was specific for the discharge and clinical isolates, but not for the upstream isolates. When MRG results were sorted by gene mechanism, the ribosomal methylation (erm) and protection genes (msr) were the most frequently detected among both the discharge and the clinical isolates. Following sequencing, high nucleotide sequence similarity was observed between ermB in the discharge isolates and the clinical streptococcal isolates, suggesting a possible transfer of the ermB gene between bacteria of clinical and environmental origin. Our study highlights the importance of environmental bacterial populations as reservoirs for clinically relevant macrolide-resistance genes.

Molecular characterization of Streptococcus pneumoniae isolated from pediatric patients in Shanghai, China

BACKGROUND

Streptococcus pneumoniae is a major cause of bacterial infection among infants and young children with high morbidity and mortality. The serotype distribution of S. pneumoniae varies with geography, time, age, and disease.

AIM

We aimed to investigate the current status of molecular characteristics of S. pneumoniae strains isolated from pediatric patients in Shanghai, China.

METHODS

Between 2016 and 2018, 73 clinical S. pneumoniae isolates were characterized by capsular serotype, multilocus sequence typing, antibiotic susceptibility, and resistant genes.

RESULTS

The most common serotypes were 19F (39.7%), 19A (16.4%), 6A (11.0%), 14 (9.6%), and 6B (8.2%). The coverage rates of the 7-, 10- and 13-valent pneumococcal conjugate vaccines were 64.4%, 64.4%, and 91.8%, respectively. The five predominant sequence types were ST271 (37.0%), ST320 (19.2%), ST3173 (11.0%), ST876 (6.8%), and ST81 (4.1%), which were mainly associated with serotypes 19F, 19A, 6A, 14, and 23F, respectively. The rates of resistance to penicillin and ceftriaxone were 21.9% and 39.7%, respectively. All strains displayed resistance to macrolides, 54.8% of which possessed both erm(B) and mef(A/E) genes, and 41.1% carried the erm(B) gene alone. Tn2010 (41.1%) was the most common transposon.

CONCLUSIONS

Clonal complex 271 (Taiwan19F-14 clone) played a dominant role in the dissemination of pneumococcal isolates. The prevalent serotypes indicated a lack of the 7-valent pneumococcal conjugate vaccine, which has not been included in national immunization programs in mainland China. The high rate of macrolide resistance made the empirical use of macrolides alone not suitable for treating pediatric pneumococcal disease.

Proteomic variation and diversity in clinical Streptococcus pneumoniae isolates from invasive and non-invasive sites

Streptococcus pneumoniae is responsible for a variety of invasive and non-invasive human infections. There are over 90 serotypes of S. pneumoniae differing in their ability to adapt to the different niches within the host. Two-dimensional gel electrophoresis was used to discriminate clinical S. pneumoniae isolates recovered from either blood cultures (invasive site isolates) or other sites, including sputum, tracheal aspirate, ear, eye and skin swabs (non-invasive site isolates). Global protein expression profiles for five invasive site and six non-invasive site isolates representing five different serotypes (serotypes 4, 6, 9, 14 and 23) were obtained for each isolate and combined into a single data set using Progenesis SameSpots^™ software. One-hundred and eighty six protein spots (39% of the protein spots in the dataset) differed significantly (ANOVA, p<0.05) in abundance between the invasive site (101 upregulated protein spots) and non-invasive site (85 upregulated protein spots) isolates. Correlations between the bacterial proteomes and their sites of isolation were determined by Principal Component Analysis (PCA) using the significantly different protein spots. Out of the 186 variable protein spots, 105 exhibited a serotype-associated pattern of variability. The expression of the remaining 81 protein spots was concluded to be uniquely linked to the site of bacterial isolation. Mass spectrometry was used to identify selected protein spots that showed either constant or differential abundance levels. The identified proteins had a diverse range of functions including, capsule biogenesis, DNA repair, protein deglycation, translation, stress response and virulence as well as amino acid, carbohydrate, lipid and nucleotide metabolism. These findings provide insight on the proteins that contribute towards the adaptation of the bacteria to different sites within the host.

Identification of A2059G 23S rRNA and G439A rplC gene mutations in Streptococcus criceti strain OMZ 61, a strain resistant to azithromycin, josamycin and clindamycin

Streptococcus criceti is a cariogenic organism that belongs to the mutans streptococci. Of the four S. criceti strains, strain OMZ 61 has been identified as being resistant to erythromycin. Antimicrobial susceptibility testing showed that strain OMZ 61 is also resistant to azithromycin, josamycin and clindamycin but susceptible to tetracycline and tiamulin. DNA hybridization analysis of the 23S rRNA genes revealed that the hybridization patterns in strain OMZ 61 differed from those in the other three strains. We further analyzed the nucleotide sequences of a ribosomal RNA operon, the rrnD operon, and the rpsJ-rpsQ region including rplC and rplD genes for ribosomal proteins L3 and L4, respectively, in the four strains studied. Nucleotide sequence analysis indicated that strain OMZ 61 contains an A-to-G substitution at nucleotide position 2059, equivalent to Escherichia coli numbering 2058, in a 23S rRNA gene (rrlD) and a G-to-A substitution at nucleotide position 439 in the rplC gene, suggesting an amino acid residue change at position 147 from valine to isoleucine, whereas no mutation in the rplD gene was found. DNA sequencing and polymerase chain reaction-restriction fragment length polymorphism analysis showed that most or all of the 23S rRNA genes in strain OMZ 61 contain the A2059G mutation. These findings suggest that the resistance to erythromycin, azithromycin, josamycin and clindamycin in strain OMZ 61 is conferred by alterations in 23S rRNA and/or ribosomal protein L3. This is the first description of mutations in the 23S rRNA and rplC genes in mutans streptococci.

Streptococcus pneumoniae proteomics: determinants of pathogenesis and vaccine development

Streptococcus pneumoniae is a major pathogen that is responsible for a variety of invasive diseases. The bacteria gain entry initially by establishing a carriage state in the nasopharynx from where they migrate to other sites in the body. The worldwide distribution of the bacteria and the severity of the diseases have led to a significant level of interest in the development of vaccines against the bacteria. Current vaccines, based on the bacterial polysaccharide, have a number of limitations including poor immunogenicity and limited effectiveness against all pneumococcal serotypes. There are many challenges in developing vaccines that will be effective against the diverse range of isolates and serotypes for this highly variable bacterial pathogen. This review considers how proteomic technologies have extended our understanding of the pathogenic mechanisms of nasopharyngeal colonization and disease development as well as the critical areas in developing protein-based vaccines.

Antibiotic susceptibility and molecular mechanisms of macrolide resistance in streptococci isolated from adult cystic fibrosis patients

The cystic fibrosis (CF) airways are colonized by polymicrobial communities with high bacterial load and are influenced by frequent antibiotic exposures. This community includes diverse streptococci, some of which have been directly or indirectly associated with pulmonary exacerbations. As many streptococci are naturally competent, horizontal transfer of antibiotic-resistant determinants coupled with frequent and/or chronic antibiotic exposure may contribute to high resistance rates. In this study, we assessed antibiotic resistance in 413 streptococcal isolates from adult CF patients against nine antibiotics relevant in CF treatment. We observed very low rates of cephalosporin resistance [cefepime and ceftriaxone ( < 2%)], and higher rates of resistance to tetracycline (∼34%) and sulfamethoxazole/trimethoprim (∼45%). The highest rate of antibiotic resistance was to the macrolides [azithromycin (56.4%) and erythromycin (51.6%)]. We also investigated the molecular mechanisms of macrolide resistance and found that only half of our macrolide-resistant streptococci isolates contained the mef (efflux pump) or erm (methylation of 23S ribosomal target site) genes. The majority of isolates were, however, found to have point mutations at position 2058 or 2059 of the 23S ribosomal subunit - a molecular mechanism of resistance not commonly reported in the non-pyogenic and non-pneumococcal streptococci, and unique in comparison with previous studies. The high rates of resistance observed here may result in poor outcomes where specific streptococci are contributing to CF airway disease and serve as a reservoir of resistance genes within the CF airway microbiome.

Future Trends in Antimicrobial Chemotherapy: Expert Opinion on the 43rdICAAC

The current document bestows an expert synopsis of key new information presented at the 43rd Interscience Conference on Antimicrobial Agents and Chemotherapy (ICAAC) meeting in 2003. Data is presented on the socio-political aspects of and policies on antimicrobial prescribing, novel mechanisms of resistance in Streptococcus pneumoniae, and current epidemiological trends in global resistance. Novel information on new (and existing) antimicrobial agents--new penicillins, cephalosporins, monobactams and oxipenem inhibitors, ketolides, glycopeptides, fluoroquinolones (and hybrids), peptides, daptomycin, aminomethylcyclines, glycylcyclines, and newer formulations of agents such as amoxycillin-clavulanate--provides renewed hope that resistant pathogens can be controlled through use of more potent agents. Improved strategies for the use of existing antimicrobial agents, such as the use of high-dose regimens, short-course therapy, also may delay or reduce the development of resistance and preserve the value of our antibiotic armamentarium.

Characterization of Tn5801.Sag, a variant of Staphylococcus aureus Tn916 family transposon Tn5801 that is widespread in clinical isolates of Streptococcus agalactiae

Tn5801, originally detected in Staphylococcus aureus Mu50, is a Tn916 family element in which a unique int gene (int5801) replaces the int and xis genes in Tn916 (int916 and xis916). Among 62 tet(M)-positive tetracycline-resistant Streptococcus agalactiae isolates, 43 harbored Tn916, whereas 19 harbored a Tn5801-like element (Tn5801.Sag, ∼20.6 kb). Tn5801.Sag was characterized (PCR mapping, partial sequencing, and chromosomal integration) and compared to other Tn5801-like elements. Similar to Tn5801 from S. aureus Mu50, tested in parallel, Tn5801.Sag was unable to undergo circularization and conjugal transfer.

Molecular characteristics of erythromycin-resistant Streptococcus pneumoniae from pediatric patients younger than five years in Beijing, 2010

Background

Streptococcus pneumoniae is the main pathogen that causes respiratory infections in children younger than five years. The increasing incidence of macrolide- and tetracycline-resistant pneumococci among children has been a serious problem in China for many years. The molecular characteristics of erythromycin-resistant pneumococcal isolates that were collected from pediatric patients younger than five years in Beijing in 2010 were analyzed in this study.

Results

A total of 140 pneumococcal isolates were collected. The resistance rates of all isolates to erythromycin and tetracycline were 96.4% and 79.3%, respectively. Of the 135 erythromycin-resistant pneumococci, 91.1% were non-susceptible to tetracycline. In addition, 30.4% of the erythromycin-resistant isolates expressed both the ermB and mef genes, whereas 69.6% expressed the ermB gene but not the mef gene. Up to 98.5% of the resistant isolates exhibited the cMLS_B phenotype, and Tn6002 was the most common transposon present in approximately 56.3% of the resistant isolates, followed by Tn2010, with a proportion of 28.9%. The dominant sequence types (STs) in all erythromycin-resistant S. pneumoniae were ST271 (11.9%), ST81 (8.9%), ST876 (8.9%), and ST320 (6.7%), whereas the prevailing serotypes were 19F (19.3%), 23F (9.6%), 14 (9.6%), 15 (8.9%), and 6A (7.4%). The 7-valent pneumococcal conjugate vaccine (PCV7) and 13-valent pneumococcal conjugate vaccine (PCV13) coverage of the erythromycin-resistant pneumococci among the children younger than five years were 45.2% and 62.2%, respectively. ST320 and serotype 19A pneumococci were common in children aged 0 to 2 years. CC271 was the most frequent clonal complex (CC), which accounts for 24.4% of all erythromycin-resistant isolates.

Conclusions

The non-invasive S. pneumoniae in children younger than five years in Beijing presented high and significant resistance rates to erythromycin and tetracycline. The expressions of ermB and tetM genes were the main factors that influence pneumococcal resistance to erythromycin and tetracycline, respectively. Majority of the erythromycin-resistant non-invasive isolates exhibited the cMLS_B phenotype and carried the ermB, tetM, xis, and int genes, suggesting the spread of the transposons of the Tn916 family. PCV13 provided higher serotype coverage in the childhood pneumococcal diseases caused by the erythromycin-resistant isolates better than PCV7. Further long-term surveys are required to monitor the molecular characteristics of the erythromycin-resistant S. pneumoniae in children.

Genetic diversity of Tn916-related transposons among drug-resistant Streptococcus pneumoniae isolates colonizing healthy children in Venezuela

Among a collection of 48 multidrug-resistant pneumococcal strains colonizing healthy children in a small municipality of Mérida, Venezuela, we identified sequence types (STs) related to a variety of internationally spreading drug-resistant clones, as well as ST135, thus far isolated only in Europe. The clones invariably harbored one or more of the Tn916-related transposons Tn3872, Tn5253, Tn6002, Tn2009, and Tn2010. Finally, our data suggest both structural rearrangements in certain transposons and occurrence of novel transposable elements.

Molecular characterization of erm(B)- and mef(E)-mediated erythromycin-resistant Streptococcus pneumoniae in China and complete DNA sequence of Tn2010

AIMS

To characterize the erm(B)- and mef(E)-mediated erythromycin-resistant Streptococcus pneumoniae clinical isolates obtained from ten hospitals located different cities in China.

METHODS AND RESULTS

Totally 83 S. pneumoniae were collected, and eighteen representative strains of 66 strains that exhibited erythromycin resistance were used for further characterization by antibiograms, serotyping, PFGE, MLST, DNA sequencing of the macrolide-resistance elements and mapping of the elements on the chromosome. Twelve isolates showed a high-level resistance to erythromycin, and six other isolates showed a low-level resistance to erythromycin. Thirteen isolates harboured a Tn2010 transposon (26·4 kbp) encoding the erm(B), tet(M) and mef(E) genes and were classified into three types by Tn2010 structures. The remaining five isolates harboured a Tn6002 transposon (20·9 kbp) encoding the erm(B) and tet(M) genes and were classified into three types by Tn6002 locations on the chromosome. Three of the Tn6002 elements were located within the Tn5252-like element, implying that these composed a large mobile element. The MLST analyses showed that several clones had been disseminated and that the CC271 strains carrying the Tn2010 element expressing the high-level resistance to erythromycin were predominant in China. Four new MLST strains, which were designated as ST3262, ST3263, ST3397 and ST3398 were also identified.

CONCLUSIONS

The erythromycin resistance determinant of S.pneumoniae that had been isolated in China was located in Tn2010 or the Tn6002 element and several clones had been disseminated, and the CC271 strains carrying the Tn2010 element expressing the high-level resistance to erythromycin were predominant in China.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first molecular analysis of erythromycin-resistant Streptococcus pneumoniae clinical isolates in China, and the first report of the complete nucleotide sequence of Tn2010 (26,390 bp).

Characterization and transfer studies of macrolide resistance genes in Streptococcus pneumoniae from Denmark

Over the last decade, erythromycin resistance has been increasing in frequency in Streptococcus pneumoniae in Denmark. In the present study, 49 non-related erythromycin-resistant S. pneumoniae isolates from invasive sites and 20 isolates from non-invasive sites were collected; antimicrobial susceptibility was tested, and they were genotyped and serotyped. Gene transfer was studied for selected isolates. The frequency of erm(B) was significantly higher in non-invasive isolates compared to invasive isolates (p = 0.001). For the first time, mef(I) was detected in 1 isolate in Denmark. All tested mef(E) isolates had an identical mef(E) sequence, apart from 1 gene with a point mutation, and mef(E) was correlated to 7 different sero-types. The tested erm(B) sequences were 99.3% similar with 5 point mutations at different positions distributed among different serotypes, which did not cause a detectable influence on the protein. Transformation was detectable in 5 out of 13 isolates and transfer of erm(B), mef(I) and mef(E) was detected. To our knowledge, this is the first time mef(I) has been proved transformable. Gene transfer by conjugation was not detectable. Erythromycin resistance in pneumococcal isolates is likely to be caused primarily by horizontal spread of mef(E) and erm(B), as well as clonal spread of a serotype 14 strain carrying mef(A) primarily detected in invasive isolates.

Population structure, virulence factors and resistance determinants of invasive, non-invasive and colonizing Streptococcus agalactiae in Poland

OBJECTIVES

To analyse Streptococcus agalactiae (group B Streptococcus; GBS) isolates collected in Poland from various human infections and carriage in respect of their clonality, distribution of virulence factors and antimicrobial resistance determinants, including the detection of transposons involved in the dissemination of antimicrobial resistance.

METHODS

One hundred and fourteen GBS isolates were analysed by multilocus sequence typing (MLST), serotyping and detection of alp genes of the alpha-like-protein (Alp) family. Determinants of resistance to macrolides and tetracycline, and associated transposons, were detected by PCR and analysed by sequencing.

RESULTS

GBS isolates represented 30 different sequence types (STs), grouped in four clonal complexes (CCs), and belonged to seven serotypes. Serotype III was predominant (36.0%), followed by Ia, V, Ib, II, IV and VI. The most common alp genes were rib (26.3%) and alp1/alp5 (23.7%). The bac gene encoding the beta-compound of the surface C-protein was present in 17.5% of isolates. Erythromycin resistance (18.4% of isolates) was found in all CCs, but was associated with serotype V and ST1. The most prevalent determinant of resistance was erm(B), usually located on the Tn3872-like transposon. Several changes were observed in the regulatory region of erm(B), some of them resulting in elevated ketolide MICs. Resistance to tetracycline was ubiquitous (91.2%) and its most common determinant was tet(M), occurring in several variants that were typically carried on Tn916-family transposons.

CONCLUSIONS

Analysis of bacterial serotypes, alp genes and antimicrobial resistance determinants in the background of MLST-based population structure strengthened evidence of the importance of horizontal gene transfer in GBS evolution.

Molecular characterization of macrolide resistance determinants [erm(B) and mef(A)] in Streptococcus pneumoniae and viridans group streptococci (VGS) isolated from adult patients with cystic fibrosis (CF)

OBJECTIVES

Although long-term use of azithromycin has shown a significant clinical improvement for patients with cystic fibrosis (CF), its long-term effect on the susceptibility of commensal flora within CF airways has not yet been examined. We therefore suggest that long-term use of azithromycin increases macrolide resistance in commensal streptococci.

METHODS

Erythromycin susceptibility in naturally colonizing viridans group streptococci (VGS) was characterized, as well as macrolide resistance gene determinants through sequence analysis, in pneumococci (n = 15) and VGS [n = 84; i.e. Streptococcus salivarius (n = 30), Streptococcus mitis (n = 17), Streptococcus sanguinis (n = 11), Streptococcus oralis (n = 10), Streptococcus parasanguinis (n = 6), Streptococcus gordonii (n = 3), Streptococcus infantis (n = 3), Streptococcus cristatus (n = 2), Streptococcus anginosus (n = 1) and Streptococcus australis (n = 1)] isolated from sputum from 24 adult CF patients, who were on oral azithromycin therapy for at least the previous 7 months.

RESULTS

Almost three-quarters of isolates (74; 74.7%) were resistant to erythromycin, whilst a further 15 (15.2%) had reduced susceptibility, leaving only 10 (10.1%) isolates susceptible to erythromycin. The majority (89.8%) were not susceptible to erythromycin, as demonstrated by possession of the erm(B) gene in 25/99 (25.3%), the mef(A) gene in 1/99 (1.0%), the mef(E) gene in 75/99 (75.8%) and both erm(B) and mef(E) genes simultaneously in 11/99 (11.1%). These results indicate that genotypic resistance for macrolides is common in VGS in adult CF patients, with efflux being over three times more frequent.

CONCLUSIONS

Long-term treatment with azithromycin in CF patients may reduce antibiotic susceptibility in commensal VGS, where these organisms may potentially act as a reservoir of macrolide resistance determinants for newly acquired and antibiotic-susceptible pathogens.

Temporal trends of antimicrobial resistance and clonality of invasive Streptococcus pneumoniae isolates in Finland, 2002 to 2006

The antimicrobial resistance of Streptococcus pneumoniae, or pneumococcus, is a growing global problem. In our study, 3,571 invasive pneumococcal isolates, recovered from blood and cerebrospinal fluid samples from patients in Finland between the years 2002 and 2006, showed an increase in erythromycin nonsusceptibility from 16% to 28% (P < 0.0001) over the 5-year study period, as well as a doubling of penicillin nonsusceptibility from 8% to 16% (P < 0.0001). Erythromycin nonsusceptibility increased especially in isolates derived from 0- to 2-year-old children and was 46% for this age group in 2006. Although multiresistance, defined as nonsusceptibility to penicillin, erythromycin, and tetracycline, was fairly rare (5.1% in 2006), 38% of the erythromycin-nonsusceptible isolates were also penicillin nonsusceptible, while 74% of the penicillin-nonsusceptible isolates were nonsusceptible to erythromycin. In contrast to the situation in continental Europe, but mirroring that in North America, the most frequent macrolide resistance determinant carried by 56% of the tested macrolide-resistant pneumococci was the mef gene. Serotypes 14, 9V, 19A, 6B, and 19F were most frequently nonsusceptible to erythromycin or penicillin. The penicillin-resistant invasive isolates (n = 88) were genotyped by multilocus sequence typing, which revealed the presence of 25 sequence types, 9 of which were novel. The majority of the isolates were related to one of several globally disseminated penicillin- or multiresistant clones, most importantly the rlrA adhesion pilus carrying clones Spain(9V) ST156 and Taiwan(19F) ST236. The penicillin-resistant pneumococcal population in Finland is therefore a combination of internationally recognized genotypes as well as novel ones.

Characterization of macrolide efflux pump mef subclasses detected in clinical isolates of Streptococcus pyogenes isolated between 1999 and 2005

The macrolide efflux mechanism of resistance, mef, was characterized in community-acquired respiratory tract infections with Streptococcus pyogenes. Fifty-four (4.6%) M phenotype isolates were screen tested as negative for mef(A). Of these 54 isolates, 5 (0.4%), 27 (2.3%), and 1 (0.1%) were considered to be mef(I) positive, a novel mosaic variant of mef, or a novel subclass of mef, respectively. This study shows (i) the definitive presence of mef(E) in S. pyogenes and its global distribution, (ii) the presence of a mosaic variant of mef composed of mef(A) and mef(E), (iii) the previously undescribed presence of mef(I) in S. pyogenes, and (iv) the presence of a novel subclass of mef in S. pyogenes.

The prevalence of erythromycin resistance in group B streptococcal isolates at a University Hospital in Taiwan

Due to reduced antibiotic consumption in Taiwan, erythromycin resistance rate had decreased in Streptococcus pyogenes, but it increased in Streptococcus pneumoniae. The objectives of the present study were (1) to determine the erythromycin and clindamycin resistance rate and minimum inhibitory concentration (MIC) of the group B streptococcus (GBS) clinical isolates, and (2) to investigate the mechanism responsible for the macrolide, lincosamide, and group B streptogramin (MLS(B)) resistance. A total of 1,395 GBS isolates were collected from June 2001 to April 2007. Forty-four percent of the GBS isolates were resistant to erythromycin, and 39% were resistant to clindamycin. The annual erythromycin resistance rate increased from 32% in 2001 to 51% in 2004; a significant decrease was observed in 2005 (47%), 2006 (42%), and 2007 (38%). Percentage of erythromycin-resistant isolates with erm(B) gene significantly increased from 72% in 2001 to 90% in 2007. We found that the plasmid encoded zeta gene was present in 13% of the resistant isolates, along with erm(B). When compared to our previous study (1991 to May 2001), the overall erythromycin resistance rate increased from 30% to 44%. erm(B) was the major resistant determinant, and zeta toxin encoding plasmid has a limited role in mediating erythromycin resistance unlike in GAS isolates as reported earlier.

Decrease in bacterial load versus resistance selection of pneumococcal subpopulations by beta-lactam physiological concentrations over time: an in vitro pharmacodynamic simulation

To investigate beta-lactam effects on Streptococcus pneumoniae-mixed cultures, a computerized pharmacodynamic model simulating over 24-hr concentrations obtained after several beta-lactam regimens was used. Strain 1 (no penicillin binding protein [PBP] mutations) and strain 2 (mutation in pbp1a) were penicillin/amoxicillin susceptible. Strain 3 (mutations in pbp1a, pbp2x, and pbp2b) and strain 4 (mutations in pbp1a, pbp2x, and pbp2b [10 changes]) were penicillin/amoxicillin resistant. Initial inoculum was approximately 6 x 10(6) CFU (colony forming units)/ml (with a 1:1:1:1 proportion of each strain). Population analysis profile was performed pre- and post-simulations. Strain 1 exhibited the best fitness (growth over 24 hr) in individual cultures, and strain 2 did so in mixed cultures in antibiotic-free simulations. In antibiotic simulations with the mixed inocula, penicillin/amoxicillin-susceptible strains were eradicated with all study drugs (time that concentrations exceed the minimal inhibitory concentration [T>MIC >or= 43%]). Penicillin-resistant strains showed different evolution depending on the antibiotic: (a) cefditoren produced >2 log(10) reduction of initial inocula at 12-24 hr (T>MIC >or=45%), with a remaining population growing in plates with >or=4 mg/L amoxicillin; (b) cefuroxime, cefixime, and cefaclor did not decrease initial inocula at 12-24 hr (T>MIC=0%), with minor subpopulations growing in plates with 4 mg/L amoxicillin; (c) amoxicillin produced 2.6 log(10) decrease of initial inocula at 12 hr (T>MIC=47.5%), but 1.1 log(10) increase of initial inocula at 24 hr, with a significant population growing in plates with 4 mg/L amoxicillin. Antibiotic activity against mixed inocula (susceptible and resistant strains) depends on intrinsic activity (as well as its subsequent pharmacodynamic activity: T>MIC against resistant strains), and on possible selection of intra-strain-resistant subpopulations.

Phenotypic and genotypic characterization of macrolide resistant Streptococcus pneumoniae in Tunisia

One hundred of non duplicate Streptococcus pneumoniae resistant to erythromycin collected from three teaching hospitals in Tunisia from January 1998 to December 2004 were investigated to evaluate determine their resistance level to different macrolides and the mechanisms involved. Most erythromycin resistant S. pneumoniae were isolated from respiratory tract (34%). Eighty-three percent showed constitutive MLS(B) phenotype with high MICs of macrolides and lincosamides (MIC90 >256 microg/ml), 12% M phenotype with moderately increased MICs of macrolides (MIC90: 12 microg/ml) and low MICs of lincosamides (MIC90=0.75 microg/ml) and 5% inducible MLS(B) with high MICs of macrolides (MIC90 >256 microg/ml) and moderately increased MICs of lincosamides (MIC90=8 microg/ml). All strains were susceptible to quinupristun-dafopristin association and linezolid (MIC90=1 microg/ml). Strains belonging to MLS(B) phenotype were PCR positive for the erm B gene (88%). Twelve percent categorized as M phenotype carried the mef A gene. The rates of associated resistance were 68% to penicillin G, 53% to tetracyclines, 61% to cotrimoxazole, 21% to chloramphenicol and 13% to ciprofloxacin. MLS(B) constitutive phenotype conferring cross resistance to macrolides, lincosamides and streptogramins B with high level of resistance was the most prevalent. Thus, quinupristin-dalfopristin association and linezolid remain the most active molecules.

erm(B)-carrying elements in tetracycline-resistant pneumococci and correspondence between Tn1545 and Tn6003

This study investigated the genetic organization of erm(B)-carrying transposons of Streptococcus pneumoniae and their distribution in tetracycline-resistant clinical isolates. By comparatively analyzing reference pneumococci carrying erm(B)/tet(M) transposon Tn1545, Tn6003, Tn6002, or Tn3872, we demonstrated a substantial correspondence between Tn1545 and Tn6003, which have the same resistance gene combination [tet(M) (tetracycline), erm(B) (erythromycin), and aphA-3 (kanamycin)]; share the macrolide-aminoglycoside-streptothricin element, containing a second erm(B); and only differ by a ca. 1.2-kb insertion (containing a putative IS1239 insertion sequence) detected in Tn1545 from S. pneumoniae reference strain BM4200. These results enabled elucidation of the structure of Tn1545, the first erm(B)-carrying transposon described in S. pneumoniae. A collection of 83 erythromycin- and tetracycline-resistant clinical pneumococci, representative of recent Italian isolates carrying erm(B) as the sole erythromycin resistance gene, was used to investigate the distribution of the different transposons. All 83 organisms were positive for tet(M) and bore an erm(B)/tet(M) transposon that could be characterized by using a specific set of primer pairs; Tn3872 was detected in 18 isolates, Tn6002 in 59 isolates, and Tn6003 in 6 (the sole kanamycin-resistant) isolates. The genetic organization of transposon Tn1545, with its specific insertion, was not detected in any of the isolates tested. The erm(B)-carrying elements of tetracycline-resistant pneumococci substantially corresponded to those [bearing a silent tet(M) gene] recently detected in tetracycline-susceptible pneumococci. Overall, in erm(B)-positive pneumococci, Tn6003 was the least common erm(B)-carrying Tn916-related element and Tn6002 the most common.

The macrolide resistance genes erm(B) and mef(E) are carried by Tn2010 in dual-gene Streptococcus pneumoniae isolates belonging to clonal complex CC271

The genetic elements carrying macrolide resistance genes in Streptococcus pneumoniae isolates belonging to CC271 were investigated. The international clone Taiwan(19F)-14 was found to carry Tn2009, a Tn916-like transposon containing tet(M) and mef(E). The dual erm(B) mef(E) isolates carried Tn2010, which is similar to Tn2009 with the addition of a putative new transposon, the erm(B) genetic element.

Composite structure of Streptococcus pneumoniae containing the erythromycin efflux resistance gene mefI and the chloramphenicol resistance gene catQ

In recent years mef genes, encoding efflux pumps responsible for M-type macrolide resistance, have been investigated extensively for streptococci. mef(I) is a recently described mef variant detected in particular isolates of Streptococcus pneumoniae instead of the more common mef(E) and mef(A). This study shows that mef(I) is located in a new composite genetic element, whose sequence was completely analyzed and the left and right junctions determined, demonstrating a unique genetic organization. The new composite structure (30,505 bp), designated the 5216IQ complex, consists of two halves: a left one (15,316 bp) formed by parts of the known transposons Tn5252 and Tn916, and a right one (15,115 bp) formed by a new fragment, designated the IQ element. While the defective Tn916 contained a silent tet(M) gene, the IQ element, ending with identical transposase genes on both sides and containing the mef(I) gene with an adjacent new msr(D) gene variant and a catQ chloramphenicol acetyltransferase gene, was completely different from the genetic elements carrying other mef genes in pneumococci. This is the first report demonstrating catQ in S. pneumoniae and showing its linkage with a mef gene. Analysis of the chromosomal region beyond the left junction revealed an organization more similar to that of S. pneumoniae strain TIGR4 than to that of strain R6. The 5216IQ complex was apparently nonmobile, with no detectable transfer of erythromycin resistance being obtained in repeated transformation and conjugation assays.

Serotypes, Clones, and Mechanisms of Resistance of Erythromycin-Resistant Streptococcus pneumoniae Isolates Collected in Spain

The aim of this study was to analyze the distributions of antibiotic susceptibility patterns, serotypes, phenotypes, genotypes, and macrolide resistance genes among 125 nonduplicated erythromycin-resistant Streptococcus pneumoniae clinical isolates collected in a Spanish point prevalence study. The prevalence of resistance to macrolides in this study was 34.7%. Multiresistance (to three or more antimicrobials) was observed in 81.6% of these strains. Among 15 antimicrobials studied, cefotaxime, moxifloxacin, telithromycin, and quinupristin-dalfopristin were the most active drugs. The most frequent serotypes of erythromycin-resistant isolates were 19F (25%), 19A (17%), 6B (12%), 14 (10%), and 23F (10%). Of the 125 strains, 109 (87.2%) showed the MLS(B) phenotype [103 had the erm(B) gene and 6 had both erm(B) and mef(E) genes]. Sixteen (12.8%) strains showed the M phenotype [14 with mef(E) and 2 with mef(A)]. All isolates were tested by PCR for the presence of the int, xis, tnpR, and tnpA genes associated with conjugative transposons (Tn916 family and Tn917). Positive detection of erm(B), tet(M), int, and xis genes related to the Tn916 family was found in 77.1% of MLS(B) phenotype strains. In 16 strains, only the tndX, erm(B), and tet(M) genes were detected, suggesting the presence of Tn1116, a transposon recently described for Streptococcus pyogenes. Five clones, namely, Sweden(15A)-25, clone(19F) ST87, Spain(23F)-1, Spain(6B)-2, and clone(19A) ST276, accounted for half of the MLS(B) strains. In conclusion, the majority of erythromycin-resistant pneumococci isolated in Spain had the MLS(B) phenotype, belonged to multiresistant international clones, and carried the erm(B), tet(M), xis, and int genes, suggesting the spread of transposons of the Tn916 family.

Presence of plasmid pA15 correlates with prevalence of constitutive MLS(B) resistance in group A streptococcal isolates at a university hospital in southern Taiwan

OBJECTIVES

To investigate the role of a plasmid bearing the erm(B) gene on the prevalence of the macrolide, lincosamide and group B streptogramin (MLS(B)) phenotype of group A streptococci (GAS) and to characterize the plasmid and determine the clonal relation between the erythromycin-resistant isolates.

METHODS

Two hundred and five erythromycin-resistant GAS isolates were collected from 1990 to 2006. Colony hybridization, PCR, plasmid curing and PFGE techniques were used to analyse the mechanisms behind the phenotypes.

RESULTS

Among the 56 isolates with constitutive MLS(B) (cMLS(B)) resistance, 53 isolates harboured a plasmid, pA15, of 19 kb. erm(B) was on pA15 and it confered a cMLS(B) resistance phenotype. The prevalence rate of the pA15-containing isolates was 36.3% from 1993 to 1995, but the plasmid could not be detected from 2004 to 2006. To link the high-level resistance to pA15, clinical isolate A15 was selected and pA15 was cured by novobiocin. In the plasmid-cured strain SW503, the erythromycin MIC decreased from 256 to 0.032 mg/L. By electroporation, pA15 was re-introduced into the plasmid-cured erythromycin-susceptible strain, and the high-level erythromycin resistance was restored. Plasmid pA15 was also transferred to group B streptococci and group C streptococci by electroporation. In all the pA15-containing isolates, emm1 type was present and pulse type J was predominant (48 of 54 isolates).

CONCLUSIONS

The plasmid pA15 mediated cMLS(B) resistance in the mid-1990s, but pA15 was not detected in the clinical isolates from 2004 onwards, which correlates with the absence of cMLS(B) resistance in this region.

Rapid Spread in Norway of an Erythromycin-Resistant Pneumococcal Clone, Despite Low Usage of Macrolides

During the last 4 years, Norway has experienced an increase in macrolide resistance among systemic isolates of Streptococcus pneumoniae. The Norwegian reference laboratory for pneumococci received the isolates from over 85% of the Norwegian cases of systemic pneumococcal disease in the period studied. To study the details of the increased macrolide resistance, all macrolide-resistant systemic pneumococcal isolates (410 isolates) collected in the period from 1995 to 2005 were characterized phenotypically, and a representative selection of 68 strains was also studied genotypically. The serogroups most frequently associated with macrolide resistance in the studied period were 14, 6, 23, 19, and 9. The resistance M-type was expressed in 85% of the resistant isolates. Of the 68 isolates analyzed by multilocus sequence typing, 19 different sequence types (STs) were represented, including several of the international resistant clones. All but one of the clones appeared at a low frequency; mainly as isolated cases. The increase in macrolide resistance seen from 2001 to 2005 proved to be caused by ST-9, defined as the England(14)-9 clone by the Pneumococcal Molecular Epidemiology Network. All ST-9 isolates tested, carried the mef(A) gene and expressed the resistance M-type. This clone first appeared in the Oslo region in 1993, but was by 2005 isolated from all over the country. Children were overrepresented among the cases caused by this clone; however, people aged 20-29, possibly involving the parent generation, were also represented at an increased frequency. The England(14)-9 clone has been able to spread successfully in the Norwegian population despite a relatively low consumption of macrolides.

Clonal spread of mef-positive macrolide-resistant Streptococcus pneumoniae isolates causing invasive disease in adults in Germany

Isolates (3,845) obtained from German adults with invasive pneumococcal disease between 1992 and 2004 were investigated. Of these, 430 isolates (11.2%) were erythromycin A nonsusceptible. Macrolide resistance genotypes and multilocus sequence types were determined. Among the isolates, 35.6% were erm(B) positive and 63.5% were mef positive. Over the study period, the frequency of resistance rose significantly from 2.2 to 17.0% (P < 0.001). A serotype 14, sequence type 9 clone was the most widespread.

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).

Molecular epidemiology of macrolide and tetracycline resistances in commensal Gemella sp. isolates

The epidemiologic relatedness of 29 erythromycin-resistant Gemella sp. strains from normal flora, characterized previously, were evaluated by pulsed-field gel electrophoresis (PFGE). Three isolates carried the tet(O) gene and the tet(M) gene. The msr(A) gene was found in two Gemella morbillorum strains in combination with the erm(B) or mef(E) gene. The sequences of the mef(A/E), erm(B), and msr(A) genes showed a high similarity to the corresponding sequences of other gram-positive cocci. All the strains harboring the mef(A/E) gene and the msr(D) gene possessed open reading frame 3 (ORF3)/ORF6. The 16 G. morbillorum isolates represented 15 distinct DNA profiles. Four clusters were identified (>or=80% genetic relatedness). The 12 Gemella haemolysans strains belonged to different PFGE types. The clonal diversity found suggests that horizontal transfer may be the main route through which erythromycin resistance is acquired.

Genetic elements carrying erm(B) in Streptococcus pyogenes and association with tet(M) tetracycline resistance gene

This study was directed at characterizing the genetic elements carrying the methylase gene erm(B), encoding ribosome modification-mediated resistance to macrolide, lincosamide, and streptogramin B (MLS) antibiotics, in Streptococcus pyogenes. In this species, erm(B) is responsible for MLS resistance in constitutively resistant isolates (cMLS phenotype) and in a subset (iMLS-A) of inducibly resistant isolates. A total of 125 erm(B)-positive strains were investigated, 81 iMLS-A (uniformly tetracycline susceptible) and 44 cMLS (29 tetracycline resistant and 15 tetracycline susceptible). Whereas all tetracycline-resistant isolates carried the tet(M) gene, tet(M) sequences were also detected in most tetracycline-susceptible isolates (81/81 iMLS-A and 7/15 cMLS). In 2 of the 8 tet(M)-negative cMLS isolates, erm(B) was carried by a plasmid-located Tn917-like transposon. erm(B)- and tet(M)-positive isolates were tested by PCR for the presence of genes int (integrase), xis (excisase), and tndX (resolvase), associated with conjugative transposons of the Tn916 family. In mating experiments using representatives of different combinations of phenotypic and genotypic characteristics as donors, erm(B) and tet(M) were consistently cotransferred, suggesting their linkage in individual genetic elements. The linkage was confirmed by pulsed-field gel electrophoresis and hybridization studies, and different elements, variably associated with the different phenotypes/genotypes, were detected and characterized by amplification and sequencing experiments. A previously unreported genetic organization, observed in all iMLS-A and some cMLS isolates, featured an erm(B)-containing DNA insertion into the tet(M) gene of a defective Tn5397, a Tn916-related transposon. This new element was designated Tn1116. Genetic elements not previously described in S. pyogenes also included Tn6002, an unpublished transposon whose complete sequence is available in GenBank, and Tn3872, a composite element resulting from the insertion of the Tn917 transposon into Tn916 [associated with a tet(M) gene expressed in some cMLS isolates and silent in others]. The high frequency of association between a tetracycline-susceptible phenotype and tet(M) genes suggests that transposons of the Tn916 family, so far typically associated solely with a tetracycline-resistant phenotype, may be more widespread in S. pyogenes than currently believed.

The mef(E)-carrying genetic element (mega) of Streptococcus pneumoniae: insertion sites and association with other genetic elements

The structure of the macrolide efflux genetic assembly (mega) element, its genomic locations, and its association with other resistance determinants and genetic elements were investigated in 16 Streptococcus pneumoniae isolates carrying mef(E), of which 1 isolate also carried tet(M) and 4 isolates also carried tet(M) and erm(B). All isolates carried a mega element of similar size and structure that included the operon mef(E)-msr(D) encoding the efflux transport system. Among tetracycline-susceptible isolates, six different integration sites were identified, five of which were recognized inside open reading frames present in the R6 genome. In the five isolates also carrying tet(M), mega was inserted in different genetic contexts. In one isolate, it was part of previously described Tn916-like element Tn2009. In another isolate, mega was inserted in a transposon similar to Tn2009 that also included an erm(B) element. This new composite transposon was designated Tn2010. Neither Tn2009 nor Tn2010 could be transferred by conjugation to pneumococcal or enterococcal recipients. In the three isolates in which mega was not physically linked with tet(M), this gene was associated with erm(B) in transposon Tn3872, a Tn916-like element. Homologies between the chromosomal insertions of these composite transposons and sequences of multidrug-resistant pneumococcal genomes in the databases indicate the presence of preferential sites for the integration of composite Tn916-like elements carrying multiple resistance determinants in S. pneumoniae.

Increase of the M phenotype among erythromycin-resistant Streptococcus pneumoniae isolates from Spain related to the serotype 14 variant of the Spain9V-3 clone

Between 1998 and 2003 the rate of erythromycin resistance among pneumococci in Spain was 34.4%. Although the MLS(B) phenotype was prevalent (94.7%), the rate of the M phenotype increased from 3.3% to 8.9% (P < 0.01). Clonal dissemination of mef(E)-carrying strains of serotype 14 variant of the Spain(9V)-3 clone was the major contributor to this increase.

The use of macrolides in treatment of upper respiratory tract infections

Antimicrobial resistance is a growing problem among upper respiratory tract pathogens. Resistance to beta-lactam drugs among Streptococcus pneumoniae, Haemophilus influenzae, and Streptococcus pyogenes is increasing. As safe and well-tolerated antibiotics, macrolides play a key role in the treatment of community-acquired upper respiratory tract infections (RTIs). Their broad spectrum of activity against gram-positive cocci, such as S. pneumoniae and S. pyogenes, atypical pathogens, H. influenzae (azithromycin and clarithromycin), and Moraxella catarrhalis, has led to the widespread use of macrolides for empiric treatment of upper RTIs and as alternatives for patients allergic to beta-lactams. Macrolide resistance is increasing among pneumococci and recently among S. pyogenes, and is associated with increasing use of the newer macrolides, such as azithromycin. Ribosomal target modification mediated by erm(A) and erm(B) genes and active efflux due to mef(A) and mef(E) are the principal mechanisms of resistance in both S. pneumoniae and S. pyogenes. Recently, ribosomal protein and RNA mutations have been found to be responsible for acquired resistance to macrolides in S. pneumoniae, S. pyogenes, and H. influenzae. Although macrolides are only weakly active against macrolide-resistant streptococci species, producing an efflux pump (mef), and are inactive against pathogens with ribosomal target modification (erm), treatment failures are uncommon. Therefore, macrolide therapy, for now, remains a good alternative for treatment of upper RTIs; however, continuous monitoring of the local resistance patterns is essential.

Macrolide resistance can be transferred by conjugation from viridans streptococci to Streptococcus pyogenes

Efflux pumps encoded by mef genes are among the most common mechanisms of resistance to macrolides. These genes are often located on horizontally transferable elements such as transposons. We present data indicating conjugative transfer of the mef(E) gene from viridans streptococci to the pathogen Streptococcus pyogenes. The mef(E) gene is located on the previously described MEGA (macrolide efflux genetic assembly) element. Of 110 isolates tested, 85% of those that carried the mef(A/E) gene carried it on MEGA, and in all cases of conjugal transfer of the mef(E) gene it was carried on MEGA. It therefore appears reasonable to draw the conclusion that this element is important in the lateral transfer of macrolide resistance between streptococci.

Serotypes and antimicrobial susceptibilities of 1033 pneumococci isolated from children in Greece during 2001–2004

Pneumococci (n = 1033) isolated in the major paediatric hospitals of Athens during 2001-2004 from children with invasive infections (n = 186), non-invasive infections (n = 641) and healthy carriers (n = 206) were studied. The most prevalent serotypes were serotypes 14 (44.6%), 19F (43.5%) and 6B (22.8%) in invasive, non-invasive and carriage isolates, respectively. Among invasive isolates, the potential coverage by the seven-valent conjugate vaccine was 75.3%. Resistance rates to penicillin, amoxycillin, cefotaxime, erythromycin, co-trimoxazole, clindamycin, tetracycline and chloramphenicol were 44.6%, 2.7%, 1.2%, 43.6%, 43.5%, 12.4%, 34.7% and 5.9%, respectively. The M-phenotype accounted for 68.0% of the erythromycin-resistant isolates. All isolates were susceptible to ofloxacin.

Molecular characterization of pneumococci with efflux-mediated erythromycin resistance and identification of a novel mef gene subclass, mef(I)

The molecular genetics of macrolide resistance were analyzed in 49 clinical pneumococci (including an "atypical" bile-insoluble strain currently assigned to the new species Streptococcus pseudopneumoniae) with efflux-mediated erythromycin resistance (M phenotype). All test strains had the mef gene, identified as mef(A) in 30 isolates and mef(E) in 19 isolates (including the S. pseudopneumoniae strain) on the basis of PCR-restriction fragment length polymorphism analysis. Twenty-eight of the 30 mef(A) isolates shared a pulsed-field gel electrophoresis (PFGE) type corresponding to the England14-9 clone. Of those isolates, 27 (20 belonging to serotype 14) yielded multilocus sequence type ST9, and one isolate yielded a new sequence type. The remaining two mef(A) isolates had different PFGE types and yielded an ST9 type and a new sequence type. Far greater heterogeneity was displayed by the 19 mef(E) isolates, which fell into 11 PFGE types, 12 serotypes (though not serotype 14), and 12 sequence types (including two new ones and an undetermined type for the S. pseudopneumoniae strain). In all mef(A) pneumococci, the mef element was a regular Tn1207.1 transposon, whereas of the mef(E) isolates, 17 carried the mega element and 2 exhibited a previously unreported organization, with no PCR evidence of the other open reading frames of mega. The mef gene of these two isolates, which did not match with the mef(E) gene of the mega element (93.6% homology) and which exhibited comparable homology (91.4%) to the mef(A) gene of the Tn1207.1 transposon, was identified as a novel mef gene variant and was designated mef(I). While penicillin-nonsusceptible isolates (three resistant isolates and one intermediate isolate) were all mef(E) strains, tetracycline resistance was also detected in three mef(A) isolates, due to the tet(M) gene carried by a Tn916-like transposon. A similar mechanism accounted for resistance in four of the five tetracycline-resistant isolates carrying mef(E), in three of which mega was inserted in the Tn916-like transposon, giving rise to the composite element Tn2009. In the fifth mef(E)-positive tetracycline-resistant isolate (the S. pseudopneumoniae strain), tetracycline resistance was due to the presence of the tet(O) gene, apparently unlinked to mef(E).

Erythromycin resistance and genetic elements carrying macrolide efflux genes in Streptococcus agalactiae

The macrolide resistance determinants and genetic elements carrying the mef(A) and mef(E) subclasses of the mef gene were studied with Streptococcus agalactiae isolated in 2003 and 2004 from 7,084 vaginorectal cultures performed to detect carrier pregnant women. The prevalence of carriage was 18% (1,276 isolates), and that of erythromycin resistance 11.0% (129 of the 1,171 isolates studied). erm(B), erm(A) subclass erm(TR), and the mef gene, either subclass mef(A) or mef(E), were found in 72 (55.8%), 41 (31.8%), and 12 (9.3%) erythromycin-resistant isolates, while 4 isolates had more than 1 erythromycin resistance gene. Of the 13 M-phenotype mef-containing erythromycin-resistant S. agalactiae isolates, 11 had the mef(E) subclass gene alone, one had both the mef(E) and the erm(TR) subclass genes, and one had the mef(A) subclass gene. mef(E) subclass genes were associated with the carrying element mega in 10 of the 12 mef(E)-containing strains, while the single mef(A) subclass gene found was associated with the genetic element Tn1207.3. The nonconjugative nature of the mega element and the clonal diversity of mef(E)-containing strains determined by pulsed-field gel electrophoresis suggest that transformation is the main mechanism through which this resistance gene is acquired.