Erythromycin-resistant Streptococcus Pyogenes Research Articles

Extremely Low Prevalence of Erythromycin-Resistant Streptococcus pyogenes Isolates and Their Molecular Characteristics by M Protein Gene and Multilocus Sequence Typing Methods

Background: Group A streptococci (GAS) are notorious bacteria causing a wide variety of clinical manifestations ranging from mild, acute streptococcal pharyngitis to chronic non-suppurative diseases and immunological sequelae. They are further complicated by the global rise on the emergence of macrolide resistance among these bacteria in which several M protein gene (emm) and sequence types are associated with invasive diseases. Objectives: The current study aimed at determining the erythromycin resistance patterns and molecular characteristics of GAS clinical strains by emm and multilocus sequence typing (MLST) methods. Methods: Thirty-five GAS clinical isolates were subjected to antibiotic susceptibility testing by disk diffusion method. The minimum inhibitory concentration (MIC) of erythromycin against GAS by E-test was determined. Clinical and laboratory standards institute (CLSI) guideline was used for the interpretation of results. Detection of ermA, ermB, and mefA genes by polymerase chain reaction (PCR) was performed and emm typing was done by amplification and sequencing of emm genes per standard protocol. Allele and sequence type (ST) of GAS were obtained using the S. pyogenes MLST database. Results: All the isolates were sensitive to erythromycin, penicillin, clindamycin, chloramphenicol, and vancomycin (100%). Resistance to tetracycline was 54.3%. The mefA gene was found in one erythromycin susceptible isolate. No other erythromycin resistance genes were detected in the isolates. Twenty different emm types were found and the most frequent emm types/subtypes detected were emm1, emm18.21, emm28.5, emm97.4, and emm102.2 (each 8.6%). However, no new emm type was detected. A total of 15 sequence types (STs), eight clonal clusters (CCs), and eight singletons were identified among 21 representative isolates. Three isolates exhibited CC1 (ST28/emm1). Conclusions: High susceptibility of GAS isolates against erythromycin could be due to low antibiotic selective pressure in Malaysian clinical settings. High diversity of emm and ST types revealed the heterogenic nature of the strains circulating in Malaysian hospitals. Continuous epidemiological monitoring by molecular typing methods is warranted to improve the management strategies of GAS infections in future.

Molecular Characteristics of Erythromycin-Resistant Streptococcus pyogenes Strains Isolated from Children Patients in Tunis, Tunisia.

The aims of our study were to characterize phenotypically and genotypically erythromycin-resistant Streptococcus pyogenes or group A streptococci (ERGAS) isolates, to evaluate macrolide resistance and to analyze the association between emm types and virulence factors. Included in this study were all ERGAS strains isolated from 2000 to 2013 at the Children's hospital of Tunis. Antimicrobial susceptibility was performed according to the CA-SFM guidelines. Macrolide resistance genes were revealed by polymerase chain reaction (PCR) method. Virulence factor genes (pyrogenic exotoxin genes and superantigen gene) were detected by PCR, and the emm types were defined by the sequencing of the variable 5' end of the emm gene. Among the 289 GAS isolates collected, 15 (5.2%) were resistant to erythromycin; 7 of the strains were assigned to the cMLSB phenotype (46.6%); 5 harbored ermB gene alone (33.3%); and 2 strains coharbored ermB and mefA (13.3%). The remaining (53.4%) were assigned to the M phenotype and harbored the mefA gene. The frequency of detection of each toxin gene among ERGAS was 13.4% for speA (2 strains), 53.4% for speC (8 strains), and 13.4% for ssa (2 strains). Emm types 1, 58, 11, and 78 were the most frequent among ERGAS strains. The distribution of the cMLSB and M phenotypes changed over the period of investigation with a decrement of cMLSB phenotype and ermB gene that predominated between 2000 and 2006 and an increase of M phenotype and mefA gene between 2007 and 2013, but this difference was nonstatistically significant because of the low number of resistant strains. Emm types 1, 58, and 4 were only present among strains assigned to the M phenotype. However strains assigned to the cMLSB phenotype were associated to emm11, emm22, emm28, emm78, or emm76. There was diversity in emm distribution in ERGAS between the two study periods. There was diversity in emm distribution among ERGAS particularly in 2000-2006. Indeed, from 2000 to 2006, the 6 ERGAS belonged to 5 different emm types (22, 28, 76, 11, and 4), while between 2007 and 2013, seven among the nine ERGAS belonged to only 2 emm types 58 and 1. The speA gene was present only among emm1 isolates, and the ssa gene was associated with emm4 and emm78 types. All emm78, emm28, and emm11 strains harbored speC gene. Our study revealed a low frequency of ERGAS and few emm types were associated with these strains.

Phenotypes and genotypes of erythromycin-resistant Streptococcus pyogenes strains isolated from invasive and non-invasive infections from Mexico and the USA during 1999–2010

To compare the prevalence, phenotypes, and genes responsible for erythromycin resistance among Streptococcus pyogenes isolates from Mexico and the USA. Eighty-nine invasive and 378 non-invasive isolates from Mexico, plus 148 invasive, 21 non-invasive, and five unclassified isolates from the USA were studied. Susceptibilities to penicillin, erythromycin, clindamycin, ceftriaxone, and vancomycin were evaluated according to Clinical and Laboratory Standards Institute (CLSI) standards. Phenotypes of erythromycin resistance were identified by triple disk test, and screening for mefA, ermTR, and ermB genes was carried out by PCR. All isolates were susceptible to penicillin, ceftriaxone, and vancomycin. Erythromycin resistance was found in 4.9% of Mexican strains and 5.2% of USA strains. Phenotypes in Mexican strains were 95% M and 5% cMLS; in strains from the USA, phenotypes were 33.3% iMLS, 33.3% iMLS-D, and 33.3% M. Erythromycin resistance genes in strains from Mexico were mefA (95%) and ermB (5%); USA strains harbored ermTR (56%), mefA (33%), and none (11%). In Mexico, all erythromycin-resistant strains were non-invasive, whereas 89% of strains from the USA were invasive. Erythromycin resistance continues to exist at low levels in both Mexico and the USA, although the genetic mechanisms responsible differ between the two nations. These genetic differences may be related to the invasive character of the S. pyogenes isolated.

Bactericidal effect of silver nanoparticles against multidrug-resistant bacteria

Infections caused by drug-resistant microorganisms result in significant increases in mortality, morbidity, and cost related to prolonged treatments. The antibacterial activity of silver nanoparticles against some drug-resistant bacteria has been established, but further investigation is needed to determine whether these particles could be an option for the treatment and prevention of drug-resistant microbial infections. Hence, we challenged different drug-resistant pathogens of clinical importance (multidrug-resistant Pseudomonas aeruginosa, ampicillin-resistant Escherichia coli O157:H7 and erythromycin-resistant Streptococcus pyogenes) with a suspension of silver nanoparticles. By means of a luciferase-based assay, it was determined that silver nanoparticles (1) inactivate a panel of drug-resistant and drug-susceptible bacteria (Gram positive and Gram negative), (2) exert their antibacterial activity through a bactericidal rather than bacteriostatic mechanism, and (3) inhibit the bacterial growth rate from the time of first contact between the bacteria and the nanoparticles. Additionally, strains with a resistant phenotype to silver nanoparticle were developed and used to explore the bactericidal mode of action of silver nanoparticles. Through a Kirby–Bauer test, it was shown that silver nanoparticles’ general mechanism of bactericidal action is based on inhibition of cell wall synthesis, protein synthesis mediated by the 30s ribosomal subunit, and nucleic acid synthesis. Our data suggest that silver nanoparticles are effective broad-spectrum biocides against a variety of drug-resistant bacteria, which makes them a potential candidate for use in pharmaceutical products and medical devices that may help to prevent the transmission of drug-resistant pathogens in different clinical environments.

Activities of 16-membered ring macrolides and telithromycin against different genotypes of erythromycin-susceptible and erythromycin-resistant Streptococcus pyogenes and Streptococcus pneumoniae

To test four 16-membered macrolides (josamycin, spiramycin, midecamycin and rokitamycin) along with other compounds in the same class (erythromycin, clarithromycin, roxithromycin and azithromycin) plus clindamycin and telithromycin, against Streptococcus pyogenes and Streptococcus pneumoniae isolates with well-characterized resistance genotypes. Four hundred and eighty-six isolates of S. pyogenes and 375 isolates of S. pneumoniae were assayed for their macrolide susceptibilities and investigated by PCR to detect their different erythromycin resistance genes. All strains had been isolated over the period 2002-2003 from specimens of different human origin obtained in 14 different Italian centres. All 16-membered macrolides showed very low MICs (MIC(50)s and MIC(90)s, < or =0.06-0.5 mg/L) for the erythromycin-susceptible isolates and for those with the M phenotype, but the telithromycin MICs for the M-type isolates were at least four times higher (MIC(90)s, 0.5 mg/L). In S. pyogenes, the MIC(50)s of 16-membered macrolides for the cMLS(B) isolates were > or = 256 mg/L, whereas that for telithromycin was 4 mg/L; the MIC(50)s of 16-membered macrolides and telithromycin ranged from < or = 0.06 to 0.5 mg/L for the iMLS(B) isolates with erm(A) and from 0.12 to > or = 256 mg/L for those with erm(B). In S. pneumoniae, the MIC(50)s of the 16-membered macrolides for the cMLS(B) isolates ranged from 0.5 to 128 mg/L, whereas for the iMLS(B) isolates their values ranged from < or = 0.06 to 4 mg/L; the MIC(50)s and MIC(90)s of telithromycin for both the cMLS(B) and the iMLS(B) isolates ranged from < or = 0.06 to 0.12 mg/L. MICs ranged for all the drugs, except telithromycin, from < or = 0.06 to > or = 256 mg/L, with 15% to 30% resistant S. pyogenes for all drugs tested except clindamycin (8%) and telithromycin (5.4%) and 10% to 40% resistant S. pneumoniae for all drugs tested except telithromycin (0.3%). In both S. pyogenes and S. pneumoniae, erythromycin resistance related to a mef gene meant that telithromycin MICs were definitely higher than in erythromycin-susceptible isolates, although telithromycin susceptibility was preserved in all cases. In S. pyogenes, the activity of both 16-membered macrolides and telithromycin against the iMLS(B) strains proved to be dependent on the erm gene involved, being greater against isolates with erm(A).

Erythromycin resistance associated to mefA gene and emm75 allele in Streptococcus pyogenes from uncomplicated pharyngitis in Mexico

Erythromycin-resistant Streptococcus pyogenes strains have been reported in many parts of the world; however, few reports have shown the prevalence of the erythromycin-resistant genes and their relationship to M-serotype of the bacteria. A total of 391 S. pyogenes isolates collected from different hospitals in Mexico City between 2001 and 2004 were analyzed. Erythromycin resistance was evaluated by susceptibility discs and resistance phenotype by double-disc test with erythromycin and clindamycin discs. Identification of mefA, ermTR and ermB resistance genes was performed by PCR. Resistance genotype was associated with the emm allele (M protein gene) of each strain, which was performed previously by emm typing. Thirty isolates (7.7%) were resistant to erythromycin. Virtually, all (28/30, 93%) showed the resistance phenotype designated as “M” and had the mefA gene (efflux-mediated mechanism). Twenty-seven mefA positive isolates had the emm75 allele. The other three erythromycin-resistant organisms were emm77( mefA), emm4( ermTR) and emm41 (undetermined resistance mechanism). The prevalence of erythromycin-resistant isolates was of 7.7%; however, the 50% of emm75 organisms evaluated were resistant to erythromycin. This study emphasizes the need to establish an epidemiological surveillance in order to follow the distribution of erythromycin-resistant clones in this population.

Erythromycin-resistant Streptococcus pyogenes

Streptococcus pyogenes is the most prevalent cause of tonsillopharyngitis in children. The drug of choice for infections caused by this microorganism is penicillin. The problem of treating such infections arises when erythromycin-resistant strains occur. The aim of the study was to determine the prevalence of Streptococcus pyogenes resistant to erythromycin. The organism was recovered from the pharynx of children hospitalized or treated on outpatient basis at the University Children's Hospital in Belgrade. Streptococcus pyogenes was identified on blood agar, using bacitracin disc, and confirmed by latex agglutination test (Slidex bioMerieux). Disc diffusion test was carried out to estimate the penicillin resistance. Erythromycin disc was used as screening method to detect erythromycin-resistant Streptococcus pyogenes. MIC for erythromycin was performed by broth dilution method. In the study period from January 2001 to December 2003, all 1100 isolates of Streptococcus pyogenes had usual level of penicillin sensitivity. In 2001, only 0.45% of isolates were erythromycin-resistant. In 2002, erythromycin resistance was 0.63%, while in 2003, it was 1.09%. MIC for erythromycin was from 1 to 128 mg/l. Three strains had constitutive and one strain had inducible resistance to clindamycin. According to the results, our conclusion is that, despite sensitivity to penicillin, resistance to macrolides is the emerging phenomenon. Reasonable use of macrolide antibiotics is necessary to maintain the resistance at the lowest level.

Clonal relationships among isolates of erythromycin-resistant Streptococcus pyogenes of different geographical origin.

The clonal relationships among 261 erythromycin-resistant Streptococcus pyogenes isolates collected in 1986-1997 from nine countries in Europe and North and South America were studied by using two molecular typing methods: Vir typing and random amplified polymorphic DNA (RAPD) analysis. A total of 49 different Vir genotypes (VTs) and 33 different RAPD patterns were noted among the 261 isolates. Isolates that shared the same VT and RAPD pattern were considered to belong to the same clone. Although as many as 60 different clones were found among the isolates studied, only seven clones, comprising 157 of the 261 (60%) isolates, were found in more than one country. Five of these seven clones expressed the M phenotype known to be associated with the drug efflux mechanism, and only two clones expressed the macrolide-lincosamide-streptogramin B-resistance phenotype. The results indicate a polyclonal spread of erythromycin-resistant Streptococcus pyogenes. Furthermore, predominance of the seven clones indicates that erythromycin-resistant Streptococcus pyogenes of the same clonal origin may be widely distributed and found in several different countries.

Telithromycin: an oral ketolide for respiratory infections.

The ketolides represent a new subclass of antibiotics among the macrolide-lincosamide-streptogramin group. Telithromycin, the first ketolide to be awarded approvable status for clinical use, demonstrates in vitro activity against community-acquired respiratory pathogens including penicillin- and erythromycin-resistant Streptococcus pneumoniae. An extended half-life permits once-daily oral administration. Telithromycin is a substrate for cytochrome P450 (CYP) 3A4 and also inhibits drugs metabolized by CYP3A4. A relatively high frequency of mild-to-moderate gastrointestinal adverse effects has been reported. Similar clinical and microbiologic efficacy has been demonstrated with oral dosing in comparative clinical trials for community-acquired pneumonia, acute sinusitis, acute exacerbations of chronic bronchitis, and pharyngitis. Although limited data on penicillin-resistant S. pneumoniae and erythromycin-resistant Streptococcus pyogenes are available from clinical trials, this drug appears promising for respiratory infections caused by these pathogens.

The emergence of erythromycin-resistant Streptococcus pyogenes in Seoul, Korea.

High frequencies of erythromycin-resistant streptococci were reported in Japan in the mid-1970s, and in Finland in the late 1980s, related to an increase in the consumption of macrolide antibiotics in these countries. The frequency of erythromycin-resistant Streptococcus pyogenes was reported to be only 2% in 1994, but we know that the susceptibility of the strains to antibiotics had not been tested routinely. We studied the resistance rates of Streptococcus pyogenes to various antibiotics in Seoul, Korea, where antibiotics could be purchased without prescription. From January through December, 1998, 92 isolates of group A streptococci were collected from inpatients and outpatients with pharyngotonsillitis or invasive streptococcal infections, from institutions in five different geographic areas of Seoul; one pediatric clinic, three university hospitals, and one general hospital. All isolates were serotyped by T-agglutination, and minimum inhibitory concentrations (MICs) were determined by agar dilution methods, according to the guidelines of the National Committee for Clinical Laboratory Standards (NCCLS). The most common T-serotype was T12 (44.6%), followed by T4 (19.6%). All the isolates tested were susceptible to penicillin, vancomycin, and cefotaxime. However, 38 isolates (41.3%) were resistant to erythromycin, 32 (34.8%) were resistant to clindamycin, and 48 (52.1%) were resistant to tetracycline. Twenty-seven of 41 isolates serotyped T12 and 3 of 18 isolates serotyped T28 were multiresistant to erythromycin, clindamycin, and tetracycline. Almost half of the isolates obtained from the five different areas in Seoul showed erythromycin resistance in Streptococcus pyogenes. Routine monitoring of antibiotic susceptibility tests and further extensive nationwide surveys are needed to determine the frequency and the extent of the spread of resistant strains in various geographic regions in Korea.

Epidemiological survey of bacterial resistance in upper respiratory tract infections in Italy

The vast majority of infections in the upper airways are caused by four bacterial species;, in Italy as elsewhere, antibiotics resistant strains are emerging. Enzymatic resistance to β-lactams in Haemophilus influenzae is becoming more important and affects 15% of isolates. On the other hand less than 0.3% of H. influenzae strains are fluoroquinolone-resistant. The number of β-lactamase-producing Moraxella catarrhalis strains in Italy has been thought to be lower than in other countries, but recent studies suggest 90% of strains are positive, a figure similar to figures reported in the international literature. The most recent data estimate high-level resistance to penicillin in pneumococci to be around 5%, but varies greatly in different geographical areas and with the different origins of the isolates. In spite of the low incidence of penicillin-resistant strains, the most recent figures for macrolide-resistance in Streptococcus pneumoniae range from 26.4 to 31.7%. More than 3 years after the dramatic increase in erythromycin-resistant Streptococcus pyogenes, the resistance levels in Italy are still among the highest in the world. Unlike the experience in other countries, resistance is often related not to the active efflux of antibiotic from the bacterial cell but to ribosomal methylation, thus affecting not only 14- and 15-membered macrolides, but also 16-membered compounds and lincosamides.

Erythromycin resistance genes in group A streptococci of different geographical origins. The Macrolide Resistance Study Group.

A total of 238 erythromycin-resistant Streptococcus pyogenes isolates were collected in 1986-1997 from eight different countries in Europe and North and South America. The antibiotic susceptibility patterns of all isolates and the resistance genes of 92 isolates of known clonal origin were studied. The mefA gene was detected in all 54 isolates with the M-phenotype and was found in every country. The ermTR and the ermB genes were detected in 27 and 11, respectively, of the 38 isolates with the macrolide-lincosamide-streptogramin B resistance phenotypes. In addition to the mefA gene, the recently sequenced ermTR gene was also widely distributed among isolates of different clonal origin.

Present situation of antimicrobial resistance in Korea.

Resistance of bacteria to antimicrobial agents is a worldwide concern. In Korea, resistant bacteria are more prevalent than in other industrialized countries. Methicillin-resistant Staphylococcus aureus, erythromycin-resistant Streptococcus pyogenes, penicillin non-susceptible pneumococci, beta-lactamase-producing gonococci, extended-spectrum beta-lactamase (ESBL)-producing Escherichia coli and Klebsiella pneumoniae, class C beta-lactamase-producing E. coli, fluoroquinolone-resistant E. coli, and aminoglycoside-resistant Acinetobacter baumannii and Pseudomonas aeruginosa are examples of resistant bacteria prevalent in Korea, and their presence suggests a high level of antimicrobial selective pressure and the nosocomial spread of resistant bacteria. Recently observed rapid increases in the incidence of vancomycin-resistant Enterococcus faecium and carbapenem-resistant P. aeruginosa present new threats in Korea.

Phenotypes and genotypes of erythromycin-resistant Streptococcus pyogenes strains in Italy and heterogeneity of inducibly resistant strains.

A total of 387 clinical strains of erythromycin-resistant (MIC, >/=1 microg/ml) Streptococcus pyogenes, all isolated in Italian laboratories from 1995 to 1998, were examined. By the erythromycin-clindamycin double-disk test, 203 (52.5%) strains were assigned to the recently described M phenotype, 120 (31.0%) were assigned to the inducible macrolide, lincosamide, and streptogramin B resistance (iMLS) phenotype, and 64 (16.5%) were assigned to the constitutive MLS resistance (cMLS) phenotype. The inducible character of the resistance of the iMLS strains was confirmed by comparing the clindamycin MICs determined under normal testing conditions and those determined after induction by pregrowth in 0.05 microg of erythromycin per ml. The MICs of erythromycin, clarithromycin, azithromycin, josamycin, spiramycin, and the ketolide HMR3004 were then determined and compared. Homogeneous susceptibility patterns were observed for the isolates of the cMLS phenotype (for all but one of the strains, HMR3004 MICs were 0.5 to 8 microg/ml and the MICs of the other drugs were >128 microg/ml) and those of the M phenotype (resistance only to the 14- and 15-membered macrolides was recorded, with MICs of 2 to 32 microg/ml). Conversely, heterogeneous susceptibility patterns were observed in the isolates of the iMLS phenotype, which were subdivided into three distinct subtypes designated iMLS-A, iMLS-B, and iMLS-C. The iMLS-A strains (n = 84) were highly resistant to the 14-, 15-, and 16-membered macrolides and demonstrated reduced susceptibility to low-level resistance to HMR3004. The iMLS-B strains (n = 12) were highly resistant to the 14- and 15-membered macrolides, susceptible to the 16-membered macrolides (but highly resistant to josamycin after induction), and susceptible to HMR3004 (but intermediate or resistant after induction). The iMLS-C strains (n = 24) had lower levels of resistance to the 14- and 15-membered macrolides (with erythromycin MICs increasing two to four times after induction), were susceptible to the 16-membered macrolides (but resistant to josamycin after induction), and remained susceptible to HMR3004, also after induction. The erythromycin resistance genes in 100 isolates of the different groups were investigated by PCR. All cMLS and iMLS-A isolates tested had the ermAM (ermB) gene, whereas all iMLS-B and iMLS-C isolates had the ermTR gene (neither methylase gene was found in isolates of other groups). The M isolates had only the macrolide efflux (mefA) gene, which was also found in variable proportions of cMLS, iMLS-A, iMLS-B, and iMLS-C isolates. The three iMLS subtypes were easily differentiated by a triple-disk test set up by adding a josamycin disk to the erythromycin and clindamycin disks of the conventional double-disk test. Tetracycline resistance was not detected in any isolate of the iMLS-A subtype, whereas it was observed in over 90% of both iMLS-B and iMLS-C isolates.

Molecular typing of erythromycin-resistant streptococcus pyogenes strains with the M phenotype isolated in Italy.

To assess the spread of the new M phenotype, various erythromycin-resistant Streptococcus pyogenes strains from three Italian cities (Verona, Monza, Florence) were characterised. Each strain was analysed for the presence of genes ermAM and mefA, for the ability to accumulate radioactive erythromycin in the absence of sodium arsenate, for the protein T serological type, and for the DNA macrorestriction profile identified by means of pulsed-field gel electrophoresis. In a number of strains, the presence of the inducible ermAM gene was demonstrated; all these strains were negative in the efflux-pump detection assay, did not possess the mefA gene, and had similar restriction profiles. The strains with the efflux mechanism and mefA gene belonged to different serotypes. Of these, only one serotype, T4, was isolated in all three cities. The restriction profile analysis with SmaI and SfiI revealed a very close correlation between strains with the same serotype.

Increased activity of 16-membered lactone ring macrolides against erythromycin-resistant Streptococcus pyogenes and Streptococcus pneumoniae: characterization of South African isolates.

The susceptibility of 40 erythromycin-resistant isolates of Streptococcus pyogenes and 40 multiply-resistant isolates of Streptococcus pneumoniae to six macrolide antibiotics, representing 14-, 15- and 16-membered lactone ring structures, was tested. The genetic basis for macrolide resistance in the strains was also determined. Both erm and mef determinants were encountered in the 36 S. pneumoniae isolates tested, but only mef in the five S. pyogenes isolates tested. All isolates showed cross-resistance among the 14-membered macrolides erythromycin, clarithromycin and roxithromycin and the 15-membered macrolide, azithromycin. However, the erythromycin-resistant S. pyogenes isolates retained full susceptibility to spiramycin and josamycin (16-membered agents). These latter two antibiotics were also more active than the other macrolides against erythromycin-resistant S. pneumoniae isolates, especially josamycin which was 8-64 times more active than erythromycin; spiramycin was only two to eight times more active than erythromycin.

Erythromycin resistance of Streptococcus pyogenes in Madrid.

Erythromycin is considered to be an adequate alternative to penicillin for patients who are allergic to penicillin. Erythromycin-resistant Streptococcus pyogenes strains have been reported in some parts of the world. The in vitro activity of erythromycin and other antimicrobial agents was determined in a total of 1310 clinical Streptococcus pyogenes isolates collected in the city of Madrid from January, 1993, through December, 1996. All strains showed susceptibility to penicillin, rifampin, vancomycin and chloramphenicol. Tetracycline resistance was 8.5%. In 36 of the strains (2.7%) MIC was 4 microg/ml for ofloxacin. Clindamycin resistance was observed in only 18 strains (1.4%); this resistance was constitutive in 15 and inducible in 3 strains. Resistance to erythromycin was observed in 14.3% of the strains, showing an increase during the study period (2.0% in 1993 vs. 22.4% in 1996; chi square for linear trend 68.8, P < 0,0001); >90% of them showed the novel resistance phenotype described by Seppälä et al. and 32 of 32 of these strains showed by PCR the 1.4-kb fragment of the mefA gene recently described as the novel macrolide efflux resistance determinant. The erythromycin-resistant strains were isolated more often in pediatric patients (144 of 872) than in adults (44 of 438) (chi square 9.9, P = 0.0016). The study emphasizes the need to screen for resistance to macrolides in S. pyogenes and indicates that resistance to erythromycin in S. pyogenes has increased significantly in Madrid.

Emergence of Streptococcus pyogenes strains resistant to erythromycin in Gipuzkoa, Spain.

The aim of this study was to determine the evolution of resistance to macrolides and other antibiotics in strains of Streptococcus pyogenes isolated in the province of Gipuzkoa, Spain. During the period 1984-1996, all 2561 strains of Streptococcus pyogenes studied showed full susceptibility to penicillin. Until 1990, only 1.2% of Streptococcus pyogenes isolates were resistant to erythromycin. Since then, resistance to erythromycin increased every year until 1995, when 34.8% (87/250) of Streptococcus pyogenes strains were found to be resistant. In 1996 the rate of resistance to erythromycin was 17.8% (75/422). During the study period, 96.1% (246/256) of the Streptococcus pyogenes isolates resistant to erythromycin were susceptible to clindamycin. Of the remaining erythromycin-resistant Streptococcus pyogenes strains, resistance to clindamycin was constitutive in seven strains and inducible in three. When investigated by the polymerase chain reaction (PCR), all Streptococcus pyogenes strains resistant to erythromycin and susceptible to clindamycin showed the 1.4 kb fragment of the mefA gene, recently described as the novel macrolide-efflux-resistance determinant. The most frequent T-agglutination patterns among Streptococcus pyogenes resistant to erythromycin were T4 and T8,25. The emergence and rapid spread of erythromycin-resistant Streptococcus pyogenes in Gipuzkoa and its relationship to the presence of the mefA gene are described.

In vitro activity of YM133, a new semisynthesized macrolide

YM133, the 4"-O-(4-methoxyphenyl)acetyltylosin, is a new macrolide. The in vitro activity of YM133 was compared with those of erythromycin, josamycin, and rokitamycin by an agar dilution method. YM133 inhibited 90% of the tested isolates of Streptococcus pneumoniae, Legionella spp., and anaerobic bacteria at less than or equal to 1.56 micrograms/ml. The drug inhibited 90% of erythromycin-resistant staphylococci and Streptococcus pyogenes at less than or equal to 50 micrograms/ml. YM133 showed activity against erythromycin-, josamycin-, and rokitamycin-resistant (MIC greater than or equal to 100 micrograms/ml) strains of staphylococci, streptococci, Bacteroides spp., and Clostridium spp. Enterococci were less susceptible to other YM133-like macrolides. Unlike other macrolides, YM133 showed killing activity, and the MBC/MIC ratios of YM133 for several strains were 1:32, whereas those of erythromycin were 4:1,024. In a time-kill curve study, the reduction of viable cells started within 2 h after the addition of YM133.