Survey of macrolide resistance phenotypes in Swedish clinical isolates of Streptococcus pyogenes

Epidemiological markers of Streptococcus pyogenes strains in Tunisia

To further understand the epidemiology of Streptococcus pyogenes or group A streptococcus (GAS) infections in Tunisia, phenotypic and genomic markers of GAS isolates, including antibiotic susceptibility, biotypes, T and emm types and toxin gene profiles, have been characterized. A total of 103 isolates, collected between 2000 and 2006, were investigated; 47 were recovered from invasive infections, and 56 from non-invasive infections. Rates of resistance to tetracycline, erythromycin, clindamycin and rifampin were 70.8%, 4.8%, 4.8% and 0.9%, respectively. High levels of resistance to streptomycin and kanamycin were observed in 1.9% and 4.8% of isolates, respectively. Biotype 3 was most common. Twenty different T patterns were observed, with a predominance of T3/13/B3264, and 38 different emm types. In both invasive and non-invasive isolates, emm118 (9.7%), emm42 (8.7%), emm1 (7.8%), st432 (6.8%), emm28 (5.8%) and emm76 (5.8%) were the most prevalent types; emm1, emm76 and emm18 were mainly observed among invasive infections, whereas emm118 (12.5%), emm42 (10.7%) and emm28 (8.9%) were predominant among non-invasive infections. The speB gene was detected in all isolates, but there were variable frequencies of speA, speC and ssa (20.3%, 32% and 25.2% respectively). Significant associations of emm1, emm18 and emm3 with speA and of emm4 and st432 with ssa were found. This first report from Tunisia revealed a unique emm distribution of GAS that differs from those of other regions. This information on the distribution of such emm types will be useful for the development of an appropriate vaccine in a country where the incidence of rheumatic fever remains high.

The use of erythromycin as a gastrointestinal prokinetic agent in adult critical care: benefits versus risks

Erythromycin A, the first macrolide, was introduced in the 1950s and after years of clinical experience it still remains a commonly relied upon antibiotic. In the past, pharmacodynamic characteristics of macrolides beyond antimicrobial action such as anti-inflammatory and immune-modulating properties have been of scientific and clinical interest. The function of erythromycin as a prokinetic agent has also been investigated for a range of gastrointestinal motility disorders and more recently within the context of critically ill patients. Prokinetic agents are drugs that increase contractile force and accelerate intraluminal transit. Whilst the anti-inflammatory action may be a desirable side effect to its antibiotic action, using erythromycin A merely for its prokinetic effect alone raises the concern about promoting emergence of macrolide resistance. The objectives of this review article are: (i) to briefly summarize the modes and epidemiology of macrolide resistance, particularly in respect to that found in the Streptococcus species (a potential reservoir for the dissemination of macrolide resistance on the critical care unit); (ii) to discuss in this context the evidence for conditions promoting bacterial resistance against macrolides; and (iii) to assess the potential clinical benefit of using erythromycin A as a prokinetic versus the risks of promoting emergence of macrolide resistance in the clinical setting. We conclude, that in view of the growing weight of evidence demonstrating the potential epidemiological impact of the increased use of macrolides upon the spread of resistance, versus a lack of sufficient and convincing evidence that erythromycin A is a superior prokinetic agent to potential alternatives in the critically ill patient population, at this stage we do not advocate the use of erythromycin A as a prokinetic agent in critically ill patients unless they have failed all other treatment for impaired gastrointestinal dysmotility and are intolerant of metoclopramide. Further large and methodologically robust studies are needed to ascertain the effectiveness of erythromycin A and other alternative agents in the critically ill.

Macrolide, lincosamide and tetracycline susceptibility and emm characterisation of invasive Streptococcus pyogenes isolates in Israel

Group A beta-haemolytic streptococcus (GAS) causes a variety of infections, including life-threatening illnesses. Although the species is uniformly penicillin susceptible, resistance to other antibiotics is becoming more common. We studied the prevalence of resistance and associated factors in a nationwide, prospective, population-based study of invasive infections in Israel. Isolates were collected in collaboration with 24 hospitals in Israel during 1996-1999. Minimal inhibitory concentrations (MICs) of erythromycin (ERY), clindamycin (CLI) and tetracycline (TET) were determined as well as ERY and TET resistance phenotypes and genotypes. Five hundred isolates were examined: 136 (27.2%) were not susceptible to TET, 10 (2.0%) to ERY and 5 (1%) to CLI. ERY resistance was associated with emm types 12 and 83 (P<0.001 for both). MICs of TET had a bimodal distribution distinguishing sensitive and resistant populations. Non-susceptibility to TET was mainly due to the presence of tet(M) and was associated with T types 3, 3/13/B3624 and 9 and emm types 9, 33, 64, 73, 74, 76, 77 and 83. TET susceptibility was associated with T types 1, 2 and 11, emm types 1-4, 11, 12, 22, 26 and 75 and the presence of speA and speC. In Israel, resistance of invasive GAS isolates to ERY remains low and is associated with specific T and emm types, as is TET resistance. TET resistance is less frequent than previously reported in Israel and is associated with a lower prevalence of speA and speC.

DNA methylase activity as a marker for the presence of a family of phage-like elements conferring efflux-mediated macrolide resistance in streptococci

Recently, two related chimeric genetic elements (Tn1207.3 and Phi10394.4) were shown to carry the macrolide efflux gene mef in Streptococcus pyogenes (group A streptococci [GAS]). The dissemination of elements belonging to the Tn1207.3/Phi10394.4 family in recent isolates of GAS, Streptococcus dysgalactiae subsp. equisimilis, Streptococcus pneumoniae, and Streptococcus agalactiae recovered in Portugal was surveyed. In total, 149 GAS, 18 S. pneumoniae, 4 S. dysgalactiae subsp. equisimilis, and 5 S. agalactiae isolates from infections, presenting the M phenotype of macrolide resistance and containing the mef gene, were screened for the presence of Tn1207.3/Phi10394.4 by PCR targeting open reading frames (ORFs) specific for these related elements. All the GAS isolates tested and one of the S. dysgalactiae subsp. equisimilis isolates carried Tn1207.3. However, neither of these elements was found in the isolates of the other streptococcal species. It was also noted that the DNAs of the isolates carrying Tn1207.3 were resistant to cleavage by the endonuclease SmaI. Cloning and expression of ORF12 of Tn1207.3 in Escherichia coli showed that it encoded a methyltransferase that rendered DNA refractory to cleavage by SmaI (M.Spy10394I). Using this characteristic as a marker for the presence of the Tn1207.3/Phi10394.4 family, we reviewed the literature and concluded that these genetic elements are widely distributed among tetracycline-susceptible GAS isolates presenting the M phenotype from diverse geographic origins and may have played an important role in the dissemination of macrolide resistance in this species.

Antibiotic Resistance and Genotypic Characteristics of Group A Streptococci Associated with Acute Pharyngitis in Korea

Group A streptococci (GAS) is the most common pathogen of bacterial pharyngitis. GAS were isolated from pediatric outpatients with symptomatic acute pharyngitis. T typing and emm genotyping were performed for an epidemiologic study. The phenotypes of erythromycin (EM) resistance were evaluated, and the frequencies of ermB, ermTR(A), and mefA genes were determined by polymerase chain reaction. A total of 125 (50.8%) of 246 children yielded GAS. The two most frequent T types were T12 (35.2%) and T nontypeable (30.4%). The most frequent emm type was emm 12 (28.5%), followed by emm75 (18.7%), emm22 (13.0%), emm2 (12.2%), and emm8 (8.1%). The resistance rates to erythromycin and clindamycin were 44.8% and 19.2%, respectively. Among the EM-resistant strains, constitutive resistance, inducible resistance, and the M phenotype were observed in 42.1%, 0%, and 57.9%, respectively. The ermB, ermA, and mefA genes were present in 39.3%, 0%, and 58.9%, respectively. Most of the emm12 strains showed constitutive resistance, while emm18 and emm75 demonstrated the M phenotype. The organisms with other emm genotypes were susceptible to both EM and clindamycin. These results indicate that some emm genotypes might be associated with a specific mechanism of EM resistance.

Émergence de la résistance aux macrolides chez Streptococcus pyogenes en pédiatrie

A total of 206 recent throat isolates of Streptococcus pyogenes collected between 2002 and 2004 from children were tested for their susceptibility to penicillin, amoxycillin, erythromycin, clarythromycin and clindamycin. The erythromycin resistant isolates were further studied for their genetic mechanism of resistance by means of PCR. In all, 14.5% of the strains were erythromycin resistant and 13.5 and 1% expressed the constitutive MLS(B) and M resistance phenotypes and harbored the ermB and mef A genes respectively.

Evaluation of 5-day therapy with telithromycin, a novel ketolide antibacterial, for the treatment of tonsillopharyngitis

A pooled analysis of two double-blind, multicentre, Phase III studies compared oral telithromycin 800 mg once-daily for 5 days with penicillin V 500 mg three-times-daily or clarithromycin 250 mg twice-daily for 10 days in the treatment of Streptococcus pyogenes (group A beta-haemolytic streptococcus; GABHS) tonsillopharyngitis. Patients aged > or = 13 years with acute GABHS tonsillopharyngitis were randomised to receive telithromycin (n = 430), penicillin (n = 197) or clarithromycin (n = 231). Clinical isolates of S. pyogenes (n = 590) obtained from throat swab samples on study entry were tested for their in-vitro susceptibility to telithromycin, clarithromycin and azithromycin. Telithromycin demonstrated in-vitro activity against the clinical isolates of S. pyogenes (MIC50/90 0.03/0.06 mg/L) higher than clarithromycin or azithromycin (MIC50/90 0.06/0.06 mg/L and 0.12/0.25 mg/L, respectively), including erythromycin-resistant strains. At the post-therapy/test of cure (TOC) visit (days 16-23), satisfactory bacteriological outcome was demonstrated for 88.3% (234/265) and 88.6% (225/254) of telithromycin- and comparator-treated patients, respectively (per-protocol population). Overall, GABHS eradication rates were 88.7% (235/265) for telithromycin and 89.0% (226/254) for comparators. The clinical cure rates at the post-therapy/TOC visit were 93.6% (248/265) and 90.9% (220/242) for telithromycin and pooled comparators, respectively. Telithromycin was generally well-tolerated. Most adverse events considered to be possibly related to study medication were gastrointestinal and of mild intensity. Discontinuations as a result of adverse events were few in both treatment groups. In conclusion, telithromycin 800 mg once-daily for 5 days was as effective as penicillin V or clarithromycin for 10 days in the treatment of GABHS tonsillopharyngitis.

Dissemination of emm28 erythromycin-, clindamycin- and bacitracin-resistant Streptococcus pyogenes in Spain

Reported here is an unusual cluster of non-invasive infections caused by an emm28 Streptococcus pyogenes strain resistant to bacitracin, erythromycin and clindamycin detected in Santander, Spain. Since one of the characteristics of group A streptococci is their almost uniform susceptibility to bacitracin, this finding was unusual, and a search for bacitracin-resistant Streptococcus pyogenes strains was conducted in two other distant cities of Spain (Madrid and San Sebastián) where their presence was confirmed. These strains were frequently associated with erythromycin- and clindamycin-resistance, and most of them belonged to a unique emm28 T28, ST52 clone.

Clinical and bacteriological efficacy of the ketolide telithromycin against isolates of key respiratory pathogens: a pooled analysis of phase III studies

A pooled analysis of data from 13 phase III studies of telithromycin in the treatment of community-acquired pneumonia, acute exacerbations of chronic bronchitis, acute sinusitis or group A beta-haemolytic streptococcal pharyngitis and tonsillitis was undertaken. Causative key respiratory tract pathogens (Streptococcus pneumoniae, Haemophilus influenzae, Moraxella catarrhalis, Staphylococcus aureus and Streptococcus pyogenes) were isolated at entry to the studies from cultures of relevant respiratory samples and tested for their susceptibility to telithromycin, penicillin and macrolides (erythromycin A). The combined clinical and bacteriological efficacy of telithromycin at the post-therapy, test-of-cure visit (days 17-24) was assessed in patients from whom a microbiologically evaluable pathogen was isolated at entry. More than 98% of key respiratory pathogens isolated, including penicillin G- and macrolide (erythromycin A)-resistant strains of S. pneumoniae, demonstrated full or intermediate susceptibility to telithromycin in vitro at the breakpoints of < or = 1.0 mg/L (susceptible) and 2.0 mg/L (intermediate) used for the purpose of evaluating the susceptibility of isolates recovered during the clinical trials. Treatment with telithromycin 800 mg once-daily for 5, 7 or 7-10 days resulted in high rates of clinical cure (88.5%) and a satisfactory bacteriological outcome (88.9%), similar to the figures seen with comparator antibacterial agents. Clinical cure and eradication rates were good for all key respiratory pathogens, including penicillin G- and macrolide (erythromycin A)-resistant S. pneumoniae. The results suggest that telithromycin will provide effective empirical therapy for community-acquired upper and lower respiratory tract infections.

Development of macrolide resistance by ribosomal protein L4 mutation in Streptococcus pyogenes during miocamycin treatment of an eight-year-old Greek child with tonsillopharyngitis

Streptococcus pyogenes isolates with the same pulsed-field patterns were recovered from the throat cultures of a child with tonsillopharyngitis before and after treatment with miocamycin, a 16-membered macrolide. The initial isolate was macrolide-susceptible, but the isolates after the treatment were resistant to 14 and 15-membered macrolides and had two amino acid (65WR66) deletions in ribosomal protein L4.

Activity of telithromycin compared with seven other agents against 1039 Streptococcus pyogenes pediatric isolates from ten centers in central and eastern Europe

In total, 1039 pediatric Streptococcus pyogenes isolates from Bulgaria, Croatia, the Czech Republic, Hungary, Latvia, Lithuania, Poland, Romania, Slovakia and Slovenia were studied. All strains were susceptible to penicillin G, levofloxacin, and quinupristin-dalfopristin, 91-100% to telithromycin, and 82-100% to erythromycin, azithromycin, and clarithromycin, and 90-100% to clindamycin. Macrolide resistance occurred mainly in Slovakia (25%), the Czech Republic (17.3%), and Croatia (15.8%). Overall, 9.7% of S. pyogenes isolates were erythromycin resistant due to erm(B)- or erm(A)-encoded methylases (72.3%) or to a mef(A)-encoded efflux pump (25.7%). One strain had alterations of both 23S rRNA (A2058G Escherichia coli numbering) and ribosomal protein L22 (G95D).

Efficacy and tolerability of 5-day, once-daily telithromycin compared with 10-day, twice-daily clarithromycin for the treatment of group A beta-hemolytic streptococcal tonsillitis/pharyngitis: a multicenter, randomized, double-blind, parallel-group study

BACKGROUND

Telithromycin, a ketolide antibacterial, has been developed for the treatment of community-acquired respiratory infections.

OBJECTIVE

This study compared the efficacy and tolerability of 5-day, once-daily telithromycin with 10-day, twice-daily clarithromycin in adolescents and adults with acute tonsillitis/pharyngitis caused by group A beta-hemolytic streptococci ([GABHS] Streptococcus pyogenes).

METHODS

In this multicenter, randomized, double-blind, parallel-group study, adolescent (aged > or = 13 years) and adult patients with a diagnosis of GABHS tonsillitis/pharyngitis received once-daily telithromycin 800 mg for 5 days (followed by placebo for 5 days) or twice-daily clarithromycin 250 mg for 10 days. Bacteriologic and clinical outcomes were assessed at a test-of-cure visit (days 16 to 23) and a late posttherapy visit (days 31 to 45).

RESULTS

A total of 526 patients were enrolled in the study, of which 463 (288 females, 175 males) were randomized to receive treatment (telithromycin, n = 232; clarithromycin, n = 231). The mean age of the telithromycin group was 30.9 years; in the clarithromycin group, it was 30.0 years. Bacterial eradication was achieved in 91.3% of telithromycin-treated patients and 88.1% of clarithromycin recipients (difference, 3.2%; 95% CI, -4.5 to 11.0). Clinical cure was achieved in 92.7% of telithromycin recipients and 91.1% of clarithromycin-treated patients (difference, 1.6%; 95% CI, -5.5 to 8.6). Bacteriologic and clinical cures for the 2 treatment groups also were similar at the late posttherapy visit. Treatment-related adverse events occurred more frequently in the telithromycin group than the clarithromycin group (67.2% vs 57.5%, respectively); diarrhea, nausea, and vomiting were significantly more common with telithromycin than with clarithromycin (P = 0.004, 0.010, and 0.001, respectively). Adverse events were generally mild.

CONCLUSION

This study demonstrates that telithromycin 800 mg once daily for 5 days was an effective and generally well-tolerated treatment for tonsillitis/pharyngitis caused by GABHS, providing similar bacteriologic and clinical efficacy to clarithromycin 250 mg twice daily for 10 days in the per-protocol population.

Clinical isolates of macrolide-resistant Streptococcus pyogenes in Central Greece

A total of 300 Streptococcus pyogenes isolates, collected during 2001 from five hospitals in the Thessalia district (Central Greece), were examined for their resistance to macrolides. Resistance to erythromycin was detected in 58 isolates (19.3%). Of these, 68.9% were susceptible to clindamycin (M-phenotype) and carried the mefA gene. Of the remaining isolates, 18 expressed the MLS(B) phenotype: 12 and six exhibited inducible and constitutive resistance to clindamycin, respectively. All of these strains were found to be ermA(TR) positive, except for four that had the ermB gene. Of the erythromycin-resistant strains, none was found to be resistant to penicillin, tetracycline or quinupristin-dalfopristin. Molecular typing by PFGE showed the presence of a limited number of clones.

Macrolide and tetracycline resistance and molecular relationships of clinical strains of Streptococcus agalactiae

Mechanisms for tetracycline and macrolide resistance in 54 isolates of erythromycin-resistant Streptococcus agalactiae were analyzed by PCR. The erm(B), erm(A), and mef(A) genes, either alone or in combination, were detected in all the erythromycin-resistant isolates. The tet(M) and tet(O) genes were responsible for tetracycline resistance. Random amplification of polymorphic DNA indicated different clonal origins of the isolates.

Rokitamycin: bacterial resistance to a 16-membered ring macrolide differs from that to 14- and 15-membered ring macrolides

Rokitamycin is the latest semi-synthetic 16-membered ring macrolide introduced into clinical practice. It is characterized by greater hydrophobicity, better bacterial uptake and a slower release, more cohesive ribosomal binding, and a longer post-antibiotic-effect (PAE) than can be observed with other available 14-, 15- and 16-membered ring macrolides. Rokitamycin exerts its activity on strains that harbor inducible erm genes or the efflux gene, mef(A). It has also been reported to be more active in vitro than other 16-membered ring macrolides. However, these recognized features are not fully exploited yet because current automated test procedures used in many microbiological laboratories determine susceptibility only to erythromycin or clarithromycin. Resistance to 16-membered ring macrolides cannot be predicted solely on the basis of known resistance to erythromycin or clarithromycin as revealed by an automated susceptibility assay. At least equally important is the knowledge of the bacterial resistance phenotype. This is underlined by the existence of Gram-positive coccal strains resistant to erythromycin and other 14-,15-membered ring macrolides but susceptible to 16-membered ring macrolides. Since the local prevalence of erythromycin phenotypes is generally unknown but might determine the outcome of treatment, the procedure for identifying the phenotypes in erythromycin-resistant strains (which can be easily and cheaply performed using the two- or three-disk assay) should become routine, at least in the countries in which 16-membered ring macrolides are used. This approach should help to optimize the use of macrolides, improve our knowledge of the local prevalence of phenotypes resistant to erythromycin, and offer the possibility of treating infections caused by certain types of erythromycin-resistant pathogens.

Susceptibility to telithromycin in 1,011 Streptococcus pyogenes isolates from 10 central and Eastern European countries

Among 1,011 recently isolated Streptococcus pyogenes isolates from 10 Central and Eastern European centers, the MICs at which 50% of isolates are inhibited (MIC(50)s) and the MIC(90)s were as follows: for telithromycin, 0.03 and 0.06 microg/ml, respectively; for erythromycin, azithromycin, and clarithromycin, 0.06 to 0.125 and 1 to 8 microg/ml, respectively; and for clindamycin, 0.125 and 0.125 microg/ml, respectively. Erythromycin resistance occurred in 12.3% of strains. Erm(A) [subclass erm(TR)] was most commonly encountered (60.5%), followed by mef(A) (23.4%) and erm(B) (14.5%). At <0.5 microg/ml, telithromycin was active against 98.5% of the strains tested.

Activities of a new fluoroketolide, HMR 3787, and its (des)-fluor derivative RU 64399 compared to those of telithromycin, erythromycin A, azithromycin, clarithromycin, and clindamycin against macrolide-susceptible or -resistant Streptococcus pneumoniae and S. pyogenes

Activities of HMR 3787 and RU 64399 were compared to those of three macrolides, telithromycin, and clindamycin against 175 Streptococcus pneumoniae isolates and 121 Streptococcus pyogenes isolates. HMR3787 and telithromycin were the most active compounds tested against pneumococci. Telithromycin and RU 64399 were equally active against macrolide-susceptible (MICs, 0.008 to 0.06 microg/ml) and -resistant S. pyogenes isolates, but HMR 3787 had lower MICs for ermB strains.

In vitro activity of midecamycin diacetate, a 16-membered macrolide, against Streptococcus pyogenes isolated in France, 1995-1999

OBJECTIVE

To compare the in vitro activity of midecamycin diacetate to that of five other macrolides (erythromycin, clarithromycin, roxithromycin, azithromycin, and josamycin) and of clindamycin against 146 clinical isolates of Streptococcus pyogenes, with regard to three different phenotypes of erythromycin resistance.

METHODS

Susceptibility pattern and resistance phenotype were determined by disk diffusion method and double disk test. Minimal inhibitory concentrations of antibiotics were obtained by the agar dilution method and evaluated according to the recommendations of the 'Comité de l'Antibiogramme de la Société Française de Microbiologie' (CA-SFM). The major determinants of erythromycin resistance in S. pyogenes (ermB, ermTR and mefA genes) were investigated by specific amplification protocols.

RESULTS

Most of the isolates of S. pyogenes collected during 1995-99 were susceptible to midecamycin (93.8%), erythromycin (90.4%), clarithromycin (93.2%), roxithromycin (91.8%), azithromycin (88.4%), josamycin (94.5%), and clindamycin (94.5%). According to the CA-SFM criteria, 132 of the 146 isolates studied were susceptible to erythromycin (MICs < or = 1 mg/L), four were intermediate (MICs 2-4 mg/L), and 10 were resistant (MICs > 4 mg/L). Only nine isolates were midecamycin resistant (MICs > 4 mg/L), and the others were susceptible. The increased activity of midecamycin (MIC90 < or = 0.06 mg/L), as compared to erythromycin (MIC90 = 0.5 mg/L) and to other 14- or 15-membered macrolides, was related to the absence of the ermB determinant in seven isolates which displayed an efflux phenotype (five isolates) or an inducible resistance phenotype due to an ermTR determinant (two isolates).

CONCLUSION

Midecamycin diacetate is active against most S. pyogenes strains isolated in France and may represent an attractive alternative to the treatment of streptococcal infections due to resistant isolates with efflux of erythromycin.

Unusual occurrence of M type 77, antibiotic-resistant group A streptococci in southern Sweden

For many years group A streptococci of T type 28 (T28) have been common in southern Sweden; however, since 1995 resistance to both macrolide-lincosamide-streptogramin B (MLS) antibiotics and tetracycline was observed among T28 isolates, which prompted the present studies on clonal relatedness of antibiotic-resistant T28 strains. By extended T typing, 95 of 100 examined tetracycline-resistant strains showed the combination T9-T13-T28; of these, 94 belonged to M type 77 (M77) and one belonged to M73. Three strains were T28-M28 and two were T28-M nontypeable. The serological M77 was confirmed by PCR capture enzyme-linked immunosorbent assay, emm amplicon restriction profiling, and emm sequence typing. Fifty strains were examined for superantigen genes: speA was detected in three blood isolates only, whereas all isolates harbored speB, and only two of the strains were negative for speC. Eighty-nine of the 100 strains were also macrolide resistant, of which 59 were inducibly MLS resistant (IR) and 21 were constitutively MLS resistant (CR), 6 were noninducibly resistant (NI), and 3 had novel subphenotypes recently reported by our group. Resistance genes were determined by PCR and hybridization methods. Eighty-four of the 100 strains harbored tetM. ermB was detected in all CR and IR strains, and mefA was found in all NI strains; both ermB and mefA were identified in two strains with novel subphenotypes. Pulsed-field gel electrophoresis showed that these antibiotic-resistant M77 strains belonged to at least five different clones.

Prevalence of polyclonal mefA-containing isolates among erythromycin-resistant group A streptococci in Southern Taiwan

A total of 204 nonrepetitive isolates of group A streptococci (GAS), including 107 randomly collected between 1992 and 1995 and 66 and 31 consecutively collected in 1997 and 1998, respectively, from a university hospital in southern Taiwan were examined to determine the prevalence and mechanisms of erythromycin resistance among these isolates. Resistance to erythromycin was detected in 129 isolates (63.2%) by the agar dilution test. Of these, 42 isolates (32.6%) were assigned to the constitutive macrolide, lincosamide, and streptogramin B resistance (cMLS) phenotype, and all carried the ermB gene; 4 (3.1%) were assigned to the inducible MLS resistance (iMLS) phenotype, and all harbored the ermTR gene; and 83 (64.3%) were erythromycin resistant but susceptible to clindamycin (M phenotype), and all possessed the mefA gene. Distributed by years, the rates of erythromycin resistance and different phenotypes were 61.7% (53.0% cMLS, 6.1% iMLS, and 40.9% M phenotype) between 1992 and 1995, 62.1% (12.2% cMLS and 87.8% M phenotype) in 1997, and 71. 0% (9.1% cMLS and 90.9% M phenotype) in 1998. Pulsed-field gel electrophoresis showed that all but 2 cMLS isolates were clonal in origin, and 17 clones were detected among the M-phenotype isolates. These results indicate that the high incidence and increasing rate of erythromycin-resistant GAS in southern Taiwan are due to the prevalence of multiple M-phenotype clones and that clindamycin may be the drug of choice for the treatment of infections with GAS in penicillin-hypersensitive patients in this area.

Resistance to macrolides in Streptococcus pyogenes in France in pediatric patients

A total of 1,500 recent throat isolates of Streptococcus pyogenes collected between 1996 and 1999 from children throughout France were tested for their susceptibility to erythromycin, azithromycin, josamycin, clindamycin, and streptogramin B. The erythromycin-resistant isolates were further studied for their genetic mechanism of resistance, by means of PCR. The clonality of these strains was also investigated by means of serotyping and ribotyping. In all, 6.2% of the strains were erythromycin resistant, and 3.4 and 2.8% expressed the constitutive MLS(B) and M resistance phenotypes and harbored the ermB and mefA genes, respectively; ermTR was recovered from one isolate which also harbored the ermB gene. Ten serotypes and 8 ribotypes were identified, but we identified 17 strains by combining serotyping with ribotyping. Among the eight ribotypes, the mefA gene was recovered from six clusters, one being predominant, while the ermB gene was recovered from four clusters, of which two were predominant.

High rate of tetracycline resistance in Streptococcus pyogenes in Iran: an epidemiological study

Streptococcus pyogenes, a major human pathogen, is still considered susceptible to beta-lactams, but for other relevant antibiotics, highly variable resistance rates have been reported. Since no data were available from Iran, we tested 1,335 throat isolates from two different regions of the country for their antibiotic susceptibilities and, for comparison, a collection of 80 strains isolated from 1989 to 1991. Erythromycin resistance was uncommon (0.6%), whereas an overall high rate of tetracycline resistance was found, increasing between 1989-1991 and 1995-1997 from 23 to 42%. The tetracycline-resistant strains belonged to more than 10 different T types, the majority being types 4, 11, and B3264. By conventional M typing of 406 tetracycline-resistant isolates, more than 20 different M types were found. Approximately 50% of the strains were nontypeable by T agglutination as well as serological M typing; however, by genotyping by a combined PCR-capture-enzyme-linked immunosorbent assay, many of these strains were successfully emm typed. We conclude that the high rate of tetracycline resistance among Iranian S. pyogenes isolates is due to multiclonal dissemination of resistance within the streptococcal population rather than epidemic spread of single clones.

Streptococcus pyogenes isolated in Portugal: macrolide resistance phenotypes and correlation with T types. Portuguese Surveillance Group for the Study of Respiratory Pathogens

From January 1998 to June 1999, 302 clinical isolates of Streptococcus pyogenes were collected from 10 microbiology laboratories in Portugal. All strains were highly sensitive to penicillin (MIC90 = 0.012 mg/liter). The prevalence of erythromycin resistance was 35.8% and of tetracycline resistance 41.4%. The majority (79.6 %) of erythromycin-resistant strains were of the MLSB constitutive resistance (CR) phenotype with high-level resistance to erythromycin (MIC90 >256 mg/liter) and to clindamycin (MIC90 >256 mg/liter), 16.7% showed the M phenotype with low-level erythromycin-resistance (MIC90 = 24 mg/liter) and susceptibility to clindamycin, and four isolates showed a phenotype characterized by low-level erythromycin resistance (MIC90 = 8 mg/liter) and high-level clindamycin resistance (MIC90 >256 mg/liter), not previously described. Erythromycin resistance was not associated with invasive strains. Only minor discrepancies between disk diffusion and E-test methods were observed. T serotyping was very useful for the epidemiological characterization of the strains. The most prevalent T types were T1, T4, T9, T12, T13, and T28. A statistically significant association with resistance patterns was found: T12 with erythromycin resistance MLS(B) CR phenotype (p< 0.001), T4 with erythromycin resistance M phenotype (p<0.001), and T13 with tetracycline resistance (p<0.01). Because of the high prevalence of resistance, careful surveillance of S. pyogenes isolates in Portugal is essential, routine antimicrobial susceptibility testing in clinical microbiology laboratories should be strongly encouraged, antibiotic prescription should be reviewed, and macrolides should no longer be used in the empirical therapy of acute pharyngitis.

Macrolide resistance and erythromycin resistance determinants among Belgian Streptococcus pyogenes and Streptococcus pneumoniae isolates

Resistance of streptococci to macrolide antibiotics is caused by target-site modification or drug efflux. The phenotypic expression of target-site modification can be inducible or constitutive. The prevalence of the three phenotypes among Belgian erythromycin-resistant Group A streptococci (GAS) and Streptococcus pneumoniae isolates was surveyed, their MICs for seven antibiotics were determined and the clonality of the isolates was explored. Of the 2014 GAS isolates tested 131(6.5%) were erythromycin resistant (MIC > 1 mg/L): 110 (84.0%) showed the M-resistance phenotype whereas the remaining 21 strains (16.0%) were constitutively resistant. No inducibly resistant strains were detected. Of 100 S. pneumoniae isolates, 33 were erythromycin resistant (MIC > 1 mg/L). In contrast to the GAS isolates, only 9.1% of the 33 erythromycin-resistant S. pneumoniae isolates showed the M-resistance phenotype. The presence of mefA/E and ermB genes in the M-resistant and constitutively and inducibly resistant strains, respectively, was confirmed by PCR analysis. Genomic analysis based on pulsed-field gel electrophoresis (PFGE) using the restriction enzyme SfiI, revealed 54 different PFGE patterns among the 131 erythromycin-resistant GAS isolates, of which an M6 clone represented 16.0% of the strains; all other clones, exhibiting different M-types, represented <7% of the strains. The S. pneumoniae isolates also appeared to be polyclonally based, as determined by arbitrarily primed PCR. The macrolides miocamycin and rovamycin, the lincosamide clindamycin and the ketolide HMR 3647 showed excellent activity against the M-resistant GAS and S. pneumoniae strains.

Macrolide resistance phenotypes and mechanisms of resistance in Streptococcus pyogenes in La Rioja, Spain

One hundred and thirty seven consecutive clinical Streptococcus pyogenes isolates were evaluated for macrolide-lincosamide-streptogramin resistance (MLS). Forty of these isolates were resistant to erythromycin (29.2%), 36 of them showed the new M resistance phenotype (erythromycin resistant and clindamycin susceptible) and four isolates had the MLS(B) resistance phenotype (erythromycin and clindamycin resistant). In all 36 isolates with the M resistance phenotype, the mef gene was identified by polymerase chain reaction (PCR). In two of the four S. pyogenes isolates with the MLS(B) phenotype, both ermB and ermTR genes were found; negative results were obtained with the other two isolates which might possess a new mechanism of high level resistance against erythromycin not previously described. In summary, a high rate of erythromycin resistance was found in S. pyogenes isolates and the active efflux pump mediated by the mef gene was the mechanism most frequently involved.

Prevalence and mechanisms of macrolide resistance in clinical isolates of group A streptococci from Ontario, Canada

A total of 3,205 group A streptoccal isolates were collected in 1997 through a private laboratory which serves community physicians in southern Ontario and which represents a population base of 6 million people. Nonsusceptibility to erythromycin was detected for 67 (2.1%) isolates both by disk diffusion and by broth microdilution. Of these, 47 (70%) were susceptible to clindamycin and were found by PCR to possess the mef gene. Of the other 20 strains, 18 and 2 showed inducible and constitutive resistance, respectively, to clindamycin. Nineteen of these strains were shown by PCR to possess the ermTR gene, and a single constitutively resistant strain harbored an ermB gene. Sixteen (24%) erythromycin-resistant strains were also resistant to tetracycline. All were susceptible to penicillin and chloramphenicol.

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.

Clonal differences among erythromycin-resistant Streptococcus pyogenes in Spain

The aim of this study was to determine whether the high levels of erythromycin resistance in Streptococcus pyogenes found in Spain are due to the introduction and spread of one or more clones. Phenotypic and genotypic techniques were used to characterize all erythromycin-resistant S. pyogenes (ErR) isolated in Gipuzkoa, Spain, in the last 10 years and 128 ErR isolated in Vitoria and Madrid during 1996. Of 437 ErR, 97% had the M phenotype; all 283 of the strains studied had the mefA determinant of resistance. After biotyping, T serotyping, emm typing, and genotyping, four major clones were detected. Clones B (biotype I, type T4, emm4, pulsed-field gel electrophoresis [PFGE] II) and D (biotype V, type T8.25, emm75, PFGE IV) comprised 78.8% of all ErR. The resistance of S. pyogenes to erythromycin was mainly due to an efflux mechanism of resistance (M phenotype); few clones were responsible for it.