Conjugative transfer of resistance determinants among human and bovine Streptococcus agalactiae

Streptococcus agalactiae (GBS) is a major source of human perinatal diseases and bovine mastitis. Erythromycin (Ery) and tetracycline (Tet) are usually employed for preventing human and bovine infections although resistance to such agents has become common among GBS strains. Ery and Tet resistance genes are usually carried by conjugative transposons (CTns) belonging to the Tn916 family, but their presence and transferability among GBS strains have not been totally explored. Here we evaluated the presence of Tet resistance genes (tetM and tetO) and CTns among Ery-resistant (Ery-R) and Ery-susceptible (Ery-S) GBS strains isolated from human and bovine sources; and analyzed the ability for transferring resistance determinants between strains from both origins. Tet resistance and int-Tn genes were more common among Ery-R when compared to Ery-S isolates. Conjugative transfer of all resistance genes detected among the GBS strains included in this study (ermA, ermB, mef, tetM and tetO), in frequencies between 1.10-7 and 9.10-7, was possible from bovine donor strains to human recipient strain, but not the other way around. This is, to our knowledge, the first report of in vitro conjugation of Ery and Tet resistance genes among GBS strains recovered from different hosts.

A report on infection dynamics of inducible clindamycin resistance of Staphylococcus aureus isolated from a teaching hospital in India

<p><b>OBJECTIVE</b>To investigate the infection of hospital- and community-acquired "erythromycin-induced clindamycin resistant" strains or D-test positives of clinical isolates of Staphylococcus aureus (S. aureus) (with and without methicillin resistance) in a hospital.</p><p><b>METHODS</b>Strains of S. aureus isolated from clinical specimens were subjected to D-test and antibiotic profiling.</p><p><b>RESULTS</b>Of the total 278 isolates, 140 (50.35%) were D-test positives and the rest were D-test negatives. Further, of 140 (100%) positives, 87 (62.14%) and 53 (37.85%) strains were from males and females, respectively. Of 140 (100%) positives, 117 (83.57%) were methicillin resistant S. aureus and 23 (16.42%) were methicillin sensitive S. aureus; of 140 strains, 103 (73.57%) strains from persons with and 37 (26.42%) were without related infections; of 140 strains, 91 (65%) and 49 (35%) were from hospital- and community-acquired samples, respectively. In 140 strains, 118 (84.28%) with comorbidities and 22 (15.71%) without comorbidities cases were recorded; similarly, persons with prior antibiotic uses contributed 108 (77.14%) and without 32 (22.85%) positive strains. These binary data of surveillance were analyzed by a univariate analysis. It was evident that the prior antibiotic uses and comorbidities due to other ailments were the determinative factors in D-test positivity, corroborated by low P values, P=0.001 1 and 0.002 4, respectively. All isolates (278) were resistant to 17 antibiotics of nine groups, in varying degrees; the minimum of 28% resistance for vancomycin and the maximum of 97% resistance for gentamicin were recorded. Further, of 278 strains, only 42 (15.1%) strains were resistant constitutively to both antibiotics, erythromycin resistant and clindamycin resistant, while 45 (16.2%) strains were constitutively sensitive to both antibiotics (erythromycin sensitive and clindamycin sensitive). Further, of the rest 191 (68.7%) strains were with erythromycin resistant and clindamycin resistant, of which only 140 (50.35%) strains were D-test positives, while the rest 51 (18.34%) strains were D-test negatives.</p><p><b>CONCLUSIONS</b>In view of high prevalence of D-test positive S. aureus strains, and equally high prevalence of multidrug resistant strains both in community and hospital sectors, undertaking of D-test may be routinely conducted for suppurative infections.</p>

Antimicrobial resistance profiles and genetic characterisation of macrolide resistant isolates of Streptococcus agalactiae

In this study, 100 clinical isolates of Streptococcus agalactiae recovered from genitourinary tract specimens of non-pregnant individuals living in Rio de Janeiro were submitted for antimicrobial susceptibility testing, detection of macrolide resistance genes and evaluation of the genetic diversity of erythromycin-resistant isolates. By agar diffusion method, all isolates were susceptible to ceftazidime, penicillin and vancomycin. Isolates were resistant to levofloxacin (1 percent), clindamycin (5 percent), erythromycin (11 percent) and tetracycline (83 percent) and were intermediated to erythromycin (4 percent) and tetracycline (6 percent). Erythromycin-resistant and intermediated isolates presented the following phenotypes: M (n = 3), constitutive macrolide-lincosamide-streptogramin B (MLS B, n = 5) and inductive MLS B (n = 7). Determinants of macrolide resistance genes, erm and mef, were detected in isolates presenting MLS B and M phenotypes, respectively. Randomly amplified polymorphic DNA profiles of erythromycin-resistant isolates were clustered into two major groups of similarity.

Multicenter Study of Molecular Epidemiology and Antibiotic Resistance of Group A Streptococci in 2008-2009 in Korea / 대한임상미생물학회지

BACKGROUND: Group A Streptococcus (GAS) is responsible for a wide spectrum of human diseases. We investigated the distribution of emm types and antibiotic resistance rates of GAS from clinical specimens in several Korean medical centers. METHODS: A total of 192 strains of GAS from throat, blood, and other specimens collected in Seoul, Busan, Ulsan, Iksan, and Jeju were studied in 2008-2009. The emm genotypes were identified using PCR and sequencing. Antimicrobial susceptibility testing was performed by disk diffusion method. Phenotypes of macrolide resistance were evaluated, and macrolide resistance genes were determined by PCR. RESULTS: The emm89 (33.9%) was most frequently detected, followed by emm1 (12.5%), emm12 (8.3%), emm4 (7.8%), and emm75 (7.3%). The distribution of emm types did not show a close relation to the type of specimen and was different for each area. The resistance rates to erythromycin (ERY) and clindamycin (CLI) were 4.6% and 3.7%, respectively. Among the nine ERY-resistant strains, the rate of constitutive resistance was 88.9%, compared with 11.1% for the M phenotype. Five of the ERY-resistant strains were emm28. CONCLUSION: This multicenter study reveals heterogenous emm genotypes by geographic area. Rates of resistance to ERY and CLI were low, and most of the ERY-resistant strains showed a constitutive macrolide-lincosamide-streptogramin B (cMLSB) phenotype.

Epidemiology and Erythromycin Resistance of Streptococcus pyogenes in the Last 20 Years / 대한임상미생물학회지

Serological methods for the epidemiological study of Streptococcus pyogenes, such as T-, or M-typing, were replaced by emm typing in the 2000s. The frequency of emm types may differ according to ographical area and study period. Erythromycin resistance rates and the prevalence of erythromycin-resistant phenotypes in several countries are surveyed, and common emm genotypes associated with erythromycin resistance are described for each country. There is no correlation between erythromycin resistance and macrolide use in Korea. S. pyogenes is thought to cause severe illness, such as streptococcal toxic shock syndrome (STSS) and necrotizing fasciitis. The mortality rate of STSS is about 50%, and there have been several hundred victims of STSS in Japan in the last 2 decades. The resistance rate to macrolides peaked at 50% in 2002, and currently, <10% of strains exhibit macrolide resistance in Korea. However, the erythromycin resistance rate recently exceeded 90% in China. Considering increases of travel between neighboring countries, a vigilant survey to monitor these highly virulent and antibiotic-resistant strains is necessary.

Decline in Erythromycin Resistance in Group A Streptococci from Acute Pharyngitis due to Changes in the emm Genotypes Rather Than Restriction of Antibiotic Use / 대한진단검사의학회지

BACKGROUND: Group A streptococcus (GAS) is the most common cause of bacterial pharyngitis in children. Antibiotic resistance rates and emm genotypes of GAS isolated from patients with acute pharyngitis were studied in 2009. METHODS: Throat cultures were taken from 499 children with acute pharyngitis in Jinju, Korea, in 2008-2009. A total of 174 strains (34.9%) of GAS were isolated, and antimicrobial susceptibility testing was performed using the disk diffusion method. The phenotypes of macrolide resistance and macrolide resistance genes were determined. The emm genotypes were identified using PCR and sequencing. The data were compared with those acquired in 2002 in the same region. Data on the annual macrolide production were collected between 1999 and 2008. RESULTS: The resistance rates of GAS to erythromycin, clindamycin, and tetracycline were 4.6%, 2.9%, and 2.3%, respectively. The constitutive resistance rate was 62.5% for the erm(B) gene and 37.5% for the M phenotype of the mef(A) gene. emm4 was most frequently detected (28.2%), followed by emm89 (20.1%). Most of the erythromycin resistant strains had the emm28 genotype. We noted a gradual increase in macrolide production during the study period. CONCLUSIONS: The erythromycin resistance rate of GAS isolated from children with acute pharyngitis was significantly lower in 2009 (4.6%) than in 2002 (44.8%). We observed a remarkable change in the distribution of emm genotypes during the 7-yr period. The significant decline in erythromycin resistance in 2009 might be associated with a prominent decrease in the resistant genotype emm12 (3.4% in 2009 vs. 28.0% in 2002) rather than restriction of macrolide use.

T Types, emm Genotypes and Antibiotic Resistance of Streptococcus pyogenes Isolated fromSchool Children in Jinju, 2006 / 대한임상미생물학회지

BACKGROUND: Streptococcus pyogenes is the most common cause of bacterial pharyngitis. T antigens and emm genotypes are essential markers for an epidemiological study of S. pyogenes. Macrolide resistance of S. pyogenes is a serious obstracle to successfully treating a sore throat. METHODS: One-hundred forty-seven strains of S. pyogenes isolated from healthy school children in 2006 were subjected to T typing and emm genotyping. A disk diffusion method was applied for several antibiotics. A double disk diffusion test was performed to evaluate the phenotype distribution of macrolide resistance. RESULTS: Among T antigens and emm genotypes, T11 (19.7%) and emm78 (16.7%), respectively, were the most common in 2006. Both T5/27/44 (2.3%) and emm44/61 (9.1%) declined to a great extent from about 29% in 2004. The rate of resistance to antibiotics were 11.6% to erythromycin, 4.8% to clindamycin, 21.8% to tetracycline, and 7.5% to ofloxacin. M and cMLSB phenotypes were 52.9% and 41.2% respectively. CONCLUSION: T typing and emm genotyping proved a dynamic change in their distribution in 2006 compared to the results of 2004. Erythromycin and clindamycin resistance remained low as in 2004, whereas ofloxacin resistance increased slightly. M and cMLSB phenotypes were equivalent in 2006, whereas cMLSB was predominant in 2004.

A Decrease in Erythromycin Resistance Rate of Streptococcus pyogenes in 2004 in Jinju / 대한임상미생물학회지

BACKGROUND: The erythromycin (EM) resistance rates and emm genotypes of Streptococcus pyogenes could vary by geographical location and study period. The purpose of this study, involving a large number of children, was to determine EM resistance rate and its resistance mechanism of S. pyogenes, and to compare these results with those of previous studies performed at the same area. METHODS: Throat cultures were taken from 2,351 healthy children of four elementary schools from October through December, 2004 in Jinju. A total of 328 strains of S. pyogenes were isolated. Antimicrobial susceptibility test was performed by the agar dilution method against six antimicrobial agents. The phenotypes of EM resistance were evaluated by the double-disk diffusion test and the frequency of ermB and mefA genes was determined by polymerase chain reaction. RESULTS: Resistance rates of S. pyogenes to EM, clindamycin and tetracycline were 9.8%, 8.8% and 18.3%, respectively. Almost all isolates were susceptible to ofloxacin, levofloxacin and chloramphenicol. Constitutive resistance (CR) was observed in 87.5%, M phenotype in 9.4%, and inducible resistance only in 3.1%. The ermB and mefA genes were present in 90.6% and 9.4% of the isolates, respectively. CONCLUSION: The resistance rate to EM of S. pyogenes was 9.8% in 2004, which was a large drop from the 51% shown in 2002. CR with the ermB gene was predominant, suggesting that most of the EM resistant isolates have a high level of resistance.

Clonality Analysis Using Pulsed-Field Gel Electrophoresis of Erythromycin Resistant Group A Streptococci / 대한임상미생물학회지

BACKGROUND: Antibiotic resistance of group A streptococci (GAS) is increasing nationwide. Pulsed-field gel electrophoresis (PFGE) is useful for investigating genetic relationship among outbreaks of bacterial infection. Erythromycin (EM) resistance is mediated by either ermB, ermTR, or mefA gene.The emm gene encodes M protein which is the most important virulence factor of GAS. METHODS: The clonal relationship among 56 EM resistant GAS isolated from the children with acute pharyngitis in Jinju was investigated by analysis of chromosomal DNA restriction pattern with SmaI enzyme. The ermB and mefA genes were amplified and emm genotype was identified with PCR and sequencing. Their relationship with PFGE pattern was investigated. RESULTS: The emm genotyes were identified as 2, 3, 12, 18, and 75. Mostly emm12 had ermB gene, while emm 3, 18 and 75 had mefA resistance gene. All strains with mefA gene were not restricted with SmaI. The emm12 strains showed 5 different PFGE patterns. CONCLUSIONS: The emm genotypes were closely related with resistance genes. Analysis of macrorestriction fragment patterns by PFGE showed that EM resistant GAS were polyclonal at least in Jinju. GAS strains with mefA gene were not restricted with SmaI suggesting mefA gene might inhibit chromosomal digestion with SmaI.

Analysis of Phenotypic and Genotypic Distribution of Erythromycin and Clindamycin Resistance of Group A Streptococci Isolated from Acute Pharyngitis / 대한진단검사의학회지

BACKGROUND: Erythromycin (EM) or other macrolides have been used commonly for the treatment of bacterial pharyngitis. Recently, however, EM-resistant group A streptococci (GAS) are being reported with increasing frequency. The phenotypic expression of macrolide resistance is classified as constitutive, inducible, and M. EM resistance is mediated by ermB, ermTR, or mefA genes. The emm gene encoding M protein has variable sequences at 5'end terminus. METHODS: GAS was isolated from patients with acute pharyngitis at a local clinic in Jinju from November 2001 to May 2002. Antimicrobial susceptibility testing was performed using the disk diffusion method. The phenotypes of EM and clindamycin (CC) resistance were evaluated, and the frequency of ermB and mefA genes was determined by PCR. The emm genotype was identified with PCR and sequencing. RESULTS: A total of 125 strains of group A streptococci was isolated. The resistance rate to EM and CC was 44.8% and 19.2%, respectively. Constitutive resistance was observed in 42.1%, M phenotype in 57.9%, but inducible resistance was not seen. The ermB and mefA genes were positive in 39.3% and 58.9%, respectively. Most emm12 strains showed constitutive resistance, while emm18 and emm75 showed M phenotype. CONCLUSIONS: The EM and CC resistance rates of group A streptococci isolated from acute pharyngitis were remarkably high compared to the previous reports. M phenotype was more common than constitutive resistance in acute pharyngitis. The resistance pattern was variable according to the emm types, suggesting an association between the emm gene and resistant genes.

Antibiotic Susceptibility of Streptococcus pyogenes and Association of Ery-thromycin Resistance Phenotype with Resistance to Tetracycline / 대한진단검사의학회지

BACKGROUND: Streptococcus pyogenes is the most common bacterial cause of acute pharyngitis in children. The resistance rate and phenotype distribution of S. pyogenes could be different by geo-graphical locations and study periods. The purpose of this study was to determine the minimal inhibitory concentration (MIC), resistance rate to antimicrobial agents, and association of erythromycin (EM) resistance phenotype with resistance to tetracycline (TC) among S. pyogenes isolated in Jinju, Korea. METHODS: A total of 223 isolates of S. pyogenes were obtained from pediatric pharyngitis patients and asymptomatic carriers during the period from November 2001 to May 2002. Antibiotic susceptibility test was performed by the agar dilution and the disk diffusion methods against eight antimicro-bial agents. The phenotypes of EM resistance were determined by the double-disk diffusion test. RESULTS: Resistance rates of S. pyogenes to EM, clindamycin (CC), and TC were 48.9%, 22.0% and 29.6%, respectively. MIC(50) and MIC(90) were 0.25 mg/L and > or =256 mg/L of EM, or =256 mg/L of CC, and < or =0.5 mg/L and 64 mg/L of TC respectively. Almost all isolates were suscep-tible to penicillin, ampicillin, ofloxacin, levofloxacin and chloramphenicol. The M phenotype (55.0%) was slightly more common than the constitutive resistance (45.0%); the inducible resistance pheno-type was not detected. All strains of constitutive resistance phenotype were highly resistant to TC (MIC higher than 32 mg/L), while only 3.3% of M phenotype strains was resistant to TC. CONCLUSIONS: Almost all S. pyogenes isolated in the Jinju area were susceptible to penicillin, ampi-cillin, ofloxacin, levofloxacin and chloramphenicol, but resistance rates of S. pyogenes to EM, CC and TC were relatively high. This study showed that the EM phenotypes are associated with resistance to TC.

Macrolide Resistance in beta-Hemolytic Streptococci: Changes after the Implementation of the Separation of Prescribing and Dispensing of Medications Policy in Korea

This study evaluated the antimicrobial susceptibilities and macrolide resistance mechanisms of beta-hemolytic streptococci (BHS), and an additional objective was to assess the effects of 'the separation of prescribing and dispensing (SPD) of medications' on bacterial resistance rate and distribution of phenotypes and genotypes of erythromycin-resistant BHS by comparing the antimicrobial susceptibility data before (1990- 2000) and after the implementation of SPD at one tertiary care hospital in South Korea. Between the period of January 2001 and December 2002, the minimal inhibitory concentrations of six antimicrobials were determined for 249 clinical isolates of BHS. Resistance mechanisms of erythromycin-resistant (intermediate and resistant) isolates were studied by using the double disk test and PCR. Overall, the resistance rates to tetracycline, erythromycin, and clindamycin were 75.5%, 32.9%, and 32.5%, respectively. Sixty-seven (81.7%) of 82 erythromycin- resistant isolates expressed constitutive resistance to macrolide- lincosamide-streptogramin B antibiotics (a constitutive MLSB phenotype) ; 11 isolates (13.4%) expressed an M phenotype; and four isolates (4.9%) had an inducible MLSB resistance phenotype. erm (A) was found in isolates with constitutive/ inducible MLSB phenotypes, erm (B) with the constitutive/ inducible MLSB phenotype, and mef (A) with the M phenotype. We found that resistance rates to erythromycin and clindamycin among S. agalactiae, S. pyogenes, and group C streptococci isolates were still high after the implementation of the SPD policy in Korea, and that the constitutive MLSB resistance phenotype was dominant among erythromycin- resistant BHS in this Korean hospital.

Antibiotic Resistance and Its Mechanism of Group A Streptococci in School Children of Jinju / 대한임상미생물학회지

BACKGROUND: Group A streptococci (GAS) is the most common cause of bacterial pharyngitis. Recently, a high frequency of resistance to erythromycin (EM), the drug of choice for penicillin-allergic patients, has been reported, especially in countries where antibiotics are overused. Resistance is classified as constitutive, inducible, or M according to the sensitivity results with EM and clindamycin (CC). These EM resistance phenotype is attributable to the erm , ermTR, and mefA genes, respectively. Although EM resistance of GAS is a serious problem in our country, there are very few reports regarding to its mechanism. METHODS: GAS were isolated from elementary school children of Jinju in 2002. Antibiotic sensitivity testing by disk diffusion was performed against tetracycline (TC), ofloxacin, EM and CC, and the results were compared to the previous one in 1995 at the same area. The phenotypes of EM resistance were evaluated, and the frequency of ermB and mefA genes was determined by PCR. The resistance pattern was analyzed by each emm genotype. RESULTS: The resistance rate to EM and CC was 51% and 34%, respectively, which is significantly higher than the rate of 25% and 9% recorded in 1995. Constitutive resistance was seen in 64% of the EM-resistant strains, the M phenotype in 34%, and inducible resistance in only 2%, compared to 38% of constitutive resistance and 62% of M phenotype in 1995. The ermB and mefA genes were present in 64% and 34% of strains, respectively. Most (88%) of the emm12 strains showed constitutive resistance, while emm18 and emm75 showed M phenotype. The organisms with most of the other emm genotypes were susceptible to EM. CONCLUSION: The EM and CC resistance rate had increased more than twofold. Constitutive resistance was twice as common as the M phenotype, whereas the mefA gene was more common in 1995. The resistance pattern was variable according to emm type, which suggests an association between the emm and resistance genes. Continuous microbiologic and epidemiological surveillance should be conducted and the seriousness of antibiotic resistance should be underscored in our community.

Antimicrobial Susceptibility of beta-emolytic Streptococci Isolated during the Period of 1999 / 대한임상병리학회지

BACKGROUND: Erythromycin is currently recommended as an alternative antibiotic for treatment of streptococcal infections in patients allergic to penicillins. Less than 5% of the group A streptococci are known as resistant to erythromycin but the resistance pattern differs among time and region. The purpose of this study was to determine the antimicrobial susceptibility of beta-emolytic streptococcal strains isolated during 1999 in Wonju. METHODS: A total of 107 beta-emolytic streptococci were isolates from the Wonju Christian Hospital during 1999. The susceptibility to penicillin, erythromycin, tetracycline, vancomycin, ceftriaxone, chloramphenicol, and clindamycin was tested with agar dilution method. RESULTS: No beta-emolytic streptococci strain was resistant to penicillin, ceftriaxone and vancomycin. Among beta-emolytic streptococci strains, 20-1%, 18-0% and 14-7% were resistant to tetracycline, erythromycin and clindamycin, respectively. CONCLUSIONS: It appears prudent that active surveillance of the beta-emolytic streptococci for antibiotic resistance be implemented since there are no currently effective vaccines or other methods for controlling the spread of infections due to these virulent organisms.

Antimicrobial Susceptibility of beta-emolytic Streptococci Isolated during the Period of 1999 / 대한임상병리학회지

BACKGROUND: Erythromycin is currently recommended as an alternative antibiotic for treatment of streptococcal infections in patients allergic to penicillins. Less than 5% of the group A streptococci are known as resistant to erythromycin but the resistance pattern differs among time and region. The purpose of this study was to determine the antimicrobial susceptibility of beta-emolytic streptococcal strains isolated during 1999 in Wonju. METHODS: A total of 107 beta-emolytic streptococci were isolates from the Wonju Christian Hospital during 1999. The susceptibility to penicillin, erythromycin, tetracycline, vancomycin, ceftriaxone, chloramphenicol, and clindamycin was tested with agar dilution method. RESULTS: No beta-emolytic streptococci strain was resistant to penicillin, ceftriaxone and vancomycin. Among beta-emolytic streptococci strains, 20-1%, 18-0% and 14-7% were resistant to tetracycline, erythromycin and clindamycin, respectively. CONCLUSIONS: It appears prudent that active surveillance of the beta-emolytic streptococci for antibiotic resistance be implemented since there are no currently effective vaccines or other methods for controlling the spread of infections due to these virulent organisms.

Erythromycin Resistance Phenotype of Streptococcus pyogenes / 대한임상미생물학회지

BACKGROUND: The erythromycin-resistance rate and phenotype distribution of Streptococcus propenes are quite different by geographical variation and study period. The aim of the present study was to determine the evolution of resistance to erythromycin and the frequency of erythromycin resistance phenotype of S. pyogenes isolated from Wonju Christian Hospital. METHODS: The minimal inhibitory concentrations (MICs) of erythromycin and clindamycin for 94 S. pyogenes isolated from clinical specimens between 1990 to 1998 were investigated. Double disk test of erythromycin (78microgram) and clindamycin (25microgram) were performed for 15 isolates of erythromycin resistant S. pyogenes to evaluate the erythromycin resistance phenotype. RESULTS: The resistance rates of 94 isolates of S. pyogenes were 16%(15/94) to erythromycin and 4%(4/94) to clindamycin. The frequency of erythromycin resistance phenotype in decreasing order were M phenotype (47%), inducible resistance phenotype (40%), and constitutive resistance phenotype (13%). Erythromycin-resistant S. pyogenes did not exist until 1993, but was isolated since 1994, and ranged from 14.0% to 24.0% during the period of 1994-1998. CONCLUSIONS: Our finding documents the emergence of high resistance rates to erythromycin in S. pyogenes at Wonju area since 1994. The M phenotype (47%) and inducible resistance phenotype (40%) account for the majority of erythromycin-resistant S. pyogenes.

Detection of ermAM Gene and mefA Gene in Erythromycin-resistant Streptococcus Pyogenes / 감염

BACKGROUND: The mechanism of erythromycin resistance of Streptococcus pyogenes results from target modification or active efflux. The purpose of this study was to determine the positive rate of ermAM gene modifying 23S rRNA and that of mefA gene related with efflux for erythromycin-resistant S. pyogenes. METHODS: The minimal inhibitory concentrations (MICs) of erythromycin, azithromycin, clarithromycin, and clindamycin against S. pyogenes were tested by agar dilution method. ermAM and mefA genes were amplified by polymerase chain reaction (PCR) for 32 strains of erythromycin-resistant S. pyogenes. RESULTS: Among the 32 erythromycin-resistant S. pyogenes strains, 20 (62.5%) strains were positive for ermAM gene and 10 (31.1%) for mefA gene. Eighteen (90.0%) out of 20 strains with ermAM gene showed high-level erythromycin resistance (MIC> OR =64 microgram/mL), while all ten strains with mefA gene had low-level erythromycin resistance (MIC< OR =16 microgram/mL). CONCLUSION: Two-thirds of the S. pyogenes strains acquired erythromycin resistance by modification of target site, while the others by active efflux. Each mechanism of resistance is closely associated with range of MICs of erythromycin.

Antimicrobial Resistance and Serotypes in the Clinical Isolates of Group B Streptococci / 대한임상미생물학회지

BACKGROUND: This study is designed to provide data on the trend of resistance by year of isolation in the clinical isolates of group B streptococci(GBS) during recent eight years and to elucidate the relationship between serotypes and antimicrobial resistance patterns. METHODS: The minimal inhibitory concentrations (MIC) of seven antimicrobial agents and serotypes for 150 strains of GBS isolated from clinical specimens between 1990 and 1997 were investigated. RESULTS: The resistance rate of 150 clinical isolates of GBS were 20.0% to clindamycin, 16.0% to erythromycin, 4.0% to chloramphenicol, and 95.3% to tetracycline. None was resistant to penicillin, ceftriaxone, or vancomycin. Of the 24 isolates resistant to erythromycin, 20 (83.3%) were resistant to clindamycin. Resistance rates of erythromycin according to serotypes in decreasing order were 69.2% (V), 23.2% (III), and 3.5% (Ib). All serotypes Ia and II were susceptible to erythromycin and clindamycin. CONCLUSIONS: Striking emergence of resistant strains to erythromycin and clindamycin in our clinical isolates of GBS was mainly due to sudden increase of serotype V and III which shows multi-drug resistance phenotype.