Background and Objectives: Staphylococcus aureus is an important cause of nosocomial and community-acquired infections in every region of the world. Clindamycin is one of the alternative agents used to treat S. aureus infections and accurate identification of clindamycin resistance is important to prevent therapeutic failure. Unfortunately, inducible clindamycin resistance is not detected by standard susceptibility tests. This study aimed to determine the prevalence of the macrolides-lincosamides-streptogramins B (MLSB) resistance in S. aureus isolated in four university hospitals in Tehran, Iran.Material & Methods: Two hundreds and forty-four non-duplicate clinical isolates of S. aureus [133 methicillin resistant S. aureus (MRSA) and 111 methicillin susceptible (MSSA) S. aureus] were collected in 2008. Antimicrobial susceptibilities were determined by the D-test.Results: Altogether, 68% and 61.1% of isolates were resistant to erythromycin and clindamycin, respectively; with higher resistance in MRSA isolates compared to MSSA isolates. The constitutive MLSB (cMLSB) resistance phenotype was recognized in 61.1%, while 5.3% had shown inducible MLSB (iMLSB) resistance phenotype. Constitutive MLSB resistance phenotype predominated over inducible MLSB resistance phenotype and susceptible phenotype (83.9, 9.3 and 6.8%, respectively) among the MRSA isolates, whereas susceptible phenotype predominated over constitutive MLSB resistance phenotype and inducible MLSB resistance phenotype (62.6, 31.3 and 2%, respectively) among the MSSA isolates.Conclusion: Considering the higher prevalence of clindamycin resistance in MRSA isolates compared MSSA isolates, routine D-test of MRSA isolates is strongly recommended to prevent treatment failure.

Background: Development of drug resistance to Staphylococcus aureus (S. aureus) has led to the use of older antibiotics such as macrolide-lincosamide-streptogramin B (MLSB) for the treatment of infections. MLSB resistance can be caused by several mechanisms, however, one of the predominant reasons is target modification mediated by erm genes. The objective of this study is to determine the prevalence of erm genes and the frequency of constitutive MLSB (cMLSB), inducible MLSB (iMLSB), and MS phenotypes using D-test and polymerase chain reaction (PCR) methods. Methods: D-test was performed on 110 clinical specimens of S. aureus collected from Kashani and Hajar Hospitals in Shahrkord from October 2014 to May 2015. After sampling, DNA extraction was performed by simple boiling method and, in order to detect erm genes, multiplex PCR was carried out on erythromycin resistant isolates using specific primers. Results: The result of this study revealed that among 110 S. aureus isolates examined, 35 (31. 8%) were MRSA and frequency of cMLSB, iMLSB, and MS resistant phenotypes were 22 (20%), 9 (8. 2%), and 2 (1. 8%), respectively. The genes ermA, ermB, and ermC were detected in 27 (24. 5%), 28 (25. 4%), and 26 (23. 6%) isolates. Conclusion: This study demonstrated that cMLSB was the most common phenotype among isolated S. aureus. Moreover, another interesting point to notice in our study was the high frequency of the ermB gene in iMLSB resistant phenotypes.

Background and Objectives: Macrolide, lincosamide and streptogramin type B (MLSB) antibiotics are important in the treatment of Staphylococcus aureus infections and existence of isolates with ability to resist against MLSB antibiotics is worrisome.Materials and Methods: In this cross sectional study, 101 S. aureus isolates were collected from patients of five selected hospitals in Tehran over a period of five months. Disk diffusion tests and differentiation between constitutive and inducible resistances were carried out by D-test. The presence of mecA, msrA, ermA and ermC genes were detected using PCR or multiplex PCR.Results: Out of 101 S. aureus isolates, 58 (57.4%) were methicillin resistant and 57 (56.4%) expressed resistance to erythromycin. The prevalence of constitutive MLSB (cMLSB), inducible MLSB (iMLSB) and MS (Negative) phenotype in all erythromycin resistant isolates were 71.9, 26.3 and 1.7%, respectively. Out of all the erythromycin resistant isolates, 57.8% harbored both ermA and ermC genes which possessed constitutive resistance. 8.7% of the isolates contained ermA gene alone which possessed inducible resistance with D phenotype and 5.2% of isolates just contained ermC gene which had inducible resistance with D+ phenotype. msrA gene was detected in 3.5% of the erythromycin resistant S. aureus isolates with constitutive resistance. None of the genes were detected among MS phenotypes.Conclusion: In this study, most of S. aureus isolates carried both ermA and ermC genes and there was a significant relationship (P value ≤0.05) between different resistance phenotypes and erm genes.

Background and Objectives: Macrolide, lincosamide and streptogramin B (MLSB) are noteworthy antibiotics for the treatment of Staphylococcus aureus infections. The purpose of this study, was to determine the phenotypic and genotypic characterization of macrolide resistance, among S. aureus, isolated from clinical samples and nasal swabs. Materials and Methods: Totally, 162 non-duplicate S. aureus isolates were collected from clinical samples and nasal swabs, from patients and healthcare workers (HCWs), between March 2016 and September 2016, at four teaching hospitals in Isfahan. The antibiotic resistance profile was determined using disk diffusion test and the presence of resistance genes was detected, using PCR. Results: Of 162 S. aureus isolates, 43. 8% (71/162) and 34% (55/162) isolates were erythromycin-resistant and methicillin-resistant S. aureus (MRSA), respectively. The prevalence of constitutive MLSB (cMLSB), inducible MLSB (iMLSB), macrolide-streptogramin B-resistant (MSB) and lincosamide-streptogramin-A resistance (LSA) phenotype was 32%, 6%, 6% and 2%, respectively. The most common erythromycin resistance genes, in S. aureus isolates were ermC (35. 2%), followed by ermA (20. 4%) and msrA (17. 3%). Meanwhile, msrA was detected in 43. 6% of MRSA isolates. The frequency of coexistence of ermA+ermC+msrA, in S. aureus isolates was 7% and it was only detected in MRSA isolates. Conclusion: In the current study, cMLSB phenotype was the most common erythromycin resistance pattern and ermC was the most prevalent gene in erythromycin-resistant isolates. The results revealed that the various mechanisms of erythromycin resistance are expanding in Isfahan.

Background: Antibiotic resistance among Staphylococcus aureus is of great concern worldwide. This resistance is further complicated by the ability of S. aureus to confer cross-resistance to other antibiotics due to the presence of resistance genes, such as erythromycin resistance methylase (erm) genes, which render the bacterium resistant to macrolide-lincosamide-streptogramin B (MLSB) antibiotics. Resistance to these antibiotics can lead to therapeutic failure, resulting in significant morbidity and mortality in patients with S. aureus infections. Objectives: This study was performed to examine the distribution of MLSB-resistant strains of methicillin-susceptible S. aureus (MSSA), which were obtained from hospitalized patients and normal healthy individuals (carriers) using phenotypic methods, such as the double-disk diffusion (D-test) and the genotypic method by polymerase chain reaction (PCR). Methods: A total of 183 nonduplicative MSSA isolates obtained from hospitalized patients (133) and carriers (50) in our previous studies were randomly selected for the D-test. The guidelines of the Clinical and Laboratory Standards Institute (CLSI) were used for the interpretation of the results of this test. The detection of ermA, ermB, ermC and msrA genes by PCR was performed for isolates that had positive D-test results and that were resistant to erythromycin. Results: Of the 183 MSSA isolates, 97. 2% and 98. 4% were highly susceptible to erythromycin and clindamycin, respectively. MSLB resistance was detected in four isolates (2. 2%). Of the 133 MSSA isolated from hospitalized patients, only 3. 0% (4/133) and 2. 3% (3/133) exhibited resistance to erythromycin and clindamycin, respectively. With regard to the MLSB resistance phenotypes, only 1. 6% and 0. 6% exhibited inducible MLSB (iMLSB) and MS phenotypes, respectively. The ermC gene was detected in all three iMLSB phenotypes, and the msrA gene was detected in the MS phenotype. Surprisingly, all MSSA isolates (100%) from carriers exhibited extremely high susceptibility to both antibiotics. Conclusions: The prevalence rates of iMLSB MSSA isolates vary according to geographical locations and the local antibiotic policy. The low prevalence rate of iMLSB MSSA isolates could probably be related to the judicious use of antibiotics for treating S. aureus infections in our studied population. Nonetheless, continuous antibiotic surveillance is still necessary to control any emergence of resistance isolates so that targeted therapy and effective control can be implemented accordingly.

Background: Documented streptococcal resistance to erythromycin has recently been raised. The aim of this study is to identify the molecular mechanism of erythromycin resistance among group B Streptococcus (GBS) strains and to correlate with the clinical origin of strains. Materials and Methods: A total number of 134 colonizing (n = 36), invasive (n = 36), noninvasive (n = 46), and asymptomatic (n = 16) GBS isolates were characterized by the detection of dltS gene, capsular serotyping, antibiotic susceptibility profiles using disc diffusion method, and screening of the ermB, ermTR, and mefA resistance genes. Results: The distribution of capsular serotypes was as follow: serotype III (24. 6%), Ia (21. 6%), V (17. 9%), Ib (14. 9%), II (8. 9%), IV (8. 9%), VI (1. 5%), and VII (1. 5%). From 134 GBS isolates, 51 (38%) isolates were resistant to erythromycin. The constitutive macrolide lincosamide streptogrmin B (MLSB) was the most common resistance phenotype (62. 7%), followed by inducible MLSB (27. 4%) and M phenotype (9. 8%). Erythromycin resistance rate was higher among asymptomatic GBS strains (13/16, 81. 2%). Serotype III was the most prevalent type among resistant isolates (41. 1%). The ermB gene highly distributed among resistant strains (64. 7%), followed by ermTR (21. 5%) and mefA (9. 8%). The ermB gene was related to constitutive MLSB phenotype (84. 3%, P < 0. 05) and serotypes III (61. 9%), Ib (87. 5%), and V (83. 3%). All M phenotype strains harbored mefA gene and were in association with serotype Ia (90%). Conclusion: The current study suggests that ribosomal modification with erm genes is the main mechanism of erythromycin resistance. Because of relatively high prevalence of erythromycin resistance, double disc test highly recommended for GBS disease treatment and intrapartum prophylaxis among penicillin intolerant patients in our region.

Background: Staphylococcus aureusis the most common agent of nosocomial infections. Macrolide Lincosamide-Streptogramin B (MLS B) antibiotics are the therapeutic choices for treatment of infections due to methicillin resistant S. aureus(MRSA) isolates. The most frequent mechanism for inducible resistance in S. aureusis modification in target site by erm( erythromycin ribosome methylase) genes. Objectives: The aim of this research was to determine inducible MLSB (iMLS B) and detection the ermgenes in clinical samples of S. aureusisolated from hospitalized patients in the Imam Reza hospital of Kermanshah, west of Iran. Methods: This study performed on 126 samples of S. aureus. Identification of isolates were performed using microbiological and biochemical procedures. Inducible resistance to clindamycin was tested by D-test. The prevalence of genes, such as femB, mecA, ermAand ermBwas assessed by polymerase chain reaction (PCR). Results: Eighty-three cases (65.9%) of isolates were methicillin resistant S. aureus(MRSA). The resistance rate against erythromycin and clindamycin was 67.4% and 52.2%, respectively. Totally, 49 cases (38.9%) of isolates were resistant to both erythromycin and clindamycin indicating constitutive MLSB phenotype (cMLS B); 20 cases (15.9%) isolates showed positive D test indicating inducible MLSB phenotype (iMLS B), while 16 cases (12.7%) were negative for D test indicating MS phenotype. Among 20 cases with iMLS Bphenotype, ermCand ermAgenes were showed in 7 cases (35%) and 4 cases (20%) isolates, respectively. The ermBgene is not detected in any cases and 9 cases (45%) isolates did not have any ermgenes. Conclusions: In general, findings of this study showed high frequency of resistance to clindamycin and erythromycin among S. aureusisolates and cMLS Bto be the most pattern phenotype and ermCgene is the most common gene in iMLS Bphenotype. Because variation of antimicrobial resistance pattern in geographic regions obtaining local results is useful for detecting and more appropriate control of nosocomial infection due to S. aureusisolates.