Constitutive Macrolide-lincosamide-streptogramin B Research Articles

Inducible Clindamycin Resistance in Staphylococcus aureus Isolates in Kermanshah, Iran

Background: Staphylococcus aureus is the most common agent of nosocomial infections. Macrolide Lincosamide-Streptogramin B (MLSB) 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. aureus is modification in target site by erm (erythromycin ribosome methylase) genes. Objectives: The aim of this research was to determine inducible MLSB (iMLSB) and detection the erm genes in clinical samples of S. aureus isolated 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, ermA and ermB was 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 (cMLSB); 20 cases (15.9%) isolates showed positive D test indicating inducible MLSB phenotype (iMLSB), while 16 cases (12.7%) were negative for D test indicating MS phenotype. Among 20 cases with iMLSB phenotype, ermC and ermA genes were showed in 7 cases (35%) and 4 cases (20%) isolates, respectively. The ermB gene is not detected in any cases and 9 cases (45%) isolates did not have any erm genes. Conclusions: In general, findings of this study showed high frequency of resistance to clindamycin and erythromycin among S. aureus isolates and cMLSB to be the most pattern phenotype and ermC gene is the most common gene in iMLSB phenotype. 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. aureus isolates.

The antimicrobial activity of cethromycin against Staphylococcus aureus and compared with erythromycin and telithromycin

BackgroundThis study aims to explore the antibacterial activity of cethromycin against Staphylococcus aureus (S. aureus), and its relationship with multilocus sequence typing (MLST), erythromycin ribosomal methylase (erm) genes and macrolide-lincosamide-streptogramin B (MLSB) phenotypes of S. aureus.ResultsThe minimum inhibitory concentrations (MICs) of cethromycin against 245 S. aureus clinical isolates ranged from 0.03125 to ≥ 8 mg/L, with the resistance of 38.8% in 121 methicillin-resistant S. aureus (MRSA). This study also found that cethromycin had strong antibacterial activity against S. aureus, with the MIC ≤ 0.5 mg/L in 55.4% of MRSA and 60.5% of methicillin-sensitive S. aureus (MSSA), respectively. The main MLSTs of 121 MRSA were ST239 and ST59, and the resistance of ST239 isolates to cethromycin was higher than that in ST59 isolates (P = 0.034). The top five MLSTs of 124 MSSA were ST7, ST59, ST398, ST88 and ST120, but there was no difference in the resistance of MSSA to cethromycin between these STs. The resistance of ermA isolates to cethromycin was higher than that of ermB or ermC isolates in MRSA (P = 0.016 and 0.041, respectively), but the resistance of ermB or ermC isolates to cethromycin was higher than that of ermA isolates in MSSA (P = 0.019 and 0.026, respectively). The resistance of constitutive MLSB (cMLSB) phenotype isolates to cethromycin was higher than that of inducible MLSB (iMLSB) phenotype isolates in MRSA (P < 0.001) or MSSA (P = 0.036). The ermA, ermB and ermC genes was mainly found in ST239, ST59 and ST1 isolates in MRSA, respectively. Among the MSSA, the ermC gene was more detected in ST7, ST88 and ST120 isolates, but more ermB genes were detected in ST59 and ST398 isolates. The cMLSB phenotype was more common in ST239 and ST59 isolates of MRSA, and was more frequently detected in ST59, ST398, and ST120 isolates of MSSA.ConclusionCethromycin had strong antibacterial activity against S. aureus. The resistance of MRSA to cethromycin may had some clonal aggregation in ST239. The resistance of S. aureus carrying various erm genes or MLSB phenotypes to cethromycin was different.

Inhibition of Erythromycin and Erythromycin-Induced Resistance among Staphylococcus aureus Clinical Isolates.

The increasing incidence of erythromycin and erythromycin-induced resistance to clindamycin among Staphylococcus aureus (S. aureus) is a serious problem. Patients infected with inducible resistance phenotypes may fail to respond to clindamycin. This study aimed to identify the prevalence of erythromycin and erythromycin-induced resistance and assess for potential inhibitors. A total of 99 isolates were purified from various clinical sources. Phenotypic detection of macrolide-lincosamide-streptogramin B (MLSB)-resistance phenotypes was performed by D-test. MLSB-resistance genes were identified using PCR. Different compounds were tested for their effects on erythromycin and inducible clindamycin resistance by broth microdilution and checkerboard microdilution methods. The obtained data were evaluated using docking analysis. Ninety-one isolates were S. aureus. The prevalence of constitutive MLSB, inducible MLSB, and macrolide-streptogramin (MS) phenotypes was 39.6%, 14.3%, and 2.2%, respectively. Genes including ermC, ermA, ermB, msrA, msrB, lnuA, and mphC were found in 82.6%, 5.8%, 7.7%, 3.8%, 3.8%, 13.5%, and 3.8% of isolates, respectively. Erythromycin resistance was significantly reduced by doxorubicin, neomycin, and omeprazole. Quinine, ketoprofen, and fosfomycin combated and reversed erythromycin/clindamycin-induced resistance. This study highlighted the significance of managing antibiotic resistance and overcoming clindamycin treatment failure. Doxorubicin, neomycin, omeprazole, quinine, ketoprofen, and fosfomycin could be potential inhibitors of erythromycin and inducible clindamycin resistance.

Phenotypic and genotypic characterization of macrolide resistance in Staphylococcus aureus isolates from wound infection

Microbiologists are increasingly concerned about the rise in S. aureus MLSB (macrolide, lincosamide, streptogramin B) drug resistance. Clindamycin has been effective in treating infections by S. aureus, and the variations in clindamycin sensitivity patterns cause treatment to fail. Inducible clindamycin resistance in S. aureus is expressed via erythromycin ribosome methylase genes. In the current study, 25 S. aureus isolates were identified by conventional chemical tests and the Vitek®2 system. Specific primers were used for the amplification of Macrolide genes by PCR. Among 25 S. aureus isolates, 23(92%) isolates were methicillin resistant and 2(8%) isolates were methicilin sensitive. The 5(20%) isolates showed resistance to Erythromycin and sensitivity to Clindamycin with a positive D test which was identified as inducible MLSB, while 2(8%) isolates showed resistance criteria for both Erythromycin and Clindamycin which identity as a constitutive MLSB and 18(92%) isolates were given the sensitivity for both Erythromycin and Clindamycin. The erm resistance genes (ermA, ermB, ermC, ermF, and ermG) were detected in 5(20%), 17(68%), 25(100%), 24(96%),11(44%) respectively. The D-test, and Vitek ®2 system should be routinely done to avoid treatment failure due to clindamycin resistance.

Inducible Clindamycin Resistance and Biofilm Production among Staphylococci Isolated from Tertiary Care Hospitals in Nepal.

Resistance to antibiotics, biofilm formation and the presence of virulence factors play important roles in increased mortality associated with infection by staphylococci. The macrolide lincosamide streptogramin B (MLSB) family of antibiotics is commonly used to treat infections by methicillin-resistant isolates. Clinical failure of clindamycin therapy has been reported due to multiple mechanisms that confer resistance to MLSB. This study aims to find the incidence of different phenotypes of MLSB resistance and biofilm production among staphylococci. A total of 375 staphylococci were isolated from different clinical samples, received from two tertiary care hospitals in Nepal. Methicillin resistance was detected by cefoxitin disc diffusion method and inducible clindamycin resistance by D test, according to CLSI guidelines. Biofilm formation was detected by the tissue culture plate method and PCR was used to detect ica genes. Of the total staphylococci isolates, 161 (42.9%) were Staphylococcus aureus, with 131 (81.4%) methicillin-resistant strains, and 214 (57.1%) isolates were coagulase-negative staphylococci, with 143 (66.8%) methicillin-resistant strains. The overall prevalence of constitutive MLSB (cMLSB) and inducible MLSB (iMLSB) phenotypes was 77 (20.5%) and 87 (23.2%), respectively. Both iMLSB and cMLSB phenotypes predominated in methicillin-resistant isolates. The tissue culture plate method detected biofilm formation in 174 (46.4%) isolates and ica genes in 86 (22.9%) isolates. Among biofilm producing isolates, cMLSB and iMLSB phenotypes were 35 (20.1%) and 27 (15.5%), respectively. The cMLSB and iMLSB were 11 (12.8%) and 19 (22.1%), respectively, in isolates possessing ica genes. Clindamycin resistance in the form of cMLSB and iMLSB, especially among MRSA, emphasizes the need for routine D tests to be performed in the lab.

Distribution of Macrolide-Lincosamide-Streptogramin B Antibiotics Resistance Genes in Clinical Isolates of Staphylococci.

Staphylococci are posing threat due to increasing trend of antimicrobial resistance particularly methicillin. Macrolide lincosamide streptogramin B (MLSB) family of antibiotics is commonly used to treat such infections. This study was aimed to determine the prevalence of inducible clindamycin resistance and observation of erm and msr genes among Staphylococci isolated from tertiary care hospital of Nepal during July 2017 to March 2018. Staphylococci from different clinical specimens were identified and antibiotic susceptibility profile was assessed following Kirby Bauer disc diffusion method. The double disc diffusion or D-zone test as outlined in CLSI document M100-S24 was performed to examine inducible clindamycin resistant isolates. Multiplex PCR was performed for detection of erm and msr gene in isolates using specific primers for ermA, ermB, ermC, msrA and msrB genes. Of the 60 Staphylococci isolates, 39 (65%) were S. aureus and 21 (35%) were coagulase negative Staphylococci (CNS) with 25 (64%) and 15 (71%) representing methicillin resistant S. aureus and CNS respectively. Constitutive and inducible MLSB phenotype was observed among 24 (40%) and 14 (23%) isolates respectively by D test. The most prevalent resistant gene was ermC (37%) followed by msrB (12%), ermB (10%) and msrA (10%). None of the isolates were found to possess ermA gene. The presence of constitutive and inducible MLSB as well as resistant genes among Staphylococci necessitates detection of such isolates to minimize treatment failure. The result from this study may help elucidate the predominant resistant characteristics in clinical Staphylococci isolated from tertiary care hospital of Nepal.

Nasal colonisation, antimicrobial susceptibility and genotypic pattern of Staphylococcus aureus among agricultural biotechnology students in Besut, Terengganu, east coast of Malaysia.

This study aimed to profile the antimicrobial susceptibility and presence of resistance and virulence genes of methicillin-susceptible Staphylococcus aureus (MSSA) and MRSA nasal carriage, by means of genotypic analyses, in students of a tertiary institution in the state of Terengganu, east coast of Malaysia. A total of 370 agricultural biotechnology students from Universiti Sultan Zainal Abidin in Besut, Terengganu, were enrolled in this study. Antimicrobial susceptibility profiles were evaluated by standard methods. PCR detection of resistance and virulence genes was performed on S. aureus that were methicillin-resistant, macrolide-lincosamide-streptogramin B (MLSB )-positive phenotype and/or positive for the leukocidin (pvl) gene followed by staphylococcal cassette chromosome mec (SCCmec), staphylococcal protein A (spa) and accessory gene regulator (agr) typing. One hundred and nineteen of 370 students carried S. aureus (32%); 18 of the isolates were MRSA (15%). Erythromycin resistance was detected in 20% (24/119) of which 15% (18/119) were MRSA and 5% (6/119) MSSA. Among the 24 erythromycin-resistant isolates, D-test was positive in 29% (7/24) displaying inducible MLSB , whereas the remaining 71% (17/24) showed constitutive MLSB phenotypes. Nine (7.6%) of 119 isolates were pvl positive: 44% MRSA (4/9) and 56% MSSA (5/9). Staphylococcal surface protein sasX gene was present in 92% of MRSA and 8% of MSSA isolates. The majority of MRSA isolates were agr type I (15/18; 83%). Five spa types identified with spa t037 were predominant, followed by spa types (t304 and t8696) as newly reported Malaysian MRSA in a community setting. The presence of MRSA with SCCmec of hospital-associated features and globally recognised spa types in community setting is worrisome. Furthermore, the presence of MLSB strains among multidrug-resistant (MDR) S. aureus with sasX as well as pvl-positive isolates highlights the potential risk of a community setting in facilitating the dissemination of both virulence and resistance determinants.

Healthcare-Associated Methicillin-Resistant Staphylococcus aureus: Clinical characteristics and antibiotic resistance profile with emphasis on macrolide-lincosamide-streptogramin B resistance.

Healthcare-associated methicillin-resistant Staphylococcus aureus (MRSA) is a common pathogen worldwide and its multidrug resistance is a major concern. This study aimed to determine the clinical characteristics and antibiotic susceptibility profile of healthcare-associated MRSA with emphasis on resistance to macrolide-lincosamide-streptogramin B (MLSB) phenotypes and vancomycin. This cross-sectional study was carried out between February 2014 and February 2015 across four tertiary care hospitals in Mangalore, South India. Healthcare-associated infections among 291 inpatients at these hospitals were identified according to the Centers for Disease Control and Prevention guidelines. Clinical specimens were collected based on infection type. S. aureus and MRSA isolates were identified and antibiotic susceptibility tests performed using the Kirby-Bauer disk diffusion method. The minimum inhibitory concentration of vancomycin was determined using the Agar dilution method and inducible clindamycin resistance was detected with a double-disk diffusion test (D-test). Out of 291 healthcare-associated S. aureus cases, 88 were MRSA (30.2%). Of these, 54.6% were skin and soft tissue infections. All of the isolates were susceptible to teicoplanin and linezolid. Four MRSA isolates exhibited intermediate resistance to vancomycin (4.6%). Of the MRSA strains, 10 (11.4%) were constitutive MLSB phenotypes, 31 (35.2%) were inducible MLSB phenotypes and 14 (15.9%) were macrolide-streptogramin B phenotypes. Healthcare-associated MRSA multidrug resistance was alarmingly high. In routine antibiotic susceptibility testing, a D-test should always be performed if an isolate is resistant to erythromycin but susceptible to clindamycin. Determination of the minimum inhibitory concentration of vancomycin is necessary when treating patients with MRSA infections.

Distribution of erm genes among Staphylococcus aureus isolates with inducible resistance to clindamycin in Isfahan, Iran.

Background:The rising frequency of methicillin resistant Staphylococcus aureus (MRSA) has led to an increased use of antibiotics such as macrolide, lincosamide, streptogramin B (MLSB) for the treatment of S. aureus infections. Resistance to MLSB in S. aureus is commonly encoded by erm genes, which can be constitutive MLSB (cMLSB) or inducible MLSB (iMLSB). The purpose of this study was to determine the frequency of cMLSB, iMLSB, and MS phenotypes using D-test and polymerase chain reaction (PCR) methods.Materials and Methods:A total of 215 isolates of S. aureus were collected from January 2010 to May 2012 from Al-Zahra Hospital in Isfahan. PCR was performed for detection of mecA gene on all isolates using specific primers. The frequency of MLSB-resistant isolates was determined using D-test, and then a multiplex PCR was performed for detection of ermA, ermB, and ermC genes.Results:Among 215 S. aureus isolates examined, 82 (40.9%) were MRSA, and iMLSB, cMLSB, and MS resistance phenotypes had a frequency of 9 (4.18%), 58 (26.9%), and 11 (5.1%), respectively. Among nine isolates with iMLSB resistance phenotype, four isolates contained ermC gene, two isolates ermB gene, and one isolate ermA gene. Two isolates did not have any erm gene.Conclusion:In the current study, cMLSB was the most frequent phenotype and ermC was the most common gene in iMLSB resistant phenotypes.

Clindamycin microbial resistance in clinical isolates of Staphylococcus sp. derived from blood cultures of hospitalized patients

Introduction: Infections caused by methicillin-resistant Staphylococcus aureus (MRSA) strains have become common in hospitals, and this resistance has limited patients' treatment with beta-lactam antibiotics. Clindamycin is an important therapeutic agent for MRSA infections; however, inducible macrolide-lincosamide-streptogramin B (MLSB) resistance (iMLSB) has resulted in therapeutic failures with the use of this antimicrobial, with a consequent increase in patient mortality and length of stay. Objective: This study was carried out in order to detect phenotypes of inducible and constitutive resistance to clindamycin in blood culture samples of Staphylococcus sp. from hospitalized patients. Material and methods: A hundred bacterial samples from blood cultures of adult patients were evaluated, identified by conventional phenotypic tests, and subject to determination of susceptibility and resistance profiles with cefoxitin, erythromycin, and clindamycin discs; and to phenotypic evaluation of iMLSB resistance using the D-test. The results were interpreted in accordance with the recommendations of the Clinical and Laboratory Standards Institute (CLSI) 2014. Results: In this study, 65% of 60 bacterial strains were susceptible to cefoxitin and 35%, resistant. The constitutive MLSB (cMLSB) resistance phenotype was observed in 15.56% of the methicillin-sensitive Staphylococcus aureus (MSSA) samples, 33.33% of methicillin-sensitive coagulase-negative Staphylococcus (MSCONS), 26.67% of MRSA and 20% of methicillin-resistant coagulase-negative Staphylococcus (MRCONS), while iMLSB resistance was observed only in strains susceptible to cefoxitin, corresponding to 80% in MSSA and 20% in MSCONS. Conclusion: The D-test is a key test for the constant monitoring of the inducible resistance phenotype (which may impair the effectiveness of treatment with clindamycin), minimizing potential medication errors and adverse clinical outcomes.

Molecular epidemiology and distribution of serotypes, genotypes, and antibiotic resistance genes of Streptococcus agalactiae clinical isolates from Guelma, Algeria and Marseille, France.

This study describes, for the first time, the genetic and phenotypic diversity among 93 Streptococcus agalactiae (group B Streptococcus, GBS) isolates collected from Guelma, Algeria and Marseille, France. All strains were identified by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). The molecular support of antibiotic resistance and serotyping were investigated by polymerase chain reaction (PCR). The phylogenetic lineage of each GBS isolate was determined by multilocus sequence typing (MLST) and grouped into clonal complexes (CCs) using eBURST. The isolates represented 37 sequence types (STs), 16 of which were novel, grouped into five CCs, and belonging to seven serotypes. Serotype V was the most prevalent serotype in our collection (44.1%). GBS isolates of each serotype were distributed among multiple CCs, including cps III/CC19, cps V/CC1, cps Ia/CC23, cps II/CC10, and cps III/CC17. All isolates presented susceptibility to penicillin, whereas resistance to erythromycin was detected in 40% and tetracycline in 82.2% of isolates. Of the 37 erythromycin-resistant isolates, 75.7% showed the macrolide-lincosamide-streptogramin B (MLSB)-resistant phenotype and 24.3% exhibited the macrolide (M)-resistant phenotype. Constitutive MLSB resistance (46%) mediated by the ermB gene was significantly associated with the Guelma isolates, whereas the M resistance phenotype (24.3%) mediated by the mefA/E gene dominated among the Marseille isolates and belonged to ST-23. Tetracycline resistance was predominantly due to tetM, which was detected alone (95.1%) or associated with tetO (3.7%). These results provide epidemiological data in these regions that establish a basis for monitoring increased resistance to erythromycin and also provide insight into correlations among clones, serotypes, and resistance genes.

Detection of the efflux-mediated erythromycin resistance transposon in Streptococcus pneumoniae.

BackgroundThe present analysis focuses on phenotypic and genotypic characterizations of efflux-mediated erythromycin resistance in Streptococcus pneumoniae due to an increase in macrolide resistance in S. pneumoniae worldwide.MethodsWe investigated the prevalence of efflux-mediated erythromycin resistance and its relevant genetic elements from 186 specimens of S. pneumonia isolated from clinical and normal flora from Tehran, Iran. The presence of erythromycin resistance genes was tested by PCR with two sets of primers, specific for erm(B) and mef(A/E), and their genetic elements with tetM, xis, and int genes. Isolates were typed with the BOX PCR method and tested for resistance to six antibiotics.ResultsAntibiotic susceptibility tests revealed that 100% and 47% isolates were resistant to tetracycline and erythromycin, respectively. The erythromycin and clindamycin double-disc diffusion test for macrolide-lincosamide-streptograminB (MLSB) resistance phenotype showed 74 (84%) isolates with the constitutive MLSB phenotype and the remaining with the M phenotype. BOX PCR demonstrated the presence of 7 types in pneumococci with the M phenotype. Fourteen (16%) isolates with the M phenotype harbored mef(A/E), tetM, xis, and int genes.ConclusionsThe present results suggest dissemination of polyclonal groups of S. pneumoniae with the M phenotype carrying resistance genes attributed to transposon 2009.

Inducible clindamycin resistance among clinical isolates of Staphylococcus aureus

Introduction: The resistance to antimicrobial agents among staphylococci is an increasing problem. This has led to renewed interest in the usage of macrolide-lincosamide-streptogramin B (MLSB) antibiotics to treat Staphylococcus aureus infections. Clinical failure has been reported due to multiple mechanisms that confer resistance to MLSB antibiotics. The present study was aimed to detect inducible clindamycin resistance among S. aureus isolates and to study the relationship between clindamycin and methicillin resistance. Materials and Methods: During a period of 1 year, a total of 593 S. aureus isolates from various clinical specimens were included in the study. Antimicrobial susceptibility test was done by Kirby-Bauer's disc diffusion method as per Clinical and Laboratory Standards Institute (CLSI) guidelines. For detection of inducible clindamycin resistance, D test using erythromycin and clindamycin as per CLSI guidelines was performed, and three different phenotypes were interpreted as methicillin-sensitive (MS) phenotype (D test negative), inducible MLSB (iMLSB) phenotype (D test positive), and constitutive MLSB phenotype. Results: Of the total 593 S. aureus isolates, majority were obtained from pus (31.1%) followed by blood and body fluids (27.3%). All the isolates were sensitive to vancomycin, teicoplanin, and linezolid. Out of 306 (51.7%) erythromycin resistant isolates, 280 (91.5%) were methicillin-resistant S. aureus (MRSA) and 26 (8.5%) were methicillin-sensitive S. aureus (MSSA). iMLSB phenotype in 33.3%, MS phenotype in 44.8%, and constitutive MLSB phenotype was observed in 21.9% of isolates. Inducible clindamycin resistance was almost equal among MRSA and MSSA isolates. Conclusion: D test should be included as a mandatory method in routine disc diffusion testing to detect inducible clindamycin resistance in staphylococci for the optimum treatment of patients.

Phenotypical examination of the macrolide-lincosamide-streptogramin B resistance in Staphylococcus isolates

The aim of the present study was to evaluate the phenotypic characteristics of the macrolide-lincosamide-streptogramin B (MLSB) resistance in Staphylococcus aureus and coagulase-negative staphylococci (CNS) strains isolated from various clinical samples in our hospital. The study was conducted on 516 Staphylococcus isolates isolated from various clinical samples in Microbiology Laboratory of Diyarbakir State Hospital between January, 2009 and December, 2009. After the identification of microorganisms via conventional methods and the evaluation of their methicillin resistance profile, disk approximation test was performed using erythromycin (15 μg) and clindamycin (2 μg) disks in order to determine MLSB resistance phenotypes. Of 516 Staphylococcusisolates, 208 were determined to be S. aureus and 308 were CNS. The MLSB resistance of isolates was 56.2%, whereas the resistance due to the efflux pump was determined to be 3.5%. The MLSB resistance phenotype was determined in 38% of S. aureus strains and 68.5% of CNS strains. The presence of MLSB resistance was determined to be higher in methicillin-resistant group (74.7%) compared to the methicillin-susceptible group (23.9%). While constitutive MLSB resistance (cMLSB) and inducible MLSB resistance (iMLSB) were determined in 48.9 and 19.1% of methicillin-resistant S. aureus strains, respectively, these rates were 2.6 and 10.5% for methicillin-susceptible strains, respectively. The rate of constitutive resistance was determined to be 41.5% in methicillin resistant CNS, whereas the rate of inducible resistance was determined to be 35.9%. In methicillin-susceptible CNS group, cMLSB and iMLSB resistances were determined to be 17.6 and 23%, respectively. The cMLSB phenotype was more common among methicillin-resistant S. aureus and CNS group, whereas iMLSB phenotype was more common among methicillin-susceptible S. aureus strains. In conclusion, we suggest that the determination and reporting of the presence of inducible resistance is of great importance regarding the success of therapy; therefore, it would be beneficial to use D test in routine antibiogram studies. Key words: Staphylococcus aureus, coagulase-negative staphylococci, macrolide-lincosamide-streptogramin B

Detection of various types of resistance patterns and their correlation with minimal inhibitory concentrations against clindamycin among methicillin-resistant Staphylococcus aureus isolates

Purpose: The macrolide lincosamide streptogramin B (MLSB) family of antibiotics serves as an alternative for the treatment of skin and soft tissue infections caused by methicillin-resistant Staphylococcus aureus (MRSA). However, resistance to clindamycin too has emerged, which is of two types, inducible and constitutive. Therapeutic failure is common with inducible type of clindamycin resistance. This study was done to determine the various clindamycin resistance patterns in MRSA isolates and to compare them with minimal inhibitory concentration (MIC) of clindamycin. Materials and Methods: Fifty MRSA isolates were studied by disc approximation test (D test) to detect inducible iMLSB resistance and MIC by agar dilution technique. Results: Of the 50 isolates, 34 were sensitive to both clindamycin and erythromycin. 16 isolates showed different sensitivity patterns; nine of these were positive for D zone indicating inducible iMLSB resistance, five were positive for constitutive MLSB resistance and two showed possible efflux mechanism for macrolide resistance. Out of the 34 sensitive isolates, 5 showed isolated colonies (subpopulation) inside the clindamycin-sensitive zone. When these sub-populations were tested further, two were constitutive MLSB phenotypes, two were inducible iMLSB and one was HD (hazy D zone), which is D+ with growth up to clindamycin disc (which is also considered as constitutive MLSB phenotype). Seven isolates showed an MIC of ≥4 μg/ml to clindamycin in spite of being susceptible to both erythromycin and clindamycin by Kirby Bauer disc diffusion technique. Out of these seven isolates, five were those which grew as subpopulation inside the clindamycin-sensitive zone. Conclusion: Detection of iMLSB resistance among MRSA helps to avoid treatment failure with clindamycin. Studying the subpopulation inside the clindamycin-sensitive zone raises the question of existence of hetero-resistance or some other mechanism, which needs further study.

Penicillin Susceptibility and Macrolide-Lincosamide-Streptogramin B Resistance in Group BStreptococcusIsolates from a Canadian Hospital

Intrapartum antibiotic prophylaxis (IAP) is recommended for pregnant women who test positive for group B Streptococcus (GBS) in their genitourinary tract to prevent GBS-induced neonatal sepsis. Penicillin G is used as the primary antibiotic, and clindamycin or erythromycin as the secondary, if allergies exist. Decreased susceptibility to penicillin G has occasionally been reported; however, clindamycin and erythromycin resistance is on the rise and is causing concern over the use of clindamycin and erythromycin IAP. Antibiotic resistance was characterized phenotypically using a D-Test for erythromycin and clindamycin, while an E-Test (E-strip) was used for penicillin G. GBS was isolated from vaginal-rectal swabs and serologically confirmed using Prolex (Pro-Lab Diagnostics, Canada) streptococcal grouping reagents. Susceptibility testing of isolates was performed according to the Clinical Laboratory Standards Institute guidelines. All 158 isolates were penicillin G sensitive. Inducible macrolide-lincosamide-streptogramin B (MLSB) resistance was observed in 13.9% of isolates. Constitutive MLSB resistance was observed in 12.7% of isolates. M phenotype resistance was observed in 6.3% of isolates. In total, erythromycin resistance was present in 32.9% of the GBS isolates, while clindamycin resistance was present in 26.6%. The sampled GBS population showed no sign of reduced penicillin susceptibility, with all being well under susceptible minimum inhibitory concentration values. These data are congruent with the large body of evidence showing that penicillin G remains the most reliable clinical antibiotic for IAP. Clindamycin and erythromycin resistance was higher than expected, contributing to a growing body of evidence that suggests the re-evaluation of clindamycin and erythromycin IAP is warranted.

Phenotypic characterization of nosocomial isolates of Staphylococcus aureus with reference to MRSA

Apart from being a major cause of mortality, nosocomial infections due to Staphylococcus aureus have been imposing a burden on patients, hospitals and health care systems. The present study was designed to determine the prevalence of methicillin resistant S. aureus (MRSA) among nosocomial isolates along with their phenotypic characterization. MRSA and methicillin sensitive S. aureus (MSSA) were determined by performing four different tests viz: disc diffusion, oxacillin screen agar test, MRSA latex agglutination test, and MIC of oxacillin by E test. Of the 149 S. aureus nosocomial isolates, 44.9% were MRSA, which included 82.1% of homogeneous MRSA and 17.9% of heterogeneous MRSA. Association of MRSA infection was found to be significantly higher in skin and lower respiratory tract infections. Of the MRSA isolates, 65 were multiresistant oxacillin resistant Staphylococcus aureus (MORSA) and 2 were nonmultiresistant oxacillin resistant Staphylococcus aureus (NORSA). D tests performed on 136 isolates showed that Inducible macrolide-lincosamide-streptogramin B (MLSB) and constitutive MLSB resistance were found to be associated with MRSA. On the contrary, susceptibility to both erythromycin and clindamycin was found to be associated with MSSA. However, MSB (macrolide-streptogramin B) resistance was not found associated either with MRSA or MSSA. Furthermore, both inducible and constitutive MLSB were found to be associated with only homogenous MRSA. D tests may be made mandatory in all S. aureus isolates as inducible MLSB resistance cannot be detected in routine susceptibility test unless erythromycin and clindamycin are placed 15-26 mm apart.

Macrolide Resistance Trends in β-Hemolytic Streptococci in a Tertiary Korean Hospital

PurposeErythromycin-resistant β-hemolytic streptococci (BHS) has recently emerged and quickly spread between and within countries throughout the world. In this study, we evaluate the antimicrobial susceptibility patterns and erythromycin resistance mechanisms of BHS during 2003-2004.Materials and MethodsThe MICs of seven antimicrobials were determined for 204 clinical isolates of BHS from 2003 to 2004. Resistance mechanisms of erythromycin-resistant BHS were studied by the double disk test as well as by polymerase chain reaction (PCR).ResultsCompared with our previous study, resistance among Streptococcus pyogenes isolates to a variety of drugs decreased strikingly: from 25.7% to 4.8% in erythromycin; 15.8% to 0% in clindamycin; and 47.1% to 19.0% in tetracycline. The prevalent phenotypes and genotypes of macrolide-lincosamide-streptograminB (MLSB) resistance in Streptococcus pyogenes isolates have been changed from the constitutive MLSB phenotype carrying erm(B) to the M phenotype with mef(A) gene. In contrast with Streptococcus pyogenes, resistance rates to erythromycin (36.7%), clindamycin (43.1%), and tetracycline (95.4%) in Streptococcus agalactiae isolates did not show decreasing trends. Among the Streptococcus dysgalactiae subsp. equisimilis isolates (Lancefield group C, G), resistance rates to erythromycin, clindamycin, tetracycline and chloramphenicol were observed to be 9.4%, 3.1%, 68.8%, and 9.4%, respectively.ConclusionContinual monitoring of antimicrobial resistance among large-colony-forming BHS is needed to provide the medical community with current data regarding the resistance mechanisms that are most common to their local or regional environments.

Macrolide-Resistant Streptococcus pyogenes in the United States, 2002-2003

Increased levels of macrolide-resistant Streptococcus pyogenes in focal regions of the United States have been reported. The purpose of this study was to determine the antimicrobial susceptibility of a large collection of S. pyogenes isolates from throughout the United States and to elucidate the mechanisms of resistance and genetic relatedness of macrolide-resistant isolates. During 2002-2003, a total of 1885 S. pyogenes clinical isolates were obtained from 45 US medical centers. Susceptibility to penicillin, cefdinir, erythromycin, azithromycin, clarithromycin, clindamycin, telithromycin, and levofloxacin was determined. Macrolide resistance phenotypes were determined by double-disk diffusion, and macrolide resistance genotypes were determined by polymerase chain reaction and sequencing. All macrolide-resistant isolates and all isolates recovered from sterile sites were further characterized by pulsed-field gel electrophoresis (PFGE) and emm typing. The majority (85%) of isolates were pharyngeal. Resistance was detected to erythromycin (6.8% of isolates), azithromycin (6.9%), clarithromycin (6.6%), clindamycin (0.5%), telithromycin (0.2%), and levofloxacin (0.05%). The macrolide-resistance phenotype distribution was as follows: macrolide-lincosamide-streptogramin B (MLSB), 56% of isolates (inducible, 47%; constitutive, 9%); and M, 44%. The genotypes detected were as follows: ermA, 46% of isolates (95% with inducible MLSB phenotype); mefA, 43% (all with M phenotype); and ermB, 8.5% (45% with inducible MLSB and 45% with constitutive MLSB). Three isolates with constitutive MLSB phenotypes had 23S ribosomal RNA mutations. The 129 erythromycin-resistant isolates belonged to 28 emm types and 44 PFGE patterns, with 51% of the isolates in 4 major PFGE clones each associated with a predominant emm type (emm75, emm58, emm12, and emm114) and resistance genotype (mefA or ermA)). The population of macrolide-resistant S. pyogenes isolates in the United States is small, but it includes several large clones with potential for expansion.

In Vitro Activity of Telithromycin, Quinupristin/Dalfopristin, Linezolid and Comparator Antimicrobial Agents Against Staphylococcus aureus Clinical Isolates

We have studied the prevalence of the different macrolide, lincosamide, streptograminB (MLSB) phenotypes among clinical Staphylococcus aureus isolates erythromycin- and/or oxacillin-resistant; and also the activity of other antimicrobial agents including telithromycin, quinupristin/dalfopristin, linezolid, aminoglycosides, chloramphenicol and vancomycin. We found that 64.86% of S. aureus were oxacillin-resistant. While the most prevalent MLSB phenotype among methicillinresistant S. aureus (MRSA) was constitutive MLSB (cMLSB) (83%), among methicillin- susceptible S. aureus (MSSA) it was inducible MLSB (iMLSB) (90%). Kanamycin resistance was more frequent than resistance to other aminoglycosides, being 100% for MRSA. Telithromycin was only active against iMLSB, MS and erythromycin- susceptible isolates, although resistance rates were found among iMLSB MSSA (2.78%). Quinupristin/dalfopristin showed greater activity, with resistance rates of 2.5% for MRSA and 1.53% for MSSA. Both vancomycin and linezolid were fully active against all the isolates tested, with the highest MIC value being 2 μg/ml and 4 μg/ml, respectively. Among MRSA strains, 81.67% displayed resistance to five or more antimicrobials. This multiresistance was more frequently found among cMLSB strains (96.38% MRSA resistant to 6-9 agents).