Genomic Insights of First ermB-Positive ST338-SCCmecVT/CC59 Taiwan Clone of Community-Associated Methicillin-Resistant Staphylococcus aureus in Poland.

We report the first Polish representative of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA), lukS/F-PV-positive, encoding the ermB gene, as a genetic determinant of constitutive resistance to macrolides, lincosamides, and streptogramin B antibiotics, cMLS-B. This is the first detection of the CA-MRSA strain responsible for nosocomial infection in the Warsaw Clinical Hospital. Resistance to ß-lactams associates with a composite genetic element, SCCmec cassette type VT (5C2&5). We assigned the strain to sequence type ST338 (single-locus variant of ST59), clonal complex CC59, spa-type t437, and agr-type I. Genomic-based comparison was designated SO574/12 as an international Taiwan clone, which has been so far described mainly in the Asia-Pacific region. The ermB gene locates on the chromosome within the 14,690 bp mobile element structure, i.e., the MESPM1-like structure, which also encodes aminoglycoside- and streptothricin-resistance genes. The MESPM1-like structure is a composite transposon containing Tn551, flanked by direct repeats of IS1216V insertion sequences, which probably originates from Enterococcus. The ermB is preceded by the 273 bp regulatory region that contains the regulatory 84 bp ermBL ORF, encoding the 27 amino acid leader peptides. The latest research suggests that a new leader peptide, ermBL2, also exists in the ermB regulatory region. Therefore, the detailed function of ermBL2 requires further investigations.

Macrolide-lincosamide-streptogramin B resistance phenotypes and their associated genotypes in Staphylococcus aureus isolates from a tertiary level public hospital of Uruguay.

This study was undertaken to investigate the resistance phenotypes to macrolide-lincosamide-streptogramin B (MLSB) antibiotics and their associated genotypes in isolates of Staphylococcus aureus. We analyzed one hundred, consecutive, non-duplicate isolates (methicillin-susceptible MSSA, n=53 and methicillin-resistant MRSA, n=47) obtained from various clinical samples between July 2012 to December 2013. The resistance profile to MLSB antibiotics was determined by phenotypic methods and the resistance genes were detected by PCR assays. All of the isolates were subjected to pulsed-field gel electrophoresis (SmaI-PFGE). The overall prevalence of resistance to MLSB antibiotics was 38% and the resistance phenotype distribution was as follows: cMLSB, 22%; iMLSB, 10%; MSB, 5% and L, 1%. We detected ermA, ermC, ermB and mrsA/B genes in these resistant isolates. The single ermA gene was commonly observed mainly in those with a cMLSB R phenotype, whereas the combination ermA and ermC was more commonly observed in isolates with inducible expression. The patterns of SmaI-PFGE suggest a great genetic diversity in both MRSA and MSSA resistant to MLSB antibiotics. The results demonstrate the local presence of S. aureus resistant to MLSB antibiotics and its most frequently described responsible genes. Some of these isolates, especially those with the iMLSB phenotype, may be associated with therapeutic failure. Therefore, efforts should be directed to the correct detection of all MLSB resistant isolates using appropriate laboratory tests. PFGE results reveal a wide spread of resistance genes rather than the circulation of S. aureus clones resistant to MLSB antibiotics.

Novel inhibitors of the rRNA ErmC' methyltransferase to block resistance to macrolides, lincosamides, streptogramine B antibiotics.

In erythromycin-resistant bacteria, the N6 position of A2058 in 23S rRNA is mono- or dimethylated by Erm family methyltransferases. This modification results in cross-resistance to macrolides, lincosamides and streptogramin B. Most inhibitors of Erm methyltransferases developed up-to-date target the cofactor-binding pocket, resulting in a lack of selectivity whereas inhibitors that bind the substrate-binding pocket demonstrate low in vitro activity. In this study, a molecular docking approach followed by biochemical screening was applied to search for inhibitors targeting both cofactor- and substrate-binding pockets of ErmC' methyltransferase. Based on the results of the molecular docking-based virtual screening of the clean-leads subset of the ZINC database, 29 compounds were chosen for experimental verification. Among them inhibitor 28 (ZINC code 32747906), with an IC50 of 100 µM, decreased the minimal inhibitory concentration of erythromycin in the Escherichia coli strain overexpressing ErmC'. Docking analysis of 28 to the ErmC' structure and the competitive ligand binding assay revealed a non-competitive model of inhibition. Inhibitor 28 served as a template for similarity-based virtual screening, which resulted in the identification of two derivatives 3s (ZINC code 62022572) and 4s (ZINC code 49032257) with an IC50 of 116 µM and 110 µM, respectively. Our results provide a basis for the development of inhibitors against the Erm-family of enzymes.

Streptogramins - two are better than one!

Streptogramins are potent drugs against numerous highly resistant pathogens and therefore are used as antibiotics of last-resort human therapy. They consist of a mixture of two different types of chemical substances - the group A streptogramins, which are polyunsaturated macrolactones, and the group B streptogramins, representing cyclic hexadepsipeptides. Streptogramins are unique in their mode of action: each component alone exhibits a moderate bacteriostatic activity by binding to the bacterial 50S ribosomal subunit and thereby blocking translation, whereas the synergic combination of both substances is up to hundred fold more effective than the single compounds, resulting in a bactericidal activity. The streptogramin biosynthetic genes are organized as large antibiotic superclusters. These clusters harbour numerous regulatory genes, which encode different types of regulators that together form a complex hierarchical signalling system, which governs the regulation of streptogramin biosynthesis. Resistance is also regulated by this cascade. However, whereas resistance against streptogramins is quite well understood in diverse pathogenic organisms, only little is known about how the natural producer strains protect themselves against these toxic compounds. Here, we give an overview about the recent advances in streptogramin investigations with a main focus on the best-studied representatives, pristinamycin and virginiamycin. We concentrate on the biosynthesis of these compounds, their regulation and resistance determinants as well as their application in medicine and food industry.

Prevalence of phenotypic resistance of Staphylococcus aureus isolates to macrolide, lincosamide, streptogramin B, ketolid and linezolid antibiotics in Turkey

The incidence of drug-resistant pathogens differs greatly between countries according to differences in the usage of antibiotics. The purpose of this study was to investigate the phenotypic resistance of 321 methicillin resistance Staphylococcus aureus (MRSA) and 195 methicillin susceptible S. aureus (MSSA) in a total of 516 S. aureus strains to macrolide, lincosamide, streptogramin B (MLS B), ketolid, and linezolid. Disk diffusion method was applied to determine MLS B phenotype and susceptibility to different antibiotic agents. It was found that 54.6 percent of the isolates were resistant to erythromycin (ERSA), 48 percent to clindamycin, 55 percent to azithromycin, 58.7 percent to spiramycin, 34.7 percent to telithromycin, and 0.4 percent to quinupristin-dalfopristin, respectively. No strain resistant to linezolid was found. The prevalence of constitutive (cMLS B), inducible (IMLS B), and macrolides and type B streptogramins (M/MS B) among ERSA isolates (237 MRSA, 45 MSSA) was 69.6 percent, 18.2 percent, and 12.2 percent in MRSA and 28.9 percent, 40 percent, and 31.1 percent in MSSA, respectively. In conclusions, the prevalence of cMLS B was predominant in MRSA; while in MSSA strains, iMLS B and M/MS B phenotype were more higher than cMLS B phenotype resistance. The resistance to quinupristindalfopristin was very low, and linezolid was considered as the most effective antibiotic against all S.aureus strains.

Prevalence of Resistance to Macrolide,Lincosamide and Streptogramin B Antibiotics in Staphylococcus epidermidis Caused Nosocomial Infection / 中华医院感染学杂志

OBJECTIVE To determine the prevalence of antibiotic resistance to macrolide,lincosamide and streptograminB(MLS_B) in Staphylococcus epidermidis caused nosocomial infections and give guide for clinical antibiotics usage. METHODS Totally 126 S.epidermidis isolates were collected to test the minimal inhibitory concentrations(MIC) of erythromycin,clindamycin,clarithromycin,and azithromycin,quinupristin/dalfopristin and cefoxitin.Inducible type of MLS_B resistance(iMLS_B) and MS phenotypes were distinguished by double disk diffusion method(D test) as detailed by the NCCLS. RESULTS Among 126 S.epidermidis isolates,90(71.4%) isolates were meticillin resistant(MRSE),36(28.6%) were meticillin susceptive(MSSE).The rates of antibiotic-resistance to erythromycin,clindamycin,clarithromycin,axithromycin were 92.8%,73.8%,89.7% and 91.3%,respectively.Percentages of strains resistant to erythromycin and clindamycin were 96.7% and 85.6% in MRSE,and 83.3% and 80.6% in MSSE.Constitutive phenotype,inducible phenotype and MS phenotype were detected in 93(73.8%),13(10.3%),and 11(8.7%) isolates,respectively.In constitutive phenotype, the MRSE proportion appeared high(78.5%),in contrast,in inducible phenotype,MSSE proportion appeared high(75%).No resistance to quinupristin/dalfopristin was detected in all isolates(MIC≤1mg/L). CONCLUSIONS The prevalence of antibiotic resistance to MLS_B is high in the collected isolates.The main antibiotic phenotype is constitutive phenotype.MLS_B antibiotics should be used judiciously.

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.