Macrolide Resistance In Clinical Isolates Research Articles

Prevalence and Molecular Characterization of Macrolide Resistance in Clinical Isolates of Beta Hemolytic Streptococci from a Tertiary Care Teaching Hospital in Kerala, India

Background: Beta-hemolytic streptococci (BHS) are responsible for both invasive and noninvasive infections, and the preferred treatment for these infections is penicillin due to the distinctive characteristics of these bacteria. However, in patients who cannot tolerate β-lactam antibiotics, macrolides and clindamycin are important alternative options for treating BHS infections. This study aimed to analyse the pattern of macrolide resistance among clinical strains of beta-hemolytic streptococci (BHS).
 Methods: Beta hemolytic streptococci isolated from clinical specimens during December 2018 to May 2020 were included in this study. Identification of the isolates were done by conventional and Vitek 2 method. All isolates were subjected to serogrouping. Antibiotic susceptibility testing done by disc diffusion method. Genes encoding macrolide resistance were detected by conventional multiplex polymerase chain reaction.
 Results: A total of 129 beta hemolytic streptococcal isolates were obtained which included 27 S. pyogenes (20.9%), 77 S.agalactiae (59.7%), 23 S.dysgalactiae spp equisimilis (17.8%) and one isolate of S.anginosus and S. porcinus each (0.8%). Erythromycin, clindamycin, quinuprisitn and tetracycline resistance were found to be 20.2%, 12.1%, 16.3% and 51.2% respectively. Among the 26 erythromycin resistant isolates, 12(46.2%) were inducible clindamycin resistant phenotype. Out of 26 erythromycin resistant isolates, 7(26.9%) isolates were harbouring erm(A) gene, 10(38.5%) erm(B) and 9(34.6%) mef(A) gene.
 Conclusion: Our study highlights the importance of routine antibiotic susceptibility testing for betahaemolytic streptococci, as well as the detection of inducible resistance to prevent therapeutic failure.

Antimicrobial susceptibility and mechanisms of high-level macrolide resistance in clinical isolates of Moraxella nonliquefaciens

We investigated antimicrobial susceptibility and the molecular mechanism involved in conferring high-level macrolide resistance in 47 clinical isolates of Moraxella nonliquefaciens from Japan. Antimicrobial susceptibility was determined using Etest and agar dilution methods. Thirty-two erythromycin-non-susceptible strains were evaluated for the possibility of clonal spreading, using PFGE. To analyse the mechanism related to macrolide resistance, mutations in the 23S rRNA gene and the ribosomal proteins, and the presence of methylase genes were investigated by PCR and sequencing. The efflux system was examined using appropriate inhibitors. Penicillin, ampicillin, amoxicillin, cefixime, levofloxacin and antimicrobials containing β-lactamase inhibitors showed strong activity against 47 M. nonliquefaciens isolates. Thirty-two (68.1 %) of the 47 isolates showed high-level MICs to macrolides (MIC ≥128 mg l(-1)) and shared the A2058T mutation in the 23S rRNA gene. The geometric mean MIC to macrolides of A2058T-mutated strains was significantly higher than that of WT strains (P<0.0001). Thirty-two isolates with high-level macrolide MICs clustered into 30 patterns on the basis of the PFGE dendrogram, indicating that the macrolide-resistant strains were not clonal. In contrast, no common mutations of the ribosomal proteins or methylase genes, or overproduction of the efflux system were observed in A2058T-mutated strains. Moreover, of the 47 M. nonliquefaciens strains, 43 (91.5 %) were bro-1 and 4 (8.5 %) were bro-2 positive. Our results suggest that most M. nonliquefaciens clinical isolates show high-level macrolide resistance conferred by the A2058T mutation in the 23S rRNA gene. This study represents the first characterization of M. nonliquefaciens.

Molecular Mechanisms of Macrolide Resistance in Clinical Isolates of Mycoplasma pneumoniae from China

Fifty clinical Mycoplasma pneumoniae strains were isolated from 370 children with respiratory tract infections. Four strains were susceptible to macrolides, while the other 46 (92%) were macrolide resistant. The molecular mechanism of resistance was shown to be associated with point mutations in 23S rRNA at positions 2063 and 2064.

Molecular basis of intrinsic macrolide resistance in clinical isolates of Mycobacterium fortuitum

Some clinical isolates of Mycobacterium fortuitum are naturally resistant to macrolides, e.g. clarithromycin. Thus, the aim of this study was to identify the gene(s) conferring this resistance. M. fortuitum ATCC 6841T DNA libraries were screened for plasmids that complemented the macrolide-susceptible phenotype of Mycobacterium smegmatis variant ermKO4 [erm(38)-negative]. Macrolide-resistant M. smegmatis transformants were selected on agar containing 128 mg/L erythromycin. Genetic complementation identified an M. fortuitum rRNA methylase gene, termed erm(39), 69% identical to erm(38) of M. smegmatis. In addition, erm(39) was found to be in the same chromosomal location as erm(38) in their respective hosts. Like erm(38), erm(39) conferred resistance (MIC >128 mg/L) to macrolide-lincosamide (ML) agents, but not to streptogramin B. Analysis of erm gene expression in M. fortuitum showed that ML agents increased erm(39) RNA levels, reaching a steady state level approximately 20-fold higher than baseline. Screening of 32 M. fortuitum clinical isolates by PCR showed that all were positive for erm(39), irrespective of clarithromycin susceptibility. A majority of clarithromycin-susceptible (MIC < or = 2 mg/L) isolates were postulated to carry a disabled erm(39) gene as they had a GTG-->CTG mutation in the putative initiation codon of the erm(39) gene. The similarity of the erm genes of M. smegmatis and M. fortuitum suggests that they were inherited from a common ancestor. Although the clinical impact of erm(39) on the therapeutic utility of clarithromycin is unclear, induction of this gene is consistent with the trailing end-points commonly seen during susceptibility testing of M. fortuitum isolates against macrolides.

Prevalence and Characterization of Macrolide Resistance in Clinical Isolates of Streptococcus pneumoniae and Streptococcus pyogenes from North America

SummaryResistance to macrolides is not a new phenomenon but it deserves attention because of the widespread use of these agents and their inclusion in many clinical guidelines for respiratory tract infections. The most common mechanisms by which Streptococcus pneumoniae and Streptococcus pyogenes develop resistance to macrolides is by target site modification (erythromycin ribosome methylase, erm) and efflux of the drug out of the organisms (macrolide efflux, mef). Target site modification may be of greater concern because it confers high-level resistance to all antimicrobials in the macrolide-lincosamidestreptograminB (MLSB) group. The genotype profiles of macrolide-resistant S. pneumoniae and S. pyogenes differ somewhat across regions in the US and between the US and Canada and other countries. There is some evidence for an association between macrolide resistance and treatment failure but this must be researched more fully. S. pneumoniae and S. pyogenes isolates resistant to macrolides are generally susceptible to ketolide antimicrobials because these agents bind more strongly to the relevant domain of the ribosomal subunit (withstanding erm resistance) and are less vulnerable to efflux compared to the macrolides.

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

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

Analysis of regulatory region of ermAM genes in streptococci and enterococci highly resistant to macrolides and lincosamides.

Target modification is the major mechanism of resistance to macrolide antibiotics in streptococci and enterococci and is due to the synthesis of a methylase which modifies the ribosome (5). This modification confers cross-resistance to macrolides, lincosamides and streptogramins B, the so-called MLSB phenotype. In streptococci and enterococci, MLSB resistance is encoded by genes related to the ermAM gene from the plasmid pAM77 of Streptococcus sanguis (6) and often borne by transposons Tn 1545 (4), Tn 917 (3), or by plasmids. Expression of the resistance may be inducible by macrolides or constitutive depending upon regulatory region located upstream the ermAM gene. In the case of plasmid pAMβ1 from E. faecalis, constitutive expression of resistance was related to a deletion of the 5′ regulatory region, including leader peptide sequences, of the ermAM gene (1). We have studied the expression of macrolide resistance in clinical isolates of streptococci and enterococci and analysed the regulatory sequences of the ermAM-related genes.KeywordsRegulatory RegionConstitutive ExpressionAntimicrob AgentMacrolide AntibioticMacrolide ResistanceThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.