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Updated: Mar 10, 2026
Isolation and Identification of Waterborne Antibiotic-Resistant Bacteria and Molecular Characterization of their Antibiotic Resistance Genes
Published on: March 3, 2023
Frequency of genes encoding erythromycin ribosomal methylases among Staphylococcus aureus clinical isolates with
Sareh Sadat Hosseini1, Mohammad Niakan1, Horieh Saderi2
1Department of Microbiology, School of Medicine, Shahed University, Tehran, Iran.
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.
Insights
Most Staphylococcus aureus isolates exhibit resistance to macrolide, lincosamide, and streptogramin B (MLSB) antibiotics. The study found a strong association between specific erm genes and MLSB resistance phenotypes in these bacteria.
Area of Science:
- Microbiology
- Infectious Diseases
- Antimicrobial Resistance
Background:
- Macrolide, lincosamide, and streptogramin type B (MLSB) antibiotics are crucial for treating *Staphylococcus aureus* infections.
- The emergence of antibiotic-resistant *S. aureus* strains poses a significant public health concern.
Purpose of the Study:
- To investigate the prevalence of MLSB resistance phenotypes in *S. aureus* isolates.
- To determine the genotypic basis of MLSB resistance, focusing on *ermA*, *ermC*, and *msrA* genes.
Main Methods:
- A cross-sectional study involving 101 *S. aureus* isolates from five hospitals in Tehran.
- Disk diffusion and D-test were used to determine resistance phenotypes.
- PCR and multiplex PCR were employed to detect *mecA, msrA, ermA*, and *ermC* genes.
Main Results:
- 57.4% of isolates were methicillin-resistant, and 56.4% were resistant to erythromycin.
- Among erythromycin-resistant isolates, constitutive MLSB (cMLSB) was most prevalent (71.9%), followed by inducible MLSB (iMLSB) (26.3%).
- Co-occurrence of *ermA* and *ermC* genes was frequent (57.8%) in isolates with constitutive resistance.
Conclusions:
- The study highlights the significant prevalence of MLSB resistance in *S. aureus*.
- A strong correlation exists between specific *erm* gene profiles (*ermA*, *ermC*) and observed resistance phenotypes.
- Understanding these genetic mechanisms is vital for guiding antimicrobial therapy and infection control strategies.
