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Published on: May 8, 2013
Characterization of methicillin-resistant Staphylococcus aureus strains in sewage treatment plants in Tehran, Iran
Fateh Rahimi1, Mohammad Katouli2, Mohammad R Pourshafie3
1Department of Microbiology, Faculty of Biological Science and Technology, University of Isfahan, Isfahan, Iran
Abstract:
Multidrug-resistant Staphylococcus aureus strains have been commonly found in hospitals and communities causing wide ranges of infections among humans and animals. Typing of these strains is a key factor to reveal their clonal dissemination in different regions. We investigated the prevalence and dissemination of different clonal groups of S. aureus with resistance phenotype to multiple antibiotics in two sewage treatment plants (STPs) in Tehran, Iran over four sampling occasions. A total of 576 S. aureus were isolated from the inlet, sludge and outlet. Of these, 80 were identified as methicillin-resistant S. aureus (MRSA) and were further characterized using a combination of Phene Plate (PhP) typing, staphylococcal cassette chromosome mec (SCCmec), ccr types, prophage and antibiotic-resistant profiling. In all, eight common type (CT) and 13 single PhP type were identified in both STPs, with one major CT accounting for 38.8% of the MRSA strains. These strains belonged to three prophage patterns and five prophage types with SCCmec type III being the predominant type. Resistance to 11 out of the 17 antibiotics tested was significantly (P < 0.0059) higher among the MRSA isolates than methicillin-sensitive S. aureus (MSSA) strains. The persistence of the strains in samples collected from the outlet of both STPs was 31.9% for MRSA and 23.1% for MSSA. These data indicated that while the sewage treatment process, in general, is still useful for removing most MRSA populations, some strains with SCCmec type III may have a better ability to survive the STP process.
Insights
Multidrug-resistant Staphylococcus aureus, particularly methicillin-resistant S. aureus (MRSA), persists in sewage. Some MRSA strains, especially SCCmec type III, show enhanced survival in sewage treatment plants, indicating potential environmental dissemination risks.
Area of Science:
- Environmental microbiology
- Antimicrobial resistance
- Public health
Background:
- Multidrug-resistant Staphylococcus aureus (MRSA) is a significant global health concern, prevalent in healthcare and community settings.
- Understanding the dissemination and survival of MRSA in environmental matrices, such as sewage, is crucial for public health risk assessment.
- Sewage treatment plants (STPs) are potential hotspots for the concentration and spread of antibiotic-resistant bacteria.
Purpose of the Study:
- To investigate the prevalence and clonal dissemination of multidrug-resistant Staphylococcus aureus, including MRSA, in two STPs in Tehran, Iran.
- To characterize MRSA isolates based on Phene Plate (PhP) typing, staphylococcal cassette chromosome mec (SCCmec) types, ccr types, and prophage patterns.
- To assess the survival and persistence of MRSA and methicillin-sensitive S. aureus (MSSA) strains within the sewage treatment process.
Main Methods:
- Isolation and identification of 576 S. aureus strains from inlet, sludge, and outlet samples across four sampling occasions.
- Characterization of 80 MRSA isolates using Phene Plate (PhP) typing, SCCmec and ccr typing, prophage profiling, and antibiotic resistance profiling.
- Comparison of antibiotic resistance patterns between MRSA and MSSA isolates and assessment of strain persistence in STP effluent.
Main Results:
- Eight common types (CT) and 13 single PhP types of S. aureus were identified, with one major CT dominating MRSA isolates (38.8%).
- SCCmec type III was the predominant type among MRSA isolates, associated with specific prophage patterns.
- MRSA isolates exhibited significantly higher resistance to 11 out of 17 tested antibiotics compared to MSSA. Persistence rates were 31.9% for MRSA and 23.1% for MSSA in outlet samples.
Conclusions:
- Sewage treatment processes generally reduce MRSA populations, but certain strains, particularly those with SCCmec type III, demonstrate enhanced survival.
- The findings highlight the potential for STPs to act as reservoirs and dissemination routes for specific MRSA clones.
- Further research is needed to understand the mechanisms of MRSA survival in STPs and to mitigate potential public health risks.
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