Methicillin-Resistant Staphylococcus aureus (MRSA) Detected at Four U.S. Wastewater Treatment Plants

Rachel E. Rosenberg Goldstein,¹ Shirley A. Micallef,^1,2 Shawn G. Gibbs,³ Johnnie A. Davis,⁴ Xin He,⁵ Ashish George,¹ Lara M. Kleinfelter,¹ Nicole A. Schreiber,¹ Sampa Mukherjee,⁴ Amir Sapkota,¹ Sam W. Joseph,^1,6 and Amy R. Sapkota¹

¹Maryland Institute for Applied Environmental Health, University of Maryland School of Public Health, College Park, Maryland, USA; ²Department of Plant Science and Landscape Architecture and Center for Food Safety and Security Systems, University of Maryland, College Park, Maryland, USA; ³Department of Environmental, Agricultural & Occupational Health, College of Public Health, University of Nebraska Medical Center, Omaha, Nebraska, USA; ⁴Center for Veterinary Medicine, U.S. Food and Drug Administration, Laurel, Maryland, USA; ⁵Department of Epidemiology and Biostatistics, University of Maryland School of Public Health, College Park, Maryland, USA; ⁶Department of Cell Biology and Molecular Genetics, University of Maryland College Park, College Park, Maryland, USA


Abstract

Background: The incidence of community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) infections is increasing in the United States, and it is possible that municipal waste­water could be a reservoir of this micro­organism. To date, no U.S. studies have evaluated the occurrence of MRSA in waste­water.


Objective: We examined the occurrence of MRSA and methicillin-susceptible S. aureus (MSSA) at U.S. waste­water treatment plants.


Methods: We collected waste­water samples from two Mid-Atlantic and two Midwest waste­water treatment plants between October 2009 and October 2010. Samples were analyzed for MRSA and MSSA using membrane filtration. Isolates were confirmed using biochemical tests and PCR (polymerase chain reaction). Antimicrobial susceptibility testing was performed by Sensititre® micro­broth dilution. Staphylococcal cassette chromosome mec (SCCmec) typing, Panton-Valentine leucocidin (PVL) screening, and pulsed field gel electrophoresis (PFGE) were performed to further characterize the strains. Data were analyzed by two-sample proportion tests and analysis of variance.


Results: We detected MRSA (n = 240) and MSSA (n = 119) in 22 of 44 (50%) and 24 of 44 (55%) waste­water samples, respectively. The odds of samples being MRSA-positive decreased as treatment progressed: 10 of 12 (83%) influent samples were MRSA-positive, while only one of 12 (8%) effluent samples was MRSA-positive. Ninety-three percent and 29% of unique MRSA and MSSA isolates, respectively, were multi­drug resistant. SCCmec types II and IV, the pvl gene, and USA types 100, 300, and 700 (PFGE strain types commonly found in the United States) were identified among the MRSA isolates.


Conclusions: Our findings raise potential public health concerns for waste­water treatment plant workers and individuals exposed to reclaimed waste­water. Because of increasing use of reclaimed waste­water, further study is needed to evaluate the risk of exposure to antibiotic-resistant bacteria in treated waste­water. 


Key words: antibiotic resistance, community-acquired methicillin-resistant Staphylococcus aureus, methicillin-resistant Staphylococcus aureus, methicillin-susceptible Staphylococcus aureus, MRSA, MSSA, reclaimed waste­water, waste­water, waste­water treatment plant. 


Environ Health Perspect 120:1551–1558 (2012). http://dx.doi.org/10.1289/ehp.1205436 [Online 6 September 2012]


Address correspondence to A.R. Sapkota, University of Maryland School of Public Health, Maryland Institute for Applied Environmental Health, 2234P SPH Building, College Park, MD 20742 USA. Telephone: (301) 405-1772. Fax: (301) 314-1012. E-mail: ars@umd.edu


We thank the operators at the waste­water treatment plants for their participation and assistance. 


This work was supported by grant R03-OH009598-01 from the R03 Small Grants Program of the National Institute for Occupational Safety and Health. The Maryland Water Resources Research Center also supported this work by providing a summer fellowship to R.E.R.G. 


The authors declare they have no actual or potential competing financial interests.


Received 6 May 2012; Accepted 6 September 2012; Online 6 September 2012.