title: Methicillin-resistant Staphylococcus aureus (MRSA) detected at four U.S. wastewater treatment plants.
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.
authors.affiliation: Maryland Institute for Applied Environmental Health, University of Maryland School of Public Health, College Park, Maryland 20742, USA.
authors.forename: Rachel E
authors.initials: RE
authors.lastname: Rosenberg Goldstein
authors.forename: Shirley A
authors.initials: SA
authors.lastname: Micallef
authors.forename: Shawn G
authors.initials: SG
authors.lastname: Gibbs
authors.forename: Johnnie A
authors.initials: JA
authors.lastname: Davis
authors.forename: Xin
authors.initials: X
authors.lastname: He
authors.forename: Ashish
authors.initials: A
authors.lastname: George
authors.forename: Lara M
authors.initials: LM
authors.lastname: Kleinfelter
authors.forename: Nicole A
authors.initials: NA
authors.lastname: Schreiber
authors.forename: Sampa
authors.initials: S
authors.lastname: Mukherjee
authors.forename: Amir
authors.initials: A
authors.lastname: Sapkota
authors.forename: Sam W
authors.initials: SW
authors.lastname: Joseph
authors.forename: Amy R
authors.initials: AR
authors.lastname: Sapkota
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics; D001427:Bacterial Toxins / Q000235:genetics; D015373:Bacterial Typing Techniques; D016521:Electrophoresis, Gel, Pulsed-Field; D005098:Exotoxins / Q000235:genetics; D007956:Leukocidins / Q000235:genetics; D008712:Methicillin / Q000494:pharmacology*; D016106:Methicillin Resistance / Q000187:drug effects* / Q000235:genetics; D055624:Methicillin-Resistant Staphylococcus aureus / Q000145:classification* / Q000187:drug effects / Q000235:genetics / Q000302:isolation & purification*; D008826:Microbial Sensitivity Tests; D008836:Micrococcal Nuclease / Q000235:genetics; D008873:Mid-Atlantic Region; D015146:Midwestern United States; D046915:Penicillin-Binding Proteins; D016133:Polymerase Chain Reaction; D062065:Wastewater / Q000382:microbiology*
chemical_list: D001426:Bacterial Proteins; D001427:Bacterial Toxins; D005098:Exotoxins; D007956:Leukocidins; D008712:Methicillin; D008836:Micrococcal Nuclease; D046915:Penicillin-Binding Proteins; D062065:Wastewater; C078284:Panton-Valentine leukocidin; C487789:mecA protein, Staphylococcus aureus; C074002:nuc protein, staphylococcus