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.

Heavy Metals and Antibiotics Susceptibility Profiles of <i>Staphylococcus aureus</i> Isolated from Several Points Receiving Daily Input from the Bodija Abattoir in Ibadan, Oyo State, Nigeria

“…The percentage resistance to ciprofloxacin in this study was 9.1% which is much lower when compared to the 63.1% in the aforementioned study in the United States. Resistance to both tetracycline and vancomycin in this present study was 22.7% and 9.1% respectively, which is comparable to the 14.3% and 0% resistance, respectively, as reported by Goldstein et al [38].…”

“…The difference could be because of a better regulatory measure on abattoir management and disposal of wastes and wastewater in developed countries like Germany compared to a developing country like Nigeria. In a study carried out on strains of Methicillin Resistant Staphylococcus aureus (MRSA) obtained from wastewater treatment plants in the United States [38], it was reported that a percentage resistance of 98.8% was observed to oxacillin, and this was higher than the 63.3% resistance to the same antibiotics observed in this study. The percentage resistance to ciprofloxacin in this study was 9.1% which is much lower when compared to the 63.1% in the aforementioned study in the United States.…”

“…aureus is often found to be resistant to one or more antibiotics, including methicillin and hence infections caused by this organism are usually very difficult to treat [22]. Antibiotic resistance in human may either be hospital or community acquired.…”

Management Options for Reducing the Release of Antibiotics and Antibiotic Resistance Genes to the Environment

“…WWTPs receive direct input of resistant fecal and commensal bacteria from patients prescribed antibiotics. Most recently, methicillin-resistant Staphylococcus aureus (MRSA) was detected in the effluent of four U.S. WWTPs (Goldstein et al 2012), and bacteria resistant to clinically important antibiotics, including ciprofloxacin and vancomycin, have been found in the activated sludge (Nagulapally et al 2009). ARBs and ARGs may either decrease (i.e., via death and decay) or increase (i.e., via horizontal gene transfer and/or selective enrichment) through the treatment process.…”

Antibiotic Concentrations Decrease during Wastewater Treatment but Persist at Low Levels in Reclaimed Water

“…Methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant enterococci (VRE) have been detected in influent, activated sludge, secondary clarifier, post aeration, and effluent samples from U.S. WWTPs [14,15]. In addition, VRE have been detected at a U.S. reclaimed water spray irrigation site [16].…”