Collaborative Studies Show Clear Link Between Human Bacteria and Ocean Environments
Two Miller School collaborative studies led by Lisa Plano, M.D., Ph.D., associate professor of pediatrics and microbiology and immunology, have shown a clear link between a common human bacterium and ocean environments.
For the first time, UM researchers showed that levels of Staphylococcus aureus, commonly known as “staph,” vary in tidal waters and beach sand, based on the number of bathers. A second UM study found shared strains of S. aureus in short-finned pilot whales, their environment, and the human volunteers assisting them at a marine mammal rehabilitation facility after the pilot whales stranded in the Florida Keys.
“Demonstrating a correlation between the daily average number of bathers and S. aureus in the water was one of our most important findings,” said Plano, who led the two related studies published recently in a special issue of Microbial Ecology on “Oceans and Human Health.” She added, “However, no association between exposure to S. aureus in these waters and reported illness was found.”
In the first study, “Human-Associated Methicillin-Resistant Staphylococcus aureus from a Subtropical Recreational Marine Beach,” a team of volunteers collected 1,001 water and 36 intertidal sand samples at a subtropical recreational beach over a 17-month period. They also observed the presence of zero to 131 bathers at any given time during the samplings.
Methicillin-sensitive S. aureu_s (MSSA) and methicillin-resistant _S. aureu _(MRSA) were isolated and identified in the samples using organism-specific molecular markers. “If the weather was raining and there were no bathers in the water, the samples were unlikely to show MSSA or MRSA bacteria,” said Plano. “But on a holiday weekend with numerous bathers, more than two-thirds of the samples had these bacteria. This was the first study to show such a connection on a scientifically sound basis.”
While S. aureus has been reported in marine environments since the early 1990s, the UM investigation sought to find possible sources and identify the risks to bathers of exposure to these organisms, which can be found in approximately 30 percent of humans. S. aureus typically colonizes the skin and can cause localized infections, but also can cause serious systemic infections, including sepsis, pneumonia, endocarditis, and osteomyelitis. Historically, drug-resistant MRSA were primarily associated with hospitals and healthcare facilities. However, MRSA now commonly cause infections in healthy, non-hospitalized individuals and can be found in public places, including recreational waters.
The lack of reported illness during this study suggests that, although bathers were exposed to S. aureus, healthy beachgoers were unlikely to be affected. It is possible that the concentration of the organisms in the water was not sufficient to establish an infection in a host with a normal immune system and non-damaged skin, said Plano.
“If you plan to go to the beach, use common sense,” said Plano. “If you have an open skin wound, don’t go in the water and expose yourself, or others, to those bacteria. Shower before you go into the water and shower again after you come off the beach to decrease the level of bacteria on your skin.”
The second Miller School study focused on the infectious disease implications of a mass stranding of 26 short-finned pilot whales in the lower Florida Keys on May 5, 2011. Five of the injured whales were transferred from the original stranding site to a nearby marine mammal rehabilitation facility where they were constantly attended by a team of volunteers. Two of the five whales survived and were moved to long-term care, including one mammal with a MRSA infection that was treated successfully.
“Marine mammal stranding response and rehabilitation increases the amount and duration of contact between people and presumptively debilitated animals, a situation not dissimilar to human medical and convalescent facilities,” said Plano. “It is possible that the transfer of organisms, including S. aureus, may occur during interaction between humans and animals during these events.”
In the study, “Clonally Related Methicillin-Resistant Staphylococcus aureus Isolated from Short-Finned Pilot Whales (Globicephala macrorhynchus), Human Volunteers, and a Bayfront Cetacean Rehabilitation Facility,” the researchers reported bacterial cultures during the routine clinical care of the whales and a necropsy of a deceased whale included both MSSA and MRSA. “To our knowledge, this is the first reported instance of S. aureus isolated from stranded pilot whales,” Plano said.
To investigate potential sources of the bacteria, samples were obtained from human volunteers, whales, seawater, and sand at the facility, nearby recreational beaches, and a canal. An analysis of those samples found a 98 to 100 percent genetic match between the MRSA bacteria in the pilot whales, surrounding water, sand, and in humans participating in the rehabilitation effort.
None of the volunteers became sick, and strict hygiene protocols were maintained on site at all times. For example, potential volunteers were excused if they were ill, immune-compromised, pregnant, or had any open wounds. Volunteers were asked to sanitize their hands frequently and shower after exiting the water, and all wetsuits were subjected to a three-stage wash and disinfection process.
“These studies support the notion that S. aureus may be shed into an environment by humans and pilot whales and subsequently may colonize or infect exposed new hosts,” said Plano.
Researchers in both Miller School studies collaborated with professionals from other UM departments, as well as other academic institutions and government organizations.
Miller School co-authors on the recreational beach study were Anna C. Garza, Suzanne Hower, Ph.D., Departments of Pediatrics and Microbiology and Immunology; Timothy J. Cleary, Ph.D., professor of pathology, microbiology and immunology; and Lora E. Fleming, M.D., Ph.D., professor of public health sciences. Other UM co-authors were Tomoyuki Shibata, Ph.D., Jonathan Kish, Christopher D. Sinigalliano, Ph.D., Maribeth L. Gidley, D.O., Ph.D., Kelly Withum, and Samir M. Elmir, Ph.D., from UM’s Rosenstiel School of Marine and Atmospheric Sciences; and Helena M. Solo-Gabriele, Ph.D., Department of Civil, Architectural, and Environmental Engineering.
Additional co-authors were from the Richard B. Russell Research Center, Agricultural Research Service, U.S. Department of Agriculture (U.S.D.A.), Athens, Georgia; Center for Veterinary Medicine, U.S. Food and Drug Administration (FDA), Laurel, Maryland; Public Health Program, College of Osteopathic Medicine, Nova Southeastern University, Fort Lauderdale; National Oceanic and Atmospheric Administration (NOAA), Miami; Public Health and Health Education Programs, Northern Illinois University, DeKalb; and Miami-Dade County Health Department.
UM co-authors in the pilot whale study were Suzanne Hower, Ph.D., Departments of Pediatrics and Microbiology and Immunology; Adrienne Dameron, Norma C. Salazar, and Manuel A. Tamargo, Department of Microbiology and Immunology; and Matthew C. Phillips, Maribeth L. Gidley, D.O., Ph.D., and Christopher D. Sinigalliano, Ph.D., Department of Microbiology and Immunology and Oceans and Human Health Center, Rosenstiel School of Marine and Atmospheric Sciences.
Additional co-authors were Micah Brodsky, V.M.D., consulting veterinarian; Ruth Y. Ewing, D.V.M.; Lisa Johns; Frank E. Johnson and Olufunmilola Adebanjo, of NOAA, Miami, as well as researchers from the Richard B. Russell Research Center, U.S.D.A., and the FDA’s Center for Veterinary Medicine.