Sulfamethoxazole in the Environment

SMX is a sulfonamide antibiotic that is commonly used to treat a variety of bacterial infections in animals. Previous studies have documented that SMX is a contaminant in both U. S. streams and groundwater, and that wastewater treatment plants and septic tanks are sources of antibiotics to the environment. Although SMX has been shown to degrade in streams, groundwater may be particularly vulnerable to the persistence of SMX. The natural attenuation of SMX in groundwater appears to be constrained due to the absence of photodegradation by sunlight when compared to natural attenuation of SMX in streams.Antibiotics in Groundwater Affect Natural Bacteria

Trimethoprim - is a bacteriostatic antibiotic mainly used in the prevention and treatment of urinary tract infections.It belongs to the class of chemotherapeutic agents known as dihydrofolate reductase inhibitors. Trimethoprim was formerly marketed by GlaxoSmithKline under trade names including ProloprimMonotrim and Triprim; but these trade names have been licensed to various generic pharmaceutical manufacturers. In clinical use it is often abbreviated TRI or TMP; its common laboratory abbreviation is W

Sulfamethoxazole is most often used as part of a synergistic combination with trimethoprim in a 5:1 ratio in co-trimoxazole (abbreviated SMZ-TMP and SMX-TMP,[4] or TMP-SMZ and TMP-SMX), also known under trade names such as BactrimSeptrin, or Septra; in Eastern Europe it is marketed as Biseptol. Its primary activity is against susceptible forms of StreptococcusStaphylococcus aureus (including MRSA),Escherichia coliHaemophilus influenzae, and oral anaerobes. It is commonly used to treat urinary tract infections. In addition it can be used as an alternative to amoxicillin-based antibiotics to treat sinusitis. It can also be used to treat toxoplasmosis and it is the drug of choice for Pneumocystis pneumonia, which affects primarily patients with HIV.

U.S. Geological Survey (USGS) scientists have documented adverse health effects on populations of native soil bacteria exposed to levels of the antibiotic (SMX) below those used to treat diseases (subtherapeutic). Because SMX has been found in environmental waters by many previous studies, the scientists conducted laboratory exposure experiments to determine the effect of SMX on native bacteria. They found that SMX concentrations previously found in aquatic environments (approximately 1 microgram per liter [μg/L]) delayed the start of cell growth, limited denitrification (a critical component of global nitrogen cycles), and altered bacterial community composition. Adverse effects on soil bacteria in tests conducted at higher antibiotic levels (250 μg/L or greater), but still much less than levels prescribed to treat (therapeutic) or protect against (prophylactic) diseases, were even more pronounced.

Antibiotic Resistance Concerns

Because of well-documented cases of antibiotic resistance in hospitals and other settings, many scientists are studying the potential effects of antibiotics in the environment and the potential spread of antibiotic resistant bacteria. Other potential adverse effects on native bacterial populations in the environment remain less commonly studied.

Nitrogen Cycle May Be Affected

It is clear from this study that inhibition of critical ecological functions such as denitrification can occur when native denitrifying bacteria are exposed to environmentally relevant doses of SMX. Denitrification is the microbially facilitated process that converts nitrate to nitrogen gas, the main component of the earth’s atmosphere. Denitrification also plays a key role in soil fertility as well as in natural assimilation of nitrate pollution. The implication that these processes may be taking place in nature where wastewaters are entering water resources is of global importance to environmental and, by association, human health. Too much nitrogen, as nitrate, in groundwater used for drinking water can be harmful to infants.

Sulfamethoxazole is found in all the body excretions, especially in the urine and is rapidly excreted in most animals.

The two sulfonamides (sulfamethoxazole and sulfamethazine) and trimethoprim were found to be most toxic to plant growth in soil.

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