Extended Spectrum Beta-lactamases (ESBLs) in Aquatic Environments

Gram-negative bacteria that possess ESBL genes have proven to be a concern to the medical community because of their high resistance rates to 3^rd generation cephalosporins. ESBL production has been associated with higher morbidity and mortality rates and has been reported in Escherichia coli and Klebsiella pneumoniae species in particular. Previously, TEM and SHV were the primary ESBL genes produced by gram negative bacteria. Recently however, an emergence of novel OXA and CTX-M type ESBL genes have been reported. The majority of the ESBL related bacterial infection outbreaks occur in hospital institutions with high-risk patients followed by nursing homes. We hypothesized that aquatic environments are potential reservoirs for bacteria that harbor ESBL genes. We screened the resistance profile of the bacteria filtered and isolated from seawater and fresh water by performing a disk diffusion test. In accordance with the CLSI, we detected ESBL phenotypes by noting an increase in at least 5 mm in diameter when using the double disk diffusion test with ceftazidime (CAZ) in one disk and CAZ along with the beta-lactamse inhibitor clavulanic acid. We identified the bacteria isolates using the Matrix Assisted Laser Desorption Ionization-Time of Flight (MALDI-TOF) mass spectrometry system and we used the polymerase chain reaction (PCR) to identify the ESBL genes. We found freshwater harbored 57% of the ESBLs detected followed by 30% from seawater and 10% from ice drinking water. The ESBLs detected showed high susceptibility rates to meropenem and other clinically prescribed antibiotics. The genus Bacillus accounted for the majority of the ESBL isolates (15, 27%) and second highest was Escherichia (8, 14%). The ESBL genes were found CTX (10) and OXA (8). TEM (3) and SHV(1) were also detected but in lower frequencies. We also observed that 3 of the isolates had both CTX and OXA, one of the isolates had both CTX and SHV while one isolate had OXA, CTX and TEM. Results show that aquatic environments harbor ESBL containing bacteria.