Analysis Of The Bacterial Diversity And The Molecular Characterization Of Antibiotics Resistant Bacteria And Their Resistance Genes In Jiaozhou Bay

DAPI staining epifluorescence microscopy and bacterial cultivating method wereused to analyze the total microbial abundance and culturable microbial abundance in theseawater of Jiaozhou Bay in September and October of 2004. The abundance of totalmicrobes is in the range of 10~6-10~7 cells/ml, similar to those of most of the worldsemi-enclosed bays in the temperate areas. The highest microbial densities (10~7/ml)occurin the northeastern part of the Jiaozhou Bay, around the mouth of rivers Loushan andLicun and the Hongdao aquacultural farming areas where the culturable microbialabundance reached 5.16×10~5/ml (A5 station, around the mouth of Licun river). Thus, thedegree and characteristics of pollutants, along with geographical and hydrological effects,may be important determinants affecting the abundance and distribution of bacteria in theJiaozhou Bay. Bacterial communities inside and outside of Jiaozhou Bay can be groupedinto 3 classes based on T-RFLP and cluster analyses. Stations at the water channel of thebay mouth and outside, such as D1, D3, D5, D6 and D7, can be grouped together to standfor the bacterial community more related to the environment outside of the Jiaozhou Bay.Stations of the innermost side of Jiaozhou Bay, such as A3, A5, B2 and Y1, can begrouped together to stand for the Jiaozhou Bay residential bacteria community. StationsC1, C3 and C4 can be grouped together and may stand for the transitional bacterialassembly between the residential community and the outside community. However, thereis no obvious relationship between cyanobacterial diversity and geographic settings inJiaozhou Bay.The distribution and abundance of antibiotics resistant bacteria, which is mainlyinfluenced by the usage of antibiotics in mariculture and the condition of sewagedischarge, is one of the important standards in natural aquatic environments. The study onresistant bacteria and their resistance genes in natural aquatic environments is not onlysignificant to mariculture but also influential to the public hygiene of human beings. Thehighest oxytetracycline and chloramphenicol resistant bacterial density occurs in stationA5, around the mouth of Licun River, suggesting that the environment is the mostimportant factor influencing and determining the abundance and distribution of antibioticresistance bacteria. Based on the 16S rDNA analysis it is discovered that most of theresistant bacteria in Jiaozhou Bay belong to the γ-Proteobacteria subdivision. Obviously,Pseudomonas sp. is the predominant species in all Chloramphenicol resistant isolates.Multiplex-PCR method is used to characterize the oxytetracycline resistance genes (tetgenes) and Chloramphenicol resistance genes (cat genes) in Jaiozhou Bay. In the analysisof 84 oxytetracycline resistant isolates, tetA, tetB, tetC, tetD, tetE and tetG are alldetected. The predominant tet genes in these oxytetracycline resistance isolates are tetA(30.6%), tetB (24.5%), and tetG (36.7%). In the characterization of cat genes in 60Chloramphenicol resistant bacteria, only 12 isolates had cat genes, and only cat I and catIII were detected. But there is not obvious relationship between the types of cat/tet genesand the species of the resistant bacteria. Since there are also many resistant bacteriawhich were not detected harboring any cat/tet genes, other or even novel resistancemechanisms might also exist. And the Multi-drug resistance mechanism might alsocontribute to the antibiotic resistance in Jiaozhou Bay.