Marine microorganisms: the world also changes

In recent years, the increasing trend of pollution has been extended to the marine environment, although it has been one of natural places more stable for years, thanks to the great development of marine aquaculture worldwide at present is being severely affected. The indiscriminate use of antimicrobial compounds begins to promote an important change in the microflora of both marine and inland waters. Microorganisms previously known as non-pathogenic or even producers of antimicrobial compounds, which had been previously described as commensally or asymptomatic organisms, begin now to be described as opportunistic pathogens, being this character often associated to stress conditions. This chapter will describe the major groups of marine microorganisms previously described as asymptomatic and members of the external bacterial microflora of fish. Within these organisms is distinguished between two groups, those who were known as asymptomatic, in which recently began to appear potentially pathogenic species or even strains and a second group consisting of bacterial type previously described as pathogenic which start having antimicrobial resistance known or permitted in the actual aquaculture practices.