Antibiotic resistance, transfer microorganisms

Transfer of antibiotic resistance genes among bacteria in nature has created serious problems in the treatment of many infectious diseases such as tuberculosis, gonorrhea, pneumonia, staphylococcus, and others. The widespread use of antibiotics in agriculture and in hospitals has resulted in the selection and evolution of pathogenic microorganisms that are resistant to many, sometimes all, of the antibiotics normally used to treat infections by these microorganisms. 

A recent study by Hankin et al. (16) showed that raw milk contains substantial numbers of antibiotic-resistant microorganisms and that some organisms resistant to Streptomycin, Tetracycline and Polymyxin can survive pasteurization. Several gram-negative isolates also were capable of transferring their resistance to E. coli. 

In particular, there is growing concern on spreading transferable resistance to antibiotics, and starter microorganisms should therefore not carry genes encoding such features (EFSA, 2011 Talon Leroy, 2011 Vogel et al., 2011). 

In human medicine, selection pressure is at its most intense in hospitals, where antibiotics are extensively used. The major cause of problems of antimicrobial resistance in humans arises from overuse of antimicrobials at therapeutic levels in humans. It is generally accepted that drug resistance that develops in a bacterium as a result of mutation is only of importance within the individual host and a single bacterial strain. Because the determinant is chromosomal, the resistance cannot be transferred between different bacterial species and genera. In addition, the mutationally resistant microorganism is not usually as viable as the wild ones hence once the selective antibiotic is removed from the environment, the proportions of the mutant decrease. If exposure to the antibiotic continues, however, the mutants can become life-threatening to the patient. It should be understood that the antibiotic does not induce the mutation. The mutant simply takes advantage of its fortuitous spontaneous appearance to flourish in the presence of a selected antibiotic. 

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