The human host and the microorganisms colonizing skin and mucous surfaces constitute dynamic biological communities or ecosystems. The composition of the microbiota is relatively stable but fluctuations occur intra-individually over time, and there are also large inter-individual differences. The specific microbiota at each ecological habitat is referred to as the normal microbiota. The numerically and the most diverse human normal microbiota is found in the gastrointestinal tract, and some of the species are potential pathogens that may cause disease under certain circumstances (1). One of the functions of the gastrointestinal microbiota is to act as a barrier against overgrowth of such organisms and also to prevent colonization of pathogenic bacteria from the environment. This phenomenon is termed, "colonization resistance" (2). Treatment with antimicrobial agents disturbs the ecological balance between the host and the normal microbiota and overgrowth of yeasts and Clostridium difficile, or of intrinsically or acquired resistant microorganisms, may occur. Horizontal spread of resistance genes by conjugation or transformation to other microbial species can take place. The gastrointestinal normal microbiota plays an important role in this development (3).

Orally administered antimicrobial drugs that are incompletely absorbed or excreted via bile or transluminally, frequently give rise to a reduced colonization resistance. Other factors of importance are the antimicrobial spectrum of the agents, the dose as well as the pharmacokinetic properties of the agents. The outcome of antimicrobial treatment with respect to disturbances in the intestinal microbiota may further vary between individuals. Apart from different anatomical and physiological qualities of the host, the ability of some microorganisms to produce substances that inactivate antimicrobial agents and binding of agents to intestinal material renders the prediction of the effects difficult (4). However, the ecological impact is of great importance in the clinical situation and guidance may be acquired by knowledge of the results from studies on the ecological influence of antimicrobial agents on the normal microbiota.

Pregnancy And Childbirth

Pregnancy And Childbirth

If Pregnancy Is Something That Frightens You, It's Time To Convert Your Fear Into Joy. Ready To Give Birth To A Child? Is The New Status Hitting Your State Of Mind? Are You Still Scared To Undergo All The Pain That Your Best Friend Underwent Just A Few Days Back? Not Convinced With The Answers Given By The Experts?

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