Acquired microbial resistance

Acquired microbial resistance has been extensively investigated with various antibiotics, but similar studies with biocides are fewer and more recent. It has been confirmed that many biocides can also be rendered meffective or less effective by acquired microbial resistance. This acquired resistance to both biocides and antibiotics may be genetic and/or biochemical [16, 26]. Chromosomal gene mutation and acquisition of plasmids and transposons by the microbes are the genetic modes that have been observed. As shown in Table I, plasmid-mediated biocide resistance can occur by... 

Resistance to Tetracyclines. The tetracyclines stiU provide inexpensive and effective treatment for several microbial infections, but the emergence of acquired resistance to this class of antibiotic has limited their clinical usehilness. Studies to define the molecular basis of resistance are underway so that derivatives having improved antibacterial spectra and less susceptibiUty to bacterial resistance may be developed. Tetracyclines are antibiotics of choice for relatively few human infections encountered in daily clinical practice (104), largely as a result of the emergence of acquired tetracycline-resistance among clinically important bacteria (88,105,106). Acquired resistance occurs when resistant strains emerge from previously sensitive bacterial populations by acquisition of resistance genes which usually reside in plasmids and/or transposons (88,106,107). Furthermore, resistance deterrninants contained in transposons spread to, and become estabUshed in, diverse bacterial species (106). 

Microbial Resistance to Drugs. Figure 1 MlC-distribution showing the number of isolates of one species with a certain MIC. Some bacterial species are naturally resistant (intrinsic resistance) to drugs because their natural MIC is above the breakpoint. Naturally sensitive isolates as well as naturally resistant ones can acquire resistance and with that increase their MIC (acquired or secondary resistance). 

Note The treatment of mycobacterial infections has become an even more important and challenging problem because of the emergence of multiple-drug-resistant organisms and because of the acquired immunodeficiency syndrome (AIDS) pandemic, which has been associated with a marked increase in tuberculosis and infection caused by the M. avium complex. Because the microorganisms grow slowly and the diseases often are chronic, patient compliance, drug toxicity, and the development of microbial resistance present special therapeutic problems. 

Furthermore, esters of tylosin such as AIV (14) inhibited protein synthesis and bound to tylosin-resistant ribosomes [77], These results illustrate the dynamics of microbial resistance as antibiotics are developed to combat microorganisms which are continually evolving and acquiring new means of blocking the actions of antibiotics. 

It is, however, pertinent to mention here that a certain degree of resistance appears to be acquired in much as the same manner as in microbial resistance, such as ... 

Two major types of microbial resistance can be distinguished intrinsic and acquired resistance. Intrinsic (innate) resistance refers to a natural chromosomally controlled property, including physiological adaptation. 

Relative microbial responses to 5.1 Resistance acquired by mutation... 

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