Microbial resistance, emergence

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. 

Identifying the emergence of microbial resistance in humans and animals. 

Microbial resistance to drugs can emerge via the gradual selecting out of innately resistant mutant strains from a microbial population or, more commonly, via R-factor plasmid-mediated transmission between bacteria. The primary mechanisms of microbial resistance are shown in Table V-1-2. 

Much data have now shown that peptides, proteins, and lipids exhibit antimicrobial activity. The selective toxicity of peptides toward bacterial cells is primarily due to an initial electrostatic interaction between the peptide and the anionic phospholipid headgroups in the outer leaflet of the bacterial cytoplasmic membrane (Zasloff, 1987 Yeaman and Yount, 2003). A diversity of antimicrobial peptide sequences and structures have been discovered (Yeaman and Yount, 2003 Lai and GaUo, 2009), and this diversity underscores the reality that no single antimicrobial peptide sequence has emerged as an effective antimicrobial. Furthermore, the diversity of molecules as antimicrobials may be an evolutionary strategy to prevent or delay the development of microbial resistance to antimicrobial peptides. 

It was once believed that gentamicin would be very unlikely to cause bacterial resistance (SED VII, p. 376). Many reports have since then appeared from hospitals in several countries on the emergence and spread of gentamicin-resistant bacteria (SED VIII, p. 618), demonstrating that the antibiotic does not constitute an exception to the general rule that widespread or indiscriminate use of an antibiotic favours the development of microbial resistance. 

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). 

It is only very recently that organic componnds synthesized by humans have begun to exert a selection pressure upon natural populations, with the consequent emergence of resistant strains. Pesticides are a prime example and will be the principal subject of the present section. It should be mentioned, however, that other types of biocides (e.g., antibiotics and disinfectants) can produce a similar response in microbial populations that are exposed to them. 

The emergence of microbial antibiotic drug resistance was speeded by the indiscriminate use of antibiotics in humans and livestock. Exposure to very low concentrations of antibiotic in meat or milk may have provided a path whereby human pathogens could eventually evolve high-level antibiotic drug resistance. Recently some strains of enterococcus and tuberculosis have developed resistance to all known antibiotic drugs. Inappropriate use of antibiotics is very common, and it accelerates the development of resistance in pathogens. 

Choose the best answer for the following. The emergence of microbial antibiotic drug resistance... 

D. The indiscriminate use of antibiotics in humans is the major reason for the emergence of microbial antibiotic resistance. Such resistance, which is most apparent in hospitals, has developed to all antibiotics, including vancomycin. The use of antibiotics in livestock has compounded the problem. 

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