Tetracycline-resistant

Fig. 4. Comparison of the three types of tetracycline resistance where T represents the tetracycline molecule O, a tetracycline transporter and aaa/, the ribosome A shows the effect of tetracycline exposure on a sensitive cell B, the efflux of resistance where a cytoplasmic membrane protein ( D) pumps tetracycline out of the cell as fast as the tetracycline transporter takes it up C, the ribosomal protection type of resistance where the ribosome is modified by ( ) to block productive binding and D, the tetracycline modification type of resistance where t is an inactive form of tetracycline. Reproduced with...

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). 

Table 2. Classification and Distribution of Tetracycline Resistance Determinants in Microorganisms ...

Thiatetracyclines contain a sulphur atom at position 6 in the molecule. One derivative, thiacycline, is more active than minocycline against tetracycline-resistant bacteria. Despite toxicity problems affecting its possible clinical use, thiacycline could be the starting point in the development of a new range of important tetracycline-type antibiotics. 

Tc = Tetracycline resistant Km = Kanamycine resistant Ap = Ampicilin resistant... 

In some cases, catechins can also act in synergistic mode when used in association with currently used antibiotic molecules (Table 2). EGCG exhibited synergy with /3-lactams. Sudano Roccaro et al. [73] found that this compound is able to reverse tetracycline resistance in Staphylococcus epidermidis and S. aureus isolates. This synergistic interaction has been explained by inhibition of tetracycline efflux pump activity in microbial cells resulting in an... 

Bouanchaud DH, Hellio R, Bieth G, et al. 1975. Physical studies of a plasmid mediating tetracycline resistance and hydrogen sulfide production in Escherichia coli. Mol Gen Genet 140(4) 355-359. 

Briaux S, Gerbaud G, Jaffe-Brachet A. 1979. Studies of a plasmid coding for tetracycline resistance and hydrogen sulfide production incompatible with the prophage PI. Mol Gen Genet 170 319-325. 

Antibiotics shorten the duration of diarrhea, decrease the volume of fluid lost, and shorten the duration of the carrier state (see Table 39-3). A single dose of oral doxycycline is the preferred agent. In children younger than 7 years of age, trimethoprim-sulfamethoxazole, erythromycin, and furazolidone can be used. In areas of high tetracycline resistance, fluoroquinolones are effective. 

A number of laboratories have studied the effect of methylation on nucleosome placement and/or positioning. Methylation of several sequences did not seem to affect this parameter sequences from the tetracycline resistance gene [165], Alu repeats from human DNA [166], 5S rDNA from X. borealis [164]. On the other hand, nucleosomes were excluded from a specific region in the /6-globin gene, when methylated [167], indicating the importance of the DNA sequence. Earlier data by Keshet et al. [118] showed disappearance of nucleosome-free regions (i.e., formation of nucleosomes) in methylated promoters in vivo. This effect, however, may be only indirectly connected to the methylation status of the promoters. 

Peak N, Knapp CW, Yang RK et al (2007) Abundance of six tetracycline resistance genes in waste water lagoons at cattle feedlots with different antibiotic use strategies. Environ Microbiol 9(1) 143-151... 

Auerbach EA, Seyfried EE, McMahon KD (2007) Tetracycline resistance genes in activated sludge waste water treatment plants. Water Res 41(5) 1143-1151... 

Since patients can rarely be relied upon to take (or be given) medication after fasting, and since itis common experience that doses are omitted more or less frequently the properties of doxycycline make it appear a promising successor to the first generation tetracyclines. This is even more likely since the antibacterial spectrum and activity is at least equal to that of tetracycline, and in the case of certain tetracycline-resistant bacteria doxycycline has (of all derivatives tested) shown the highest activity [35, 41]. 

Table 3. Tetracycline Resistance in Fecal Coliforms of Pigs in Antibiotic-free Herd (No Antibiotics Since 1972)...

Age of pig months No isolates Tetracycline resistance % Multiple resistance no ... 

Exposure of animals to therapeutic levels of antibiotics will markedly raise the level of resistance and a long period of time is required for the resistance levels to return to the pre-treatment level In an experiment replicated five times (Lang lo is et al ifi.) we found that exposure of animals to subtherapeutic levels of gram-positive spectrum antibiotics also resulted in increased levels of tetracycline resistance During the course of our study we have sampled pigs on two separate occasions (1974 and 1985) from another research herd in which antibiotics have never been used as feed additives but only for therapeutic purposes Of the 100 pigs sampled in 1974 only one had been... 

In the more recent Chicago outbreak of Salmonellosis, which has been attributed to milk contaminated with a tetracycline-resistant strain of Salmonella typhimurium. there were two deaths verified as resulting from infections with the resistant strain of Salmonel la in 16 284 confirmed cases. If one pools these cases with those cited in the NRDC petition then the incidence of mortality (0.09%) is similar or than that of persons affected by antibiotic-sensitive Salmone1 la (0.21%) also cited by NRDC. Thus the similarity of risks of human infections with resistant and sensitive strains of SaImone 11a agrees with research data obtained in controlled experiments (Smith 15). 

The outbreak of Salmonella foodborne illness in Illinois in April 1985 was attributed to a tetracycline-resistant strain of Salmonella typhimurium. It evidently had no connection with feeding antibiotics in livestock. The resistant strain was of lower virulence than the average sensitive strain. 

The report (7) summarized work by Richmond and Linton in England who found that 3% of all human prescriptions in a county studied were for tetracyclines, and that sewage from hospitals contained more resistant organisms than did domestic sewage. They concluded that the main selective pressure for tetracycline-resistant organisms was from medical rather than veterinary use. Richmond stated that "no reduction had occurred in the incidence of antibiotic-resistant Ej coli in Europe following the implementation of regulations recommended in the Swann Report" (7). 

The Illinois outbreak in 1985 involved 16,284 cases with two deaths verified as infections from the tetracycline-resistant strain (0.012% mortality) (Final Task Force Report, Salmonellosis outbreak, Hillfarm Dairy, Melrose Park, IL, September 1985). 

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