Transferable resistance to trimethoprim in Shigella

Efficacy and potential of phage therapy against multidrug resistant Shigella spp

Shigella-infected bacillary dysentery or commonly known as Shigellosis is a leading cause of morbidity and mortality worldwide. The gradual emergence of multidrug resistant Shigella spp. has triggered the search for alternatives to conventional antibiotics. Phage therapy could be one such suitable alternative, given its proven long term safety profile as well as the rapid expansion of phage therapy research. To be successful, phage therapy will need an adequate regulatory framework, effective strategies, the proper selection of appropriate phages, early solutions to overcome phage therapy limitations, the implementation of safety protocols, and finally improved public awareness. To achieve all these criteria and successfully apply phage therapy against multidrug resistant shigellosis, a comprehensive study is required. In fact, a variety of phage-based approaches and products including single phages, phage cocktails, mutated phages, genetically engineered phages, and combinations of phages with antibiotics have already been carried out to test the applications of phage therapy against multidrug resistant Shigella. This review provides a broad survey of phage treatments from past to present, focusing on the history, applications, limitations and effective solutions related to, as well as the prospects for, the use of phage therapy against multidrug resistant Shigella spp. and other multidrug resistant bacterial pathogens.

General considerations in the management of typhoid fever and dysentery

Typhoid fever is diagnosed on the basis of isolation of Salmonella typhi from blood, bone marrow, or bile. S. typhi found in stool or urine may reflect chronic asymptomatic carriage. Although antimicrobial therapy may not eliminate carriage, it is effective for the treatment of clinically evident acute disease. Among the drugs currently available, chloramphenicol is the most widely used. Chloramphenicol is effective and inexpensive, but it is associated with a 3% rate of chronic carriage, a high relapse rate, and, in rare cases, aplastic anemia. For these reasons, and because of the emergence of chloramphenicol-resistant strains of S. typhi, alternative drugs need to be considered. Dysentery is characterized by the passage of unformed stools that commonly contain blood and mucus and in which large numbers of leukocytes can be detected on microscopic examination. Invasion of the intestinal epithelium is the distinguishing characteristic, and Shigella sp are the most frequent cause. Although oral rehydration is useful in dehydrated patients, dehydration is not a common problem in acute dysentery, and antimicrobial treatment is indicated for this disease. An antimicrobial agent should be selected on the basis of knowledge of the susceptibility patterns of locally isolated Shigella strains.

Characterization of transferable plasmids from Shigella flexneri 2a that confer resistance to trimethoprim, streptomycin, and sulfonamides

A set of plasmids conferring resistance to several antibiotics, including the combination of trimethoprim and sulfamethoxazole, has been isolated from Escherichia coli following conjugative cotransfer from a clinical isolate of Shigella flexneri 2a. One of the plasmids, pCN1, was shown by subcloning and DNA sequencing to carry a gene encoding a trimethoprim-insensitive dihydrofolate reductase identical to that found in E. coli transposon 7. This plasmid was also shown to confer resistance to both streptomycin and spectinomycin by production of an adenylyltransferase that inactivated the drugs and the gene encoding this enzyme has also been sequenced. A second plasmid from the set, pCN2, was shown to inactivate streptomycin by a phosphotransferase mechanism and also to confer resistance to sulfonamides. The third plasmid from the set could not be correlated with a drug-resistance phenotype, but does appear to play a crucial role in plasmid mobilization.

Sulfamethoxazole-trimethoprim-resistant Shigella flexneri in northeastern Brazil

In contrast to prior experience in northeastern Brazil, three of four Shigella flexneri strains recently isolated from patients with acute inflammatory diarrhea in this setting were found to be resistant to sulfamethoxazole-trimethoprim. The resistant strains contained large, different plasmids, two of which were transferred with sulfamethoxazole-trimethoprim resistance to Escherichia coli K-12 recipient strains.

R plasmids conferring multiple drug resistance from shigella isolated in Korea

The majority (85%) of shigella isolated in 1980 and 1981 in Korea were Shigella flexneri, the others were Sh. sonnei (14%) with only a small number of Sh. dysenteriae. Only 14 of the 459 strains of shigella isolated were susceptible to all 12 drugs tested, and 445 were resistant to three or more drugs. Strains multiply resistant to the six drugs, chloramphenicol (Cm), tetracycline (Tc), streptomycin (Sm), sulfisomidine (Su), ampicillin (Ap) and trimethoprim (Tp) were most frequently encountered, followed by those resistant to Cm, Tc, Sm, Su and Tp. The complete patterns of resistance to drugs except nalidixic acid and rifampin in approximately 73% of drug-resistant strains were co-transferred to Escherichia coli by conjugation, indicating that the resistance was R plasmid-mediated. Randomly selected R plasmids conferring various patterns of resistance markers were tested for the incompatibility groups, and almost all of them were classified into Inc FII. Two of three R plasmids conferring resistance to Cm, Tc, Sm and Su were classified into Inc B and one to Inc FII. Two R types with resistance markers of Cm, Tc, Sm and Ap were not classified with our standard plasmids used.