Search

The El Tor biotype of Vibrio cholerae O1, causing the current seventh pandemic of cholera, has replaced the classical biotype, which caused the sixth pandemic. The CTX prophages encoding cholera toxin in the two biotypes have distinct repressor (rstR) genes. Recently, new variants of El Tor strains that carry the classical type ([CTX.sup.class]) prophage have emerged. These 'hybrid' strains apparently originate through lateral gene transfer and recombination events. To explore possible donors of the [CTX.sup.class] prophage and its mode of transfer, we tested environmental V. cholerae isolates for the presence of [CTX.sup.class] prophage and mobility of the phage genome. Of the 272 environmental V. cholerae isolates tested, 6 were found to carry the [CTX.sup.class] prophage; all of these belonged to the O141 serogroup. These O141 strains were unable to produce infectious [CTX.sup.class] phage or to transmit the prophage to recipient strains in the mouse model of infection; however, the [CTX.sup.class] prophage was acquired by El Tor strains when cultured with the O141 strains in microcosms composed of filtered environmental water, a chitin substrate, and a V. cholerae O141-specific bacteriophage. The [CTX.sup.class] prophage either coexisted with or replaced the resident [CTX.sup.ET] prophage, resulting in El Tor strains with CTX genotypes similar to those of the naturally occurring hybrid strains. Our results support a model involving phages and natural chitin substrate in the emergence of new variants of pathogenic V. cholerae. Furthermore, the O141 strains apparently represent an alternative reservoir of the [CTX.sup.class] phage genome, because the classical V. cholerae O1 strains are possibly extinct. hybrid Vibrio cholerae strain | toxigenic Vibrio cholerae

Host-directed therapies (HDTs) could enhance the activity of traditional antibiotics. AR-12 is a promising HDT against intracellular pathogens including Salmonella enterica serovar Typhimurium, and has been shown to act through modulation of autophagy and the Akt kinase pathway. Since AR-12 does not inhibit the growth of planktonic bacteria but only works in conjunction with the infected host-cell, we hypothesized that AR-12 could enhance the activity of antibiotics in less-susceptible strains in the intracellular host environment. We found that repetitive passaging of S. typhimurium in macrophages in the absence of antibiotics led to a 4-fold reduction in their intracellular susceptibility to streptomycin (STR), but had no effect on the bacteria's sensitivity to AR-12. Moreover, when the host-passaged strains were treated with a combined therapy of AR-12 and STR, there was a significant reduction of intracellular bacterial burden compared to STR monotherapy. Additionally, co-treatment of macrophages infected with multi-drug resistant S. typhimurium with AR-12 and STR or ampicillin showed enhanced clearance of the intracellular bacteria. The drug combination did not elicit this effect on planktonic bacteria. Overall, AR-12 enhanced the clearance of less susceptible S. typhimurium in an intracellular environment. [ABSTRACT FROM AUTHOR]

A transposon insertion library of Vibrio cholerae O1 E1 Tor biotype strain C6706 was screened to identify bacterial genes involved in mediating the phage-resistant phenotype. The results revealed that cyclase or cyclic AMP-cAMP receptor protein (cAMP)-CRP-mediated downregulation of phage adsorption might contribute to a mechanism for the V. cholerae O1 strains to survive predation by multiple environmental phages and the cyaA or crp mutant strains might be used as suitable indicators to monitor cholera phages in the water.

Phenotypic and genotypic tolerance in 71 Listeria monocytogenes isolates from different varieties of foods to benzalkonium chloride (BC) and cadmium were investigated by susceptibility test and molecular methods. To investigate the role of efflux pumps in BC tolerance, reserpine, an efflux pump inhibitor, was added to the BC tolerant strains. Tolerance to BC and cadmium were 26.8% (19/71) and 49.3% (35/71) respectively. Strains with BC tolerance were significantly more frequent among those of serotype 4b (100%, 6/6) than among those of serotype 1/2a (or 3a) (13.5%, 5/37), which represent the predominant number of strains (52.1%, 37/71). Tolerance to cadmium was encountered among 62.2% (23/37) and 50.0% (3/6) of the serotype 1/2a (or 3a) and 4b strains, respectively, and among 19.0% (4/21) of the strains of the serotype 1/2c. All of the 10 (14.1%) isolates found to be BC and cadmium co-tolerance were isolated from raw meat or quick-frozen food made of wheat flour and rice. Five multi-drug resistant strains were tolerant to cadmium as well. Among 71 isolates examined, one contained qacA and three contained qacEΔ1-sul. To the best of our knowledge, this is the first detection of qacA and qacEΔ1-sul in L. monocytogenes, an indication of the possible horizontal transfer of the two genes. Addition of reserpine to the tolerant strains resulted in the loss of tolerance among seven out of 19 BC strains, suggesting a certain role the efflux pump played in mediating BC tolerance. Of the three distinct cadA types known to date in L. monocytogenes, the cadA1 and cadA2 genes were detected among 24 (33.8%) and three (4.2%) isolates respectively. The presence of cadA1 and cadA2 largely corresponded to the susceptibility phenotype. A subset (9/35 [25.7%]) of the cadmium-tolerant isolates lacked the known cadmium resistance determinants. These findings suggest that food products could act as a reservoir for L. monocytogenes harboring tolerance to BC and cadmium and will further our understanding of the adaptations of this organism to these two compounds., (Copyright © 2014 Elsevier B.V. All rights reserved.)

Background & Objectives: Factor causing the elimination of the classical biotype of Vibrio cholerae O1, and its replacement by the El Tor biotype causing the 7 th cholera pandemic are unclear. Possible ability of the El Tor strains to adapt better than the classical strains to undefined environmental forces have been largely implicated for the change. Here we describe an environmental bacteriophage designated JSF9 which might have contributed to the range of factors., Methods: Competition assays were conducted in the infant mice model and in microcosms between representative El Tor and classical biotype strains in the absence or in the presence of JSF9 phage., Results: The JSF9 phage was found to kill classical strains and favour enrichment of El Tor strains, when mixtures containing strains of the two biotypes and JSF9 phage were subjected to alternate passage in infant mice and in samples of environmental water. Spontaneous derivatives of the classical biotype strains, as well as transposon mutants which developed resistance to JSF9 phage were found to be defective in colonization in the infant mouse model., Interpretation & Conclusions: These results suggest that in addition to other factors, the inherent ability of El Tor biotype strains to evade predation by JSF9 or similar phages which kill classical biotype strains, might have enhanced the emergence of El Tor strains as the predominant pandemic biotype.