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Microb Pathog. 2015 Feb;79:70-9. doi: 10.1016/j.micpath.2015.01.009. Epub 2015 Jan 24.

The role of the hok/sok locus in bacterial response to stressful growth conditions.

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Department of Pathology and Infectious Diseases, Royal Veterinary College, University of London, UK; Department of Veterinary Pathology and Microbiology, University of Nigeria, Nsukka, Enugu State, Nigeria. Electronic address:
Department of Pathology and Infectious Diseases, Royal Veterinary College, University of London, UK.


The hok/sok locus is renowned for its plasmid stabilization effect via post-segregational killing of plasmid-free daughter cells. However, the function(s) of the chromosome-encoded loci, which are more abundant in pathogenic strains of a broad range of enteric bacteria, are yet to be understood. Also, the frequent occurrence of this toxin/antitoxin addiction system in multi-drug resistance plasmids suggests additional roles. In this study, the effects of the hok/sok locus on the growth of bacteria in stressful growth-limiting conditions such as high temperature and antibiotic burden were investigated using hok/sok plasmids. The results showed that the hok/sok locus prolonged the lag phase of host cell cultures, thereby enabling the cells to adapt, respond to the stress and eventually thrive in these growth-limiting conditions by increasing the growth rate at exponential phase. The hok/sok locus also enhanced the survival and growth of cells in low cell density cultures irrespective of unfavourable growth conditions, and may complement existing or defective SOS mechanism. In addition to the plasmid stabilization function, these effects would enhance the ability of pathogenic bacteria to establish infections and propagate the antibiotic resistance elements carried on these plasmids, thereby contributing to the virulence of such bacteria.


Antibiotic resistance; Bacterial growth; Hok/sok; Plasmid; Stress response

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