Serum albumin and osmolality inhibit Bdellovibrio bacteriovorus predation in human serum

Hansol Im,Sangmo Son,Cheol-Min Ghim,Robert J. Mitchell

doi:10.1038/s41598-017-06272-2

Hansol Im, Sangmo Son + Show 2 more

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https://doi.org/10.1038/s41598-017-06272-2

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Abstract

We evaluated the bactericidal activity of Bdellovibrio bacteriovorus, strain HD100, within blood sera against bacterial strains commonly associated with bacteremic infections, including E. coli, Klebsiella pneumoniae and Salmonella enterica. Tests show that B. bacteriovorus HD100 is not susceptible to serum complement or its bactericidal activity. After a two hour exposure to human sera, the prey populations decreased 15- to 7,300-fold due to the serum complement activity while, in contrast, the B. bacteriovorus HD100 population showed a loss of only 33%. Dot blot analyses showed that this is not due to the absence of antibodies against this predator. Predation in human serum was inhibited, though, by both the osmolality and serum albumin. The activity of B. bacteriovorus HD100 showed a sharp transition between 200 and 250 mOsm/kg, and was progressively reduced as the osmolality increased. Serum albumin also acted to inhibit predation by binding to and coating the predatory cells. This was confirmed via dot blot analyses and confocal microscopy. The results from both the osmolality and serum albumin tests were incorporated into a numerical model describing bacterial predation of pathogens. In conclusion, both of these factors inhibit predation and, as such, they limit its effectiveness against pathogenic prey located within sera.

Highlights

Bacteremia is defined as the presence of bacteria within the bloodstream and is a medical condition that poses a serious concern for the patient, if it leads to sepsis
The results with B. bacteriovorus HD100 stood in contrast with its prey strains as its viability remained constant even up to 24 hours (Fig. 1d)
One defense that the human body has against bacterial cells present in the serum is the complement, i.e., a group of proteins that work in conjunction with each other to kill bacterial cells

Summary

Introduction

Bacteremia is defined as the presence of bacteria within the bloodstream and is a medical condition that poses a serious concern for the patient, if it leads to sepsis. A direct correlation between HIV infection and Salmonella-associated bacteremia is supported by several studies from various countries, including Thailand, Kenya and Spain[5, 9,10,11], and by reports that found the incidence of Salmonella-related bacteremia is 20 to 100 times more likely in patients with a depressed immunity[12, 13] For these patients, the mortality rates were significantly greater when bacteremia occurred[6]. Drug-resistant strains of E. coli and Salmonella have been isolated from patients suffering from bacteremia infections[16,17,18,19] Predatory bacteria, such as Bdellovibrio bacteriovorus HD100, present another option for treatment as they have been shown to attack and kill human pathogens[20,21,22], including E. coli, Salmonella and K. pneumoniae, and to significantly attenuate drug-resistant bacterial populations and the genes conferring resistance[23,24,25]. In this study, we examined the activity and viability of B. bacteriovorus HD100 when this bacterium was exposed to human sera

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