Growth-phase regulation of lipopolysaccharide O-antigen chain length influences serum resistance in serovars of Salmonella

Abstract

The amount of lipopolysaccharide (LPS) O antigen (OAg) and its chain length distribution are important factors that protect bacteria from serum complement. Salmonella enterica serovar Typhi produces LPS with long chain length distribution (L-OAg) controlled by the wzz gene, whereas serovar Typhimurium produces LPS with two OAg chain lengths: an L-OAg controlled by Wzz ST and a very long (VL) OAg determined by Wzz fepE . This study shows that serovar Enteritidis also has a bimodal OAg distribution with two preferred OAg chain lengths similar to serovar Typhimurium. It was reported previously that OAg production by S. Typhi increases at the late exponential and stationary phases of growth. The results of this study demonstrate that increased amounts of L-OAg produced by S. Typhi grown to stationary phase confer higher levels of bacterial resistance to human serum. Production of OAg by serovars Typhimurium and Enteritidis was also under growth-phase-dependent regulation; however, while the total amount of OAg increased during growth, the VL-OAg distribution remained constant. The VL-OAg distribution was primarily responsible for complement resistance, protecting the non-typhoidal serovars from the lytic action of serum irrespective of the growth phase. As a result, the non-typhoidal species were significantly more resistant than S. Typhi to human serum. When S. Typhi was transformed with a multicopy plasmid containing the S. Typhimurium wzz fepE gene, resistance to serum increased to levels comparable to the non-typhoidal serovars. In contrast to the relevant role for high-molecular-mass OAg molecules, the presence of Vi antigen did not contribute to serum resistance of clinical isolates of serovar Typhi.

Relationship between O-antigen chain length and resistance to colicin E2 in Shigella flexneri

“…5). Interestingly, growthphase regulation of certain serovars of Salmonella expressing L-type Oag chains can also confer resistance to serum, but it is the expression of the VL-type Oag chains that confers higher levels of resistance (Bravo et al, 2008). Our study suggests that expression of both S-type and VL-type modal chain lengths by Shigella flexneri is essential for optimal virulence and for survival inside the host environment, as well as in the external environment, as a result of competition with colicinproducing Enterobacteriaceae.…”

The PmrA/PmrB regulatory system controls the expression of the wzzfepE gene involved in the O-antigen synthesis of Salmonella enterica serovar Typhimurium

“…Strains were grown to the exponential phase in L or LFe medium, and then 10 4 cells ml 21 were incubated at 37 uC for 1 h with PBS or PBS containing 20 % activated human serum (Sigma). A higher concentration of activated human serum cannot be used because the bacterial viability is drastically diminished (Bravo et al, 2008;Murray et al, 2005;Delgado et al, 2006). Survival was determined by c.f.u.…”

The cellular level of O-antigen polymerase Wzy determines chain length regulation by WzzB and WzzpHS-2 in Shigella flexneri 2a

“…The ratio of the average intensity of the bands corresponding to the S-OAg or VL-OAg relative to the intensity of the total OAg bands was calculated by quantifying the pixels in a narrow window across the centre of each lane. The densitometry analysis was calibrated using a range of loading volumes of S. flexneri 2a 2457T LPS, as described by Bravo et al (2008).…”