The CovS/CovR Acid Response Regulator Is Required for Intracellular Survival of Group B Streptococcus in Macrophages

Abstract

<jats:title>ABSTRACT</jats:title><jats:p>Group B<jats:named-content xmlns:xlink="http://www.w3.org/1999/xlink" content-type="genus-species" xlink:type="simple">Streptococcus</jats:named-content>(GBS) is a leading cause of neonatal meningitis and septicemia. The ability of this organism to survive inside phagocytic cells is poorly understood but thought to be an important step for the establishment of disease in the host. Here, we demonstrate that GBS shows prolonged survival within J774 macrophages and that the capacity to survive is not significantly changed across a diverse range of strains representing different serotypes, multilocus sequence types (MLST), and sites of clinical isolation. Using staining for the lysosome-associated membrane protein (LAMP) and by pharmacological inhibition of phagosome acidification, we demonstrate that streptococci reside in a phagosome and that acidification of the phagosome is required for GBS to survive intracellularly. Moreover, we show that the GBS two-component system CovS/CovR, which is the major acid response regulator in this organism, is required for survival inside the phagosome.</jats:p>

Differing mechanisms of surviving phagosomal stress among group BStreptococcusstrains of varying genotypes

“…1A). At 24 hr, the ST-23 strain had the greatest ability to survive inside the macrophages followed by the strains belonging to STs 17,19, and 12, which had the lowest ability to survive (Fig. 1B).…”

“…Taken together, these data suggest that diverse strains of GBS use different mechanisms to survive phagosomal stress. Since the ST-12 strain survived H 2 O 2 stress significantly better than the ST-17 strain and GBS was previously shown to prevent the induction of ROS production in the macrophage during infection, 19 we hypothesized that the ST-17 strain would have an enhanced ability to inhibit ROS production. To test this, we examined the production of ROS in placental macrophages every 30 min for 2 hr after GBS infection.…”

“…This pH requirement is congruent with a previous study that found the CovR/S acid response regulator was needed for intracellular survival. 19 When comparing the individual effect of different phagosomal stressors on each of the strains, the ST-17 strain survived better in low pH and CuCl 2 but the ST-12 strain survived better under H 2 O 2 and NO stress. Taken together, these results suggest that different GBS strains use different mechanisms to survive inside the phagosome.…”

“…19 Briefly, stationary phase cultures were washed in PBS, then resuspended in 0.1M sodium phosphate buffer pH 7.5 alone or buffer with the indicated stressor at a final concentration of approximately 1£10 6 cells/ml. Cultures were incubated for 1 hr at 37 C then diluted and plated on THA to count viable bacteria.…”

The two-component system Ihk/Irr contributes to the virulence of Streptococcus suis serotype 2 strain 05ZYH33 through alteration of the bacterial cell metabolism

“…To measure the susceptibility of S. suis to oxidative stress, we conducted H 2 O 2 -sensitivity assays according to the method reported by Cumley et al (2012) with minor modifications. Briefly, overnight-grown bacteria were diluted 100-fold into fresh THY and grown to early stationary phase at 37 uC with vigorous shaking.…”