Acid-shock responses in Staphylococcus aureus investigated by global gene expression analysis

Abstract

A general overview is presented of the changes in the genetic expression along a time curve through the first 20 min after acidification to pH 4.5 of exponentially growing cultures of the food pathogenic strain Staphylococcus aureus 50583. A newly developed method for statistical significance testing was used to detect significant gene expression responses. Most responses showed an increase or decrease from time zero to 10 min after acidification, and then generally a stabilization in expression level from 10 to 20 min. Increased urease activity appeared to be an important factor in the acid defence, along with proton excretion by NADH dehydrogenase and macromolecule repair mechanisms. Oxidative-stress responses, such as increased expression of thioredoxin genes and upregulation of pentose phosphate pathway genes to generate more reducing power, were also induced. A general reduction in the expression of genes encoding ribosomal proteins and genes involved in nucleotide synthesis, as well as fatty acid and lipoprotein metabolism, reflected the lowered growth rate after acidification. The pH shock did not appear to trigger major virulence responses or biofilm formation. Metal ion regulation and transport were affected by the acid shock, and production of several cofactors such as molybdopterin was increased. Many of the presented observations could be explained, while some represent still-unknown mechanisms. The patterns of regulation were confirmed by quantitive reverse transcriptase PCR (QRT-PCR). Together, these results showed the main responses of S. aureus and will be a good starting point for future, more specific, in-depth studies of specific gene responses that occur in conjunction with the acid-stress defence of S. aureus.

Implication of the NorB Efflux Pump in the Adaptation of Staphylococcus aureus to Growth at Acid pH and in Resistance to Moxifloxacin

“…Regarding MDR transporters, the most noticeable change in expression was that of norA, the drug transporter gene SACOL2460, and the bicyclomicin resistance gene bcr, all of which decreased at least 3-fold after 30 min at pH 4.5. In contrast, the genes encoding the NorC efflux pump and the EmrB/QacA drug transporter showed increases in their transcript titers of at least 10-fold after 20 min at pH 4.5 (2,5). These data for norA are consistent with our findings, but there are no prior data on acid stress response of norB, encoding the NorB efflux pump, or mgrA and norG, encoding transcriptional regulators of the Nor pumps.…”

“…These adaptations are multifaceted, involving changes in expression of many genes with various functions, but the specific mechanisms are not well studied. The acid stress response has been shown to include increased transcript levels of genes involved in utilization of urease (ureA, ureB, ureC, and ureF) and of nuoF, which encodes an NADH dehydrogenase, which can increase internal cell pH by assisting proton export from the bacterial cell (1,2,5,6,28). A decrease in transcripts encoding the F 0 F 1 ATPase was also observed, which was somewhat surprising since this F 0 F 1 ATPase is considered an important proton extrusion mechanism in several Gram-positive bacterial species, such as Streptococcus mutans (17).…”

“…Expression of genes encoding certain multidrug resistance (MDR) transporters, such as norA, encoding the NorA efflux pump, and bcr, encoding the bicyclomycin resistance phenotype, are downregulated under low-pH conditions. In contrast, under the same pH conditions, other genes encoding drug efflux pumps, such as emrB/qacA and norC, exhibit substantial increases (12-fold to 15-fold, respectively) in transcript levels (2,5). Our previous studies showed that the MDR efflux pump NorB, which confers resistance to certain quinolones, such as moxifloxacin, contributes to bacterial survival when it is selectively overexpressed in subcutaneous abscesses (8).…”

Staphylococcus aureus Strain Newman Photoinactivation and Cellular Response to Sunlight Exposure

“…crtN encodes squalene synthase, an enzyme involved in carotenoid biosynthesis (41). recA and rexA encode enzymes involved in various DNA repair functions (21,51,52). We also selected an additional three genes associated with basic metabolism and cell division functions (gapA, ftsZ, and pta); these genes, along with sodA and recA, were analyzed to determine appropriate reference genes for the oxic and anoxic conditions.…”

Microbial species of safety concern in milk from informal processors in Harare, Zimbabwe

“…Staphylococcus aureus among other pathogens is destroyed by pH lower than 5 (Medveďová and Valík, 2012). However, emerging research has shown that some strains of E. coli can survive the low pH (Gran et al, 2003;Bore et al, 2007). A combination of harsh conditions and prolonged exposure time has been said to result in microbes building some adaptation mechanism (Lucking et al, 2013).…”