Rat polyvinyl sponge model for the study of infections: initial investigations

Hfq is a global regulator that controls the pathogenicity of Staphylococcus aureus

The Hfq protein is reported to be an RNA chaperone, which is involved in the stress response and the virulence of several pathogens. In E. coli, Hfq can mediate the interaction between some sRNAs and their target mRNAs. But it is controversial whether Hfq plays an important role in S. aureus. In this study, we found that the deletion of hfq gene in S. aureus 8325-4 can increase the surface carotenoid pigments. The hfq mutant was more resistant to oxidative stress but the pathogenicity of the mutant was reduced. We reveal that the Hfq protein can be detected only in some S. aureus strains. Using microarray and qRT-PCR, we identified 116 genes in the hfq mutant which had differential expression from the wild type, most of which are related to the phenotype and virulence of S. aureus. Among the 116 genes, 49 mRNAs can specifically bind Hfq protein, which indicates that Hfq also acts as an RNA binding protein in S. aureus. Our data suggest that Hfq protein of S. aureus is a multifunctional regulator involved in stress and virulence.

Murine neutrophils collected from subcutaneously implanted sponges

Polyvinyl sponges implanted subcutaneously in mice were used as a source of murine neutrophils (PMNs). Yield of PMNs from sponges averaged 6.3 X 10(5) PMNs per mouse and viability of sponge PMNs was 96.5%. These results were comparable to the yield and viability of PMNs harvested from peripheral blood. The chemotactic activity of sponge PMNs was significantly greater than the chemotactic activity of peripheral blood PMNs (chemotactic index of 4.78 +/- 1.66 in sponge PMNs versus 2.16 +/- 1.08 in peripheral blood PMNs, P less than 0.001). The difference in chemotactic activity was not attributable to hypotonic injury of PMNs nor the presence of soluble factors in sponge fluids. Phagocytic activity of sponge PMNs was comparable to the activity of blood PMNs (mean of 31.3 +/- 16.4% phagocytic cells for sponge PMNs versus 33.0 +/- 23.9% for blood PMNs). In addition, the number of fluorescent spheres ingested by sponge PMNs was not different (mean of 2.81 +/- 0.86 in sponge PMNs versus 2.65 +/- 0.68 spheres per cell for blood PMNs). These studies indicate that subcutaneously implanted sponges can be used as a source of functioning murine PMNs.

Rat polyvinyl sponge model for the study of infections: host factors and microbial proliferation

Female rats were treated with several administration regimens of methylprednisolone, cobra venom anti-complementary factor, and cyclophosphamide in conjunction with polyvinyl sponge implantations. The effect of these drugs on host factors active against bacteria was evaluated with Staphylococcus aureus ATCC 25933, Escherichia coli K-12, and Pseudomonas aeruginosa CDC 7725. One of two implants in each animal was infected with 10(8) of one of the three bacteria, and bacterial and granulocyte content was determined in the infected and control sponges after 48 h. The single large dose of methylprednisolone decreased staphylococcal and E. coli clearance while promoting dissemination of P. aeruginosa. A low chronic dose of the steroid inhibited E. coli chemotaxis only. A higher dose of the steroid administered chronically interfered markedly with S. aureus and E. coli curtailment by the host while leading to enhanced dissemination of P. aeruginosa, accompanied by a precipitous decline in granulocytes. Results with cobra factor resembled the higher chronic dose of steroid enhancing, especially the dissemination of the pseudomonad and its anti-granulocytic propensity. Cyclophosphamide depression of granulocytes revealed the rat's ability to curtail the proliferation of particular S. aureus and E.coli strains even in the absence of leukocytes. This treatment resulted in the rapid spread of P. aeruginosa, leading to the death of some experimental animals. These experiments underline the versatility of this animal model in the study of host and microbial factors influential in infectious disease.