The protective effect of intravenously administred rabbit antitoxin serum was studied in lethal Pseudomonas aeruginosa bum infections in mice. Survival after infection with 2 median lethal doses of a toxigenic, low-protease-producing strain (PA103) was enhanced in antitoxin-treated mice, as compared with controls that had received anti-bovine serum albumin serum (P = 0.0004). Survival time was prolonged in other antitoxin-treated mice infected with toxigenic, highprotease-producing strains (PA86 and PA220, P = 0.0003 and P = 0.01, respectively). In contrast, antitoxin had no protective effect in mice challenged with a nontoxigenic strain (WR 5, P = 0.57). There were fewer viable bacteria in blood and liver of antitoxin-treated mice than in those of anti-bovine serum albumintreated controls after infection with toxigenic organisms, whereas there were no significant differences between the two groups after challenge with the nontoxigenic strain. These data suggest that P. aeruginosa exotoxin A contributes to lethality in this burn infection model, and this effect is diminished by passive immunization with antitoxin.
The data presented indicate that in experimental Pseudomonas aeruginosa infection of mice, protease enhances the virulence of the organism. Anesthetized CBA/Lu mice were subjected to a 15-s flame burn and infected with a wild-type protease-producing strain and two of its protease-deficient mutants. The average bacterial cell mean lethal dose (LD5o) of 3.8 ± 0.3 standard deviation logoi) for mice infected with the protease-producing P. aeruginosa was at least 1 log lower than the LD5o of the protease-deficient mutants (0.02 > P > 0.01). The addition of purified protease to the infecting inoculum of protease-deficient strains reduced the LD50. Although the generation time in vitro was the same for all three bacterial strains used, there were consistently fewer viable bacteria in the blood of mice infected with protease-deficient strains than in those infected with the protease-producing strain. When a protease-deficient strain was mixed with the protease-producing wild-type strain, the number of protease-producing pseudomonas found in the blood remained constant, whereas the number of proteasedeficient organisms increased, suggesting that protease contributed to the invasiveness of the organisms. The survival of mice infected with protease-producing pseudomonas was enhanced by antiprotease serum. Antiprotease serum had no effect in mice infected with protease-deficient mutants.
Development of a routine detection assay for Campylobacter jejuni and Campylobacter coli in clinical specimens was undertaken by using the polymerase chain reaction (PCR). An oligonucleotide primer pair from a conserved 5' region of theflaA gene of C. coli VC167 was used to amplify a 450-bp region by PCR. The primer pair specifically detected 4 strains of C. coli and 47 strains of C. jejuni; but it did not detect strains of Campylobacterfetus, Campylobacter lari, Campylobacter upsaliensis, Campylobacter cryaerophila, Campylobacter butzleri, Campylobacter hyointestinalis, WolineUa recta, Helicobacter pylori, Escherichia coli, ShigeUa spp., SalmoneUla spp., Vibrio cholerae, Citrobacterjfreundii, or Aeromonas spp. By using a nonradioactively labeled probe internal to the PCR product, the assay could detect as little as 0.0062 pg of purified C. coli DNA, or the equivalent of four bacteria. In stools seeded with C. coli cells, the probe could detect between 30 and 60 bacteria per PCR assay. The assay was also successfuly used to detect C. coli in rectal swab specimens from experimentally infected rabbits and C. jejuni in human stool samples.
An exotoxin, toxic to both mice and cultured cells, was isolated from cultures of Pseudomonas aeruginosa. Relatively small amounts of the exotoxin inhibited the uptake of uridine and amino acids by Vero cells. Within limits, this toxic action was reversible and could be inactivated by heating at 70 C or by proteolytic digestion, but it was not affected by nucleases. The inhibitory activity of the toxin could also be decreased by rabbit antiserum. Metabolic activities of Vero cells, generally associated with the production of energy, did not appear to be affected by the toxin.
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