Studies on the isolation and characterization of Proteus mirabilis siderophores provided no evidence that these bacteria synthesize catechol- or hydroxamate-type siderophores. However, gas chromatograph analysis in conjunction with mass spectroscopy revealed the presence of alpha-hydroxyisovaleric acid, a previously unknown metabolite. Additional substantiating evidence for the presence of alpha-hydroxyisovaleric acid in these bacteria was obtained from experiments involving the use of thin-layer chromatography and an ultraviolet absorption spectrum. This compound was found to be capable of removing iron from the synthetic chelator, ethylene-diamine-di-orthohydroxyphenyl acetic acid, and supplying that iron to the bacteria both in a solid agar medium and in a liquid medium. Proteus mirabilis was found to possess an enzyme capable of catalyzing the reaction by which alpha-hydroxyisovaleric acid is converted to alpha-ketoisovaleric acid, an intermediate in the valine biosynthetic pathway.

No abstract

In an attempt to gain insight into the events that take place during Actinobacillus pleuropneumoniae infection, the present study was designed to ascertain the effects of bacterial toxicity on porcine neutrophil functions and viability. Incubation of phagocytes (2 x 10(6)) with opsonized A. pleuropneumoniae 4074 (2 x 10(7) CFU) resulted in phagocytic uptake of less than or equal to 4%. At the same bacterium-to-phagocyte ratio, levels of lactate dehydrogenase activity of 74 and 81% were detected in the extracellular medium after 1.5 and 3 h of incubation, respectively. Furthermore, the ingested bacteria were not killed by the phagocytes. These effects were ascribed to hemolysin produced by the bacteria, because the presence of hemolysin-neutralizing antibody prevented overt cellular damage, significantly increased phagocytic uptake (P less than 0.001), and resulted in an approximately 10-fold decrease in the number of CFU of the ingested bacteria. Cytolytic doses of isolated hemolysin caused dose-related loss of cell viability, diminished bactericidal activity of toxin-treated phagocytes for Escherichia coli, and decreased the ability of the phagocytes to undergo a respiratory burst upon stimulation with phorbol myristic acetate. In contrast, sublytic doses of the hemolysin activated the phagocytes and caused them to respond to phorbol myristic acetate with increased generation of superoxide anion. Because heated (100 degrees C, 5 min) hemolysin preparations did not produce similar effects, we contend that the observed effects were not due to contaminating endotoxin. The data presented herein indicate that A. pleuropneumoniae hemolysin is a potent antiphagocytic virulence factor by virtue of its leukocidal activity. Sublytic doses of the toxin may have important effects on the oxidative metabolism of phagocytic cells.

Moderately iron-deficient rats were significantly less susceptible to experimentally induced Proteus mirabilis pyelonephritis than iron-sufficient or severely iron-deficient littermates, as indicated by significantly lower prevalence of infection, mean pyelonephritic lesion scores, and numbers of P. mirabilis cells recovered from the kidneys.

The role of Corynebacterium renale urease in the establishment of pyelonephritis was studied by the oral administration of acetohydroxamic acid (AHA), a urease inhibitor, to experimentally infected rats. The bacteria were introduced by surgical insertion of a zinc disc containing 1 X 10(6) colony-forming units of C-renale into the urinary bladder whereas sterile discs were implanted in the bladders of the control animals. Daily administration of AHA via the drinking water did not halt the development of pyelonephritis. Larger doses, given by gavage, did accomplish this goal; that is, the pH of the urine was lowered, the number of colony-forming units of C. renale in the kidney was reduced drastically, and pyelonephritic lesions were observed in the kidney by light-microscopic examination. All experimental rats developed cystitis in varying degrees of severity. About 70% of the intact AHA given by gavage was excreted in the urine 24 h after administration of this compound. Rats implanted with a urease-negative mutant of C. renale displayed no signs of pyelonephritis but did develop cystitis.