Acute pyelonephritis, a complication of Escherichia coli bacteriuria, must represent a bacterial invasion through the kidney epithelium. To study this process, we overlaid bacterial suspensions onto monolayers of cultured human kidney proximal tubular epithelial cells and measured cytotoxicity by release of lactate dehydrogenase (LDH). Thirty-four isolates cultured from patients with acute pyelonephritis were screened for the ability to cause pyelonephritis in CBA mice by transurethral challenge. The eight most virulent strains

Proteus mirabilis, a common cause of urinary tract infection, can lead to serious complications including pyelonephritis. Adherence factors, urease, and hemolysin may be virulence determinants. These factors were compared for bacteria cultured from 16 patients with acute pyelonephritis and 35 with catheter-associated bacteriuria and for 20 fecal isolates. Pyelonephritis isolates were more likely (P less than .05) to express the mannose-resistant/Proteus-like (MR/P) hemagglutinin in the absence of mannose-resistant/Klebsiella-like (MR/K) hemagglutinin than were catheter-associated or fecal isolates. Pyelonephritis isolates produced urease activity of 63 +/- 27 (mean +/- SD) mumol of NH3/min/mg of protein, not significantly different from catheter-associated or fecal isolates. Hybridization of Southern blots of P. mirabilis chromosomal DNA with two urease gene probes demonstrated that urease gene sequences were conserved in all isolates. Geometric mean of reciprocal hemolytic titers for pyelonephritis isolates was 27.9; for urinary catheter isolates, 18.0; and for fecal isolates, 55.7 (not significantly different, P greater than .1). Although in vivo expression of urease and hemolysin may not be reliable indexes of virulence, MR/P hemagglutination in the absence of MR/K hemagglutination may be necessary for development of pyelonephritis.

A human gastric adenocarcinoma cell line was used to evaluate the contribution of urease from Helicobacter (formerly Campylobacter) pylori to its cytotoxicity. Gastric cells cultured in medium supplemented with 20 mM urea were exposed to 5 x 10(6) CFU of H. pylori per ml with or without the addition of a urease inhibitor, acetohydroxamic acid. Viabilities of cells exposed to H. pylori for 2, 24, and 48 h, assessed by incorporation of neutral red dye, were 60, 27, and 16%, respectively; however, the viabilities of cells exposed to both H. pylori and acetohydroxamic acid were 92, 46, and 20% after 2, 24, and 48 h, respectively, (P less than 0.001). Therefore, the urease activity of H. pylori may play an important role in its pathogenicity, and inhibition of this enzyme activity may have therapeutic potential.

We concluded that bacteria lacking Hpn, cultured in vitro, are more susceptible than is the wild type to bismuth and Ni2+.

Serial passage of Pseudomonas aeruginosa ATCC 27853 or Escherichia coli ATCC 25922 on agar with subinhibitory concentrations of norfloxacin rapidly produced isolates with minimal inhibitory concentrations (MICs) of norfloxacin up to 512-fold higher than that for the original strain. Although MICs of seven unrelated antibiotics were unchanged, increasing MICs occurred in parallel with norfloxacin, cinoxacin, and nalidixic acid regardless of which of these three organic acids was used to select for increased resistance. P. aeruginosa with a norfloxacin MIC of greater than 256 F.g/ml could be selected; however, E. coli with MICs greater than the clinically achievable level of 16 Fg/ml could not be produced.Rapid selection or induction of resistance in gram-negative bacilli by passage on subinhibitory concentrations of nalidixic acid and cinoxacin is a well-described property of these organicacid antibiotics (3