Comparison of Escherichia coli O157:H7 antigen detection in stool and broth cultures to that in sorbitol-MacConkey agar stool cultures.

We evaluated the Meridian IC-STAT direct fecal and broth culture antigen detection methods with samples from children infected with Escherichia coli O157:H7 and correlated the antigen detection results with the culture results. Stools of 16 children who had recently had stool cultures positive for this pathogen (population A) and 102 children with diarrhea of unknown cause (population B) were tested with the IC-STAT device (direct testing). Fecal broth cultures were also tested with this device (broth testing). The results were correlated to a standard of the combined yield from direct culture of stools on sorbitol-MacConkey (SMAC) agar and culture of broth on SMAC agar. Eleven (69%) of the population A stool specimens yielded E. coli O157:H7 when plated directly on SMAC agar. Two more specimens yielded this pathogen when the broth culture was similarly plated. Of these 13 stool specimens, 8 and 13 were positive by direct and broth testing (respective sensitivities, 62 and 100%). Compared to the sensitivity of a simultaneously performed SMAC agar culture, the sensitivity of direct testing was 73%. Three (3%) of the population B stool specimens contained E. coli O157:H7 on SMAC agar culture; one and three of these stool specimens were positive by direct and broth testing, respectively. The direct and broth IC-STAT tests were 100% specific with samples from children from population B. Direct IC-STAT testing of stools is rapid, easily performed, and specific but is insufficiently sensitive to exclude the possibility of infection with E. coli O157:H7. Performing the IC-STAT test with a broth culture increases its sensitivity. However, attempts to recover E. coli O157:H7 by culture should not be abandoned but, rather, should be increased when the IC-STAT test result is positive.

Activities of tobramycin and six other antibiotics against Pseudomonas aeruginosa isolates from patients with cystic fibrosis.

The in vitro activity of tobramycin was compared with those of six other antimicrobial agents against 1,240 Pseudomonas aeruginosa isolates collected from 508 patients with cystic fibrosis during pretreatment visits as part of the phase III clinical trials of tobramycin solution for inhalation. The tobramycin MIC at which 50% of isolates are inhibited (MIC(50)) and MIC(90) were 1 and 8 microg/ml, respectively. Tobramycin was the most active drug tested and also showed good activity against isolates resistant to multiple antibiotics. The isolates were less frequently resistant to tobramycin (5.4%) than to ceftazidime (11.1%), aztreonam (11.9%), amikacin (13.1%), ticarcillin (16.7%), gentamicin (19.3%), or ciprofloxacin (20.7%). For all antibiotics tested, nonmucoid isolates were more resistant than mucoid isolates. Of 56 isolates for which the tobramycin MIC was > or = 16 microg/ml and that were investigated for resistance mechanisms, only 7 (12.5%) were shown to possess known aminoglycoside-modifying enzymes; the remaining were presumably resistant by an incompletely understood mechanism often referred to as "impermeability."

Microbiology of sputum from patients at cystic fibrosis centers in the United States.

During a phase III national collaborative study of aerosolized tobramycin (1 July 1995 through 30 September 1996), the microbiology of specimens from 595 patients at 69 cystic fibrosis (CF) centers was examined. Samples from three screening visits were processed in a single laboratory by means of standardized techniques for identification and susceptibility testing. From 1,753 pretreatment specimens, 5,128 pathogens were isolated (average, 2.9/specimen). Of the 3,936 Pseudomonas aeruginosa isolates, 56.7% were mucoid. The specimens of 125 patients (21.0%) yielded tobramycin-resistant P. aeruginosa (213 isolates); 61 (10.3%), Stenotrophomonas maltophilia; and 52 (8.7%), Alcaligenes xylosoxidans. Isolation of Burkholderia cepacia was an exclusion criterion. Only visit 3 sputum samples were cultured for gram-positive organisms and fungi (n = 465 patients); samples from 201 patients (43.2%) yielded Staphylococcus aureus (18.8% of isolates were oxacillin-resistant), and those from 114 (24.5%) yielded an Aspergillus species. Compared with the Cystic Fibrosis Foundation Patient Registry, the current study identified many more patients colonized with S. maltophilia, A. xylosoxidans, Aspergillus species, and oxacillin-resistant S. aureus, suggesting the utility of standardized processing of CF specimens.