Comparative susceptibilities of Klebsiella species, Enterobacter species, and Pseudomonas aeruginosa to 11 antimicrobial agents in a tertiary-care university hospital.

The in vitro activity of cefepime was compared versus that of 10 antimicrobial agents commonly used in the treatment of serious infections caused by common aerobic gram-negative bacteria: aztreonam, cefoperazone, ceftazidime, ceftriaxone, ciprofloxacin, gentamicin, imipenem, piperacillin, ticarcillin-clavulanic acid, and tobramycin. We tested 30 clinical isolates representing a cross section of Klebsiella and Enterobacter species and Pseudomonas aeruginosa collected at our tertiary-care university hospital. The most potent beta-lactams were imipenem and cefepime, which demonstrated significant activity against the majority of strains in all 3 genera of bacteria tested, as did ciprofloxacin and tobramycin. Ceftazidime was active against Pseudomonas aeruginosa but was less potent against Klebsiella and Enterobacter spp. Cefoperazone and ceftriaxone were less active than ceftazidime against Pseudomonas aeruginosa. Cefepime was found to be highly active against many resistant organisms that traditionally have been difficult to treat.

Presence of respiratory viruses in middle ear fluids and nasal wash specimens from children with acute otitis media.

During a 28-month period, 84 children with acute otitis media were studied by viral and bacterial cultures of middle ear fluid and viral cultures of nasal lavage fluid. Viruses were isolated from the middle ear fluid of 17 (20%) patients. Evidence of viral infection was demonstrated by positive viral cultures of middle ear fluid and/or nasal lavage fluid in 33 (39%) patients. Rhinovirus in one patient and influenza b virus in another were the only pathogens isolated. Influenza virus, enterovirus, and rhinovirus were the most common viruses found in middle ear fluids. Parainfluenza virus, adenovirus, and respiratory syncytial virus were found less often. In 82% of cases, the virus isolated from middle ear fluid was also isolated from nasal lavage fluid, but only 44% of viruses found in nasal lavage fluid were also found in middle ear fluid. Mixed bacterial and combined viral-bacterial infections were common. Only 15% of patients had no pathogen isolated from middle ear fluids. Using tissue culture techniques, we demonstrated that enterovirus and rhinovirus are also common middle ear pathogens. Our data reemphasize the significance of viruses as etiologic agents of acute otitis media and propose several questions regarding the viral-bacterial interactions and the types of viruses involved in the pathogenesis of the disease.

Investigation of a pseudo-outbreak of orthopedic infections caused by Pseudomonas aeruginosa.

OBJECTIVE: To report a pseudoepidemic of Pseudomonas aeruginosa infections discovered during an investigation of postoperative joint infections. DESIGN: A retrospective review of case patients' hospital charts, operative reports, and laboratory data, as well as environmental culturing, polymerase chain reaction (PCR) ribotyping of outbreak isolates, and in vitro analysis of P aeruginosa growth characteristics. SETTING: A 510-bed, university-affiliated adult tertiary care hospital. RESULTS: Between October 1 and December 1, 1992, seven postsurgical joint infections were diagnosed, including four caused by P aeruginosa. A bottle of "sterile" saline used to process tissue specimens was found to be contaminated with P aeruginosa. Further investigation revealed that P aeruginosa had grown from seven additional tissue cultures, all of which had been processed with the contaminated saline. PCR ribotypes of the contaminant matched those of the clinical isolates. In vitro, P aeruginosa strains were viable in commercial nonbacteriostatic saline, but never caused visible turbidity. Six patients received antibiotics for their presumed infections; four patients had peripherally inserted central catheters placed, and one experienced severe anaphylactic reactions to several antibiotics. CONCLUSIONS: Pseudoepidemics due to common organisms are often difficult to detect, and delayed recognition can result in substantial morbidity. This outbreak investigation illustrates the potential for contamination of diluents in the microbiology laboratory and emphasizes the need for meticulous quality control.

The detection of positive blood cultures by the AccuMed ESP-384 system: the clinical significance of three-day testing.

A total of 805 positive blood cultures obtained over a 4-month period during 1997 by the AccuMed ESP-384 system were evaluated and compared with 471 positive blood cultures obtained during 1989. Of the 805 microorganisms isolated in 5-day culture and testing by the ESP-384, 671 (83.4%) were detected within the first 2 days and 758 (94.2%) within 3 days. There were 47 (5.7%) microorganisms detected in culture Days 4 and 5 from 42 patients and review of the medical records from these patients demonstrated that no significant changes in clinical management were instituted as a result of detection and identification of these isolates. These 47 organisms were considered to be zero to equivocal clinical relevance. These data suggest that a 3-day routine blood culture incubation protocol with the ESP-384 system may be sufficient when considering detection rate, clinical relevance, and cost-effectiveness. The microbial spectrum and relative frequencies in this study were found to be similar to those of positive blood cultures obtained during 1989.

Comparison of Streptex versus PathoDx for group D typing of vancomycin-resistant Enterococcus.

Vancomycin-resistant enterococci recently isolated from patient specimens were tested with both Streptex and PathoDx group D latex agglutination antisera. Using routine protocols, all isolates from patients at Temple University Hospital were positive with the PathoDx reagents and were negative with the Streptex reagents. Isolates required extensive boiling for positive reactions to occur using Streptex reagents.

Effect of pre-stain viability on the acid-fast staining characteristics of Mycobacterium species.

Five species of mycobacteria were stained by Ziehl-Neelsen, Kinyoun and Auramine-Rhodamine after either routine autoclaving, or exposure to rifabutin and ciprofloxacin. Organisms from each treatment group were stained and compared to viable controls. ATCC strains and fresh clinical isolates of all five species were evaluated. All species in both treatment protocols presented similar staining characteristics. Viability of mycobacteria, therefore, must be established by culture.

The detection of positive blood cultures by the BACTEC NR660. The clinical importance of four-day versus seven-day testing.

A total of 471 positive blood cultures obtained over a 3-month period were identified and evaluated for day of positivity by the BACTEC NR660. Of all positive blood cultures, 73% (344) were detected within the first 2 days, and 94% (441) were detected through day 4. The proportion of positive cultures detected at day 5 was significantly lower than that at day 4 (p less than 0.01). Patient chart review revealed that two of 30 isolates (0.4% of all positive isolates) identified on days 5-7 were considered clinically significant and would have been missed if cultures would not have been evaluated for seven days. Therefore, very limited additional patient benefit is derived after greater than 4 days of growth and detection by the BACTEC NR660.

In vitro activity of beta-lactamase inhibitors against clinical isolates of Acinetobacter species.

Acinetobacter is an important cause of nosocomial infections, and it is often resistant to many antibiotics. In a search for alternative agents, three beta-lactamase inhibitors (sulbactam, clavulanate, and tazobactam) and five beta-lactam antibiotics (imipenem, ceftazidime, ceftriaxone, cefotaxime, and piperacillin) were tested against 68 unique clinical isolates of Acinetobacter species. Minimum inhibitory concentrations were determined by a broth microdilution method. Using temperature sensitivity testing, we identified 59 strains as Acinetobacter baumannii, one as Acinetobacter haemolyticus, and eight as indeterminate biotype species. We demonstrated 41 of 59 (70%) strains of A. baumannii to be multiply resistant (susceptible only to amikacin and imipenem), whereas all the nonbaumannii strains were not. Imipenem was the most active agent among the compounds investigated. All three beta-lactamase inhibitors had strong intrinsic activity, with sulbactam being the most active agent among the beta-lactamase inhibitors studied.

Evaluation of the RapID Yeast Plus System for the identification of yeast.

We evaluated the RapID Yeast Plus System using 117 fresh and frozen clinical yeast isolates. The Uni-Yeast-Tek System was used to establish the correct identification. The Vitek System was used as the arbiter for any discrepant results, along with morphology. Of 117 isolates tested, the RapID Yeast Plus System identified 96.6% correctly. The RapID Yeast Plus System is an accurate and reliable alternative to other commonly used yeast identification systems.

Comparison of AMS-Vitek, MicroScan, and Autobac Series II for the identification of gram-negative bacilli.

Identification of Gram-negative bacilli by AMS-Vitek, MicroScan, and Autobac Series II was evaluated with 434 clinical isolates comprising glucose fermenters and glucose nonfermenters. The organisms were tested in each of the three systems (the AMS Vitek GNI card, the MicroScan Combo Plus Panel, and the Autobac 18 chamber cuvette). API 20E was used as the primary reference system. MicroScan and Vitek correctly identified 96.1% and 95.6% of the organisms, respectively. The Autobac Series II identified 82.3% of the organisms correctly. Results with MicroScan, Vitek, and Autobac were available in 24-48 hours, 4-18 hours, and 3-8 hours, respectively.

A comparison of serial plate agar dilution, Bauer-Kirby disk diffusion, and the Vitek AutoMicrobic system for the determination of susceptibilities of Klebsiella spp., Enterobacter spp., and Pseudomonas aeruginosa to ten antimicrobial agents.

The use of rapid, automated technologies for assessment of antimicrobial susceptibility and determination of minimum inhibitory concentrations has been evolving for over a decade. We compared the Vitek AutoMicrobic system and Bauer-Kirby disk diffusion with the National Committee for Clinical Laboratory Standards methods of serial plate agar dilution for qualitative and quantitative susceptibilities of 301 hospital isolates of Klebsiella spp., Enterobacter spp., and Pseudomonas aeruginosa. Antibiotics tested were aztreonam, cefoperazone, ceftazidime, ceftriaxone, ciprofloxacin, gentamicin, imipenem, piperacillin, ticarcillin-clavulanic acid, and tobramycin. Agar dilution and Bauer-Kirby results were more strongly correlated for all three genera than were the results for agar dilution and Vitek. If agar dilution is presumed to be the "gold standard," Bauer-Kirby disk diffusion had only half the number of false susceptibles as did the Vitek. Thus, the Vitek AutoMicrobic system seems to be somewhat less reliable for both qualitative and quantitative measurement of susceptibility and resistance than is Bauer-Kirby disk diffusion.

Treatment of recurrent urinary tract infection with norfloxacin versus trimethoprim-sulfamethoxazole.

Norfloxacin, a broad-spectrum antimicrobial analog of nalidixic acid, was evaluated by comparing it to trimethoprim-sulfamethoxazole in 93 office patients with recurrent urinary tract infections. In this prospective randomized study, norfloxacin and trimethoprim-sulfamethoxazole were given on the same dosage schedule with the former drug given as a 400-mg tablet twice daily and the latter drug given as a double strength tablet twice daily. Overall, 50 patients received norfloxacin and 43 patients received trimethoprim-sulfamethoxazole with a cure rate of 96 percent and 79 percent, respectively. Whether a patient had one infection or multiple previous infections, norfloxacin appeared to be superior to trimethoprim-sulfamethoxazole. Only minor side effects were noted in either group, and no patient withdrew from this study as a direct result of these side effects. Minor complaints of nausea, dizziness, and headache were found in the norfloxacin group (24%) and in the trimethoprim-sulfamethoxazole group (16%). Both agents are effective in treating urinary tract infections but norfloxacin is superior to trimethoprim-sulfamethoxazole in patients with either recurrent complicated infections or one previous uncomplicated urinary tract infection.

A variant of toxic shock syndrome. Clinical, microbiologic, and autopsy findings in a fatal case.

A 16-year-old boy had toxic shock syndrome (TSS); Staphylococcus aureus bacteremia developed 11 hours prior to his death, which was three days after onset of the illness. The isoelectric focusing pattern of the staphylococcal isolate differed from both non-TSS and classic TSS S aureus isolates. Anatomic findings suggest three pathogenetic mechanisms: (1) immune complex-associated pulmonary microangiitis and vasculitis in the skin and skeletal muscle; (2) parenchymal cell "microvesicular" fatty metamorphosis in the liver, myocardium, renal tubules, and pancreas, and (3) pancarditis.