Clinical use of rifampicin during routine reporting of rifampicin susceptibilities: a lesson in selective reporting of antimicrobial susceptibility data.

Increased use of rifampicin for in-patients was noted after the laboratory began reporting rifampicin susceptibilities routinely for all Gram-positive bacterial isolates. The appropriateness of rifampicin use was evaluated by chart review for in-patients administered rifampicin during two time periods, before and during routine rifampicin susceptibility reporting, respectively. While rifampicin susceptibility was reported routinely, four patients were subjected to potentially harmful misuse of rifampicin. These findings reconfirm the necessity of interdepartmental consultation and extensive staff education whenever a modification of antimicrobial susceptibility profile reporting is contemplated. Furthermore, they underscore the role of the clinical microbiology laboratory in guiding antimicrobial therapy through limited reporting of susceptibility data.

Isolator component responsible for inhibition of Mycobacterium avium-M. intracellulare in BACTEC 12B medium.

We previously reported an inhibitory effect on Mycobacterium avium-M. intracellulare (MAI) when blood collected and processed with the Isolator system was placed in BACTEC 12B bottles for radiometric monitoring. We sought to identify the specific component(s) of the Isolator lysis-anticoagulant reagent (LAR) responsible for the inhibitory effect. We added the three components of the LAR, saponin, polyanetholesulfonate, and polypropylene glycol (PPG), to triplicate sets of BACTEC bottles separately and in various combinations. These bottles were then seeded with 10(2) CFU of MAI. The growth index (GI) was observed over a 42-day period and was compared with the GI for a growth control bottle set with no reagents and with the GI for a bottle set containing an equivalent volume of LAR. Growth in all growth control bottles and those bottles containing no PPG reached the maximum GI (GI = 999) within 8 to 10 days. Growth in bottles containing PPG never reached the maximum GI before day 14. In addition, the GIs of one bottle containing all three reagent components as well as all of the bottles containing actual Isolator LAR failed to reach the maximum within 42 days. Our data suggest that PPG is the main cause of the inhibitory effect, but that a secondary synergistic interaction between all three of the reagents may also be present.

Performance of fungal blood cultures by using the Isolator collection system: is it cost-effective?

Enhanced recovery of fungal isolates from blood by using the Isolator system has been reported previously. We examined bacterial and fungal blood cultures during a 14-month period to determine if this enhanced recovery required a separate fungal culture and to determine the differential utility between a fungal blood culture and a routine bacterial culture. During this period, 84 of 5,196 (1.6%) fungal blood cultures and 170 of 25,702 (0.6%) bacterial blood cultures were positive for yeast or filamentous fungi. Thirty-seven positive fungal cultures, simultaneously collected, had correspondingly positive bacterial cultures. An additional 15 positive fungal cultures yielded isolates that had either been previously recovered from a bacterial culture or were recovered from a bacterial culture collected within 48 h. Of the 32 unpaired fungal cultures remaining, 5 were Candida albicans whose unique isolation was believed to be the result of specimen sampling variance rather than any enhanced recovery characteristics of fungal culture methods. Examination of patient data relating to the 27 remaining isolates (24 patients episodes) showed that only five fungal blood cultures (0.096% of all collected) had any impact on patient therapy decisions, and one of these was judged to be the cause of unnecessary therapy. Our data suggest that separate fungal cultures of blood are not cost-effective for those laboratories using the Isolator for routine blood cultures and furthermore may not be cost-effective for laboratories using automated broth systems that are comparable to the Isolator in recovery of fungi.

An evaluation of the necessity of 24-hour incubation for oxacillin minimum inhibitory concentrations.

Current standards of the National Committee for Clinical Laboratory Standards (NCCLS) for microtube dilution recommend 24-hour incubation of staphylococci when testing for oxacillin/methicillin resistance. This study was conducted to quantify the need for this requirement. Standard 16-hour readings were compared with subsequent 24-hour readings of 515 fresh clinical isolates (256 Staphylococcus aureus, 259 coagulase-negative staphylococci) that were susceptible to oxacillin (microtube dilution minimum inhibitory concentration [MIC] < or equal to 2 micrograms/mL) after 16 hours. Five hundred two of the susceptible isolates (97.5%) were still susceptible at 24 hours. The remaining 13 isolates were resistant (MIC > 2 micrograms/mL) at 24 hours. Duplicate retesting, alternative method testing (Kirby-Bauer, E-Test) and mec A gene analysis were performed on these 13 isolates. All 13 isolates possessed the mec A gene. Four isolates always tested resistant (including all 16-hour repeat microtube dilution readings), and one isolate always tested susceptible. The remaining eight isolates produced variable results suggestive of an MIC very close to the resistance/susceptible break point. Overall , conversion from susceptible to resistant was entirely dependent upon the 16-hour MIC. There were 53 isolates with 16-hour MICS of 2 micrograms/mL. All 13 converters came from this group. No isolate with an oxacillin MIC < 2 micrograms/mL at 16 hours was resistant at 24 hours. Based on these results, the authors instituted a selective reincubation of only those staphylococcal isolates with oxacillin readings of 2 micrograms/mL at 16 hours.

Gonococcal arthritis in an era of increasing penicillin resistance. Presentations and outcomes in 41 recent cases (1985-1991).

BACKGROUND: To assess the impact of recent reports of disseminated gonococcal infection caused by penicillin-resistant organisms, we reviewed the presenting features, clinical course, and outcomes of a group of patients with gonococcal arthritis treated in recent years. METHODS: We reviewed the records of all cases of acute arthritis associated with a culture positive for Neisseria gonorrhoeae at our institution from July 1985 through December 1991. RESULTS: Forty-one cases were identified. Patients included 34 women and 38 blacks; the mean age was 22.6 years. Duration of symptoms averaged 4.8 days at presentation. Other features included migratory arthralgias (n = 27), urogenital symptoms or signs (n = 26), fever (n = 21), and skin lesions (n = 16). Comorbid conditions included intravenous drug use (n = 8) and systemic lupus erythematosus (n = 3). The knee was the most commonly affected joint. Positive culture results were obtained from 32 urogenital samples (86%), 14 synovial fluid samples (44%), seven rectal samples (39%), four blood samples (12%), and two throat samples (7%). All synovial fluid samples with positive culture results had white blood cell counts higher than 20.0 x 10(9)/L. Response to therapy with penicillin and/or ceftriaxone was prompt, and mean duration of hospitalization was 5.8 days. Patients who required longer hospitalization had a higher mean erythrocyte sedimentation rate and higher frequencies of positive synovial fluid culture results and comorbid conditions. Penicillin sensitivity could be determined in 30 patients on the basis of clinical response or in vitro testing. Among these patients, two cases of penicillin-resistant organisms were identified, one beta-lactamase positive and one beta-lactamase negative. CONCLUSIONS: The clinical features of patients with gonococcal arthritis have changed very little since the last large reported series over a decade ago. Underlying conditions appear to be more common, but response to antibiotic therapy and eventual outcome remain excellent. The finding of penicillin-resistant organisms in at least 5% of patients reinforces recent recommendations that third-generation cephalosporin agents be used as initial therapy for disseminated gonococcal infections until drug susceptibilities are known.

Invasive disease caused by Neisseria meningitidis relatively resistant to penicillin in North Carolina.

A case of sepsis and meningitis caused by Neisseria meningitidis with relative resistance to penicillin occurred in North Carolina in August 1992. This isolate was relatively resistant due to decreased affinity of its penicillin-binding protein 2 for penicillin. Such isolates have been reported in Spain, elsewhere in Europe, in South Africa, and in Canada, but invasive disease caused by meningococcal isolates relatively resistant to penicillin was not recognized in the United States before a preliminary report of this case in October 1992. The Centers for Disease Control and Prevention recently retrospectively identified 3 additional cases from 1991. A fifth case occurred in Kentucky in 1993. Surveillance studies of penicillin susceptibility of N. meningitidis isolates suggest such meningococci have existed sporadically in the past. Increases in prevalence and magnitude of penicillin resistance among strains of N. meningitidis would require reconsideration of current clinical practice with regard to treatment of meningococcal disease.

Tracking laboratory contamination by using a Bacillus cereus pseudoepidemic as an example.

From 1 March to 31 May 1990, Bacillus cereus was recovered from 24 of 5,534 (0.49%) blood cultures and 22 of 1,088 (2.02%) other body fluid cultures. The rarity of this organism as a pathogen and comparison with previous baseline rates led to the conclusion that it was a pseudoepidemic involving some form of culture contamination. Generalized precautions taken without specific knowledge of the contaminant source reduced the recovery rate of the organism. Recovery rates for the organism returned to normal baseline prevalence after environmental cultures and epidemiological analysis led to the sterilization of a contaminated water bath used for boiling thioglycollate media. The problems encountered in this investigation are examined, and a systematic approach to clinical laboratory epidemiology is outlined.

Beta-lactamase expression and cross-resistance to beta-lactam antibiotics in a nosocomial population of Enterobacter.

This study sought to quantitatively describe the spectrum of constitutive and inducible beta-lactamase activity present in a tertiary care center's population of Enterobacter species. beta-Lactamase activity in the absence and presence of 2 recognized beta-lactamase-inducing antibiotics, cefoxitin and imipenem, was measured. The Enterobacter cloacae (n = 35) population was strikingly bimodal, expressing 'all-or-none' cross-resistance to beta-lactams (except imipenem) corresponding to the baseline level of beta-lactamase expression. E. aerogenes (n = 14) displayed a less dichotomous pattern of resistance, and MICs of beta-lactam antibiotics were less strongly related to the magnitude of enzyme activity. We conclude that our nosocomial population of E. cloacae, like strains rendered resistant to beta-lactams in vitro, is largely dependent upon beta-lactamase as a mechanism of this resistance. Furthermore, we document the presence of a large subpopulation of beta-lactam-susceptible isolates possessing inducible beta-lactamase and therefore subject to selection for enzyme derepression.

Effectiveness of cefotaxime alone and in combination with desacetylcefotaxime against Bacteroides fragilis.

The synergistic activity of the combination cefotaxime-desacetylcefotaxime (CTX/dCTX) was compared to the effectiveness of seven other antimicrobial agents: cefoxitin (CFOX), cefotetan (CTAN), ceftizoxime (CTIZ), chloramphenicol (CLOR), clindamycin (CLIND), metronidazole (METR), and ampicillin-sulbactam (A/S) tested against 100 clinical isolates belonging to the Bacteroides fragilis group. All tests were performed using the NCCLS reference agar-dilution method. The overall susceptibility of these organisms to CTX/dCTX was 84% compared to CFOX at 78% or CTAN at 66%. The other antimicrobials inhibited greater than 90% of these isolates. There was no difference between the susceptibility rates of CTX/dCTX and CTX with the B fragilis (85%) or B. distasonis (75%) strains. Bacteroides thetaiotaomicron showed a 11% greater susceptibility to CTX/dCTX than to CTX. Of the 100 isolates tested, 40% showed either synergy or partial synergistic interactions between CTX and dCTX. Most of the isolates showed indifference (52%), while 8% demonstrated antagonism; a relatively unique finding to date.

Serum amphotericin-B assay by scanning spectrophotometer.

We describe a simple, specific, 3-min assay for amphotericin-B in serum based on the absorbance at 408 nm and spectral scanning between 450 and 350 nm of the drug in acetonitrile extracts. The method correlated well with a high-performance liquid chromatographic method.

Rapid identification of obligately anaerobic gram-positive cocci using high-performance liquid chromatography.

High-performance liquid chromatography was evaluated as a rapid means of identifying obligately anaerobic gram-positive cocci of medical interest. Isolates were inoculated into a defined chemical medium consisting primarily of amino acids and were incubated aerobically for 1 h at 35 degrees C. After removal of organisms, the supernatant fluids were derivatized for 1 min at room temperature by the addition of o-phthalaldehyde. The total time required to run a chromatogram was approximately 50 min. Standardized peak heights for each medium component and any new peaks formed were calculated for each isolate and compared with those for uninoculated control medium. Multiple isolates of various species of anaerobic gram-positive cocci gave consistent patterns of medium utilization that could be used for identification purposes. This method can easily be adapted for laboratory use and has the potential for automated microbial identification.

Adult meningitis caused by Hemophilus influenzae serotype f, biotype I.

Meningitis and septicemia developed in an adult patient as a complication of otitis media. The rare etiologic agent responsible for the infection was identified as Hemophilus influenzae serotype f, biotype I. With appropriate therapy, complete recovery was achieved without complications or relapse.

Rapid identification of Clostridium species by high-pressure liquid chromatography.

High-pressure liquid chromatography was evaluated as a rapid means of identifying various species of clostridia. Isolates were inoculated into a defined medium and incubated aerobically for 1 h at 35 degrees C. The organisms were removed, and the supernatants were derivatized for 1 min at room temperature by the addition of o-phthalaldehyde. The total time required to run each chromatogram was approximately 50 min. Standardized peak heights for each medium component and any new peaks formed were calculated for each isolate and compared with those for uninoculated control medium. Multiple isolates of various Clostridium species gave consistent patterns of medium utilization that could be used for identification. This rapid method can easily be adapted for laboratory use and has the potential for automation.