AutoMicrobic System Research Articles

Prevalence of shiga toxin-producing Escherichia coli in feces and raw milk of domestic cattle and sheep

A total of 1060 samples of raw milk and fecal from cattle and sheep were collected from farms in the Taiwan area between September 1997 and June 1998. Shiga toxin-producing E. coli (STEC) strains were isolated based on the demonstration of Vitek automicrobic system and shiga toxin-PCR after enrichment and selective procedures. The results showed that 0.4% of 231 raw milk samples were contaminated with STEC. Among the 829 fecal samples of cattle and sheep, 9% tested positive for STEC. A total of 121 STEC strains were selected and further analyzed for biochemical tests, serotype and pathogenic genes of eaeA (attaching and effacing) as well as hlyA (enterohemolysis). Results revealed that only 3% of strains lacked β-D-glucuronidase activity and 4% of strains were unable to ferment sorbitol. Thirteen percent of strains were typed as O6, O8, O15, O78, O112ac, O128, O157 and O159 with 43 O-antisera. The remaining strains were non-typeable with O-antisera. Thirty one percent of strains were determined as H2, H7, H10, H16, H19, H21, H42, H45 and H51 with 22 H-antisera. Three types of shiga toxin genes were detected with different rates, namely slt1, 39%; slt2, 33% and slt1+slt2, 28%. Seventy percent of STEC strains harbored hlyA gene and 1.6% possessed hlyA and eaeA genes. In addition, one E. coli O157:H7 strain, isolated from feces of domestic sheep, carried slt2, hlyA and eaeA genes. This study indicates that the feces of cattle and sheep were most likely the source of STEC in the Taiwan area.

In vitro drug resistance of clinical isolated Brucella against antimicrobial agents

ObjectiveTo explore the antibiotic resistance of Brucella melitensis and instruct rational use of antimicrobial agents in clinical treatment of Brucella infection. MethodsBacteria were cultured and identified by BACTEC9120 and VITEK II automicrobic system. E–test was used to detect the minimal inhibitory concentration (MIC) of antimicrobial agents in the drug susceptivity experiment. ResultsA total of 19 brucella strains (all Brucella melitensis) were isolated from 19 patients, who had fever between January 2010 and June 2012, and 17 samples were blood, one was bone marrow, the other sample was cerebrospinal fluid. The MIC range of ceftazidime was 2.0–8.0 mg/L, rifampicin was 0.06–2.0 mg/L, amikacin was 4.0–12.0 mg/L, levofloxacin was 2.0–8.0 mg/L, doxycycline was 8.0–32.0 mg/L, sulfamethoxazole–trimethoprim was 4.0–16.0 mg/L, ampicillin was 1.5–2.0 mg/L and gentamicin was 0.50–0.75 mg/L. ConclusionsThe drugs used in this experiment cover common drugs for treating Brcella. Meanwhile, the results are consistent with clinical efficacy. It is suggested personalized regimen according to patients' status in treatment of Brucella.

Pathogenesis of bloodstream infection in children with blood cancer

The aim of the present study was to characterize the distribution and antibiotic resistance of pathogens isolated from patients with bloodstream infections (BSIs) in the Hematology and Oncology department of the Affiliated Children’s Hospital of Zhejiang University Medical School (Hangzhou, China), between January and December 2010 and to provide early and appropriate support for the clinical administration of antibiotics. Out of 1,500 inpatients, 161 children who were diagnosed with BSI based on the national diagnostic criteria were retrospectively analyzed. Neutropenia was defined as an absolute neutrophil count (ANC) in the peripheral blood of less than 0.5×109 cells/l. A microbiologically documented infection (MDI) was defined as when the causative pathogen was isolated from the blood. Drug susceptibility tests were performed using a VITEK-60 AutoMicrobic System and the Kirby-Bauer disk diffusion method. The data were analyzed using STATA software (version 9.0) and a two-sided P-value of ≤0.05 was considered to indicate a statistically significant difference. A total of 79 strains were isolated from the blood specimens. The incidence of BSI was 10.73% (161/1,500). Gram-positive cocci, Gram-negative bacilli and fungi accounted for 55.70, 43.04 and 1.27% of the BSIs, respectively. Staphylococcus epidermidis (20.25%), Escherichia coli (15.19%) and Klebsiella pneumoniae (15.19%) were frequently identified isolates. The staphylococci were susceptible to vancomycin and linezolid, while Escherichia coli and Klebsiella pneumoniae were sensitive to cefoperazone/sulbactam, imipenem and meropenem. In conclusion, Gram-positive bacteria are slightly more prevalent than Gram-negative bacteria in BSI and the selection of antibiotics according to the susceptibility test results is superior to empirical treatment. It is essential to administer antimicrobial agents early and appropriately to treat child blood cancer patients with BSI.

N2O and N2 production during heterotrophic nitrification by Alcaligenes faecalis strain NR

A heterotrophic nitrifier, strain NR, was isolated from a membrane bioreactor. Strain NR was identified as Alcaligenes faecalis by Auto-Microbic system and16S rRNA gene sequence analysis. A. faecalis strain NR shows a capability of heterotrophic nitrification and N2O and N2 production as well under the aerobic condition. Further tests demonstrated that neither nitrite nor nitrate could be denitrified aerobically by strain NR. However, when hydroxylamine was used as the sole nitrogen source, nitrogenous gases were detected. With an enzyme assay, a 0.063U activity of hydroxylamine oxidase was observed, while nitrate reductase and nitrite reductase were undetectable. Thus, nitrogenous gas was speculated to be produced via hydroxylamine. Therefore, two different metabolic pathways might exist in A. faecalis NR. One is heterotrophic nitrification by oxidizing ammonium to nitrite and nitrate. The other is oxidizing ammonium to nitrogenous gas directly via hydroxylamine.

IMPROVED MEDIUM FOR DETECTION OF KLEBSIELLA IN POWDERED MILK

ABSTRACT The selectivities to pathogenic Klebsiella strains of different isolation media were compared by known standard strains. The modified MacConkey‐inositol‐carbenicillin (MCIC) medium (Named MCIAC, MacConkey‐inositol‐adonitol‐carbenicillin) supplemented with adonitol gave no false‐negative colonies, and exhibited higher selectivity. MCIC and Simmons citrate agar with inositol (SCAI) media gave two false‐negative colonies, respectively. These three media all gave two false‐positive colonies, respectively. Salmonella Shigella medium gave four false‐negative colonies and five false‐positive colonies. Violet red bile glucose agar medium gave the most false‐positive colonies, although it gave no false‐negative colonies. One hundred samples of powdered milk were examined by MCIAC, MCIC and SCAI plates. The typical positive colonies were further identified using Vitek GNI Auto Microbic system and API 20E system. The results showed that the specificity of the MCIAC medium was higher than MCIC and SCAI media.PRACTICAL APPLICATIONSMacConkey‐inositol‐carbenicillin (MCIC) is the most commonly used selective medium for the detection of Klebsiella. But some inositol‐nonfermenting Klebsiella strains would be missed when selected by this medium. We improved the MCIC medium by supplementing with 1% adonitol. The new modified medium (MacConkey‐inositol‐adonitol‐carbenicillin, MCIAC) had advantages over other selective Klebsiella media in having a higher selectivity and an incubation time of only 16–24 h. MCIAC could be routinely used for pathogenic Klebsiella selection of powdered milk and other food samples.

Serogroups, K1 antigen, and antimicrobial resistance patterns of Aeromonas spp. strains isolated from different sources in Mexico

A total of 221 strains of Aeromonas species isolated in Mexico from clinical (161), environmental (40), and food (20) samples were identified using the automated system bioMérieux-Vitek. Antisera for serogroups O1 to 044 were tested using the Shimada and Sakazaki scheme. The K1 antigen was examined using as antiserum the O7:K1C of Escherichia coli. Besides, we studied the antimicrobial patterns according to Vitek AutoMicrobic system. Among the 161 clinical strains 60% were identified as A. hydrophila, 20.4% as A. caviae, and 19.25% as A. veronii biovar sobria. Only A. hydrophila and A. veronii biovar sobria were found in food (55 and 90% respectively) and environmental sources (45 and 10% respectively). Using "O" antisera, only 42.5% (94/221) of the strains were serologically identified, 55% (121/221) were non-typable, and 2.5% (6/221) were rough strains. Twenty-two different serogroups were found, O14, O16, O19, O22, and O34 represented 60% of the serotyped strains. More than 50% of Aeromonas strain examined (112/221) expressed K1 encapsulating antigen; this characteristic was predominant among Aeromonas strains of clinical origin. Resistance to ampicillin/sulbactam and cephazolin was detected in 100 and 67% of Aeromonas strain tested for their susceptibility to antibiotics. In conclusion, antibiotic-resistant Aeromonas species that possess the K1 encapsulating antigen and represent serogroups associated with clinical syndrome in man are not uncommon among Aeromonas strains isolated from clinical, food and environmental sources in Mexico.

Clinical microbiology in the year 2025.

This article offers a mini-preview of what's to come in the field of clinical microbiology, and it's the first such undertaking that any of the authors has ever attempted without tongue firmly planted in cheek. Obviously, the scenario portrayed herein is an exercise in pure fantasy, based loosely on the evolutionary pace of clinical microbiology witnessed over the past 25 years. Unlike readers of Sports Illustrated's yearly predictions of champions and losers, however, the reader will have to wait longer than a single season to prove us right or wrong (23 years to be exact). Had the task been the opposite—i.e., to reminisce about the state of clinical microbiology a quarter century ago—we would have discussed the introduction of the Analytab Products bacterial identification system or the first-generation AutoMicrobic system (AMS, Vitek Systems, Inc.) originally designed for use in the U.S. space program. We could generate a smirk by recollecting that the role of the clinical microbiologist in the mid-1970s was to identify all microbial life forms recovered from clinical specimens and then to provide susceptibility test results for each by disk diffusion testing. It was the clinician who would then sort through the myriad of results and decide which organism(s) deserved a therapeutic response. We could prompt a grimace or two by recalling that blood cultures were monitored visually for evidence of bacterial growth once or twice per day and that all anaerobes were identified to species level no matter how much time or how many biochemical reactions were required to do the trick. Interestingly, the two aspects of clinical microbiology that haven't changed much since the mid-1970s are the identification of fungal diseases and the identification of parasitic diseases. As a discipline and profession, clinical microbiology has “come a long way baby” (Virginia Slims, circa 1970), but we have just begun the molecular diagnostics learning curve, and it's hard to predict just how far we can take this new tool from a technical, practical, and economic standpoint. Because of the recent explosion of technology, many clinical microbiologists have openly speculated that ours is a dying profession—one that will ultimately be consumed by the growing molecular diagnostic beast. With that in mind, here's a mythical take on the future of the clinical microbiology laboratory. One additional note: this might represent the only publication in the history of the Journal of Clinical Microbiology that contains no references. Why is this? The references that would have been cited haven't been written yet!

False-positive β-Lactamase results with Staphylococcus lugdunensis in the vitek autoMicrobic system

The Vitek AutoMicrobic system in combination with the Gram-positive susceptibility card detects beta-lactamase in staphylococci by utilizing penicillin as the substrate coupled with oxacillin as an inducer. The beta-lactamase activity of 21 clinical isolates and two reference strains of Staphylococcus lugdunensis was determined with this automated system and compared with a liquid nitrocefin assay after induction with oxacillin. Eight (38%) clinical isolates and the reference strain ATCC 49576 of S. lugdunensis showed production of beta-lactamase in both tests. Thirteen (62%) clinical isolates and the type strain ATCC 43809 were nitrocefin-negative. The Vitek AutoMicrobic system reported false-positive beta-lactamase results for 9 of those 13 isolates and for the type strain of S. lugdunensis. Results for disk diffusion (ampicillin) were concordant with the nitrocefin assay. With one exception, the MICs for penicillin of the nitrocefin-negative strains were in the equivocal range of 0.06-0.12 mg/l according to NCCLS. However, none of the nitrocefin-negative and Vitek-positive strains revealed any of the known staphylococcal genes for beta-lactamase as investigated by Southern hybridization, supporting the fact that false-positive beta-lactamase results may occur in the Vitek AutoMicrobic system. We conclude from our data that it may be justified to include S. lugdunensis in the quality control of Vitek cards containing beta-lactamase tests.

DRAMATIC INCREASE IN COMMUNITY-ACQUIRED METHICILLIN-RESISTANTSTAPHYLOCOCCUS AUREUS (MRSA) IN CHILDREN WITH NO PREDISPOSING RISK.† 1028

Background: MRSA is typically acquired nosocomially by patients with predisposing risks. Community-acquired (CA) infections are infrequent. Having observed several children hospitalized with CA MRSA infection, we sought to define the scope of the problem by reviewing medical records of all children with Staphylococcus aureus (SA) isolated from any site in 1993-5. For comparison, we reviewed charts of all those who had MRSA isolated in 1988-90. Methods: An isolate was defined as CA if the culture was obtained ≤ 72 h after hospitalization and the patient did not have risk factors for MRSA including prior hospitaization or antimicrobial therapy within the last 6 mo. Each SA isolate was determined to be colonizing or associated with clinical disease. Susceptibility testing was done by Vitek Auto Microbic System and/or disc diffusion. Available MRSA blood isolates in 1993-5 were characterized by pulse field gel electrophoresis (PFGE).Results: For 1993-5, 298 charts were reviewed, (57 and 241 charts from patients with MRSA and methicillin susceptible (MSSA) isolates, respectively); for 1988-90 30 charts were reviewed from patients with MRSA. The percentage of CA MRSA isolates increased from 3.3% in 1988-90 to 46.4% in 1993-5 (p=0.001). 74% of MRSA and 60% of MSSA isolates in 1993-5 were associated with disease. Among the CA disease isolates, the disease spectrum was not different when stratified by methicillin resistance. Cellulitis accounted for 48% and 43% of patients with MRSA and MSSA, respectively; abscesses accounted for 30% and 28% and pneumonia accounted for 13% and 9%, respectively. Irrespective of methicillin resistance, the disease spectrum among the nosocomially acquired SA infections differed from the CA disease spectrum; for example, bacteremia was most frequent, accounting for 21% and 37% of MRSA and MSSA disease isolates, respectively. Nosocomial MRSA had higher rates of resistance to clinda, TMP-SMX, erythro, and gent (p≤ 0.02) than did CA MRSA. Among 7 isolates subjected to PFGE, there were three patterns suggesting that a single MRSA clone was not responsible for the increased prevalence. Conclusion: The prevalence of CA MRSA infections has increased dramatically in our pediatric population. The disease spectrum of CA MRSA infection is similar to CA MSSA infection. CA MRSA were less often multiply resistant than nosocomial MRSA isolates.

Evaluation of the automicrobic system for the identification of Streptococcus mutans.

The performance of the Automicrobic System with the Vitek gram-positive identification card (bioMérieux, France) in identifying strains of Streptococcus mutans was studied. Of 160 strains assayed, 72.5% were confirmed to be Streptococcus mutans; the remainder were identified as other species of streptocci (Streptococcus bovis, Streptococcus uberis, Streptococcus anginosus, Streptococcus sanguis I and II, Streptococcus intermedius, and Streptococcus constellatus).

Identification of environmental staphylococci and coliforms by the Vitek Auto Microbic System

The Vitek Auto Microbic System (AMS) automated identification device was used in rapid identification of staphylococci and coliforms originating from food factory environments. From a total of 3324 isolates, an average of 76% were identified with a confidence > 50% (staphylococci: 61%, coliforms: 82%). AMS identifications of presumed staphylococci did not match well (24%) with ATB 32 STAPH identifications, but coliforms matched for 80% of the isolates compared with the API 20 E system. The differences observed between the AMS and ATB 32 STAPH in identifications could be due to inadequate isolation media, insufficient isolate purification, incorrect pre-screening of isolates or an incompetent AMS database. For coliforms, the overall performance proved sufficient for rapid screening of isolates from food factory bacterial ecology studies.

Comparison of Crystal Enteric/Nonfermenter system, API 20E system, and Vitek AutoMicrobic system for identification of gram-negative bacilli

A comparative evaluation of the Crystal Enteric/Nonfermenter system (Crystal; Becton Dickinson, Cockeysville, Md.), API 20E (API; bioMérieux Vitek, Inc., Hazelwood, Mo.), and the Vitek GNI card (Vitek; bioMérieux Vitek) was performed with 512 clinical isolates of gram-negative bacilli, including 381 members of the family Enterobacteriaceae and 131 nonenteric bacilli. With supplemental testing, API, Crystal, and Vitek correctly identified to the genus and species level 505 (98.6%), 489 (95.5%), and 494 (96.5%) of the 512 isolates, respectively. Supplemental testing, as specified by the manufacturer, was required to identify 119 (23.2%), 18 (3.5%), and 5 (1.0%) of the isolates with the three systems, respectively. Of the 381 isolates from the family Enterobacteriaceae, API and Crystal correctly identified 90.3 and 91.6% by 18 to 24 h without supplemental testing, respectively, and Vitek identified 92.4 and 96.1% following 10 and 18 h of incubation, respectively. Of the 131 nonenteric organisms, API and Crystal correctly identified 28.2 and 93.9% by 18 to 24 h without supplemental testing, respectively, and Vitek identified 84.0% by 10 h and 93.9% by 18 h. Errors in identification with each system were infrequent and appeared to be randomly distributed among the genera evaluated. The three systems were comparable in accuracy when either a weighted clinical laboratory profile of organisms or a group of selected isolates in a stress test sample was evaluated (P > 0.05). There were no significant differences between the three systems in their ability to identify either the isolates in the weighted group or those in the stress test (P > 0.05). Crystal compared favorably with API and Vitek, which have established track records in clinical laboratories, and is acceptable for the identification of members of the Enterobacteriaceae and nonenteric bacilli in a clinical microbiology laboratory.

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.

Failure of the Vitek AutoMicrobic System to Detect Beta-Lactam Resistance inAeromonasSpecies

The ability of the Vitek AutoMicrobic system (AMS; Vitek, Inc., Hazelwood, MO) and disk-diffusion method to detect beta-lactam resistance was assessed with 25 strains from four species of Aeromonas. A very major error was indicated when a strain was shown to be susceptible by the AMS or disk-diffusion method but resistant by the agar dilution method. The rates for very major errors for disk diffusion and the AMS were 0% and 43%, respectively. The beta-lactam agents and numbers of very major errors for the AMS were as follows: ticarcillin, 17; mezlocillin, 3; piperacillin, 4; cephalothin, 9; cefazolin, 3; cefoxitin, 1; cefotetan, 2; and cefuroxime, 1. Thus, these data suggest that the AMS currently is not reliable for testing the resistance of Aeromonas to beta-lactam agents.

AutoMicrobic System for Biochemical Identification of Listeria Species Isolated From Foods: Collaborative Study

A collaborative study was conducted to evaluate the performance of the AutoMicrobic System Gram-Positive Identification (GPI) and Gram-Negative Identification (GNI) test kits to biochemically characterize Listeria spp. Thirteen laboratories each tested 97 food and environmental isolates, representing the 7 species of Listeria, as well as 11 additional genera of Gram-positive rods. Each collaborator inoculated both a GPI and a GNI card with a pure culture of each organism. The AutoMicrobic System identified the isolates and printed out the biochemical results. The GPI card is used to obtain a species identification and a mannitol reaction result, and the GNI card is used to obtain rhamnose and xylose reaction results. Organisms are classified into species groups and can be further distinguished on the basis of hemolysis or nitrate reduction tests. The AutoMicrobic System method correctly classified 90.8% of the Listeria spp. isolates and 100% of the non-Listeria isolates. The AutoMicrobic System method was adopted first action by AOAC International for the biochemical characterization of Listeria spp. isolated from food and environmental sources.

Species identification and detection of oxacillin resistance in coagulase-negative Staphylococcus blood isolates from neutropenic patients

One hundred coagulase-negative staphylococcal isolates from septicemic neutropenic patients with hematologic malignancies were identified to a species level by means of the French API STAPH strip system and by the Automicrobic VITEK system. According to these two methods, which concurred in 95% of cases, S. epidermidis (80-82% of the isolates) was the most frequently identified species, followed by S. haemolyticus (6-7% of the isolates). The susceptibility to oxacillin was also evaluated by macrodilution MIC, Automicrobic VITEK system and agar screen, and 76, 78 and 79 of the 100 isolates, respectively, were found resistant to this antibiotic. All oxacillin-resistant isolates according to Automicrobic VITEK were confirmed resistant by agar screen. A 48h incubation was required to determine oxacillin resistance in 11 of 79 isolates with agar screen and in 10 of 76 isolates with macrodilution MIC. Automicrobic VITEK system may represent a useful method for rapid identification to a species level and early recognition of oxacillin resistance in coagulase-negative staphylococci.

Comparison of the autoSCAN-W/A rapid bacterial identification system and the Vitek AutoMicrobic system for identification of gram-negative bacilli

The autoSCAN-W/A (W/A; Baxter MicroScan, West Sacramento, Calif.) with the new fluorometric Rapid Neg Combo 1 (RNC) panel is a fully automated fluorometric system for identification of both enteric and nonenteric gram-negative bacilli within 2 h. We compared the W/A with the Vitek AutoMicrobic System (Vitek AMS; Vitek Systems, Inc., Hazelwood, Mo.) for identification of 383 clinical isolates of gram-negative bacilli. The API 20E (Analytab Products, Plainview, N.Y.) and conventional biochemical testing were used as the reference systems. The W/A correctly identified 336 isolates (87.7%) to the species level and classified an additional 29 isolates (7.6%) as correct with low probability (overall identification = 95.3%); the Vitek AMS correctly identified 355 isolates (92.7%) to the species level and classified an additional 8 isolates (2.1%) as correct with low probability (overall identification = 94.8%). A common set of 134 isolates of gram-negative bacilli was tested in both participating laboratories as a means of assessing interlaboratory agreement with both the W/A and the Vitek AMS. The overall agreements between the two laboratories were 86% with the W/A and 92% with the Vitek AMS. The W/A performed comparably to the Vitek AMS for identification of most gram-negative bacilli, actually exceeding the Vitek AMS for identification of nonenteric bacilli. Rapid time to identification and a high level of automation make the W/A an attractive system for clinical microbiology laboratories.

Prevalence of antibiotic-resistant uropathogens in obstetric patients with acute pyelonephritis

The purpose of this investigation was to determine the prevalence of antibiotic-resistant uropathogens in 121 pregnant patients hospitalized with acute pyelonephritis. We obtained urine for culture by catheterization and defined a positive culture as greater than 100 colony-forming units per milliliter of urine. We determined bacterial sensitivities with either the Bauer-Kirby disc diffusion test or the Vitek Auto Microbic System. During the 4 years of the study, the prevalence of ampicillin-resistant organisms was 26% (95% confidence interval 18-34%). However, only 4% (95% confidence interval 0-8%) of the uropathogens were resistant to limited-spectrum, first-generation cephalosporins. This observed difference in antibiotic sensitivity was highly significant (P less than .005). Therefore, we conclude that a limited-spectrum cephalosporin is more appropriate than ampicillin for empirical therapy of pyelonephritis in pregnancy.

In vitro susceptibility studies of vancomycin-resistant Enterococcus faecalis

Vancomycin resistance exhibited by Enterococcus faecalis isolates V583, V586, and V587 is described. The vancomycin MICs ranged from 32 to 64 micrograms/ml. Although resistant to vancomycin, the isolates were susceptible to teicoplanin (MIC, less than or equal to 0.5 micrograms/ml). Such a glycopeptide susceptibility profile has not been previously described for E. faecalis. Time kill studies showed that vancomycin resistance adversely affected the synergistic activity that vancomycin and aminoglycoside combinations usually demonstrate against enterococci. However, the ability to detect vancomycin resistance varied with the susceptibility testing method used. Whereas broth microdilution, broth macrodilution, and agar dilution methods detected resistance, disk-agar diffusion and the AutoMicrobic system Gram-Positive GPS-A susceptibility card (Vitek Systems Inc., Hazelwood, Mo.) did not. To detect vancomycin resistance reliably and establish the incidence of such E. faecalis isolates, adjustments in some susceptibility testing methods may be necessary.

Clinical impact of rapid identification and susceptibility testing of bacterial blood culture isolates

Two hundred twenty-six patients with bacteremia were prospectively enrolled in a randomized trial that was performed to determine the clinical impact of the receipt of in vitro microbiological data by the physician soon after organism detection as opposed to having the physicians wait until similar data were available by routine methods. Identification and antibiotic susceptibility patterns of 110 isolates were determined by direct inoculation of the Vitek AutoMicrobic system (Vitek Systems, Inc., Hazelwood, Mo.) with a sample from a positive blood culture vial. One hundred sixteen isolates were processed by routine methods. Microbiological results were available within an average of 8.8 h by the direct method versus an average of 48 h by the routine method. In both groups an infectious disease fellow used the information to make therapeutic recommendations to the responsible physician. When compared with that provided by the routine method, the information provided by the direct method was significantly more likely to result in an initiation of antibiotic therapy, a change to more effective therapy, or a change to less expensive therapy. Recommendations were significantly more likely to be followed in patients whose isolates were processed by the direct method versus the routine method. A projected savings of $158 per patient was estimated for the patients who were changed to less expensive therapy or in whom antibiotics were discontinued because results were available sooner. These cost savings, coupled with changes in therapy made for reasons of efficacy, support the usefulness of the earlier reporting of the identity and antibiotic susceptibility patterns of bacterial blood culture isolates.