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PubMed1998

Evaluation of a computerized antimicrobial susceptibility system with bacteria isolated from animals.

The BIOMIC is a computerized system used to calculate the minimal inhibitory concentration (MIC) of an antimicrobial agent from a zone of inhibition generated by a disk diffusion test. This system was developed using bacterial pathogens of human origin. This study investigated the use of the BIOMIC system for determining MICs for bacterial pathogens from animals. The MICs generated by the BIOMIC system were compared with the MICs generated using a broth microdilution testing method. A total of 663 drug-organism combinations was tested. These combinations included 3 species of gram-positive bacteria, 5 species of gram-negative bacteria, and the antimicrobial agents ampicillin, gentamicin, cephalothin, ciprofloxacin, enrofloxacin, trimethoprim/sulfamethoxazole, tetracycline, and erythromycin. Overall, the MICs generated by the BIOMIC system correlated with the broth microdilution MICs for 72% of the total drug-organism combinations tested. The Pseudomonas aeruginosa strains tested showed the highest agreement between the 2 systems, with 100% for all antibacterial agents tested, whereas Pasteurella haemolytica, Pasteurella multocida, and enterococci showed the least agreement (76%, 57%, and 47%, respectively). Among these organisms, trimethoprim-sulfa showed the least agreement (31%) and ciprofloxacin showed the greatest (91%). These results indicate that the BIOMIC system could be a useful tool in veterinary medicine for producing quantitative antimicrobial susceptibility results. However, it is currently unreliable for some drug-bacteria combinations. This discrepancy possibly could be corrected by modification of the software using data points generated by a large-scale study.

Animals↗

PubMedDate not supplied

[Study of the susceptibility of Staphylococcus sp. and Enterococcus sp. to teicoplanin and vancomycin].

PURPOSE: The study was performed in order to evaluate the susceptibility of Enterococcus and Staphylococcus to teicoplanin and vancomycin. METHODS: 150 Enterococcus strains and 450 Staphylococcus strains (298 Staphylococcus aureus and 152 negative coagulase strains) isolated in three Brazilian hospitals were studied. The MICs were determined using teicoplanin and vancomycin E Test strips. The range of the antimicrobial concentration in each strip went from 256 mcg/mL to 0.016 mcg/mL. Diffusion tests using disks impregnated with 10 mcg of teicoplanin and 30 mcg of vancomycin were also performed. RESULTS: All the 298 Staphylococcus aureus strains were susceptible to the two antimicrobials. Three of the 152 negative coagulase strains presented intermediate susceptibility to teicoplanin (MICs between 8 and 16 mcg/mL). Four of the 150 Enterococcus strains presented intermediate susceptibility to vancomycin but were totally susceptible to teicoplanin. CONCLUSION: According to these results teicoplanin and vancomycin are good therapeutical options in the treatment of staphylococcal and enterococcal infections.

Anti-Bacterial Agents↗

PubMed2000

A simplified method for testing Bordetella pertussis for resistance to erythromycin and other antimicrobial agents.

Present methods of antimicrobial susceptibility testing of Bordetella pertussis are time consuming and require specialized media that are not commercially available. We tested 52 isolates of B. pertussis for resistance to erythromycin, trimethoprim-sulfamethoxazole, chloramphenicol, and rifampin by agar dilution with Bordet-Gengou agar (BGA) containing 20% horse blood (reference method), Etest using BGA and Regan-Lowe agar without cephalexin (RL-C), and disk diffusion using BGA and RL-C. The organisms tested included four erythromycin-resistant isolates of B. pertussis from a single patient, a second erythromycin-resistant strain of B. pertussis from an unrelated patient in another state, and 47 nasopharyngeal surveillance isolates of B. pertussis from children in the western United States. The results of agar dilution testing using direct inoculation of the organisms suspended in Mueller-Hinton broth were within +/-1 dilution of those obtained after overnight passage of the inoculum in Stainer-Scholte medium, which is the traditional method of testing B. pertussis. The Etest method produced MICs similar to those of the agar dilution reference method for three of the four antimicrobial agents tested; the trimethoprim-sulfamethoxazole results were lower with Etest, particularly when the direct suspension method was used. Most of the Etest MICs, except for that of erythromycin, were on scale. Disk diffusion testing using RL-C medium was helpful in identifying the erythromycin-resistant strains, which produced no zone of inhibition around the disk; susceptible isolates produced zones of at least 42 mm. Thus, the antimicrobial susceptibility testing of B. pertussis can be simplified by using the Etest or disk diffusion on RL-C to screen for erythromycin-resistant isolates of B. pertussis.

Animals↗

PubMed2004

Clinical resistance of Staphylococcus keratitis to ciprofloxacin monotherapy.

PURPOSE: To review the in vitro susceptibility and the clinical response to 0.3% ciprofloxacin in Staphylococcus aureus keratitis. METHODS: This is a non-comparative case series derived from a prospectively collected database and analysed retrospectively. One hundred and twenty one patients presenting in the cornea service of LV Prasad Eye Institute, Hyderabad, India, between January 1993 and December 2000, and identified to have S. aureus keratitis were included in the study. All patients had received slitlamp evaluation of the cornea and diagnostic microbiologic workup. They were treated with topical antimicrobial therapy based on smear and culture results. All S. aureus isolates were tested for antibiotic susceptibility by disk diffusion and those resistant to ciprofloxacin were confirmed by testing for minimum inhibitory concentration. The patients' clinical response to the antimicrobial therapy was noted. RESULTS: Twenty-five (20.6%) of 121 isolates resistant to ciprofloxacin on in vitro susceptibility testing were further analysed in this study. Fifteen of these 25 (60%) patients were initially treated with topical ciprofloxacin. Twelve of 15 (80%) patients showed no clinical improvement (3-8 days). Based on antibiotic susceptibility results, the antibiotic therapy was modified to fortified cefazolin and gentamicin in seven (58.3%), to vancomycin in one and to chloramphenicol in four cases. The corneal infiltrate resolved in 11 (73.3%) of 15 cases. Two patients required penetrating keratoplasty (PK), one required evisceration, and one patient was lost to follow up. Nine of 25 patients were initially started on fortified cefazolin and gentamicin therapy based on smear positive for gram-positive cocci; this resulted in resolution of infiltrate in 44.4% (4/9) while three required change of antibiotics (vancomycin-2, chloramphenicol-1), one required PK and one patient was lost to follow up. One of 25 patients started and continued on chloramphenicol, showed no response and required PK. CONCLUSIONS: This study shows a significant resistance of S. aureus to many antibiotics including ciprofloxacin and highlights the need for an alternative to ciprofloxacin monotherapy for the treatment of staphylococcal keratitis.

Adolescent↗

PubMed2006

Genotypic analysis of Acinetobacter bloodstream infection isolates in a Turkish university hospital.

Acinetobacter baumannii is a significant pathogen of bloodstream infections in hospital patients that frequently causes single clone outbreaks. We aimed to evaluate the genetic relatedness and antimicrobial susceptibility of Acinetobacter spp. bloodstream isolates, in order to obtain insight into their cross-transmission. This prospective study was conducted at the Erciyes University Hospital. During a 1-y period, all patients with nosocomial BSI caused by Acinetobacter spp. were included in the study. All data with regard to the patients, underlying diseases and risk factors for BSI and the severity of disease were collected. Blood culture isolates of Acinetobacter spp. were identified according to their morphology and biochemical reactions. The antimicrobial susceptibility was determined using the Kirby-Bauer disk diffusion test according to the NCCLS; the genetic relatedness of isolates was determined by RAPD-PCR analysis and pulsed-field gel electrophoresis (PFGE). 41 patients acquired a nosocomial bloodstream infection caused by A. baumanii during this period. 88% of these infections (36 of 41) occurred while the patients were treated in the intensive care unit. Nearly 80% of the isolates belonged to 3 genotypes, suggesting cross-transmission in ICU settings where infection control practices are poor. All Acinetobacter isolates were multidrug-resistant and the crude mortality of patients infected with A. baumanii was 80.5%. We concluded that the genetic relatedness of Acinetobacter spp. causing BSI was very high, indicating cross-transmission within the ICU setting. Essential components of an infection control programme to prevent nosocomial transmission of A. baumannii are early detection of colonized patients, followed by strict attention to standard precautions and contact isolation.

APACHE↗

PubMed1993

Two percent sodium chloride is required for susceptibility testing of staphylococci with oxacillin when using agar-based dilution methods.

The need to add NaCl to agar media to ensure accuracy of results when testing staphylococci with oxacillin was investigated. The results of four antimicrobial susceptibility testing methods (agar and broth dilution, E test, and disk diffusion) in which the growth medium contained 0, 2, 4, or 5% NaCl were compared with the results of a hybridization assay using a mec gene probe. We tested 223 strains of staphylococci, 128 of which were mec gene positive. A total of 7 of the 128 positive strains were coagulase-negative staphylococci with 24-h oxacillin MICs of < or = 2 micrograms/ml. Ninety-five isolates were mec gene negative, including seven strains of Staphylococcus aureus with oxacillin MICs of > or = 4 micrograms/ml. The oxacillin MICs for mec gene-positive, oxacillin-resistant strains of staphylococci increased two- to fourfold with the addition of NaCl to the test medium, while the MICs for mec gene-negative strains did not change in the presence of added salt. Very major error rates for the agar dilution and E test methods in the absence of salt ranged from 18.2 to 20.2%. Major error rates for mec gene-negative S. aureus isolates were > 17% for all test methods when 4 or 5% NaCl was added to the test medium. The addition of 2% NaCl to Mueller-Hinton agar for testing of oxacillin resulted in very major error rates of < 1% for the agar dilution and E test methods although the major error rates for the two methods with added NaCl were 8.5 and 6.9%, respectively. The disk diffusion test did not perform well in this study, showing essential error rates of > or = 18.3%. We recommended the addition of 2% NaC1 to Mueller-Hinton agar when testing staphylococci with oxacillin by either the agar dilution or E test method. NaC1 should not be added for the disk diffusion test.

Culture Media↗

PubMed2000

Microbiologic features of adult community-acquired bacterial meningitis in Taiwan.

BACKGROUND AND PURPOSE: Community-acquired bacterial meningitis (CABM) is a life-threatening disease that requires prompt initiation of appropriate antibiotic therapy. The purpose of this study was to determine the causative microorganisms of CABM and their antimicrobial susceptibility patterns at a major teaching hospital in Taipei from 1993 to 1998. METHODS: A review of medical records and microbiologic data was used to identify cases of CABM and causative pathogens. Antimicrobial susceptibility testing for bacterial isolates was performed by the disk diffusion method. RESULTS: Among the 48 adult patients with a diagnosis of CABM during the study period, the causative pathogens were identified in 36 cases. Unlike reports from other countries, Klebsiella pneumoniae was the leading causative pathogen (33%), followed by Streptococcus pneumoniae (28%), Listeria monocytogenes (11%), Neisseria meningitidis (6%), Staphylococcus aureus (6%), streptococci (6%), and Pseudomonas aeruginosa (6%). The incidence of CABM due to K. pneumoniae increased during the study period (p = 0.012, Poisson regression), while the incidence of CABM due to other pathogens remained stable. All of the CABM-associated K. pneumoniae isolates were susceptible to cefotaxime but 25% of the CABM-associated S. pneumoniae strains were not susceptible to penicillin G. CONCLUSIONS: Penicillin G alone was not an appropriate empiric therapy for adult CABM because a high percentage of cases were due to K. pneumoniae or penicillin nonsusceptible S. pneumoniae. While the recommendations for the initial empiric regimen for CABM due to S. pneumoniae in Taiwan remain to be developed, third-generation cephalosporins appear to be an appropriate initial empiric regimen for the treatment of CABM due to K. pneumoniae.

Adolescent↗

PubMedDate not supplied

[Fulminant sepsis caused by Vibrio vulnificus. A case series].

BACKGROUND: Vibrio vulnificus is a marine bacteria associated with the ingestion of raw shellfish or contact with seawater. It can produce wound infection, diarrhea and sepsis. The main risk factor for infection is the presence of chronic liver disease. Prior studies have shown mortality from 40% to 63%. OBJECTIVE: Report of 8 cases of disseminated infection with V. vulnificus causing fulminant sepsis. DESIGN: Series of cases. METHODS: We reviewed the database of the laboratory of clinical microbiology from 1990 to 1999. A computer-based review of the worldwide medical literature was also accomplished. RESULTS: There were 8 cases of V. vulnificus infection. All patients had chronic liver disease, 3 also had diabetes mellitus and 1 received immunosuppressive agents. Five patients were known to have ingested raw shellfish. The mean duration of illness before death was 4 days. All patients presented with sepsis, seven had cutaneous lesions. Five patients received early antimicrobial treatment during the first 24 hours and all of them in the first 48 hours. Regardless of susceptibility to the antimicrobial agents used, the mortality was of 87.5%. Disk-diffusion test showed 100% susceptibility to imipenem, ceftazidime and tetracycline; 83% to cefepime, ticarcillin and cotrimoxazole and 50% to quinolones. CONCLUSION: The V. vulnificus infection appears in patients with chronic liver disease and it is associated with high mortality. This infection has to be suspected in high-risk patients who have eaten raw shellfish and therapy must be initiated as soon as possible.

Female↗

PubMedDate not supplied

[Antimicrobial sensitivity of coagulase-positive staphylococcal strains isolated from bovine mastitis in the central dairy catchment area of Argentina ].

The activity of antimicrobial agents frequently used for treating bovine mastitis was determined against 101 coagulase-positive staphylococci isolated from bovine mammary secretion. The isolates were obtained from 39 dairy farms located in the central dairy area of Argentina. The disk diffusion method was used and the following antimicrobial agents were tested: penicillin, ampicillin, oxacillin, cephacetrile, penicillin + novobiocin, erythromycin, pirlimycin, novobiocin and neomycin. The highest levels of resistance were observed against penicillin and ampicillin (47.6%), while the lowest against erythromycin (2%), pirlimycin (4%) and neomycin (2.9%). No resistant strains against oxacillin, cephacetrile and penicillin + novobiocin were detected.

Animals↗

PubMedDate not supplied

[Prevalence of glycopeptide resistant enterococci in hospitalized patients and in the community in Calabria (Italy)].

The study evaluated prevalence of glycopeptide (vancomycin and teicoplanin) resistant enterococci (VRE) in hospitalized patients and in the community in Calabria (Italy). Rectal swabs were collected from hospitalized and community subjects. Information was gathered on demographics, ward and duration of hospital stay and antibiotics administered; in community subjects information on previous hospitalizations and antibiotics use in the previous year were also collected. Rectal swabs were plated on Enterococcosel agar alone and with addition of vancomycin (6 mg/l) and incubated aerobically at 37 degrees for 24-48 hours. Typical colonies were tested for Gram stain and catalase production. Enterococci were identified to the species level by biochemical tests. Antimicrobial susceptibility test and E-test were performed by the disk diffusion method to evaluate vancomycin and teicoplanin susceptibility. t-test and chi square test were performed to evaluate difference in means and proportions, respectively. Samples were collected from 211 subjects; 132 (62.6%) from community and 79 (37.4%) from hospitals. Enterococci were isolated from 145 subjects (68.7%), 72.7% and 62% in community and in hospital, respectively. The most frequent isolates were E. faecium (30.4%), followed by E. faecalis and E. durans (25.5%), and, finally, by Leuconostoc (18.6%). Only one E. faecium strain was resistant to both vancomycin and teicoplanin, isolated from a non-hospitalized 45 years old woman (1.3%). The results did not show emergence of VRE in our area, although surveillance to confirm these findings is needed, considering the substantial spread of antibiotics in hospitals and in the community.

Adult↗

PubMedDate not supplied

Serotypes and antimicrobial susceptibility of group B Streptococcus from pregnant women in Mexico.

TITLE: Serotypes and antimicrobial susceptibility of group B Streptococcus isolated from pregnant women in México BACKGROUND: Group B streptococci (SGB) are a leading cause of neonatal sepsis and meningitis. Women colonized might also develop pregnancy-associated infections including urinary tract infection, bacteremia and postpartum endometritis. There are nine different capsular types, and with the possibility of a GBS vaccine in the future; it is essential to understand which of these types are circulating. We determined the serotype distribution of isolated rectovaginal and urine GBS obtained from an obstetric population, and also their antibiotic sensitivity patterns. METHODS: A total of 101 strains were studied: SGB were confirmed by latex agglutination (Slidex Strepto-Kit bioMérieux), and the serotype was confirmed by latex agglutination (Pastorex Streptococcus B. Becton Dickinson, EUA). Antimicrobial susceptibility testing was performed by a Kirby-Bauer disk diffusion. RESULTS: All SGB were serologically typeable; 61.3% were type I, 25.7% were type II and only 12.8 were type III. All of them were 100% susceptible to beta lactam agents. Only 5.9% strains were resistant to erythromycin. CONCLUSION: In the last years, no major changes have been observed in the distribution of serotypes of SGB in México, serotype I is still the most common. This makes us think of the possibility of a vaccine that includes serotypes I and II that represent close to 90% of the isolations.

Adult↗

PubMed1980

In vitro antimicrobial susceptibility of Salmonellae from animals in Louisiana.

A total of 56 Salmonella isolates from animals were tested for susceptibility to 12 antimicrobial agents by the standard disk diffusion and mirodilution methods. All isolates were susceptible to gentamicin, tobramycin, amikacin, chloramphenicol, crimethoprim and sulfonamide, colistin, and nitrofurantoin. Isolates were most frequently resistant to tetracycline (50%) and kanamycin (36%). A low prevalence of resistance to ampicillin (16%), carbenicillin (16%), and cephalothin (4%) was found. The differences in susceptibility results between the two methods were minor.

Ampicillin↗

PubMed2004

Comparison of prevalence and antimicrobial susceptibilities of Campylobacter spp. isolates from organic and conventional dairy herds in Wisconsin.

The prevalence and antimicrobial susceptibilities of Campylobacter spp. isolates from bovine feces were compared between organic and conventional dairy herds. Thirty organic dairy herds, where antimicrobials are rarely used for calves and never used for cows, were compared with 30 neighboring conventional dairy farms, where antimicrobials were routinely used for animals for all ages. Fecal specimens from 10 cows and 10 calves on 120 farm visits yielded 332 Campylobacter isolates. The prevalence of Campylobacter spp. in organic and conventional farms was 26.7 and 29.1%, and the prevalence was not statistically different between the two types of farms. Campylobacter prevalence was significantly higher in March than in September, higher in calves than in cows, and higher in smaller farms than in large farms. The rates of retained placenta, pneumonia, mastitis, and abortion were associated with the proportion of Campylobacter isolation from fecal samples. The gradient disk diffusion MIC method (Etest) was used for testing susceptibility to four antimicrobial agents: ciprofloxacin, gentamicin, erythromycin, and tetracycline. Two isolates were resistant to ciprofloxacin, and none of isolates was resistant to gentamicin or erythromycin. Resistance to tetracycline was 45% (148 of 332 isolates). Tetracycline resistance was found more frequently in calves than in cows (P = 0.042), but no difference was observed between organic and conventional farms. When we used Campylobacter spp. as indicator bacteria, we saw no evidence that restriction of antimicrobial use on dairy farms was associated with prevalence of resistance to ciprofloxacin, gentamicin, erythromycin, and tetracycline.

Animals↗

PubMed1981

Clinical evaluation of the Abbott MS-2 antimicrobial susceptibility testing system.

Antimicrobial susceptibilities were determined for 845 clinical isolates by the standardized Bauer-Kirby disk diffusion method and the automated Abbott Ms-2 system. There was an overall correlation of 90% between the two methods. The Abbott MS-2 susceptibility instrument offers a rapid and accurate method for the antimicrobial susceptibility testing of bacteria.

Anti-Bacterial Agents↗

PubMed1995

[In vitro susceptibility of enterohemorrhagic Escherichia coli to 11 antimicrobials. Relationship between antibiotic resistance and toxigenic genotype].

Enterohemorrhagic E coli (EHEC) has been recognized as the main etiologic agent of hemorrhagic colitis and hemolytic uremic syndrome (HUS). The usefulness of antibiotic treatment in patients with EHEC infections is a matter of current debate. Knowledge on EHEC antimicrobial susceptibility patterns in different geographic areas is important for both treatment considerations and for strain characterization. We studied by diffusion disk agar technique the antibiotic susceptibility of 83 EHEC strains obtained from stools of patients with HUS or diarrhea. Eleven antimicrobials were tested (ampicillin, cotrimoxazole, tetracycline, chloramphenicol, furazolidone, gentamycin, amikacin, ciprofloxacin, erythromycin, vancomycin, and metronidazol). Resistant strains by disk diffusion were tested for MIC (mg/ml) by agar dilution. SLT-I and SLT-II were detected with specific biotinylated gene probes. All 83 strains were susceptible to furazolidone, ciprofloxacin, gentamycin and amikacin. Resistance was detected to tetracycline 4%, chloramphenicol 5%, cotrimoxazole 24% and ampicillin 25%. As expected for EHEC strains all were resistant to erythromycin, vancomycin, and metronidazol. Resistant strains were significantly more common in non toxigenic and SLT-I producing strains (p = 0.01). Resistant strains were similarly distributed among patients who had diarrhea only and those who developed HUS (p = 0.3). In Chile, resistant EHEC strains seem to be more common and of different genotypes than those reported in more developed countries. Regional differences of EHEC antibiotic susceptibility patterns indicate a need for continuous monitoring, specially if antibiotics prove to be useful in disease prevention.

Child, Preschool↗

PubMed1993

Molecular epidemiology and antimicrobial susceptibility testing. Testing of quinolone-resistant Staphylococcus aureus strains isolated in Brazil.

An outbreak of 20 oxacillin-resistant Staphylococcus aureus (ORSA) bloodstream infections (BSIs) was detected in the intensive care unit (ICU) at Hospital Sao Paulo, Brazil. In a surveillance study, 10% of ICU personnel were defined as chronic nasal carriers of ORSA. Thirteen BSIs and five nasal isolates were available for phage typing, restriction endonuclease analysis of plasmid (REAP) and chromosomal DNA hybridized with 32P rRNA gene probe. Susceptibility testing against select antimicrobial agents, including 11 quinolones, six glycopeptides, and five topical agents, was performed by broth microdilution and the disk diffusion tests. Ten of the 13 BSI isolates and four of the five nasal strains were oxacillin and quinolone resistant. The new fluoroquinolones CI-960 and WIN57273, the glycopeptides, and the topical agents ramoplanin, bacitracin, mupirocin, and novobiocin were most active. Fourteen strains, 12 BSI isolates, and three nasal isolates showed the same REAP profile. Moreover, the same REAP and chromosomal profile was detected in at least nine BSI isolates and in two nasal isolates. These strains were nontypable by phage typing. We concluded that nosocomial cross-transmission of a single, multiresistant strain of S. aureus occurred and that the epidemic reservoir was nasal carriage by ICU personnel.

Bacteriophage Typing↗

PubMed1995

National survey of the in vitro spectrum of piperacillin-tazobactam tested against more than 40,000 aerobic clinical isolates from 236 medical centers.

Hospital microbiology laboratories from 41 states participated in a bacterial antimicrobial susceptibility study comparing in vitro results generated by the standardized disk diffusion method. Over 41,000 freshly isolated aerobic and facultative strains, representing all specimen types (except stools and urines), were tested for their susceptibility to piperacillin-tazobactam and 21 other antimicrobial agents. Enterococcus spp. was the second or third most common isolate from intraabdominal, gynecologic, and cutaneous infections, confirming its growing importance as a nosocomial pathogen. Escherichia coli was the most frequent isolate overall, despite the exclusion of urinary tract specimens from the study. Pseudomonas aeruginosa was the second most prevalent species, ranking first in frequency of recovery from lower-respiratory-tract specimens. Piperacillin-tazobactam was the most active beta-lactamase inhibitor combination tested against Gram-negative bacteria. Its activity against Gram-positive bacteria and Haemophilus influenzae was similar to that of ampicillin-sulbactam (95-97% susceptible). Imipenem and piperacillin-tazobactam displayed similar spectrums of activity against Gram-positive organisms and Haemophilus influenzae. Against Enterobacteriaceae, piperacillin-tazobactam and ceftazidime exhibited similarly wide spectrums of activity, but with some gaps, particularly among Enterobacter spp. and Citrobacter freundii. In this large-scale in vitro study, piperacillin-tazobactam and imipenem displayed the widest antimicrobial spectrums, inhibiting > 90% of all isolates tested.

Bacteria↗

PubMed2001

Evaluation of E test, disk diffusion and broth microdilution to establish tentative quality control limits and review susceptibility breakpoints for two aerobic actinomycetes.

A single laboratory study was carried out to compare E Test with broth microdilution and disk diffusion to establish tentative quality control ranges for Nocardia asteroides ATCC 19247 and Rhodococcus equi ATCC 6939 against a panel of eight antimicrobial agents. Reproducibility testing was performed on 12 consecutive days to establish tentative quality control ranges. A total of 36 clinical strains of the Nocardia asteroides complex and 5 Rhodococcus strains were used in the study. Both candidate control strains and clinical strains grew well on cation-adjusted Mueller-Hinton agar. Adequate growth occurred at 48 to 72 h for the Nocardia isolates and 24 to 48 h for Rhodococcus. A standardized primary inoculum of 5 x 10(4) CFU/mL was used for performance of E Test and disk diffusion for the Nocardia isolates. Tentative population-based error rates were calculated using current breakpoints for Enterobacteriaceae for E Test compared with disk diffusion for the 36 clinical strains of Nocardia species. Significant very major error rates were observed for imipenem (22%) and minor error rates varied from 2.7% to 50%. These methods require more extensive validation before definitive breakpoint criteria can be established.

Aerobiosis↗