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Results for “Disk Diffusion Antimicrobial Tests”

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PubMed2003

[Analysis of antimicrobial resistance of clinical isolates of enterococci from Beijing and other areas in China].

OBJECTIVE: To analyze the antimicrobial resistance of enterococci in Beijing and other areas in China. METHODS: Disk diffusion method was used to test the antimicrobial resistance of 1978 enterococcal isolates from 4 teaching hospitals in Beijing and 53 grade 3 A hospitals in other areas of China The laboratory data were analyzed by WHONET5 statistic software. RESULTS: Enterococcus. faecalis isolates and E. facium isolates accounted for 80.7% and 17.1% of the enterococcus isolates in Beijing and 79.4% and 15.2% in other areas respectively. The enterococcus isolates from urine, sputum, secretion with pus, blood, and bile accounted for 33.7%, 22.9%, 9.8%, 4.4%, and 3.0% of the enterococcus isolates in Beijing and 28.4%, 16.3%, 14.6%, 5.0%, and 4.5% in other areas respectively. The resistance rates of E. faecalis to vancomycin, teicoplanin, ampicillin, and high -level gentamicin were 2.0%, 1.4%, 17.7%, and 47.4% in Beijing, and 5.1%, 3.7%, 24%, and 49.2% in other areas; The resistance rates of E. faecium to vancomycin, teicoplanin, ampicillin, and high -level gentamicin were 1.5%, 2.6%, 64.2%, and 64.9% in Beijing, and 2.1%, 3.1%, 68.5%, and 62.3% in other areas respectively. The vancomycin-resistant rate of the total isolates of enterococci was 3.2%. CONCLUSION: Enterococcus faecalis is the main species in the enterococcus isolates from clinical samples. E. facium, as compared with E. faecalis resists many antimicrobial agents more strongly. Both of E. faecalis and E. facium show the least resistance to vancomycin and teicoplanin.

Drug Resistance, Bacterial↗

PubMed1989

[Clinical laboratory approach to estimating the effective administration dose of imipenem/cilastatin. Evaluation of the disk susceptibility test and its interpretation system].

In vitro activities of imipenem/cilastatin (IPM/CS) against 413 clinical isolates were studied through the evaluation of MICs and the results of disk susceptibility tests. The MICs were determined using the agar dilution method at an inoculum level of 10(6) CFU/ml. The MIC80s of imipenem (IPM) against Staphylococcus aureus and Staphylococcus epidermidis were 25 and 1.56 micrograms/ml, respectively, showing a bimodal MIC distribution. However, the distribution of MICs against other bacteria studied was of monomodal pattern. Group A Streptococcus, Enterococcus faecalis were inhibited by IPM at dose levels less than 0.025 and 6.25 micrograms/ml, respectively. IPM inhibited Escherichia coli at 0.20 microgram/ml, Klebsiella pneumoniae at 0.39 microgram/ml, Pseudomonas aeruginosa at 3.13 micrograms/ml except one strain showed a MIC of 25 micrograms/ml, Serratia spp. at 3.13 micrograms/ml except one with MIC greater than 100 micrograms/ml, Citrobacter freundii at 0.78 microgram/ml and Enterobacter spp. at 0.39 microgram/ml. Indole (-) Proteus and indole (+) Proteus were inhibited by this drug at levels of 3.13 and 1.56 micrograms/ml, respectively. The reliability of the IPM disk diffusion susceptibility test in quantitative estimation of antimicrobial activities was well demonstrated using commercialized 8 mm diameter Showa disks containing 30 micrograms antibiotic and also disks containing 1-30 micrograms prepared in this laboratory. For the interpretation of the Showa disk susceptibility test, a 4 category system was used. In the 4 category system for Showa IPM disk the following classification of inhibitory zone diameters has been proposed; ( ) MIC less than or equal to 3 micrograms/ml, (++) MIC greater than 3-15 micrograms/ml, (+) MIC greater than 15-60 micrograms/ml, (-) MIC greater than 60 micrograms/ml. The results of the test using Showa 30 micrograms disk against various clinical isolates were accurately classified into the 4 groups, showing false positive 8 out of 304 strains (2.6%) and false negative 1 of 304 strains (0.3%). With Showa 30 micrograms disks subclassification of strains with MIC less than 3 micrograms/ml cannot be achieved. In this study, however, the differentiation of strains with MICs less than 1 microgram/ml was made with disks containing 5-10 micrograms, which afforded to set MIC break points at 1 and 3 micrograms/ml. According to current concepts on pharmacokinetics for antibiotics including the penetration of drugs into tissues and inflammatory fluids, serum protein binding of drugs appears to be one of the important determinants of drug distribution in the body. Only free, unbound drug molecules can readily pass through capillary pores into tissue fluids except in the hepato-biliary system.(ABSTRACT TRUNCATED AT 400 WORDS)

Bacteria↗

PubMed1974

Evaluation of two standardized disk methods for testing antimicrobial susceptibility of Pseudomonas aeruginosa and of the Enterobacteriaceae.

Two standardized disk diffusion susceptibility testing methods were compared using Pseudomonas aeruginosa and members of the Enterobacteriaceae. The standard Bauer-Kirby method and the agar overlay method of Barry et al. were compared using carbenicillin (50- and 100-mug disks), gentamicin, polymyxin B, and colistin sulfate. Both methods gave nearly comparable zone sizes with the enteric bacilli. However, with P. aeruginosa the agar overlay method gave zones 1 to 2 mm smaller than the Bauer-Kirby method with all drugs except gentamicin. In spite of these small differences, further examination of minimal inhibitory concentration-zone size correlations indicated that the same interpretive zone standards can be applied to either diffusion technique. For testing carbenicillin against Pseudomonas sp., 50-mug disks were unsatisfactory, especially with the agar overlay method; 100-mug disks were far superior with both methods.

Carbenicillin↗

PubMed1989

[Effects of sulbactam on the activity of cefoperazone against various clinical isolates].

Sulbactam/Cefoperazone (SBT/CPZ) have been used in clinical infusion at ratios of 1:1 and 1:2 in Japan and U.S.A., respectively. After an administration of these drugs as a 1:1 parenteral formulation, the ratio of levels of CPZ and SBT in blood was 1:1/4 to 1:1/5 for 1 to 2 hours, whereas the ratio of free, unbound drug levels was 1:1.4 to 1:1.5. In urine these drugs were excreted at a ratio between 1:1 and 1:4 during 6 hours after the infusion. Antimicrobial interaction studies using various combinations of CPZ and SBT were performed to obtain information with respect to the effect of SBT on the antimicrobial activity of CPZ in vivo and the most appropriate ratio of these drugs for the in vitro test system. Antimicrobial activities were determined using the agar dilution method and the disk diffusion susceptibility test. SBT increased the activity of CPZ against various clinical isolates tested except Enterococcus faecalis. CPZ-SBT at a fixed ratio of 1:1/5 significantly increased the antimicrobial activity of CPZ, resulting in decreases in MIC values and increases in disk inhibitory zone diameters. These drugs at ratios 1:1 to 1:3 maximized the synergistic enhancement of the activity. Therefore, a fixed ratio between 1:1/5 and 1:1 would be appropriate for the in vitro antimicrobial test system using either the agar dilution method or the disk susceptibility test. Based on pharmacokinetic data for CPZ and SBT, results of the present study on antimicrobial activity would support that the parenteral formulation of CPZ-SBT at the fixed ratios of 1:1 and 2:1 for the intravenous infusion used in Japan and U.S.A., respectively, are appropriate. The effect of SBT on the activity of CPZ was more marked against clinical isolates with greater production abilities of beta-lactamase than against those with less production abilities. SBT/CPZ, however, exerted a synergistic effect against methicillin-resistant Staphylococcus aureus without beta-lactamase production. The MIC80 of SBT/CPZ (1:1) against various clinical isolates with 10(6) CFU/ml inoculum size were as follows: S. aureus 12.5 micrograms/ml, Staphylococcus epidermis 3.13 micrograms/ml, and E. faecalis 50 micrograms/ml. Those of Gram-negative bacilli were: Escherichia coli 0.20 microgram/ml, Klebsiella pneumoniae 0.20 micrograms/ml, Proteus mirabilis 0.78 microgram/ml, Proteus vulgaris 0.78 microgram/ml, Pseudomonas aeruginosa 12.5 micrograms/ml, Serratia marcescens 25 micrograms/ml, Enterobacter spp. 3.13 micrograms/ml, Citrobacter spp. 12.5 micrograms/ml and Acinetobacter spp. 0.78 microgram/ml.

Bacteria↗

PubMed2005

In vitro antimicrobial activity of extracts of four Achillea species: the composition of Achillea clavennae L. (Asteraceae) extract.

The extracts of aerial parts of Achillea clavennae, Achillea holosericea, Achillea lingulata and Achillea millefolium (hexane:ether:methanol=1:1:1) have been tested for antimicrobial activity in a disk diffusion assay against five bacteria (Staphylococcus aureus, Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa and Salmonella enteritidis) and two fungi (Aspergillus niger and Candida albicans). Extracts of all four species possessed a broad spectrum of antimicrobial activity against all tested strains. The composition of the extract of Achillea clavennae, which showed the strongest activity, was investigated and the structures of isolated compounds were elucidated by spectral means (1D and 2D NMR, UV, IR and MS). The extract yielded alkanes, fatty acids, monoterpenes, guaiane sesquiterpenes (rupicolin A and B, 1-deoxy-1alpha-peroxy-rupicolin A and B), and flavonoids (apigenin and centaureidin). This study confirms the ethnopharmacological use of plants from this genus and places Achillea clavennae L. on the same level as the recognized Achillea millefolium.

Achillea↗

PubMed2004

Antimicrobial resistance of Escherichia coli strains isolated from urine of women with cystitis or pyelonephritis and feces of dogs and healthy humans.

OBJECTIVE: To assess the prevalence and patterns of antimicrobial resistance among Escherichia coli strains isolated from the urine of women with cystitis or pyelonephritis and from fecal samples from dogs and healthy humans. DESIGN: Cross-sectional survey. SAMPLE POPULATION: Escherichia coli isolates from 82 women with cystitis, 170 women with pyelonephritis, 45 dogs, and 76 healthy human volunteers. PROCEDURE: Susceptibility to 12 antimicrobial agents was determined by means of disk diffusion testing as specified by the NCCLS. RESULTS: Overall, the 4 most common antimicrobial resistance patterns were resistance to ampicillin, sulfisoxazole, trimethoprim, and trimethoprim-sulfamethoxazole (n = 45 [12% of all isolates]); ampicillin alone (33 [9%]); ampicillin and sulfisoxazole (29 [8%]); and sulfisoxazole alone (14 [4%]). None of the isolates were resistant to ceftazidime, ciprofloxacin, nitrofurantoin, or piperacillin-tazobactam. Resistance was significantly more common and extensive among isolates from women with cystitis or pyelonephritis than among isolates from healthy humans or dogs. Resistance was least common among isolates from dogs. The only resistance phenotype that was more common among canine isolates than human isolates was resistance to sulfisoxazole alone. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that dogs are unlikely to be an important external reservoir of antimicrobial-resistant E. coli strains causing infections in humans. On the contrary the data suggest that dogs conceivably could acquire resistant E. coli strains from humans.

Animals↗

PubMed2003

Correlates of antibiotic-resistant group B streptococcus isolated from pregnant women.

Despite antibiotic prophylaxis for at-risk mothers during labor and delivery, group B streptococcus still causes substantial morbidity and mortality among newborns. Resistance to antibiotics recommended for penicillin-allergic pregnant women, such as erythromycin and clindamycin, has increased. A better understanding of factors associated with group B streptococcus resistance is essential to effectively prevent group B streptococcus disease.A total of 117 sequential group B streptococcus isolates were obtained between August 1999 and March 2000 from pregnant women at the University of Michigan Medical Center. Serotype and susceptibility to ten antimicrobials using disk diffusion with E-test for confirmation were determined, and the association between several host factors and colonization with a resistant strain was evaluated. Group B streptococcus was frequently resistant to erythromycin (29%) and clindamycin (21%) but was susceptible to all other antimicrobials tested. A stepwise logistic regression model revealed that black ethnicity (P =.02) and carriage of a serotype V strain (P =.01) were associated with group B streptococcus resistance. Among this population of pregnant women, black ethnicity and serotype V were the strongest predictors of colonization with an erythromycin- or clindamycin-resistant group B streptococcus strain. A better understanding of factors associated with antibiotic resistance is needed to minimize group B streptococcus disease risks and to maximize effective chemoprophylaxis.

Adolescent↗

PubMed2006

Frequency of antimicrobial resistance among invasive and colonizing Group B streptococcal isolates.

BACKGROUND: Group B Streptococcus (GBS) remains susceptible to penicillin, however, resistance to second-line antimicrobials, clindamycin and erythromycin, has increased since 1996. We describe the age-specific antibiotic susceptibility profile and capsular type distribution among invasive and colonizing GBS strains. METHODS: We tested 486 invasive GBS isolates from individuals of all ages collected by a Wisconsin surveillance system between 1998 and 2002 and 167 colonizing strains collected from nonpregnant college students during 2001 in Michigan. Antimicrobial susceptibility testing was performed by disk diffusion or Etest and capsular typing was performed using DNA dot blot hybridization RESULTS: 20.0% (97/486) of invasive and 40.7% (68/167) of colonizing isolates were resistant to clindamycin (P < .001) and 24.5% (119/486) of invasive and 41.9% (70/167) of colonizing isolates were resistant to erythromycin (P < .001). Similarly, 19.8% (96/486) of invasive and 38.3% (64/167) of colonizing isolates were resistant to both antimicrobial agents (P < .001). 29.4% (5/17) of invasive isolates from persons 18-29 years of age and 24.3% (17/70) of invasive isolates from persons 30-49 years of age were resistant to clindamycin. Similarly, 35.3% (6/17) of invasive isolates from persons 18-29 years of age and 31.4% (22/70) of invasive isolates from persons 30-49 years of age were resistant to erythromycin. 34.7% (26/75) of invasive isolates from persons < 1 year of age were capsular type Ia, whereas capsular type V predominated among isolates from adults. CONCLUSION: Clindamycin and erythromycin resistance rates were high among isolates colonizing nonpregnant college students and invasive GBS isolates, particularly among the colonizing isolates. Susceptibility profiles were similar by age although the proportion of clindamycin and erythromycin resistance among invasive isolates was highest among persons 18-49 years of age. Increasing antimicrobial resistance has implications for GBS disease treatment and intrapartum prophylaxis among penicillin intolerant patients.

Adolescent↗

PubMed2003

In vitro antimicrobial activity of the aminoglycoside arbekacin tested against oxacillin-resistant Staphylococcus aureus isolated in Brazilian hospitals.

Arbekacin is an aminoglycoside used in Japan for treating infections caused by gentamicin and oxacillin-resistant S. aureus (ORSA). The objective of this study was to determine the in vitro antimicrobial activity of arbekacin against 454 clinical isolates of ORSA. The isolates were consecutively collected between January and July, 2000, from patients hospitalized in 8 Brazilian medical centers. The antimicrobial susceptibility testing was performed by disk diffusion method according to NCCLS recommendations. The vast majority of the isolates, 453 strains (99.8%), were considered susceptible to arbekacin based on the criteria proposed by the Requirements for Antibiotic Products of Japan. Only 1 isolate (0.2%) was classified as resistant. On the other hand, high rates of resistance were demonstrated for other aminoglycosides, such as gentamicin (97.6% resistance) and amikacin (97.0% resistance). Resistance rate was also high for ciprofloxacin (98.0%). All isolates were considered susceptible to vancomycin. The excellent in vitro antimicrobial activity of arbekacin demonstrated in this study indicates that this antimicrobial agent may play an important role in the treatment of severe ORSA infections, especially those that show poor clinical response with vancomycin monotherapy. Since the aminoglycosides should not be used as monotherapy to treat Gram positive infections, further studies evaluating in vitro and in vivo synergistic activity of arbekacin combinations are necessary to clarify the clinical role of this aminoglycoside.

Aminoglycosides↗

PubMed2001

Antimicrobial resistance of Enterococci in Lebanon.

There is little information on the types of Enterococcus spp and their antibiotic resistance patterns in Lebanon. One hundred and fifty-three consecutive clinical enterococcal isolates collected between 1998 and 1999 were tested against 11 antimicrobial agents using disk diffusion and the Etest. The isolates were identified by conventional methods and API-Strep and were found to consist of Enterococcus faecalis (72.5%), Enterococcus faecium (22.9%), Enterococcus avium (3.2%) and Enterococcus gallinarum (1.3%). The percent of resistant strains of E. faecalis and E. faecium respectively were, ampicillin 0.9 and 14%, erythromycin 59% and 40%, tetracycline 72% and 34%, chloramphenicol 32 and 11%, rifampin 36% and 57%, ciprofloxacin, 23% and 34%, norfloxacin 22 and 8%. High level aminoglycoside (HLA) resistance was found in 19% E. faecalis and 9% E. faecium for gentamicin and 36% and 26% for streptomycin. Excellent correlation was observed between the high level disk tests and the Etest in the detection of HLA resistance but not with the regular disks. None of the isolates showed resistance to vancomycin or teicoplanin except for one E. gallinarum isolate which showed intermediate resistance (MIC 16 mg/l) to vancomycin. These variable antimicrobial rates of resistance suggest a surveillance programme for antimicrobial resistance in this country would be helpful to help control infection, guide empirical antibiotic therapy and implement a policy of antibiotic usage.

Aminoglycosides↗

PubMed2000

High prevalence of antibiotic resistance of common pathogenic bacteria in Taiwan. The Antibiotic Resistance Study Group of the Infectious Disease Society of the Republic of China.

We analyzed the antimicrobial susceptibilities of all clinical isolates of 14 common pathogenic bacteria recovered from patients in eight medical centers in Taiwan during 1995 and 1996. Susceptibility to commonly used antimicrobial agents was tested by the disk diffusion method as recommended by the National Committee for Clinical Laboratory Standards. Of the Staphylococcus aureus isolates, 59.3% and 62% were oxacillin-resistant in 1995 and 1996, respectively, whereas 63.2% of the coagulase-negative staphylococci isolates during the study period were oxacillin-resistant. The rate of penicillin-resistance among Streptococcus pneumoniae isolates was 39.7% in 1995 and 53.7% in 1996. Macrolide-resistance was found in 71.4%, 42.1%, and 46.7% of S. pneumoniae, beta-hemolytic streptococci, and viridans streptococci, respectively, in 1996. Less than 2% of the enterococcal isolates were vancomycin resistant, but 77% of them were gentamicin resistant. Resistance to gentamicin was also common in Enterobacteriaceae, Pseudomonas aeruginosa, and Acinetobacter baumannii. Various degrees of resistance to ampicillin, piperacillin, cephalosporins, aztreonam, and ciprofloxacin were detected in Enterobacteriaceae, P. aeruginosa, and A. baumannii. More than 55% of Haemophilus influenzae isolates were ampicillin resistant. In summary, resistance to many antimicrobial agents in various common pathogenic bacteria is very common in Taiwan. Our results implicate that antibiotic resistance in the developing countries need to be monitored closely.

Cross Infection↗

PubMed2002

[Enterobacteria isolated from cockroaches (Periplaneta americana) captured in a Brazilian hospital].

OBJECTIVE: To isolate and identify microorganisms from cockroaches that were captured in a public hospital and to test the antimicrobial susceptibility of these microorganisms. METHODS: Cockroaches were captured in the morning and at night. They were placed in flasks rinsed with 70% alcohol, transferred to sterilized flasks, and then taken to the laboratory. Only cockroaches captured whole and live were utilized for the study. After being immobilized at 0 degree C, each cockroach was placed in a test tube with sterile saline solution (0.8%) and then homogenized. The resulting solution was then placed in the following five culture media: MacConkey agar, nutrient broth, brain-heart infusion agar, Sabouraud agar, and mannitol. The cultures were examined using a stereomicroscope, and colony-forming units were counted. The disk diffusion test was used to determine antimicrobial susceptibility. RESULTS: We found a 56% prevalence of enterobacteria and an 18% prevalence of coagulase-negative staphylococci. Fifteen species of enterobacteria were identified. The most frequent were Klebsiella pneumoniae (17%), Enterobacter aerogenes (14%), Serratia marcescens (13%), Hafnia alvei (12%), Enterobacter gergoviae and Enterobacter cloacae (each 9%), and Serratia spp. (6%). Both the enterobacteria and the coagulase-negative staphylococci showed significant resistance to antimicrobials, including oxacillin. CONCLUSIONS: The prevalence of enteropathogenic bacteria and coagulase-negative staphylococci isolated from Periplaneta americana cockroaches in the studied hospital reflects the weakness of the measures adopted both for vector control and for antimicrobial use. The results show the need to implement effective health-institution programs focusing on hygiene and the rational use of antimicrobials.

Animals↗

PubMed2002

[The change in sensitivity of methicillin-resistant Staphylococcus aureus to vancomycin].

OBJECTIVE: To determine the shift of susceptibility of methicillin-resistant Staphylococcus aureus (MRSA) isolates to vancomycin in recent years. METHODS: Antimicrobial susceptibility was determined by disk diffusion test (K-B method). The t-test was used to compare the mean diameters of zone of inhibition. RESULTS: The clinical isolates of MRSA from 1994 to 2000 were 218, 187, 292, 237, 351, 886 and 652 in number respectively. The mean diameters (mm) of the inhibition zone of MRSA isolates each year were 19.9, 19.1, 18.6, 17.4, 18.4, 18.2 and 17.8. Comparison of the diameters of the inhibition zone of MRSA isolates (K-B method) showed that the mean diameter of the inhibition zone from the 652 MRSA isolates in 2000 was much less than that of the 218 MRSA isolates in 1994 and the difference was significant (P < 0.001). The resistant rates to chloramphenicol, ciprofloxacin, erythromycin, gentamicin, tetracycline and trimethoprim/sulfamethoxazole were 44.0%, 73.7%, 89.1%, 65.7%, 61.0% and 67.0%. CONCLUSION: Our observation demonstrated that the susceptibility of MRSA to vancomycin gradually decreased from 1994 to 2000. It is important to monitor the antimicrobial susceptibility of Staphylococcus aureus to vancomycin.

Anti-Bacterial Agents↗

PubMed2000

Comparison between the antimicrobial susceptibility of Burkholderia pseudomallei to trimethoprim-sulfamethoxazole by standard disk diffusion method and by minimal inhibitory concentration determination.

Melioidosis, an infection caused by Burkholderia pseudomallei, usually occurs in immunocompromised patients and requires prolonged antibiotic therapy. Previously, oral trimethoprim-sulfamethoxazole (TM/SM), an inexpensive and effective drug has been used as a maintenance therapy. The susceptibility of B. pseudomallei to TM/SM by the standard disk diffusion method is very low. However, some patients who were treated with TM/SM as a maintenance therapy despite the in vitro resistance showed good clinical responses. There were no data comparing the susceptibility of B. pseudomallei by the standard disk diffusion method with other quantitative susceptibility tests. The objective of this study was to determine the agreement between the antimicrobial susceptibility of B. pseudomallei to TM/SM by standard disk diffusion and minimal inhibitory concentration determination (MIC). We performed the susceptibility test of 144 strains of B. pseudomallei to TM/SM by both the standard disk diffusion and microbroth dilution MIC. The sensitivity results were 53.5 per cent and 84.0 per cent respectively. The agreement between the 2 tests was very poor (Kappa = 0.14; 95% CI = -0.01 to 0.29). The false resistant rate by the standard disk diffusion test was 67.9 per cent. Further in vitro susceptibility and clinical study are needed to define the interpretive criteria that correlate with clinical response.

Administration, Oral↗

PubMed2004

Use of selective media for detection of cephalothin-resistant bacteria in surgical patients.

Bacterial colonization in hospitalized patients is an important step in nosocomial infections. Frequent employment of antimicrobials can modify patients' normal microbiota, favoring colonization and infection by antimicrobial-resistant microorganisms. First-generation cephalosporins are frequently used as prophylactic antibiotics in surgery. Intestinal, oropharyngeal and skin colonization by cephalothin-resistant microorganisms were studied in 60 pre-operative patients at the Hospital Universitário Pedro Ernesto. Feces were cultured in Eosin-methylene blue medium containing 32 microg/mL of cephalothin. Swabs obtained from the oropharynx and from skin were inoculated in cistein-lactose electrolytes-deficient medium containing 32 microg/mL of cephalothin. Isolated strains were identified and tested for susceptibility to antimicrobials by disk diffusion. Cephalothin-resistant strains were isolated from the feces of 59 patients (98%), from the oropharynx of 13 patients (22%) and from skin in 10 patients (17%). Enterobacter cloacae was predominant in feces (68% of the patients) and oropharynx (13%). Acinetobacter spp. was the most frequent microorganism isolated from the skin (10%). Antimicrobial multiresistant strains were isolated from at least one of the sites in 38 patients (63%). The employment of selective medium containing antimicrobials is a relatively simple and efficient method, being useful to evaluate microorganisms from hospitalized patients' microbiota that are relevant as potential pathogens in nosocomial infections.

Anti-Bacterial Agents↗

PubMed1994

Disk diffusion versus broth microdilution susceptibility testing of Haemophilus species and Moraxella catarrhalis using seven oral antimicrobial agents: application of updated susceptibility guidelines of the National Committee for Clinical Laboratory Standards.

Susceptibility testing of Haemophilus species and Moraxella catarrhalis is medium and inoculum dependent. Seven oral agents, ampicillin, amoxicillin-clavulanic acid, cefaclor, loracarbef, cefuroxime-axetil, cefixime, and erythromycin, were tested against 400 beta-lactamase-positive and -negative clinically significant respiratory strains of Haemophilus species and 100 strains of M. catarrhalis. Sources of the strains included teaching and regional hospitals and a private laboratory. All strains were tested by broth microdilution and disk diffusion in haemophilus test medium for Haemophilus species and Mueller-Hinton broth and agar for M. catarrhalis. Appropriate National Committee for Clinical Laboratory Standards (NCCLS) standards were followed. For Haemophilus species, by disk diffusion and broth microdilution, respectively, 27 and 27% of strains were resistant to ampicillin, 37 and 5% were resistant to erythromycin, 3 and 0.5% were resistant to cefaclor, 2 and 0.5% were resistant to loracarbef, and 0% were resistant to cefuroxime-axetil, cefixime, and amoxicillin-clavulanic acid. beta-Lactamase-negative ampicillin-resistant strains were not observed. Of M. catarrhalis strains, 56% were resistant to ampicillin by disk diffusion and 95% were resistant by broth microdilution. This species was susceptible to all other agents tested by either method. The disagreements between disk diffusion results and MICs for cefaclor, ampicillin, cefuroxime, and loracarbef that occurred with use of the 1990 NCCLS tables were resolved when the 1992 NCCLS tables were used.

Administration, Oral↗

PubMed2001

Prevalence of antimicrobial resistance in Salmonellae isolated from market-age swine.

Antimicrobial resistance levels were examined for 365 Salmonella isolates recovered from the lymph nodes (n = 224) and cecal contents (n = 141) of market-age swine at slaughter. Antimicrobial resistance testing was performed by disk diffusion using 13 antibiotics common in the treatment of disease in human and veterinary medicine. Although none of the antibiotics tested were used subtherapeutically within the last 5 years on the farms sampled, resistance to chlortetracycline, penicillin G, streptomycin, and sulfisoxazole was common. Penicillin G resistance was significantly more frequent (P = 0.03) and sulfisoxazole resistance was significantly less frequent (P < 0.01) in lymph node versus cecal isolates. Multidrug resistance was observed among 94.7% of the lymph node isolates and 93.5% of the cecal isolates. The most frequent multidrug resistance pattern included three antibiotics-penicillin G, streptomycin, and chlortetracycline. Isolates in somatic serogroup B, and more specifically, Salmonella Agona and Salmonella Schwarzengrund isolates, were often resistant to a greater number of antibiotics than were isolates in the other serogroups. Streptomycin, sulfisoxazole, ampicillin (lymph node isolates), and nitrofurantoin (cecal isolates) resistance levels differed significantly between somatic serogroups. The prevalence of penicillin G-, streptomycin-, and sulfisoxazole-resistant isolates differed significantly between serovars for both lymph node and cecal isolates. Results of this study suggest that a correlation exists between the somatic serogroup or serovar of a Salmonella isolate and its antimicrobial resistance status, which is specific to the antibiotic of interest and the source of the isolate (lymph node versus cecal contents).

Animals↗

PubMed1987

Impact of prolonged incubation on disk diffusion susceptibility test results for Staphylococcus aureus.

Because strains of Staphylococcus aureus that are resistant to penicillinase-resistant penicillins may be difficult to detect in the clinical laboratory, a variety of changes in methodology have been suggested to increase their detection. In 1984, the West Los Angeles Veterans Administration Medical Center experienced an increase in clinically significant strains of oxacillin-resistant S. aureus. To insure that such strains would not be missed by the disk diffusion test methods employed for routine testing, changes in methodology were insituted. These included interpreting zone diameters around oxacillin disks at 48 h of incubation. We collected 139 isolates from patients thought to have oxacillin-resistant S. aureus based on these test results and later retested the isolates using microdilution MIC testing. Only 85 isolates (61%) had microdilution oxacillin MICs of greater than or equal to 8.0 micrograms/ml, whereas 54 (39%) had oxacillin MICs of less than or equal to 2.0 micrograms/ml. A review of medical records revealed that in 1 year there were 98 patients with isolates appearing resistant by disk diffusion but not confirmed by microdilution MICs; many patients were placed in isolation and treated with specific antimicrobial agents. We conclude that incubation of oxacillin disk diffusion tests for longer than 24 h in conjunction with disregard for resistance to other classes of antimicrobial agents may result in an unacceptably high degree of false resistance results. Because the resistance of S. aureus has important therapeutic and infection control implications, it is necessary to recognize problems that may result in ambiguous or inaccurate susceptibility results.

Humans↗