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PubMed1992

Evaluation of the standardized disk diffusion and agar dilution antibiotic susceptibility test methods by using strains of Neisseria gonorrhoeae from the United States and Southeast Asia.

Presently, most Neisseria gonorrhoeae testing is based on beta-lactamase tests and agar dilution with common therapeutic agents. The National Committee for Clinical Laboratory Standards (NCCLS) recently described a disk diffusion test that produced results similar to the reference agar dilution method for the antibiotic susceptibility of N. gonorrhoeae. We obtained 71 gonococcal isolates from active-duty males aboard a United States Navy vessel while deployed in the Western Pacific during 1989. In addition, 47 isolates of N. gonorrhoeae were obtained from sexually transmitted disease clinics within the branch clinic operations of the Naval Hospital, San Diego (SD), and tested. Antibiotic susceptibility tests by using the NCCLS agar dilution and disk diffusion techniques were compared. Among the Southeast Asia (SEA) isolates, 47% were beta-lactamase producers compared with 10.5% of the SD isolates. The mean MICs (SEA/SD) in micrograms per milliliter for both groups were as follows: penicillin, 88/15; tetracycline, 2.2/0.95; erythromycin, 1.2/0.49; ceftriaxone, 0.016/0.012; cefotaxime, 0.034/0.03; cefuroxime, 0.44/0.17; cefoxitin, 1.3/0.97; spectinomycin, 150/131; ciprofloxacin, 0.07/0.034; norfloxacin, 0.77/0.29; lomefloxacin, 0.15/0.0.056; and ofloxacin, 0.07/0.036. The established NCCLS interpretive criteria for both susceptibility methods appear applicable to domestic gonococcal strains. However, modifications may be necessary for the more antimicrobial agent-resistant SEA isolates on the basis of the clinical success and cure rates following the indicated single-dose regimens for the geographic region.

Asia, Southeastern↗
PubMed1997

The activity of a combination of penicillin and novobiocin against bovine mastitis pathogens: development of a disk diffusion test.

The combination of penicillin and novobiocin is currently available for the treatment of bovine mastitis, but methods are not available for susceptibility testing of the combination by veterinary diagnostic laboratories. The minimum inhibitory concentration (MIC) and disk diffusion data were determined for penicillin, novobiocin, and a combination of the two in a 1:2 ratio for 225 staphylococcal, streptococcal, and Gram-negative isolates from bovine intramammary infections. Based on the drug concentrations in milk following infusion, linear regression analysis, and error rate bounding, the interpretive zone diameters selected were < or = 16 mm for resistant isolates and > or 17 mm for susceptible isolates with a disk containing 10 U of penicillin and 30 micrograms of novobiocin. Additionally, MIC breakpoints of < or = 2 micrograms/ml of penicillin and 4 micrograms/ml of novobiocin were selected to categorize isolates as susceptible and > or = 4 micrograms/ml of penicillin and 8 micrograms/ml of novobiocin were selected to categorize isolates as resistant. The MIC and disk diffusion results, as well as studies to monitor bacterial killing by antimicrobial agents over time, indicated that the combination of penicillin and novobiocin in a 1:2 ratio was more active than were the individual drugs. Kinetics of the kill curves with the penicillin and novobiocin combination (1:2 ratio) showed that the combination was bactericidal for Staphylococcus aureus and Staphylococcus xylosus.

Animals↗
PubMed2002

Antimicrobial susceptibility of Haemophilus influenzae among children in Beijing, China, 1999-2000.

UNLABELLED: A study on the nasopharyngeal carriage and antimicrobial susceptibility of Haemophilus influenza among children was conducted in Beijing Children's Hospital from April to May 2000. The study included 292 children between 1 and 60 mo of age with acute upper respiratory tract infection. Nasopharyngeal swabs from these patients were cultured, and 105 Haemophilus influenzae strains were isolated, 3 of which were type b. Antibiotic susceptibility of the strains was determined using disk diffusion and E-tests and the results compared with those of isolates from children with pneumonia in 1999. The carriage rate of Haemophilus influenzae was 36.0% (105/292). It was found that 4.8% and 1.0% of isolates were resistant to ampicillin and cefaclor, respectively, and 5.7%, 16.2% and 77.1% were resistant to chloramphenicol, tetracycline, and sulphamethoxazole/trimethoprim, respectively. Amoxicillin/clavulanic acid, cefuroxime, ceftriaxone, azithromycin, and clarithromycin were uniformly active to all strains. Compared with the data from 1999, there was a significant increase in resistance to tetracycline (from 12.7% in 1999 to 16.2%) and sulphamethoxazole/trimethoprim (from 40.5% in 1999 to 77.1%). CONCLUSION: H. influenzae isolates from outpatients in Beijing Children's Hospital had low ampicillin resistance and were sensitive to amoxicillin/clavulanic acid. Sulphamethoxazole/ trimethoprim resistance rates increased rapidly compared with those in the 1999 data. Further surveillance investigations are important for the choice of empiric therapy of acute respiratory tract infection.

Ampicillin Resistance↗
PubMed1999

Detection and reporting of organisms producing extended-spectrum beta-lactamases: survey of laboratories in Connecticut.

Extended-spectrum beta-lactamases (ESBLs) are enzymes produced in some gram-negative bacilli that mediate resistance to extended-spectrum cephalosporins and aztreonam. They are most common in Klebsiella spp. and Escherichia coli but are present in a variety of Enterobacteriaceae. Resistance mediated by these enzymes can be difficult to detect depending on the antimicrobial agents tested. AmpC beta-lactamases are related to the chromosomal enzymes of Enterobacter and Citrobacter spp. and also mediate resistance to extended-spectrum cephalosporins and aztreonam in addition to cephamycins, such as cefoxitin. Unlike ESBLs, however, AmpC beta-lactamases are not inhibited by clavulanic acid or other similar compounds. To assess the abilities of various antimicrobial susceptibility testing methods to detect ESBLs, we sent three ESBL-producing organisms, one AmpC-producing organism, and a control strain that was susceptible to extended-spectrum cephalosporins to 38 laboratories in Connecticut for testing. Eight (21.0%) of 38 labs failed to detect extended-spectrum cephalosporin or aztreonam resistance in any of the ESBL- or AmpC-producing isolates. Errors were encountered with both automated and disk diffusion methods. Conversely, seven (18.4%) labs categorized at least some of the four resistant isolates as potential ESBL producers and reported the results with the extended-spectrum cephalosporins and aztreonam as resistant as suggested by current National Committee for Clinical Laboratory Standards (NCCLS) guidelines. The percentage of laboratories that failed to detect resistance in the ESBL or AmpC isolates ranged from 23.7 to 31.6% depending on the type of enzyme present in the test organism. This survey suggests that many laboratories have difficulty detecting resistance in ESBL and AmpC-producing organisms and may be unaware of the NCCLS guidelines on modifying susceptibility testing reports for ESBL-producing strains.

Aztreonam↗
PubMed2004

In vitro activities of 28 antimicrobial agents against Staphylococcus aureus isolates from tertiary-care hospitals in Korea: a nationwide survey.

Staphylococcus aureus, one of the most frequently isolated pathogens in both hospitals and the community, has been particularly efficient at developing resistance to antimicrobial agents. As methicillin-resistant S. aureus (MRSA) has prevailed and, furthermore, as S. aureus with reduced susceptibility to vancomycin has emerged, the therapeutic options for the treatment of S. aureus infections have become limited. To update the current status of antibiotic resistance, clinical S. aureus isolates were collected from eight university-affiliated hospitals from June 1999 to January 2001. Susceptibility tests with 28 antibiotics were performed by the disk diffusion method. Among a total of 682 isolates, the methicillin resistance rate was 64% (439 of 682), and most of the MRSA isolates were resistant to multiple classes of antibiotics. Although a constitutive macrolide-lincosamide-streptogramin B resistance phenotype was common, no isolates were resistant to quinupristin-dalfopristin or linezolid. Rifampin, fusidic acid, trimethoprim-sulfamethoxazole, and arbekacin showed superior in vitro activity compared with the other antibiotics against the MRSA isolates. No isolates showed reduced susceptibility to vancomycin.

Anti-Bacterial Agents↗
PubMed1996

Development of interpretive criteria and quality control limits for macrolide and clindamycin susceptibility testing of Streptococcus pneumoniae.

A six-laboratory collaborative study was conducted to develop MIC and zone diameter quality control limits and interpretive criteria for antimicrobial susceptibility testing of Streptococcus pneumoniae with azithromycin, clarithromycin, dirithromycin, and clindamycin. The MICs of all of the agents plus erythromycin for 302 clinical isolates of pneumococci that had been selected with an emphasis on resistant strains were determined by use of the National Committee for Clinical Laboratory Standards (NCCLS)-recommended broth microdilution procedure. The zone diameters of the isolates were also determined for the same agents except erythromycin by the NCCLS disk diffusion test procedure. Repeated testing of S. pneumoniae ATCC 49619 with different sources and lots of media and disks allowed development of MIC and zone diameter quality control ranges for these agents. Interpretive criteria for the MIC of azithromycin were established and were as follows: susceptible, < or = 0.5 microgram/ml; intermediate, 1 microgram/ml; and resistant, > or = 2 micrograms/ml. The interpretive criteria advocated for the MICs of clarithromycin and clindamycin were as follows: susceptible, < or = 0.25 microgram/ml; intermediate, 0.5 microgram/ml; and resistant, > or = 1 microgram/ml. Comparison of MICs and disk diffusion zone diameters led to the development of interpretive criteria for the zone diameters for azithromycin, clarithromycin, and clindamycin that correlated well with these MIC breakpoints. Testing of this organism collection also led to the reestablishment of the erythromycin MIC breakpoints as being identical to those of clarithromycin, which resulted in equivalent cross-susceptibility and cross-resistance for the three macrolides that are currently marketed in the United States. Thus, the susceptibility of pneumococci to azithromycin and clarithromycin can be predicted accurately by testing only erythromycin in clinical laboratories. This recommendation, as well as the interpretive and quality control criteria that are described, have been accepted by NCCLS and are included in the latest NCCLS susceptibility testing guidelines.

Anti-Bacterial Agents↗
PubMed1999

Penicillin-nonsusceptible Streptococcus pneumoniae infections in children.

The emergence of penicillin-nonsusceptible Streptococcus pneumoniae (PNSSP) has brought a new clinical challenge. In Taiwan, reports of the prevalence and clinical features of PNSSP infections in children are limited. This study reviewed the resistance patterns of all clinical isolates of S. pneumoniae obtained from patients under 17 years of age from January 1993 through July 1998 in a medical center. Their clinical features and treatment responses were analyzed, with special attention paid to those patients with invasive PNSSP infections. Totally, 170 clinical isolates of S. pneumoniae were obtained from 168 patients aged under 17 years. Among those infections, there were 56 sinusitis (including 4 sinusitis with bacteremia), 44 pneumonia (including 23 pneumonia with bacteremia or empyema), 23 otitis media (including 5 otitis media with bacteremia), 9 simple bacteremia, 9 conjunctivitis, 8 meningitis, 4 peritonitis, 3 skin infections and the other 14 isolates were colonization. One hundred eleven isolates (65.3%) showed reduced penicillin susceptibility by the disk diffusion method. A trend of increasing percentiles of PRSP was noted: 27.3% (3/11) in 1993, 37.5% (9/24) in 1994, 55.5% (10/18) in 1995, 77.5% (31/40) in 1996, 66.0% (31/47) in 1997, and 87.1% (27/31) in 1998. Minimum inhibitory concentration (MIC) determinations by the E-test showed some of the isolates were intermediately resistant. Prior antibiotic usage was associated with a higher incidence of PNSSP infections. However, most children responded well to antimicrobial treatment.

Adolescent↗
PubMed1999

Antimicrobial susceptibilities and serogroups of clinical strains of Clostridium difficile isolated in France in 1991 and 1997.

Glycopeptides (vancomycin and teicoplanin) and metronidazole are the drugs of choice for the treatment of Clostridium difficile infections, but trends in susceptibility patterns have not been assessed in the past few years. The objective was to study the MICs of glycopeptides and metronidazole for unrelated C. difficile strains isolated in 1991 (n = 100) and in 1997 (n = 98) by the agar macrodilution, the E-test, and the disk diffusion methods. Strain susceptibilities to erythromycin, clindamycin, tetracycline, rifampin, and chloramphenicol were also determined by the ATB ANA gallery (bioMérieux, La Balme-les-Grottes, France). The MICs at which 50% of isolates are inhibited (MIC(50)s) and MIC(90)s of glycopeptides and metronidazole remained stable between 1991 and 1997. All the strains were inhibited by concentrations that did not exceed 2 microgram/ml for vancomycin and 1 microg/ml for teicoplanin. Comparison of MICs determined by the agar dilution method recommended by the National Committee for Clinical Laboratory Standards and the E test showed correlations (+/-2 dilutions) of 86. 6, 95.9, and 99% for metronidazole, vancomycin, and teicoplanin, respectively. The E test always underestimated the MICs. Strains with decreased susceptibility to metronidazole (MICs, >/=8 microgram/ml) were isolated from six patients (n = 4 in 1991 and n = 2 in 1997). These strains were also detected by the disk diffusion method (zone inhibition diameter, </=21 mm); they belonged to nontoxigenic serogroup D (n = 5) and toxigenic serogroup H (n = 1). Decreased susceptibility to erythromycin (MICs, >/=1 microgram/ml), clindamycin (MICs, >/=2 microgram/ml), tetracycline (MICs, >/=8 microgram/ml), rifampin (MICs, >/=4 microgram/ml), and chloramphenicol (MICs, >/=16 microgram/ml) was observed in 64.2, 80.3, 23.7, 22.7, and 14.6% of strains, respectively. Strains isolated in 1997 were more susceptible than those isolated in 1991, and this trend was correlated to a major change in serogroup distribution. Periodic studies are needed in order to detect changes in serogroups and the emergence of strains with decreased susceptibility to therapeutic drugs.

Adult↗
PubMed2004

In vitro and in vivo activities of antimicrobials against Nocardia brasiliensis.

In Mexico mycetomas are mostly produced by Nocardia brasiliensis, which can be isolated from about 86% of cases. In the present work, we determined the sensitivities of 30 N. brasiliensis strains isolated from patients with mycetoma to several groups of antimicrobials. As a first screening step we carried out disk diffusion assays with 44 antimicrobials, including aminoglycosides, cephalosporins, penicillins, quinolones, macrolides, and some others. In these assays we observed that some antimicrobials have an effect on more than 66% of the strains: linezolid, amikacin, gentamicin, isepamicin, netilmicin, tobramycin, minocycline, amoxicillin-clavulanic acid, piperacillin-tazobactam, nitroxolin, and spiramycin. Drug activity was confirmed quantitatively by the broth microdilution method. Amoxicillin-clavulanic acid, linezolid, and amikacin, which have been used to treat patients, were tested in an experimental model of mycetoma in BALB/c mice in order to validate the in vitro results. Linezolid showed the highest activity in vivo, followed by the combination amoxicillin-clavulanic acid and amikacin.

Animals↗
PubMed1990

Stability of viable-bacterium counts in liquid media used for preparation of inocula and subsequent impact on antimicrobial susceptibility test results.

We evaluated the consequences of prolonging the time between initial bacterial inoculum suspension preparation and susceptibility test inoculation. Extending the current National Committee for Clinical Laboratory Standards-recommended time of 15 min between suspension preparation and test inoculation should allow laboratories more flexibility to optimize efficiency from the standpoint of workflow. We assessed the length of time for which viable-bacterium counts remain stable in three liquid media at room temperature. Fifty isolates were examined in water, saline, and cation-supplemented Mueller-Hinton broth (CSMHB). Disk diffusion and microdilution MIC tests were performed on nine of these. Our results suggest that directly prepared inoculum suspensions of members of the family Enterobacteriaceae, Pseudomonas aeruginosa, staphylococci, and enterococci can be held for up to 6 h in water or saline prior to inoculation of disk diffusion and MIC tests without compromising test accuracy. The same organisms can be held for at least 1 h in CSMHB. Viridans group streptococci can be held for up to 6 h in saline and CSMHB and for up to 3 h in water. Similarly, Haemophilus influenzae and Streptococcus pneumoniae isolates may be held in CSMHB for up to 3 h. Because of an early decrease in viable-bacterium counts in water and saline with some H. influenzae and S. pneumoniae isolates, we recommend that National Committee for Clinical Laboratory Standards recommendations be followed for these species.

Anti-Bacterial Agents↗
PubMed1998

Evaluation of the in vitro Activity of Cefprozil Relative to Other Oral Antimicrobial Agents Against Bacteria in Clinical Specimens from Patients in São Paulo With Respiratory Tract Infections.

Cefprozil is a new oral second generation cephalosporin. Its in vitro antimicrobial activity was evaluated against 371 recent clinical isolates from patients with respiratory infections. We tested the susceptibility of 244 streptococci (96 Streptococcus pneumoniae, 105 group viridans streptococci, 32 Streptococcus agalactiae, and 11 group A beta-hemolitic streptococci) 107 Haemophilus influenzae, and 20 oxacillin-susceptible S.aureus (OSSA). The isolates were susceptibility tested against cefprozil, cefaclor and amoxicillin/clavulanic acid by the E-test method; and against cefadroxil, cefuroxime, cefetamet, erythromycin, and azythromycin by disk diffusion. The methods and the susceptibility categorization followed the National Committee for Clinical Laboratory Standards (NCCLS) procedures. Amoxicillin/clavulanic acid was slightly more active againstH.influenzae (MICs(90) 0.5µg/mL) than cefprozil or cefaclor (MICs(90) 4 and 2µg/mL respectively). Cefprozil demonstrated potent activity against streptococci. Against S.pneumoniae, cefprozil was 2-4 fold more active than cefaclor (MICs(90)0.125 and 0.38µg/mL, respectively). S. pneumoniae susceptibility was 84% to penicillin, 95% to erythromycin and 97% to azithromycin by disk diffusion. Viridans streptococci showed higher MICs for cefprozil and cefaclor (MICs(90) 4µg/mL and 8µg/mL, respectively) and only 50% susceptibility to the macrolides. Cefprozil was four times more active than cefaclor and as active as amoxieillin/clavulanic acid against group A beta-hemolytic streptococci and S.agalactiae. These three compounds showed similar activity against OSSA. In conclusion, cefprozil demonstrated excellent in vitro activity against bacterial species responsible for respiratory infections in São Paulo.

Journal Article↗
PubMed1993

Determination of MICs for staphylococci using the API ATB quinolone and API ATB macrolide systems.

The determination of minimal inhibitory concentrations (MICs) is cumbersome, but remains necessary in certain cases. We tested the two ATB MIC experimental strips (Biomérieux SA), of which each contains 4 antimicrobials of the same class. These strips can be read automatically. The MIC quinolone strip contains nalidixic acid, pefloxacin, ofloxacin and ciprofloxacin, whereas the MIC macrolide (lincosamide-streptogramin) strip contains erythromycin, clindamycin, lincomycin, and pristinamycin. In order to evaluate these strips, 102 S. aureus and 63 coagulase negative staphylococci were used. Correlation coefficients for these MICs (micrograms/ml) and disk diffusion inhibition zone diameters (mm) were nalidixic acid -0.59, pefloxacin -0.95, ofloxacin -0.95, ciprofloxacin -0.91, erythromycin -0.98, clindamycin -0.96, lincomycin -0.96, and pristinamycin -0.64. Using the Biomic system (Giles Scientific USA), the same zone diameters were converted to MICs (micrograms/ml). Rates of agreement (+/- 1 dilution) between ATB MICs and Biomic MICs were nalidixic acid 96 p. cent, ciprofloxacin 98 p. cent, erythromycin 99 p. cent and clindamycin 98 p. cent. Rates of agreement between MICs for the same strains determined using agar dilution and ATB MICs were nalidixic acid 93 p. cent, pefloxacin 100 p. cent, ciprofloxacin 99 p. cent, ofloxacin 94 p. cent and erythromycin 96 p. cent. The ATB MIC strips are an easy-to-use tool for MIC determination and their composition is well-suited to the study of phenotypic resistance and detection of low-level resistance.

Ciprofloxacin↗
PubMed2004

[Resistance to linezolid in Staphylococcus aureus before its release].

UNLABELLED: Resistance to antibiotics is a global problem in geriatric centres. OBJECTIVE: The aim of this study was to determine the frequency of the resistance to linezolid in Staphylococcus aureus strains before its release in a geriatric centre. METHOD: From 03-01-01 to 03-04-30 linezolid was included in the panel of antibiotics tested in S. aureus strains. The susceptibilities were estimated by the disk diffusion test in routine clinical microbiology practice. RESULTS: A total of 213 strains of S. aureus was analysed. All of them were susceptible to the following antibiotics: linezolid, cotrimoxazol, fosfomycin, and glycopeptides. The meticillin-resistant S. aureus (MRSA) represented 67.1% (60.3-73.3) strains. The resistance to pefloxacin, tobramycin and erythromycin concerned 92.3% (86.3-95.9), 73.4% (65.3-80.3) and 31.5% (24.1-39.8) of MRSA strains respectively. The MRSA strains were less resistant to the following antimicrobial drugs: gentamicin 7.0% (3.6-12.8), fusidic acid 2.1% (0.5-6.5) and rifampicin 1.4% (0.2-5.5). The resistance concerning at the same time gentamicin, pefloxacin and fucidic acid represented 2.1% (0.5-6.5) of SARM strains, rifampicin was not interested. CONCLUSION: Linezolid was effective in vitro in S. aureus strains regardless their susceptibilities in meticillin. According to its effectiveness in vivo, linezolid may be of use for the treatment of infections due to MRSA. However, there has been two reports of resistance of MRSA in clinical infections. The use of linezolid has to follow the instructions and it should be carefully monitored.

Acetamides↗
PubMed2004

Preliminary susceptibility testing guidelines for AZD2563, a long-acting oxazolidinone.

Rapid expansion of antimicrobial resistance has led to the development of new antimicrobial agents. AZD2563 is a novel oxazolidinone that has activity similar to linezolid and the potential for extended dosing intervals. Recent Gram-positive clinical organisms (1572 strains) were tested including four oxazolidinone-resistant enterococci. Strains processed were: 313 Staphylococcus aureus, 299 coagulase-negative staphylococci, 305 enterococci, 305 Streptococcus pneumoniae, 300 other streptococci (beta-haemolytic and viridans group) and 50 other rarely isolated Gram-positive species. The methods (agar and broth dilution, disk diffusion) of the National Committee for Clinical Laboratory Standards (NCCLS; M7-A6, M2-A8) were followed and linezolid was used as a control agent. A tentative MIC breakpoint ( or=20 mm), intermediate at 4 mg/l (17-19 mm) and resistant at >or=8 mg/l (<or=16 mm). These tentative AZD2563 interpretive guidelines should facilitate in vitro susceptibility testing during clinical trials and detect all oxazolidinone-resistant isolates.

Anti-Bacterial Agents↗
PubMed2003

[Sensitivity of methicillin resistant staphylococci to linezolid and some other antimicrobial agents].

Linezolid is a synthetic antimicrobial agent which was introduced into clinical therapy in the early 2001. It has an inhibitory effect against most of the Gram positive bacteria, including methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin resistant enterococci. In this study, in-vitro activities of linezolid, teicoplanin, vancomycin, ciprofloxacin, gentamicin, erythromycin, clindamycin, trimethoprim/sulfamethoxazole and rifampicin, were tested against 164 methicillin-resistant Staphylococcus spp. (96 S. aureus and 68 coagulase negative staphylococci) isolated from clinical specimens, by using disk diffusion method. None of the strains were found to be resistant to linezolid, vancomycin and teicoplanin. The resistance rates to other drugs were as follows; 80.5% to ciprofloxacin, 78.0% to gentamicin, 76.8% to erythromycin, 65.5% to clindamycin, 57.3% to trimethoprim/sulfamethoxazole and 41.5% to rifampicin. It was concluded that linezolid can be used as an alternative drug in severe infections caused by methicillin-resistant Staphylococcus spp., especially if the isolate was found to be resistant to teicoplanin or a side effect of vancomycin was observed.

Acetamides↗
PubMed1986

Prevalence of antimicrobial resistance among clinical isolates of Haemophilus influenzae: a collaborative study.

The prevalence of antimicrobial resistance was assessed among a total of 3,356 clinical isolates of Haemophilus influenzae obtained from 22 medical centers distributed throughout the United States during the period July, 1983 through June, 1984. All strains were examined for beta-lactamase production with a rapid acidometric assay and for resistance to ampicillin, chloramphenicol, cephalothin, cefamandole, cefaclor, tetracycline, and erythromycin with a standardized disk diffusion procedure. The overall rate of beta-lactamase production was 15.2%, although results of disk diffusion tests suggested that the overall rate of ampicillin resistance was 19.5%. Twenty-one percent of encapsulated type b strains produced beta-lactamase; 12.1% of non-type b strains were beta-lactamase positive. Specific rates of beta-lactamase production obtained at individual study centers varied widely with no evidence of geographic clustering. The highest rates of beta-lactamase production were observed with isolates of H. influenzae recovered from infants and young children, and from blood and cerebrospinal fluid specimens. The overall rate of chloramphenicol resistance was 0.6%. The prevalence of cephalothin, cefamandole, cefaclor, tetracycline, and erythromycin resistance was 9.9%, 2.4%, 2.8%, 6.4%, and 64.2%, respectively. beta-Lactamase positive isolates of H. influenzae had higher rates of resistance to all of the cephalosporins than did strains that lacked beta-lactamase.

Adolescent↗
PubMed2002

Re-evaluations of disk diffusion quality control ranges for 11 drugs: report from the QC working group of the national committee for clinical laboratory standards.

A multi-laboratory re-evaluation protocol was initiated in 2001 to address broad-based concerns about the appropriateness of contemporary disk diffusion quality control (QC) guidelines of several antimicrobials in the tables of the M2-A7 standard of the National Committee for Clinical Laboratory Standards (NCCLS). This study that conformed to the NCCLS M23-A2 guideline demonstrates the dynamic processes that result in modification or development of these 11 QC zone diameter ranges. These changes included long-term QC problems for cefazolin (new range, 21-27 mm) and trimethoprim/sulphamethoxazole (new range, 23-29 mm) when tested against Escherichia coli ATCC 25922, and ticarcillin (new range, 21-27 mm) versus Pseudomonas aeruginosa ATCC 27853. All proposed ranges have been approved by the NCCLS for publication in M100-S12 tables in 2002.

Anti-Bacterial Agents↗
PubMed2005

Antibacterial susceptibility of extended-spectrum beta-lactamase-producing Klebsiella pneumoniae and Escherichia coli.

BACKGROUND: The prevalence of extended-spectrum beta-lactamase-producing organisms and their antimicrobial resistance patterns may vary between geographic areas. OBJECTIVES: To evaluate the prevalence and susceptibility of ESBL-producing organisms among Klebsiella pneumoniae and Escherichia coli isolated from adult and pediatric patients in two Israeli hospitals. METHODS: ESBL production was tested according to recommendations of the Clinical and Laboratory Standards Institute, using ceftazidime (30 microg) and a combination of ceftazidime/clavulanate (30/ 10 microg) disks with a > or =5 mm difference indicating positivity. Antibiotic susceptibilities were determined by the disk diffusion method according to CLSI standards. Minimal inhibitory concentrations were determined by the E-test. RESULTS: The prevalence of ESBL-producing organisms was significantly higher among K. pneumoniae than E. coli isolates - 32% (241/765) vs. 10% (57/547) respectively (P < 0.001), and more frequently isolated from adults than children (odds ratio 2.27 for K. pneumoniae and 12.94 for E. coli). Resistance rates for amoxicillin/ clavulanate, piperacillin-tazobactam, amikacin, and ciprofloxacin among the ESBL-producing K. pneumoniae and E. coli isolates were 95%, 82%, 49% and 77% for K. pneumoniae, and 77%, 35%, 25% and 100% for E coli. Two (0.8%) ESBL-producing and 4 (0.7%) ESBL-negative K. pneumoniae isolates showed intermediate susceptibility (MIC 6 microg/ml) to meropenem. All isolates were sensitive to ertapenem and colistin. CONCLUSION: ESBL production among K. pneumoniae and E. coli is more prevalent in the adult population than the pediatric population and is associated with multidrug resistance.

Adult↗