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PubMed1993

Guidelines for management of patients with methicillin-resistant Staphylococcus aureus in acute care hospitals and long-term care facilities. The MRSA Interagency Advisory Committee in conjunction with the Connecticut Department of Public Health and Addiction Services, July 1993.

Methicillin-resistant Staphylococcus aureus (MRSA) is a bacterium that can colonize or infect people. MRSA strains are not more virulent than methicillin susceptible strains. Colonized and infected patients represent the most important reservoir of MRSA in hospitals. MRSA is transmitted by direct person-to-person contact, usually on the hands of health care workers. Limiting the spread of MRSA is desirable because the organism is resistant to oxacillin, nafcillin, cephalosporins, and imipenem. Treatment of choice for MRSA infection is usually intravenous vancomycin. The preferred methods for antimicrobial susceptibility testing of S. aureus include oxacillin-salt screening plates, microdilution broth tests with 2% NaCI, and disk diffusion tests incubated for 24 hours at 35 degrees C. Hospitals and LTCFs should monitor the incidence of nosocomial transmission of MRSA in their facility. Hospital admission because of MRSA infection is acceptable medical practice because treatment can best be accomplished in an acute care setting. However, given special circumstances, treatment of MRSA infection can be accomplished in an extended care facility or at home. This decision is based on the clinical judgement of the attending physician. Hospital admission solely because of MRSA colonization is unwarranted. MRSA colonization is not a contraindication to discharge from an acute care hospital to home or another facility. When a hospitalized patient who is colonized with MRSA no longer needs to receive acute nursing care (i.e. their MRSA infection and/or other acute medical problems are under control), they can be discharged. If they are discharged to another institution, that institution should be notified in advance that the patient is colonized with MRSA.

Cross Infection↗

PubMed1991

Quantitative antimicrobial susceptibility testing of Haemophilus influenzae and Streptococcus pneumoniae by using the E-test.

The E-test (PDM Epsilometer; AB Biodisk, Solna, Sweden) is an antimicrobial agent gradient-coated plastic test strip which allows MIC determinations on agar media. The test is performed in a manner similar to the agar disk diffusion procedure. A collection of Haemophilus influenzae and Streptococcus pneumoniae strains possessing various resistance mechanisms was used to evaluate the E-test method. H. influenzae strains were tested with both Haemophilus test medium (HTM) and PDM ASM II chocolate agar, while the S. pneumoniae strains were tested on Mueller-Hinton sheep blood agar. E-test MICs for a total of 10 antimicrobial agents were compared with broth microdilution MICs determined according to National Committee for Clinical Laboratory Standards methods. In general, E-test MICs for both species were quickly and easily interpreted and agreed within one log2 MIC increment in 89.8% of tests with H. influenzae and in 80.4% of pneumococcal tests. The majority of disagreements between the E-test and conventional MICs occurred with trimethoprim-sulfamethoxazole because of trailing and diffuse E-test MIC endpoints with both species. Ampicillin MICs for beta-lactamase-producing H. influenzae determined by the E-test differed at times from those determined by conventional testing because of the vagaries of interpreting colonies growing within the E-test inhibition ellipses. E-test penicillin MICs for pneumococci tended to be 1 to 2 log2 dilutions lower than those determined by using Mueller-Hinton broth supplemented with lysed horse blood. Nevertheless, strains of both species with documented resistance to the study drugs were detected by E-tests, i.e., 0.7% of the tests had very major errors with H. influenzae and 0.8% had very major errors with S. pneumoniae. Thus, the E-test represents a potential alternative method for antimicrobial susceptibility testing of these two fastidious bacterial species.

Culture Media↗

PubMed1982

Reliability of the MS-2 system in detecting methicillin-resistant Staphylococcus aureus.

The MS-2 system (Abbott Diagnostics, Division of Abbott Laboratories, Dallas, Tex.) is an automated system capable of rapid antimicrobial susceptibility testing. However, the short incubation periods used by the device may adversely affect its ability to detect slowly growing resistant organisms. Shortly after the introduction of the MS-2 system into the University of Mississippi Medical Center clinical microbiology laboratory, we noted discrepancies between the MS-2 and the disk diffusion susceptibility reports when methicillin-resistant Staphylococcus aureus isolates were tested. Subsequently, we determined the susceptibilities of 75 such isolates by the MS-2 and Kirby-Bauer disk diffusion methods and measured the minimum inhibitory concentrations of methicillin, oxacillin, and cephalothin for 33 of the 75 isolates by standardized agar dilution techniques. There was only 47% overall agreement between the MS-2 and disk diffusion methods when methicillin was tested and 15% agreement when cephalothin was the test drug. There was 93% or more overall agreement between the two methods when other antimicrobial agents were tested. The minimum inhibitory concentration of methicillin was greater than or equal to 16 micrograms/ml for all 33 isolates evaluated by the agar dilution method. A comparison of the MS-2 and agar dilution results revealed an overall agreement of 49% when the susceptibilities to methicillin were determined. The MS-2 system reported that multiple methicillin-resistant S. aureus isolates obtained from a single patient were either resistant, intermediate, or sensitive to methicillin. Inconsistent results were also obtained when a single isolate was tested simultaneously in 10 cuvette cartridges. We conclude that the MS-2 system does not reliably detect methicillin and cephalothin resistance among S. aureus.

Cephalothin↗

PubMedDate not supplied

Comparative susceptibility of clinical group A, B, C, F, and G beta-hemolytic streptococcal isolates to 24 antimicrobial drugs.

A total of 312 clinical beta-hemolytic streptococcal isolates (Streptococcus pyogenes, group A = 63; Streptococcus agalactiae, group B = 145; group C = 50; group F = 27; group G = 27) were examined for susceptibility to 23 and 24 antimicrobial drugs with the Bauer-Kirby agar disk diffusion and the agar dilution method, respectively. Sheep blood Mueller-Hinton agar served as the reference medium. Wilkins-Chalgren agar supported optimal growth of group A and B, but not of all group C, F, and G streptococci. The group A streptococci were susceptible to all beta-lactam antibiotics, clindamycin, chloramphenicol, rifampin, teicoplanin, and vancomycin, but resistant to cotrimoxazole, fusidic acid, and, except for 2 strains, to fosfomycin. Resistance (R)/intermediate susceptibility (I) rates (R/I%) to ciprofloxacin (0/2%), ofloxacin (1/2%), erythromycin (1.6/0%), and clarithromycin (0/1%) were low. Higher resistance rates were noted with tetracyclines (doxycycline 23.8/15.9%; tetracycline 39.7/3.2%). Among the group B streptococcal isolates, one strain was resistant against oxacillin and of intermediate susceptibility to penicillin G and cefoxitin. All isolates were susceptible to teicoplanin and rifampin. Conversely, all group B isolates were resistant to cotrimoxazole and fusidic acid; 69% and 51% of these isolates were susceptible to fosfomycin and rifampin, respectively. R/I rates of the group B streptococcal isolates were low for ciprofloxacin and ofloxacin (0/0.7%), clindamycin (0.7/0%), erythromycin (1.4/ 3.5%), clarithromycin (1.4/0%), and chloramphenicol (0.7/0%). Resistance to tetracyclines was significant (doxycycline: 72.4/2.1%; tetracycline; 74.5/1.4%). Among the non-A, non-B beta-hemolytic streptococci, 2 group C strains were resistant to oxacillin and showed intermediate susceptibility to penicillin G. All isolates were susceptible to third and fourth-generation cephalosporins, imipenem, chloramphenicol, rifampin, teicoplanin, and vancomycin. R/I rates to the other antimicrobial drugs were: ciprofloxacin (3.9/1.9%), ofloxacin (2.9/1.9%), clindamycin (2.9/1%), erythromycin (5.8/0%), clarithromycin (3.8/2.9%), and cotrimoxazole (16.4/3.9%). Resistance against tetracyclines was more frequent (doxycycline: 18.3/2.9%; tetracycline: 20.2/6.7%). On the basis of various minor discrepancies between MIC and disk diffusion test results, it is proposed that the current NCCLS inhibition zone (diameter, mm) criteria indicative of intermediate susceptibility of beta-hemolytic streptococci be changed for the following antimicrobial drugs: ampicillin: 22-27 mm (only for group A and B beta-hemolytic streptococci); ciprofloxacin: 16-18 mm; clindamycin: 15-18 mm; doxycycline: 17-19 mm; tetracycline: 17-19 mm, and erythromycin: 14-19 mm.

Anti-Bacterial Agents↗

PubMed2006

Outbreak of infection with Acinetobacter strain RUH 1139 in an intensive care unit.

OBJECTIVE: To investigate a nosocomial outbreak of infection with Acinetobacter strain RUH 1139, in the unit of high neonatal risk at University Hospital of The Andes (Merida, Venezuela). METHODS: Twenty-eight Acinetobacter strains were detected by biochemical testing and further identified to the species level by examination of the gene encoding 16S ribosomal DNA, using restriction analysis and gene sequencing. The epidemiological relationship between the strains was established by means of repetitive extragenic palindromic polymerase chain reaction (REP-PCR) and pulsed-field gel electrophoresis (PFGE), and antimicrobial susceptibilities were determined by disk diffusion. RESULTS: The spread of an epidemic strain of Acinetobacter RUH 1139 among 16 patients over a period of 3 months was demonstrated using antimicrobial susceptibility testing, PFGE, and REP-PCR. The epidemic strain was also isolated in 2 of the sampled parenteral nutrition solutions. All the patients involved in the infection outbreak had received parenteral solution. Moreover, strains of Acinetobacter RUH 1139 with another PFGE pattern and of A. baumannii were sporadically isolated before and during the outbreak. CONCLUSION: This is the first description of an outbreak of infection with this genospecies of Acinetobacter in which parenteral nutrition solution was potentially the infection source.

Acinetobacter↗

PubMed2002

Minimum inhibitory concentration breakpoints and disk diffusion inhibitory zone interpretive criteria for tilmicosin susceptibility testing against Pasteurella multocida and Actinobacillus pleuropneumoniae associated with porcine respiratory disease.

Tilmicosin is a novel macrolide antibiotic developed for exclusive use in veterinary medicine. Tilmicosin has been approved as a feed premix to control porcine respiratory disease associated with Pasteurella multocida and Actinobacillus pleuropneumoniae. The development of antimicrobial susceptibility testing guidelines for tilmicosin was predicated on the relationship of clinical efficacy studies that demonstrated a favorable therapeutic outcome, on pharmacokinetic data, and on in vitro test data, as recommended by the National Committee for Clinical Laboratory Standards (NCCLS). The approved breakpoints for the minimum inhibitory concentration dilution testing for both species are resistant, > or = 32 microg/ml, and susceptible, < or = 16 microg/ml. The zone of inhibition interpretive criteria for disk diffusion testing with a 15-microg tilmicosin disk are resistant, < or = 10 mm, and susceptible, > or = 11 mm.

Actinobacillus Infections↗

PubMed2003

The World Health Organization's External Quality Assurance System Proficiency Testing Program has improved the accuracy of antimicrobial susceptibility testing and reporting among participating laboratories using NCCLS methods.

A total of 150 laboratories in 33 countries that followed the NCCLS testing procedures participated in the World Health Organization's External Quality Assurance System for Antimicrobial Susceptibility Testing (EQAS-AST) from January 1998 through March 2001. Laboratories tested seven bacterial isolates for antimicrobial resistance and reported the results to the Centers for Disease Control and Prevention (CDC) in Atlanta, Ga. The results were compared to the results generated at the CDC with the NCCLS broth microdilution and disk diffusion reference methods. Although there were few testing errors with Salmonella enterica subsp. enterica serovar Enteritidis, drugs that are not appropriate for therapy of Salmonella infections were tested and reported by 136 (91%) of 150 laboratories. In addition, 29 (20%) of 150 laboratories used the Staphylococcus aureus breakpoints to report oxacillin results for Staphylococcus saprophyticus. For a vanB-containing Enterococcus faecalis strain, 124 (83%) of 150 laboratories correctly reported vancomycin results that were +/-1 doubling dilution from the reference MIC or +/-3 mm from the reference disk diffusion result. Of the laboratories that tested Streptococcus agalactiae by disk diffusion, 17% reported nonsusceptible results for penicillin in error. While 110 laboratories (73%) tested the S. pneumoniae challenge isolate against a fluoroquinolone, 83% tested it against ciprofloxacin, for which there are no NCCLS interpretive criteria. Ten of 12 laboratories testing levofloxacin and 4 of 4 laboratories testing ofloxacin by an MIC method correctly reported resistant results for the isolate. Feedback letters sent to participating laboratories highlighted areas of susceptibility testing in individual laboratories that needed improvement. The positive impact of the feedback letters and the overall effectiveness of the EQAS program were documented in repeat testing challenges with pneumococci and staphylococci. The 31 and 19% increases in the numbers of laboratories using appropriate testing methods for pneumococci and staphylococci, respectively, in 2000 versus 1998 indicate that laboratory performance is improving.

Anti-Bacterial Agents↗

PubMed1977

Laboratory evaluation of an automated antimicrobial susceptibility system.

A newly introduced automated method for antibiotic susceptibility testing, AUTOBAC 1, has been evaluated by comparison with the disk agar diffusion method (Bauer-Kirby). A total of 2,518 strains of gram-positive (540) and gram-negative (1,978) organisms isolated from clinical specimens was examined by both methods with eight or ten antibiotics, including Tobramycin. An overall agreement of 97.4% was obtained when results were compared by individual antibiotic. However, many discrepancies were observed when individual genera or species were analyzed. Of 2,518 strains examined, 651 (26%) showed discrepancies in response to one or more antibiotics. Strains, showing discrepancies were re-examined by the broth dilution susceptibility method. The results obtained favored the disk agar diffusion method. Reproducibility experiments revealed a greater inconsistency in the AUTOBAC 1 system than in the agar diffusion test. It is concluded that although a rapid automated system for antibiotic sensitivity testing is desirable, the conventional disk agar diffusion method is easier to perform, more reliable, and a less expensive procedure for antibiotic sensitivity determination.

Anti-Bacterial Agents↗

PubMed1979

Antibiotic susceptibilities of human isolates of Pasteurella multocida.

Seventeen human strains of Pasteurella multocida, biochemically similar to, if not identical with, isolates of animal origins, were tested for susceptibility to 16 antimicrobial agents utilizing a microtiter broth dilution technique. Ten of these isolates were also tested against 11 antibiotics by disk diffusion. The most active drugs with respect to the median minimal inhibitory concentration (micrograms per milliliter) were tetracycline (0.09), penicillin G (0.78), ampicillin (0.78), carbenicillin (1.56), cephalothin (1.56), and chloramphenicol (1.56). With the exception of tetracycline, the median minimal inhibitory concentration and minimal bactericidal concentration values were equal or differed by no more than a factor of two. The semisynthetic penicillins clindamycin, erythromycin, and aminoglycosides had relatively low activities, suggesting that these agents would be poor choices for the treatment of P. multocida infections.

Anti-Bacterial Agents↗

PubMed2001

National epidemiologic surveys of Enterobacter aerogenes in Belgian hospitals from 1996 to 1998.

Two national surveys were conducted to describe the incidence and prevalence of Enterobacter aerogenes in 21 Belgian hospitals in 1996 and 1997 and to characterize the genotypic diversity and the antimicrobial resistance profiles of clinical strains of E. aerogenes isolated from hospitalized patients in Belgium in 1997 and 1998. Twenty-nine hospitals collected 10 isolates of E. aerogenes, which were typed by arbitrarily primed PCR (AP-PCR) using two primers and pulsed-field gel electrophoresis. MICs of 10 antimicrobial agents were determined by the agar dilution method. Beta-lactamases were detected by the double-disk diffusion test and characterized by isoelectric point. The median incidence of E. aerogenes colonization or infection increased from 3.3 per 1,000 admissions in 1996 to 4.2 per 1000 admissions in the first half of 1997 (P < 0.01). E. aerogenes strains (n = 260) clustered in 25 AP-PCR types. Two major types, BE1 and BE2, included 36 and 38% of strains and were found in 21 and 25 hospitals, respectively. The BE1 type was indistinguishable from a previously described epidemic strain in France. Half of the strains produced an extended-spectrum beta-lactamase, either TEM-24 (in 86% of the strains) or TEM-3 (in 14% of the strains). Over 75% of the isolates were resistant to ceftazidime, piperacillin-tazobactam, and ciprofloxacin. Over 90% of the strains were susceptible to cefepime, carbapenems, and aminoglycosides. In conclusion, these data suggest a nationwide dissemination of two epidemic multiresistant E. aerogenes strains in Belgian hospitals. TEM-24 beta-lactamase was frequently harbored by one of these epidemic strains, which appeared to be genotypically related to a TEM-24-producing epidemic strain from France, suggesting international dissemination.

Anti-Bacterial Agents↗

PubMed1997

Interpretive criteria and quality control parameters for testing of susceptibilities of Haemophilus influenzae and Streptococcus pneumoniae to trimethoprim and trimethoprim-sulfamethoxazole. The Antimicrobial Susceptibility Testing OC Group.

Two hundred twenty-eight strains of Haemophilus influenzae and 234 strains of Streptococcus pneumoniae were tested by broth microdilution and disk diffusion methods for susceptibility to trimethoprim (TMP) and TMP-sulfamethoxazole (SMX) to evaluate proposed criteria. Data are presented to support the proposed TMP MIC breakpoints of < or = 2.0 micrograms/ml for susceptibility and > or = 4.0 micrograms/ml for resistance for both species and TMP-SMX MIC breakpoints of < or = 2.0-38 micrograms/ml for susceptibility and > or = 4.0-76 micrograms/ml for resistance. Corresponding zone diameter breakpoints for H. influenzae for both drugs are proposed: < or = 10 mm = resistant; > or = 16 mm = susceptible. A 10-laboratory study documented reproducibility of such tests with standard control strains. The following control limits are proposed for tests of H. influenzae ATCC 49247 against TMP; MIC, 0.12 to 0.5 microgram/ml; zone diameter, 27 to 33 mm. The current limits for TMP-SMX were confirmed. For tests of S. pneumoniae ATCC 49619, MICs of TMP were 1.0 to 4.0 micrograms/ml and the current TMP-SMX MIC range was confirmed. Disk susceptibility tests of either drug against pneumococci were not reproducible, and consequently neither quality control limits nor interpretive criteria could be established. Endpoint interpretation and lot-to-lot variability in Mueller-Hinton agars were significant factors leading to interlaboratory variability.

Anti-Bacterial Agents↗

PubMed2002

In vitro antimicrobial activity of a new series of 1,4-naphthoquinones.

The antibacterial activity of a series of 1,4-naphthoquinones was demonstrated. Disk diffusion tests were carried out against several Gram-positive and Gram-negative bacteria. The compound 5-amino-8-hydroxy-1,4-naphthoquinone was the most effective, presenting inhibition zones measuring 20 mm against staphylococci, streptococci and bacilli at 50 microg/ml. Methicillin-resistant Staphylococcus aureus and several clinical isolates of this bacterium were also inhibited. Naphthazarin, 5-acetamido-8-hydroxy-1,4-naphthoquinone, and 2,3-diamino-1,4-naphthoquinone were the next most active compounds. The minimal inhibitory concentration of the active compounds was determined against S. aureus, ranging from 30 to 125 microg/ml. All compounds presented a minimal bactericidal concentration higher than 500 microg/ml, indicating that their effect was bacteriostatic. The EC50, defined as the drug concentration that produces 50% of maximal effect, was 8 microg/ml for 5-amino-8-hydroxy-1,4-naphthoquinone against S. aureus, S. intermedius, and S. epidermidis. These results indicate an effective in vitro activity of 5-amino-8-hydroxy-1,4-naphthoquinone and encourage further studies for its application in antibiotic therapy.

Animals↗

PubMedDate not supplied

[Antimicrobial activity of ciprofloxacin and netilmicin compared to various antibiotics in Lome, Togo].

We report the antimicrobial activity of ciprofloxacin and netilmicin on 577 strains such as S. aureus, Pseudomonas, E. coli, Salmonella, Proteus, Klebsiella and Enterobacter. Isolation and identification were performed by standard methods. Disk diffusion tests were performed to evalute the susceptibility. The percentage resistance to ciprofloxacin for bacteria was: E. coli = 15%, Enterobacter = 13%, Proteus = 10%, Pseudomonas = 9%, S. aureus and Klebsiella = 4%. The percentage resistance to netilmicin for bacteria was: Pseudomonas = 29%, Proteus = 26%, S. aureus = 21%, Enterobacter = 16%, Klebsiella = 14% and E. coli = 5%. The antimicrobial activity of ciprofloxacin and netilmicin was higher than that of others antibiotics.

Anti-Infective Agents↗

PubMed2004

Reduced susceptibility to ciprofloxacin and gyra gene mutation in North Indian strains of Salmonella enterica serotype Typhi and serotype Paratyphi A.

The emergence of reduced susceptibility to ciprofloxacin among Salmonella enterica serotype Typhi and serotype Paratyphi A leading to clinical failure of treatment poses a great therapeutic challenge. The mechanism of fluoroquinolone resistance in clinical isolates of S. Typhi and S. Paratyphi A is not very well documented. The present study was carried out with the objective of molecular characterization of reduced quinolone susceptibility amongst the strains of S. Typhi and S. Paratyphi A isolated from the patients with enteric fever during January, 2000, to April, 2003, in a North Indian hospital. A total of 422 culture-positive cases of enteric fever were reported to the hospital during the period of study, of which S. Typhi was isolated from 350 cases and S. Paratyphi A from 72 cases. The antimicrobial susceptibility of these strains was determined by disk diffusion and agar dilution method according to NCCLS guidelines, and E-test method. A total of 140 randomly selected strains, isolated during the years 1993-1999, that were available from the laboratory stocks were also studied to compare with the present strains. To study the quinolone susceptibility, the strains were divided into nalidixic acid sensitive (NAS), nalidixic acid intermediate resistant, (NAI) and nalidixic acid resistant (NAR) on the basis of susceptibility to nalidixic acid. Clinical history was available from 174 patients, of which 93 needed hospitalization due to severe disease. Of these, 82 patients were infected with NAR strains and 22 patients had a documented evidence of clinical failure to ciprofloxacin therapy. The patients infected with NAR strains were younger and had a significantly longer duration of fever (p value < 0.05) than those infected with NAS strains. It was observed that the proportion of NAR strains increased gradually over the years. These strains had a significantly higher range of MIC of ciprofloxacin (0.023-1.0 microg/ml) as compared to the NAS strains (0.002-0.125 microg/ml) (p value < 0.05). The sequencing of quinolone resistance determining region (QRDR) of the gyrA gene showed the presence of mutation at either Ser 83 or at Asp 87 in all the NAR and NAI strains. None of the NAS strains had a mutation, suggesting that the gyrA gene mutation is sufficient to confer resistance to nalidixic acid and reduced susceptibility to ciprofloxacin. This mutation, although phenotypically expressed as decreased susceptibility to ciprofloxacin, goes undetected by the disk diffusion method using the present NCCLS guidelines. Hence, it can increase morbidity and mortality due to delay in appropriate antibiotic treatment.

Adolescent↗

PubMed2000

Potent synergism of the combination of fluconazole and cyclosporine in Candida albicans.

Several types of drugs currently used in clinical practice were screened in vitro for their potentiation of the antifungal effect of the fungistatic agent fluconazole (FLC) on Candida albicans. These drugs included inhibitors of multidrug efflux transporters, antimicrobial agents, antifungal agents, and membrane-active compounds with no antimicrobial activity, such as antiarrhythmic agents, proton pump inhibitors, and platelet aggregation inhibitors. Among the drugs tested in an agar disk diffusion assay, cyclosporine (Cy), which had no intrinsic antifungal activity, showed a potent antifungal effect in combination with FLC. In a checkerboard microtiter plate format, however, it was observed that the MIC of FLC, as classically defined by the NCCLS recommendations, was unchanged when FLC and Cy were combined. Nevertheless, if a different reading endpoint corresponding to the minimal fungicidal concentration needed to decrease viable counts by at least 3 logs in comparison to the growth control was chosen, the combination was synergistic (fractional inhibitory concentration index of <1). This endpoint fitted to the definition of MIC-0 (optically clear wells) and reflected the absence of the trailing effect, which is the result of a residual growth at FLC concentrations greater than the MIC. The MIC-0 values of FLC and Cy tested alone in C. albicans were >32 and >10 microg/ml, respectively, and decreased to 0.5 and 0.625 microg/ml when the two drugs were combined. The combination of 0.625 microg of Cy per ml with supra-MICs of FLC resulted in a potent antifungal effect in time-kill curve experiments. This effect was fungicidal or fungistatic, depending on the C. albicans strain used. Since the Cy concentration effective in vitro is achievable in vivo, the combination of this agent with FLC represents an attractive perspective for the development of new management strategies for candidiasis.

Agar↗

PubMed1999

Assessment of laboratory performance with Streptococcus pneumoniae antimicrobial susceptibility testing in the United States: a report from the College of American Pathologists Microbiology Proficiency Survey Program.

OBJECTIVE: To assess the performance of clinical microbiology laboratories in the United States when conducting in vitro susceptibility tests with Streptococcus pneumoniae. METHODS: The results of a nationwide College of American Pathologists Proficiency Survey test sample, in which susceptibility testing of an isolate of S. pneumoniae was performed, were assessed with respect to precision and accuracy. RESULTS: Wide variability was noted among participating laboratories with both minimum inhibitory concentration procedures and disk diffusion susceptibility tests when both methods were applied to S. pneumoniae. Despite this high degree of variation, categorical interpretive errors were uncommon. Numerous laboratories reported results for antimicrobial agents that are not recommended by the National Committee for Clinical Laboratory Standards for tests with S. pneumoniae. CONCLUSIONS: Current susceptibility testing practices with S. pneumoniae in the United States indicate limited precision and a tendency for laboratories to test and report results obtained with antimicrobial agents of questionable therapeutic value against this organism. Continued efforts to standardize susceptibility testing of S. pneumoniae in the United States are warranted. In addition, modifications of existing interpretive criteria may be necessary.

Anti-Bacterial Agents↗

PubMed1998

In vitro evaluation of sparfloxacin activity and spectrum against 24,940 pathogens isolated in the United States and Canada, the final analysis.

Sparfloxacin, a recently marketed oral fluoroquinolone, was tested against 24,940 recent clinical strains isolated from blood stream and respiratory tract cultures at 187 hospitals in the USA and Canada. Sparfloxacin activity was compared with 5 to 13 antimicrobial agents using either Etest (AB BIODISK, Solna, Sweden) and a reference broth microdilution or a standardized disk diffusion method. When applying recommended MIC breakpoint criteria of sparfloxacin susceptibility (< or = 0.5 microgram/mL) for Streptococcus pneumoniae (4,410 strains) and other Streptococcus spp. (554 isolates), 93% and 88% were inhibited, respectively. Furthermore, at < or = 1 microgram/mL sparfloxacin susceptibility rates for streptococci increased to 98% overall and 99.3% for S. pneumoniae. In contrast, only 46% and 68% of pneumococci were susceptible to ciprofloxacin (MIC90, 3 micrograms/mL; susceptible at < or = 1 microgram/mL) and penicillin (MIC90, 1.5 microgram/mL; susceptible at < or = 0.06 microgram/mL), respectively. Differences between regions in the USA for rates of penicillin-resistant pneumococcal strains were observed (greatest resistances in southeast and midwest), but results indicate that the sparfloxacin potency was not adversely influenced (MIC90, 0.5 microgram/mL). Also pneumococcal isolates from the lower respiratory tract were more resistant to penicillin and other beta-lactams. Nearly all Haemophilus species and Moraxella catarrhalis strains, including those harboring beta-lactamases, were susceptible to tested fluoroquinolones (sparfloxacin, ciprofloxacin), amoxicillin/clavulanic acid, and newer oral cephalosporins. Sparfloxacin was very active against oxacillin-susceptible Staphylococcus aureus (MIC90, 0.12 microgram/mL; 96-97% susceptible), Klebsiella spp. (MIC90 0.12 microgram/mL), and other tested enteric bacilli (92-95% susceptible). Comparisons between the broth microdilution MIC and disk diffusion interpretive results demonstrated excellent intermethod susceptibility category agreement (> 95%) using current sparfloxacin breakpoints, but some compounds (cefpodoxime disk diffusion tests for S. aureus) may require modifications. These results demonstrate that new Gram-positive focused fluoroquinolones (sparfloxacin) possess an excellent in vitro activity and spectrum against pathogens that cause respiratory tract infections. This spectrum of activity includes strains resistant to other antimicrobial classes, including the oral cephalosporins, macrolides, amoxicillin/clavulanic acid, and earlier fluoroquinolones (ciprofloxacin, ofloxacin). Overall, sparfloxacin inhibited 89% to nearly 100% of the isolates (species variable) tested against those species against which it has Food and Drug Administration indications for clinical use.

Anti-Infective Agents↗

PubMedDate not supplied

Quality control limits for disk diffusion and broth microdilution susceptibility tests with Haemophilus test medium.

A six-center collaborative study was performed with the aim of developing quality control test limits for both disk diffusion and broth microdilution susceptibility tests with Haemophilus influenzae ATCC 49247 using Haemophilus test medium. Quality control ranges are presented for 18 antimicrobials: ampicillin, amoxicillin-clavulanate, ampicillin-sulbactam, cefuroxime, cefamandole, cefonicid, cefotaxime, ceftriaxone, ceftizoxime, ceftazidime, cefixime, chloramphenicol, tetracycline, trimethoprim-sulfamethoxazole, rifampin, imipenem, aztreonam, and ciprofloxacin.

Anti-Bacterial Agents↗