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Methicillin-resistente Staphylococcus aureus-Stämme (MRSA) sind inzwischen in vielen Ländern verbreitete Erreger, denen eine besondere Aufmerksamkeit geschenkt wird. In der vorliegenden Übersichtsarbeit werden der Resistenzmechanismus, die Epidemiologie der Verbreitung im Krankenhaus (H-MRSA) bzw. in Einrichtungen des Gesundheitswesens (HCA-MRSA) und außerhalb des Krankenhauses (C-MRSA), Ursachen der Zunahme des Nachweises, Besiedlungsdynamik, Erkrankungsrisiko und Letalität, das Vorgehen bei MRSA-Nachweis, Methoden zur Dekolonisierung, Überwachungskulturen sowie therapeutische Optionen diskutiert. Methicillin-resistant strains of Staphylococcus aureus(MRSA) are now widespread pathogens in many countries. The increasing number of MRSA is a challenge to clinicians and health care systems. In this review, mechanism of resistance, epidemiological patterns in hospitals (H-MRSA), health care institutions (HCA-MRSA) and in the community (C-MRSA), reasons for increase, dynamic of colonization, risk of disease and mortality, guidelines in case of detection, decolonization of patients, surveillance cultures and therapeutic options are discussed.

Eine Kombination aus β-Laktam-Antibiotikum und β-Laktamase-Inhibitor (Clavulansäure, Tazobactam, Sulbactam) erweitert das Wirkungsspektrum des Antibiotikums (z. B. Anaerobier) und führt dazu, dass Erreger mit β-Laktamase-Bildung zumindest teilweise wieder sensibel gegenüber dem Antibiotikum als eigentlich wirksamer Substanz werden. In Deutschland sind die β-Laktamase-Inhibitoren Tazobactam und Sulbactam zur Therapie schwerer Infektionen in Kombination mit Piperacillin zugelassen. In dieser Übersichtsarbeit werden pharmakokinetische, pharmakodynamische und klinische Daten von Piperacillin/Tazobactam und Piperacillin/Sulbactam verglichen. Insgesamt ist die klinische Wirksamkeit von Piperacillin/Tazobactam bei nosokomial erworbener Pneumonie, schweren intraabdominalen Infektionen oder Fieber bei neutropenischen Patienten sehr gut dokumentiert und der Wirksamkeit von Carbapenem oder Cefalosporinen der 3. Generation (z. B. Ceftazidim) gleichwertig oder überlegen. Da kontrollierte klinische Studien zu Piperacillin/Sulbactam weitestgehend fehlen, ist eine Einschätzung seiner Effektivität im Vergleich zu anderen Substanzen nicht möglich. Combination of β-lactam antibiotics and β-lactamase inhibitors (clavulanic acid, tazobactam, sulbactam) extends the spectrum of the β-lactam (e. g. anaerobes) and makes pathogens with β-lactamase production at least partially sensitive to the antibiotic. In Germany, tazobactam and sulbactam are both licensed for therapy of severe infections in combination with piperacillin. This review compares pharmacokinetic, pharmacodynamic and clinical data of piperacillin/tazobactam and piperacillin/sulbactam. The efficacy of piperacillin/tazobactam in the treatment of patients with nosocomial pneumonia, severe intra-abdominal infections or fever of unknown origin in neutropenic patients is equivalent or better than comparators like carbapenems or 3rdgeneration cefalosporins (e. g. ceftazidime). Because there is a paucity of controlled clinical data, an estimation of the clinical efficacy of piperacillin/sulbactam in comparison to other substances is not possible.

Since the middle of the 1980s,? reports of invasive infections caused by streptococcus pyogenes are increasing world wide. In a retrospective study the frequency, symptoms, course, therapeutic possibilities, and microbiological characterization of this disease were examined. In the study, all 10 patients (seven females/ three males, average age 45.0 [4–71]) of the district hospital of Reutlingen were included who had a proven streptococcus pyogenes infection between Sept. 1994 and May 1996, defined by isolation of group A streptococci from a sterile site. Isolates were analyzed for serotype and production of exotoxins in the National Reference Center (Jena) of that time. In relation to the approx. 272,000 inhabitants of the district of Reutlingen, our numbers for invasive infections are within the range of the data established in the USA on population-based studies (incidence between 1.5 to 4.3 per 100,000). In seven patients,? influenza-like symptoms were observed previous to the acute deterioration of the disease. There was a conspicuous accumulation of the severe courses of toxic shock-like syndrome (TSLS) with the following criteria: shock, multiorgan failure, soft tissue necrosis, and generalized erythema (n=6). All surviving patients with TSLS had to be treated during several days with assisted respiration (7–16 days). One female patient with TSLS died on the day of admittance due to an intensive septic shock. In the analysis of the isolated strains,? no uniform results regarding the serotypes and the production of exotoxins were found. The following therapeutic measures are required immediately: antibiotic treatment, surgical treatment of the infective focus, and the established intensive care therapy in cases with multiorgan failure. The observed prodromal symptoms underline emphatically the possibility of an early intervention in the course of the disease. Seit Mitte der achtziger Jahre häufen sich weltweit Berichte über invasive Infektionen verursacht durch Streptococcus pyogenes. In einer retrospektiven Studie wurden Häufigkeit, Symptomatik, Verlauf, Therapiemöglichkeiten und mikrobiologische Charakterisierung der Erkrankung untersucht. In die Studie wurden alle zehn Patienten (sieben weibliche/drei männliche, Durchschnittsalter 45,0 [4–71] Jahre) des Kreiskrankenhauses Reutlingen eingeschlossen, bei denen zwischen September 1994 und Mai 1996 Streptococcus pyogenes an sterilen Entnahmeorten nachgewiesen wurde. Die Isolate wurden am damaligen Nationalen Referenzzentrum (Jena) bezüglich Typisierung und Toxinbestimmung analysiert. Bezogen auf die ca. 272000 Einwohner des Landkreises Reutlingen liegen unsere Zahlen für invasive Infektionen im Bereich der in Nordamerika anhand von Populationsstudien ermittelten Daten (Inzidenzen zwischen 1,5–4,3/100000). Bei sieben Patienten war vor der akuten Krankheitsverschlechterung eine grippeähnliche Prodromalsymptomatik zu beobachten. Auffällig war eine Häufung des schwer verlaufenden „toxic shock-like syndrome“ (TSLS) mit den Kriterien: Schocksymptomatik, Multiorganversagen, Weichteilnekrose und generalisiertes Erythem (n=6). Alle überlebenden Patienten mit TSLS mußten mit mehrtägiger Respiratortherapie behandelt werden (7–16 Tage). Eine Patientin mit TSLS starb am Aufnahmetag aufgrund eines fulminanten septischen Schocks. Die Analyse der isolierten Stämme zeigte kein einheitliches Bild bezüglich der Serotypen und der Toxinbildung. Folgende sofortige therapeutische Maßnahmen sind erforderlich: antibiotische Behandlung, chirurgische Sanierung des Infektherdes und typische Intensivtherapie bei Multiorganversagen. Die beobachtete Prodromalsymptomatik unterstreicht nachdrücklich die Möglichkeit eines frühzeitigen Eingreifens in das Krankheitsgeschehen.

Summary Bacterial interactions in mixed infections may interfere with antimicrobial therapy. Thein-vitro efficacy of ampicillin alone, combination sulbactam/ampicillin, and metronidazole was studied. Strains ofBacteroides fragilis, Escherichia coli, andEnterococcus faecalis, alone and in association, were tested by means of a broth dilution method. Minimal bactericidal concentrations (MBC) of ampicillin forB. fragilis 74 in association withE. coli 68 were up to 16-fold higher than forB. fragilis 74 alone (256 compared to 16 mg/l), but only 2-fold higher for sulbacta(5 mg/l)/ampicillin (0.5 and 0.25 g/l). Association ofB. fragilis 45 andE. faecalis 186 increased ampicillin MBC ofE. faecalis 186 from 2 to 16 mg/l, but the combination sulbactam/ampicillin restored activity of ampicillin. In association withE. faecalis, metronidazole MBCs ofB. fragilis increased up to 64-fold. Strains ofE. faecalis andE. coli were able to destroy 10 mg/l metronidazole within 8 to 20 h. The present experiments demonstrated effectiveness of sulbactam/ampicillin to inhibit ß-lactamases of associated pathogens. Destruction of metronidazole byE. faecalis lends additional support to the use of the combination in aerobic/anaerobic infections includingE. faecalis.

Summary Time and accuracy required for diagnosis are two of the most important factors in medical microbiology. Computer-assisted diagnosis is one tool to overcome these problems. The software of such systems, much more than the hardware, is of utmost importance and both have to fulfill several items. 1) High flexibility and integration within the already existing working schemes of the laboratory. 2) Terminals in every laboratory. 3) High speed of calculation. 4) Online data transfer from automated instruments. 5) External terminals on intensive care units. 6) Epidemiological and etiopathological investigations have to be possible at any time. In the laboratory the burden of simple, repeating tasks is diminished, inquiries can be made in a minute and precise information about the epidemiological situation can be gained within a few hours. Thus, calculated antimicrobial therapy depending on the incidence of certain pathogens in given specimens in different departments is possible. In the case of fast-growing bacteria, preliminary reports, including susceptibility testing available within the first 24 h, are possible and will be of great help to the clinician in monitoring the calculated antimicrobial regimen. External terminals will allow continuous flow of data from the laboratory to wards and vice versa.

Summary The aim of automated susceptibility testing systems like the Cobas Bact is to provide the clinicians with rapid and reliable results for the care of patients and to decrease the work load in microbiological laboratories. Because data about accuracy on mezlocillin, azlocillin and ciprofloxacin were lacking, we investigated 184 bacterial strains and compared the results of the Cobas Bact susceptibility testing to standardized agar dilution and agar diffusion methods. Essential correlations for all methods compared exceeded 90% for the three chemotherapeutics and all species investigated, with the exception ofPseudomonas aeruginosa. On an average only 1.5% very major errors were observed with the several species of Enterobacteriaceae, whereasP. aeruginosa andEnterococcus faecalis were characterized by the complete absence of very major errors when Cobas Bact was correlated to NCCLS agar diffusion.

Summary Computer-assisted diagnostic systems may accelerate transmission of microbiological reports and facilitate evaluation of the epidemiological situation and thus improve the collaboration between microbiologists and clinicians. This possible benefit is demonstrated by four examples. It became evident that incidences of pathogens in urinary tract and respiratory tract infections varied within a great range, depending on patient groups and clinical departments involved. Even within a department, different incidences of penicillin G and oxacillin-resistant coagulase-negative staphylococci were demonstrated. An apparent homogeneity of distribution of pathogenic bacteria in a hospital tends to be the result of a nondiscriminating overall evaluation, thus necessarily misleading the clinician especially in empirical chemotherapy. In the last example the evaluation of susceptibility testing revealed changing patterns of some pathogens during the observation period. By rapid exchange of data between the laboratories and the clinical departments supplying the clinicians with information relevant for actual therapeutical decisions, an empiric therapy may change into a so-called calculated therapy based upon data directly related to the site of infection, department and susceptibility patterns.

The effectiveness of gastrointestinal and topical decontamination, as well as isolation in laminar airflow (LAF) units were investigated in 20 patients. On a weekly basis, surveillance cultures were taken. Environmental controls were taken on the medical ward outside the two LAF units and from the LAF unit itself when being used by a patient. The use of LAF units seems to be of benefit in preventing exogenous infections, but there are two weak points in the isolation techniques: the opening of the tent (with a free entry into the tent itself) and the water delivery system. By using appropriate decontamination measures, it was possible to greatly reduce the number of bacteria and species of the normal flora in all regions with the exception of the oropharynx. Individual patients with oxacillin resistant coagulase-negative staphylococci and/orCandida albicanscontinued to show the presence of these organisms during this time. The detection ofClostridium difficileand/or its toxin B in eight patients at the beginning of the individual observation period was significant. Four out of 15 fever episodes were attributable to endogenous bacterial infections. Each of the causative organisms had been previously isolated in the surveillance cultures, thus the clinician was able to initiate a calculated antimicrobial therapy. As evident from the low incidence of infectious complications, gastrointestinal and topical decontamination of the skin as well as reverse isolation in LAF units are efficient protective measures for bone marrow transplant patients.

Summary The antimicrobial susceptibility of 195 recent clinical isolates of anaerobic bacteria was studied to ampicillin alone, ampicillin +1 mg/l sulbactam, ampicillin +5 mg/l sulbactam, and cefoxitin by means of agar dilution tests. The ampicillin-sulbactam combinations were the most effective drugs against species of theBacteroides fragilis group, the MIC90 of ampicillin +5 mg/l sulbactam forB. fragilis being <1 mg/l, compared to 256 mg/l of ampicillin, 4 mg/l of ampicillin +1 mg/l sulbactam, and 8 mg/l of cefoxitin. No significant difference between ampicillin alone and in combination with sulbactam was observed against gram-positive anaerobic rods,Peptococcus spp. andPeptostreptococcus spp. with MIC's <2 mg/l.

The in vitro activity of daptomycin-metronidazole combinations against mixed cultures of gram-positive facultative cocci and strains of theBacteroides fragilis group was investigated. Metronidazole did not influence the high activity of daptomycin against strains ofStaphylococcus aureus, Staphylococcus epidermidis andEnterococcus faecalis in the absence or presence of the co-culturedBacteroides strains. In contrast, theEnterococcus faecalis isolates protected the co-culturedBacteroides strains against the killing effect of metronidazole, even at a concentration four- or eightfold the MIC of metronidazole. Killing curve experiments confirmed this protective effect of different isolates ofEnterococcus faecalis.

The reliability of four commercially available broth microdilution systems (ATB ANA, MHK-Anaerob-Biotest, Dynatech MIC system, Sceptor Anaerobe MIC system) for routine susceptibility testing was evaluated using agar dilution and broth macrodilution as reference methods. Using the categories “susceptible”, “moderately susceptible” and “resistant”, the rate of essential agreement (complete agreement plus minor errors) of all four systems compared to the two reference methods was satisfactory, ranging from 93% (Dynatech system and agar dilution) to 98 % (Sceptor system and agar dilution). The rate of complete agreement compared to the agar dilution and broth dilution method respectively was 61 % and 60 % for the MHK-Anaerob-Biotest, 65 % and 63 % for the Dynatech system, 72 % and 72 % for ATB ANA, and 85 % and 80 % for the Sceptor system. The Sceptor system was thus superior to the other systems. The systems were easy to operate and inoculate, although arrangement of antimicrobial agents in the Dynatech panels was apt to be confusing.

The results of susceptibility tests performed by the Cobas-Bact system were compared with those of the NCCLS agar diffusion (Kirby-Bauer) and NCCLS agar dilution methods. A total of 998 clinical isolates were tested against 10 to 18 antimicrobial agents. Essential agreement (comprising full agreement and minor discrepancies) varied from 90.5 % to 99.2 % on comparison of Cobas-Bact with Kirby-Bauer results, depending on the bacterial group (mean for all 998 strains tested 95.7 %). These figures ranged from 91 % to 99.2 % (mean 96.3 %) for the Cobas-Bact/MIC comparison and from 95.2 % to 99.7 % (mean 98.7 %) for the Kirby-Bauer/MIC comparison. The best results were found forEnterobacteriaceae andStaphylococcus aureus, whereas for enterococci and coagulase-negative staphylococci there was a lower rate of essential agreement in all three comparisons. In the case ofPseudomonas aeruginosa there was a good rate of essential agreement but many minor discrepancies, resulting in a disappointing rate of full agreement of between 67.5 % and 78.9 % in the three comparisons. The Cobas-Bact system would appear to provide satisfactory susceptibility test results in most cases, however there are still some major problems in the system which should be resolved.

The applicability of whole-cell protein patterns obtained by sodium dodecylsulfate-polyacrylamide gel electrophoresis as a typing method forClostridium difficile was examined using a total of 227 strains isolated from 191 patients and their surroundings. Computer-aided densitometric analysis was used to establish a reliable standardization technique with which a large number of protein patterns could be efficiently classified. The normalized tracks could be electronically superimposed and compared to give reproducible results. The influence of sample preparation for electrophoresis was found to be negligible. By this technique 35 subgroups could be differentiated, and further discrimination was possible within each subgroup using minor, even very weak protein bands. Epidemiologically related strains ofClostridium difficile yielded absolutely identical patterns, allowing unequivocal identification. Thus protein electrophoresis combined with densitometric analysis was shown to be useful for typingClostridium difficile isolates.

Summary Infections due to coagulase negative staphylococci (CNS) are of growing concern mainly in patients hospitalized in intensive care units (ICU). The ability of CNS to adhere and to grow on plastic devices and resistance to many antibiotics, including oxacillin, contributes to their pathogenicity. Using the computer assisted system of the Medical Microbiology Department, the incidences of different pathogens and the coincidence of CNS with other bacteria were evaluated in a surgical department.Staphylococcus aureus revealed to be the predominant pathogen; however, CNS showed an increasing incidence in wound specimens and blood cultures of patients on the ICU. Coincidence of CNS withS. aureus and the nine most frequent species of gram negative bacteria could be shown in 6%. To investigate the influence ofß-lactamases produced by CNS in mixed infections, association experiments were performed. Association means a controlled growth of two or even more bacteria in a susceptibility testing system, either a broth dilution method or an automated broth disk elution method (Cobas Bact). The association experiments showed a significant increase of amoxicillin MIC's of the pathogen associated with CNS. Addition of clavulanic acid restored activity of amoxicillin. It could be shown that in mixed infections CNS may contribute to the failure of antibiotic regimens by production ofß-lactamases.

Summary To demonstrate the value of a computer assisted microbiological diagnosis and database system for clinical use, epidemiological aspects of three important infections were investigated: urinary tract, respiratory tract and wound infections. The first two examples presented revealed significant differences in incidence of pathogens between a single patient group and the overall statistic. The third example demonstrates that even within a department susceptibility patterns ofstaphylococcus epidermidis were changing in dependence of the ward investigated. In the last example the evaluation of susceptibility testing revealed changing patterns of some pathogens during the observation periods. By means of a computer assisted diagnosis and database on file at the moment of diagnosis thus allowing statistical evaluations at every time within a few hours. The clinician provided with actual data concerning his ward or department may administer an empiric therapy according to the real situation. Besides this, automated susceptibility testing may shorten the time required for diagnosis up to 24 h, thus further contributing to a more rational antimicrobial therapy. In conclusion computer assisted diagnosis and automated instruments support the clinician by means of actual epidemiological data and rapid reporting in choosing and controlling antimicrobial therapy.

Summary In infections of polymicrobial etiology, it seems mandatory to combine an antibiotic with marginal activity against anaerobes with an anti-anaerobic drug, e. g. metronidazole or clindamycin. We investigated the effect of associations of anaerobic and facultatively anaerobic pathogens on MBCs of enoxacin, clindamycin, metronidazole, and combinations of enoxacin plus clindamycin or metronidazole. Single testing, and associations ofBacteroides fragilis withEscherichia coli orEnterococcus faecalis revealed MBCs of 64 mg/l for enoxacin. However, investigating metronidazole, MBCs forB. fragilis increased from 0.5–1 mg/l to 2–4 mg/l in association withE. coli. The combination of enoxacin with metronidazole restored MBCs of 0.5 and 1 mg/l for theB. fragilis strains.B. fragilis associated withE. faecalis showed MBCs of 2 to 64 mg/l for metronidazole, an increase of up to 64-fold. The enoxacin MBCs forE. coli in association withB. fragilis were up to eight-fold higher than forE. coli alone (2 mg/l compared to 0.25 mg/l). Association ofE. coli withE. faecalis andB. fragilis showed a low to moderate increase for MBCs ofE. coli when enoxacin was tested alone or in combination with metronidazole or clindamycin. In contrast, MBCs forE. faecalis did not change significantly with any of the associations or combinations tested. It is evident thatin vitro antimicrobial susceptibility of associations of pathogens can be modified by interactions between strains, and/or antimicrobials.

The antimicrobial susceptibility of 196 recent clinical isolates of anaerobic bacteria to ampicillin alone, ampicillin plus 1 μg/ml sulbactam, ampicillin plus 5 μg/ml sulbactam, and cefoxitin was studied by means of agar dilution tests. The ampicillin/sulbactam combination was most effective against species of the Bacteroides fragilis group, the minimum inhibitory concentration (MIC)90 of ampicillin plus 5 μg/ml sulbactam for B. fragilis being 1 μg/ml, compared with 256 μg/ml of amoicillin, 4 μg/ml of ampicillin plus 1 μg/ml sulbactam, and 8 μg/ml of cefoxitin. No significant difference between ampicillin alone and in combination with sulbactam was observed against Gram-positive anaerobic rods or cocci.

Ewingella americana (familyEnterobacteriaceae) was isolated separately from both eyes of a 30-year-old woman. Clinical signs and symptoms included adhesive eyelids, itching and edematous upper and lower lids. Therapy with amoxicillin-clavulanate resulted in the relief of symptoms.Ewingella americana can be isolated worldwide, but seems to be a rare pathogen.

Summary To assess thein vitro activity of cefpodoxime against anaerobic respiratory tract and oropharyngeal pathogens 77 strains belonging to 18 gram-negative and 7 gram-positive species were studied by means of agar dilution tests. For comparison cefuroxime, amoxicillin, amoxicillin + clavulanic acid and clindamycin were also tested. Cefpodoxime was found to be active at concentrations of = 0.125 mg/l againstPrevotella oralis, Prevotella buccalis, Prevotella bivia, Porphyromonas asaccharolytica, Bacteroides corporis, Bacteroides gracilis, Fusobacterium necrophorum, Fusobacterium naviforme andPropionibacterium acnes. Prevotella oris, Prevotella buccae, Fusobacterium nucleatum, Peptostreptococcus asacharolyticus, andRuminococcus bromii were inhibited at concentrations of = 1 mg/l andPrevotella denticola, Prevotella melaninogenica, Prevotella intermedia, Porphyromonas gingivalis, Bacteroides pneumosintes, andPeptostreptococcus micros at concentrations of = 4 mg/l. Strains ofVeillonella parvula were inhibited by cefpodoxime at 0.25 – 8 mg/l, and single strains ofPeptostreptococcus anaerobius andPetostreptococcus magnus showed MICs of 32 and 64 mg/l, respectively. The results obtained warrant the use of cefpodoxime in therapy of anaerobic and mixed aerobic-anaerobic infections of the upper and lower respiratory tract and similar infections not involvingBacteroides fragilis.

Zusammenfassung Die minimalen Hemmkonzentrationen (MHK) von Enoxacin, Clindamycin und Metronidazol wurden bei klinischen Isolaten saccharolytischer intestinalerBacteroides spp. mittels der Agardilutionsmethode entsprechend den NCCLS-Richtlinien bestimmt. Mit den Kombinationen Enoxacin-Clindamycin und Enoxacin-Metronidazol wurden Schachbrett-Titrationen auf Wilkins-Chalgren-Agar durchgeführt, Inokulation, Inkubation und Ablesung der Platten erfolgte wie bei der MHK-Bestimmung. Die MHK90 von Metronidazol betrug beiBacteroides fragilis (23 Stämme) und beiBacteroides thetaiotaomicron (23 Stämme) in beiden Fällen 0,5 mg/l; die MHK90 von Clindamycin war beiB. fragilis 1 mg/l und beiB. thetaiotaomicron 8 mg/l, bei Enoxacin betrugen die entsprechenden Werte 16 bzw. 64 mg/l. Die Auswertung der Ergebnisse der Kombinationstestung Enoxacin-Metronidazol zeigte bei elfB. fragilis-Stämmen eine additive Wirkung, Indifferenz bei sieben und Antagonismus bei einem Stamm. BeiB. thetaiotaomicron lauteten die Ergebnisse Addition bei fünf Stämmen, Indifferenz bei 17 und Antagonismus bei einem Stamm. Die Kombination Enoxacin-Clindamycin war bei zehn Stämmen vonB. fragilis additiv wirksam, indifferent bei sechs und antagonistisch bei einem Stamm, beiB. thetaiotaomicron war ein Synergismus bei einem Stamm, Addition bei vier und Indifferenz bei 17 Stämmen zu beobachten. Der fehlende Antagonismus und das Überwiegen additiver oder indifferenter Effekte läßt den Gebrauch der Kombinationen Enoxacin-Clindamycin bzw. Enoxacin-Metronidazol in klinischen Untersuchungen bei der Behandlung anaerob-aerober Mischinfektionen sinnvoll erscheinen.

To assess the specificity and sensitivity of Fluorocult media for the identification of Escherichia coli, the beta-glucuronidase activities of 1,258 bacterial strains, as well as 20 strains of Candida spp., were investigated. Fluorescence of colonies combined with positive indole reaction resulted in specificities of 99.6 to 99.8%. Sensitivities were 59.1% (MacConkey agar), 69.9% (brolacin agar), 85.5% (Columbia agar), and 85.8% (ECD agar).

A multilaboratory collaborative study was undertaken to determine whether the anaerobic disk diffusion test of Horn et al. could be performed reproducibly and accurately. Tests with nine different antimicrobial disks were evaluated. Reproducibility of the agar diffusion disk method was similar to that of the reference agar dilution test procedure. The anaerobic disk diffusion procedure was found to be a potentially useful method for testing some antimicrobial agents against rapidly growinganaerobes belonging to the Bacteroides fragilis group. These promising results warrant further investigations and validations.