Methicillin-resistant S.aureus (MRSA) is a highly virulent pathogen associated with serious healthcare-associated (HCA-MRSA) and community-associated (CA-MRSA) infections. MRSA is an increasingly important cause of skin and skin-structure, bloodstream and other invasive infections including pneumonia and endocarditis. The pharmacodynamics of existing treatments and anovel cephalosporin with activity against MRSA were studied in an in vitro infection model comparing the antibacterial effects of monotherapy and combination therapy under standard and altered environmental conditions. The activity of monotherapy with vancomycin, daptomycin, linezolid and ceftobiprole against clinical MRSA isolates were tested along with combinations of vancomycin-ceftobiprole, daptomycin-ceftobiprole and linezolid-ceftobiprole. Antibacterial response under standard conditions supporting optimal bacterial growth were compared to altered conditions with acidic pH 5.5, diluted nutrient broth (1:2) and increased temperature 40°C. Two clinical isolates including one HCA-MRSA (#81655) and one CA-MRSA (#79002) were studied in an in vitro pharmacodynamic model (IPDM) over 24 hours. Clinical dosing regimens equivalent to vancomycin 1500 mg intravenously every 12 hours (peak =24.4 mg/L, trough =7.4 mg/L), daptomycin 6 mg/kg (420 mg) intravenously every 24 hours (peak =8.2 mg/L, trough =0.8 mg/L) and linezolid 600 mg intravenously every 12 hours (peak =9.2 mg/L, trough =2.8 mg/L) were tested. Ceftobiprole was administrated as a bolus dose followed by constant infusion of 10 mg/L. Antibacterial effects were quantified as initial bacterial kill rate over 4 hours (KR4) and absolute bacterial kill at 24 hours (BK24). Minimum inhibitory concentrations (MIC) were measured via E-test® methods using initial isolates and those recovered after 24 hours of therapy. The KR4 with daptomycin and vancomycin were equivalent (P=0.14), yet daptomycin was more rapid than ceftobiprole (P=0.03) and linezolid (P<0.0001). The BK24 was greatest with ceftobiprole and vancomycin which were superior to linezolid (P<0.0001, P<0.0001, respectively) and daptomycin (P=0.0001, P=0.0001, respectively). Daptomycin was associated with bacterial re-growth and increasing MICs from 0.25 mg/L to 2-4 mg/L during therapy for isolate #79002 under standard conditions. Furthermore, daptomycin activity against both isolates was significantly reduced under altered conditions (KR4, P=0.0001; BK24, P=0.04). Combination therapy with vancomycin-ceftobiprole was indifferent compared with either agent alone. Although daptomycin-ceftobiprole prevented daptomycin non-susceptibility during therapy and resulted in significantly greater BK24 compared with daptomycin alone (BK24 difference of 4.07 log10 cfu/mL, P=0.0001), the combination was indifferent from ceftobiprole alone. Finally, linezolid-ceftobiprole was similar to linezolid but significantly less active than ceftobiprole alone (BK24 difference of 1.39 log10 cfu/mL, P=0.005) raising concerns of potential antagonism with this combination. In conclusion, this study provides important data regarding antimicrobial pharmacodynamics against MRSA. Overall, monotherapy with either ceftobiprole or vancomycin was most active. Combination therapy with ceftobiprole prevented the emergence of daptomycin non-susceptibility during therapy, but demonstrated potential antagonism with linezolid.

Methicillin-resistant S.aureus (MRSA) is a highly virulent pathogen associated with serious healthcare-associated (HCA-MRSA) and community-associated (CA-MRSA) infections. MRSA is an increasingly important cause of skin and skin-structure, bloodstream and other invasive infections including pneumonia and endocarditis. The pharmacodynamics of existing treatments and anovel cephalosporin with activity against MRSA were studied in an in vitro infection model comparing the antibacterial effects of monotherapy and combination therapy under standard and altered environmental conditions. The activity of monotherapy with vancomycin, daptomycin, linezolid and ceftobiprole against clinical MRSA isolates were tested along with combinations of vancomycin-ceftobiprole, daptomycin-ceftobiprole and linezolid-ceftobiprole. Antibacterial response under standard conditions supporting optimal bacterial growth were compared to altered conditions with acidic pH 5.5, diluted nutrient broth (1:2) and increased temperature 40°C. Two clinical isolates including one HCA-MRSA (#81655) and one CA-MRSA (#79002) were studied in an in vitro pharmacodynamic model (IPDM) over 24 hours. Clinical dosing regimens equivalent to vancomycin 1500 mg intravenously every 12 hours (peak =24.4 mg/L, trough =7.4 mg/L), daptomycin 6 mg/kg (420 mg) intravenously every 24 hours (peak =8.2 mg/L, trough =0.8 mg/L) and linezolid 600 mg intravenously every 12 hours (peak =9.2 mg/L, trough =2.8 mg/L) were tested. Ceftobiprole was administrated as a bolus dose followed by constant infusion of 10 mg/L. Antibacterial effects were quantified as initial bacterial kill rate over 4 hours (KR4) and absolute bacterial kill at 24 hours (BK24). Minimum inhibitory concentrations (MIC) were measured via E-test® methods using initial isolates and those recovered after 24 hours of therapy. The KR4 with daptomycin and vancomycin were equivalent (P=0.14), yet daptomycin was more rapid than ceftobiprole (P=0.03) and linezolid (P<0.0001). The BK24 was greatest with ceftobiprole and vancomycin which were superior to linezolid (P<0.0001, P<0.0001, respectively) and daptomycin (P=0.0001, P=0.0001, respectively). Daptomycin was associated with bacterial re-growth and increasing MICs from 0.25 mg/L to 2-4 mg/L during therapy for isolate #79002 under standard conditions. Furthermore, daptomycin activity against both isolates was significantly reduced under altered conditions (KR4, P=0.0001; BK24, P=0.04). Combination therapy with vancomycin-ceftobiprole was indifferent compared with either agent alone. Although daptomycin-ceftobiprole prevented daptomycin non-susceptibility during therapy and resulted in significantly greater BK24 compared with daptomycin alone (BK24 difference of 4.07 log10 cfu/mL, P=0.0001), the combination was indifferent from ceftobiprole alone. Finally, linezolid-ceftobiprole was similar to linezolid but significantly less active than ceftobiprole alone (BK24 difference of 1.39 log10 cfu/mL, P=0.005) raising concerns of potential antagonism with this combination. In conclusion, this study provides important data regarding antimicrobial pharmacodynamics against MRSA. Overall, monotherapy with either ceftobiprole or vancomycin was most active. Combination therapy with ceftobiprole prevented the emergence of daptomycin non-susceptibility during therapy, but demonstrated potential antagonism with linezolid.

Background: There is a potential drug interaction between linezolid and antidepressants resulting in serotonin syndrome. Thus, clinicians often avoid this drug combination. However, little empirical data exists to support this avoidance. The objective of this study was to describe the risk of serotonin syndrome in patients receiving linezolid and how this risk changed with concomitant antidepressant use. Methods: A population based retrospective cohort study was conducted using the administrative databases at ICES. The patient population consisted of outpatients aged 66 years or older who were prescribed oral linezolid of any duration from 2014 to 2021 in Ontario, Canada. Patients who were also taking antidepressants during linezolid treatment were compared to patients not on antidepressants during linezolid treatment. The primary outcome was clinically significant serotonin syndrome requiring emergency room visit or hospitalization based on physician diagnosis, Sternbach criteria or Hunter criteria within 30 days of starting linezolid. Secondary outcomes included altered mental status, hospitalization and death due to any cause within 30 days. Results: Of 1,134 patients who were prescribed linezolid, 215 (19.0%) patients were also taking antidepressants. Less than 6 (<0.5%) patients had serotonin syndrome. The proportion of patients with serotonin syndrome was numerically lower in the antidepressant group. In a propensity score matched cohort, the adjusted risk difference for serotonin syndrome in the antidepressant group minus the no antidepressant group was -1.2% (95% CI -2.9% to 0.5%). The risk of altered mental status, hospitalization and death were similar between the two groups. Conclusions: The risk of serotonin syndrome was low in patients taking linezolid. Concurrent antidepressants did not significantly increase the risk of serotonin syndrome. These findings suggest that linezolid can be safely used in patients also on antidepressants when indicated. / Thesis / Master of Science (MSc) / Linezolid is an antibiotic that can potentially cause serotonin syndrome as an adverse effect when combined with antidepressants. In serotonin syndrome, dysfunction of the nervous system leads to a variety of symptoms that can be life threatening. This study examined people in Ontario aged 66 years or older who were prescribed linezolid from 2014 to 2021 to describe the risk of serotonin syndrome due to linezolid and how antidepressants change this risk. Patients were followed for 30 days from start of linezolid treatment to determine if they had serotonin syndrome based on diagnoses in emergency room or hospital visit records. Of 1,134 patients in the study, 215 (19.0%) patients took antidepressants. The risk of serotonin syndrome was low at less than 0.5%. This risk was not significantly different in patients on antidepressants when compared to those who were not. Therefore, linezolid is likely safe for patients receiving antidepressants.

Η αυξανόμενη τάση εμφάνισης ανθεκτικών στελεχών μικροβίων στα αντιβιοτικά δημιουργεί την ανάγκη για την εύρεση νέων αντιβιοτικών περισσότερο αποτελεσματικών των υπαρχόντων. Η ανάγκη αυτή έχει ως αποτέλεσμα την ανάπτυξη νέων αντιβιοτικών, προϊόντων οργανικής σύνθεσης, μεταξύ των οποίων σημαντική θέση κατέχει η λινεζολίδη. Η λινεζολίδη είναι ένα αντιβιοτικό που ανήκει στην οικογένεια των οξαζολιδινονών. Χρησιμοποιείται κλινικά από το 2000 και μετά, για τη θεραπεία ενός φάσματος λοιμώξεων που προκαλούνται κυρίως από θετικούς κατά Gram παθογόνους μικροοργανισμούς. Το μόριο της αποτελείται από τρεις αρωματικούς δακτυλίους με μία ακεταμιδομεθυλο ουρά προσδεδεμένη στον οξαζολιδινικό φαρμακοκινητικό δακτύλιο. Η κρυσταλλογραφική ανάλυση του προσδεδεμένου αντιβιοτικού στη μεγάλη ριβοσωματική υπομονάδα στα αρχαία και τα βακτήρια αποκαλύπτει ότι η λινεζολίδη προσδένεται στην Α- θέση του ριβοσώματος, στο κέντρο δηλαδή της πεπτιδυλοτρανσφεράσης, σε μία θέση που επικαλύπτει τις θέσεις πρόσδεσης της ανισομυκίνης, της χλωραμφαινικόλης καθώς επίσης και του αμινοακυλικού άκρου ενός αμινοάκυλο tRNA. Αν και αποτελεί αντιβιοτικό νέας γενιάς και η χρήση του είναι ακόμα περιορισμένη, εν τούτοις έχουν ήδη αναφερθεί ανθεκτικά βακτηριακά στελέχη. Η ανθεκτικότητα έχει συσχετισθεί με συγκεκριμένες μεταλλάξεις κυρίως στο 23S rRNA και δευτερευόντως με συγκεκριμένες μεταλλάξεις στις ριβοσωματικές πρωτεΐνες. Πρόσφατα δημοσιεύτηκε ότι το στέλεχος του Staphylococcus epidermidis Α2864 το οποίο φέρει παρόμοιες μεταλλάξεις ανθεκτικότητας στο 23 S rRNA και στην ριβοσωματική πρωτεΐνη L3, όχι μόνο δεν αναστέλλεται από τη λινεζολίδη, αλλά παρουσία του αντιβιοτικού αναπτύσσεται ταχύτερα από το στέλεχος αγρίου τύπου. Επειδή το ριβόσωμα είναι ο κύριος στόχος δράσης του αντιβιοτικού, προσπαθήσαμε να διερευνήσουμε πιθανές μεταβολές που προκαλεί η παρουσία της λινεζολίδης στη λειτουργία των ριβοσωμάτων του συγκεκριμένου στελέχους. Απομονώσαμε λειτουργικά ριβοσώματα από το στέλεχος αγρίου τύπου, αλλά και το μεταλλαγμένο, που αναπτύσσεται είτε απουσία είτε παρουσία λινεζολίδης. Σύμφωνα με τα αποτελέσματά μας, υπάρχουν σημαντικές διαφορές στη δομή και στη λειτουργία των ριβοσωμάτων που έχουν απομονωθεί από κύτταρα που αναπτύχθηκαν παρουσία του αντιβιοτικού. Η καταλυτική ενεργότητα της πεπτιδύλοτρανσφεράσης, δηλαδή της ενζυμικής ενεργότητας η οποία είναι υπεύθυνη για το σχηματισμό του πεπτιδικού δεσμού και εκφράζεται με το λόγο kcat/KM, είναι σημαντικά υψηλότερη στα ριβοσώματα που έχουν απομονωθεί από το μεταλλαγμένο στέλεχος που καλλιεργήθηκε παρουσία λινεζολίδης. Τη διαφορά όμως αυτή την εκφράζουν μόνο παρουσία του αντιβιοτικού. Μία άλλη σημαντική διαφορά αυτών των ριβοσωμάτων είναι η αδυναμία τους να διαχωριστούν αποτελεσματικά στις υπομονάδες τους απουσία του αντιβιοτικού, ενώ παρουσία της λινεζολίδης διαχωρίζονται σχεδόν ικανοποιητικά στις υπομονάδες τους. Όλες αυτές οι παρατηρήσεις οδηγούν στο συμπέρασμα ότι η παρουσία του αντιβιοτικού έχει τροποποιήσει τη δομή και λειτουργία του ριβοσώματος είτε επηρεάζοντας την καθορισμένη ιεραρχία της συναρμολόγησης των ριβοσωμάτων, είτε σχηματίζοντας ένα καινούριο ριβοσωματικό υβρίδιο, λειτουργικό μόνο παρουσία του αντιβιοτικού. / The rising tide of bacterial resistance has created an urgent need for new effective antibiotics. This need has resulted in the development of new synthetic antibiotics, with linezolid being one of them. Linezolid belongs to the family of oxazolidinones. It has been introduced into clinical practice since 2000, for the treatment of a variety of infections caused by Gram-positive pathogen microorganisms. This molecule comprises three aromatic rings with an acetamidomethyl tail attached to the pharmacokinetic oxazolidinone ring. Crystal structures of linezolid bound the bacterial and archaeal large subunits reveal that linezolid binds to the A- site of the ribosome, in the PTC, in a position overlapping the binding sites of anisomycin, chloramphenicol as well as the aminoacyl moiety of an A- site bound tRNA. Although it belongs to the new generation of antibiotics and its use is still limited, antibiotic resistance has already been manifested and is associated with specific mutations mainly located on 23S rRNA and specific ribosomal proteins. Recently, it has been published that Staphylococcus epidermidis strain A2864, is not only resistant to linezolid but additionally it grows remarkably faster in the presence of the antibiotic, as well as the wild type strain. Since ribosome is the main target of the antibiotic, we tried to investigate possible changes in ribosome’s function that are induced by the presence of the antibiotic. We isolated functionally active ribosomes from wild type strain and mutant strain growing in the absence and presence of linezolid. According to our data, there are serious differences in the structure and function of mutant ribosomes assembled in the presence of the antibiotic. The catalytic activity of peptidyltransferase, the enzymatic activity which is responsible for peptide bond formation and is expressed with the ratio kcat/KM is significantly higher in the mutant strain in the presence of linezolid, but only for ribosomes assembled in the presence of the antibiotic. Another important difference of the same ribosomes is their inability to be efficiently dissociated into subunits in the absence of the antibiotic, while in the presence of the antibiotic the separation of subunits was successfully restored. These observations imply that, the presence of the antibiotic has modified the structure and the function of the ribosome either by modifying the defined hierarchy of ribosomes assembly or by leading to the formation of a new functional specie, active only in the presence of the antibiotic.

Thesis (doctoral)--Universität, Giessen, 2004.

Universiẗat, Diss., 2004--Gießen. / Zsfassung in dt. und engl. Sprache.

Les staphylocoques sont des bactéries commensales de la peau et des muqueuses. On distingue Staphylococcus aureus qui est un pathogène virulent bien connu, des staphylocoques à coagulase négative (SCoN), qui sont de plus en plus impliqués dans les infections sur matériel et multirésistants aux antibiotiques. Le linézolide (LZD) est un antibiotique de la classe des oxazolidinones qui inhibent la synthèse protéique au niveau de la SU ribosomale 50S. La résistance est liée à des mutations dans l’ADNr23S (rrl) et les protéines ribosomales ainsi qu’à l’acquisition des gènes cfr et optrA. L’objectif de la thèse était d’étudier la cinétique d’acquisition des mécanismes de résistance au LZD chez les staphylocoques. Nous avons montré in vitro chez les SCoN, que la résistance était liée à une accumulation des différents mécanismes de résistance avec une cinétique d’acquisition identique commençant par l’apparition de mutations dans les protéines ribosomales facilitant possiblement l’acquisition secondaire de mutation dans rrl. Nous avons décrit in vivo chez un patient atteint de mucoviscidose sur 5 ans que l’émergence de la résistance au LZD chez S. aureus pouvait être rapide et de haut niveau sous traitement, avec une adaptation du niveau de résistance dans le temps. Nous avons pu décrire les différentes adaptations liées à la résistance au LZD, telle que la perte d’une copie d’opéron ribosomique, ainsi que le développement d’une dépendance partielle au LZD liée à la présence du gène cfr associé à d’autres mécanismes de résistance. En conclusion, nous avons montré le rôle facilitant de certaines mutations dont le dépistage pourrait prévenir l’émergence de résistance sous traitement ainsi que le rôle de cfr dans la dépendance expliquant potentiellement sa dissémination. Enfin le rôle de mutations apparues dans des gènes non liés directement à la résistance lors de l’émergence de celle-ci devra être précisé. / Staphylococci are commensal bacteria from skin and mucous membrane. Staphylococcus aureus a well-known virulent species could be distinguish from coagulase negative staphylococci (CoNS) which are increasingly implied in indwelling devices infections and are frequently multiresistant to antibiotics. Linezolid (LZD) is an antibiotic of the oxazolidinone family inhibiting protein synthesis by binding to the 50S ribosomal SU. Resistance is related to mutations in 23S rDNA (rrl) and in ribosomal protein as well as to the acquisition of the cfr and optrA genes. We aimed to investigate resistance emergence timeline in staphylococci. We reported in vitro that resistance in CoNS was due to accumulation of resistance mechanism with a similar timeline of acquisition including firstly resistance in ribosomal proteins that probably facilitated second mutation in 23S rRNA. Our in vivo study in a cystic fibrosis patient over a 5 years that LZD resistance emergence in S. aureus could be fast with a high level under treatment and with resistance level adaptation over time. We also described different consequences of LZD resistance such as the loss of a copy of the ribosomal operon, but also the presence of a partial LZD dependence linked to the cfr gene associated with others mutations. In conclusion, we showed the facilitating role of ribosomal mutation whose screening could prevent the emergence of resistance as well as the role of the cfr gene in LZD dependence thus potentially explaining its dissemination. Finally, the role of mutations appeared in genes not directly linked to the resistance during the emergence of it should be further studied.

Bacillus anthracis, the etiological agent of anthrax, is a spore- forming, toxin- producing bacterium. Currently, treatment of B. anthracis infections requires a 60- day antibiotic regimen. However, better therapeutics are required. Therefore, this study looked at the effect of levofloxacin and linezolid on B. anthracis cell viability, toxin production and spore formation using in vitro static models and a pharmacodynamic model. It was hypothesized that the combination would be the most effective at preventing toxin and spore production resulting in greater bacterial killing. However, these studies suggest otherwise. Nevertheless, clinically, the combination therapy may be more effective in rapid killing of vegetative B. anthracis and may be able to reduce the duration of therapy (by reducing the likelihood of spore survival). Therefore, the clinical benefit of combined therapy on long-term recurrence cannot be determined from these in vitro models. Further investigation with combination therapy is warranted. / October 2015

Activation of the NLRP3 inflammasome has been shown in response to numerous activators; here we show that the oxazolidinone antibiotic linezolid results in both the NLRP3-dependent in vitro release of the proinflammatory cytokine IL-1 Α; and in vivo neutrophilic influx following its intraperitoneal administration. Clinical use of linezolid is commonly limited by hematologic side effects; herein we also show NLRP3-deficiency protected animals against linezolid-induced effects on the bone marrow. Importantly, all previously described activators of the NLRP3 inflammasome have required the generation of reactive oxygen species (ROS). Linezolid is however unique amongst NLRP3 agonists in that its ability to activate the NLRP3 inflammasome in a ROS-independent manner. The pathways for ROS-dependent and ROS-independent NLRP3 activation converge upon mitochondrial dysfunction and specifically the mitochondrial lipid cardiolipin. We demonstrated that interference with cardiolipin synthesis specifically inhibits NLRP3 inflammasome activation. These findings firstly suggests that ROS generation is not the canonical activator of NLRP3 but rather an intermediary step leading to the mitochondrial perturbation that is tied to NLRP3 inflammasome activation and also implicate the involvement of mitochondrial lipid cardiolipin in this process; secondarily, linezolid-induced NLRP3 activation may account for thetoxicity associated with prolonged usage of this antibiotic.

In der vorliegenden Arbeit wurden neue Untersuchungsmöglichkeiten mit dem BacT/Alert 3D Mykobakterien-Testsystem erprobt. Erstens wurden Untersuchungen durchgeführt, um die Testkonzentrationen für Protionamid (PTH) und Linezolid (LIZ) für die standardmäßige Empfindlichkeitstestung von M. tuberculosis (Mtb) mit dem BacT/Alert 3D-System festzulegen. Dazu wurden die MHK-Werte für 32 Mtb-Stämme bestimmt: Referenzstamm Mtb H37Rv, sensible Patientenstämme, Patientenstämme mit verschiedenen Resistenzen (u. a. PTH-Resistenz) sowie eigens für die Arbeit isolierte LIZ-resistente Mutanten. Die PTH-MHK betrug für 20 von 21 sensiblen Mtb-Stämmen einschließlich des Referenzstammes Mtb H37Rv 0,125 - 1 mg/l (0,25 mg/l bei 11 von 21 Stämmen). Lediglich ein Stamm mit Resistenz gegenüber Isoniazid, Ethambutol und Streptomycin fiel mit einer etwas erhöhten PTH-MHK von 2 mg/l auf. Sechs PTH-resistente Stämme (z. T. mit anderen Resistenzen gegenüber Erstrang-Antituberkulotika) zeigten PTH-MHK von 4 - 16 mg/l. Die Gruppen der PTH-sensiblen und resistenten Stämme zeigten ein bimodales Verteilungsmuster, das mit einem Schwellenwert von 2 mg PTH/l gut zu differenzieren ist. Für die standardmäßige Durchführung der Empfindlichkeitstestung gegenüber PTH mit dem BacT/Alert 3D-System empfehlen wir deshalb eine PTH-Testkonzentration von 2 mg/l. Die LIZ-MHK betrug für 20 sensible Mtb-Stämme (inklusive Referenzstamm Mtb H37Rv) und sieben Stämme mit verschiedenen Resistenzen gegenüber Erstrang-Antituberkulotika 0,25 - 2 mg/l (0,5 mg/l bei 17 von 27 Stämmen). Für die vier isolierten LIZ-resistenten Mutanten betrug die LIZ-MHK 8 - 16 mg/l. Es zeigt sich auch bei der Verteilung der LIZ-MHK ein bimodales Verteilungsmuster; die Gruppen der sensiblen und resistenten Stämme sind gut zu differenzieren. Wir empfehlen für die standardmäßige Durchführung der Empfindlichkeitstestung gegenüber LIZ mit dem BacT/Alert 3D-System eine LIZ-Testkonzentration von 4 mg/l. Die festgestellten MHK-Werte von PTH und LIZ und die vorgeschlagenen Testkonzentrationen entsprechen Ergebnissen aus der Literatur, die mit ähnlichen Methoden erhoben wurden. Zweitens wurden mit dem BacT/Alert 3D-System Untersuchungen zur Kombinationstestung von Antituberkulotika bei Mtb und Stämmen des MAC-Komplexes durchgeführt, bisher liegen keine Publikationen für Untersuchungen von Wirkstoff-Kombinationen bei Mykobakterien mit diesem System vor. Es wurde geprüft, ob die MHK eines Antituberkulotikums durch die Zugabe einer subinhibitorischen Menge eines anderen Antituberkulotikums verändert wird. Bei Mtb wurden dazu folgende Kombinationen geprüft: Rifampicin (RMP) + LIZ, Moxifloxacin + LIZ, Isoniazid + PTH, RMP + PTH, PTH + LIZ. In keinem Fall konnten signifikante Effekte beobachtet werden. Ein tendenziell synergistischer Effekt der PTH-RMP-Kombination beim Stamm Mtb H37Rv (Reduktion der RMP-MHK um eine Stufe) wurde durch die Analyse der Wachstumskinetik des Stammes unterstützt. Bei zufällig ausgewählten Stämmen des MAC-Komplexes wurde die Kombination Ciprofloxacin (CIP) + Ethambutol (EMB) geprüft. Es zeigte sich bei sieben von zehn Stämmen eine Reduzierung der CIP-MHK um mindestens drei Stufen bei Zugabe einer subinhibitorischen Konzentration von EMB. Dieser synergistische Effekt wurde bereits in den 1990er Jahren mit einer ähnlichen Methode festgestellt, allerdings ohne die Stämme des MAC-Komplexes zu differenzieren (Arbeitsgruppe von S. Hoffner). Interessanterweise handelte es sich bei den von uns untersuchten Stämmen, bei denen dieser synergistische Effekt nachgewiesen wurde, um M. avium-Stämme. Diese Problematik sollte weiter verfolgt werden, da sich daraus Konsequenzen für die Therapieempfehlung ergeben könnten.