Summary
In this study 80 clinical isolates ofHaemophilus influenzae type b from 60 patients were used to analyze if heterogeneous populations of ampicillin resistant and sensitive cells were simultaneously present within each strain and to determine how common this phenomenon was among clinical isolates. A total of 50 ampicillin sensitive clinical isolates were screened for resistance to this antibiotic. It was observed that 32 ampicillin sensitive strains did not contain resistant subpopulations. Furthermore, even with the inducement of resistant subgroups to proliferate under antibiotic-mediated selection using maximum subinhibitory concentrations of ampicillin, no subpopulations of resistant cells were discovered among 18 additional strains. In order to determine whether ampicillin resistance was stable in β-lactamase-producingH. influenzae clinical isolates, 20 strains from 16 patients were examined. No tendency to segregate into a heterogeneous population of sensitive and resistant clones was found. Furthermore, ampicillin resistance was still uniformly expressed after the treatment of ten strains with the curing agent acridine orange. These results suggest that after extensive evaluation no heterogeneous populations existed with ampicillin resistant and sensitiveH. influenzae clinical isolates, indicating that this phenomenon is not a prevalent one.
Zusammenfassung
In der vorliegenden Studie wurden 80 klinische Isolate vonHaemophilus influenzae Typ b von 60 Patienten untersucht, um festzustellen, ob im selben Stamm heterogene Populationen von ampicillinresistenten und ampicillinempfindlichen Zellen vorhanden sind und wie häufig dieses Phänomen in klinischen Isolaten ist. Insgesamt wurden 50 ampicillinempfindliche Isolate auf eine Resistenz gegen dieses Antibiotikum untersucht. Unter 32 ampicillinempfindlichen Isolaten fanden sich keine resistenten Subpopulationen. Selbst mit Methoden zur Induktion resistenter Subpopulationen durch Antibiotika-vermittelte Selektion unter Verwendung maximaler subinhibitorischer Konzentrationen von Ampicillin wurden in 18 weiteren Stämmen keine Subpopulationen von resistenten Zellen entdeckt. 20 Stämme von 16 Patienten wurden untersucht, um festzustellen, ob in klinischen Isolaten von β-Lactamase bildendenH. influenzae eine stabile Ampicillinresistenz bestand. Eine Tendenz zur Segregation in eine heterogene Population empfindlicher und resistenter Stämme konnte nicht festgestellt werden. Nach Behandlung von zehn Stämmen mit Akridinorange wurde weiterhin gleichförmig Ampicillinresistenz exprimiert. Da umfassende Untersuchungen keine heterogenen Populationen ampicillinresistenter und ampicillinempfindlicher Zellen in klinischen Isolaten vonH. influenzae aufdeckten, ist anzunehmen, daß dieses Phänomen nicht vorrangig ist.
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La Scolea, L.J., Muller, E. Characterization of clinical isolates of haemophilus influenzae type b for heterogeneous populations of susceptibility to ampicillin. Infection 13, 73–77 (1985). https://doi.org/10.1007/BF01660418
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DOI: https://doi.org/10.1007/BF01660418