Although QS-deficiency is a
common feature amongst P. aeruginosa CF isolates [16, 52, 53], QS regulates a number of factors of relevance to CF, including pyocyanin and LasA production . Our previous studies suggested that LES populations in CF comprise a mixture of QS-positive and QS-deficient bacteria [7, 9, 54], which is what we have observed in this study in ASM. The QS-deficient populations could benefit at the cost of QS-positive populations. MK5108 manufacturer The main phenotypic variations involved changes in colony morphology, pyocyanin production and antimicrobial susceptibilities. A high diversity in the antimicrobial susceptibility profiles of CF isolates within adult sputum OSI-027 in vivo samples has been demonstrated previously , BTSA1 in vivo highlighting the limitations of performing antimicrobial susceptibility tests on a single isolate from a CF patient sputum sample.
It was also shown that using one antibiotic could lead to enhanced resistance to a different, unrelated antibiotic . A similar pattern was observed in this study, when exposure to one antibiotic altered the antibiotic susceptibility profiles to unrelated antibiotics. In particular, exposure to azithromycin, tobramycin or ceftazidime led to an increase in resistance to tazobactam/piperacillin. This could have serious clinical consequences for the CF patient, in terms of the generation of antimicrobial resistant P. aeruginosa populations, because CF patients are regularly exposed to a number of different antibiotics. In our study, the presence of meropenem had a weaker effect on diversification compared to the other antibiotics, despite having a similar mechanism of action to ceftazidime. However, it is possible that cell death was occurring in these populations, Protein kinase N1 since the numbers of cells obtained following culture were generally lower. This is despite the meropenem concentration in ASM being 8-fold less than the minimum inhibitory concentration of this antibiotic. Therefore, the apparent reduction in diversity could be attributed to the populations
exhibiting cell death. This suggests that there may be a clinical advantage to using some antibiotics (eg. meropenem) rather than others. It would also be interesting to analyse combinations of two antibiotics, since it is often the case that dual therapy is used clinically. The identification of individual mutations within the LESB58 populations to explain the changes in individual phenotypic traits would have been beyond the scope of this work. Conclusions This study suggests that the exposure to sub-inhibitory concentrations of certain antibiotics can drive phenotypic diversification of P. aeruginosa populations in the ASM model. This may help to explain the observed diversification of P. aeruginosa in natural CF lung infections, although other factors such as the host immune response, other members of the microflora, or bacteriophages may also contribute. Understanding P.