Microbial biofilms are a serious threat to human health. Recent studies have indicated that many clinically relevant biofilms are polymicrobial. In the present study, multispecies biofilms were grown in a reproducible manner in a 96-well microtiter plate. The efficacy of nine commercially available disinfectants against Staphylococcus aureus, Candida albicans, and Pseudomonas aeruginosa in multispecies biofilms was determined and compared. The results showed that the direction and the magnitude of the effect in a multispecies biofilm depend on the strain and the disinfectant used and challenge the common belief that organisms in multispecies biofilms are always less susceptible than in monospecies biofilms.

Multispecies biofilms are an important healthcare problem and may lead to persistent infections. These infections are difficult to treat, as cells in a biofilm are highly resistant to antimicrobial agents. While increasingly being recognized as important, the properties of multispecies biofilms remain poorly studied. In order to do so, the quantification of the individual species is needed. The current cultivation-based approaches can lead to an underestimation of the actual cell number and are time-consuming. In the present study we set up a culture-independent approach based on propidium monoazide qPCR (PMA-qPCR) to quantify Pseudomonas aeruginosa in a multispecies biofilm. As a proof of concept, we explored the influence of the combined presence of Staphylococcus aureus, Streptococcus anginosus and Burkholderia cenocepacia on the antimicrobial susceptibility of P. aeruginosa using this PMA-qPCR approach.

The lungs of patients with cystic fibrosis (CF) are colonised by a microbial community comprised of pathogenic species, such as Pseudomonas aeruginosa and Staphylococcus aureus, and microorganisms that are typically not associated with worse clinical outcomes (considered as commensals). Antibiotics directed at CF pathogens are often not effective and a discrepancy is observed between activity of these agents in vitro and in the patient. This review describes how interspecies interactions within the lung microbiome might influence the outcome of antibiotic treatment targeted at common CF pathogens. Protective mechanisms by members of the microbiome such as antibiotic degradation (indirect pathogenicity), alterations of the cell wall, production of matrix components decreasing antibiotic penetration, and changes in metabolism are discussed. Interspecies interactions that increase bacterial susceptibility are also addressed. Furthermore, we discuss how experimental conditions, such as culture media, oxygen levels, incorporation of host–pathogen interactions, and microbial community composition may influence the outcome of microbial interaction studies related to antibiotic activity. Hereby, the importance to create in vitro conditions reflective of the CF lung microenvironment is highlighted. Understanding the role of the CF lung microbiome in antibiotic efficacy may help find novel therapeutic and diagnostic approaches to better tackle chronic lung infections in this patient population.

In young cystic fibrosis (CF) patients, is typically the most prevalent organism, while in adults, is the major pathogen. More recently, it was observed that also plays an important role in exacerbations of respiratory symptoms. These species are often coisolated from CF lungs, yet little is known about whether antibiotic killing of one species is influenced by the presence of others. In the present study, we compared the activities of various antibiotics against, , and when grown in monospecies biofilms with the activity observed in a multispecies biofilm. Our results show that differences in antibiotic activity against species grown in mono- and multispecies biofilms are species and antibiotic dependent. Fewer cells are killed by antibiotics that interfere with cell wall synthesis (amoxicillin plus sulbactam, cefepime, imipenem, meropenem, and vancomycin) in the presence of and , while for ciprofloxacin, levofloxacin, and tobramycin, no difference was observed. In addition, we observed that the cell-free supernatant of, but not that of biofilms, also caused this decrease in killing. Overall, was more affected by antibiotic treatment in a multispecies biofilm, while for , no differences were observed between growth in mono- or multispecies biofilms. The results of the present study suggest that it is important to take the community composition into account when evaluating the effect of antimicrobial treatments against certain species in mixed biofilms.

Growth in multispecies biofilms can have an impact on the expression of genes related to cell wall synthesis and on the cell wall thickness of S. anginosus.