AUTHOR=Chan Chun L. , Richter Katharina , Wormald Peter-John , Psaltis Alkis J. , Vreugde Sarah 

TITLE=Alloiococcus otitidis Forms Multispecies Biofilm with Haemophilus influenzae: Effects on Antibiotic Susceptibility and Growth in Adverse Conditions

JOURNAL=Frontiers in Cellular and Infection Microbiology

VOLUME=7

YEAR=2017

URL=https://www.frontiersin.org/journals/cellular-and-infection-microbiology/articles/10.3389/fcimb.2017.00344

DOI=10.3389/fcimb.2017.00344

ISSN=2235-2988

ABSTRACT=<p>Otitis media with effusion (OME) is a biofilm driven disease and commonly accepted otopathogens, such as <italic>Haemophilus influenzae, Streptococcus pneumonia, and Moraxella catarrhalis</italic>, have been demonstrated to form polymicrobial biofilms within the middle ear cleft. However, <italic>Alloiococcus otitidis</italic> (<italic>A. otitidis</italic>), which is one of the most commonly found bacteria within middle ear aspirates of children with OME, has not been described to form biofilms. The aim of this study was to investigate whether <italic>A. otitidis</italic> can form biofilms and investigate the impact on antibiotic susceptibility and survivability in polymicrobial biofilms with <italic>H. influenzae in vitro</italic>. The ability of <italic>A. otitidis</italic> to form single-species and polymicrobial biofilms with <italic>H. influenzae</italic> was explored. Clinical and commercial strains of <italic>A. otitidis</italic> and <italic>H. influenzae</italic> were incubated in brain heart infusion with and without supplementation. Biofilm was imaged using confocal laser scanning microscopy and scanning electron microscopy. Quantification of biofilm biomass and viable bacterial number was assessed using crystal violet assays and viable cell counting in both optimal growth conditions and in adverse growth conditions (depleted media and sub-optimal growth temperature). Antimicrobial susceptibility and changes in antibiotic resistance of single-species and multi-species co-culture were assessed using a microdilution method to assess minimal bactericidal concentration and E-test for amoxicillin and ciprofloxacin. <italic>A. otitidis</italic> formed single-species and polymicrobial biofilms with <italic>H. influenzae</italic>. Additionally, whilst strain dependent, combinations of polymicrobial biofilms decreased antimicrobial susceptibility, albeit a small magnitude, in both planktonic and polymicrobial biofilms. Moreover, <italic>A. otitidis</italic> promoted <italic>H. influenzae</italic> survival by increasing biofilm production in depleted media and at suboptimal growth temperature. Our findings suggest that <italic>A. otitidis</italic> may play an indirect pathogenic role in otitis media by altering <italic>H. influenzae</italic> antibiotic susceptibility and enhancing growth under adverse conditions.</p>