Effect of RpoN, RpoS and LuxS pathways on the biofilm formation and antibiotIc sensitivity of Borrelia burgdorferi

Abstract

Borrelia burgdorferi, the causative agent of Lyme disease, is capable of forming biofilm in vivo and in vitro, a structure well known for its resistance to antimicrobial agents. For the formation of biofilm, signaling processes are required to communicate with the surrounding environment such as it was shown for the RpoN–RpoS alternative sigma factor and for the LuxS quorum-sensing pathways. Therefore, in this study, the wild-type B. burgdorferi and different mutant strains lacking RpoN, RpoS, and LuxS genes were studied for their growth characteristic and development of biofilm structures and markers as well as for their antibiotic sensitivity. Our results showed that all three mutants formed small, loosely formed aggregates, which expressed previously identified Borrelia biofilm markers such as alginate, extracellular DNA, and calcium. All three mutants had significantly different sensitivity to doxycyline in the early log phase spirochete cultures; however, in the biofilm rich stationary cultures, only LuxS mutant showed increased sensitivity to doxycyline compared to the wild-type strain. Our findings indicate that all three mutants have some effect on Borrelia biofilm, but the most dramatic effect was found with LuxS mutant, suggesting that the quorum-sensing pathway plays an important role of Borrelia biofilm formation and antibiotic sensitivity.

Lyme Disease Frontiers: Reconciling Borrelia Biology and Clinical Conundrums

“…Moreover, drug responses of stationary phase ∆rel Bbu Bb have not yet been tested, so it remains unclear whether the relationship between the stringent response and Borrelia antibiotic tolerance is causal or correlational. Meanwhile, there is some indication that eliminating LuxS, the enzyme responsible for biosynthesis of the quorum sensing autoinducer, impacts both borrelial viability and aggregate structures of stationary phase cultures treated with sub-MBC concentrations of doxycycline [271]. Ultimately, clarity is required around the contributions of these and other environmental response networks to Borrelia pathophysiology and persistence.…”

Antimicrobial Activity of Bee Venom and Melittin against Borrelia burgdorferi

“…In the past several years, a novel aggregate form, called biofilm, was found for Borrelia and was shown to be very antimicrobial resistant vitro and in vivo especially in attached forms [ 6 , 22 , 25 , 26 , 33 ]. Therefore, in subsequent experiments we tested all antimicrobials for effectiveness in eliminating the attached biofilm form.…”

“…Based on findings from different techniques, we concluded that both whole bee venom and melittin could have significant effects on all Borrelia morphological forms including inhibiting the recovery of spirochetal cells and persisters as evidenced by recovery cultures in antimicrobial free media. Whole bee venom and melittin also significantly reduced the number and/or viability of attached biofilms, which based on previous research, is the most antibiotic resistant form of B. burgdorferi [ 6 , 25 , 26 ]. The MIC concentration values for melittin, for example, were in good agreement with previous studies that evaluated melittin on Borrelia spirochetes [ 29 ] and on several other gram-negative microorganisms such as S. enterica and Y. kristensenii [ 30 ].…”

“…These defensive forms were reported to have high resistance to the antimicrobials agents that are currently used to treat Lyme disease (7, 21, 22). For example, while Doxycycline is very effective eliminating spirochetes in vitro, it did not reduce antibiotic resilient persisters and/or biofilms [ 6 , 7 , 22 , 25 ]. Furthermore, it was demonstrated that none of the antibiotics currently used to treat Lyme disease effective against the “persister” and attached biofilm forms of Borrelia [ 7 , 8 , 9 , 10 , 22 , 25 , 26 ].…”

“…For example, while Doxycycline is very effective eliminating spirochetes in vitro, it did not reduce antibiotic resilient persisters and/or biofilms [ 6 , 7 , 22 , 25 ]. Furthermore, it was demonstrated that none of the antibiotics currently used to treat Lyme disease effective against the “persister” and attached biofilm forms of Borrelia [ 7 , 8 , 9 , 10 , 22 , 25 , 26 ]. It was also reported that several antibiotics (Cefoperazone, Daptomycin) might have potential in effectively eliminating Borrelia persisters especially when in combination with Doxycycline [ 8 , 10 ].…”