VIII CONGRESO ARGENTINO DE MICROBIOLOGIA GENERAL -SAMIGE-

ZURITA, MARIA EUGENIA; ERREA, AGUSTINA; MORENO, GRISELDA; ORMAZABAL, MAXIMILIANO; RUMBO, MARTIN; HOZBOR, DANIELA

Congreso; VIII CONGRESO ARGENTINO DE MICROBIOLOGIA GENERAL -SAMIGE-; 2012

We have recently demonstrated the presence of the event known as stimulated innate resistance (STIR) in Bordetella pertussis infections. STIR consists in a non-specific enhancement of the airways innate response that abrogates diverse lung infections such as influenza A, Streptococcus pneumoniae, and Aspergillus niger. Specifically in B. pertussis infection, we observed that the enhancement of innate response activation, in a TLR4-dependent way, could efficiently impair B. pertussis colonization (P < 0.001). In fact, our previous results indicate that during the early stage of infection, specific anti-microbial mechanisms triggered by TLR4 stimulation are able to impair B. pertussis colonization. This scenario where B. pertussis is quickly removed from the lungs of the infected host allows the investigation of the mechanisms by which it is possible to prevent the progression of B. pertussis infection. Here we first analyzed the kinetics of LPS action in vivo using the mice infection model. To this end Balb/c mice were inoculated intranasally with purified LPS (1 µg) and at different times post treatment, mice were infected with a subletal dosis of B. pertussis (5x107 CFU). The time between inoculation of LPS and challenge with B. pertussis tested, were 24 and 48 h. We also evaluated both the effect of LPS inoculation after B. pertussis infection (24 and 48 h after infection) and the co-administration of LPS plus B. pertussis. After all these treatments we analyzed the number of recovered bacteria from the lungs of the infected mice. To this aim, mice were killed by cervical dislocation at the indicated times and the lungs were removed and homogenized in 1 ml of sterile PBS. Appropriate dilutions were plated on Bordet -Gengou blood agar plates and counted after 4 days of incubation at 37ºC to determine CFU per lung. No bacteria were recovered from lungs of any of the treated mice. Based on these results and for practical reasons, coadministration of LPS with B. pertussis inoculum was selected for the following assays. Under this condition, kinetics of B. pertussis clearance was analyzed at early times, specifically at 2, 6 and 24 h post treatment. Interestingly we found that even at times as short as 2 h, no viable bacteria were recovered from the lungs of LPS treated animals. In contrast, in control animals inoculated only with B. pertussis we recovered 106 CFU / lung. This timing suggests that the STIR event should be mediated by fast-acting  antimicrobial mechanisms. In order to evaluate the possible role of free radicals in the STIR, we co-administered intranasally N-acetyl cysteine (NAC), an antioxidant used therapeutically in inflammatory lung diseases, plus LPS and B. pertussis. The results obtained showed that NAC blocked at least in part the LPS action. These preliminary results seem to indicate that free radicals are involved in B. pertussis clearance by LPS administration.