The effect of Lactobacillus acidophilus on the clearance of pneumococcus pathogen from mice lung

In the present study, we investigate the preventive effect of intraperitoneal inoculation of Lactobacillus acidophilus against intranasally challenge with Streptococcus pneumonia using a mouse experimental model.Five days before challenge with Capsulated S. pneumonia the treated group injected intraperitoneally with 0.5 ml of heat –killed Lactobacillus acidophilus, while the positive control group injected with 0.5 ml of phosphate buffer saline. Mice were infected by dropping 25 μl of the inoculums containing 108 log- phase colony forming unit S.pneumonia in PBS into each nostril and allowing it to be inhaled by holding the mice in head-up vertical positionfor 2 min . Animals were sacrificed by cervical dislocation on day 1st, 2ed and 3rd day of infections.The study showed that numbers of pneumococcal pathogen that recovered from lungs of positive control mice was increased from the first day of infection (Log 5.7±1.19) and the increasing rate continued in the next 2 days (Log 6.9±1.06 at 3rd day).In contrast the animal treated with L. acidophilus showed greater resistance to pneumococcal challenge, as their pathogen count in lung was significantly lower than those in positive control at same intervals (on day one was Log 2.5±0.65 to end as Log2±0.43 at third day), likewise the log mean number of bacteria found in blood stream of untreated animal increased steadily over the 3 days of the experiments starting with Log 3.3 ± 0.94 to Log 4.96 ± 0.7 at the last day, while the treated mice showed significant low level of Bacteremia gradually reaching to Log 0.5 ± 0.1 at the last, also the challenge with S. pneumonia increased the number of blood leukocytes in both experimental group of our study, but the pretreated mice with L. acidophilus present a significant higher value than positive control group. Also, the neutrophils were the principlecell population responsible for the increasing leukocyte of both study groups, followed by lymphocytes cells.These results showed that administration of intraperitoneal L. acidophilus may increases the clearance rate of S. pneumoniae from lung and prevent the dissemination of pneumococci into blood and that may due to activation of immune system by increasing the total count and efficacy of leukocytes especially neutrophils and lymphocytes