Three different find more inoculum doses (105, 106 and 107 CFU/ml) of S. aureus 43300 were selected for establishing the organism in the nares of BALB/c mice. The inoculum of 105 CFU/ml showed persistence of the organism in the nares only till day 5 post selleck chemical colonisation and the organism was cleared thereafter. At an inoculum dose of 106 and 107 CFU/ml, S. aureus 43300 persisted well till day 10 post colonisation with a load of 3.98 log CFU/ml (106 CFU/ml)

and 4.08 log CFU/ml (107 CFU/ml) respectively and no counts observed on day 15 post colonisation. Since not much difference in the bacterial load of S. aureus 43300 in nares was observed with either of the two inoculum doses, hence 106 CFU/ml was selected for establishing the nasal colonisation with S. aureus 43300 (Data depicting the nasal counts at all

three different doses is shown in Additional file 1: Table S3). Bacterial load and phage titer The nasal load of S. aureus 43300 on different days post treatment is presented in Figure 3A. Mice administered with phage twice (group 2) showed PF-6463922 ic50 significant reduction (p < 0.01) of 2.8 log-cycles in bacterial counts on day 2 itself. This was followed by further decrease in counts with 3.67 log CFU/g obtained on day 5 and minimal load of 1.14 log CFU/g seen on day 7. The nares became completely sterile as no growth of S. aureus 43300 was observed beyond day 7. Similarly, mupirocin given once (group 3) also showed significant reduction of ~2log cycles in comparison to control (group 1) on day 2. On day 7, minimal bacterial count of 2.21 log CFU/g was obtained after which there was complete clearance of S. aureus (Figure 3A). Figure 3 Bacterial burden in terms of A) Mean log CFU/gram of mice tissue of S. aureus 43300

following treatment of colonised nares with IMP dehydrogenase different anti-bacterial agents on different days post treatment; Phage counts in terms of B) Mean log PFU/g count in the anterior nares of mice belonging to group 2 and group 4 on various days post phage treatment. Error bars represent the standard deviation. The group receiving combined therapy (group 4) showed maximum reduction in bacterial load in the anterior nares with complete clearance of MRSA 43300 by day 5 itself The bacterial load was significantly reduced (p < 0.05) to 5.17 log CFU/g (~3 log-cycles) on day 2 and this decrease continued till day 3. By day 5, S. aureus 43300 was completely eradicated from the nasal tissue of BALB/c mice. The combined treatment option gave maximum protection against nasal colonisation by S. aureus 43300. The animals receiving 2 doses of phage (107 PFU/ml at an interval of 24 hours) showed a peak phage titre of 5.74 log PFU/g on day 2 (Figure 3B). Despite giving two doses of phage (107 PFU/ml), only 105 PFU/ml was present by day 2. A minimal phage titre (2.2 log PFU/g) was seen on day 7 with no plaques visible thereafter.