pseudomallei , B. mallei , and B. thailandensis infection studies. The black arrows show the locations where bacteria were inoculated into the dorsal abdominal section of the MH cockroach, between the third and the fifth terga from the posterior. Figure 2 B. pseudomallei is virulent for the MH cockroach and T6SS-1 mutants are attenuated. Groups of eight MH cockroaches were challenged by the intra-abdominal

route of infection and MH cockroach deaths were Dactolisib monitored Y-27632 clinical trial for 5 days at 37°C. (A) 101 cfu. (B) 102 cfu. (C) 103 cfu. (D) 104 cfu. (E) 105 cfu. Bp, K96243; Bp Δhcp1, DDS1498A; Bp ΔvgrG1-5’, DDS1503-1A; Bp ΔvgrG1-3’, DDS1503-2A. Figure 2A shows that only one MH cockroach survived for 5 days after challenge with 101 B. pseudomallei K96243 (Bp), demonstrating that the 50% lethal dose (LD50) is <10 bacteria. Similarly, the LD50 for K96243 in the hamster model of infection was <10 bacteria check details [9]. B. pseudomallei Δhcp1 is a derivative of K96243 that lacks the essential tail tube component

of the T6SS-1 structural apparatus (Hcp1) and is highly attenuated in the hamster [9, 26]. B. pseudomallei Δhcp1 was also attenuated in the MH cockroach (Figure 2A-E) and the LD50 was ~ 2 x 102 bacteria on day 5, which was >20 times higher than the K96243 LD50 (Table 1). In addition, a dose response was readily apparent with this strain. As the challenge dose increased from 101 to 105 bacteria, the number and rate of MH cockroach deaths increased accordingly stiripentol (Figure 2A-E). It took a challenge dose of 104 Δhcp1 to kill all eight MH cockroaches, whereas the minimum lethal dose for K96243 was only 102 bacteria (Figure 2). The results demonstrate that B. pseudomallei is highly virulent in MH cockroaches and that T6SS-1 is a critical virulence factor in this insect host. Furthermore, there is a clear correlation between the virulence capacity of B. pseudomallei in the MH cockroach and the hamster (Table 1). Table 1 Relative virulence of bacterial strains in Syrian hamsters and Madagascar hissing cockroaches Bacterial strain Syrian hamster LD50 a Madagascar hissing cockroach LD50 E. coli

MC4100 NDb > 105 B/r ND >105 B. pseudomallei K96243 <10 <10 DDS1498A (Δhcp1) >1000 207 DDS0518A (Δhcp2) <10 <10 DDS2098A (Δhcp3) <10 <10 DDS0171A (Δhcp4) <10 <10 DDS0099A (Δhcp5) <10 <10 DDL3105A (Δhcp6) <10 <10 DDS1503-1A (ΔvgrG1-5’) 102 <10 DDS1503-2A (ΔvgrG1-3’) >450 <10 1026b <10 <10 MSHR305 ND <10 B. mallei SR1 <10 <10 DDA0742 (Δhcp1) >103 >103 B. thailandensis DW503 ND <10 DDII0868 (Δhcp1) ND >103 a LD50, 50% lethal dose [9, 25, 33]; b ND, not determined. B. pseudomallei ΔvgrG1 5’ and ΔvgrG1 3’ are K96243 derivatives that have deletions within the gene encoding the tail spike protein (VgrG1) of the T6SS-1 structural apparatus [9, 26]. These mutants were more virulent than B. pseudomallei Δhcp1 in the hamster model of infection [9], but were less virulent than K96243 (Table 1).

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