Antimycobacterial activity of cyclic dipeptides isolated from Bacillus sp. N strain associated with entomopathogenic nematode

Figures & data

Table 1. List of diketopiperazines used in this study.

S. No.	Compounds	Antimicrobial classes	Targets	Structures
1.	Cyclo-(l-Pro-l-Leu)	Cyclic dipeptide	Unknown
2.	Cyclo-(d-Pro-l-Leu)	Cyclic dipeptide	Unknown
3.	Cyclo-(d-Pro-l-Tyr)	Cyclic dipeptide	Unknown
4.	Cyclo-(l-Pro-l-Tyr)	Cyclic dipeptide	Unknown
5.	Cyclo-(l-Pro-l-Met)	Cyclic dipeptide	Unknown
6.	Cyclo-(d-Pro-l-Phe)	Cyclic dipeptide	Unknown

Table 2. Antimycobacterial activity of diketopiperazines.

Test compound and antibiotics	MIC (µg/ml)	MBC (µg/ml)	Zone of inhibition (Dia. in mm)
Cyclo-(l-Pro-l-Leu)	–	–	–
Cyclo-(d-Pro-l-Leu)	8	16	14
Cyclo-(d-Pro-l-Tyr)	–	–	–
Cyclo-(l-Pro-l-Tyr)	–	–	–
Cyclo-(l-Pro-l-Met)	4	4	21
Cyclo-(d-Pro-l-Phe)	16	32	16
Rifampicin	0.06	0.06	27

–: No activity.

Figure 1. Growth of M. tuberculosis in Middlebrook 7H9 broth supplemented with the three active cyclic dipeptides or rifampicin at their MIC concentration.

Figure 2. Time-kill curves of diketopiperazines against M. tuberculosis. CFU: colony-forming unit. [A] cyclo-(d-Pro-l-Leu), [B] cyclo-(l-Pro-l-Met) and [C] cyclo-(d-Pro-l-Phe). 1×, 2× and 4× are the 1-fold, 2-fold and 4-fold MIC concentration of compounds, respectively.