TABLE 2.
Resuscitation of stationary phase cultures of M. tuberculosis rpf deletion mutants after maintenance in shaking sealed tubes for 3.5 monthsa
| Strain | CFU per ml | MPN per mlb
|
||
|---|---|---|---|---|
| MPN | 95% Confidence limits
|
|||
| Lower | Higher | |||
| H37Rv | <5 | 5.4 × 105 | 1.5 × 105 | 1.7 × 106 |
| ΔrpfB | <5 | 5.4 × 105 | 1.5 × 105 | 1.7 × 106 |
| KDT8 (ΔrpfA ΔrpfC ΔrpfB) | <5 | <103* | 6.8 × 103 | |
| KDT9 (ΔrpfA ΔrpfC ΔrpfD) | <5 | <103* | 6.8 × 103 | |
The starting cell density of all cultures was ∼104 CFU/ml (OD600 < 0.1). After 9 days of incubation, the cultures reached a density of 108 CFU/ml (OD600 ≈2.0). After 24 days, the CFU values had dropped to 2×106 CFU/ml (OD600 ≈0.2) and, after 100 days, were <5 CFU/ml (OD600 ≈0.2).
Where small aggregates were observed after the 3.5-month oxygen starvation period, the aggregates did not contain more than four cells (determined by microscopy). However, a significant difference in CFU versus MPN would not be expected to arise were there significant aggregation, since one aggregate represents one propagule when introduced onto solid medium (CFU) or into liquid medium (MPN). Aggregation might cause some slight underestimation of both CFU and MPN compared with the total count (by microscopy) but would not affect the ratio of MPN to CFU. *, Significantly different from the wild type at a P of <0.001.