Radiation-resistant mutants of Salmonella typhimurium LT2: development and characterization

A series of repeated exposures to gamma irradiation with intervening outgrowth of survivors was used to develop radioresistant cultures of Salmonella typhimuium LT2. Stepwise increases in resistance to both ionizing and ultraviolet irradiation were obtained independently of the presence or absence of integrated P22 prophage. Single clonal isolates, representing parent and radioresistant populations, retained the general characteristics of the LT2 parent, including serological properties, phage typing, antibiotic sensitivities, mouse virulence, and most biochemical test reactions. Resistant cells were generally larger and contained 1.8 to 2.1 times more ribonucleic acid and protein than parent cells, but deoxyribonucleic acid (DNA) contents were similar. Heterogeneity in the populations with respect to release of H(2)S, utilization of carbon sources, and growth on minimal medium is considered to be ancillary, rather than causally related, to increased radioresistance. The resistant isolates displayed an increased ability to reactivate gamma-irradiated P22 phage. DNA polymerase I and polynucleotide-joining enzyme activities were elevated in extracts of radioresistant cells relative to parent cells. It is suggested that the observed increases in radioresistance result from a selection of mutations leading to an increased capacity to repair DNA.

Recurring spontaneous pneumothorax concomitant with menstruation

Details are given of nine cases of recurrent spontaneous pneumothorax concomitant with menstruation; of these, four are culled from the literature. In every case the time interval between the onset of menstruation and the development of a pneumothorax has been very close, and from the evidence presented some causal relationship is envisaged. Endometriosis is considered as a possible cause. Two of the patients had proven endometriosis of the diaphragm and this condition was almost certainly present in a third patient. Three patients had pelvic endometriosis. The pneumothorax always occurred on the right side, and the possible significance of this is discussed.