Growth suppression in early-stationary-phase nutrient broth cultures of Salmonella typhimurium and Escherichia coli is genus specific and not regulated by sigma S

Abstract

We have studied the growth suppression seen in early-stationary-phase LB broth cultures of Salmonella typhimurium. Multiplication of small numbers of an antibiotic-resistant S. typhimurium mutant was prevented when the mutant was added to 24-h cultures of the antibiotic-sensitive parent strain, whereas an antibioticresistant mutant of an Escherichia coli strain added to the same culture grew well. A 24-h E. coli culture produced a similar specific bacteriostatic inhibition against E. coli. In older cultures, a specific bactericidal effect similar to that observed by M. M. Zambrano and R. Kolter (J. Bacteriol. 175:5642-5647, 1993) was also observed. Whether incubated statically or shaken, sufficient nutrients were present in the filtered supernatants of 24-h cultures for small inocula of the same strain to multiply to ca. 10 9 CFU/ml after reincubation. Introduction of the rpoS mutation had no effect on the specific bacteriostatic inhibition. Similar specific inhibition was also observed in strains of Citrobacter freundii, Klebsiella pneumoniae, Enterobacter agglomerans, and Shigella spp. Experiments in which the 24-h culture was physically separated from the antibiotic-resistant mutant by using a dialysis membrane were carried out. These results indicated that the inhibition might be mediated by a diffusible but labile chemical mediator.The observed reduction in the rate of bacterial multiplication in broth cultures toward the end of logarithmic phase has been well documented in standard bacteriology texts for many years (8,29), and at least some of the factors that cause it are understood.A combination of composition of the growth medium and particular organisms may induce conditions which are inimical to bacterial multiplication and might even be bactericidal. The low pH that results from the fermentation of carbohydrates by different bacterial groups and the production of inhibitory concentrations of hydrogen peroxide by Streptococcus pneumoniae are well-known examples (29).Limitation of nutrient concentrations is another factor that can induce a cessation of growth rate. Carbon starvation is accompanied by the induction of at least 50 bacterial proteins (12,18,19) and a generalized resistance to other harmful agents such as heat shock and hydrogen peroxide (16). This type of nongrowing, stationary-phase behavior is a result of the starvation conditions to which the cells are subjected. This regulon (9) is complex, and the production of different starvation-induced proteins is regulated by cyclic AMP (23), oxidative stresses (16), osmotic shock (15), and the sigma factor s (RpoS, KatF) (7,17,20). It is, however, unclear whether the conditions that induce these changes are equivalent or similar to those present in early stationary phase in broth cultures, in which nutrient limitation might not always be a major problem.The factors responsible for growth suppression in stationaryphase nutrient broth cultures have been of interest for a long time and were studied in the early decades of this century (for review ...

Influence of genes encoding proton-translocating enzymes on suppression of Salmonella typhimurium growth and colonization

“…However, the F 0 F 1 proton-translocating ATPase plays a significant role under both aerobic and anaerobic conditions, which could explain why stationary-phase cultures of the unc mutant did not suppress growth. The data support the hypothesis that growth suppression in vitro operates due to the absence of a utilizable carbon source or available electron acceptor, in contrast to previous suppositions (6). The cytochrome d oxidase complex is required under conditions of low oxygen tension (12), as probably occurs in the 24-h-old cultures described here.…”

“…Attempts are currently under way to elucidate the mechanisms responsible for this effect. An analogous phenomenon in vitro has been observed with 24-h-old stationaryphase nutrient broth cultures of S. typhimurium (6,8,11). When such cultures are inoculated with small numbers of genetically tagged (antibiotic resistant) but otherwise identical derivatives, the growth of the inoculum is suppressed.…”

“…This type of growth suppression is also genus specific. For example, cultures of S. typhimurium cells do not suppress the growth of Escherichia coli or other genera and vice versa (6,8). We have identified different mutations that affect the ability of an avian strain of S. typhimurium, F98, to suppress growth in vitro and affect colonization inhibition in vivo.…”

“…These resistance determinants do not affect growth suppression or colonization inhibition (8,10,11). Using the rationale that bacterial surface functions were likely to be involved in interaction with the environment, a total of 450 independent TnphoA (19) mutants, which were produced as described previously (11) and showed alkaline phosphatase activity, were screened with the in vitro growth suppression assay (6,8). Two mutants (LB145 and GM129) were identified that, as 24-h-old cultures, did not suppress the growth of an S. typhimurium F98 Spc r inoculum.…”

Characterization of an autostimulatory substance produced by Escherichia coli

“…Induction of certain E. coli genes by the addition of supernatant has been described (Baca-DeLancey et al, 1999 ;Li et al, 1997), and growthinhibiting effects of supernatants have been reported in E. coli and other organisms (Barrow et al, 1996 ;Gray et al, 1996 ;Srinivasan et al, 1998). So far, however, the substances involved in these processes have not been identified.…”