Modification of Dienes Mutual Inhibition Test for Epidemiological Characterization of Pseudomonas aeruginosa Isolates

Abstract

Pseudomonas aeruginosa is an important cause of community-associated and nosocomial infections related to exposure to aqueous environments. Such infections often occur in the setting of a common-source outbreak, in which case epidemiological characterization of isolates may be necessary. In this preliminary study, a modification of the Dienes mutual inhibition test, ordinarily used to assess the relatedness of swarming Proteus mirabilis strains, was used to study 15 P. aeruginosa isolates, with the results compared to those obtained by ribotype analysis. Complete concordance was noted between the results of the Dienes test and those of ribotyping. These observations suggest that further studies are warranted to assess the utility of the modified Dienes test as a simple, inexpensive, and reliable means for epidemiological typing of P. aeruginosa.Pseudomonas aeruginosa is a ubiquitous gram-negative bacillus that is often found in moist environments (6). Community-associated P. aeruginosa infections may occur as a consequence of exposure to the organism in hot tubs, whirlpools, water slides, or swimming pools (8) or by use of contaminated sponges (2, 11). Keratitis due to P. aeruginosa may occur in individuals who store contact lenses in tap water and/or contaminated contact lens solutions (4). Intravenous drug users may develop endocarditis and osteomyelitis as a result of injection of contaminated injectables (9).P. aeruginosa is also of nosocomial significance. The organism has been isolated from a variety of solutions including soaps, ointments, irrigation and dialysis fluids, eyedrops, and disinfectants, as well as from fomites such as showerheads, respiratory therapy equipment, sinks, and baths (12). Populations at risk for significant morbidity and mortality include intubated patients in intensive care units (17), patients on chronic ambulatory peritoneal dialysis (1), and burn patients (13).Epidemiological investigations of P. aeruginosa infection have used molecular typing methods (10), as well as tools such as biotyping, phage typing, bacteriocin typing, and serotyping (7). The Dienes mutual inhibition test has been used as an epidemiological tool to characterize isolates of Proteus mirabilis (15,18,19,20). In this test, if two different P. mirabilis colonies growing on an agar plate are genetically dissimilar, a clear line of demarcation forms at the point of intersection of swarming growth; conversely, if two isolates are identical or highly similar, the swarming edges merge without a conspicuous line of demarcation (3,18,19). Colonies of P. aeruginosa usually have a spreading morphology on agar media (8) and have the capability of adhering to central venous catheters (CVCs), including those impregnated with minocycline and rifampin (E. L. Munson et al., unpublished data). In this preliminary report, we propose a modified Dienes test for the epidemiological characterization of P. aeruginosa isolates.Ten clinical isolates of P. aeruginosa, previously identified by the Vitek GNIϩ card (bioMérieux, Marcy l...

Positively Frequency-Dependent Interference Competition Maintains Diversity and Pervades a Natural Population of Cooperative Microbes

“…Cells that migrate into territory numerically dominated by a distinct social type will suffer the PFD disadvantage of being rare. Together, then, as shown in Figure 3, colony-merger incompatibilities [43,49,50] and PFD acting against inter-group migration can promote the maintenance of structured diversity by benefiting genotypes that would be severely inferior if local migration were unlimited and genotype frequencies were spatially homogenized. Also, although all of the strains examined here are highly proficient at development in clonal groups [39,43], PFD antagonisms may also function together with colony-merger incompatibilities to limit the spread of socially defective cheaters across kin groups and thus increase equilibrium levels of withingroup cooperation [51].…”

Multicellular Bacteria Deploy the Type VI Secretion System to Preemptively Strike Neighboring Cells

“…[33], [34], [35]. However, this phenomenon, known as colony incompatibility, is thought to be due to bacteriophages, bacteriocins, or through production and excretion of antibiotics [33], [34].…”

Rapid and widespread de novo evolution of kin discrimination

“…This phenomenon was first documented in 1946 with the observation of "Dienes lines" that formed between distinct nonmerging colonies of the bacterium Proteus mirabilis (21) and has since been found in several other species (20,22). For example, a large number of such colonymerger incompatibilities evolved among closely related genotypes of the cooperative bacterium Myxococcus xanthus in a natural centimeter-scale population (20).…”