Skip to main page content
Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
, 185 (10), 3111-7

Swarm-cell Differentiation in Salmonella Enterica Serovar Typhimurium Results in Elevated Resistance to Multiple Antibiotics

Affiliations

Swarm-cell Differentiation in Salmonella Enterica Serovar Typhimurium Results in Elevated Resistance to Multiple Antibiotics

Wook Kim et al. J Bacteriol.

Abstract

Although a wealth of knowledge exists about the molecular and biochemical mechanisms governing the swimming motility of Salmonella enterica serovar Typhimurium, its surface swarming behavior has not been extensively characterized. When inoculated onto a semisolid agar medium supplemented with appropriate nutrients, serovar Typhimurium undergoes a morphological differentiation whereby single cells hyperflagellate and elongate into nonseptate, multinucleate swarm cells. Swarm migration is a collective behavior of groups of cells. We have isolated a MudJ insertion mutant of serovar Typhimurium 14028 that failed to swarm under any conditions. The site of the MudJ insertion was determined to be in the pmrK locus within the pmrHFIJKLM operon, which was previously demonstrated to confer resistance to cationic antimicrobial peptides. beta-Galactosidase assays, using the pmrK::lacZ transcriptional fusion, showed increased expression of the pmr operon in swarm cells compared to that in vegetative cells. In concurrence with the expression data, swarm cells exhibited greater tolerance to polymyxin. To compare the profiles of vegetative and swarm-cell resistance to other antibiotics, E-test strips representing a wide range of antibiotic classes were used. Swarm cells exhibited elevated resistance to a variety of antibiotics, including those that target the cell envelope, protein translation, DNA replication, and transcription. These observations, in addition to the dramatic morphological changes associated with the swarming phenotype, provide an intriguing model for examining global differences between the physiological states of vegetative and swarm cells of serovar Typhimurium.

Figures

FIG. 1.
FIG. 1.
Characterization of swarm mutants of serovar Typhimurium 14028. (A) Schematic representation of MudJ insertion sites in swarm mutants CS031 and CS004. Δ indicates an insertion site, and the arrow represents the orientation of the lacZ fusion. (B) Comparison of swarming and swimming motility between wild-type and mutant strains. Strain 7953s is a phoPQ::Tn10 mutant of serovar Typhimurium LT2. All strains were inoculated onto swarm and swim plates and incubated at 37°C for 5 h.
FIG. 2.
FIG. 2.
Transcriptional analysis of pmrK in serovar Typhimurium CS031 grown in various agar concentrations. β-Galactosidase assays of cells in the vegetative state (swim and solid) and cells grown under conditions that promote swarm-cell differentiation were performed. All cells were grown in NB with 0.5% glucose supplemented with agar at the concentrations indicated.
FIG. 3.
FIG. 3.
E-test strip comparison of polymyxin resistance of strain 14028 in the vegetative and swarm states. Cells were plated on NB containing either 0.25 or 1.5% agar (vegetative cells) or 0.5% agar (swarm cells). In addition, cells were also spread plated on LB plates containing 0.5% agar because this growth condition does not promote swarming.
FIG. 4.
FIG. 4.
Representative E-test strip analyses of vegetative and swarm cells of strain 14028. Swarm cells exhibit either no difference (imipenem) or elevated resistance (ciprofloxacin, tobramycin, and nalidixic acid) compared to vegetative cells (solid and swim). Note the formation of a secondary swarm front in response to ciprofloxacin. All of the E-test strip results obtained are summarized in Table 1.

Similar articles

See all similar articles

Cited by 51 PubMed Central articles

See all "Cited by" articles

Publication types

MeSH terms

LinkOut - more resources

Feedback