High-level resistance to mecillinam produced by inactivation of soluble lytic transglycosylase in Salmonella enterica serovar Typhimurium

Abstract

By screening for high-level mecillinam resistant derivatives of a low-level resistant strain (cysB403 galE1922 relA21::Tn10) of Salmonella enterica serovar Typhimurium, a MudJ insertion in the gene for soluble lytic transglycosylase (slt) was isolated. This insertion (slt-1::MudJ) increased the resistance to mecillinam of cysB and cysE strains (MIC: about 20-40 microg mL(-1)) to a strikingly high level (MIC: 160 microg mL(-1)). As in Escherichia coli K-12, the slt mutation slightly increased the sensitivity of the wild type and of several strains that carried mutations that did not increase mecillinam resistance. All the strains acquired a spherical cell shape when treated with mecillinam. The effect of slt-1::MudJ was limited to mecillinam, the response to several other antibiotics remaining unaltered by the insertion. The results presented in this paper demonstrate that soluble lytic transglycosylase performs an important role in the response to mecillinam, which only becomes evident when failure of CysB/CysE function causes medium-level resistance. The results also suggest that soluble lytic transglycosylase interacts with, and is partially inhibited by normal lipopolysaccharide.

l-Cysteine is required for induced antibiotic resistance in actively swarming Salmonella enterica serovar Typhimurium

“…Cross-talk between metabolic pathways could help the bacterium coordinate utilization of a metabolite in one metabolic pathway with those in another (Quan et al, 2002). In addition, cysB and cysE mutants of S. typhimurium and E. coli have been reported to have increased resistance to the b-lactam antibiotic mecillinam and the quinolone novobiocin (Anton, 2000;Costa & Anton, 2006;Lilic et al, 2003;Oppezzo & Anton, 1995;Rakonjac et al, 1991). Since swarming motility in both cysB and cysE is restored by the inclusion of cysteine in the swarm medium, a CysBregulated gene outside of the cysteine biosynthetic genes is not the reason that these strains are incapable of swarming on standard swarm medium.…”

Amdinocillin (Mecillinam) Resistance Mutations in Clinical Isolates and Laboratory-Selected Mutants of Escherichia coli

“…The gene trxB encodes thioredoxin, an enzyme that is involved in the cysteine biosynthesis pathway (54). Inactivation of this pathway has previously, as well as in this study, been shown to confer Amd resistance (31,32).…”

“…CysB protein is the major positive regulator of cysteine biosynthesis in Enterobacteriaceae (54), and mutations in the cysteine biosynthesis pathway genes cysB and cysE have previously been shown to confer Amd resistance on laboratory-selected mutants of S. enterica serovar Typhimurium (31,32). Although the mechanism by which cysB confers resistance has not been fully elucidated, it is at least partly due to increased intracellular levels of ppGpp (32).…”

“…Although the mechanism by which cysB confers resistance has not been fully elucidated, it is at least partly due to increased intracellular levels of ppGpp (32). isolates (CI) in MH medium and urine, showing (from top to bottom) the maximum fitness value, the upper quartile, the median, the lower quartile, and the minimum fitness value.…”

“…This finding is seemingly a paradox, since a large number of genes (Table 1) can, when mutated, confer resistance to Amd, resulting in a high frequency of mutation to resistance during laboratory selection. Resistance mutations found in mutants isolated in laboratory selections affect many different cellular functions, for instance, (i) cell elongation and division (10,11,(18)(19)(20)(21)(22); (ii) cellular amino acid levels and tRNA synthetases (23)(24)(25); (iii) composition of lipopolysaccharide in combination with cya/crp (26)(27)(28); (iv) the Rcs global regulatory system that controls, for example, capsule production and cell division (29,30); and (v) cysteine biosynthesis (31,32). Some of these mutations are associated with an intracellular increase in the concentration of the molecule ppGpp-the signal for the stringent response.…”