First salmonella resistant to all antibiotics
Salmonella enterica, a cholera serotype, usually causes systemic infections in people who need antibiotic therapy. A strain of S. choleraesuis (SCB67), resistant to ceftriaxone and ciprofloxacin, was isolated.
Salmonella enterica, the choleraesuis serotype usually causes systemic infections in people requiring antibiotic therapy. In 2002, a strain S. choleraesuis (SCB67) was isolated from the blood in a 58-year-old patient with a history of esophageal cancer hospitalized for sepsis, which was found to be resistant to all antibiotics commonly used to treat salmonella (ampicillin, chloramphenicol, streptomycin, sulfanilamides, tetracyclines, gentamicin, kanamycin, trimethoprim, ceftriaxone, ciprofloxacin). Treatment with imipenem / cilastatin was started, but the patient died on day 7 after hospitalization.
The identification of the strain was carried out by standard methods (biochemical tests and agglutination with antisera specific to the group and to the type). The sensitivity was determined by the method of micro-dilutions in the broth.
The MIC for ceftriaxone and ciprofloxacin for this strain was 16 mg / L, located in the resistance range. Other tests showed that the MIC of cefotaxime and ceftazidime (32 mg / l) did not change depending on the presence or absence of clavulanic acid in the culture medium, and the strain was also resistant cefoxitin (64 mg / l). This meant that the strain could be producing AmpC beta-lactamase, but not broad spectrum beta-lactamase.
PCR analysis showed the presence of a strain S. choraraesuis of plasmid specific to the serotype weighing 50 kb. AmpC represents a group of resistance genes that includes blaCMY-2. It was found that this gene is located on a non-conjugative, but potentially transmitted plasmid, of the studied strain of 140 kb. To characterize the gene, the authors cloned the corresponding part of the DNA sequence of this plasmid. The cloned fragment contained 4 genes, including the class C beta-lactamase gene, and evidence was also obtained that the fragment was an insert in the finQ gene for the plasmid of the strain studied. No identical or homologous sequence to the ampR gene in Salmonella has been found.
A double mutation in the gyrA gene, described above, and a new mutation in the parC gene (amino acid substitution Ser80 → Ile) also were found in the strain studied. who determined his resistance to fluoroquinolones.
Thus, the unique genetic organization of the AmpC gene of plasmid origin was identified in the isolate of S. chooleraesuis. The gene is located in the composition of the mobile genetic element, next to the sequence which determines its translocation and, thus, can be transmitted between bacteria. S. chooleraesuis could acquire from the outside a specific transposon-type element, which determined the phenotype of resistance to wide spectrum cephalosporins. The presence of the blaCMY-2 gene in ciprofloxacin-resistant S. choraraesuis is a serious threat to public health, so constant monitoring is necessary to prevent its spread.