Clinical isolate of a porinless Salmonella typhi resistant to high levels of chloramphenicol

Abstract

We studied a clinical isolate of Salmonella typhi (strain 1895) characterized by resistance to 200 micrograms of chloramphenicol per ml despite the absence of chloramphenicol-inactivating activity. The outer membrane protein profile analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis indicated a deficiency of one of the major protein species which may serve as a porin for entry of chloramphenicol. When the strain was transformed with a plasmid encoding chloramphenicol acetyltransferase, chloramphenicol added to the culture was not inactivated, suggesting a drastic reduction of permeability towards the drug. Moreover, transformants bearing a plasmid coding for the Escherichia coli OmpF porin became considerably more susceptible to chloramphenicol (40 micrograms/ml). On the other hand, transformants carrying a plasmid encoding the Salmonella typhi ompC gene remained as resistant to the drug as the parental strain, even though they overexpressed OmpC. These findings indicate that the lack of OmpF plays a major role in the resistance to chloramphenicol in strain 1895.

Antimicrobial resistance pattern of Salmonella enterica servars in Southern Delhi

“…In 1990s rapid emergence MDR S. typhi was reported in many parts of India due to the acquisition of R-plasmid encoding acetyl transferase inactivating chloramphenicol and loss of OMP. 25 Dihydrfolate reductase VII and TEM-1 beta lactamase were found responsible for conferring resistance to ampicillin and cotrimoxazole. 26 In India, MDR was first reported in Mumbai in 1990, an outbreak came to known as dombivalli fever.…”

Increase in incidence of resistance to ampicillin, chloramphenicol and trimethoprim in clinical isolates of Salmonella serotype Typhimurium with investigation of molecular epidemiology and mechanisms of resistance

“…Tor0 et al [45] found that the lack of OmpF played a major role in the high level of chloramphenicol resistance in a S. Typhi strain. In this strain, chloramphenicol acetyl-transferase activity was not detected.…”

The Structure of the Chloramphenicol Resistance Gene on a Transferable R Plasmid from the Fish Pathogen, Pasteurella piscicida

“…In gram-negative bacteria, resistance to CP is due to the presence of the CP acetyltransferase (CAT) which is coded by the gene (cat) localized on plasmids or transposons and is expressed constitutively (1,15,16,22). Another resistant mechanism to CP, that is, chromosomal gene associated resistance which is ascribed to a permeability barrier to the drug, has also been reported (7,8,25 In human pathogenic bacteria, CP resistance mechanisms, including cat itself, have been studied in detail. However, little is known about them in fish-pathogenic bacteria (27).…”