Interaction of Vibrio cholerae cells with beta-lactam antibiotics: emergence of resistant cells at a high frequency

Abstract

Unlike other gram-negative enteric bacteria, Vibrio cholerae cells were equally susceptible to penicillin and ampicillin and in general more susceptible than Escherichia coli to most of the beta-lactam antibiotics. The turbidity of penicillin-treated cultures continued to increase exponentially for about 3 h, although the cell viability declined rapidly within 30 min of penicillin addition. Prolonged treatment with beta-lactam antibiotics produced cells resistant to these antibiotics. A fluctuation test indicated that this resistance might be due to adaptive mutation. Cells resistant to a beta-lactam exhibited broad cross-resistance to other beta-lactam antibiotics. A new 12,000-Da outer membrane protein was detected both in beta-lactam-resistant cells and in wild-type cells growing in medium containing beta-lactam antibiotics. While the penicillin-resistant cells had all of the penicillin-binding proteins (PBPs) present in the parental cells, significant differences in the relative proportion of low-molecular-weight PBPs were seen. The low-molecular-weight PBPs from resistant cells seemed to form more stable complexes with penicillin than those from the parental strain.Vibrio cholerae, a noninvasive enteropathogen and the etiological agent of cholera, adheres to epithelial cells of the proximal small intestine and excretes a potent enterotoxin which causes severe diarrhea. Several models simulating the important features of the interaction between the bacterium and the epithelial surface have been proposed (8,11,15,26). The outer membrane of enteric gram-negative bacteria plays an important role in conferring resistance to bile salts and to host defense factors such as lysozyme and leukocyte proteins (19). Studies of the cell surface architecture of V. cholerae were thus considered necessary for a better understanding of the cell-cell interaction. It has recently been reported that the cell surface of a hypertoxinogenic strain of V. cholerae, 569B, has exposed phospholipids in the outer leaflet of the outer membrane and that these cells are highly sensitive to a wide range of chemicals in general and to hydrophobic compounds and neutral and anionic detergents in particular. The lipopolysaccharide (LPS) moiety has relatively less negative charge (21).Previous studies have indicated the relatively fragile nature of the murein network of V. cholerae (12, 13). These cells lyse rapidly in hypotonic media and in the presence of chelating agents such as Tris and EDTA (13). Purified outer membranes can be directly isolated from whole cells by treatment with protein denaturants such as urea at room temperature (12).These observations suggest that the murein network of V. cholerae is relatively weak and prompted us to examine the effect of beta-lactam antibiotics which inhibit the final stages of murein synthesis in V. cholerae. Eleven penicillin-binding proteins (PBPs) were detected in V. cholerae, and when they were compared with the PBPs of Eschenichia coli, several interesting differences were observed (23). The pres...

In vitro and in vivo antimicrobial efficacy of natural plant-derived compounds against Vibrio cholerae of O1 El Tor Inaba serotype

“…Thus, these cells are highly sensitive to a wide range of chemicals. 31) Indeed, V. cholerae possess the highest mean values of susceptibility to ten different plant polyphenols. 32) Taken together, our results indicate that these cell surface features of V. cholerae may be causative of the critical susceptibility to honokiol and magnolol compared to other pathogenic bacteria.…”

Use of RNA Arbitrarily Primed-PCR Fingerprinting To Identify Vibrio cholerae Genes Differentially Expressed in the Host following Infection

“…The structure of the murein network plays a significant role in determining the stability of cell surfaces of bacteria. Several studies have indicated the delicate nature of the murein networks of V. cholerae cells (4,13,25). It is a real mystery how these cells survive in the human intestine.…”

“…In fact, several studies have indicated the fragile nature of the murein networks of V. cholerae cells (4,13,25). In E. coli, the peptidoglycan network is thin but "more than a monolayer" (10).…”

“…The murein network of V. cholerae is weak, and the cells lyse rapidly in hypotonic medium as well as in the presence of chelating agents such as Tris and EDTA (13). Unlike other gram-negative organisms which are resistant to penicillin, V. cholerae cells are equally sensitive to penicillin and ampicillin and are much more sensitive to most of the beta-lactam antibiotics than E. coli (25).…”

“…The murein network of V. cholerae is weak, and the cells lyse rapidly in hypotonic medium as well as in the presence of chelating agents such as Tris and EDTA (13). Unlike other gram-negative organisms which are resistant to penicillin, V. cholerae cells are equally sensitive to penicillin and ampicillin and are much more sensitive to most of the beta-lactam antibiotics than E. coli (25).Recently, using a method based on tnpR operon fusions encoding a site-specific DNA recombinase, 13 transcriptional units of V. cholerae were identified that were induced during infection in an infant-mouse model of cholera. Five of these were predicted to encode polypeptides with diverse functions in metabolism, biosynthesis, and motility.…”