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Enterohemorrhagic Escherichia coli (EHEC) O157:H7 strain EDL933 harbors multiple prophage-associated open reading frames (ORFs) in its genome which are highly homologous to the chromosomal nanS gene. The latter is part of the nanCMS operon, which is present in most E. coli strains and encodes an esterase which is responsible for the monodeacetylation of 5-N-acetyl-9-O-acetyl neuraminic acid (Neu5,9Ac2). Whereas one prophage-borne ORF (z1466) has been characterized in previous studies, the functions of the other nanS-homologous ORFs are unknown.

In the current study, the nanS-homologous ORFs of EDL933 were initially studied in silico. Due to their homology to the chromosomal nanS gene and their location in prophage genomes, we designated them nanS-p and numbered the different nanS-p alleles consecutively from 1 to 10. The two alleles nanS-p2 and nanS-p4 were selected for production of recombinant proteins, their enzymatic activities were investigated, and differences in their temperature optima were found. Furthermore, a function of these enzymes in substrate utilization could be demonstrated using an E. coli C600ΔnanS mutant in a growth medium with Neu5,9Ac2 as the carbon source and supplementation with the different recombinant NanS-p proteins. Moreover, generation of sequential deletions of all nanS-p alleles in strain EDL933 and subsequent growth experiments demonstrated a gene dose effect on the utilization of Neu5,9Ac2. Since Neu5,9Ac2 is an important component of human and animal gut mucus and since the nutrient availability in the large intestine is limited, we hypothesize that the presence of multiple Neu5,9Ac2 esterases provides them a nutrient supply under certain conditions in the large intestine, even if particular prophages are lost.

Importance

In this study, a group of homologous prophage-borne nanS-p alleles and two of the corresponding enzymes of enterohemorrhagic E. coli (EHEC) O157:H7 strain EDL933 that may be important to provide alternative genes for substrate utilization were characterized.

Escherichia coli O157:H7 strain EDL933 harbors multiple functional prophage-associated genes necessary for the utilization of 5-N-acetyl-9-O-acetyl neuraminic acid as a growth substrate

Appl. Environ. Microbiol. October 2016 vol. 82 no. 19 5940-5950, posted online 29 July 2016, doi: 10.1128/AEM.01671-16

Nadja Saile, Anja Voigt, Sarah Kessler, Timo Stressler, Jochen Klumpp, Lutz Fischer and Herbert Schmidt

http://aem.asm.org/content/82/19/5940.abstract?etoc

Plasmids are pieces of independent DNA that often carry multiple antibiotic resistance genes. Plasmids can jump from one bacterium to another, spreading that resistance. A team of French investigators now shows that bacteria that acquire plasmids containing resistance genes rarely lose them. The research is published in Antimicrobial Agents and Chemotherapy, a journal of the American Society for Microbiology.

In the study, the investigators focused on plasmids carrying resistance to extended spectrum cephalosporins. “Cephalosporins are antimicrobials that are critical to human health, as they are used to treat urinary tract, and other infections,” said corresponding author Isabelle Kempf, D.V.M., head of the Mycoplasmology-Bacteriology Unit, the Agence Nationale de Securité Sanitaire, Université de Bretagne Loire, Ploufragan, France. The gene for resistance to extended spectrum cephalosporins is frequently carried on plasmids, often along with multiple genes for resistance to other antimicrobials.

The investigators inoculated pigs with an extended spectrum cephalosporin-resistant, non-pathogenic strain of Escherichia coli, and placed the pigs in pens with non-inoculated pigs. A plasmid in the E. coli carried the gene for extended spectrum cephalosporin resistance, as well as four other resistance genes. The investigators collected fecal samples from the pigs, at different time points following inoculation. From these, they grew 353 isolates of E. coli.

During the experiment, the pigs did not receive extended spectrum cephalosporin antibiotics. That meant that there was no selection pressure that might have favored the persistence of extended spectrum cephalosporin resistance in the bacterial populations. Nonetheless, all but three of the 353 isolates carried the resistance gene.

“Our results show that once a plasmid encoding resistance genes is transferred to a bacterial host, the probability that the bacteria will lose the encoded resistances is quite low, even absent a selective pressure,” said Kempf

“Plasmids have developed sophisticated mechanisms to ensure their transmission to daughter cells during cell division,” Kempf explained. “A better knowledge of these mechanisms and development of innovative tools to counteract them could result in new strategies to combat antimicrobial resistance.”

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Plasmid way: E. coli be swapping genes

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