Recombination-deficient mutants of Salmonella typhimurium are avirulent and sensitive to the oxidative burst of macrophages

Mutations in the genes recA and recBC were constructed in the virulent Salmonella typhimurium strain 14028s. Both the recA and recBC mutants were attenuated in mice. The mutants were also sensitive to killing by macrophages in vitro. The recombination mutants were no longer macrophage sensitive in a variant line of J774 macrophage-like cells that fail to generate superoxide. This suggests that repair of DNA damage by Salmonella is necessary for full virulence in vivo and that the oxidative burst of phagocytes is one source of such DNA damage.     

Identification and sequence analysis of lpfABCDE, a putative fimbrial operon of Salmonella typhimurium.

A chromosomal region present in Salmonella typhimurium but absent from related species was identified by hybridization. A DNA probe originating from 78 min on the S. typhimurium chromosome hybridized with DNA from Salmonella enteritidis, Salmonella heidelberg, and Salmonella dublin but not with DNA from Salmonella typhi, Salmonella arizonae, Escherichia coli, and Shigella serotypes. Cloning and sequence analysis revealed that the corresponding region of the S. typhimurium chromosome encodes a fimbrial operon. Long fimbriae inserted at the poles of the bacterium were observed by electron microscopy when this fimbrial operon was introduced into a nonpiliated E. coli strain. The genes encoding these fimbriae were therefore termed lpfABCDE, for long polar fimbriae. Genetically, the lpf operon was found to be most closely related to the fim operon of S. typhimurium, both in gene order and in conservation of the deduced amino acid sequences.     

Ethanolamine utilization in Salmonella typhimurium: nucleotide sequence, protein expression, and mutational analysis of the cchA cchB eutE eutJ eutG eutH gene cluster.

A fragment of the Salmonella typhimurium ethanolamine utilization operon was cloned and characterized. The 6.3-kb nucleotide sequence encoded six complete open reading frames, termed cchA, cchB, eutE, eutJ, eutG, and eutH. In addition, the nucleotide sequences of two incomplete open reading frames, termed eutX and eutI, were also determined. Comparison of the deduced amino acid sequences and entries in the GenBank database indicated that eutI encodes a phosphate acetyltransferase-like enzyme. The deduced amino acid sequences of the EutE and EutG proteins revealed a significant degree of homology with the Escherichia coli alcohol dehydrogenase AdhE sequence. Mutations in eutE or eutG completely abolished the ability of mutants to utilize ethanolamine as a carbon source and reduced the ability to utilize ethanolamine as a nitrogen source. The product of eutE is most probably an acetaldehyde dehydrogenase catalyzing the conversion of acetaldehyde into acetyl coenzyme A. The product of the eutG gene, an uncommon iron-containing alcohol dehydrogenase, may protect the cell from unconverted acetaldehyde by converting it into an alcohol. The deduced amino acid sequence of cchA resembles that of carboxysome shell proteins from Thiobacillus neapolitanus and Synechococcus sp. as well as that of the PduA product from S. typhimurium. CchA and CchB proteins may be involved in the formation of an intracellular microcompartment responsible for the metabolism of ethanolamine. The hydrophobic protein encoded by the eutH gene possesses some characteristics of bacterial permeases and might therefore be involved in the transport of ethanolamine. Ethanolamine-utilization mutants were slightly attenuated in a mouse model of S. typhimurium infection, indicating that ethanolamine may be an important source of nitrogen and carbon for S. typhimurium in vivo.     

Molecular genetic analysis of the Escherichia coli phoP locus.

We have cloned the Escherichia coli phoP gene, a member of the family of environmentally responsive two-component systems, and found its deduced amino acid sequence to be 93% identical to that of the Salmonella typhimurium homolog, which encodes a major virulence regulator necessary for intramacrophage survival and resistance to cationic peptides of phagocytic cells. The phoP gene was mapped to kilobase 1202 on the Kohara map (25-min region) of the E. coli genome (Y. Kohara, K. Akiyama, and K. Isono, Cell 50:495-508, 1987) and found to be transcribed in a counterclockwise direction. Both E. coli and S. typhimurium phoP mutants were more sensitive than their isogenic wild-type strains to the frog-derived antibacterial peptide magainin 2, suggesting a role for PhoP in the response to various stresses in both enteric species.     

Origin of the TEM-beta-lactamase gene found on plasmids.

A sequence of deoxyribonucleic acid of 2.7 times 10-6 to 3.3 times 10-6 daltons which includes the TEM beta-lactamase gene is present on the small plasmid RSF 1030 (R-Amp). This same sequence is present on plasmid derivatives that have received a translocation of deoxyribonucleic acid specifying the TEM beta-lactamase and is also present on naturally occurring plasmids of the F1, F11, N, X, O, I, C, and W incompatibility groups that do not specify ampicillin resistance or specify O-type beta-lactamases.     

Vaginal microbiome-hormonal contraceptive interactions associate with the mucosal proteome and HIV acquisition

Alterations to the mucosal environment of the female genital tract, such as genital inflammation, have been associated with increased HIV acquisition in women. As the microbiome and hormonal contraceptives can affect vaginal mucosal immunity, we hypothesized these components may interact in the context of HIV susceptibility. Using previously published microbiome data from 685 women in the CAPRISA-004 trial, we compared relative risk of HIV acquisition in this cohort who were using injectable depot medroxyprogesterone acetate (DMPA), norethisterone enanthate (NET-EN), and combined oral contraceptives (COC). In women who were Lactobacillus-dominant, HIV acquisition was 3-fold higher in women using DMPA relative to women using NET-EN or COC (OR: 3.27; 95% CI: 1.24–11.24, P = 0.0305). This was not observed in non-Lactobacillus-dominant women (OR: 0.95, 95% CI: 0.44–2.15, P = 0.895) (interaction P = 0.0686). Higher serum MPA levels associated with increased molecular pathways of inflammation in the vaginal mucosal fluid of Lactobacillus-dominant women, but no differences were seen in non-Lactobacillus dominant women. This study provides data suggesting an interaction between the microbiome, hormonal contraceptives, and HIV susceptibility.