ABSTRACT A small number of cases of human immunodeficiency virus (HIV) infection have been reported in individuals with no identified risk factors for transmission. We report on the seroconversion of the 61-year-old mother and the subsequent finding of HIV seropositivity in the 66-year-old father of a 31-year-old AIDS patient. Extensive investigation failed to identify any risk factor for intrafamilial transmission. We conducted a genetic analysis and determined the amino acid signature patterns of the V3, V4, and V5 hypervariable domains and flanking regions in the HIV-1 gp120 env gene of 26 clones derived from proviral DNA in peripheral blood mononuclear cells of the members of the family. env sequences of the viruses isolated from the patients were compared with sequences of HIV-1 subtype B viruses from Europe and local field isolates. Phylogenetic analysis revealed that the sequences of the viruses isolated from the patients were genetically related and formed an intrafamilial cluster of HIV-1 distinct from other subtype B viruses. Interindividual nucleotide variability in the C2-V3 and V4-C4-V5 domains ranged between 1.2 and 5.0% and between 2.2 and 7.5%, respectively, whereas divergence between HIV strains from the patients and control viral strains ranged from 6.6 to 29.3%. The amino acid signature patterns of viral clones from the three patients were closely related. In the C2-V3 region, two minor clones derived from the son’s virus showed less nucleotide divergence (mean, 3.5 and 3.9%) than did the clones derived from the viruses of both parents or the seven other predominant clones derived from the virus from the son (mean, 5.4%). The top of the V3 loop of the last two clones and of all viral clones from the parents exhibited an unusual GPGG sequence. This is the first report of genotypic relatedness of HIV-1 in three adults of the same family in the absence of identified risk factor for transmission between the members of the family. Our findings suggest that atypical transmission of HIV may occur.
The β-lactam antibiotics mimic the d-alanyl4-d-alanine5 extremity of peptidoglycan precursors and act as "suicide" substrates of the dd-transpeptidases that catalyze the last cross-linking step of peptidoglycan synthesis. We have previously shown that bypass of the dd-transpeptidases by the ld-transpeptidase of Enterococcus faecium (Ldtfm) leads to high level resistance to ampicillin. Ldtfm is specific for the l-lysyl3-d-alanine4 bond of peptidoglycan precursors containing a tetrapeptide stem lacking d-alanine5. This specificity was proposed to account for resistance, because the substrate of Ldtfm does not mimic β-lactams in contrast to the d-alanyl4-d-alanine5 extremity of pentapeptide stems used by the dd-transpeptidases. Here, we unexpectedly show that imipenem, a β-lactam of the carbapenem class, totally inhibited Ldtfm at a low drug concentration that was sufficient to inhibit growth of the bacteria. Peptidoglycan cross-linking was also inhibited, indicating that Ldtfm is the in vivo target of imipenem. Stoichiometric and covalent modification of Ldtfm by imipenem was detected by mass spectrometry. The modification was mapped into the trypsin fragment of Ldtfm containing the catalytic Cys residue, and the Cys to Ala substitution prevented imipenem binding. The mass increment matched the mass of imipenem, indicating that inactivation of Ldtfm is likely to involve rupture of the β-lactam ring and acylation of the catalytic Cys residue. Thus, the spectrum of activity of β-lactams is not restricted to transpeptidases of the dd-specificity, as previously thought. Combination therapy with imipenem and ampicillin could therefore be active against E. faecium strains having the dual capacity to manufacture peptidoglycan with transpeptidases of the ld- and dd-specificities.
Forty-seven bronchoalveolar lavages (BAL) were obtained from 41 patients with acute pneumonia attending an intensive care unit. By molecular diagnosis, 30% of total BAL and 63% of bacteria-negative BAL were positive for respiratory viruses. Molecular detection allows for high-rate detection of respiratory viral infections in adult patients suffering from severe pneumonia.
The L,D-transpeptidase Ldt(fm) catalyzes peptidoglycan cross-linking in beta-lactam-resistant mutant strains of Enterococcus faecium. Here, we show that in Escherichia coli Ldt(fm) homologues are responsible for the attachment of the Braun lipoprotein to murein, indicating that evolutionarily related domains have been tailored to use muropeptides or proteins as acyl acceptors in the L,D-transpeptidation reaction.
