Listeria monocytogenes cross-contamination in a nursery [corrected].

Molecular evidence of Listeria monocytogenes cross-contamination in a nursery is presented. Listeria monocytogenes serotype 4b was isolated from the blood and the conjunctiva of a baby with neonatal sepsis who was born after septic amnionitis and premature rupture of membrane. Nine days later, the same bacterium was isolated from the cerebrospinal fluid of a second baby presenting with meningitis. Cervical cultures from the second baby's healthy mother were negative for Listeria sp. An in-depth epidemiologic investigation revealed that the same nurse administered routine treatments to both babies in the nursery during a 1-hour interval of time [corrected]. Pulse-field gel electrophoresis analysis of both strains with 2 different restriction enzymes demonstrated that they were identical and differ from other wild strains of L monocytogenes serotype 4b isolated in Israel. This fact strongly suggests that the second baby was infected during admittance to the nursery as a result of a hospital cross-contamination.

Unusual portal of entry of Vibrio vulnificus: evidence of its prolonged survival on the skin.

Vibrio vulnificus biotype 3 is an emerging pathogen isolated from cultures of skin and blood samples obtained from patients who were directly injured by the fins of tilapia fish bred in artificial ponds. We describe a patient infected with this pathogen after being punctured by a wire. Meticulous anamnestic investigation demonstrated for the first time that this pathogen can survive on the skin for at least 24 hours.

Shigella flexneri IpaH(7.8) facilitates escape of virulent bacteria from the endocytic vacuoles of mouse and human macrophages.

The behavior of Shigella flexneri ipaH mutants was studied in human monocyte-derived macrophages (HMDM), in 1-day-old human monocytes, and in J774 mouse macrophage cell line. In HMDM, strain pWR700, an ipaH(7.8) deletion mutant of S. flexneri 2a strain 2457T, behaved like the wild-type strain 2457T. This strain caused rapid host cell death by oncosis, and few bacterial CFU were recovered after incubation in the presence of gentamicin as previously described for 2457T-infected HMDM. However, analysis of bacterial compartmentalization within endocytic vacuoles with gentamicin and chloroquine indicated that more pWR700 than 2457T was present within the endocytic vacuoles of HMDM, suggesting that ipaH(7.8) deletion mutant transited more slowly from the vacuoles to the cytoplasm. In contrast to findings with HMDM, CFU recovered from pWR700-infected mouse J774 cells were 2 to 3 logs higher than CFU from 2457T-infected J774 cells. These values exceeded CFU recovered after infection of J774 cells with plasmid-cured avirulent strain M4243A1. Incubation with gentamicin and chloroquine clearly showed that pWR700 within J774 cells was mostly present within the endocytic vacuoles. This distribution pattern was similar to that seen with M4243A1 and contrasted with the pattern seen with 2457T. Complementation of pWR700 with a recombinant clone expressing ipaH(7. 8) restored the intracellular distribution of bacteria to that seen with the wild-type strain. Strains with deletions in ipaH(4.5) or ipaH(9.8), however, behaved like 2457T in both HMDM and J774 cells. The distribution profile of pWR700 in 1-day-old monocytes was similar to that seen in J774 cells. Like infected J774 cells, 1-day-old human monocytes demonstrated apoptosis upon infection with virulent Shigella. These results suggest that a role of the ipaH(7. 8) gene product is to facilitate the escape of the virulent bacteria from the phagocytic vacuole of monocytes and macrophages.

The nature of the nucleotide at the 5' side of the tRNA Su9 anticodon affects UGA suppression in Escherichia coli.

In Escherichia coli a UGA codon can be efficiently suppressed by a suppressor tRNA(Trp) called Su9. Here, we show that the level of UGA suppression is determined by the nature of the nucleotide at the 5' side of the anticodon of the suppressor (position 33). UGA suppression occurs when a pyrimidine residue is located in position 33 of the tRNA, and suppression is more efficient with a U than with a C in this position. On the other hand, when a purine residue is located at this position UGA suppression is extremely low. These results show that in the case of tRNA Su9, the UGA codon context effect does not require base pairing between the nucleotide at the 3' side of the codon and the 5' side of the anticodon.

Influence of codon context on UGA suppression and readthrough.

We studied the influence of the codon context on UGA suppression by a suppressor tRNA and on UGA readthrough by a normal tRNA in Escherichia coli. This was done by a series of constructs where only the immediate context of the TGA codon was varied by only one nucleotide at a time. For both UGA suppression and UGA readthrough the codon context had a similar influence according to the following rules. (1) The nature of the nucleotide immediately adjacent to the 3' side of the UGA is an important determinant; at that position the level of UGA translation is influenced by the nucleotides in the order A greater than G greater than C greater than U. (2) At extremely high or low levels of UGA translation this influence of the adjacent 3' nucleotide is not seen. (3) In all cases, the nature of both the nucleotide immediately adjacent to the 5' side of the codon and that following the base adjacent to the 3' side of the codon have little effect, if any, on UGA translation. The varying influence of the codon context effect on UGA translation is discussed in relation to its role in gene expression.

Modulation of Escherichia coli tryptophan (trp) attenuation by the UGA readthrough process.

We constructed plasmid pAtrp46 in which lacZ gene expression is regulated by the attenuator of the Escherichia coli tryptophan (trp) operon. The attenuation of trp, which occurs in the presence of an excess of tryptophan, is reflected by a decrease in the expression of the lacZ gene of pAtrp46 in a trpR- strain. Experiments with pAtrp46 further support our previous results (Engelberg-Kulka et al. 1982b) that suppression of a UGA termination codon by normal charged tRNATrp, a process called UGA readthrough, is a necessary mechanism in trp attenuation. Our experiments also suggest that plasmid pAtrp46 is useful for studies of other aspects of trp attenuation.