Population structure of Pseudomonas aeruginosa through a MLST approach and antibiotic resistance profiling of a Mexican clinical collection.

Pseudomonas aeruginosa is one of the most important pathogens worldwide. Population genetics studies have shown that the P. aeruginosa population has an epidemic structure with highly conserved clonal complexes. Nonetheless, epidemiological studies of P. aeruginosa have been historically absent or infrequent in developing countries, in which different medical treatments, conditions and infrastructure may have an impact in population dynamics and evolutionary outcomes, including antibiotic resistance profiles. In this study we contribute to fill this gap by analyzing 158 P. aeruginosa isolates from the most extensive nosocomial collection in Mexico City. We investigated the population genetic structure through a MLST approach together with a classical microbiology antibiotic resistance profiling, one of the associated concerns in the evolution of this pathogen. On the one hand, our results are in accordance with previous studies on the epidemic structure of P. aeruginosa, as well as the existence of three main phylogroups, that are not related to environmental parameters. On the other hand, antibiotic resistance profiles indicate higher prevalence in our sample of multi drug resistant (75.15%), extremely drug resistant (17.72%) and pan-drug resistant (9.49%) than resistance reported in developed countries. It is important to reflect on the causes that make less developed countries hotspots of antibiotic resistance, considering the multifactorial aspects of the socio-political context of such countries that include, but are not restricted to, public policy implementation and enforcement regarding access to antibiotics, as well as health care personnel education and other obstacles related to poverty and unequal access to health services and information.

Characterization of wild lambdoid bacteriophages: detection of a wide distribution of phage immunity groups and identification of a nus-dependent, nonlambdoid phage group.

Temperate phages were isolated from fresh human fecal samples. Lambdoid phages were screened for growth on Nus+ but not Nus- bacteria. Approximately 100 independent lysogens of Nus-dependent phages were constructed and tested for immunity to superinfection by the same Nus-dependent phages. This identified 20 different phage immunity groups, 18 of which belonged to the lambdoid phage family. The DNA from the majority of these phages hybridized with a lambda DNA probe, and approximately 50% were recognized by anti-lambda antibodies. Furthermore most were inducible by UV light. Eleven phage recombinants with different immunity were obtained when a phage from each group was coinfected with lambda or its derivative lambdaBLK20. We also identified another immunity group with 48 members. None of these hybridized with either lambda or phi80 DNA probes nor were they recognized by anti-lambda serum. Most were not induced by UV light treatment, and no recombinants were obtained when crossed with either lambda or lambdaBLK20. Consequently, this group of Nus-dependent phages represent a new nonlambdoid phage family.

Genetic uncoupling of the dsRNA-binding and RNA cleavage activities of the Escherichia coli endoribonuclease RNase III--the effect of dsRNA binding on gene expression.

RNase III, a double-stranded RNA-specific endonuclease, is proposed to be one of Escherichia coli's global regulators because of its ability to affect the expression of a large number of unrelated genes by influencing post-transcriptional control of mRNA stability or mRNA translational efficiency. Here, we describe the phenotypes of bacteria carrying point mutations in rnc, the gene encoding RNase III. The substrate recognition and RNA-processing properties of mutant proteins were analysed in vivo by measuring expression from known RNase III-modulated genes and in vitro from the proteins' binding and cleavage activities on known double-stranded RNA substrates. Our results show that although the point mutation rnc70 exhibited all the usual rnc null-like phenotypes, unlike other mutations, it was dominant over the wild-type allele. Multicopy expression of rnc70 could suppress a lethal phenotype of the wild-type rnc allele in a certain genetic background; it could also inhibit the RNase III-mediated activation of lambdaN gene translation by competing for the RNA-binding site of the wild-type endonuclease. The mutant protein failed to cleave the standard RNase III substrates in vitro but exhibited an affinity for double-stranded RNA when passed through poly(rI):poly(rC) columns. Filter binding and gel-shift assays with purified Rnc70 showed that the mutant protein binds to known RNase III mRNA substrates in a site-specific manner. In vitro processing reactions with purified enzyme and labelled RNA showed that the in vivo dominant effect of the mutant enzyme over the wild-type was not necessarily caused by formation of mixed dimers. Thus, the rnc70 mutation generates a mutant RNase III with impaired endonucleolytic activity but without blocking its ability to recognize and bind double-stranded RNA substrates.

Translational repression by a transcriptional elongation factor.

One of the classical positive regulators of gene expression is bacteriophage lambda N protein. N regulates the transcription of early phage genes by participating in the formation of a highly processive, terminator-resistant transcription complex and thereby stimulates the expression of genes lying downstream of transcriptional terminators. Also included in this antiterminating transcription complex are an RNA site (NUT) and host proteins (Nus). Here we demonstrate that N has an additional, hitherto unknown regulatory role, as a repressor of the translation of its own gene. N-dependent repression does not occur when NUT is deleted, demonstrating that N-mediated antitermination and translational repression both require the same cis-acting site in the RNA. In addition, we have identified one nut and several host mutations that eliminate antitermination and not translational repression, suggesting the independence of these two N-mediated mechanisms. Finally, the position of nutL with respect to the gene whose expression is repressed is important.

RNaselll activation of bacteriophage lambda N synthesis.

The bacteriophage lambda N gene product is one of the first genes expressed during phage development. N protein allows the expression of other phage genes by altering the transcription elongation process so as to prevent transcription termination. We have found that N levels may be modulated soon after induction or infection. Using N-lacZ fusions, we determined that cells containing RNaselll have at least a fourfold greater expression than cells defective for RNaselll. This effect is exerted at the post-transcriptional level. RNaselll processes an RNA stem structure in the N-leader RNA. Removal of the stem structure by deletion increases N expression and prevents further stimulation by RNaselll. The base of this stable stem is adjacent to the N ribosome binding site. We present a model for control of N synthesis in which this stable stem inhibits ribosome access to the N mRNA.

[The correlation between the productive capacity of carcinoembryonic antigen (CEA) and prognosis in gastric cancer].

In 130 resected specimens of gastric cancer, CEA was stained by the enzyme labeled antibody method. The positive rate of CEA stain was 74.6% and higher in well differentiated adenocarcinoma, mucinous adenocarcinoma, and signet ring cell carcinoma. The positive rate was lower in poorly differentiated adenocarcinoma. The 5-year survival rate was higher in the CEA (-) group in stage II, and higher in the CEA (+) group in stage III (p less than 0.05) and stage IV. This suggests that the correlation of the CEA stain and the prognosis varies with the stage of cancer.