TB incidence is increased among SOT recipients. The risk factors identified were age and receipt of a lung transplant. TB-attributable mortality (9.5%) is still high.

Klebsiella pneumoniae is a common cause of gram-negative bacterial nosocomial pneumonia. Two surface polysaccharides, lipopolysaccharide (LPS) O side chain and capsular polysaccharide (CPS), are critical for the microorganism in causing sepsis, but little is known about their role in pneumonia. To investigate their contribution in the pathogenesis of K. pneumoniae pneumonia, we characterized the host response to bacterial challenge with a highly virulent clinical isolate or with isogenic insertion-duplication mutants deficient in CPS or LPS O side chain in a murine model of pneumonia. Animals challenged intratracheally with the wild-type or LPS O side chain-deficient strain developed pneumonia and became bacteremic before death. Extensive lung lesions as well as pleuritis, vasculitis, and edema were observed by histopathological examination, and polymorphonuclear infiltration was also demonstrated. In contrast, none of the animals challenged with the unencapsulated strain developed pneumonia or bacteremia. Examination of tissue from this group did not identify lung lesions, and none of the infected animals died. Analysis of the early host defense mechanisms that contributed to the clearance of the unencapsulated mutant showed that the levels of C3 deposited on the unencapsulated mutant surface were threefold higher than those for the wild-type and LPS O side chaindeficient strains. Furthermore, phagocytosis of the unencapsulated mutant by human alveolar macrophages (AM) was more efficient than that of the wild-type and LPS O side chain-deficient strains. We conclude that CPS, but not LPS O side chain, is essential for Klebsiella pneumonia because it modulates the deposition of C3 and protects the microorganisms against human AM phagocytosis.

Clinical isolates of Pseudomonas aeruginosa that hyperproduce a dark-brown pigment are quite often found in the lungs of chronically infected patients, suggesting that they may have an adaptive advantage in chronic infections. We have screened a library of random transposon insertions in P. aeruginosa. Transposon insertions resulting in the hyperproduction of a darkbrown pigment were found to be located in the hmgA gene, which putatively encodes the enzyme homogentisate-1,2-dioxygenase. Complementation studies indicate that hmgA disruption is responsible for the hyperproduction of pyomelanin in both laboratory and clinical isolates. A relationship between hmgA disruption and adaptation to chronic infection was explored and our results show that the inactivation of hmgA produces a slight reduction of killing ability in an acute murine model of lung infection. On the other hand, it also confers decreased clearance and increased persistence in chronic lung infections. Whether pyomelanin production is the cause of the increased adaptation to chronicity or just a side effect of hmgA inactivation is a question to be studied in future; however, this adaptation is consistent with the higher resistance to oxidative stress conferred in vitro by the pyomelanin pigment. Our results clearly demonstrate that hmgA inactivation leads to a better adaptation to chronic infection, and strongly suggest that this mechanism may be exploited in naturally occurring P. aeruginosa strains.

Background Urinary tract infection (UTI) is the most common infection in renal transplant patients, but it is necessary to determine the risk factors for bacterial UTI in recipients of other solid organ transplants (SOTs), as well as changes in etiology, clinical presentation, and prognosis. Methods In total, 4388 SOT recipients were monitored in 16 transplant centers belonging to the Spanish Network for Research on Infection in Transplantation (RESITRA). The frequency and characteristics of bacterial UTI in transplant patients were obtained prospectively from the cohort (September 2003 to February 2005). Results A total of 192 patients (4.4%) presented 249 episodes of bacterial UTI (0.23 episodes per 1000 transplantation days); 156 patients were kidney or kidney–pancreas transplant recipients, and 36 patients were liver, heart, and lung transplant recipients. The highest frequency was observed in renal transplants (7.3%). High frequency of cystitis versus pyelonephritis without related mortality was observed in both groups. The most frequent etiology was Escherichia coli (57.8%), with 25.7% producing extended‐spectrum β‐lactamase (ESBL). In all transplants but renal, most cases occurred in the first month after transplantation. Cases were uniformly distributed during the first 6 months after transplantation in renal recipients. Age (odds ratio [OR] per decade 1.1, 95% confidence interval [CI] 1.02–1.17), female gender (OR 1.74, 95% CI 1.42–2.13), and the need for immediate post‐transplant dialysis (OR 1.63, 95% CI 1.29–2.05) were independent variables associated with bacterial UTI in renal and kidney–pancreas recipients. The independent risk factors identified in non‐renal transplants were age (OR per decade 1.79, 95% CI 1.09–3.48), female gender (OR 1.7, 95% CI 1.43–2.49), and diabetes (OR 1.02, 95% CI 1.001–1.040). Conclusions UTI was frequent in renal transplants, but also not unusual in non‐renal transplants. Because E. coli continues to be the most frequent etiology, the emergence of ESBL‐producing strains has been identified as a new problem. In both populations, most cases were cystitis without related mortality. Although the first month after transplantation was a risk period in all transplants, cases were uniformly distributed during the first 6 months in renal transplants. Age and female gender were identified as risk factors for UTI in both populations. Other particular risk factors were the need for immediate post‐transplant dialysis in renal transplants and diabetes in non‐renal transplants.

Identification of Aeromonas species, emergent pathogens for humans, has long been controversial due to their phenotypic and genomic heterogeneities. Computer analysis of the published 16S rRNA gene sequences revealed that restriction fragment length polymorphism of the PCR-amplified 16S rRNA gene is a good and rapid way of assessing the identities of all known species of Aeromonas. The method was evaluated with the reference strains of all species (or DNA homology groups) and 76 clinical isolates of diverse origin. Most results from the two approaches were in agreement, but some discrepancies were discerned. Advantages over previous phenotypic and genetic methods are discussed.