Adhesive properties and antibiotic resistance of Klebsiella, Enterobacter, and Serratia clinical isolates involved in nosocomial infections

Presence and Role of the Type 3 Fimbria in the Adherence Capacity of Enterobacter hormaechei subsp. hoffmannii

Enterobacter hormaechei, one of the species within the Enterobacter cloacae complex, is a relevant agent of healthcare-associated infections. In addition, it has gained relevance because isolates have shown the capacity to resist several antibiotics, particularly carbapenems. However, knowledge regarding colonization and virulence mechanisms of E. hormaechei has not progressed to the same extent as other Enterobacteriaceae species as Escherichia coli or Klebsiella pneumoniae. Here, we describe the presence and role of the type 3 fimbria, a chaperone-usher assembled fimbria, which was first described in Klebsiella spp., and which has been detected in other representatives of the Enterobacteriaceae family. Eight Chilean E. cloacae isolates were examined, and among them, four E. hormaechei isolates were found to produce the type 3 fimbria. These isolates were identified as E. hormaechei subsp. hoffmannii, one of the five subspecies known. A mutant E. hormaechei subsp. hoffmannii strain lacking the mrkA gene, encoding the major structural subunit, displayed a significantly reduced adherence capacity to a plastic surface and to Caco-2 cells, compared to the wild-type strain. This phenotype of reduced adherence capacity was not observed in the mutant strains complemented with the mrkA gene under the control of an inducible promoter. Therefore, these data suggest a role of the type 3 fimbria in the adherence capacity of E. hormaechei subsp. hoffmannii. A screening in E. hormaechei genomes contained in the NCBI RefSeq Assembly database indicated that the overall presence of the type 3 fimbria is uncommon (5.94-7.37%), although genes encoding the structure were detected in representatives of the five E. hormaechei subspecies. Exploration of complete genomes indicates that, in most of the cases, the mrkABCDF locus, encoding the type 3 fimbria, is located in plasmids. Furthermore, sequence types currently found in healthcare-associated infections were found to harbor genes encoding the type 3 fimbria, mainly ST145, ST78, ST118, ST168, ST66, ST93, and ST171. Thus, although the type 3 fimbria is not widespread among the species, it might be a determinant of fitness for a subset of E. hormaechei representatives.

From Klebsiella pneumoniae Colonization to Dissemination: An Overview of Studies Implementing Murine Models

Klebsiella pneumoniae is a Gram-negative pathogen responsible for community-acquired and nosocomial infections. The strains of this species belong to the opportunistic group, which is comprised of the multidrug-resistant strains, or the hypervirulent group, depending on their accessory genome, which determines bacterial pathogenicity and the host immune response. The aim of this survey is to present an overview of the murine models mimicking K. pneumoniae infectious processes (i.e., gastrointestinal colonization, urinary, pulmonary, and systemic infections), and the bacterial functions deployed to colonize and disseminate into the host. These in vivo approaches are pivotal to develop new therapeutics to limit K. pneumoniae infections via a modulation of the immune responses and/or microbiota.

Antimicrobials Affect the Fat Body Microbiome and Increase the Brown Planthopper Mortality

Symbionts in the abdomen fat body of brown planthopper (BPH) play an important role in the growth and reproduction of their host, Nilaparvata lugens Stål (Hemiptera: Delphacidae). Thus, controlling BPH infection on rice by inhibiting symbionts with antimicrobials is feasible. However, the effect of antimicrobials on the microbiome in the fat body and the relationship between microbial community and mortality have not been fully elucidated. A decrease in the total number of yeast-like symbiotes in the fat body and elevated mortality were observed after exposure to toyocamycin, tebuconazole, and zhongshengmycin. Additionally, we found that the antimicrobials reduced bacterial diversity and increased fungal diversity in the fat body and altered the bacterial and fungal community structure. Although the total absolute abundance of bacteria and fungi decreased after antimicrobial exposure, the absolute abundance of Serratia increased, indicating that Serratia, which was the most dominant in the fat body, is an important symbiont involved in resistance to antimicrobials. After antimicrobial exposure, seven genera, which probably participated in the nutrition and development function of the host, were totally eliminated from the fat body. Overall, our study enriches the knowledge of microbiomes in the fat body of BPH under antimicrobial treatment and the disturbance of symbionts would be further used to help other pesticides to control pests.

Adherence to Human Colon Cells by Multidrug Resistant Enterobacterales Strains Isolated From Solid Organ Transplant Recipients With a Focus on Citrobacter freundii

Enterobacteria species are common causes of hospital-acquired infections, which are associated with high morbidity and mortality rates. Immunocompromised patients such as solid organ transplant (SOT) recipients are especially at risk because they are frequently exposed to antibiotics in the course of their treatments. In this work, we used a collection of 106 Escherichia coli, 78 Klebsiella pneumoniae, 25 Enterobacter spp., and 24 Citrobacter spp. multidrug resistant strains isolated from transplant patients (hepatic, renal or renal/pancreatic) in order to examine their ability to adhere in vitro to HT-29 human colon cells, and to determine if some adhesive characteristics are associated with prevalence and persistence of these strains. A total of 33 E. coli (31%), 21 K. pneumoniae (27%), 7 Enterobacter spp. (28%), and 5 Citrobacter spp. (21%), adhered to the colon epithelial cells. Two main adherence patterns were observed in the four species analyzed, diffuse adherence, and aggregative adherence. Under transmission electronic microscopy (TEM), most bacteria lacked visible fimbria on their surface, despite their strong adherence to epithelial cells. None of the strains studied was able to induce any cytotoxic effect on HT-29 cells although some of them strongly colonizing both cells and glass coverslips at high density. Some of the strains failed to adhere to the epithelial cells but adhered strongly to the cover-slide, which shows that microscopy studies are mandatory to elucidate the adherence of bacteria to epithelial cells in vitro, and that quantitative assays using colony forming unit (CFUs) counting need to be supplemented with pictures to determine definitively if a bacterial strain adheres or not to animal cells in vitro. We report here, for the first time, the aggregative adherence pattern of two multidrug resistant (MDR) Citrobacter freundii strains isolated from human patients; importantly, biofilm formation in Citrobacter is totally dependent on the temperature; strong biofilms were formed at room temperature (RT) but not at 37°C, which can play an important role in the colonization of hospital surfaces. In conclusion, our results show that there is a great variety of adhesion phenotypes in multidrug-resistant strains that colonize transplanted patients.

The hydrophobicity of enterobacteria and their co-aggregation with Enterococcus faecalis isolated from Serbian cheese

In this paper, we investigated the hydrophobicity, ability to adhere to solvents and the pig epithelium and co-aggregation of members of family Enterobacteriaceae and Enterococcus faecalis KGPMF 49. The bacteria used in this study were isolated from traditionally made autochthonous cheese from Southeastern Serbia (Sokobanja). The percentage of adhered bacteria was different in three solvents (chloroform, ethyl acetate and xylene). The highest percentage was detected in the presence of chloroform, and the lowest percentage was detected in the presence of xylene (chloroform < ethyl acetate < xylene). A different degree of co-aggregation of enterobacteria with E. faecalis KGPMF 49 was observed. Klebsiella ornithinolytica KGPMF 8 demonstrated the highest percentage of co-aggregation with E. faecalis KGPMF49 (32.29%). Klebsiella pneumoniae KGPMF 13, K. ornithinolytica KGPMF 9 and Serratia marcescens biogp 1 KGPMF 19 were found to have the ability to adhere to the pig epithelium, whereas Escherichia coli KGPMF 22 showed no such ability. The ability to co-aggregate with other species and the ability to adhere to the pig epithelium are very important characteristics of the isolated bacteria.

Shotgun proteomic analysis of ESBL-producing and non-ESBL-producing Klebsiella Pneumoniae clinical isolates

Klebsiella pneumoniae is a pathogenic bacterium that is responsible for a wide range of infections in humans. An increased rate of infections caused by multi-drug-resistant K. pneumoniae has been noted in the last two decades. The association between antimicrobial resistance and virulence is an important topic of study. Genomic tools have been used widely for the detection of virulence. In our study, we used proteomic analysis with mass spectrometry and bioinformatics tools to explore the virulence factors of both ESBL-producing and non-ESBL-producing K. pneumoniae and to determine the association between virulence and antimicrobial resistance in these clinical isolates. We have revealed different proteomic profiles and different pathways between the ESBL- and non-ESBL-producing groups. Many proteins involved in stress responses have been reported in the shared proteome between ESBL-and non-ESBL producers, such as ElaB protein, Lon protease, and universal stress proteins G and A. The virulence and pathogenicity of ESBL-producing bacteria were stronger than those of the non-ESBL-producing bacteria. Several unique virulence determinants were identified in ESBL-producing K. pneumoniae, such as proteins with lyase, catalase, isochorismatase, and oxidoreductase activity.

IscR Regulation of Type 3 Fimbriae Expression in Klebsiella pneumoniae CG43

In Klebsiella pneumoniae, we have previously shown that IscR, an Fe–S cluster-containing transcriptional factor, plays a dual role in controlling capsular polysaccharide biosynthesis and iron-acquisition systems by switching between its holo and apo forms. In this study, the effect of IscR on type 3 fimbriae expression and biofilm formation was investigated. We found that production of the major subunit of type 3 fimbriae, MrkA, was increased in the ΔiscR and iscR_3CA strains, a strain expressing a mutant IscR that mimics apo-IscR, at both the translational and transcriptional levels. Based on the fact that type 3 fimbriae expression is the major factor affecting biofilm formation, increased biofilm formation was also found in ΔiscR or iscR_3CA, suggesting that holo-IscR represses biofilm formation. However, the repression of type 3 fimbriae expression by IscR is indirect. To further understand the regulatory mechanism of IscR, the effect of IscR on the expression of mrkHIJ, which encodes cyclic di-GMP (c-di-GMP)-related regulatory proteins that control type 3 fimbriae expression, was studied. We found that holo-IscR could directly repress mrkHI transcription, indicating that MrkHI is required for IscR regulation of type 3 fimbriae expression. Finally, deletion of iscR attenuated K. pneumoniae virulence in a peritonitis model of mouse infection, while the absence of the [2Fe–2S] cluster of IscR had no effect on K. pneumoniae virulence during infection. Taken together, our results demonstrate the underlying mechanism of the [2Fe–2S] cluster of IscR in controlling type 3 fimbriae expression and its effect on K. pneumoniae pathogenesis.

The KP1_4563 gene is regulated by the cAMP receptor protein and controls type 3 fimbrial function in Klebsiella pneumoniae NTUH-K2044

Klebsiella pneumoniae (K. pneumoniae) is an opportunistic pathogen that can adhere to host cells or extracellular matrix via type 1 and type 3 fimbriae. KP1_4563 is a gene encoding a hypothetical protein in K. pneumoniae NTUH-K2044. KP1_4563 is located between the type 1 and type 3 fimbrial gene clusters and is likely associated with fimbrial function given its putative conserved domains of unknown function (DUF1471). Cyclic AMP receptor protein (CRP) regulates virulence-related gene expression and is a crucial transcriptional regulator in many bacteria. The predicted DNA recognition motif of CRP is present in the KP1_4563 promoter region. This study aimed to investigate the function of KP1_4563 in fimbriae and its transcriptional regulation mechanism by CRP. We generated Kp-Δ4563 mutant and complementation strains. We utilized phenotype and adhesion assays to evaluate the role of KP1_4563 in fimbriae. We conducted quantitative RT-PCR (qRT-PCR), LacZ fusion, electrophoretic mobility shift, and DNase I footprinting assays to study the transcriptional regulation of KP1_4563 gene by CRP. We found that KP1_4563 negatively regulates the function of type 3 fimbriae. Compared with NTUH-K2044, the absence of KP1_4563 enhanced the ability of Kp-Δ4563 to adhere to A549 cells. CRP negatively regulates KP1_4563 by directly binding to its promoter region. KP1_4563 plays an important role in type 3 fimbrial function. This novel insight will assist in the development of strategies for preventing K. pneumoniae infection.

CRP-Cyclic AMP Regulates the Expression of Type 3 Fimbriae via Cyclic di-GMP in Klebsiella pneumoniae

Klebsiella pneumoniae is the predominant pathogen isolated from liver abscesses of diabetic patients in Asian countries. However, the effects of elevated blood glucose levels on the virulence of this pathogen remain largely unknown. Type 3 fimbriae, encoded by the mrkABCDF genes, are important virulence factors in K. pneumoniae pathogenesis. In this study, the effects of exogenous glucose and the intracellular cyclic AMP (cAMP) signaling pathway on type 3 fimbriae expression regulation were investigated. The production of MrkA, the major subunit of type 3 fimbriae, was increased in glucose-rich medium, whereas cAMP supplementation reversed the effect. MrkA production was markedly increased by cyaA or crp deletion, but slightly decreased by cpdA deletion. In addition, the mRNA levels of mrkABCDF genes and the activity of P_mrkA were increased in Δcrp strain, as well as the mRNA levels of mrkHIJ genes that encode cyclic di-GMP (c-di-GMP)-related regulatory proteins that influence type 3 fimbriae expression. Moreover, the activities of P_mrkHI and P_mrkJ were decreased in ΔlacZΔcrp strain. These results indicate that CRP-cAMP down-regulates mrkABCDF and mrkHIJ at the transcriptional level. Further deletion of mrkH or mrkI in Δcrp strain diminished the production of MrkA, indicating that MrkH and MrkI are required for the CRP regulation of type 3 fimbriae expression. Furthermore, the high activity of P_mrkHI in the ΔlacZΔcrp strain was diminished in ΔlacZΔcrpΔmrkHI, but increased in the ΔlacZΔcrpΔmrkJ strain. Deletion of crp increased the intracellular c-di-GMP concentration and reduced the phosphodiesterase activity. Moreover, we found that the mRNA levels of multiple genes related to c-di-GMP metabolism were altered in Δcrp strain. These indicate that CRP regulates type 3 fimbriae expression indirectly via the c-di-GMP signaling pathway. In conclusion, we found evidence of a coordinated regulation of type 3 fimbriae expression by the CRP-cAMP and c-di-GMP signaling pathways in K. pneumoniae.

Carbapenem resistance confers to Klebsiella pneumoniae strains an enhanced ability to induce infection and cell death in epithelial tissue-specific in vitro models

BACKGROUND

Carbapenem-resistant Klebsiella pneumoniae strains (KPC-Kp) are emerging worldwide causing different nosocomial infections including those of the urinary tract, lung or skin wounds. For these strains, the antibiotic treatment is limited to only few choices including colistin, whose continuous use led to the emergence of carbapenem-resistant KPC-Kp strains resistant also to this treatment (KPC-Kp Col-R).

AIM

Very little is known about the capacity of the different strains of KPC-Kp to invade the epithelial cells in vitro. To verify if the acquisition of carbapenem-resistant and the colistin-resistant phenotypes are correlated with a different ability to infect a series of epithelial cell lines of various tissutal origin and with a different capacity to induce cellular death.

MATERIALS & METHODS

We used Klebsiella pneumoniae (KP), KPC-Kp and KPC-Kp Col-R strains, isolated from different patients carrying various tissue-specific infections, to infect a series of epithelial cell lines of different tissutal origin. The invasive capacity of the strains and the extent and characteristics of the cell damage and death induced by the bacteria were evaluated and compared.

CONCLUSION

Our results show that both KPC-Kp and KPC-Kp Col-R display a greater ability to infect the epithelial cells, with respect to KP, and that the bacterial cell invasion results in a nonprogrammed cell death.

Patterns of Adherence of Helicobacter pylori Clinical Isolates to Epithelial Cells, and its Association with Disease and with Virulence Factors

BACKGROUND AND AIM

Adherence to the gastric epithelium is one of the most important steps of Helicobacter pylori to remain and cause disease. The aim of this study was to analyze whether H. pylori isolates from patients with different gastroduodenal diseases present differences in the pattern of adherence to gastric epithelial cells (AGS), in the ability to induce IL-8, and in the presence of virulence genes.

METHODS

We tested 75 H. pylori strains isolated from nonatrophic gastritis, gastric cancer, and duodenal ulcer patients. The adhesion pattern and IL-8 induction were determined in AGS cells, and invasion of AGS cells was studied using a gentamicin protection assay. The IL-8 levels induced were determined by ELISA.

RESULTS

Helicobacter pylori strains presented diffuse adherence (DA) and localized (LA) adherence patterns, similar to those described for enteropathogenic E. coli (EPEC), were observed in AGS cells. A DA pattern was observed in 57% and LA in 43% of the strains, and DA was more frequent in isolates from patients with gastric cancer (p = 0.044). Strains with a LA pattern induced higher levels of IL-8 (p = 0.042) in AGS cells.

CONCLUSION

The adherence pattern was not associated with neither invasiveness nor with the presence of virulence genes. Our study shows that H. pylori strains present adherence patterns to AGS cells resembling those observed in EPEC and that these patterns may be associated with disease and with activity on AGS cells.

Correlation between antimicrobial resistance and virulence in Klebsiella pneumoniae

Klebsiella pneumoniae is responsible for a wide range of infections, including urinary tract infections, pneumonia, bacteremia, and liver abscesses. In addition to susceptible clinical isolates involved in nosocomial infections, multidrug-resistant (MDR) and hypervirulent (hvKP) strains have evolved separately in distinct clonal groups. The rapid geographic spread of these isolates is of particular concern. However, we still know little about the virulence of K. pneumoniae except for hvKP, whose secrets are beginning to be revealed. The treatment of K. pneumoniae infections is threatened by the emergence of antimicrobial resistance. The dissemination of resistance is associated with genetic mobile elements, such as plasmids that may also carry virulence determinants. A proficient pathogen should be virulent, resistant to antibiotics, and epidemic. However, the interplay between resistance and virulence is poorly understood. Here, we review current knowledge on the topic.

Effect of Nosocomial Infections Due to Antibiotic-Resistant Organisms on Length of Stay and Mortality in the Pediatric Intensive Care Unit

Objective.

To determine the prevalence, risk factors, and outcomes of nosocomial infection due to antimicrobial resistant bacteria in patients treated in the pediatric intensive care unit (PICU).

Design.

Nested case-cohort study. Patient data were collected prospectively, and antimicrobial susceptibility data were abstracted retrospectively.

Setting.

A large pediatric teaching hospital.

Patients.

All PICU patients admitted from September 1, 1999, to September 1, 2001, unless they died within 24 hours after PICU admission, were 18 years old or older, or were neonatal intensive care unit patients receiving extracorporeal membrane oxygenation.

Results.

A total of 135 patients with more than 1 nosocomial bacterial infection were analyzed; 52% were male, 75% were white, the mean Pediatric Risk of Mortality score was 10.5, and the mean age was 3.5 years. Of these patients, 37 (27%) had nosocomial infections due to antibiotic-resistant organisms. In univariate analysis, transplantation (odds ratio [OR], 2.83 [95% confidence interval (CI), 1.05-7.66]) and preexisting lung disease (OR, 2.63 [95% CI, 1.18-5.88]) were associated with nosocomial infections due to antibiotic-resistant organisms. Age, Pediatric Risk of Mortality score at admission, length of hospital stay before infection, and other underlying conditions were not associated with infections due to antibiotic-resistant organisms. Patients infected with antibiotic-resistant organisms had greater mean PICU lengths of stay after infection, compared with patients infected with antibiotic-susceptible organisms (22.9 vs 12.8 days;P= .004), and higher crude mortality rates (OR, 2.40 [95% CI, 1.03-5.61]).

Conclusions.

Identifiable risk factors exist for nosocomial infections due to antibiotic-resistant organisms. In univariate analysis, infections due to antibiotic-resistant bacteria are associated with increased length of stay in the PICU after onset of infection and increased mortality.

Genome Sequence of Klebsiella pneumoniae Respiratory Isolate IA565

Klebsiella pneumoniae is a clinically significant opportunistic bacterial pathogen as well as a normal member of the human microbiota. K. pneumoniae strain IA565 was isolated from a tracheal aspirate at the University of Iowa Hospitals and Clinics. Here, we present the genome sequence of K. pneumoniae IA565.

Antibiotic Resistance Related to Biofilm Formation in Klebsiella pneumoniae

The Gram-negative opportunistic pathogen, Klebsiella pneumoniae, is responsible for causing a spectrum of community-acquired and nosocomial infections and typically infects patients with indwelling medical devices, especially urinary catheters, on which this microorganism is able to grow as a biofilm. The increasingly frequent acquisition of antibiotic resistance by K. pneumoniae strains has given rise to a global spread of this multidrug-resistant pathogen, mostly at the hospital level. This scenario is exacerbated when it is noted that intrinsic resistance to antimicrobial agents dramatically increases when K. pneumoniae strains grow as a biofilm. This review will summarize the findings about the antibiotic resistance related to biofilm formation in K. pneumoniae.

Transcriptional activation of the mrkA promoter of the Klebsiella pneumoniae type 3 fimbrial operon by the c-di-GMP-dependent MrkH protein

The Gram-negative bacterial pathogen Klebsiella pneumoniae forms biofilms to facilitate colonization of biotic and abiotic surfaces. The formation of biofilms by K. pneumoniae requires the expression of type 3 fimbriae: elongate proteinaceous filaments extruded by a chaperone-usher system in the bacterial outer membrane. The expression of the mrkABCDF cluster that encodes this fimbrial system is strongly positively regulated by MrkH, a transcriptional activator that responds to the second messenger, c-di-GMP. In this study, we analyzed the mechanism by which the MrkH protein activates transcriptional initiation from the mrkA promoter. A mutational analysis supported by electrophoretic mobility shift assays demonstrated that a 12-bp palindromic sequence (the MrkH box) centered at -78.5 is the binding site of MrkH. Deletion of half a turn, but not a full turn, of DNA located between the MrkH box and the mrkA promoter destroyed the ability of MrkH to activate mrkA transcription. In addition, a 10-bp AT-rich sequence (the UP element) centered at -63.5 contributed significantly to MrkH-dependent mrkA transcription. In vivo analysis of rpoA mutants showed that the R265 and E273 determinants in the C-terminal domain of RNA polymerase α subunit are needed for MrkH-mediated activation of mrkA transcription. Furthermore, results from mutagenesis of the mrkH gene suggest that the N-terminal region of the protein is involved in transcriptional activation. Taken together, our results suggest that MrkH activates mrkA expression by interacting directly with RNA polymerase, to overcome the inefficient transcriptional initiation caused by the presence of defective core promoter elements.

Structural and population characterization of MrkD, the adhesive subunit of type 3 fimbriae

Type 3 fimbriae are adhesive organelles found in enterobacterial pathogens. The fimbriae promote biofilm formation on biotic and abiotic surfaces; however, the exact identity of the receptor for the type 3 fimbriae adhesin, MrkD, remains elusive. We analyzed naturally occurring structural and functional variabilities of the MrkD adhesin from Klebsiella pneumoniae and Escherichia coli isolates of diverse origins. We identified a total of 33 allelic variants of mrkD among 90 K. pneumoniae isolates and 10 allelic variants among 608 E. coli isolates, encoding 11 and 9 protein variants, respectively. Based on the level of accumulated silent variability between the alleles, mrkD was acquired a relatively long time ago in K. pneumoniae but recently in E. coli. However, unlike K. pneumoniae, mrkD in E. coli is actively evolving under a strong positive selection by accumulation of mutations, often targeting the same positions in the protein. Several naturally occurring MrkD protein variants from E. coli were found to be significantly less adherent when tested in a mannan-binding assay and showed reduced biofilm-forming capacity. Functional examination of the MrkD adhesin in flow chamber experiments determined that it interacts with Saccharomyces cerevisiae cells in a shear-dependent manner, i.e., the binding is catch-bond-like and enhanced under increasing shear conditions. Homology modeling strongly suggested that MrkD has a two-domain structure, comprising a pilin domain anchoring the adhesin to the fimbrial shaft and a lectin domain containing the binding pocket; this is similar to structures found in other catch-bond-forming fimbrial adhesins in enterobacteria.

Role of Klebsiella pneumoniae type 1 and type 3 fimbriae in colonizing silicone tubes implanted into the bladders of mice as a model of catheter-associated urinary tract infections

Catheter-associated urinary tract infections are biofilm-mediated infections that cause a significant economic and health burden in nosocomial environments. Using a newly developed murine model of this type of infection, we investigated the role of fimbriae in implant-associated urinary tract infections by the Gram-negative bacterium Klebsiella pneumoniae, which is a proficient biofilm former and a commonly isolated nosocomial pathogen. Studies have shown that type 1 and type 3 fimbriae are involved in attachment and biofilm formation in vitro, and these fimbrial types are suspected to be important virulence factors during infection. To test this hypothesis, the virulence of fimbrial mutants was assessed in independent challenges in which mouse bladders were inoculated with the wild type or a fimbrial mutant and in coinfection studies in which the wild type and fimbrial mutants were inoculated together to assess the results of a direct competition in the urinary tract. Using these experiments, we were able to show that both fimbrial types serve to enhance colonization and persistence. Additionally, a double mutant had an additive colonization defect under some conditions, indicating that both fimbrial types have unique roles in the attachment and persistence in the bladder and on the implant itself. All of these mutants were outcompeted by the wild type in coinfection experiments. Using these methods, we are able to show that type 1 and type 3 fimbriae are important colonization factors in the murine urinary tract when an implanted silicone tube is present.

Aggregative adherent strains of Corynebacterium pseudodiphtheriticum enter and survive within HEp-2 epithelial cells

Corynebacterium pseudodiphtheriticum is a well-known human pathogen that mainly causes respiratory disease and is associated with high mortality in compromised hosts. Little is known about the virulence factors and pathogenesis of C. pseudodiphtheriticum. In this study, cultured human epithelial (HEp-2) cells were used to analyse the adherence pattern, internalisation and intracellular survival of the ATCC 10700 type strain and two additional clinical isolates. These microorganisms exhibited an aggregative adherence-like pattern to HEp-2 cells characterised by clumps of bacteria with a "stacked-brick" appearance. The differences in the ability of these microorganisms to invade and survive within HEp-2 cells and replicate in the extracellular environment up to 24 h post infection were evaluated. The fluorescent actin staining test demonstrated that actin polymerisation is involved in the internalisation of the C. pseudodiphtheriticum strains. The depolymerisation of microfilaments by cytochalasin E significantly reduced the internalisation of C. pseudodiphtheriticum by HEp-2 cells. Bacterial internalisation and cytoskeletal rearrangement seemed to be partially triggered by the activation of tyrosine kinase activity. Although C. pseudodiphtheriticum strains did not demonstrate an ability to replicate intracellularly, HEp-2 cells were unable to fully clear the pathogen within 24 h. These characteristics may explain how some C. pseudodiphtheriticum strains cause severe infection in human patients.

Multi-functional analysis of Klebsiella pneumoniae fimbrial types in adherence and biofilm formation

Klebsiella pneumoniae is an opportunistic pathogen frequently associated with nosocomially acquired infections. Host cell adherence and biofilm formation of K. pneumoniae isolates is mediated by type 1 (T1P) and type 3 (MR/K) pili whose major fimbrial subunits are encoded by the fimA and mrkA genes, respectively. The E. coli common pilus (ECP) is an adhesive structure produced by all E. coli pathogroups and a homolog of the ecpABCDE operon is present in the K. pneumoniae genome. In this study, we aimed to determine the prevalence of these three fimbrial genes among a collection of 69 clinical and environmental K. pneumoniae strains and to establish a correlation with fimbrial production during cell adherence and biofilm formation. The PCR-based survey demonstrated that 96% of the K. pneumoniae strains contained ecpA and 94% of these strains produced ECP during adhesion to cultured epithelial cells. Eighty percent of the strains forming biofilms on glass produced ECP, suggesting that ECP is required, at least in vitro, for expression of these phenotypes. The fim operon was found in 100% of the strains and T1P was detected in 96% of these strains. While all the strains examined contained mrkA, only 57% of them produced MR/K fimbriae, alone or together with ECP. In summary, this study highlights the ability of K. pneumoniae strains to produce ECP, which may represent a new important adhesive structure of this organism. Further, it defines the multi-fimbrial nature of the interaction of this nosocomial pathogen with host epithelial cells and inert surfaces.

Changes in bacterial composition of zucchini flowers exposed to refrigeration temperatures

Microbial spoilage is one of the main factors affecting the quality of fresh fruits and vegetables, leading to off-flavor, fermented aroma, and tissue decay. The knowledge of microbial growth kinetics is essential for estimating a correct risk assessment associated with consuming raw vegetables and better managing the development of spoilage microorganisms. This study shows, for the first time, that only a part of total microbial community, originally present on fresh harvested female zucchini flowers, was able to adapt itself to refrigerated conditions. Through the study of microbial growth kinetics it was possible to isolate forty-four strains belonging to twenty-two species of the genera Acinetobacter, Arthrobacter, Bacillus, Enterobacter, Erwinia, Klebsiella, Pantoea, Pseudoclavibacter, Pseudomonas, Serratia, Staphylococcus, and Weissella, suggesting Enterobacteriaceae as potentially responsible for pistil spoilage.

Influence of consumption of probiotics on presence of enterobacteria in the oral cavity

Clinical benefits of probiotics have been clearly reported in different gastrointestinal disorders, many of them caused by enterobacteria. The oral cavity is a port of entry and can be an important reservoir of these microorganisms. This work evaluated whether consumption of probiotics was able to influence the presence of enterobacteria in the oral cavity and the specific secretory response against these microorganisms. Saliva samples of healthy individuals were collected and plated in MacConkey agar. Carriers of Gram-negative, rod-shaped microorganisms in the oral cavity were selected and instructed to use the probiotic Yakult LB for 20 days. Saliva was then collected and enterobacteria species were identified using the API 20 E system and by ELISA using anti-enterobacteria IgA. The results showed reduction in the prevalence of enterobacteria, but no significant changes in enterobacterial counts (log CFU/mL; p = 0.3457). The species most frequently isolated were Enterobacter cloacae and Klebsiella oxytoca, both before and after probiotic consumption. No significant changes were observed in anti-enterobacteria IgA levels. In conclusion, probiotic consumption had some influence on enterobacterial presence in the oral cavity, but did not affect enterobacterial counts or the specific immune secretory response against them.

Association of antibiotic resistance in agricultural Escherichia coli isolates with attachment to quartz

Surface water can be contaminated by bacteria from various sources, including manure from agricultural facilities. Attachment of these bacteria to soil and organic particles contributes to their transport through the environment, though the mechanism of attachment is unknown. As bacterial attachment to human tissues is known to be correlated with antibiotic resistance, we have investigated here the relationship between bacterial attachment to environmental particles and antibiotic resistance in agricultural isolates. We evaluated 203 Escherichia coli isolates collected from swine facilities for attachment to quartz, resistance to 13 antibiotics, and the presence of genes encoding 13 attachment factors. The genes encoding type I, EcpA, P pili, and Ag43 were detected, though none was significantly related to attachment. Quartz attachment was positively and significantly (P < 0.0038) related to combined resistance to amoxicillin/streptomycin/tetracycline/sulfamethazine/tylosin/chlortetracycline and negatively and significantly (P < 0.0038) related to combined resistance to nalidixic acid/kanamycin/neomycin. These results provide clear evidence for a link between antibiotic resistance and attachment to quartz in agricultural isolates. We propose that this may be due to encoding by the responsible genes on a mobile genetic element. Further exploration of the relationship between antibiotic resistance and attachment to environmental particles will improve the understanding and modeling of environmental transport processes, with the goal of preventing human exposure to antibiotic-resistant or virulent microorganisms.

Extended-spectrum beta-lactamase production is associated with an increase in cell invasion and expression of fimbrial adhesins in Klebsiella pneumoniae

Extended-spectrum beta-lactamase (ESBL)-producing Klebsiella pneumoniae strains are suggested to possess higher pathogenic potential than non-ESBL producers. Microbial adherence to and invasion of host cells are critical steps in the infection process, so we examined the expression of type 1 and 3 fimbrial adhesins by 58 ESBL-producing and 152 nonproducing isolates of K. pneumoniae and their abilities to invade ileocecal and bladder epithelial cells. Mannose-sensitive hemagglutination of guinea pig erythrocytes and mannose-resistant hemagglutination of ox erythrocytes were evaluated to determine the strains' abilities to express type 1 and type 3 fimbriae, respectively. Bacterial adhesion to and invasion of epithelial cells were tested by enzyme-linked immunosorbent assay and imipenem killing assay, respectively. The adherence of ESBL- and non-ESBL-producing strains to epithelial cells did not differ significantly (P > 0.05). In contrast, the proportion of strains capable of invading (>5% relative invasion) ileocecal and bladder epithelial cells was significantly higher among ESBL producers (81%, n = 47/58, and 27.6%, n = 16/58, respectively) than among non-ESBL producers (61%, n = 93/152, and 10%, n = 15/152, respectively) (P = 0.0084, odds ratio [OR] = 2.711, 95% confidence interval [CI] = 1.302 to 5.643 and P = 0.0021, OR = 4.79, 95% CI = 1.587 to 7.627). The mean invasion by ESBL producers (5.5% +/- 2.8% and 3.3% +/- 2.7%, respectively) was significantly higher than that by non-ESBL producers (2.9% +/- 2.6% and 1.8% +/- 2%, respectively) (P < 0.0001). Likewise, the proportion of ESBL producers coexpressing both fimbrial adhesins was significantly higher (79.3%; n = 46/58) than that of non-ESBL producers (61.8%; n = 94/152) (P = 0.0214; OR = 2,365; 95% CI = 1.157 to 4.834). Upon acquisition of SHV-12-encoding plasmids, two transconjugants switched on to produce type 3 fimbriae while expression of type 1 fimbriae was not affected. The acquisition of an ESBL plasmid appeared to upregulate the phenotypic expression of one or more genes, resulting in greater invasion ability.

Characterization of Klebsiella pneumoniae type 1 fimbriae by detection of phase variation during colonization and infection and impact on virulence

Klebsiella pneumoniae is recognized as an important gram-negative opportunistic pathogen. The ability of bacteria to adhere to host structures is considered essential for the development of infections; however, few studies have examined the influence of adhesion factors on K. pneumoniae virulence. In this study, we cloned and characterized the type 1 fimbria gene cluster of a clinical K. pneumoniae isolate. Although this cluster was not identical to the Escherichia coli type 1 fimbria gene cluster, an overall high degree of structural resemblance was demonstrated. Unique to the K. pneumoniae fim gene cluster is the fimK gene, whose product contains an EAL domain, suggesting that it has a role in regulation of fimbrial expression. Like expression of type 1 fimbriae in E. coli, expression of type 1 fimbriae in K. pneumoniae was found to be phase variable, and an invertible DNA element (fim switch) was characterized. An isogenic type 1 fimbria mutant was constructed and used to evaluate the influence of type 1 fimbriae in different infection models. Type 1 fimbriae did not influence the ability of K. pneumoniae to colonize the intestine or infect the lungs, but they were determined to be a significant virulence factor in K. pneumoniae urinary tract infection. By use of a PCR-based assay, the orientation of the fim switch during colonization and infection was investigated and was found to be all "off" in the intestine and lungs but all "on" in the urinary tract. Our results suggest that during colonization and infection, there is pronounced selective pressure in different host environments for selection of either the type 1 fimbriated or nonfimbriated phenotype of K. pneumoniae.

Type 3 fimbriae, encoded by the conjugative plasmid pOLA52, enhance biofilm formation and transfer frequencies in Enterobacteriaceae strains

The conjugative plasmid pOLA52, which confers resistance to olaquindox and other antimicrobial agents through a multidrug efflux pump, was investigated for its ability to promote biofilm formation in Escherichia coli. Screening of a transposon-mutagenized pOLA52 clone library revealed several biofilm-deficient mutants, which all mapped within a putative operon with high homology to the mrkABCDF operon of Klebsiella pneumoniae, where these genes are responsible for type 3 fimbriae expression, attachment to surfaces and biofilm formation. Biofilm formation in microtitre plates and in urinary catheters of clones containing pOLA52 with a disrupted putative mrk operon was reduced by more than 100-fold and 2-fold, respectively, compared to mutants with an intact mrk operon. The conjugative transfer rate of pOLA52 was also significantly lower when the mrk operon was disrupted. Through reverse transcriptase analysis, it was demonstrated that the genes contained in the putative mrk operon were linked and likely to be expressed as a single operon. Immunoblotting with type 3 fimbriae (MrkA)-specific antibodies further verified expression of type 3 fimbriae. When transferred to other, potentially pathogenic, members of the family Enterobacteriaceae, including Klebsiella pneumoniae, Salmonella Typhimurium, Kluyvera sp. and Enterobacter aerogenes, pOLA52 facilitated increased biofilm formation. pOLA52 is believed to represent the first example of a conjugative plasmid encoding type 3 fimbriae, resulting in enhanced conjugation frequencies and biofilm formation of the plasmid-harbouring strain.

Prevalence and genetic diversity of Enterobacter sakazakii in ingredients of infant foods

Various food samples in Korea were examined for the presence of Enterobacter sakazakii. Dried shrimp had the highest contamination rate among the examined dried fish products. E. sakazakii isolates were confirmed using an API 20E kit and a polymerase chain reaction (PCR) targeting the rDNA operons. The isolates were subtyped by pulsed-field gel electrophoresis (PFGE) using XbaI to elucidate the genetic diversity of the organisms. Ten pulsotypes were identified using PFGE and 22 types were identified from the random amplified polymorphism DNA (RAPD) assay. An antibiotic resistance test was performed by disk diffusion assay using eight antibiotics: nalidixic acid, ciprofloxacin, chloramphenicol, ampicillin, tetracycline, gentamicin, kanamycin, and cephalothin. Most of the E. sakazakii isolates were resistant to ampicillin or cephalothin but susceptible to the other antibiotics. The analysis of E. sakazakii isolates using PFGE, RAPD, and the antibiotic resistance test identified 18 composite types from 113 isolates, suggesting diverse sources of contamination.

Occurrence of Periodontopathic and Superinfecting Bacteria in Chronic and Aggressive Periodontitis Subjects in a Colombian Population

BACKGROUND

Differences in the composition of subgingival microbiota in periodontitis have been observed in different geographic locations. Some of these microbial differences could have clinical significance. This study describes clinical parameters and the composition of the subgingival microbiota in chronic periodontitis (CP) and aggressive periodontitis (AgP) patients in a Colombian population.

METHODS

Clinical parameters (probing depth, clinical attachment level, bleeding on probing, and plaque index) and plaque samples from 68 CP, 12 AgP, and 30 periodontally healthy subjects were analyzed. Subgingival samples were processed using culture, biochemical tests, and polymerase chain reaction for the detection of periodontal and superinfecting pathogens. The analysis of variance, chi(2), and Kruskal-Wallis tests were used to evaluate differences between groups for clinical parameters and microbiologic composition (P <or=0.05).

RESULTS

Clinical parameters were significantly increased in CP and AgP patients compared to healthy subjects (P <0.001), but no differences were found between periodontitis groups. Porphyromonas gingivalis, Tannerella forsythensis, and Eikenella corrodens showed higher frequencies in AgP compared to CP and healthy subjects (P <0.05). Extension (localized and generalized) of the periodontal destruction had no effect on the composition of the subgingival microbiota. Gram-negative enteric rods were more frequent in AgP patients (P <0.01).

CONCLUSIONS

This study demonstrated a high prevalence of P. gingivalis, T. forsythensis, and E. corrodens in AgP patients. Gram-negative enteric rods were frequent in AgP and CP patients. Differences in the composition of subgingival microbiota in periodontitis patients need to be taken into account when considering the best therapeutic approach for each individual, including the use of antibiotics.

Influence of capsule and extended-spectrum beta-lactamases encoding plasmids upon Klebsiella pneumoniae adhesion

Interaction with cells is believed to be a crucial step in the process of colonization by Klebsiella pneumoniae. In this study, we investigated the adhesion properties of 17 extended-spectrum beta-lactamases (ESBLs) producing clinical isolates using 2 intestinal cells (Int-407 and HT-29 cells) and components of the extracellular matrix (ECM) (fibrinogen, collagen, fibronectin). Since the capsule formed by K. pneumoniae potentially masks bacterial cell surface components, we created mutants defective in capsular synthesis. The levels of adhesion of the acapsulated mutants were higher than their corresponding wild-type strains for 7 and 4 isolates with Int-407 and HT-29 cells, respectively, whereas 2 mutants displayed lower adhesion indexes with HT-29 cells. Nine mutants adhered at higher levels than their corresponding wild-type strains to all 3 components of ECM tested and 13 only to collagen. Transfer by mating of ESBL-encoding plasmids did not correlate with the acquisition of adhesive properties by the transconjugants, which suggests that these plasmids were not involved in adhesion expression. The presence of ESBL-encoding plasmids alters the basal adhesion capacity of the recipient strain, and cured strains adhered more than the parental strains. The possessing of capsule or plasmid-encoded factors would have a bacterial cost, including a weaker capacity for adhesion.

Adhesive properties of Enterobacter sakazakii to human epithelial and brain microvascular endothelial cells

Background

Enterobacter sakazakii is an opportunistic pathogen that has been associated with sporadic cases and outbreaks causing meningitis, necrotizing enterocolitis and sepsis especially in neonates. However, up to now little is known about the mechanisms of pathogenicity in E. sakazakii. A necessary state in the successful colonization, establishment and ultimately production of disease by microbial pathogens is the ability to adhere to host surfaces such as mucous membranes, gastric and intestinal epithelial or endothelial tissue.

This study examined for the first time the adherence ability of 50 E. sakazakii strains to the two epithelial cell lines HEp-2 and Caco-2, as well as the brain microvascular endothelial cell line HBMEC. Furthermore, the effects of bacterial culture conditions on the adherence behaviour were investigated. An attempt was made to characterize the factors involved in adherence.

Results

Two distinctive adherence patterns, a diffuse adhesion and the formation of localized clusters of bacteria on the cell surface could be distinguished on all three cell lines. In some strains, a mixture of both patterns was observed. Adherence was maximal during late exponential phase, and increased with higher MOI. The adhesion capacity of E. sakazakii to HBMEC cells was affected by the addition of blood to the bacteria growth medium. Mannose, hemagglutination, trypsin digestion experiments and transmission electron microscopy suggested that the adhesion of E. sakazakii to the epithelial and endothelial cells is mainly non-fimbrial based.

Conclusion

Adherence experiments show heterogeneity within different E. sakazakii strains. In agreement with studies on E. cloacae, we found no relationship between the adhesive capacities in E. sakazakii and the eventual production of specific fimbriae. Further studies will have to be carried out in order to determine the adhesin(s) involved in the interaction of E. sakazakii with cells and to enhance knowledge of the pathogenesis of E. sakazakii infection.

Seroepidemiology of Klebsiella pneumoniae in an Australian Tertiary Hospital and its implications for vaccine development

The aim of this study was to determine the diversity of Klebsiella pneumoniae capsular serotypes in an Australian setting. Consecutive (n = 293) nonrepetitive isolates of K. pneumoniae from a large teaching hospital laboratory were analyzed. The majority of isolates were from urinary specimens (60.8%); the next most common source was sputum (14.3%), followed by blood (14%). Serotyping revealed a wide range of capsule types. K54 (17.1%), K28 (4.1%), and K17 (3.1%) were the most common, and K54 isolates displayed a high degree of clonality, suggesting a common, nosocomial source. In vitro, one K54 isolate was more adherent to urinary catheters and HEp-2 cells than four other tested isolates; it was slightly more resistant to chlorhexidine but was more susceptible to drying than heavily encapsulated strains. This is the first seroprevalence survey of K. pneumoniae to be performed on Australian isolates, and the high level of diversity of serotypes suggests that capsule-based immunoprophylaxis might not be useful for Australia. In addition there are significant differences in the predominance of specific serotypes compared to the results of surveys performed overseas, which has important implications for capsule-based immunoprophylaxis aimed at a global market.

Pseudomonas aeruginosa isolates recovered from clinical and environmental samples in Buea, Cameroon: current status on biotyping and antibiogram

OBJECTIVE

The study was aimed at determining the prevalent biotypes of Pseudomonas aeruginosa in the environment of Buea and the susceptibility of isolates to antibiotics.

METHODS

One hundred and fifty clinical specimens (urine, wound and sputum) collected from patients attending various health institutions in Buea, and 50 environmental swabs from furniture, appliances and surroundings of these institutions were screened for P. aeruginosa using standard microbiological and biochemical methods. Antimicrobial susceptibility of the isolates was determined by the disc diffusion assay.

RESULTS

Fifty-one (25.5%) of the 200 specimens were positive for the organism with urine (30%) being the most common source of isolation. Biochemical characterization grouped the isolates into eight biotypes with biotypes B III (25.59%), B II (23.53%) and B I (21.57%) being the most prevalent. Antimicrobial susceptibility results of isolates revealed 13 antibiotype patterns based on resistance to the antimicrobial agents investigated. The resistance pattern, cefotaxime, gentamicin and tetracycline (CTX(R) GEN(R) TET(R)) was the most common (21.6%) amongst the isolates. Over 40% of the isolates exhibited multi-drug resistance to five or more antibiotics, especially environmental isolates. However, there was a significant difference (P < 0.05) in the susceptibility of isolates to ciprofloxacin (98%), amikacin (90.2%) and netilmicin (80.4%) compared with other drugs used in the study.

CONCLUSION

A combination of biotyping and antibiogram, which are relatively cheap and routinely available methods in our environment, could be useful for clinical and epidemiological studies particularly in laboratories in the developing world with limited resources.

Increased serum resistance in Klebsiella pneumoniae strains producing extended-spectrum beta-lactamases

The aim of this study was to determine whether there is an association between serum resistance, O serotypes, and the production of extended-spectrum beta-lactamases (ESBLs) in Klebsiella pneumoniae. Ninety ESBL-producing and 178 non-ESBL-producing K. pneumoniae isolates gathered in five European countries were O serotyped and tested for sensitivity to the serum's bactericidal effect. The frequency of serum-resistant isolates was higher among ESBL-producing strains (30%; 27/90 isolates) than among non-ESBL-producing strains (17.9%; 32/178 isolates) (P = 0.037; odds ratio [OR] = 1.96; 95% confidence interval [95% CI] = 1.08 to 3.53). Although O1 was the most common O serotype in both Klebsiella groups, its frequency among ESBL-producing strains was significantly higher (59%; 53/90 isolates) than among non-ESBL producers (36%; 64/178 isolates) (P = 0.0006; OR = 2.5; 95% CI = 1.52 to 4.29). Furthermore, the prevalence of the O1 serotype was higher among serum-resistant strains of both ESBL-producing (74%; 20/27isolates) and non-ESBL producers (75%; 24/32 isolates) than among serum-sensitive ESBL producers (52.4%; 33/63 isolates) and non-ESBL producers (27.4%; 40/146 isolates). Serum resistance among ESBL-producing strains (36%; 17/47 isolates) versus non-ESBL-producing strains (16%; 27/166 isolates) was also significantly higher after the exclusion of clonal strains (P = 0.0056; OR = 2.9; 95% CI = 1.41 to 6.01). Sixteen ESBL types were detected, among which the frequency of serum resistance was significantly lower among the SHV-producing strains (9/48 isolates) than among the TEM producers (16/35 isolates) (P = 0.016; OR = 3.65; CI = 1.3 to 9.7). Curing ESBL-coding plasmids did not influence the serum resistance of the bacteria; all six plasmid-cured derivatives maintained serum resistance. The present findings suggest that ESBL-producing strains have a greater pathogenic potential than non-ESBL-producing strains, but the linkage between O serotypes, serum resistance, and ESBL production remains unclear at this stage.

Pathogenic potential of environmental Klebsiella pneumoniae isolates

Klebsiella pneumoniae is an important opportunistic pathogen and a frequent cause of nosocomial infections. K. pneumoniae infections can occur at nearly any body site; however, urinary tract infections and infections of the respiratory tract predominate. Infections are frequently preceded by gastrointestinal colonization, and the gastrointestinal tract is believed to be the most important reservoir for transmission of the bacteria. In contrast to many other bacterial pathogens, K. pneumoniae is ubiquitous in nature. Several studies have described Klebsiella isolates of environmental origin to be nearly identical to clinical isolates with respect to several phenotypic properties. However, the pathogenic potential of environmental K. pneumoniae isolates is essentially unknown. We have evaluated the virulence of K. pneumoniae strains of environmental and clinical origin directly in animal models, i.e. in urinary tract infection and intestinal colonization models. Furthermore, the ability to adhere to and invade human epithelial cell lines was examined. Although strain-to-strain differences were observed in the individual infection models, overall, strains of environmental origin were found to be as virulent as strains of clinical origin. The ubiquity of K. pneumoniae in nature and the general ability of K. pneumoniae strains to infect susceptible hosts might explain the high frequency of opportunistic infections caused by this species.

Impairment of respiratory burst in polymorphonuclear leukocytes by extended-spectrum beta-lactamase-producing strains of Klebsiella pneumoniae

The ability of extended-spectrum beta-lactamase (ESBL)-producing and non-ESBL-producing Klebsiella pneumoniae strains to induce a respiratory burst in polymorphonuclear leukocytes (PMNLs) was investigated. Ninety ESBL-producing and 178 non-ESBL-producing Klebsiella pneumoniae isolates were serotyped and their ability to induce a respiratory burst in PMNLs tested by monitoring the cells' chemiluminescence (CL) response. The percentage of isolates inducing high levels of CL response (CL>75%) was significantly higher among non-ESBL producers (52%) than among ESBL producers (32.2%) ( P<0.0001; OR=3.396; 95%CI=2.036-5.664). The median CL response was significantly higher among the non-ESBL producers (76.9%) than among the ESBL producers (52.6%) ( P=0.034). The two groups did not differ in their ability to resist intracellular killing by PMNLs ( P>0.05), with strains inducing high levels of CL response having significantly lower survival rates (31.8% vs. 42.4%) than strains inducing low levels of CL response (164% vs. 200%) ( P<0.01). The frequencies of the K2 and the K25 serotypes were significantly higher among ESBL-producing strains (17.8% and 22.2%, respectively) than among the non-ESBL producers (6.2% and 1.7%, respectively) ( P=0.0057 and P<0.0001). Of the 77 Klebsiella K serotypes, 71 were detectable among the non-ESBL producers, but only 24 were detectable among the ESBL producers. ESBL-producing Klebsiella pneumoniae strains might have a greater pathogenic potential by virtue of their ability to escape the phagocytic activity of PMNLs.

Nosocomial infections in adult intensive-care units

Nosocomial infections affect about 30% of patients in intensive-care units and are associated with substantial morbidity and mortality. Several risk factors have been identified, including the use of catheters and other invasive equipment, and certain groups of patients-eg, those with trauma or burns-are recognised as being more susceptible to nosocomial infection than others. Awareness of these factors and adherence to simple preventive measures, such as adequate hand hygiene, can limit the burden of disease. Management of nosocomial infection relies on adequate and appropriate antibiotic therapy, which should be selected after discussion with infectious-disease specialists and adapted as microbiological data become available.

Molecular epidemiology and antibiotic resistance of Enterobacter spp. from three distinct populations in Grampian, UK

The distribution of Enterobacter spp. within the population of Aberdeen Royal Infirmary was compared with the outpatient population with regard to molecular epidemiology and antibiotic resistance. Enterobacter spp. from 60 patients and one environmental site were characterised as ITU, non ITU and outpatients' isolates. Thirty-five percent were blood culture isolates. Cefotaxime resistant strains in the hospital were frequent. Cefotaxime (64%) sensitive isolates were inducible for hyperproduction of Bush group 1 beta-lactamase. Isolates were further investigated by PFGE. Isolates (27%) were clonally related and typed in four clusters. Consecutive isolates were studied in selected patients showing minor genomic changes. One environmental isolate from a deep sink at ITU was related to a patient's isolate.

Antibiotic resistance and virulence properties of Pseudomonas aeruginosa strains from mechanically ventilated patients with pneumonia in intensive care units: comparison with imipenem-resistant extra-respiratory tract isolates from uninfected patients

We investigated the epidemiology of antibiotic resistance and virulence properties among Pseudomonas aeruginosa clinical isolates collected in 1999 from patients hospitalized in the intensive care units of the centre hospitalier d'Orléans, in France. We compared the totality of the strains from mechanically ventilated patients with pneumonia (33 non-duplicate isolates, group 1) to 15 randomly chosen, imipenem-resistant, extra-respiratory tract isolates, collected from non-infected patients hospitalized in the same units (group 2). The isolates were serotyped, typed by random amplified polymorphic DNA (RAPD), and screened for their pneumocyte cell adherence, cytotoxicity, and antibiotic resistance. A total of 35 RAPD profiles were found, and only two profiles were encountered in both groups, demonstrating a high genetic diversity. 84.8% of the group 1 and 93.3% of the group 2 isolates adhered to A549 cells. Three non-exclusive adhesive patterns were observed: a diffuse adhesion in 38 isolates, a localized adhesion in 14 isolates, and an aggregative adhesion in seven isolates. 78.8% of the group 1 and 93.3% of the group 2 isolates were cytotoxic. Considering all 48 isolates, there was a strong and statistically significant correlation between cytotoxicity and adherence. Among the three dominant serotypes, O:12 isolates were in majority avirulent, but the great majority of O:1 and all the O:11 isolates were found adherent and cytotoxic. Gentamicin was the least active antibiotic for both groups, and ceftazidime was the most active antibiotic for group 1 and amikacin for group 2. The penicillinase production phenotype was significantly correlated with a decrease in P. aeruginosa virulence.

Subgingival occurrence and antimicrobial susceptibility of enteric rods and pseudomonads from Brazilian periodontitis patients

The occurrence and in vitro antimicrobial sensitivity of isolates of enteric rods and pseudomonads were examined in 80 periodontitis patients, 17 to 58 years of age, in São Paulo, Brazil. Speciation and in vitro antimicrobial susceptibility testing were performed using the BBL Crystal enteric/nonfermenter system and the Etest for amoxicillin/clavulanic acid, ciprofloxacin and doxycycline. A total of 30 strains were isolated from 25 (31.2%) of the study subjects. Pseudomonas aeruginosa occurred in nine patients, Serratia marcescens in seven, and five other species were recovered in lower prevalence. All study organisms demonstrated high susceptibility to ciprofloxacin but exhibited variable susceptibility patterns to the other antimicrobial agents tested. In conclusion, the high occurrence of enteric rods and pseudomonads in these subjects may be important in the pathogenesis of periodontitis, and ciprofloxacin might be the antibiotic of choice to eradicate these pathogens from periodontal pockets.

Human health hazards associated with the administration of antimicrobials to slaughter animals. Part II. An assessment of the risks of resistant bacteria in pigs and pork

Risks for the consumer regarding the acquisition of resistant bacteria and/or resistance genes via the consumption of pork are discussed. In general, Salmonella spp. and Escherichia coli that originate from animals do not easily transfer their resistance genes to the resident intestinal flora of humans. The prevalence of resistant E. coli in humans seems more associated with being a vegetarian (odds ratio (OR) 1.89) than with the consumption of meat and meat products. Other risk factors are treatment with antimicrobials (OR 2-5), becoming hospitalized (OR 5.93), or working in a health setting (OR 4.38). In the Netherlands, annually an estimated 45,000 people (0-150,000) become a carrier of resistant E. coli and/or resistance genes that ori ginate from pigs, while an estimated 345,000 persons (175,000-600,000) become a carrier of resistant E. coli and/or resistance genes that originate from hospitals, e.g. other patients. Any problems with resistant Salmonella spp. that stem from pigs are, in fact, an integral part of the total problem of food-borne salmonellosis. Sometimes there are outbreaks of a specific multi-resistant clone of S. typhimurium that causes problems in both farm animals and humans. The probability that in the next 30 years there is no or maximally one outbreak of a specific clone that originates from pig herds is estimated at about 75%. Antimicrobials used as a growth promoter can have a measurable influence on the prevalence of resistant bacteria. The likely chain of events regarding avoparcin and the selection and dissemination of resistance against vancomycin in the enterococci gives the impression that the impact of the use of antimicrobials in animals on the prevalence of resistance in humans is largely determined by whether resistance genes are, or become, located on a self-transferable transposon. Furthermore, consumer health risks of antimicrobials used in slaughter pigs are mainly determined by the selection and dissemination of bacterial resistance and much less by the toxicological properties of any residues in pork. It is also concluded that most of the problems with resistant bacteria in humans are associated with the medical use of antimicrobials, and that the impact of particularly the veterinary use of antimicrobials is limited. However, the impact of antimicrobials used as a feed additive appears to be much greater than that of antimicrobials used for strictly veterinary purposes. The use of antimicrobials as a feed additive should therefore be seriously reconsidered.

Epidemiological analysis of bacterial strains involved in hospital infection in a university hospital from Brazil

Hospital infections cause an increase in morbidity and mortality of hospitalized patients with significant rise in hospital costs. The aim of this work was an epidemiological analysis of hospital infection cases occurred in a public University Hospital in Rio de Janeiro. Hence, 238 strains were isolated from 14 different clinical materials of 166 patients hospitalized in the period between August 1995 and July 1997. The average age of the patients was 33.4 years, 72.9% used antimicrobials before having a positive culture. The most common risk conditions were surgery (19.3%), positive HIV or AIDS (18.1%) and lung disease (16.9%). 24 different bacterial species were identified, S. aureus (21%) and P. aeruginosa (18.5%) were predominant. Among 50 S. aureus isolated strains 36% were classified as MRSA (Methicillin Resistant S. aureus). The Gram negative bacteria presented high resistance to aminoglycosides and cephalosporins. A diarrhea outbreak, detected in high-risk neonatology ward, was caused by Salmonella serovar Infantis strain, with high antimicrobial resistance and a plasmid of high molecular weight (98Mda) containing virulence genes and positive for R factor.

Most Enterobacter aerogenes strains in France belong to a prevalent clone

The aim of this study was to determine the distribution in France of the Enterobacter aerogenes prevalent clone isolated in the hospitals of the Marseille area (A. Davin-Regli, D. Monnet, P. Saux, C. Bosi, R. Charrel, A. Barthelemy, and C. Bollet, J. Clin. Microbiol. 34:1474-1480, 1996). A total of 123 E. aerogenes isolates were collected from 23 hospital laboratories and analyzed by random amplification of polymorphic DNA and enterobacterial repetitive intergenic consensus-PCR to determine their epidemiological relatedness. Molecular typing revealed that 21 of the 23 laboratories had isolated this prevalent clone harboring the plasmid encoding for extended-spectrum beta-lactamase of the TEM-24 type. Most isolates were susceptible only to imipenem and gentamicin. Their dissemination seems to be clonal and was probably the result of the general use of broad-spectrum cephalosporins and quinolones. Four isolates showed an alteration of their outer membrane proteins, causing decrease of susceptibility to third-generation cephalosporins and imipenem and leading to the critical situation of having no alternative therapeutic. The large dissemination of the E. aerogenes prevalent clone probably results from its good adaptation to the antibiotics administered in France and the hospital environment, particularly in intensive care units.

Consequences of reduction of Klebsiella pneumoniae capsule expression on interactions of this bacterium with epithelial cells

Most Klebsiella pneumoniae clinical isolates are fully encapsulated and adhere in vitro to intestinal cell lines with an aggregative pattern. In this study, the influence of the capsule on interactions with epithelial cells was investigated by creating an isogenic mutant defective in the synthesis of the capsule. Determination of the uronic acid content of bacterial extracts confirmed that the mutant did not produce capsular polysaccharides whereas, with the wild-type strain, the level of encapsulation was growth phase dependent and reached a maximum during the lag and early log phases. Assays performed with different epithelial cell lines, Int-407, A-549, and HEp-2, showed that the capsule-defective mutant demonstrated greater adhesion than did the wild-type strain and that the aggregative pattern was maintained, indicating that the capsule was not related to the adhesion phenotype. In contrast, when the mucus-producing HT-29-MTX cells were used, the encapsulated wild-type strain adhered more strongly than did the capsule-defective mutant. No invasion properties were observed with any of the capsular phenotypes or cell lines used. The K. pneumoniae adhesin CF29K was detected by Western blot analysis and enzyme-linked immunosorbent assay on the surface of transconjugants obtained after transfer of a conjugative plasmid harboring the CF29K-encoding genes into both the wild-type and the capsule-defective strains. The amounts of adhesin detected were greater in the capsule-defective background strain than in the wild-type encapsulated strain and were associated with an increase in the level of adhesion to Caco-2 cells. Moreover, RNA slot blot experiments showed that transcription of the adhesin-encoding gene was markedly increased in the capsule-defective mutant compared to the wild-type encapsulated background. These results suggest (i) that the capsule plays an active role during the initial steps of the pathogenesis by interacting with mucus-producing cells but is subsequently not required for the adhesin-related interaction with the epithelial cell surface and (ii) that the expression of the adhesin is modulated by the presence of a capsule at a transcriptional level.

Recent advances in intestinal macromolecular drug delivery via receptor-mediated transport pathways

Receptor-mediated transport mechanisms provide a pathway for the trafficking of extracellular macromolecules into (endocytosis) and across (transcytosis) the cell. This comprises the binding of a ligand to a specific cell-surface receptor, clustering of the ligand-receptor complexes in endocytotic vesicles and vesicular sorting. This review focuses on recent advances in cellular and molecular biology pertaining to receptor-mediated endocytosis. A concise overview is presented of current and potential future applications of targeting to RME mechanisms to improve oral macromolecular drug delivery.