Pathogenicity and other genomic islands in plant pathogenic bacteria

Pathogenicity islands (PAIs) were first described in uropathogenic E. coli. They are now defined as regions of DNA that contain virulence genes and are present in the genome of pathogenic strains, but absent from or only rarely present in non-pathogenic variants of the same or related strains. Other features include a variable G+C content, distinct boundaries from the rest of the genome and the presence of genes related to mobile elements such as insertion sequences, integrases and transposases. Although PAIs have now been described in a wide range of both plant and animal pathogens it has become evident that the general features of PAIs are displayed by a number of regions of DNA with functions other than pathogenicity, such as symbiosis and antibiotic resistance, and the general term genomic islands has been adopted. This review will describe a range of genomic islands in plant pathogenic bacteria including those that carry effector genes, phytotoxins and the type III protein secretion cluster. The review will also consider some medically important bacteria in order to discuss the range, acquisition and stabilization of genomic islands.

The role of prophage in plant-pathogenic bacteria

A diverse set of phage lineages is associated with the bacterial plant-pathogen genomes sequenced to date. Analysis of 37 genomes revealed 5,169 potential genes (approximately 4.3 Mbp) of phage origin, and at least 50 had no function assigned or are nonessential to phage biology. Some phytopathogens have transcriptionally active prophage genes under conditions that mimic plant infection, suggesting an association between plant disease and prophage transcriptional modulation. The role of prophages within genomes for cell biology varies. For pathogens such as Pectobacterium, Pseudomonas, Ralstonia, and Streptomyces, involvement of prophage in disease symptoms has been demonstrated. In Xylella and Xanthomonas, prophage activity is associated with genome rearrangements and strain differentiation. For other pathogens, prophage roles are yet to be established. This review integrates available information in a unique interface (http://propnav.esalq.usp.br) that may be assessed to improve research in prophage biology and its association with genome evolution and pathogenicity. © Copyright ©2013 by Annual Reviews. All rights reserved.

A secreted Salmonella protein with homology to an avirulence determinant of plant pathogenic bacteria

Bacterial pathogens have evolved sophisticated mechanisms to interact with their hosts. A specialized type III protein secretion system capable of translocating bacterial proteins into host cells has emerged as a central factor in the interaction between a variety of mammalian and plant pathogenic bacteria with their hosts. Here we describe AvrA, a novel target of the centisome 63 type III protein secretion system of Salmonella enterica. AvrA shares sequence similarity with YopJ of the animal pathogen Yersinia pseudotuberculosis and AvrRxv of the plant pathogen Xanthomonas campestris pv. vesicatoria. These proteins are the first examples of putative targets of type III secretion systems in animal and plant pathogenic bacteria that share sequence similarity. They may therefore constitute a novel family of effector proteins with related functions in the cross-talk of these pathogens with their hosts.

Molecular battles between plant and pathogenic bacteria in the phyllosphere

The phyllosphere, i.e., the aerial parts of the plant, provides one of the most important niches for microbial colonization. This niche supports the survival and, often, proliferation of microbes such as fungi and bacteria with diverse lifestyles including epiphytes, saprophytes, and pathogens. Although most microbes may complete the life cycle on the leaf surface, pathogens must enter the leaf and multiply aggressively in the leaf interior. Natural surface openings, such as stomata, are important entry sites for bacteria. Stomata are known for their vital role in water transpiration and gas exchange between the plant and the environment that is essential for plant growth. Recent studies have shown that stomata can also play an active role in limiting bacterial invasion of both human and plant pathogenic bacteria as part of the plant innate immune system. As counter-defense, plant pathogens such as Pseudomonas syringae pv tomato (Pst) DC3000 use the virulence factor coronatine to suppress stomate-based defense. A novel and crucial early battleground in host-pathogen interaction in the phyllosphere has been discovered with broad implications in the study of bacterial pathogenesis, host immunity, and molecular ecology of bacterial diseases.

Antibacterial potentiality of Argemone mexicana solvent extracts against some pathogenic bacteria

The sensitivity of two Gram positive (Staphylococcus aureus and Bacillus subtilis) and two Gram negative (Escherichia coli and Pseudomonas aeruginosa) pathogenic multi-drug resistant bacteria was tested against the crude extracts (cold aqueous, hot aqueous, and methanol extracts) of leaves and seeds of Argemone mexicana L. (Papaveraceae) by agar well diffusion method. Though all the extracts were found effective, yet the methanol extract showed maximum inhibition against the test microorganisms followed by hot aqueous extract and cold aqueous extract.

The use of fluorescent probes to assess viability of the plant pathogenic bacterium Clavibacter michiganensis subsp. michiganensis by flow cytometry

Determination of the viability of bacteria by the conventional plating technique is a time-consuming process. Methods based on enzyme activity or membrane integrity are much faster and may be good alternatives. Assessment of the viability of suspensions of the plant pathogenic bacterium Clavibacter michiganensis subsp. michiganensis (Cmm) using the fluorescent probes Calcein acetoxy methyl ester (Calcein AM), carboxyfluorescein diacetate (cFDA), and propidium iodide (PI) in combination with flow cytometry was evaluated. Heat-treated and viable (non-treated) Cmm cells labeled with Calcein AM, cFDA, PI, or combinations of Calcein AM and cFDA with PI, could be distinguished based on their fluorescence intensity in flow cytometry analysis. Non-treated cells showed relatively high green fluorescence levels due to staining with either Calcein AM or cFDA, whereas damaged cells (heat-treated) showed high red fluorescence levels due to staining with PI. Flow cytometry also allowed a rapid quantification of viable Cmm cells labeled with Calcein AM or cFDA and heat-treated cells labeled with PI. Therefore, the application of flow cytometry in combination with fluorescent probes appears to be a promising technique for assessing viability of Cmm cells when cells are labeled with Calcein AM or the combination of Calcein AM with PI.

Diffusible Signal Factor (DSF)-dependent quorum sensing in pathogenic bacteria and its exploitation for disease control

Cell-to-cell signals of the Diffusible Signal Factor (DSF) family are cis-2-unsaturated fatty acids of differing chain length and branching pattern. DSF signalling has been described in diverse bacteria to include plant and human pathogens where it acts to regulate functions such as biofilm formation, antibiotic tolerance and the production of virulence factors. DSF family signals can also participate in interspecies signalling with other bacteria and interkingdom signaling such as with the yeast Candida albicans. Interference with DSF signalling may afford new opportunities for the control of bacterial disease. Such strategies will depend in part on detailed knowledge of the molecular mechanisms underlying the processes of signal synthesis, perception and turnover. Here, I review both recent progress in understanding DSF signalling at the molecular level and prospects for translating this knowledge into approaches for disease control.

The Relevance of Ribonuclease III in Pathogenic Bacteria

Dissertation presented to obtain the Ph.D degree in Biology.

Non-biting flying insects as carriers of pathogenic bacteria in a Brazilian hospital

IntroductionInsects have been described as mechanical vectors of nosocomial infections.MethodsNon-biting flying insects were collected inside a pediatric ward and neonatal-intensive care unit (ICU) of a Brazilian tertiary hospital.ResultsMost (86.4%) of them were found to carry one or more species of bacteria on their external surfaces. The bacteria isolated were Gram-positive bacilli (68.2%) or cocci (40.9%), and Gram-negative bacilli (18.2%).ConclusionsInsects collected inside a hospital were carrying pathogenic bacteria; therefore, one must consider the possibility they may act as mechanical vectors of infections, in especially for debilitated or immune-compromised patients in the hospital environments where the insects were collected.

Synergistic interactions in mixed-species biofilms of pathogenic bacteria from the respiratory tract

IntroductionMixed-species biofilms are involved in a wide variety of infections. We studied the synergistic interactions during dual-species biofilm formation among isolates of Pseudomonas aeruginosa, Acinetobacter baumannii, and Stenotrophomonas maltophilia.MethodsIsolates were cultured as single-species and all possible combinations of dual-species biofilms.ResultsThe 61 A. baumannii biofilms increased by 26-fold when cultured with S. maltophilia isolates; 62 A. baumannii biofilms increased by 20-fold when cultured with S. maltophilia isolates; and 31 P. aeruginosa biofilms increased by 102-fold when cultured with S. maltophilia 106.ConclusionsSynergy was observed between two isolates, including those that inherently lacked biofilm formation ability.

Detection of pathogenic bacteria in skin lesions of patients with chiclero's ulcer: reluctant response to antimonial treatment

We investigated the bacterial flora present in skin lesions of patients with chiclero's ulcer from the Yucatan peninsula of Mexico using conventional culture methods (11 patients), and an immunocolorimetric detection of pathogenic Streptococcus pyogenes (15 patients). Prevalence of bacteria isolated by culture methods was 90.9% (10/11). We cultured, from chiclero's ulcers (60%), pathogenic bacterial such as Staphylococcus aureus (20%), S. pyogenes (1.6%), Pseudomonas aeruginosa (1.6%), Morganella morganii (1.6%), and opportunist pathogenic bacteria such as Klebsiella spp. (20.0%), Enterobacter spp. (20%), and Enterococcus spp. (20%). We also cultured coagulase-negative staphylococci in 40% (4/10) of the remaining patients. Micrococcus spp. and coagulase-negative staphylococci constituted the bacterial genuses more frequently isolated in the normal skin of patients with chiclero's ulcer and healthy individuals used as controls. We also undertook another study to find out the presence of S. pyogenes by an immunocolorimetric assay. This study indicated that 60% (9/15) of the ulcerated lesions, but not normal controls, were contaminated with S. pyogenes. Importantly, individuals with purulent secretion and holding concomitant infections with S. pyogenes, S. aureus, P. aeruginosa, M. morganii, and E. durans took longer to heal Leishmania (L.) mexicana infections treated with antimonial drugs. Our results suggest the need to eliminate bacterial purulent infections, by antibiotic treatment, before starting antimonial administration to patients with chiclero's ulcer.

Using a top predator as a sentinel for environmental contamination with pathogenic bacteria: the Iberian wolf and leptospires

The Iberian wolf (Canis lupus) is the top predator in the Iberian environments in which it lives, feeding on a wide range of species, thus encountering a wide range of disease agents. Therefore, the wolf can serve as sentinel of environmental contamination with pathogens. We investigated the exposure of free-living wolves to 14 serovars of Leptospira interrogans sensu lato. Kidney samples from 49 wolves collected from 2010-2013 in northwestern Spain were analysed by culture, direct immunofluorescence and polymerase chain reaction. Tissue fluids were analysed for antibodies by a microscopic agglutination test. Ten wolves (observed prevalence: 20%, 95% confidence interval = 11-33%) showed evidence of contact with leptospires, eight through direct detection and nine through serology (7 wolves were positive according to both techniques). Titres below the cut-off level were also detected in seven cases. Serovars confirmed were Canicola (n = 4), Icterohaemorrhagiae (n = 3) and Sejroë, Ballum and Grippotyphosa (n = 1 each), indicating that wolves were infected with serovars for which dogs, rodents and ungulates, are the natural hosts and supporting the utility of the wolf and other large predators as environmental sentinels for pathogens.