Biofilm Formation in Campylobacter concisus: The Role of the luxS Gene.

Campylobacter concisus is a bacterium that inhabits human oral cavities and is an emerging intestinal tract pathogen known to be a biofilm producer and one of the bacterial species found in dental plaque. In this study, biofilms of oral and intestinal C. concisus isolates were phenotypically characterized. The role of the luxS gene, which is linked to the regulation of biofilm formation in other pathogens, was assessed in relation to the pathogenic potential of this bacterium. Biofilm formation capacity was assessed using phenotypic assays. Oral strains were shown to be the highest producers. A luxS mutant was created by inserting a kanamycin cassette within the luxS gene of the highest biofilm-forming isolate. The loss of the polar flagellum was observed with scanning and transmission electron microscopy (SEM and TEM). Furthermore, the luxS mutant exhibited a significant reduction (p < 0.05) in biofilm formation, motility, and its expression of flaB, in addition to the capability to invade intestinal epithelial cells, compared to the parental strain. The study concluded that C. concisus oral isolates are significantly higher biofilm producers than the intestinal isolates and that LuxS plays a role in biofilm formation, invasion, and motility in this bacterium.

Structural and functional characterization of the Helicobacter pylori cytidine 5'-monophosphate-pseudaminic acid synthase PseF: molecular insight into substrate recognition and catalysis mechanism.

The bacterium Helicobacter pylori is a human gastric pathogen that can cause a wide range of diseases, including chronic gastritis, peptic ulcer and gastric carcinoma. It is classified as a definitive (class I) human carcinogen by the International Agency for Research on Cancer. Flagella-mediated motility is essential for H. pylori to initiate colonization and for the development of infection in human beings. Glycosylation of the H. pylori flagellum with pseudaminic acid (Pse; 5,7-diacetamido-3,5,7,9-tetradeoxy-l-glycero-l-manno-nonulosonic acid) is essential for flagella assembly and function. The sixth step in the Pse biosynthesis pathway, activation of Pse by addition of a cytidine 5'-monophosphate (CMP) to generate CMP-Pse, is catalyzed by a metal-dependent enzyme pseudaminic acid biosynthesis protein F (PseF) using cytidine 5'-triphosphate (CTP) as a cofactor. No crystal-structural information for PseF is available. This study describes the first three-dimensional model of H. pylori PseF obtained using biocomputational tools. PseF harbors an α/ß-type hydrolase fold with a ß-hairpin (HP) dimerization domain. Comparison of PseF with other structural homologs allowed identification of crucial residues for substrate recognition and the catalytic mechanism. This structural information would pave the way to design novel therapeutics to combat bacterial infection.

Emergence of bla TEM Type Extended-Spectrum ß -Lactamase Producing Salmonella spp. in the Urban Area of Bangladesh.

Salmonellosis, an acute invasive enteric infection, is endemic in Bangladesh. We analyzed 128,312 stool samples of diarrheal patients to identify Salmonella spp. during 2005-2013. A total of 2120 (1.7%) Salmonella spp. were isolated and the prevalence of Salmonella spp. decreased significantly over time (2→1%, P < 0.001). Among the typhoidal Salmonella (TS) serogroups, S. Typhi was predominant (404, [65.1%]) followed by S. Paratyphi B (139, [22.4%]) and S. Paratyphi A (78, [12.6%]). Of the nontyphoidal Salmonella (NTS) isolates, the serogroup C1 (560, [37%]) was predominant followed by B (379, [25%]), C2 (203, [14%]), E (127, [9%]), and D (94, [6%]). Most of the resistance was found towards nalidixic acid (40%), ampicillin (36%), cotrimoxazole (20%), chloramphenicol (13%), ciprofloxacin (4%), and ceftriaxone (4%). Interestingly, 32% of the isolates showed reduced susceptibility to Cip. Multiantibiotic resistance (MAR, ≥3 drugs) was more common among TS than NTS strains (P < 0.001). Among the representative ceftriaxone-resistant isolates, bla TEM gene was detected among 88% (7/8) of the strains, whereas only one strain of S. Typhi was positive for both bla TEM and bla CTX-M genes. The study reflects higher prevalence of MAR Salmonella spp. and is the first to report the bla TEM gene mediated ESBL production among Salmonellae in Bangladesh. Emergence of MAR Salmonella spp. in particular ESBL strains should be considered a public health concern.