Hyperbiofilm phenotype of Pseudomonas aeruginosa defective for the PlcB and PlcN secreted phospholipases

Biofilms are dense communities of bacteria enmeshed in a protective extracellular matrix composed mainly of exopolysaccharides, extracellular DNA, proteins, and outer membrane vesicles (OMVs). Given the role of biofilms in antibiotic-tolerant and chronic infections, novel strategies are needed to block, disperse, or degrade biofilms. Enzymes that degrade the biofilm matrix are a promising new therapy. We screened mutants in many of the enzymes secreted by the type II secretion system (T2SS) and determined that the T2SS, and specifically phospholipases, play a role in biofilm formation. Mutations in the xcp secretion system and in the plcB and plcN phospholipases all resulted in hyperbiofilm phenotypes. PlcB has activity against many phospholipids, including the common bacterial membrane lipid phosphatidylethanolamine, and may degrade cell membrane debris or OMVs in the biofilm matrix. Exogenous phospholipase was shown to reduce aggregation and biofilm formation, suggesting its potential role as a novel enzymatic treatment to dissolve biofilms.

Oxidative stress and metabolic perturbations in Escherichia coli exposed to sublethal levels of 2,4-dichlorophenoxyacetic acid

The chlorophenoxy herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) is used extensively worldwide despite its known toxicity and our limited understanding of how it affects non-target organisms. Escherichia coli is a suitable model organism to investigate toxicity and adaptation mechanisms in bacteria exposed to xenobiotic chemicals. We developed a methodical platform that uses atomic force microscopy, metabolomics and biochemical assays to quantify the response of E. coli exposed to sublethal levels of 2,4-D. This herbicide induced a filamentous phenotype in E. coli BL21 and a similar phenotype was observed in a selection of genotypically diverse E. coli strains (A0, A1, B1, and D) isolated from the environment. The filamentous phenotype was observed at concentrations 1000 times below field levels and was reversible upon supplementation with polyamines. Cells treated with 2,4-D had more compliant envelopes, significantly remodeled surfaces that were rougher and altered vital metabolic pathways including oxidative phosphorylation, the ABC transport system, peptidoglycan biosynthesis, amino acid, nucleotide and sugar metabolism. Most of the observed effects could be attributed to oxidative stress, consistent with increases in reactive oxygen species as a function of 2,4-D exposure. This study provides direct evidence that 2,4-D at sublethal levels induces oxidative stress and identifies the associated metabolic changes in E. coli.

Enhanced diagnosis of pneumococcal meningitis with use of the Binax NOW immunochromatographic test of Streptococcus pneumoniae antigen: a multisite study

BACKGROUND

Accurate etiological diagnosis of meningitis in developing countries is needed, to improve clinical care and to optimize disease-prevention strategies. Cerebrospinal fluid (CSF) culture and latex agglutination testing are currently the standard diagnostic methods but lack sensitivity.

METHODS

We prospectively assessed the utility of an immunochromatographic test (ICT) of pneumococcal antigen (NOW Streptococcus pneumoniae Antigen Test; Binax), compared with culture, in 5 countries that are conducting bacterial meningitis surveillance in Africa and Asia. Most CSF samples were collected from patients aged 1-59 months.

RESULTS

A total of 1173 CSF samples from suspected meningitis cases were included. The ICT results were positive for 68 (99%) of the 69 culture-confirmed pneumococcal meningitis cases and negative for 124 (99%) of 125 culture-confirmed bacterial meningitis cases caused by other pathogens. By use of culture and latex agglutination testing alone, pneumococci were detected in samples from 7.4% of patients in Asia and 15.6% in Africa. The ICT increased pneumococcal detection, resulting in similar identification rates across sites, ranging from 16.2% in Nigeria to 20% in Bangladesh. ICT detection in specimens from culture-negative cases varied according to region (8.5% in Africa vs. 18.8% in Asia; P< .001), prior antibiotic use (24.2% with prior antibiotic use vs. 12.2% without; P< .001), and WBC count (9.0% for WBC count of 10-99 cells/mL, 22.1% for 100-999 cells/mL, and 25.4% for >or=1000 cells/mL; P< .001 by test for trend).

CONCLUSIONS

The ICT provided substantial benefit over the latex agglutination test and culture at Asian sites but not at African sites. With the addition of the ICT, the proportion of meningitis cases attributable to pneumococci was determined to be similar in Asia and Africa. These results suggest that previous studies have underestimated the proportion of pediatric bacterial meningitis cases caused by pneumococci.

Evaluation of alternative diagnostic techniques for diagnosis of cerebral malaria in a tertiary referral hospital in Bangladesh

Five alternative techniques for diagnosis of malaria were evaluated in 124 clinically diagnosed cerebral malaria cases admitted in a tertiary hospital in Bangladesh. Clinical diagnosis of cerebral malaria was done by WHO criteria. The tests were conventional routine malaria microscopy; prolonged microscopy; dipstick antigen capture assay (Para Sight TM-F test); pigments in peripheral leucocytes and routine microscopy repeated at 12 hours interval. First four tests were done at 0 hours of hospital admission and repeat routine microscopy was added at 12 hours interval. Diagnostic capability of the test was 64%, 65%, 69%, 27% and 63% respectively. None of the tests except pigments in peripheral leucocytes was superior at initial evaluation. Only the dipstick test added 5% more diagnostic possibility compared with routine microscopy as standard. Stratification of diagnostic capability in different ways improved diagnosis 15% and 11% in smear negative cases by dipstick and prolonged microscopy respectively. It was increased by 50% (5/10 patients) with dipstick test in the smear negative patients with history of anti-malarials prior to hospital admission.