Antibody isotype analysis of malaria-nematode co-infection: problems and solutions associated with cross-reactivity

<p>Abstract</p> <p>Background</p> <p>Antibody isotype responses can be useful as indicators of immune bias during infection. In studies of parasite co-infection however, interpretation of immune bias is complicated by the occurrence of cross-reactive antibodies. To confidently attribute shifts in immune bias to the presence of a co-infecting parasite, we suggest practical approaches to account for antibody cross-reactivity. The potential for cross-reactive antibodies to influence disease outcome is also discussed.</p> <p>Results</p> <p>Utilising two murine models of malaria-helminth co-infection we analysed antibody responses of mice singly- or co-infected with <it>Plasmodium chabaudi chabaudi </it>and <it>Nippostrongylus brasiliensis </it>or <it>Litomosoides sigmodontis</it>. We observed cross-reactive antibody responses that recognised antigens from both pathogens irrespective of whether crude parasite antigen preparations or purified recombinant proteins were used in ELISA. These responses were not apparent in control mice. The relative strength of cross-reactive versus antigen-specific responses was determined by calculating antibody titre. In addition, we analysed antibody binding to periodate-treated antigens, to distinguish responses targeted to protein versus carbohydrate moieties. Periodate treatment affected both antigen-specific and cross-reactive responses. For example, malaria-induced cross-reactive IgG1 responses were found to target the carbohydrate component of the helminth antigen, as they were not detected following periodate treatment. Interestingly, periodate treatment of recombinant malaria antigen Merozoite Surface Protein-1₁₉(MSP-1₁₉) resulted in increased detection of antigen-specific IgG2a responses in malaria-infected mice. This suggests that glycosylation may have been masking protein epitopes and that periodate-treated MSP-1₁₉may more closely reflect the natural non-glycosylated antigen seen during infection.</p> <p>Conclusions</p> <p>In order to utilize antibody isotypes as a measure of immune bias during co-infection studies, it is important to dissect antigen-specific from cross-reactive antibody responses. Calculating antibody titre, rather than using a single dilution of serum, as a measure of the relative strength of the response, largely accomplished this. Elimination of the carbohydrate moiety of an antigen that can often be the target of cross-reactive antibodies also proved useful.</p

A short Communication: Distribution of heterotrophic bacteria in the sediments in the mangrove swamp at Gazi Bay, Kenya

In the first ever study of microorganisms in an East African mangrove swamp, the number of aerobic heterotrophic bacteria in the mangrove swamp sediment was investigated and found to range from 7.44 × 106 to 4.70 × 108 cfu/g dry wt, (cfu = colony forming units; g dry wt = gram dry weight). The anaerobic heterotrophic bacteria ranged from 7.45 × 106 to 1.82 × 108 cfu/g dry wt. There was no significant difference between the Avicennia marina, Ceriops tagal and Rhizophora mucronata sediments with respect to the number of aerobic and anaerobic bacteria. The exercise was conducted between October and February and generally lower numbers of bacteria were recorded between mid December and February. Key words: Mangrove swamps, heterotrophic bacteria Journal of Tropical Microbiology Vol.1(1) 2002: 41-4

In vitro activity of selected medicinal plant extracts against pathogenic bacteria and HIV/AIDS related Mycobacterium spp.

Methanolic extracts of six medicinal plants, Entada abyssinica (stem bark), Terminalia spinosa (young branches), Harrisonia abyssinica (roots), Ximenia caffra (roots), Azadirachta indica (stem bark) and Spilanthes mauritiana (roots) were tested against 35 strains of bacteria from four genera (Staphylococcus, Pseudomonas, Salmonella and Mycobacteria). The minimum inhibitory concentration reached by 50% (MIC50) and 90% (MBC90) were between 1–8 mg/ml and 1–>8 mg/ml. H. abyssinica extracts had low activity on salmonella spp. (>8 mg/ml) but were quite active against the other arganisms (0.25–2 mg/ml). S. mauritiana was barely active since most values were >8 mg/ml. Mycobacteria spp. such as M. avium, M. chelonae and M. intracellulare were inhibited at between 90–100% by H. abyssinica, E. abyssinica, T. spinosa, X. caffra and A. indica. It is concluded that carefully guided extraction and characterization of these plant compounds may yield useful antibiotic principles. Journal of Tropical Microbiology Vol.1(1) 2002: 29-3

Salmonella and Vibrio cholerae in Nile perch (Lates niloticus) Processing Establishments in Kenya.

The Nile perch (Lates niloticus) industry in East Africa has suffered severe economic losses in the last few years due to failure to comply with the microbiological standards of European Union (E.U). Fresh and frozen products have been suspected to be contaminated with Salmonella and Vibrio cholerae. This has led to a substantial rejection of consignments and severe economic losses. A survey of incidence of these organisms was conducted in two fish processing establishments in Kenya for a period of 6 months. Samples of fish, fish-contact surface swabs and swabs from hands of personnel handling fish were collected from selected steps along the processing line and analysed for Salmonella and V. cholerae. Samples of water and ice used during the processing operations were also taken and tested for these organisms. Results showed that Salmonella was present in 1 % of fish, 1.6 % of fish-contact surface swabs and 1 % of swabs from hands of personnel handling fish. V. cholerae was isolated in 1.4 % of fish and 0.15 % of fish-contact surface swabs. No isolations of Salmonella and V. cholerae were made from water and ice samples. Key Words: Salmonella; Vibrio cholerae; Seafood; Incidence. J. Trop. Microbiol Vol.1 2002: 79-8

The kill kinetics of Ximenia caffra sond. (Olacaceae) extracts against selected bacteria and fungi

Bacteria are tested against antibiotics because of the resistance these bacteria show against known anti-microbial agents. Similar tests are done on plant extracts and isolated plant compounds. In this study, crude extracts of Ximenia caffra sond. (Ol acaceae) which were previously determined to have strong antibacterial activity were tested for the rate of killing bacteria in given time (kill kinetics). They were tested against strains of Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa and Candida albicans. Inoculated strains were tested against serial dilutions at time intervals of 0, 2, 4, 6, 8 and 24 h. Results obtained showed that X. caffra killed all S. aureus strains at 4mg/ml after 2h. Both 2mg/ml and 1mg/ml concentrations killed the same organism in 6 h. In comparison, the population of E. coli was reduced by a concentration of 8mg/ml from 2.03 ×106cfu/ml to 2.0 × 103cfu/ml in 24 h. C. albicans was killed by 8 mg/ml in 24 h. There was no effect on P. aeruginosa at all levels of the concentrations tested. It is concluded that the killing by X. caffra extracts is both time and concentration dependent and is cell wall related. Keywords : kill kinetics, Mueller Hinton Agar (MHA), Ximenia caffra, Minimum Inhibitory concentration (MIC), Killing curves, Minimum bactericidal Concentration (MBC). Journal of Tropical Microbiology Vol.3 2004: 88-9