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tat Exon 1 Exhibits Functional Diversity during HIV-1 Subtype C Primary Infection
Human immunodeficiency virus type 1 (HIV-1) Tat is a mediator of viral transcription and is involved in the control of virus replication. However, associations between HIV-1 Tat diversity and functional effects during primary HIV-1 infection are still unclear. We estimated selection pressures in tat exon 1 using the mixed-effects model of evolution with 672 viral sequences generated from 20 patients infected with HIV-1 subtype C (HIV-1C) over 500 days postseroconversion. tat exon 1 residues 3, 4, 21, 24, 29, 39, and 68 were under positive selection, and we established that specific amino acid signature patterns were apparent in primary HIV-1C infection compared with chronic infection. We assessed the impact of these mutations on long terminal repeat (LTR) activity and found that Tat activity was negatively affected by the Ala21 substitution identified in 13/20 (65%) of patients, which reduced LTR activity by 88% (±1%) (P < 0.001). The greatest increase in Tat activity was seen with the Gln35/Lys39 double mutant that resulted in an additional 49% (±14%) production of LTR-driven luciferase (P = 0.012). There was a moderate positive correlation between Tat-mediated LTR activity and HIV-1 RNA in plasma (P = 0.026; r = 0.400) after 180 days postseroconversion that was reduced by 500 days postseroconversion (P = 0.043; r = 0.266). Although Tat activation of the LTR is not a strong predictor of these clinical variables, there are significant linear relationships between Tat transactivation and patients' plasma viral loads and CD4 counts, highlighting the complex interplay between Tat mutations in early HIV-1C infection
Antimicrobial susceptibility of staphylococci species from cow foremilk originating from dairy farms around Gaborone, Botswan
Objective: To determine the prevalence of antibiotic susceptibility of Staphylococcus species isolated from foremilk samples.
Setting: Milk was collected from five farms within a 70 km radius of Gaborone, Botswana.
Subjects: Two hundred and twenty five staphylococci isolates from foremilk samples.
Main outcome measures: Antibiotic susceptibility tests to penicillin G, ampicillin, tetracycline, erythromycin, cephalothin, chloramphenicol, methicillin, gentamicin and vancomycin.
Results: The susceptibility patterns of the staphylococcal strains to the antibiotics were as follows: penicillin G (47.1%), ampicillin (58.7%), tetracycline (62.7%), erythromycin (72%), cephalothin (72.9%), chloramphenicol (79.1%), methicillin (86.2%), gentamicin (88.9%) and vancomycin (100%). Lower susceptibility to chloramphenicol, ethicillin and gentamicin was displayed by Staphylococcus epidermidis, S. haemolyticus and S. saprophyticus. Only 19 (8.5%) of the isolates were susceptible to all the antibiotics tested. The most common multiple resistance patterns encountered were penicillin-ampicillin (9.3%), penicillin-erythromycinampicillin (6.1%) and erythromycin-tetracycline - ampicillin (3.6%).
Conclusion: Most of the Staphylococcus isolates were resistant to one or more of the antimicrobial agents, with none being resistant to vancomycin. Inappropriate use of antibiotics is suspected to be a major contributory factor in the relatively high level of resistance to antimicrobial agents observed in this study. Therefore, milk can act as a very good source of antibiotic resistant Staphylococcus species posing a threat to consumers.
(East African Medical Journal: 2002 79(1): 45-48
Novel alkaline proteases from alkaliphilic bacteria grown using chicken feather.
Two alkaline protease producing alkaliphilic bacterial strains, designated as AL-20 and AL-89, were isolated from a naturally occurring alkaline habitat. The two strains were identified as Nesternkonia sp. and Bacillus pseudofirmus, respectively. Both strains grew and produced alkaline protease using feather as the sole source of carbon and nitrogen. Addition of 0.5% glucose to the feather medium increased protease production by B. pseudofirmus AL-89 and suppressed enzyme production by Nesternkonia sp. AL-20. The enzymes from both organisms were purified to electrophoretic homogeneity following ammonium sulphate precipitation, ion exchange, hydrophobic interaction, and gel filtration chromatography. The molecular weight, determined using SDS–PAGE, was 23 kDa for protease AL-20 and 24 kDa for protease AL-89. Protease AL-20 was active in a broad pH range displaying over 90% of its maximum activity between pH 7.5 and 11.5 with a peak at pH 10. The enzyme is unique in that unlike all other microbial serine proteases known so far, it did not require Ca2+ for activity and thermal stability. Its optimum temperature for activity was at 70 °C and was stable after 1 h incubation at 65 °C both in the presence and absence of Ca2+. These properties make protease AL-20 an ideal candidate for detergent application. Protease AL-89 on the other hand require Ca2+ for activity and stability at temperature values above 50 °C. Its optimum activity was at 60 and 70 °C in the absence and presence of Ca2+, respectively. It displayed a pH optimum of 11 and retained about 70% or more of its original activity between pH 6.5 and 11. B. pseudofirmus AL-89, and the protease it produce offers an interesting potential for the enzymatic and/or microbiological hydrolysis of feather to be used as animal feed supplement