Isolation and characterization of pectolytic bacterial pathogens infecting potatoes in Nakuru County, Kenya.

AIMS: Isolation and characterization of pectolytic bacteria associated with soft rot disease of potatoes in Nakuru, Kenya, to provide the basis for the development of disease control measures. METHODS AND RESULTS: Potato tubers showing symptoms of soft rot were collected from different farms in Molo and Mau Narok regions within Nakuru county. Isolation was done using crystal violet pectate medium (CVPM). Out of the 71 isolates that showed growth on CVPM, pathogenicity tests revealed that 36 of them had the ability to macerate tissues of potato tubers. All the isolates yielded a fragment of approximately 1500 bp after 16S rDNA amplification. Using the BIOLOG microbial identification system, 20 bacterial isolates were identified as Pectobacterium carotovorum subsp. carotovorum, 7 were Pseudomonas fluorescens B while 9 were Ps. fluorescens A. Y1/Y2 primers successfully amplified pectate lyase-encoding (pel) gene, approximately 434 bp, in all the 20 P. carotovorum species. The virulence of the isolated strains to cause disease, according to pectinolytic tests, varied with change in incubation temperature of the test samples. Pectobacterium carotovorum strains were the most virulent at 30°C while disease severity due to infection by Ps. fluorescens A strains was high at 20°C compared to the other isolates. CONCLUSION: This study reveals the identity of pectolytic bacterial species from two genera, Pectobacterium and Pseudomonas, as causative agents of potato soft rot in Nakuru, Kenya. SIGNIFICANCE AND IMPACT OF THE STUDY: Research findings from this study will aid in developing suitable risk mitigation methods for adoption by farmers to prevent losses due to soft rot.

Agglutinins for brucellae antigens in blood sera of an urban and rural population in Kenya.

The antibody titres for Brucella arbotus and Br. melitensis in 364 sera from healthy individuals in Nairobi and Naivasha are presented. A majority (96%) had no detectable agglutinins. Reactivity was markedly higher in the Naivasha serum samples, than in those from Nairobi. In Naivasha, seven per cent showed reactivity, whereas in Nairobi a larger majority (98%), showed no reactivity, with antibody titres ranging from 1:20-1:160. Age and sex were found to have no effect on antibody titre distribution in the two populations. The presence of brucellae antibodies in the healthy population screened (with titres upto 1:80) may be due to exposure to brucellae antigens, rather than denoting brucellosis, this titre could therefore be taken as the baseline in the healthy Kenyan population.

Salmonella typhi and Salmonella paratyphi antibodies in Kenya.

The distribution of Salmonella typhi, S. paratyphi A. and S. paratyphi C. agglutinins among 364 sera from a randomly selected group of healthy individuals in Nairobi and Naivasha (Kenya) were analysed in relation to bacteriologically confirmed cases of typhoid fever at the Kenyatta National Hospital (KNH). Out of these, 30% of the healthy individuals had no detectable Widal titres. Overall agglutinin titres obtained for the healthy population showed that 96% of the individuals had low level reactivity with titres < 1:80 for both H and O antigens of S. typhi, while 4% had titres of 1:160 or above. Agglutinins for S. paratyphi A and C were rarely present in the sera tested. Age and sex were found to have no effect on antibody titre distribution in the two populations but differences in the water source may have affected the percentage of positive tests recorded. In this typhoid endemic region titres upto 1:80 are not uncommon but both H and O titres of 1:160 and above found in conjunction with the clinical picture may be taken to be suggestive of typhoid fever.