Microbiology
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Item Pectobacterium spp. isolated from rotting carrots obtained from markets in Gampaha district, Sri Lanka exhibit the potential of having broad host ranges(Eur J Plant Pathol, 2022) Naligama, K.N.; Halmillawewa, A.P.Carrot production in Sri Lanka faces severe post-harvest losses due to bacterial soft rot. The quality deterioration of vegetables owing to typical bacterial soft rot can greatly affect the market value and consumer preference. Although the carrot soft rot causing bacteria occur all over the world, and are well-studied and characterized, the scarcity of data on the precise identification of the causal agents of the disease in Sri Lanka acts as a great barrier in managing such post-harvest losses. In an attempt to bridge this knowledge gap, we have isolated potential causative agents of bacterial soft rot from diseased carrot samples collected from Gampaha district, Sri Lanka.All the seven bacterial isolateswere confirmed for their ability to exhibit pectolysis, and vegetable disk assays were used to evaluate the pathogenicity of bacterial isolates. The pathogenicity assays showed that these isolates have the ability to infect not only carrot, but also potato, radish, beetroot and Napa cabbage, suggesting their possible broad host range. The ITS–PCR RELP profiles of the pectobacterial isolates and hierarchical clustering of the resulting profiles have placed the strains isolated in this study into four groups. The 16S rRNA gene sequencing and subsequent analyses aided in identifying isolates as Pectobacterium carotovorum (C1B5, C2B6, C2B7 and C2B8), P. aroidearum (C1B3 and C1B4), and P. polaris (C3B9). The study indicated the possibility of different Pectobacterium spp. being involved in causing carrot soft rot in the area, emphasizing the need to carry out an island-wide, comprehensive analysis to understand the distribution of the pathogen, which could be used in implementing successful disease management strategies.Item Phenotypic and genotypic characterization of antibiotic resistance of Listeria monocytogenes isolated from raw milk samples collected from Polonnaruwa, Sri Lanka(Emirates Journal of Food and Agriculture, 2022) Harshani, H.B.C.; Ramesh, R.; Halmillawewa, A.P.; Wijendra, W.A.S.Listeria monocytogenes is a food-borne pathogen that can cause severe invasive infection called ‘listerosis’ in humans. Development of antibiotic resistance is a major setback in the management of conditions caused by Listeria in both human and veterinary medicine. In this study, antibiotic resistance of fifty L. monocytogenes strains isolated from raw milk samples collected from farms in Polonnaruwa district, Sri Lanka was determined for four commonly used antibiotics; penicillin, ampicillin, streptomycin and tetracycline. The strains were also tested for the presence of selected antibiotic resistant genes (penA, ampC, strA, strB, tetA and tetB). L monocytogenes isolates showed resistance to ampicillin (60%), penicillin (40%) streptomycin (16%) and tetracycline (8%) in diffusion assays. Phenotypic multidrug resistance was exhibited by twenty isolates. The tetracycline resistant gene (tetA) was detected in seven isolates, while tetB was not detected in any. Presence of streptomycin resistant genes (strA or strB) was confirmed in seven isolates. Ampicillin (ampC) and penicillin (penA) resistant genes were not detected in any of the tested isolates. Except from the samples collected from Sungavila area, isolates from other sampling areas showed resistance to at least one of the antibiotics tested, suggesting that raw milk samples are prone to be contaminated with L. monocytogenes strains with different antibiotic resistant profiles. Therefore, necessary hygienic precautions are recommended to avoid any potential public health threats and to safeguard the health of raw milk consumers.