Conjugative plasmids in multi-resistant bacterial isolates from Indian soil

Aims: Determination of heavy metal and antibiotic resistance and presence of conjugative plasmids in bacteria isolated from soil irrigated with wastewater. Methods and Results: Composite soil samples were collected from Ghaziabad, Uttar Pradesh, India. Forty different bacteria were selected from nutrient agar and characterized by morphological, cultural and biochemical tests. All the isolates were tested for their resistance to different heavy metals and antibiotics. The DNA derived from multiple metal and antibiotic-resistant bacterial isolates was PCR amplified and plasmid-specific sequences (IncP, IncN, IncW, IncQ and pMV158-type) were analysed by dot blot hybridization. All isolates gave PCR products with trfA2 and oriT primers of the IncP group. These PCR products also hybridized with the RP4-derived probes. However, the samples were negative for all the other investigated plasmids as proved by PCR and dot blots. Conclusions: The presence of conjugative/mobilizable IncP plasmids in the isolates indicates that these bacteria have gene-mobilizing capacity with implications for potential dissemination of introduced recombinant DNA. Significance and Impact of the Study: The detection of IncP plasmids in all the bacterial isolates is another proof for the prevalence of these plasmids. We propose that IncP plasmids are mainly responsible for the spread of multi-resistant bacteria in these soils.