Escherichia coli EC93 deploys two plasmid-encoded class I contact-dependent growth inhibition systems for antagonistic bacterial interactions
The phenomenon of contact-dependent growth inhibition (CDI) and the genes required for CDI (cdiBAI) were identified and isolated in 2005 from an Escherichia coli isolate (EC93) from rats. Although the cdiBAI EC93 locus has been the focus of extensive research during the past 15 years, little is known about the EC93 isolate from which it originates. Here we sequenced the EC93 genome and find two complete and functional C Dubai loci (including the previously identified cdi locus), both carried on a large 127 kb plasmid.
- These cdiBAI systems are differentially expressed in laboratory media, enabling EC93 to outcompete E. coli cells lacking cognate cdiI immunity genes. The two CDI systems deliver distinct effector peptides that each dissipate the membrane potential of target cells, although the two toxins display different toxic potencies.
- Despite the differential expression and toxic potencies of these CDI systems, both yielded similar competitive advantages against E. coli cells lacking immunity.
- This can be explained by the fact that the less expressed cdiBAI system (cdiBAIEC93-2) delivers a more potent toxin than the highly expressed cdiBAIEC93-1 system.
- Moreover, our results indicate that unlike most sequenced CDI+ bacterial isolates, the two cdi loci of E. coli EC93 are located on a plasmid and are expressed in laboratory media.
Contagious Antibiotic Resistance: Plasmid Transfer Among Bacterial Residents of the Zebrafish Gut
By characterizing the trajectories of antibiotic resistance gene transfer in bacterial communities such as the gut microbiome, we will better understand the factors that influence this spread of resistance. Our aim was to investigate the host network of a multi-drug resistance broad-host-range plasmid in the culturable gut microbiome of zebrafish.
This was done through in vitro and in vivo conjugation experiments with Escherichia coli as donor of the plasmid pB10::gfp When this donor was mixed with the extracted gut microbiome, only transconjugants of Aeromonas veronii were detected.
In separate matings between the same donor and four prominent isolates from the gut microbiome, the plasmid transferred to two of these four isolates, A. veronii and Plesiomonas shigelloides, but not to Shewanella putrefaciens and Vibrio mimicus When these A. veronii and P. shigelloides transconjugants were the donors in matings with the same four isolates, the plasmid now also transferred from A. veronii to S. putrefaciens P. shigelloides was unable to donate the plasmid and V. mimicus was unable to acquire it.
Finally, when the E. coli donor was added in vivo to zebrafish through their food, plasmid transfer was observed in the gut but only to Achromobacter sp., a rare member of the gut microbiome. This work shows that the success of plasmid-mediated antibiotic resistance spread in a gut microbiome depends on the donor-recipient species combinations and therefore their spatial arrangement.
It also suggests that rare gut microbiome members should not be ignored as potential reservoirs of multi-drug resistance plasmids from food.
- To understand how antibiotic resistance plasmids end up in human pathogens it is crucial to learn how, where and when they are transferred and maintained in members of bacterial communities such as the gut microbiome.
- To gain insight into the network of plasmid-mediated antibiotic resistance sharing in the gut microbiome, we investigated the transferability and maintenance of a multi-drug resistance plasmid among the culturable bacteria of the zebrafish gut.
- We show that the success of plasmid-mediated antibiotic resistance spread in a gut microbiome can depend on which species are involved, as some are important nodes in the plasmid-host network and others dead-ends.
- Our findings also suggest that rare gut microbiome members should not be ignored as potential reservoirs of multi-drug resistance plasmids from food.
Plasmid profiles and antibiotic susceptibility patterns of bacteria isolated from abattoirs wastewater within Ilorin, Kwara, Nigeria
Background and objectives: Waste water from abattoirs could harbour bacteria some of which are pathogenic. Therefore, this study aimed to assess the quality of wastewater from some abattoirs in Ilorin, Nigeria.
Materials and methods: The counts of viable bacteria, total coliform, faecal coliform, enterococci, S. aureus, P. aeruginosa and Salmonella/Shigella spp. of the wastewater was determined using selective media.
The sanitary condition appraisal, antibiotic susceptibility test and plasmid profile of the isolates were assessed using standard methods.
Results: The highest count of viable bacteria and total coliform obtained were 9.0 × 107 and 3.0 × 107 CFU/ml respectively.
Faecal coliform and enterococcal count had the same highest value of 3.0 × 105 CFU/ml. The highest count of pathogenic bacteria: Staphylococcus aureus, Pseudomonas aeruginosa and Salmonella spp. were 2.5 × 108, 1.9 × 107 and 3.0 × 104 CFU/ml respectively. The abattoirs sanitary scores ranged from 28.6-57.1%. The isolates showed multiple antibiotic resistance (MAR) index ranging from 0.5-1.0. Plasmid curing with 0.1 mg/ml of acridine orange solution led to a reduction in the MAR index of most of the Gram-negative bacteria. Pseudomonas stutzeri was susceptible to all the antibiotics while Proteus Vulgaris was resistant to all the antibiotics after curing.
Most of the Gram-negative bacteria isolated belong to the families Enterobacteriaceae and Pseudomonadaceae while the Gram-positive bacteria belong to the families Staphylococcaceae, Enterococcaceae, and Streptococcaceae.
Conclusion: It was concluded from this study that wastewaters from the abattoirs were contaminated by bacteria with a high MAR index. Most of these bacteria borne their antibiotic-resistant factors in their plasmid.