Inactivation of Critically Ranked Carbapenem Resistant Bacteria and Genes in a Batch Atmospheric Plasma Reactor.

Abstract

Wastewater treatment plants (WWTPs) have been observed to be direct key reservoir of both antibiotic resistant bacteria (ARBs) and antibiotic resistant genes (ARGs) associated with human infection as high concentrations of ARBs and ARGs have been detected in recycled hospital water. Among the ARBs, the carbapenem-resistant Acinetobacter baumannii and carbapenem-resistant Pseudomonas aeruginosa are ranked as priority 1 (critical) pathogens by the World Health Organisation (WHO) as they constitute a major threat to public health. Moreover, from the heuristic search of literature, it was observed that not only do conventional WWTPs fail to efficiently prevent the discharge of ARBs and ARGs into freshwater environments, but majority of extant advanced treatment technologies are also riddled with bottlenecks that oftentimes outweigh their proficiency. This has warranted the need for treatment technologies that have the capacity to completely obliterate pathogens (ARBs) as well as inactivate their resistance genes (ARGs). In this regard, this study investigated non-thermal plasma (NTP) technology as an alternative disinfection step to inactivate these bacteria and their ARGs. Culture based method and polymerase chain reaction (PCR) were employed in confirming the carbapenem resistance gene blaNDM-1 in Acinetobacter baumannii (BAA 1605) and Pseudomonas aeruginosa (27853). Suspensions of carbapenem-resistant Acinetobacter baumannii (24 h culture) and ATCC Pseudomonas aeruginosa (16 hr culture) were prepared from the confirmed isolates and were subjected to plasma treatment at varying time intervals (3 min, 6 min, 9 min, 12 min and 15 min) in triplicates. The plasma treated samples were evaluated for re-growth and the presence of the resistance gene. The treatment resulted in a 1.13 log reduction after 3 min and the highest ≥8 log reduction (i.e. 99.999999 %) after 15 min for Acinetobacter baumannii. For Pseudomonas aeruginosa, the treatment resulted in a 0.68 log reduction after 3 min and the highest ≥8 log reduction after 12 min. The concentration of the blaNDM-1 gene decreased with time, proving that NTP can inactivate ARGs. The log reduction and gel images suggest that plasma disinfection has a great potential to be an efficient tertiary treatment step for WWTPs. However, there are many factors that still need to be optimised, such as reaction time to completely inactivate the ARGs and removal of biofilms in the way of the treatment of ARBs such as Pseudomonas aeruginosa; before implementation is possible as this technology is yet gradually gaining commercial and industrial espousal.