Isolation and characterization of human pathogenic multidrug resistant bacteria associated with plastic litter collected in Zanzibar.

Plastic pollution is a growing problem, not at least in areas where poor waste management results in direct pollution of coastal zones, such as South Asia and regions in Africa. In addition to the effect on ecosystems and their related services, plastic pollution may also affect human health indirectly as vectors for infectious disease. As plastic offers a suitable surface for the attachment of biofilm forming bacteria, it may contribute to disease outbreaks and antimicrobial resistance. To investigate the role of plastic litter as potential vectors for pathogenic bacteria, we collected plastic litter from four rural sites in Zanzibar, and isolated adhered bacteria. Isolates were short-read sequenced for further molecular analysis. This revealed that collected plastic litter was associated with diverse bacterial species, including human pathogens Citrobacter freundii, Klebsiella pneumoniae and Vibrio cholerae. Furthermore, most isolates were found to be multidrug resistant. Our findings confirm that plastic litter, serve as novel reservoir for human multidrug resistant pathogenic bacteria that combined with poor sanitation and waste handling, may lead to transmission of infectious diseases and antimicrobial resistance. These findings add a new level to the environmental challenges with plastic pollution; the potential health risk associated with exposure to plastic litter.

Membrane protein extraction and purification using partially-esterified SMA polymers.

Styrene maleic acid (SMA) polymers have proven to be very successful for the extraction of membrane proteins, forming SMA lipid particles (SMALPs), which maintain a lipid bilayer around the membrane protein. SMALP-encapsulated membrane proteins can be used for functional and structural studies. The SMALP approach allows retention of important protein-annular lipid interactions, exerts lateral pressure, and offers greater stability than traditional detergent solubilisation. However, SMA polymer does have some limitations, including a sensitivity to divalent cations and low pH, an absorbance spectrum that overlaps with many proteins, and possible restrictions on protein conformational change. Various modified polymers have been developed to try to overcome these challenges, but no clear solution has been found. A series of partially-esterified variants of SMA (SMA 2625, SMA 1440 and SMA 17352) has previously been shown to be highly effective for solubilisation of plant and cyanobacterial thylakoid membranes. It was hypothesised that the partial esterification of maleic acid groups would increase tolerance to divalent cations. Therefore, these partially-esterified polymers were tested for the solubilisation of lipids and membrane proteins, and their tolerance to magnesium ions. It was found that all partially esterified polymers were capable of solubilising and purifying a range of membrane proteins, but the yield of protein was lower with SMA 1440, and the degree of purity was lower for both SMA 1440 and SMA 17352. SMA 2625 performed comparably to SMA 2000. SMA 1440 also showed an increased sensitivity to divalent cations. Thus, it appears the interactions between SMA and divalent cations are more complex than proposed and require further investigation.