Antibacterial and antibiofilm activities of gold and silver nanoparticles against extensively drug-resistant acinetobacter baumannii clinical isolates

The genus Acinetobacter currently contains 34 species, the vast majority of which are not regularly implicated in causing infection. However, incidences of hospital-acquired infection with Acinetobacter species are increasing, mainly due to the rise in the number of infections caused by the species Acinetobacter baumannii in immunocompromised patients, particularly in intensive care units (ICUs). One hundred fifty clinical isolates were collected from burn units and wounds of both genders attending a burn hospital in Medical City in Baghdad, Iraq. All collected isolates were cultured on MacConkey agar, blood agar, and CHROMagar orientation medium for the diagnosis of Acinetobacter baumannii isolates based on morphological and biochemical characteristics. The Vitek system was also used to identify the isolates at the species level. A PCR assay was used to confirm the identification of Acinetobacter baumannii depending on blaOXA-51-like genes, and the results showed that all 150 isolates were Acinetobacter baumannii. The antibiotic susceptibility test was done by the Kirby-Bauer method and the Vitek-2 system. The results showed that out of 150 isolates, 125 (83.33%) were multi-drug resistant (MDR-AB), only 25 (16.67%) were non-MDR-AB, and out of 125 MDR-AB, 30 were extremely drug resistant (XDR-AB) isolates. The results of biofilm production showed that all of the XDR A. baumannii isolates (30) demonstrated positive biofilm formation (100%), 4 (13.4%) isolates were strong biofilm producers, while 7 (23.3%) isolates were weak biofilm producers, and the majority of isolates (19 (63.3%) were moderate biofilm producers. Silver nanoparticles (AgNPs)prepared from the hot extracts of Eucalyptus, and gold nanoparticles (AuNPs) were prepared from thegelatinizing of sodium alginate withChloroauric acid, and the crystallinity of synthesized AuNPs and AgNPs was investigated by an X-ray diffraction (XRD) technique and corresponding XRD patterns. In this study, we evaluated the antimicrobial and anti-biofilm activity of AuNPs and AgNPs against XDR A. baumannii. The results of the anti-biofilm activity showed AuNPs exhibited inhibition or reduction in biofilm formation at concentrations of 600, 300, 150, and 75 µg/ml, while AgNPs were at concentrations of 150, 75, and 37.5 µg/ml. Also the results of antimicrobial activity in Minimal Inhibitory Concentration (MIC) exhibited by the Eucalyptus critriodoraSilver Nitra)EK AG)against tested A.baumannii showed the concentration 31.5.µg/ml was inhibiting the growth of A.baumannii isolates in percent of 50% (4/8), while concentrations 18.7µg/ml were inhibitory for isolates, whilst antimicrobial activity in MIC exhibited by the EK plant against tested A.baumannii the concentration 150.µg/ml was inhibiting the growth of A.baumannii isolates in percent of 50%(4/8), while concentrations 75 µg/ml were inhibitory for isolates, and antimicrobial activity in MIC exhibited by the Chloroauric acidsodium alginate solution(AU ALG)against tested A.baumannii MICs ranged at (150- 75 µg/ml),the concentration 150 µg/ml was inhibiting the growth of most A.baumannii isolates in percent of 62.5%(5/8). In conclusion, the silver nanoparticles (AgNPs) and gold nanoparticles (AuNPs) have antimicrobial and antibiofilm activities against the XDR A. baumannii isolates under study.