Acinetobacter baumannii is a nosocomial pathogen capable of causing serious infections associated with high rates of morbidity and mortality. Due to its antimicrobial drug resistance profile, A. baumannii is categorized as an urgent priority pathogen by the Centers for Disease Control and Prevention in the United States and a priority group 1 critical microorganism by the World Health Organization. Understanding how A. baumannii adapts to different host environments may provide critical insights into strategically targeting this pathogen with novel antimicrobial and biological therapeutics. Exposure to human fluids was previously shown to alter the gene expression profile of a highly drug-susceptible A. baumannii strain A118 leading to persistence and survival of this pathogen. Herein, we explore the impact of human pleural fluid (HPF) and human serum albumin (HSA) on the gene expression profile of a highly multi-drug-resistant strain of A. baumannii AB5075. Differential expression was observed for ~30 genes, whose products are involved in quorum sensing, quorum quenching, iron acquisition, fatty acid metabolism, biofilm formation, secretion systems, and type IV pilus formation. Phenotypic and further transcriptomic analysis using quantitative RT-PCR confirmed RNA-seq data and demonstrated a distinctive role of HSA as the molecule involved in A. baumannii’s response.

Acinetobacter baumannii has become a serious threat to human health due to its extreme antibiotic resistance, environmental persistence, and capacity to survive within the host. Two A. baumannii strains, A118 and AB5075, commonly used as model systems, and three carbapenem-resistant strains, which are becoming ever more dangerous due to the multiple drugs they can resist, were exposed to 3.5% human serum albumin (HSA) and human serum (HS) to evaluate their response with respect to antimicrobial resistance, biofilm formation, and quorum sensing, all features responsible for increasing survival and persistence in the environment and human body. Expression levels of antibiotic resistance genes were modified differently when examined in different strains. The cmlA gene was upregulated or downregulated in conditions of exposure to 3.5% HSA or HS depending on the strain. Expression levels of pbp1 and pbp3 tended to be increased by the presence of HSA and HS, but the effect was not seen in all strains. A. baumannii A118 growing in the presence of HS did not experience increased expression of these genes. Aminoglycoside-modifying enzymes were also expressed at higher or lower levels in the presence of HSA or HS. Still, the response was not uniform; in some cases, expression was enhanced, and in other cases, it was tapered. While A. baumannii AB5075 became more susceptible to rifampicin in the presence of 3.5% HSA or HS, strain A118 did not show any changes. Expression of arr2, a gene involved in resistance to rifampicin present in A. baumannii AMA16, was expressed at higher levels when HS was present in the culture medium. HSA and HS reduced biofilm formation and production of N-Acyl Homoserine Lactone, a compound intimately associated with quorum sensing. In conclusion, HSA, the main component of HS, stimulates a variety of adaptative responses in infecting A. baumannii strains.

Acinetobacter baumannii is a nosocomial pathogen capable of causing serious infections associated with high rates of morbidity and mortality. Due to its antimicrobial drug resistance profile, A. baumannii is categorized as an urgent priority pathogen by the Centers for Disease Control and Prevention in the United States and priority group 1 critical microorganism by the World Health Organization. Understanding how A. baumannii adapts to different host environments may provide critical insights into strategically targeting this pathogen with novel antimicrobial and biological therapeutics. Exposure to human fluids was previously shown to alter the gene expression profile of a highly drug susceptible A. baumannii strain A118 leading to persistence and survival of this pathogen. Herein, we explore the impact of human pleural fluid (HPF) and human serum albumin (HSA) on the gene expression profile of a highly multi-drug resistant strain of A. baumannii AB5075. Differential expression was observed for ~30 genes, whose products are involved in quorum sensing, quorum quenching, iron acquisition, fatty acid metabolism, biofilm formation, secretion systems and type IV pilus formation. Phenotypic and further transcriptomic analysis using quantitative RT-PCR confirmed RNA-seq data and pointed out a distinctive role of HSA as the molecule involved in A. baumannii response.

Background: Acute diarrheal diseases constitute a world public health problem because they are the second cause of death in children under 5 years of age. Colloidal bismuth hydroxide gel (CBHG) is an active ingredient in low-cost, antidiarrhetic drugs for oral use; it does not inhibit intestinal motility, and it features very low intestinal absorption of <1%. Materials and Methods: We analyzed the sensitivity by determining the minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC); the effect on bacterial growth by studying the specific growth velocity and the generation time in growth curves; and bacterial attachment by counting viable plaques, of enteropathogenic Escherichia coli, shigatoxigenic E. coli O157:H7, Klebsiella pneumoniae, Salmonella spp., and Shigella flexneri in the commercial cream (Chobet^® bismuth cream with pectin [CBCHP]), its active ingredient (CBHG), and its excipients (E) separately. Results: CBCHP: MIC 6–10 mg/ml and MBC 7.5–15 mg/ml of bismuth; CBHG: MIC 6–10 mg/ml of bismuth. E: No inhibition was observed at the concentration studied in this study. At very low subinhibitory concentrations of CBCHP and CBHG, there was already evidence of a significant decrease in growth, which could not be recorded for E. CBCHP and CBHG presented an elevated capacity for bacterial displacement, significantly greater than E. Conclusions: We believed that the results obtained in this study are very promising from the treatment standpoint, as a possible treatment for cases of diagnosis or suspicion of bacterial gastroenteritis. The antimicrobial and attachment effects of CBCHP are exclusively due to its active ingredient CBHG; these effects are promoted in the presence of E.