Biocide resistance in Acinetobacter baumannii: appraising the mechanisms

A global upsurge in antibiotic-resistant Acinetobacter baumannii requires supervised selection of biocides and disinfectants to avert nosocomial infections by reducing its spread. Moreover, inadequate and improper biocides have been reported as a contributing factor in antimicrobial resistance. Regardless of the manner of administration, a biocidal concentration that does not kill the target bacteria creates a stress response, propagating the resistance mechanisms. This is an essential aspect of the disinfection programme and the overall bio-contamination management plan. Knowing the mechanisms of action of biocides and resistance modalities may open new avenues to discover novel agents. This review describes the mechanisms of action of some biocides, resistance mechanisms, and approaches to study susceptibility/resistance to these agents.

The synergistic effect of turmeric aqueous extract and chitosan against multidrug-resistant bacteria

We aimed to investigate the antibacterial and antibiofilm effects of turmeric and chitosan against the planktonic and biofilm forms of multidrug-resistant (MDR) bacteria. A group of MDR bacteria, including clinical isolates of methicillin-resistant Staphylococcus aureus, carbapenem-resistant Pseudomonas, carbapenem-resistant Enterobacteriaceae and AmpC-producing Enterobacteriaceae, were collected by phenotypic and genotypic assays. The broth microdilution method was used to investigate the MIC of turmeric aqueous extract and chitosan. To investigate the synergistic effect of the combination of these natural compounds, we used the checkerboard assay. According to the results of this study, turmeric and chitosan showed inhibitory effects on MDR bacteria, especially on the planktonic form of methicillin-resistant S. aureus as a Gram-positive compared to tested Gram-negative bacteria (carbapenem-resistant Pseudomonas, carbapenem-resistant Enterobacteriaceae and AmpC-producing Enterobacteriaceae). The antibiofilm effect of turmeric and chitosan was found more often in carbapenem-resistant Pseudomonas isolates. There was no significant difference between the tested Gram-negative bacteria because most of the tested strains were inhibited in 512 and 1024 μg/mL concentrations of chitosan and turmeric aqueous extract. In this study, turmeric aqueous extract and chitosan exhibited significant antibacterial and antibiofilm properties. However, the effect of these compounds should be investigated using in vivo models for use in pharmaceutical and disinfectant formulations.

Current advances in aptamer-assisted technologies for detecting bacterial and fungal toxins

Infectious diseases are among the common leading causes of morbidity and mortality worldwide. Associated with the emergence of new infectious diseases, the increasing number of antimicrobial-resistant isolates presents a serious threat to public health and hospitalized patients. A microbial pathogen may elicit several host responses and use a variety of mechanisms to evade host defences. These methods and mechanisms include capsule, lipopolysaccharides or cell wall components, adhesions and toxins. Toxins inhibit phagocytosis, cause septic shock and host cell damages by binding to host surface receptors and invasion. Bacterial and fungal pathogens are able to apply many different toxin-dependent mechanisms to disturb signalling pathways and the structural integrity of host cells for establishing and maintaining infections Initial techniques for analysis of bacterial toxins were based on in vivo or in vitro assessments. There is a permanent demand for appropriate detection methods which are affordable, practical, careful, rapid, sensitive, efficient and economical. Aptamers are DNA or RNA oligonucleotides that are selected by systematic evolution of ligands using exponential enrichment (SELEX) methods and can be applied in diagnostic applications. This review provides an overview of aptamer-based methods as a novel approach for detecting toxins in bacterial and fungal pathogens.

Thymol and carvacrol strongly inhibit biofilm formation and growth of carbapenemase-producing Gram negative bacilli

Discovery of novel drugs with new mechanisms of action and without cross-reaction with current therapeutic agents is crucial in the management of infections caused by multi-drug resistant (MDR) bacteria. The aim of the present study was to investigate effects of carvacrol and thymol on biofilm formation and antimicrobial activity against different carbapenemase-producing Gram negative bacilli. The antimicrobial and antibiofilm effect of thymol and carvacrol was investigated against strains harboring different genes related to carbapenemase resistance. Antimicrobial resistance was examined by an agar dilution method and antibiofilm effect was evaluated by microtiter plate assay and staining by crystal violet. Thymol and carvacrol had antibacterial effects ranging from 200-1600 μg/mL and 62-250 μg/mL respectively, and antibiofilm effect from 125-500 and 400-1600 μg/mL respectively. Seoul imipenemase- (SIM) producing isolates had the highest sensitivity, and NDM (New Delhi metallo-beta-lactamase) producing isolates had the lowest sensitivity to these components. Findings of the present study indicated a potential role of carvacrol and thymol in controlling carbapenemase-producing gram negative bacterial infections. These findings helped to develop herbal drugs for replacing antibiotics. In addition, their antibiofilm effects showed that carvacrol and thymol inhibit biofilm formation of carbapenemase-producing strains.