Effects of Sub-Minimum Inhibitory Concentrations of Imipenem and Colistin on Expression of Biofilm-Specific Antibiotic Resistance and Virulence Genes in Acinetobacter baumannii Sequence Type 1894

Pharmacovigilance Strategies to Address Resistance to Antibiotics and Inappropriate Use-A Narrative Review

The spread of antimicrobial resistance (AMR) is a global challenge. Close and continuous surveillance for quick detection of AMR can be difficult, especially in remote places. This narrative review focuses on the contributions of pharmacovigilance (PV) as an auxiliary tool for identifying and monitoring the ineffectiveness, resistance, and inappropriate use of antibiotics (ABs). The terms "drug ineffective", "therapeutic failure", "drug resistance", "pathogen resistance", and "multidrug resistance" were found in PV databases and dictionaries, denoting ineffectiveness. These terms cover a range of problems that should be better investigated because they are useful in warning about possible causes of AMR. "Medication errors", especially those related to dose and indication, and "Off-label use" are highlighted in the literature, suggesting inappropriate use of ABs. Hence, the included studies show that the terms of interest related to AMR and use are not only present but frequent in PV surveillance programs. This review illustrates the feasibility of using PV as a complementary tool for antimicrobial stewardship activities, especially in scenarios where other resources are scarce.

Lippia graveolens Essential Oil to Enhance the Effect of Imipenem against Axenic and Co-Cultures of Pseudomonas aeruginosa and Acinetobacter baumannii

This research focuses on assessing the synergistic effects of Mexican oregano (Lippia graveolens) essential oil or carvacrol when combined with the antibiotic imipenem, aiming to reduce the pathogenic viability and virulence of Acinetobacter baumannii and Pseudomonas aeruginosa. The study highlighted the synergistic effect of combining L. graveolens essential oil or carvacrol with imipenem, significantly reducing the required doses for inhibiting bacterial growth. The combination treatments drastically lowered the necessary imipenem doses, highlighting a potent enhancement in efficacy against A. baumannii and P. aeruginosa. For example, the minimum inhibitory concentrations (MIC) for the essential oil/imipenem combinations were notably low, at 0.03/0.000023 mg/mL for A. baumannii and 0.0073/0.000023 mg/mL for P. aeruginosa. Similarly, the combinations significantly inhibited biofilm formation at lower concentrations than when the components were used individually, demonstrating the strategic advantage of this approach in combating antibiotic resistance. For OXA-51, imipenem showed a relatively stable interaction during 30 ns of dynamic simulation of their interaction, indicating changes (<2 nm) in ligand positioning during this period. Carvacrol exhibited similar fluctuations to imipenem, suggesting its potential inhibition efficacy, while thymol showed significant variability, particularly at >10 ns, suggesting potential instability. With IMP-1, imipenem also displayed very stable interactions during 38 ns and demonstrated notable movement and positioning changes within the active site, indicating a more dynamic interaction. In contrast, carvacrol and thymol maintained their position within the active site only ~20 and ~15 ns, respectively. These results highlight the effectiveness of combining L. graveolens essential oil and carvacrol with imipenem in tackling the difficult-to-treat pathogens A. baumannii and P. aeruginosa.

Sub-inhibitory concentrations of colistin and imipenem impact the expression of biofilm-associated genes in Acinetobacter baumannii

Acinetobacter baumannii is an opportunistic pathogen that is responsible for nosocomial infections. Imipenem and colistin are drugs that are commonly used to treat severe infections caused by A. baumannii, such as sepsis, ventilator-associated pneumonia, and bacteremia. However, some strains of A. baumannii have become resistant to these drugs, which is a concern for public health. Biofilms produced by A. baumannii increase their resistance to antibiotics and the cells within the inner layers of biofilm are exposed to sub-inhibitory concentrations (sub-MICs) of antibiotics. There is limited information available regarding how the genes of A. baumannii are linked to biofilm formation when the bacteria are exposed to sub-MICs of imipenem and colistin. Thus, this study's objective was to explore this relationship by examining the genes involved in biofilm formation in A. baumannii when exposed to low levels of imipenem and colistin. The study found that exposing an isolate of A. baumannii to low levels of these drugs caused changes in their drug susceptibility pattern. The relative gene expression profiles of the biofilm-associated genes exhibited a change in their expression profile during short-term and long-term exposure. This study highlights the potential consequences of overuse and misuse of antibiotics, which can help bacteria become resistant to these drugs.

Sub-minimum inhibitory concentrations (sub-MICs) of colistin on Acinetobacter baumannii biofilm formation potency, adherence, and invasion to epithelial host cells: an experimental study in an Iranian children's referral hospital

Here, we described the efficacy of colistin sub-minimum inhibitory concentrations (sub-MICs) on biofilm-forming activity, host epithelial cell adherence, and invasion capacity of Acinetobacter baumannii strains collected from children admitted to the Children's Medical Center Hospital. Biofilm formation potency of A. baumannii clinical isolates was measured using a 96-well microtiter plate assay. Distribution of biofilm-related genes, including bap, abaI, ompA, csuE, and blaPER-1, was detected by PCR. The mRNA expression level of ompA and csuE was measured by qPCR in the presence of ¼ and ½ MICs of colistin. A. baumannii adhesion and invasion to eukaryotic host cells were phenotypically assayed at sub-MICs of colistin. Eighty percent (56/70) and 35.7% (25/70) of A. baumannii isolates were multidrug-resistant (MDR) and extensively drug-resistant (XDR) phenotypes, respectively. The strong, moderate, and weak biofilm producers of A. baumannii were 37.1% (26/70), 32.8%, (23/70), and 22.8% (16/70), respectively. The frequencies of biofilm-associated genes were 100% for abaI, ompA, and csuE, followed by 22.8% (16/70) and 24.3% (17/70) for bap and blaPER-1, respectively. The downregulation of csuE and ompA expression levels was observed in the sub-MIC of colistin. In vitro cell culture study showed a decreased capability of A. baumannii to adhere to the human epithelial cells at sub-inhibitory doses of colistin; however, none of the isolates could invade HEp-2 cells. Our study showed that the genes encoding biofilm-associated proteins undergo downregulation in expression levels after exposure to sub-MICs of colistin in A. baumannii. Longitudinal in vivo studies are needed to fully understand the clinical aspects of pathogenicity mechanisms and evolutionary dynamics of drug resistance.IMPORTANCESince the toxicity of colistin is dose dependent, there is a focus on strategies that reduce the dose while maintaining the therapeutic effect of the drug. Our findings about sub-inhibitory doses of colistin provide a novel insight into the logical use of colistin to treat and control Acinetobacter baumannii-related infections in clinical practice.

Evaluation of the in vitro effects of concentrations of antibiotics on three Enterobacteriaceae isolates

Due to the misuse and overuse of antibiotics, bacteria are now exposed to sub-minimum inhibitory concentrations (sub-MICs) of antibiotics in various environments. In recent years, exposure of bacteria to sub-MICs of antibiotics has led to the widespread emergence of antibiotic-resistant bacteria. In this study, three bacterial species from the Enterobacteriaceae family (Raoultella ornithinolytica, Pantoea agglomerans and Klebsiella quasivariicola) were isolated from water. The antibiotic susceptibility of these bacteria to 16 antibiotics was then investigated. The effects of sub-MICs of four selected antibiotics (kanamycin, chloramphenicol, meropenem, and ciprofloxacin) on the growth, biofilm formation, surface polysaccharide production, siderophore production, morphology, and expression of the translational/transcriptional regulatory transformer gene rfaH of these bacteria were analysed. The MICs of kanamycin, chloramphenicol, meropenem, and ciprofloxacin were determined to be 1, 2, 0.03 and 0.03 µg/mL for R. ornithinolytica; 0.6, 6, 0.03 and 0.05 µg/mL for P. agglomerans; and 2, 5, 0.04 and 0.2 µg/mL for K. quasivariicola. The growth kinetics and biofilm formation ability decreased for all three isolates at sub-MICs. The surface polysaccharides of R. ornithinolytica and P. agglomerans increased at sub-MICs. There was no significant change in the siderophore activities of the bacterial isolates, with the exception of MIC/2 meropenem in R. ornithinolytica and MIC/2 kanamycin in K. quasivariicola. It was observed that the sub-MICs of meropenem and ciprofloxacin caused significant changes in bacterial morphology. In addition, the expression of rfaH in R. ornithinolytica and K. quasivariicola increased with the sub-MICs of the selected antibiotics.

Synergistic Effects of Gentamicin, Cefepime, and Ciprofloxacin on Biofilm of Pseudomonas aeruginosa

Background

Pseudomonas aeruginosa is an opportunistic pathogen involved in number of hospital-acquired infections such as catheter-associated urinary tract infections, bacteremia, septicemia, skin infections, and ventilator-associated pneumoniae. Biofilm formation is an important trait implicated in chronic infections, such as cystic fibrosis and chronic pulmonary obstruction. We evaluated effects of gentamicin, cefepime, and ciprofloxacin on biofilm of P. aeruginosa.

Materials and Methods

A total of 266 isolates were collected from the Armed Forces Institute of Pathology (AFIP). Antibiotic susceptibility was assessed by double disk synergy testing. ESBL and carbapenemase detection was performed by phenotypic testing. Molecular screening of the genes was done by PCR. Micro-dilution broth method was used to determine minimum inhibitory concentrations of antibiotics. Biofilm formation was done by micro-titer plate assay.

Results

Overall, 20% of the P. aeruginosa isolates were extensively drug-resistant (XDR-PA), and 25% were multi-drug-resistant (MDR-PA). Likewise, 43% of the isolates were ESBL producers, and carbapenemase production was detected in 40% of the isolates. Molecular analysis confirmed occurrence of different resistant factors in ESBL-positive isolates; 67% carried blaTEM, 62% blaCTXM-15, 41% blaSHV, 34% blaCTXM-14, and 33% blaOXA-1. In addition, 68% of the carbapenem-resistant isolates were positive for blaNDM-1, 25% for blaOXA-48, and 22% for blaKPC-2. Biofilm formation was assessed for 234 isolates, out of which 28% were strong biofilm formers. Moderate and weak biofilm formers constituted 46% and 23%, respectively. Overall, ciprofloxacin, levofloxacin, and cefepime showed inhibitory effects on P. aeruginosa biofilms. Antibiotics in combination showed strong synergistic effects (ciprofloxacin and cefepime), while gentamicin and cefepime resulted in complete eradication of P. aeruginosa biofilm.

Conclusion

We confirm strong synergistic effects of gentamicin and cefepime that completely eradicated P. aeruginosa biofilm. We further confirm inhibitory effects of ciprofloxacin, levofloxacin, and cefepime on P. aeruginosa biofilms. Hence, combination therapy can be more effective against biofilm-associated infections.

Impairment of novel non-coding small RNA00203 inhibits biofilm formation and reduces biofilm-specific antibiotic resistance in Acinetobacter baumannii

Small RNAs (sRNAs) are post-transcriptional regulators of many biological processes in bacteria, including biofilm formation and antibiotic resistance. The mechanisms by which sRNA regulates the biofilm-specific antibiotic resistance in Acinetobacter baumannii have not been reported to date. This study aimed to investigate the influence of sRNA00203 (53 nucleotides) on biofilm formation, antibiotic susceptibility, and expression of genes associated with biofilm formation and antibiotic resistance. The results showed that deletion of the sRNA00203-encoding gene decreased the biomass of biofilm by 85%. Deletion of the sRNA00203-encoding gene also reduced the minimum biofilm inhibitory concentrations for imipenem and ciprofloxacin 1024- and 128-fold, respectively. Knocking out of sRNA00203 significantly downregulated genes involved in biofilm matrix synthesis (pgaB), efflux pump production (novel00738), lipopolysaccharide biosynthesis (novel00626), preprotein translocase subunit (secA) and the CRP transcriptional regulator. Overall, the suppression of sRNA00203 in an A. baumannii ST1894 strain impaired biofilm formation and sensitized the biofilm cells to imipenem and ciprofloxacin. As sRNA00203 was found to be conserved in A. baumannii, a therapeutic strategy targeting sRNA00203 may be a potential solution for the treatment of biofilm-associated infections caused by A. baumannii. To the best of the authors' knowledge, this is the first study to show the impact of sRNA00203 on biofilm formation and biofilm-specific antibiotic resistance in A. baumannii.

Role of efflux pumps, their inhibitors, and regulators in colistin resistance

Colistin is highly promising against multidrug-resistant and extensively drug-resistant bacteria clinically. Bacteria are resistant to colistin mainly through mcr and chromosome-mediated lipopolysaccharide (LPS) synthesis-related locus variation. However, the current understanding cannot fully explain the resistance mechanism in mcr-negative colistin-resistant strains. Significantly, the contribution of efflux pumps to colistin resistance remains to be clarified. This review aims to discuss the contribution of efflux pumps and their related transcriptional regulators to colistin resistance in various bacteria and the reversal effect of efflux pump inhibitors on colistin resistance. Previous studies suggested a complex regulatory relationship between the efflux pumps and their transcriptional regulators and LPS synthesis, transport, and modification. Carbonyl cyanide 3-chlorophenylhydrazone (CCCP), 1-(1-naphthylmethyl)-piperazine (NMP), and Phe-Arg-β-naphthylamide (PAβN) all achieved the reversal of colistin resistance, highlighting the role of efflux pumps in colistin resistance and their potential for adjuvant development. The contribution of the efflux pumps to colistin resistance might also be related to specific genetic backgrounds. They can participate in colistin tolerance and heterogeneous resistance to affect the treatment efficacy of colistin. These findings help understand the development of resistance in mcr-negative colistin-resistant strains.

Phenotypic Traits and Probiotic Functions of Lactiplantibacillus plantarum Y42 in Planktonic and Biofilm Forms

Bacteria in planktonic and biofilm forms exhibit different phenotypic properties. In this study, the phenotypic traits and probiotic functions of Lactiplantibacillus plantarum Y42 in planktonic and biofilm forms were assessed. After 36 h of static culture, scanning electron microscopy and confocal laser scanning microscopy showed that the L. plantarum Y42 bacterial cells contained interconnected adhesive matter on the surface, forming a ~18 μm layer of dense biofilms. The surface properties of L. plantarum Y42 in biofilm form, including autoaggregation ability, hydrophobicity, acid-base charge, and adhesiveness, were all higher than those in the planktonic form. Biofilm L. plantarum Y42 showed a higher tolerance to adverse environmental conditions and a higher survival rate, enzymatic activity, and integrity after vacuum lyophilization. And biofilm L. plantarum Y42 had higher adhesion to human enterocyte HT-29 cell monolayers, inhibited the expressions of proinflammatory factors IL-6 and TNF-α, and promoted the expressions of the anti-inflammatory factor IL-10 and barrier proteins Claudin-1 and Occludin. In addition, L. plantarum Y42 in biofilm form can inhibit the adhesion and invasion of Listeria monocytogenes ATCC 19115 to HT-29 cell monolayers and is more effective in relieving the inflammatory reactions and injuries of HT-29 cells caused by L. monocytogenes ATCC 19115. In conclusion, L. plantarum Y42 in biofilm form exhibited better probiotic functions compared to that in planktonic form. This indicated that L. plantarum Y42 can form biofilms to enhance its probiotic functions, which provided a theoretical basis for better development and utilization of L. plantarum Y42.

Therapeutic Potential of an Azithromycin-Colistin Combination against XDR K. pneumoniae in a 3D Collagen-Based In Vitro Wound Model of a Biofilm Infection

A therapeutic combination of azithromycin (AZM) and colistin methanesulfonate (CMS) was shown to be effective against both non-PDR and PDR Klebsiella pneumoniae biofilms in vitro. These anti-biofilm effects, however, may not correlate with effects observed in standard plate assays, nor will they representative of in vivo therapeutic action. After all, biofilm-associated infection processes are also impacted by the presence of wound bed components, such as host cells or wound fluids, which can all affect the antibiotic effectiveness. Therefore, an in vitro wound model of biofilm infection which partially mimics the complex microenvironment of infected wounds was developed to investigate the therapeutic potential of an AZM-CMS combination against XDR K. pneumoniae isolates. The model consists of a 3D collagen sponge-like scaffold seeded with HEK293 cells submerged in a fluid milieu mimicking the wound bed exudate. Media that were tested were all based on different strengths of Dulbecco's modified Eagles/high glucose medium supplemented with fetal bovine serum, and/or Bacto Proteose peptone. Use of this model confirmed AZM to be a highly effective antibiofilm component, when applied alone or in combination with CMS, whereas CMS alone had little antibacterial effectiveness or even stimulated biofilm development. The wound model proposed here proves therefore, to be an effective aid in the study of drug combinations under realistic conditions.

Genomics: Infectious Disease and Host-Pathogen Interaction

Infectious diseases, which are caused by pathogens such as bacteria, viruses, fungi, and parasites, pose a serious threat to humans, animals, and plants [...].

Correlation between Perturbation of Redox Homeostasis and Antibiofilm Capacity of Phytochemicals at Non-Lethal Concentrations

Biofilms are the multicellular lifestyle of microorganisms and are present on potentially every type of biotic or abiotic surface. Detrimental biofilms are generally targeted with antimicrobial compounds. Phytochemicals at sub-lethal concentrations seem to be an exciting alternative strategy to control biofilms, as they are less likely to impose selective pressure leading to resistance. This overview gathers the literature on individual phytocompounds rather than on extracts of which the use is difficult to reproduce. To the best of our knowledge, this is the first review to target only individual phytochemicals below inhibitory concentrations against biofilm formation. We explored whether there is an overall mechanism that can explain the effects of individual phytochemicals at sub-lethal concentrations. Interestingly, in all experiments reported here in which oxidative stress was investigated, a modest increase in intracellular reactive oxygen species was reported in treated cells compared to untreated specimens. At sub-lethal concentrations, polyphenolic substances likely act as pro-oxidants by disturbing the healthy redox cycle and causing an accumulation of reactive oxygen species.