Evaluation of multidrug efflux pump expression in clinical isolates of Staphylococcus.aureus

Unravelling the complex mechanisms of multidrug resistance in bovine mastitis pathogens: Insights into antimicrobial resistance genes, biofilm dynamics, and efflux systems

Mastitis remains a paramount economic threat to dairy livestock, with antibiotic resistance severely compromising treatment efficacy. This study provides an in-depth investigation into the multidrug resistance (MDR) mechanisms in bacterial isolates from bovine mastitis, emphasizing the roles of antimicrobial resistance genes (ARGs), biofilm formation, and active efflux systems. A total of 162 Staphylococci, eight Escherichia coli, and seven Klebsiella spp. isolates were obtained from 215 milk samples of clinical and subclinical mastitis cases. Antibiotic susceptibility testing identified Twenty Staphylococci (12.35 %), six E. coli (75 %) and seven Klebsiella (100 %) identified as MDR displaying significant resistance to β-lactams and tetracyclines The Multiple Antibiotic Resistance (MAR) index of these isolates ranged from 0.375 to 1.0, highlighting extensive resistance. Notably, 29 of the 33 MDR isolates produced biofilms on Congo red agar, while all exhibited biofilm formation in the Microtitre Plate assay. Critical ARGs (blaZ, blaTEM, blaCTX-M, tetM, tetA, tetB, tetC, strA/B, aadA) and efflux pump genes (acrB, acrE, acrF, emrB, norB) regulating active efflux were identified. This pioneering study elucidates the synergistic contribution of ARGs, biofilm production, and efflux pump activity to MDR in bovine mastitis pathogens. To our knowledge, this comprehensive study is the first of its kind, offering novel insights into the complex resistance mechanisms. The findings underscore the imperative need for advanced antibiotic stewardship and strategic interventions in dairy farming to curb the rise of antibiotic-resistant infections, thereby protecting both animal and public health.

Antimicrobial and antibiofilm activity of highly soluble polypyrrole against methicillin-resistant Staphylococcus aureus

AIMS

The purpose was to evaluate the antimicrobial activity of highly soluble polypyrrole (Hs-PPy), alone or combined with oxacillin, as well as its antibiofilm potential against methicillin-resistant Staphylococcus aureus strains. Furthermore, the in silico inhibitory mechanism in efflux pumps was also investigated.

METHODS AND RESULTS

Ten clinical isolates of methicillin-resistant Staphylococcus aureus (MRSA) and two reference strains were used. Antimicrobial activity was determined by broth microdilution, and the combination effect with oxacillin was evaluated by the checkerboard assay. The biofilm formation capacity of MRSA and the interference of Hs-PPy were evaluated. The inhibitory action of Hs-PPy on the efflux pump was evaluated in silico through molecular docking. Hs-PPy showed activity against the isolates, with inhibitory action between 62.5 and 125 µg ml-1 and bactericidal action at 62.5 µg ml-1, as well as synergism in association with oxacillin. The isolates ranged from moderate to strong biofilm producers, and Hs-PPy interfered with the formation of this structure, but not with mature biofilm. There was no in silico interaction with the efflux protein EmrD, the closest homolog to NorA.

CONCLUSIONS

Hs-PPy interferes with biofilm formation by MRSA, has synergistic potential, and is an efflux pump inhibitor.

Employment of Spore-Forming Probiotics to Combat Persister Cells of Staphylococcus Epidermidis

Background

In this study, spore-forming probiotics were employed to eradicate Staphylococcus epidermidis biofilms and the presence and expression of genes involved in stress response was examined.

Methods

Polymerase chain reaction (PCR) assay was used to detect rpoS, relA and mazF genes in S. epidermidis ATCC 12228. Biofilm production was investigated by microtiter plate (MTP) assay. 100X minimum inhibitory concentration (MIC) of gentamycin was used to induce persister cells in planktonic and biofilm bacterial cells. The expression of rpoS, relA, and mazF genes was assessed at different time intervals of 2, 8, and 24 h using real-time PCR assay. Then, dilutions of 1, 0.5, and 0.25 µg/ml of the supernatant of Bacillus coagulans culture was used to eradicate the persister cells and the number of colonies was determined.

Results

Persister cells of S. epidermidis were formed after 7 h in planktonic and 5 h in the biofilm structure after exposure to 50 µg/ml of gentamycin. The expression of mazF and rpoS in biofilm structure and the expression of rpoS and relA in persister cells were significantly higher compared to the control (p< 0.05). The number of persister cells showed a reduction of log 2.4 and log 0.8 after exposure to 1 and 0.5 µg/ml B. coagulans supernatant, respectively, but no reduction was observed at the concentration of 0.25 µg/ml.

Conclusion

The results showed that the supernatant of probiotics containing their secretive metabolites can be used as a novel approach to combat persister cells.

Multidrug Efflux System-mediated resistance in Staphylococcus aureus under a One Health approach

The aim of the study was to track the spread of antimicrobial resistance among the different sectors of One Health through the detection of Multidrug-Efflux-System in multidrug-resistant Staphylococcus aureus isolates. Multidrug-resistant (MDR) and methicillin-resistant (MRSA) S. aureus isolates were selected: 25 of human, one of animal and eight of food origin. The efflux system genes norA, norB, norC, LmrS, tet38 and msrA were screened by PCR. The activity of the efflux systems was determined by the minimum inhibitory concentration (MIC) of tetracycline and ciprofloxacin in the presence and absence of CCCP and in the quantification of ethidium bromide efflux. Furthermore, biofilm formation was determined in the presence and absence of the CCCP. The molecular epidemiology of the isolates was traced with the aid of PFGE. The gene norC was the most prevalent, detected in all isolates and msrA was the least prevalent, detected in only two isolates from humans. There was no difference in the MICs of tetracycline and ciprofloxacin in the presence of CCCP, but 55.9% of isolates showed ethidium bromide efflux. The presence of CCCP decreased the biofilm formation. Regarding the molecular epidemiology, in three clusters was a mixture of the isolates from different origins. Therefore, S. aureus MDR with active multidrug efflux systems are circulating between One Health domains and it is necessary to consider strategies to decrease this circulation in order to prevent the dissemination of resistance mediated by MES.

Investigating the role of Bacillus subtilis type II toxin-antitoxin system in drought stress survival

Toxin-antitoxin (TA) systems, present in plasmids and bacterial chromosomes, are widespread in bacteria such as Bacillus subtilis and are known to be involved in growth regulation, bacterial tolerance to environmental stress conditions as well as biofilm formation. The aim of the current study was to investigate the role of TA systems in drought condition stress in B. subtilis isolates. The presence of TA systems including mazF/mazE and yobQ/yobR in B. subtilis (strain 168) was investigated using the polymerase chain reaction (PCR) method. TA system expression at 438 and 548 g/L of ethylene glycol concentrations was evaluated using real-time PCR method and sigB gene was used as internal control. The expression rate (fold change) of mazF toxin gene treated with 438 and 548 g/L of ethylene glycol was 6 and 8.4, respectively. This indicates an increase in the expression of this toxin in drought stress condition. Also, the fold change of mazE antitoxin in the treatment with 438 and 548 g/L of ethylene glycol was 8.6 and 5, respectively. While yobQ/yobR showed a decrease in expression in 438 and 548 g/L of ethylene glycol concentrations. So that the highest expression reduction (8.3) was observed for yobQ gene at the concentration of 548 g/L of ethylene glycol. Results of this study revealed the significant role of B. subtilis TA systems in drought stress which can be considered as the resistance mechanism of this bacterium under stress conditions.

Efflux Pump Mediated Antimicrobial Resistance by Staphylococci in Health-Related Environments: Challenges and the Quest for Inhibition

The increasing emergence of antimicrobial resistance in staphylococcal bacteria is a major health threat worldwide due to significant morbidity and mortality resulting from their associated hospital- or community-acquired infections. Dramatic decrease in the discovery of new antibiotics from the pharmaceutical industry coupled with increased use of sanitisers and disinfectants due to the ongoing COVID-19 pandemic can further aggravate the problem of antimicrobial resistance. Staphylococci utilise multiple mechanisms to circumvent the effects of antimicrobials. One of these resistance mechanisms is the export of antimicrobial agents through the activity of membrane-embedded multidrug efflux pump proteins. The use of efflux pump inhibitors in combination with currently approved antimicrobials is a promising strategy to potentiate their clinical efficacy against resistant strains of staphylococci, and simultaneously reduce the selection of resistant mutants. This review presents an overview of the current knowledge of staphylococcal efflux pumps, discusses their clinical impact, and summarises compounds found in the last decade from plant and synthetic origin that have the potential to be used as adjuvants to antibiotic therapy against multidrug resistant staphylococci. Critically, future high-resolution structures of staphylococcal efflux pumps could aid in design and development of safer, more target-specific and highly potent efflux pump inhibitors to progress into clinical use.

Effect of sub-lethal doses of nisin on Staphylococcus aureus toxin production and biofilm formation

Staphylococcus aureus is one of the commonest food-borne pathogens that can cause gastroenteritis owing to having several enterotoxins. Also, biofilm formation can complicate infections caused by this microorganism. Nisin is a safe food bio preservative which is usually used as an agent to prevent pathogen growth; however, it is important to identify the exact impact of nisin on the growth of S. aureus and to determine the suitable concentration needed for elimination of this pathogen in food. In this study, after MIC determination of nisin against S. aureus ATCC 29213, this strain was treated with sub-MIC (1/2) of nisin (4 μg/ml) and transcript levels of toxin-encoding (hla, SEA, SEB, and SED) and biofilm-associated (fnb, ebpS, eno, and icaA) genes were determined using Quantitative Real-time PCR at 2, 8, and 24 h post exposure. All toxin genes were down-regulated following exposure to sub-MIC of nisin, whereas biofilm-associated genes were up-regulated. The expression levels of fnb and icaA in S. aureus were highest after 8 h (4.5-fold and 6.8-fold increase, respectively), while the expression levels of eno and ebpS genes were highest after 2 h (3.3 and 4.5-fold increase, respectively). According to these results, although transcriptional levels of toxin genes were reduced, sub-MIC concentrations of nisin could trigger the expression of biofilm-associated genes in S. aureus. This can further lead to bacteriocin tolerance such that even its higher concentrations cannot kill bacterial cells after exposure to sub-lethal doses. Therefore, it is pivotal to add appropriate concentrations of nisin to food products for preservation purposes.

The Efficacy of AgNO3 Nanoparticles Alone and Conjugated with Imipenem for Combating Extensively Drug-Resistant Pseudomonas aeruginosa

INTRODUCTION

The extensive drug-resistant (XDR) Pseudomonas aeruginosa (P. aeruginosa) causes a range of infections with high mortality rate, which inflicts additional costs on treatment. The use of nano-biotechnology-based methods in medicine has opened a new perspective against drug-resistant bacteria. The aim of this study was to evaluate the effectiveness of the AgNO3 nanoparticles alone and conjugated with imipenem (IMI) to combat extensively drug-resistant P. aeruginosa.

METHODS

Antibiotic susceptibility was carried out using disc diffusion method. Detection of different resistant genes was performed using standard polymerase chain reaction (PCR). The chemically synthesized AgNO3 particles were characterized using scanning electron microscope (SEM), dynamic light scattering (DLS) and X-ray diffraction (XRD) methods. Fourier transform infrared spectroscopy (FTIR) was accomplished to confirm the binding of AgNO3 with IMI. The microdilution broth method was used to obtain minimum inhibitory concentration (MIC) of AgNO3 and IMI-conjugated AgNO3. MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay was carried out on L929 cell line to study the cytotoxicity of nanoparticles. The data were analyzed by Eta correlation ratio and chi-square (X 2) test.

RESULTS

Analysis of the antibiotic resistance pattern showed that 12 (24%) isolates were XDR, and MIC values of IMI were between 64 and 128 μg/mL. Frequency of SHV, TEM, CTX M, IMP, VIM, OPR, SIM, SPM, GIM, NDM, VEB, PER, KPC, OXA, intI, intII, and intIII genes were 29 (58%), 26 (52%), 26 (52%), 32 (64%), 23 (46%), 43 (86%), 3 (6%), 6 (12%), 3 (6%), 4 (8%), 7 (14%), 6 (12%), 18 (36%), 4 (8%), 19 (38%), 16 (32%), and 2 (4%), respectively. The XRD, SEM, DLS, and FTIR analysis confirmed the synthesis of AgNO3 nanoparticles and their conjugation with IMI. The AgNO3 nanoparticles had antimicrobial activity, and their conjugation with IMI showed enhanced effectiveness against XDR isolates. The synthesized AgNO3 showed no cytotoxic effects.

CONCLUSION

The results suggest that IMI-conjugated AgNO3 has a strong potency as a powerful antibacterial agent against XDR P. aeruginosa.