Investigating the Antagonistic Effect of Indigenous Probiotics on Carbapenem-Resistant Pseudomonas aeruginosa Strains

Introduction

With the increase of hospital infections due to the indiscriminate use of antibiotics, multidrug resistance has increased, decreasing the effectiveness of antibiotics against these infections. For this reason, the identification of alternative agents such as probiotics has been considered. The aim of this study was to isolate and identify effective probiotics against carbapenem-resistant Pseudomonas aeruginosa strains. Material and Methods. During a period of eight months, isolates of P. aeruginosa were collected from patients in three hospitals in Isfahan. The presence of metallo-beta-lactamase enzymes was determined by the combination disc test (CDT). The inhibitory and antimicrobial activities of 20 probiotic bacteria isolated from local dairy products against these strains were investigated by agar dilution. Two probiotic strains that showed broader inhibition results were selected, and the values of the lowest inhibitory concentration (MIC) and the lowest lethal concentration (MBC) and their antibiofilm effect were determined using the microtiter plate method. The concentration of organic acids was done by HPLC. Findings. Of the 100 samples isolated and identified, 61 samples (61%) exhibited multiple drug resistance (MDR) and were selected for further investigation. Phenotypic diagnosis of the presence of metallo-beta-lactamase enzymes revealed that 74.5% of the strains were positive. The results showed that these two probiotics killed P. aeruginosa strains after only one hour, and the inhibition mechanism was due to the presence of lactic acid and acetic acid. The antibiofilm effect of these two probiotics was at concentrations of 1/2 and 1/4.

Conclusion

The two Lactobacillus isolates had potential antimicrobial and antibiofilm properties against all carbapenem-resistant P. aeruginosa strains, even at thinner dilutions. Considering the broad activity of this strain, it can potentially be used for biocontrol of these strains.

Relative Abundance and Detection of Pseudomonas aeruginosa from Chronic Wound Infections Globally

Pseudomonas aeruginosa is a difficult-to-treat pathogen that is frequently involved with chronic wound infections. Here, we conducted a literature search of world-wide studies published between 2005 and 2022 that described the microbiological profiles of chronic wound infections. For each continent, a hierarchy of pathogens was created to define the organisms that were most frequently isolated in each region. Except for South America, P. aeruginosa was the second most common organism in each major continent, with Staphylococcus aureus being the most abundant pathogen overall. When individual countries were evaluated, P. aeruginosa was the most frequently isolated organism in several Southeast Asia nations including India and Malaysia. P. aeruginosa was less commonly isolated from diabetic foot infections in North America, Europe, and Africa in comparison to other types of chronic wound infections. Additionally, the Levine wound swab technique may be a quick and painless way to isolate P. aeruginosa from wound infections, but the isolation of P. aeruginosa does not seem to be an informative predictor of the patient's clinical course. A multivariate risk assessment that accounts for the regional frequency of P. aeruginosa isolation may be an appropriate way to guide empiric management of chronic wound infections.

Evaluation of the Pathogenic-Mixed Biofilm Formation of Pseudomonas aeruginosa/Staphylococcus aureus and Treatment with Limonene on Three Different Materials by a Dynamic Model

Background: Biofilms have been found growing on implantable medical devices. This can lead to persistent clinical infections. The highly antibiotic-resistant property of biofilms necessitates the search for both potent antimicrobial agents and novel antibiofilm strategies. Natural product-based anti-biofilm agents were found to be as efficient as chemically synthesized counterparts with fewer side effects. In the present study, the effects of limonene as an antibiofilm agent were evaluated on Pseudomonas aeruginosa and Staphylococcus aureus biofilm formed on different surfaces using the CDC model system in continuous flow. The flgK gene and the pilA gene expression in P. aeruginosa, and the icaA gene and eno gene in S. aureus, which could be considered as efficient resistance markers, were studied. Methods: Mono- and dual-species biofilms were grown on polycarbonate, polypropylene, and stainless-steel coupons in a CDC biofilm reactor (Biosurface Technologies, Bozeman, MT, USA). To evaluate the ability of limonene to inhibit and eradicate biofilm, a sub-MIC concentration (10 mL/L) was tested. The gene expression of P. aeruginosa and S. aureus was detected by SYBR Green quantitative Real-Time PCR assay (Meridiana Bioline, Brisbane, Australia). Results: The limonene added during the formation of biofilms at sub-MIC concentrations works very well in inhibiting biofilms on all three materials, reducing their growth by about 2 logs. Of the same order of magnitude is the ability of limonene to eradicate both mono- and polymicrobial mature biofilms on all three materials. Greater efficacy was observed in the polymicrobial biofilm on steel coupons. The expression of some genes related to the virulence of the two microorganisms was differently detected in mono- and polymicrobial biofilm. Conclusions: These data showed that the limonene treatment expressed different levels of biofilm-forming genes, especially when both types of strains alone and together grew on different surfaces. Our findings showed that limonene treatment is also very efficient when biofilm has been grown under shear stress causing significant and irreversible damage to the biofilm structure. The effectiveness of the sanitation procedures can be optimized by applying antimicrobial combinations with natural compounds (e.g., limonene).

Sub-Inhibitory Antibiotic Exposure and Virulence in Pseudomonas aeruginosa

Pseudomonas aeruginosa is a prime opportunistic pathogen, one of the most important causes of hospital-acquired infections and the major cause of morbidity and mortality in cystic fibrosis lung infections. One reason for the bacterium's pathogenic success is the large array of virulence factors that it can employ. Another is its high degree of intrinsic and acquired resistance to antibiotics. In this review, we first summarise the current knowledge about the regulation of virulence factor expression and production. We then look at the impact of sub-MIC antibiotic exposure and find that the virulence-antibiotic interaction for P. aeruginosa is antibiotic-specific, multifaceted, and complex. Most studies undertaken to date have been in vitro assays in batch culture systems, involving short-term (<24 h) antibiotic exposure. Therefore, we discuss the importance of long-term, in vivo-mimicking models for future work, particularly highlighting the need to account for bacterial physiology, which by extension governs both virulence factor expression and antibiotic tolerance/resistance.

Single-Cell Imaging Reveals That Staphylococcus aureus Is Highly Competitive Against Pseudomonas aeruginosa on Surfaces

Pseudomonas aeruginosa and Staphylococcus aureus frequently occur together in polymicrobial infections, and their interactions can complicate disease progression and treatment options. While interactions between P. aeruginosa and S. aureus have been extensively described using planktonic batch cultures, little is known about whether and how individual cells interact with each other on solid substrates. This is important because both species frequently colonize surfaces to form aggregates and biofilms in infections. Here, we performed single-cell time-lapse fluorescence microscopy, combined with automated image analysis, to describe interactions between P. aeruginosa PAO1 with three different S. aureus strains (Cowan I, 6850, JE2) during microcolony growth on agarose surfaces. While P. aeruginosa is usually considered the dominant species, we found that the competitive balance tips in favor of S. aureus on surfaces. We observed that all S. aureus strains accelerated the onset of microcolony growth in competition with P. aeruginosa and significantly compromised P. aeruginosa growth prior to physical contact. Upon direct contact, JE2 was the most competitive S. aureus strain, simply usurping P. aeruginosa microcolonies, while 6850 was the weakest competitor itself suppressed by P. aeruginosa. Moreover, P. aeruginosa reacted to the assault of S. aureus by showing increased directional growth and expedited expression of quorum sensing regulators controlling the synthesis of competitive traits. Altogether, our results reveal that quantitative single-cell live imaging has the potential to uncover microbial behaviors that cannot be predicted from batch culture studies, and thereby contribute to our understanding of interactions between pathogens that co-colonize host-associated surfaces during polymicrobial infections.

Capability of Enterococcus faecalis to shield Gram-negative pathogens from aminoglycoside exposure

BACKGROUND

Enterococcus faecalis commonly produce aminoglycoside-modifying enzymes (AMEs) and are implicated in polymicrobial infections.

OBJECTIVES

To determine if AME-producing E. faecalis is capable of protecting Enterobacteriaceae and Pseudomonas aeruginosa from gentamicin exposure.

METHODS

Two Klebsiella pneumoniae isolates, two Escherichia coli isolates, and two Pseudomonas aeruginosa isolates were investigated in monoculture time-kill experiments, and each Gram-negative organism was also evaluated during co-culture with either AME-producing or AME-deficient E. faecalis. A pharmacokinetic/pharmacodynamics analysis that utilized Log Ratio Areas and a Hill-type mathematical model was used to determine if the maximal killing or potency of gentamicin against the Gram-negative organisms was altered by the presence of the E. faecalis.

RESULTS

The maximal killing and potency of gentamicin was the same during monoculture and co-culture experiments for both K. pneumoniae isolates and one E. coli isolate (P > 0.05). In contrast, the maximal killing of gentamicin was attenuated against one E. coli isolate and both P. aeruginosa isolates during co-culture with E. faecalis (P < 0.05). The potency of gentamicin was variable against the three aforementioned isolates. Against the E. coli isolate, the potency of gentamicin was significantly reduced by the presence of either E. faecalis isolate (EC50 95% CI = 4.23-4.43 mg/L monoculture versus 3.86-4.19 mg/L and 3.55-3.96 mg/L during co-culture with AME-producing and AME-deficient E. faecalis, respectively). The potency of gentamicin increased or decreased for P. aeruginosa depending on which E. faecalis isolate was investigated.

CONCLUSIONS

The AME-producing E. faecalis did not provide a consistent protective effect from aminoglycosides for the Gram-negative pathogens.

Interaction of Staphylococcus aureus and Acinetobacter baumannii during In Vitro β-Lactam Exposure

We sought to determine if Acinetobacter baumannii is capable of altering the pharmacodynamics of an antistaphylococcal β-lactam. Two strains of methicillin-susceptible Staphylococcus aureus (MSSA) and two A. baumannii isolates were studied in 24-h static time-killing experiments under monoculture or coculture conditions. Bacterial killing of meropenem was described using an empirical pharmacokinetics/pharmacodynamics model that was developed using Hill functions. A mechanism-based pharmacodynamic model was also used to describe the effect of meropenem on each species of bacterium, interspecies interactions, and strain-based covariate effects. Monte Carlo simulations of bacterial killing effects were generated based on the population pharmacokinetics of meropenem in 2,500 simulated critically ill subjects over 48 h. Against one of the two MSSA isolates, the magnitude of bacterial killing (E _Δ) decreased from -4.61 (95% confidence interval [CI], -5.85 to -3.38) to -2.23 (95% CI, -2.85 to -1.61) when cultured in the presence of carbapenem-resistant A. baumannii (CRAB). Similarly, the data were best described by a mechanism-based model where the number of A. baumannii cells produced a systematic increase in the S. aureus concentration for a 50% maximum killing effect (KC₅₀) of 3.53-fold, thereby decreasing MSSA sensitivity to meropenem. A covariate effect by the CRAB isolate resulted in a more pronounced increase in the MSSA KC₅₀ for meropenem (31.8-fold increase). However, Monte Carlo simulations demonstrated that a high-intensity meropenem regimen is capable of sustained killing against both MSSA isolates despite protection from A. baumannii Thus, A. baumannii and MSSA engage in complex interactions during β-lactam exposure, but optimal antimicrobial dosing is likely capable of killing MSSA despite the potentially beneficial interplay with A. baumannii.

Friends or enemies? The complicated relationship between Pseudomonas aeruginosa and Staphylococcus aureus

Pseudomonas aeruginosa (Pa) and Staphylococcus aureus (Sa) are opportunistic pathogens that are most commonly co-isolated from chronic wounds and the sputum of cystic fibrosis patients. Over the last few years, there have been plenty of contrasting results from studies involving P. aeruginosa and S. aureus co-cultures. The general concept that P. aeruginosa outcompetes S. aureus has been challenged and there is more evidence now that they can co-exist. Nevertheless, it still remains difficult to mimic polymicrobial infections in vitro and in vivo. In this review, we discuss recent advances in regard to Pa-Sa molecular interactions, their physical responses, and in vitro and in vivo models. We believe it is important to optimize growth conditions in the laboratory, determine appropriate bacterial starting ratios, and consider environmental factors to study the co-existence of these two pathogens. Ideally, optimized growth media should reflect host-mimicking conditions with or without host cells that allow both bacteria to co-exist. To further identify mechanisms that could help to treat these complex infections, we propose to use relevant polymicrobial animal models. Ultimately, we briefly discuss how polymicrobial infections can increase antibiotic tolerance.

A coup d'état by NDM-producing Klebsiella pneumoniae overthrows the major bacterial population during KPC-directed therapy

The objective of this study was to utilize a co-culture hollow-fiber infection model (HFIM) to characterize the interplay between a small, difficult-to-detect, New Delhi metallo-β-lactamase-producing Klebsiella pneumoniae (NDM-Kp) minor population and a larger K. pneumoniae carbapenemase (KPC)-producing K. pneumoniae population in the presence of KPC-directed antibacterial therapy. Selective plating onto agar with ceftazidime-avibactam was used to track the density of the NDM-Kp population. Susceptibility testing and the Verigene System failed to identify the small initial NDM-Kp population. However, a ceftazidime-avibactam Etest detected resistant colonies that were confirmed to be NDM-Kp. In the HFIM, all of the investigated drug regimens caused regrowth within 24 h and resulted in >10⁹ CFU/mL of NDM-Kp. Our study demonstrates that the HFIM is a powerful tool for studying the population dynamics of multiple pathogens during antimicrobial exposure and also highlights that difficult-to-detect minor populations of drug-resistant bacteria may cause treatment failure without appropriate antibacterial therapy.