Ampicillin Treatment of Intracellular Listeria monocytogenes Triggers Formation of Persistent, Drug-Resistant L-Form Cells

Experience and Perspectives on Antibacterial Therapy for Listeriosis in a Tertiary Teaching Hospital in China: A Retrospective Study and Health Care Provider Survey

Listeriosis is a rare, life-threatening bacterial infection. Prompt, appropriate antibiotic treatment is essential to save lives. We aimed to investigate antibiotic selection and listeriosis knowledge among health care providers. We first performed a retrospective study on patients with listeriosis who were treated in a hospital in China from January 2013 to March 2023. Patient characteristics and antibiotic selections were recorded. Antibiotics were classified as effective or ineffective based on the efficacy classifications listed in The Sanford Guide to Antimicrobial Therapy (50th edition). We then conducted a questionnaire survey of health care providers to investigate their listeriosis knowledge and practices between April 2023 to May 2023. Fifteen listeriosis patients were identified, with a case fatality rate of 26.7% (4/15). Empirical treatments assessed as effective antibiotics or ineffective antibiotics were given to 33.3% (5/15) and 66.7% (10/15) of the patients, respectively. After Listeria monocytogenes was identified, 40% (6/15) of the patients received an adjustment to their antibiotics, although 50% (3/6) patients still received ineffective antibiotics. The questionnaire survey of 77 participating health care providers showed that 32.9% (24/73) of the clinicians were unaware of the appropriate antibiotics for listeriosis. Most participants (83.1%, 64/77) would read the drug sensitivity report before selecting the antibiotics. The selection of effective antibiotics differed between the infectious diseases department and other departments (p < 0.001), but did not differ between junior title and other titles (p = 0.088). Most patients with listeriosis did not receive appropriate antibiotics, which might have accounted for the high fatality rate, and may have resulted from inadequate listeriosis knowledge. More education and correct reporting of drug sensitivity results are urgently needed.

Molecular mechanism and application of emerging technologies in study of bacterial persisters

Since the discovery of antibiotics, they have served as a potent weapon against bacterial infections; however, natural evolution has allowed bacteria to adapt and develop coping mechanisms, ultimately leading to the concerning escalation of multidrug resistance. Bacterial persisters are a subpopulation that can survive briefly under high concentrations of antibiotic treatment and resume growth after lethal stress. Importantly, bacterial persisters are thought to be a significant cause of ineffective antibiotic therapy and recurrent infections in clinical practice and are thought to contribute to the development of antibiotic resistance. Therefore, it is essential to elucidate the molecular mechanisms of persister formation and to develop precise medical strategies to combat persistent infections. However, there are many difficulties in studying persisters due to their small proportion in the microbiota and their non-heritable nature. In this review, we discuss the similarities and differences of antibiotic resistance, tolerance, persistence, and viable but non-culturable cells, summarize the molecular mechanisms that affect the formation of persisters, and outline the emerging technologies in the study of persisters.

Listeria monocytogenes in the seafood industry: Exploring contamination sources, outbreaks, antibiotic susceptibility and genetic diversity

Fish and seafood are rich sources of protein, vitamins, and minerals, significantly contributing to individual health. A global increase in consumption has been observed. Listeria monocytogenes is a known problem in food processing environments and is found in various seafood forms, including raw, smoked, salted, and ready-to-eat. Without heat treatment and given L. monocytogenes' ability to multiply under refrigerated conditions, consuming seafood poses a substantial health hazard, particularly to immunocompromised individuals. Numerous global outbreaks of listeriosis have been linked to various fish products, underscoring the importance of studying L. monocytogenes. Different strains exhibit varying disease-causing abilities, making it crucial to understand and monitor the organism's virulence and resistance aspects for food safety. This paper aims to highlight the genetic diversity of L. monocytogenes found in fish products globally and to enhance understanding of contamination routes from raw fish to the final product.

Prevalence and Antimicrobial Resistance of Listeria monocytogenes in Different Raw Food from Reynosa, Tamaulipas, Mexico

Listeria (L.) monocytogenes is an opportunistic foodborne pathogen that causes listeriosis in humans and animals, reaching up to 30% case mortality. There are only a few reports in Mexico about the L. monocytogenes strains found in various foods. The aim of this study was to determine the prevalence of L. monocytogenes, serogroups, virulence genes, and antimicrobial resistance in different foods from Reynosa, Tamaulipas, Mexico. L. monocytogenes strains were characterized by microbiological and molecular methods. Susceptibility to 12 antibiotics was determined according to CLSI and EUCAST. A total of 300 samples of seafood, pasteurized and raw milk, cheese, beef, and chicken were collected from supermarkets and retail markets. The presence of L. monocytogenes was detected in 5.6% of the samples. Most strains belonged to serogroups 4b, 4d, and 4e (68.4%). All strains presented a minimum of four virulence genes; the most common were actA, hly, and plcB (92.1%). A high percentage of antimicrobial susceptibility was observed, with resistance only to STX-TMP (78.9%), STR (26.3%), MEM (21.0%), and E (2.6%). These results show that the foods in Reynosa, Tamaulipas, are a reservoir of L. monocytogenes and represent a potential health risk.

New Strategies to Kill Metabolically-Dormant Cells Directly Bypassing the Need for Active Cellular Processes

Antibiotic therapy failure is often caused by the presence of persister cells, which are metabolically-dormant bacteria capable of surviving exposure to antimicrobials. Under favorable conditions, persisters can resume growth leading to recurrent infections. Moreover, several studies have indicated that persisters may promote the evolution of antimicrobial resistance and facilitate the selection of specific resistant mutants; therefore, in light of the increasing numbers of multidrug-resistant infections worldwide, developing efficient strategies against dormant cells is of paramount importance. In this review, we present and discuss the efficacy of various agents whose antimicrobial activity is independent of the metabolic status of the bacteria as they target cell envelope structures. Since the biofilm-environment is favorable for the formation of dormant subpopulations, anti-persister strategies should also include agents that destroy the biofilm matrix or inhibit biofilm development. This article reviews examples of selected cell wall hydrolases, polysaccharide depolymerases and antimicrobial peptides. Their combination with standard antibiotics seems to be the most promising approach in combating persistent infections.

L-form conversion in Gram-positive bacteria enables escape from phage infection

At the end of a lytic bacteriophage replication cycle in Gram-positive bacteria, peptidoglycan-degrading endolysins that cause explosive cell lysis of the host can also attack non-infected bystander cells. Here we show that in osmotically stabilized environments, Listeria monocytogenes can evade phage predation by transient conversion to a cell wall-deficient L-form state. This L-form escape is triggered by endolysins disintegrating the cell wall from without, leading to turgor-driven extrusion of wall-deficient, yet viable L-form cells. Remarkably, in the absence of phage predation, we show that L-forms can quickly revert to the walled state. These findings suggest that L-form conversion represents a population-level persistence mechanism to evade complete eradication by phage attack. Importantly, we also demonstrate phage-mediated L-form switching of the urinary tract pathogen Enterococcus faecalis in human urine, which underscores that this escape route may be widespread and has important implications for phage- and endolysin-based therapeutic interventions.

Characterization and Preliminary Application of Phage Isolated From Listeria monocytogenes

Listeria monocytogenes (LM) is one of the four major foodborne bacteria that cause bacteremia and meningitis. To explore the control of listeriosis with natural phages, we used the double-layer agar plate method to isolate LM from slaughterhouse sewage and designated LP8. The result of electron microscopy indicated that the phage belonged to the family of Myoviridae. Whole-genome sequencing indicated that the genome size of LP8 is 87,038 bp and contains 120 genes. Mice were infected with LM and treated with penicillin G sodium, LP8, and the combination of these two. From the levels of lymphocyte subsets (CD4+, CD8+), the expression of cytokines (TNF-α, IL1β, IL-10, and IFN-γ), observation of pathological changes in organs (heart, liver, spleen, kidney, and brain), and the bacterial load of the spleen, we concluded the therapeutic effect of LP8 against listeriosis and demonstrate the feasibility of a combined therapy to reduce the use of antibiotics. This provides a new avenue for the treatment of listeriosis.