Emerging resistance to aminoglycosides in lactic acid bacteria of food origin—an impending menace

Multidrug resistance profile in Lactobacillus delbrueckii: a food industry species with probiotic properties

Lactobacillus delbrueckii, a widely used lactic acid bacterium in the food industry, has been studied for its probiotic properties and reservoir of antibiotic-resistant genes, raising safety concerns for probiotic formulations and fermented products. This review consolidates findings from 60 articles published between 2012 and 2023, focusing on the global antibiotic resistance profile and associated genetic factors in L. delbrueckii strains. Resistance to aminoglycosides, particularly streptomycin, kanamycin, and gentamicin, as well as resistance to glycopeptides (vancomycin), fluoroquinolones (ciprofloxacin), and tetracyclines was predominant. Notably, although resistance genes have been identified, they have not been linked to mobile genetic elements, reducing the risk of dissemination. However, a significant limitation is the insufficient exploration of responsible genes or mobile elements in 80% of studies, hindering safety assessments. Additionally, most articles originated from Asian and Middle Eastern countries, with strains often isolated from fermented dairy foods. Therefore, these findings underscore the necessity for comprehensive analyses of new strains of L. delbrueckii for potential industrial and biotherapeutic applications and in combating the rise of antibiotic-resistant pathogens.

Safety assessment of Enterococcus lactis strains complemented with comparative genomics analysis reveals probiotic and safety characteristics of the entire species

BACKGROUND

The gut microbiota is considered a rich source for potential novel probiotics. Enterococcus genus is a normal component of a healthy gut microbiota, suggesting its vital role. Nosocomial infections caused mainly by E. facalis and E. faecium have been attributed to the plasticity of the Enterococcus genomes. In this study, we assessed the probiotic and safety characteristics of two E. lactis strains isolated from the human gut microbiota using in-vitro and in silico approaches. Additionally, the safety of the E. lactis species was evaluated using comparative genomics analysis.

RESULTS

The two E. lactis strains 10NA and 50NA showed resistance to bile salts and acid tolerance with antibacterial activity against Escherichia coli, Salmonella typhi, and Clostridioides difficile. For safety assays, the two strains did not display any type of hemolysis on blood agar, and the survival of Caco-2 cells was not significantly different (P-value > 0.05) compared to the control using cell free supernatants at 100% (v/v), 50% (v/v), 10% (v/v), and 5% (v/v) concentrations. Regarding antibiotic susceptibility, both strains were sensitive to vancomycin, tetracycline, and chloramphenicol. Comprehensive whole-genome analysis revealed no concerning associations between virulence or antibiotic resistance genes and any of the identified mobile genetic elements. Comparative genome analysis with closely related E. faecium species genomes revealed the distinctive genomic safety of the E. lactis species.

CONCLUSIONS

Our two E. lactis strains showed promising probiotic properties in-vitro. Their genomes were devoid of any transferable antibiotic resistance genes. In silico comparative analysis confirmed the safety of the E. lactis species. These results suggest that E. lactis species could be a potential source for safer Enterococcus probiotic supplements.

Innovative Phospholipid Carriers: A Viable Strategy to Counteract Antimicrobial Resistance

The overuse and misuse of antibiotics have led to the emergence and spread of multidrug-resistant (MDR), extensively drug-resistant (XDR), and pan-drug-resistant (PDR) bacteria strains, usually associated with poorer patient outcomes and higher costs. In order to preserve the usefulness of these life-saving drugs, it is crucial to use them appropriately, as also recommended by the WHO. Moreover, innovative, safe, and more effective approaches are being investigated, aiming to revise drug treatments to improve their pharmacokinetics and distribution and to reduce the onset of drug resistance. Globally, to reduce the burden of antimicrobial resistance (AMR), guidelines and indications have been developed over time, aimed at narrowing the use and diminishing the environmental spread of these life-saving molecules by optimizing prescriptions, dosage, and times of use, as well as investing resources into obtaining innovative formulations with better pharmacokinetics, pharmacodynamics, and therapeutic results. This has led to the development of new nano-formulations as drug delivery vehicles, characterized by unique structural properties, biocompatible natures, and targeted activities such as state-of-the-art phospholipid particles generally grouped as liposomes, virosomes, and functionalized exosomes, which represent an attractive and innovative delivery approach. Liposomes and virosomes are chemically synthesized carriers that utilize phospholipids whose nature is predetermined based on their use, with a long track record as drug delivery systems. Exosomes are vesicles naturally released by cells, which utilize the lipids present in their cellular membranes only, and therefore, are highly biocompatible, with investigations as a delivery system having a more recent origin. This review will summarize the state of the art on microvesicle research, liposomes, virosomes, and exosomes, as useful and effective tools to tackle the threat of antibiotic resistance.

Characterization and Molecular Mechanism of Aminoglycoside-6-Adenyl Transferase Associated with Aminoglycoside Resistance from Elizabethkingia meningoseptica

Purpose

Elizabethkingia meningoseptica (EM) is a multi-drug-resistant bacterium of global concern for its role in nosocomial infection and is generally resistant to aminoglycoside antibiotics. In the whole genome of an EM strain (FMS-007), an aminoglycoside-6-adenyl transferase gene (ant(6)FMS-007) was predicted. This study aimed to characterize the biochemical function of ANT(6)FMS-007 and analyze the relationship between genotype and phenotype of ant(6) in clinical EM isolates, so as to provide evidence for clinical precision drug use. This study could establish a method for the verification of known or unknown functionally resistant genes.

Methods

A total of 42 EM clinical isolates were collected from clinical departments during 2015-2023. The phenotype of aminoglycoside antibiotics was analyzed by broth microdilution (BMD) and Kirby-Bauer (K-B) methods. The whole-length ant(6) from EM clinical isolates was analyzed by polymerase chain reaction (PCR) and sequencing. The biochemical function of predictive ANT(6)FMS-007 from the FMS-007 whole genome was identified by 3D plate experiment and mass spectrometry analysis. Candidate active sites were predicted by multi-species sequence alignment and molecular docking, and other important sites were identified in the comparison of ant(6) genotypes and phenotypes of EM clinical isolates. Drug susceptibility test was used to verify the function of these sites.

Results

The predictive ANT(6)FMS-007 protein could inactivate STR by modifying STR with ATP to form STR-AMP. Four active sites (Asp-38, Asp-42, Lys-95, and Lys-213) of ANT(6)FMS-007 were identified. Thirty-one EM clinical isolates (74%) carried the ant(6) gene. Eight EM clinical isolates containing the ant(6) gene had MIC values (<=32μg/mL) lower by at least 16-fold than FMS-007 (512μg/mL) for STR, and N59H and K204Q were the common mutations in the ant(6) gene.

Conclusion

This assay verified the biochemical function of the predictive gene ant(6)FMS-007 and could provide an alternative method to study resistant gene function in multi-drug-resistant bacteria. The inconsistency between genotype and phenotype of resistant genes indicated that the combination of resistance gene detection and functional analysis could better provide precision medicine for clinical use.

Antibiotic resistance in potential probiotic lactic acid bacteria of fermented foods and human origin from Nigeria

INTRODUCTION

Probiotic lactobacilli are generally recognized as safe (GRAS) and are being used in several food and pharma formulations. However, growing concern of antibiotic resistance in bacterial strains of food origin and its possible transmission via functional foods is increasingly being emphasized.

OBJECTIVES

This study screened potential probiotic lactic acid bacteria (LAB) strains for their phenotypic and genotypic antibiotic resistance profiles.

METHODS

Susceptibility to different antibiotics was assayed by the Kirby Bauer standard disc diffusion protocol. Both conventional and SYBR-RTq-PCR were used for detection of resistance coding genes.

RESULTS

A variable susceptibility pattern was documented against different antibiotic classes. LAB strains irrespective of origin displayed marked phenotypic resistance against cephalosporins, aminoglycosides, quinolones, glycopeptides; and methicillin among beta-lactams with few exceptions. In contrast, high sensitivity was recorded against macrolides, sulphonamides and carbapenems sub-group of beta-lactams with some variations. parC, associated with ciprofloxacin resistance was detected in 76.5% of the strains. Other prevalent resistant determinants observed were aac(6?)Ii (42.1%), ermB, ermC (29.4%), and tetM (20.5%). Six (?17.6%) of the isolates were free from genetic resistance determinants screened in this study.

CONCLUSION

Study revealed presence of antibiotic resistance determinants among lactobacilli from both fermented foods and human sources.

Affinity-Based Analysis Methods for the Detection of Aminoglycoside Antibiotic Residues in Animal-Derived Foods: A Review

With the increasingly serious problem of aminoglycoside antibiotic residues, it is imperative to develop rapid, sensitive and efficient detection methods. This article reviews the detection methods of aminoglycoside antibiotics in animal-derived foods, including enzyme-linked immunosorbent assay, fluorescent immunoassay, chemical immunoassay, affinity sensing assay, lateral flow immunochromatography and molecular imprinted immunoassay. After evaluating the performance of these methods, the advantages and disadvantages were analyzed and compared. Furthermore, development prospects and research trends were proposed and summarized. This review can serve as a basis for further research and provide helpful references and new insights for the analysis of aminoglycoside residues. Accordingly, the in-depth investigation and analysis will certainly make great contributions to food safety, public hygiene and human health.

Antibiotics and Bacterial Resistance-A Short Story of an Endless Arms Race

Despite the undisputed development of medicine, antibiotics still serve as first-choice drugs for patients with infectious disorders. The widespread use of antibiotics results from a wide spectrum of their actions encompassing mechanisms responsible for: the inhibition of bacterial cell wall biosynthesis, the disruption of cell membrane integrity, the suppression of nucleic acids and/or proteins synthesis, as well as disturbances of metabolic processes. However, the widespread availability of antibiotics, accompanied by their overprescription, acts as a double-edged sword, since the overuse and/or misuse of antibiotics leads to a growing number of multidrug-resistant microbes. This, in turn, has recently emerged as a global public health challenge facing both clinicians and their patients. In addition to intrinsic resistance, bacteria can acquire resistance to particular antimicrobial agents through the transfer of genetic material conferring resistance. Amongst the most common bacterial resistance strategies are: drug target site changes, increased cell wall permeability to antibiotics, antibiotic inactivation, and efflux pumps. A better understanding of the interplay between the mechanisms of antibiotic actions and bacterial defense strategies against particular antimicrobial agents is crucial for developing new drugs or drug combinations. Herein, we provide a brief overview of the current nanomedicine-based strategies that aim to improve the efficacy of antibiotics.

Safety assessment and characterisation of Ligilactobacillus salivarius PS21603 as potential feed additive for swine

The present study aimed to characterise in vitro properties of the strain Ligilactobacillus salivarius PS21603 and evaluate in vivo piglets’ tolerance for its use as feed additive in swine. The ability of L. salivarius PS21603 of inhibiting enteropathogens’ growth in vitro was evaluated using a co-culture assay. Low pH tolerance, bile tolerance, and resistance to osmotic changes were evaluated. The antibiotic susceptibility profile of L. salivarius PS21603 was assessed through broth microdilution method. Whole genome sequencing (WGS) was performed to exclude the presence of antibiotic resistance genes. L. salivarius PS21603 showed a high antimicrobial activity in vitro, reducing in a mean of 6.16 log cfu/ml eight different enterotoxigenic Escherichia coli strains. Moreover, L. salivarius PS21603 showed resistance to osmotic changes and was able to survive to a pH above 3.5 during 24 h and up to pH 2 at least during 2 h. In addition, WGS revealed that L. salivarius PS21603 did not harbour any resistance genes and thus there was no risk of transmissibility. Finally, an in vivo 28-days safety and tolerance study was performed. For that, 384 healthy piglets (28±2 days old and 7.5±1.5 kg, at weaning) were divided into three treatment groups receiving a different dose of L. salivarius PS21603: T1, 109 cfu/day; T2, 107 cfu/day; T3, control. Piglet’s health status was daily controlled. Individual bodyweight and feed intake per pen were weekly recorded to determine performance parameters. Blood samples were collected in 16 piglets from each treatment group on days 0 and 28 for determination of cytokine profiles. L. salivarius PS21603 was safe and well tolerated by piglets, there were no differences in performance nor cytokine profile between treatment groups. In conclusion, L. salivarius PS21603 is a potential candidate for a probiotic prevention strategy against pig diarrhoea.

Wildlife symbiotic bacteria are indicators of the health status of the host and its ecosystem

Lactic acid bacteria (LAB) are gut symbionts that can be used as a model to understand the host-microbiota crosstalk under unpredictable environmental conditions such as wildlife ecosystems. The aim of this study was to determine whether viable LAB can be informative of the health status of wild boar populations. We monitored the genotype and phenotype of LAB based on markers that included safety and phylogenetic origin, antibacterial activity and immunomodulatory properties. A LAB profile dominated by lactobacilli appears to stimulate protective immune responses and relates to strains widely used as probiotics, resulting in a potentially healthy wildlife population whereas microbiota overpopulated by enterococci was observed in a hostile environment. These enterococci were closely related to pathogenic strains that have developed mechanisms to evade innate immune system, posing a potential risk for the host health. Furthermore, our LAB isolates displayed antibacterial properties in a species-dependent manner. Nearly all of them were able to inhibit bacterial pathogens, raising the possibility of using them as a la carte antibiotic alternative in the unexplored field of wildlife disease mitigation. Our study highlights that microbiological characterization of LAB is a useful indicator of wildlife health status and the ecological origin from which they derive. Significance Statement The wildlife symbiotic microbiota is an important component to the greater for greater diversity and functionality of their bacterial populations, influencing the host health and adaptability to its ecosystem. Although many microbes are partly responsible for the development of multiple physiological processes, only certain bacterial groups such as lactic acid bacteria (LAB) have the capacity to overpopulate the gut, promoting health (or disease) when specific genetic and environmental conditions are present. LAB have been exploited in many ways due to their probiotic properties, in particular lactobacilli, however their relationship with wildlife gut-associated microbiota hosts remains to be elucidated. On the other hand, it is unclear whether LAB such as enterococci, which have been associated with detrimental health effects, could lead to disease. These important questions have not been properly addressed in the field of wildlife, and therefore, should be clearly attained.

Synergy of the Bacteriocin AS-48 and Antibiotics against Uropathogenic Enterococci

The genus Enterococcus comprises a ubiquitous group of Gram-positive bacteria that can cause diverse health care-associated infections. Their genome plasticity enables easy acquisition of virulence factors as well as antibiotic resistances. Urinary tract infections (UTIs) and catheter-associated UTIs are common diseases caused by enterococci. In this study, Enterococcus strains isolated from UTIs were characterized, showing that the majority were E. faecalis and contained several virulence factors associated to a better colonization of the urinary tract. Their susceptibility against the bacteriocin AS-48 and several antibiotics was tested. AS-48 is a potent circular bacteriocin that causes bacterial death by pore formation in the cell membrane. The interest of this bacteriocin is based on the potent inhibitory activity, the high stability against environmental conditions, and the low toxicity. AS-48 was active at concentrations below 10 mg/L even against antibiotic-resistant strains, whereas these strains showed resistance to, at least, seven of the 20 antibiotics tested. Moreover, the effect of AS-48 combined with antibiotics commonly used to treat UTIs was largely synergistic (with up to 100-fold MIC reduction) and only occasionally additive. These data suggest AS-48 as a potential novel drug to deal with or prevent enterococcal infections.

Rapid detection of antibiotic resistance genes in lactic acid bacteria using PMMA-based microreactor arrays

The emergence of lactic acid bacteria (LABs) resistant to existing antimicrobial drugs is a growing health crisis. To decrease the overuse of antibiotics, molecular diagnostic systems that can rapidly determine the presence of antibiotic resistance (AR) genes in LABs from yogurt samples are needed. This paper describes a fully integrated, miniaturized plastic chip and closed-tube detection chemistry that performs multiplex nucleic acid amplification. High-throughput identification of AR genes was achieved through this approach, and six AR genes were analyzed simultaneously in < 2 h. This time-to-result included the time required for the extraction of DNA. The detection limit of the chip was 10³ CFU mL^-1, which was consistent with that of tube LAMP. We detected and identified multiple DNAs, including streptomycin, tetracycline, and vancomycin resistance-associated genes, with complete concordance to the Kirby-Bauer disk diffusion method.Key Points• A miniaturized chip was presented, and multiplex nucleic acid amplification was performed.• The device can be integrated with LAMP for rapid detection of antibiotic resistance genes.• The approach had a high throughput of AR gene analysis in lactic acid bacteria.

Sensitive lateral flow immunoassay of an antibiotic neomycin in foodstuffs

Aminoglycosides belong to a class of antibiotics now widely used in agriculture and veterinary medicine and expected to contaminate food products. In this study, a sensitive lateral flow immunoassay (LFIA) of an aminoglycoside neomycin (NEO) was developed. Two methods of immunochromatographic detection based on various techniques of gold nanoparticles (AuNPs) introduction as a label were compared. It was demonstrated that the indirect labeling (a conjugation of anti-species antibodies with a marker) allowed for an increase in assay sensitivity by 80 times. The test system was characterized by an instrumental limit of detection of 0.1 ng/mL and the cutoff level of 10 ng/mL; the assay duration was 15 min. Specificity only toward NEO was demonstrated. The developed LFIA has been tested to detect NEO in different foodstuffs. It has been demonstrated that 70-119% of NEO (coefficients of variations < 10%) can be determined in milk, turkey meat, honey, and eggs using simple procedures of preliminary sample preparation. Testing the samples showed the coincidence of the results for the developed lateral flow assay and for commercial ELISA kit.

Techno-functional characterization of indigenous Lactobacillus isolates from the traditional fermented foods of Meghalaya, India

The rural tribal people of Meghalaya depend mostly on their ethnic fermented foods as a part of their regular diet and these fermented foods are considered to be a hub of healthy microorganisms. However, the efficacy of probiotic microorganisms is considered to be population-specific because of gut microflora variation in food habits and specific host-microbial interactions. Hence, a strong need for exploring novel indigenous microorganisms with rich probiotic potentiality is required. A few indigenous Lactobacillus isolates (from traditional fermented foods of Meghalaya) were studied extensively for its technological and probiotic attributes. The isolates could survive at pH 2–3 (L. fermentum K16 showed high cell count: pH 2–5.12 log CFU/ml; pH 3–5.76 log CFU/ml), against bile salts (L. fermentum K7 showed high cell count-5.36 log CFU/ml), gastric juices (pepsin and trypsin), and intestinal juice (pancreatin). The isolates showed α-galactosidase activity from 0.104-0.412 μM/ml and β-glucosidase activity ranging from 0.122-0.409 μM/ml. Exopolysaccharide production was in between 410 and 950 mg/L. Cell surface hydrophobicity was 71.57% (L. rhamnosus K4E) and auto-aggregation was 83% (L. fermentum K16) during the study. Highest proteolytic activity (0.671 nm) and cholesterol assimilation (52.57%) was exhibited by L. fermentum K16. The isolates showed high free radical scavenging activity by ABTS method up to 80.78% by isolate L. fermentum K7. Antibacterial activity and co-aggregation efficacy was also tested against B. cereus, E. faecalis, S. dysenteriae, S. aureus, E. coli, L. monocytogenes, S. typhi. These indigenous Lactobacillus isolates with high probiotic potentials could be exploited in the development of the traditional fermented foods of Meghalaya.

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Technological and probiotic attributes (in vitro) of eight indigenous Lactobacillus strains were studied.

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Lactobacillus strains were isolated from the traditional fermented foods of Meghalaya, India.

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L. rhamnosus K4E, L. fermentum K16, L. fermentum K7 and L. plantarum RD7 were considered predominant over the rest of the strains.

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The isolates could be employed for development of novel functional fermented foods.

Gut commensal bacteria show beneficial properties as wildlife probiotics

Probiotics are noninvasive, environmentally friendly alternatives for reducing infectious diseases in wildlife species. Our aim in the present study was to evaluate the potential of gut commensals such as lactic acid bacteria (LAB) as wildlife probiotics. The LAB selected for our analyses were isolated from European badgers (Meles meles), a wildlife reservoir of bovine tuberculosis, and comprised four different genera: Enterococcus, Weissella, Pediococcus, and Lactobacillus. The enterococci displayed a phenotype and genotype that included the production of antibacterial peptides and stimulation of antiviral responses, as well as the presence of virulence and antibiotic resistance genes; Weissella showed antimycobacterial activity owing to their ability to produce lactate and ethanol; and lactobacilli and pediococci modulated proinflammatory phagocytic responses that associate with protection against pathogens, responses that coincide with the presence of immunomodulatory markers in their genomes. Although both lactobacilli and pediococci showed resistance to antibiotics, this was naturally acquired, and almost all isolates demonstrated a phylogenetic relationship with isolates from food and healthy animals. Our results show that LAB display probiotic benefits that depend on the genus, and that lactobacilli and pediococci are probably the most obvious candidates as probiotics against infectious diseases in wildlife because of their food-grade status and ability to modulate protective innate immune responses.

Update on Tetracycline Susceptibility of Pediococcus acidilactici Based on Strains Isolated from Swiss Cheese and Whey

Bacterial strains used as starter cultures in the production of fermented foods may act as reservoirs for antibiotic resistance (AbR) genes. To avoid the introduction of such genes into the food chain, the presence of acquired AbR in bacterial strains added to food must be tested. Standard protocols and microbiological cut-off values have been defined to provide practitioners with a basis for evaluating whether their bacterial isolates harbor an acquired resistance to a given antibiotic. Here, we tested the AbR of 24 strains of Pediococcus acidilactici by using the standard protocol and microbiological cut-off values recommended by the European Food Safety Authority. Phenotypic data were complemented by searching for known AbR genes using an in silico analysis of whole genomes. The majority (54.2%) of the strains were able to grow at a tetracycline concentration above the defined cut-off, even though only one strain carried a known tetracycline resistance gene, tetM. The same strain also carried the AbR gene of an erythromycin resistance methylase, ermA, and displayed resistance toward clindamycin and erythromycin. Our results bolster the scarce data on the sensitivity of P. acidilactici to tetracycline and suggest that the microbiological cut-off recommended by the European Food Safety Authority for this antibiotic should be amended.

Detection of acetyltransferase modification of kanamycin, an aminoglycoside antibiotic, in bacteria using ultrahigh-performance liquid chromatography tandem mass spectrometry

RATIONALE

The occurrence of antibiotic-resistant bacteria is a worldwide issue that has the potential, if not addressed, to eliminate classes of antibiotics that have extended life expectancy in the last century. An approach to confront this threat is the development of technologies that greatly accelerate the detection of antibiotic resistance to minimize unnecessary treatment involving antibiotics. Development of an analytical method for rapid detection of aminoglycoside resistance using liquid chromatography/mass spectrometry (LC/MS) has not been reported in the literature and is described here.

METHODS

A strain of Escherichia coli carrying a plasmid encoding an aminoglycoside-modifide enzyme (N-acetyltransferase) was incubated with kanamycin, an aminoglycoside. The antibiotic and its modified form were observed using LC/MS. An ABSciex QTrap 6500+ was used for kinetic and quantitative analysis and high-resolution structural elucidation was performed using a Thermo Fisher Q-Exactive hybrid quadrupole-orbitrap mass spectrometer.

RESULTS

Detection of kanamycin modification was achieved in less than an hour of incubation. Calibration curves for both modified and unmodified kanamycin from 0.5 to 50 μg mL^-1 were obtained. Generation and depletion of modified and unmodified kanamycin as a function of time were performed. High-resolution mass spectrometry was employed for confirmation and structural elucidation of the novel precursor and product ion biomarkers with high mass accuracy (≤7 ppm).

CONCLUSIONS

A newly developed analytical method is able to determine bacterial resistance to aminoglycosides (via acetylation of kanamycin), qualitatively and quantitatively, within 30 minutes and 6 hours of incubation with kanamycin, respectively. High-resolution data support the placement of an acetyl group on kanamycin confirming aminoglycoside resistance and its mechanism. Quantification was achieved for both forms of the antibiotic 50- to 100-fold lower than the minimum inhibitory concentration for the resistant bacteria and can be used to replace conventional antimicrobial susceptibility tests.

Antibiotic Resistance Genetic Markers and Integrons in White Soft Cheese: Aspects of Clinical Resistome and Potentiality of Horizontal Gene Transfer

Antibiotic resistance poses an important threat to global public health and has become a challenge to modern medicine. The occurrence of antibiotic-resistant bacteria in a broad range of foods has led to a growing concern about the impact that food may have as a reservoir of antibiotic resistance genes. Considering Minas Frescal Cheese (MFC)-a typical Brazilian white soft cheese-and its economic and cultural values, in this study, medically relevant antimicrobial-resistance genetic markers (AR genes) were screened, and the occurrence of integrons were evaluated in manufactured MFC using culture-independent approaches. Through a fingerprinting analysis, the tested MFCs were brand-clustered, indicating reproducibility along the production chain. A common core of resistance markers in all brands evaluated and related antimicrobials such as β-lactams, tetracyclines, quinolones, and sulfonamide was detected. Several other markers, including efflux pumps and aminoglycosides-resistance were distributed among brands. Class 1 and 2 integrons were observed, respectively, in 77% and 97% of the samples. The presence of AR genes is of special interest due to their clinical relevance. Taken together, the data may suggest that the production chain of MFC might contribute to the spread of putative drug-resistant bacteria, which could greatly impact human health. Furthermore, detection of class 1 and class 2 integrons in MFC has led to discussions about resistance gene spread in this traditional cheese, providing evidence of potential horizontal transfer of AR genes to human gut microbiota.

Antibiotic Resistance-Susceptibility Profiles of Streptococcus thermophilus Isolated from Raw Milk and Genome Analysis of the Genetic Basis of Acquired Resistances

The food chain is thought to play an important role in the transmission of antibiotic resistances from commensal and beneficial bacteria to pathogens. Streptococcus thermophilus is a lactic acid bacterium of major importance as a starter for the dairy industry. This study reports the minimum inhibitory concentration (MIC) of 16 representative antimicrobial agents to 41 isolates of S. thermophilus derived from raw milk. Strains showing resistance to tetracycline (seven), erythromycin and clindamycin (two), and streptomycin and neomycin (one) were found. PCR amplification identified tet(S) in all the tetracycline-resistant strains, and ermB in the two erythromycin/clindamycin-resistant strains. Hybridisation experiments suggested each resistance gene to be located in the chromosome with a similar genetic organization. Five antibiotic-resistant strains -two resistant to tetracycline (St-2 and St-9), two resistant to erythromycin/clindamycin (St-5 and St-6), and one resistant to streptomycin/neomycin (St-10)- were subjected to genome sequencing and analysis. The tet(S) gene was identified in small contigs of 3.2 and 3.7 kbp in St-2 and St-9, respectively, flanked by truncated copies of insertion sequence (IS) elements. Similarly, ermB in St-6 and St-5 was found in contigs of 1.6 and 28.1 kbp, respectively. Sequence analysis and comparison of the largest contig showed it to contain three segments (21.9, 3.7, and 1.4 kbp long) highly homologous to non-collinear sequences of pRE25 from Enterococcus faecalis. These segments contained the ermB gene, a transference module with an origin of transfer (oriT) plus 15 open reading frames encoding proteins involved in conjugation, and modules for plasmid replication and segregation. Homologous stretches were separated by short, IS-related sequences, resembling the genetic organization of the integrative and conjugative elements (ICEs) found in Streptococcus species. No gene known to provide aminoglycoside resistance was seen in St-10. Four strain-specific amino acid substitutions in the RsmG methyltransferase were scored in this strain; these might be associated to its streptomycin/neomycin resistance. Under yogurt manufacturing and storage conditions, no transfer of either tet(S) or ermB from S. thermophilus to L. delbrueckii was detected. The present results contribute toward characterisation of the antibiotic resistance profiles in S. thermophilus, provide evidence for the genetic basis of acquired resistances and deepen on their transference capability.

Sub-inhibitory concentrations of gentamicin triggers the expression of aac(6')Ie-aph(2″)Ia, chaperons and biofilm related genes in Lactobacillus plantarum MCC 3011

The study aimed to analyze the effects of sub-inhibitory concentrations of gentamicin on the expressions of high level aminoglycoside resistant (HLAR) bifunctional aac(6')Ie-aph(2″)Ia, biofilm and chaperone genes in Lactobacillus plantarum. The analysis of the biofilm formation in five isolates obtained from chicken sausages indicated their role in exhibiting phenotypic resistance based on the varied MIC values despite carrying the bifunctional gene. The biofilm formation significantly increased when L. plantarum MCC 3011 was grown in sub-inhibitory concentrations of gentamicin (4 μg/ml), kanamycin (8 μg/ml) and streptomycin (2 μg/ml). Thirty day gentamicin selection increased minimum inhibitory concentration (MIC) values from 4 to 64 and 2 to 256 fold for gentamicin and kanamycin, respectively when compared to the parental cultures. Expression studies revealed that constant exposure to gentamicin had induced chaperon [groEL] and the bifunctional gene, aac(6')Ie-aph(2″)Ia upto nine fold. Induction of groEL, groES and lamC genes in gentamicin (4 μg/ml) preincubated MCC 3011 indicated their significant role in aminoglycoside mediated response. Our study indicates that constant exposure to sub inhibitory concentrations of gentamicin allows L. plantarum to adapt against higher doses of aminoglycosides. This highlights the risks and food safety issues associated with the use of aminoglycosides in livestock and consumption of farm oriented fermented food products.

Physiological Role of Two-Component Signal Transduction Systems in Food-Associated Lactic Acid Bacteria

Two-component systems (TCSs) are widespread signal transduction pathways mainly found in bacteria where they play a major role in adaptation to changing environmental conditions. TCSs generally consist of sensor histidine kinases that autophosphorylate in response to a specific stimulus and subsequently transfer the phosphate group to their cognate response regulators thus modulating their activity, usually as transcriptional regulators. In this review we present the current knowledge on the physiological role of TCSs in species of the families Lactobacillaceae and Leuconostocaceae of the group of lactic acid bacteria (LAB). LAB are microorganisms of great relevance for health and food production as the group spans from starter organisms to pathogens. Whereas the role of TCSs in pathogenic LAB (most of them belonging to the family Streptococcaceae) has focused the attention, the roles of TCSs in commensal LAB, such as most species of Lactobacillaceae and Leuconostocaceae, have been somewhat neglected. However, evidence available indicates that TCSs are key players in the regulation of the physiology of these bacteria. The first studies in food-associated LAB showed the involvement of some TCSs in quorum sensing and production of bacteriocins, but subsequent studies have shown that TCSs participate in other physiological processes, such as stress response, regulation of nitrogen metabolism, regulation of malate metabolism, and resistance to antimicrobial peptides, among others.