Genetic diversity and safety aspects of enterococci from slightly fermented sausages

Non-faecium non-faecalis enterococci: a review of clinical manifestations, virulence factors, and antimicrobial resistance

SUMMARYEnterococci are a diverse group of Gram-positive bacteria that are typically found as commensals in humans, animals, and the environment. Occasionally, they may cause clinically relevant diseases such as endocarditis, septicemia, urinary tract infections, and wound infections. The majority of clinical infections in humans are caused by two species: Enterococcus faecium and Enterococcus faecalis. However, there is an increasing number of clinical infections caused by non-faecium non-faecalis (NFF) enterococci. Although NFF enterococcal species are often overlooked, studies have shown that they may harbor antimicrobial resistance (AMR) genes and virulence factors that are found in E. faecium and E. faecalis. In this review, we present an overview of the NFF enterococci with a particular focus on human clinical manifestations, epidemiology, virulence genes, and AMR genes.

Antimicrobial Resistance and Virulence Factor Gene Profiles of Enterococcus spp. Isolated from Giant Panda Oral Cavities

Introduction

The objective of this study was to determine the prevalence and characteristics of antimicrobial-resistant Enterococcus faecalis and E. faecium isolated from the oral cavities of captive giant pandas in China.

Material and Methods

The virulence-associated determinant and antimicrobial resistance genes were detected and antimicrobial susceptibility tests were performed on 54 strains of each bacterium.

Results

All isolates showed 100% multidrug resistance. E. faecalis isolates showed a higher percentage of strains resistant to gentamicin (48.1%), vancomycin (55.6%), linezolid (100%), and streptomycin (33.3%) than E. faecium isolates. The resistance genes of Enterococcus spp. were present to highly varying extents according to antibiotic type, their presence breaking down for E. faecalis and E. faecium respectively as aac(6')/aph(2″) 5.56% and 5.56%; aph(3')-Ⅲ 0% and 14.81%; ant(6)-I 0% and 3.7%; ant(4')-Ia 0% and 64.81%; tetL 20.37% and 100%; vanA 92.59% and 46.3%; vanB 0% and 0%; cfr 0% and 90.74%; optrA 96.3% and 3.7%; blaZ 0% and 1.85%; blaTEM 0% and 0%; tetA 20.37% and 0%; tetC 24.07% and 100%; tetM 0% and 0%; ermA 12.96% and 100%; ermB 5.56% and 3.7%; and ermC 0% and 1.85%.Virulence-associated determinants were detected in this research, which typically include efaA, gelE, asa1, ace, cylA, esp and hyl; however, the latter three were not detected. High proportions of the isolates carried the efaA, gelE, asa1, and ace genes. Respectively for E. faecalis and E. faecium their detection was efaA 98.1% and 85.2%; gelE 98.1% and 87%; asa1 92.6% and 87%; and ace 87% and 85.2%.

Conclusion

This is the first study on the potential disease risk and antimicrobial-resistant characteristics of E. faecalis and E. faecium isolates in giant panda oral cavities. The results of this study show that the antimicrobial resistance rate of Enterococcus spp. isolated from the oral cavity of captive pandas is very high, and thus needs to be monitored.

CRISPR-cas system in the acquisition of virulence genes in dental-root canal and hospital-acquired isolates of Enterococcus faecalis

Enterococcus faecalis is one of the important causative agents of nosocomial and life-threatening infections in human. Several studies have demonstrated that the presence of CRISPR-cas is associated with antibiotic susceptibility and lack of virulence traits. In this study, we aimed to assess the phenotypic and genotypic virulence determinants in relation to CRISPR elements from the dental-root canals and hospital-acquired isolates of E. faecalis. Eighty-eight hospital-acquired and 73 dental-root canal isolates of E. faecalis were assessed in this study. Phenotypic screening of the isolates included biofilm formation, and gelatinase and hemolysis activities. Genotypical screening using PCR was further used to evaluate the presence of CRISPR elements and different virulence-associated genes such as efaA, esp, cylA, hyl, gelE, ace, ebpR, and asa1. Biofilm formation, gelatinase, and hemolysis activities were detected in 93.8%, 29.2%, and 19.2% of the isolates, respectively. The most prevalent virulence-associated gene was ace, which was followed by efaA, whereas cylA was the least identified. The presence of CRISPR1-cas, orphan CRISPR2, and CRISPR3-cas was determined in 13%, 55.3%, and 17.4% of the isolates, respectively. CRISPR elements were significantly more prevalent in the dental-root canal isolates. An inverse significant correlation was found between CRISPR-cas loci, esp, and gelE, while direct correlations were observed in the case of cylA, hyl, gelE (among CRISPR-loci 1 and 3), asa1, ace, biofilm formation, and hemolysis activity. Findings, therefore, indicate that CRISPR-cas might prevent the acquisition of some respective pathogenicity factors in some isolates, though not all; so selective forces could not influence pathogenic traits. Abbreviations: BHI: brain-heart infusion agar; CRISPRs: Clustered regularly interspaced short palindromic repeats; Esp: Cell wall-associated protein; ENT: ear-nose-throat; ICU: intensive care units; OD: optical densities; PCR: polymerase chain reaction; SDS: sodium dodecyl sulfate; UTI: urinary tract infection.

Safety, beneficial and technological properties of enterococci for use in functional food applications - a review

Enterococci are ubiquitous lactic acid bacteria (LAB) that predominantly reside in the gastrointestinal tract of humans and animals but are also widespread in food and the environment due to their robust nature. Enterococci have the paradoxical position of providing several benefits of technological interest in food fermentations but are also considered as opportunistic pathogens capable of causing infection in immunocompromised patients. Several species of the genus have been correlated with disease development in humans such as bacteremia, urinary tract infections, and endocarditis. The pathogenesis of enterococci has been attributed to the increasing incidence of antibiotic resistance and the possession of virulence determinants. On the contrary, enterococci have led to improvements in the aroma, texture, and flavor of fermented dairy products, while their beneficial use as probiotic and protective cultures has also been documented. Furthermore, they have emerged as important candidates for the generation of bioactive peptides, particularly from milk, which provide new opportunities for the development of functional foods and nutraceuticals for human nutrition and health. The detection of pathogenic traits among some species is compromising their use in food applications and subsequently, the genus neither has Generally Regarded as Safe (GRAS) status nor has it been included in the Qualified Presumption of Safety (QPS) list. Nevertheless, the use of certain enterococcal strains in food has been permitted on the basis of a case-by-case assessment. Promisingly, enterococcal virulence factors appear strain specific and food isolates harbor fewer determinants than clinical isolates, while they also remain largely susceptible to clinically relevant antibiotics and thus, have a lower potential for pathogenicity. Ideally, strains considered for use in foods should not possess any virulence determinants and should be susceptible to clinically relevant antibiotics. Implementation of an appropriate risk/benefit analysis, establishment of a strain's innocuity, and consideration for relevant guidelines, legislation, and regulatory aspects surrounding functional food development, may help industry, health-staff and consumers accept enterococci, like other LAB, as important candidates for useful and beneficial applications in food biotechnology.

Biochemical Characterization of Heat-Tolerant Recombinant L-Arabinose Isomerase from Enterococcus faecium DBFIQ E36 Strain with Feasible Applications in D-Tagatose Production

D-Tagatose is a ketohexose, which presents unique properties as a low-calorie functional sweetener possessing a sweet flavor profile similar to D-sucrose and having no aftertaste. Considered a generally recognized as safe (GRAS) substance by FAO/WHO, D-tagatose can be used as an intermediate for the synthesis of other optically active compounds as well as an additive in detergent, cosmetic, and pharmaceutical formulations. This study reports important features for L-arabinose isomerase (EC 5.3.1.4) (L-AI) use in industry. We describe arabinose (araA) gene virulence analysis, gene isolation, sequencing, cloning, and heterologous overexpression of L-AI from the food-grade GRAS bacterium Enterococcus faecium DBFIQ E36 in Escherichia coli and assess biochemical properties of this recombinant enzyme. Recombinant L-AI (rL-AI) was one-step purified to homogeneity by Ni²⁺-agarose resin affinity chromatography and biochemical characterization revealed low identity with both thermophilic and mesophilic L-AIs but high degree of conservation in residues involved in substrate recognition. Optimal conditions for rL-AI activity were 50 °C, pH 5.5, and 0.3 mM Mn²⁺, exhibiting a low cofactor concentration requirement and an acidic optimum pH. Half-life at 45 °C and 50 °C were 1427 h and 11 h, respectively, and 21.5 h and 39.5 h at pH 4.5 and 5.6, respectively, showing the high stability of the enzyme in the presence of a metallic cofactor. Bioconversion yield for D-tagatose biosynthesis was 45% at 50 °C after 48 h. These properties highlight the technological potential of E. faecium rL-AI as biocatalyst for D-tagatose production.

Antimicrobial Resistance, Virulence Determinants, and Biofilm Formation of Enterococcus Species From Ready-to-Eat Seafood

Enterococcus species form an important population of commensal bacteria and have been reported to possess numerous virulence factors considered significantly important in exacerbating diseases caused by them. The present study was designed to characterize antibiotic-resistant and virulent enterococci from ready-to-eat (RTE) seafood. A total of 720 RTE shrimp samples comprising sauced shrimp (n = 288), boiled shrimp (n = 216), and smoked shrimp (n = 216) obtained from open markets in Delta State, Nigeria, were assessed. Standard classical methods and polymerase chain reaction (PCR) were used in identifying the Enterococcus species. Potential virulence factors (β-hemolysis, gelatinase activity, S-layer, and biofilm formation) were assessed using standard procedures. The antibiotic susceptibility profile of the identified enterococci isolates was assayed using the Kirby–Bauer disc diffusion method. PCR was further used to screen selected antibiotic resistance and virulence genes. Prevalence of Enterococcus species from shrimp varieties is as follows: sauced, 26 (9.03%); boiled, 6 (2.78%); and smoked, 27 (12.50%), with an overall prevalence of 59 (8.19%) based on the occurrence of black hallow colonies after incubation. Enterococcus species detected include E. faecalis, 17 (28.8%); E. faecium, 29 (49.2%); E. gallinarum, 6 (10.2%); E. casseliflavus, 2 (3.4%); E. hirae, 3 (5.1%); and E. durans, 2 (3.4%). Biofilm occurrence among the shrimp varieties is as follows: 19/26 (73.1%) for sauced shrimps, 5/6 (83.3%) for boiled shrimps, and 16/27 (59.3%) for smoked shrimps. The phenotypic expression of the enterococci virulence revealed the following: S-layer, 59 (100%); gelatinase production, 19 (32.2%); and β-hemolysis, 21 (35.6%). An average of 3–11 virulence genes were detected in the Enterococcus species. The resistance profile of Enterococcus species is as follows: erythromycin, 29 (49.2%); vancomycin, 22 (37.3%); and tetracycline, 27 (45.8%). The frequency of occurrence of antibiotic resistance genes from the phenotypic resistant enterococci isolates to the macrolide, glycopeptide, and tetracycline antibiotics is as follows: ermA, 13/29 (44.8%); vanA, 14/22 (63.6%); tetA, 14/27 (51.9%); tetM, 15/27 (55.6%); ermB, 4/29 (13.8%); and vanB, 5/22 (22.7%). Findings from this study reveal the antibiotic resistance of enterococci strains of such species as E. durans, E. casseliflavus, E. gallinarum, and E. hirae. This study further revealed that RTE food products are reservoirs of potential virulent enterococci with antibiotic-resistant capabilities. This provides useful data for risk assessment and indicates that these foods may present a potential public health risk to consumers.

Differential Responses of Colorectal Cancer Cell Lines to Enterococcus faecalis' Strains Isolated from Healthy Donors and Colorectal Cancer Patients

The metabolites produced by the host’s gut microbiota have an important role in the maintenance of intestinal homeostasis, but can also act as toxins and induce DNA damage in colorectal epithelial cells increasing the colorectal cancer (CRC) chance. In this scenario, the impact of some of the components of the natural human gastrointestinal microbiota, such as Enterococcus faecalis (E. faecalis), at the onset of CRC progression remains controversial. Since under dysbiotic conditions it could turn into a pathogen, the aim of this study was to compare the effect of E. faecalis’ strains (isolated from CRC patients and healthy subjects’ stools) on the proliferation of different colorectal cells lines. First, we isolated and genotyping characterized the Enterococcus faecalis’ strains. Then, we analyzed the proliferation index (by 3-(4,5-Dimethylthiazol-2-yl)-2,5-Diphenyltetrazolium Bromide (MTT) assay) of three tumor and one normal intestinal cell lines, previously exposed to E. faecalis strains pre-cultured medium. Stool samples of CRC patients demonstrated a reduced frequency of E. faecalis compared to healthy subjects. In addition, the secreted metabolites of E. faecalis’ strains, isolated from healthy donors, decreased the human ileocecal adenocarcinoma cell line HCT-8 and human colon carcinoma cell line HCT-116 cell proliferation without effects on human colorectal adenocarcinoma cell line SW620 and on normal human diploid cell line CLR-1790. Notably, the metabolites of the strains isolated from CRC patients did not influence the cell growth of CRC cell lines. Our results demonstrated a new point of view in the investigation of E. faecalis’ role in CRC development, which raises awareness of the importance of not only associating the presence/absence of a unique microorganism, but also in defining the specific characteristics of the different investigated strains.

Enterococci from ready-to-eat food - horizontal gene transfer of antibiotic resistance genes and genotypic characterization by PCR melting profile

BACKGROUND

The aim of this study was to evaluate the possibility of the horizontal transfer of genes encoding resistance to aminoglycosides (aac(6')-Ie-aph(2″)-Ia, aph(2″)-Ib, aph(2″)-Ic, aph(2″)-Id, ant(4')-Ia and ant(6')-Ia), tetracyclines (tetM, tetL, tetK, tetO and tetW), and macrolides (ermA, ermB, ermC, msrC, mefAB) in Enterococcus strains isolated from ready-to-eat dishes purchased in bars and restaurants in Olsztyn, Poland.

RESULTS

It was found that 74% of tested strains were able to conjugal transfer at least one of the antibiotic resistance genes. Transfer of resistance to tetracyclines in strains was observed with a frequency ranging from 1.3 × 10^-6 to 8.7 × 10^-7 transconjugants/donor. The int gene and the tetM gene were transferred simultaneously, which indicated that a transposon of the Tn916/Tn1545 also participated in the conjugation process. The frequency of transferring genes of resistance to macrolides ranged from 3.2 × 10^-6 to 2.4 × 10^-8 transconjugants/donor. The ermB gene was transferred the most frequently. The frequency of acquisition of genes encoding aminoglycosides in strains isolated from food ranged from 1.7 × 10^-6 to 3,2 × 10^-8 transconjugants/donor. Transfer of the aac(6')-Ie-aph(2″) gene was the most frequent. In all reactions, the clonal character of transconjugants and recipients was confirmed by the polymerase chain reaction melting profile (PCR MP) method, which is an alternative to the pulsed field gel electrophoresis (PFGE) method.

CONCLUSION

The findings of this study indicate that Enterococcus isolated from ready-to-eat food is able to horizontally transfer genes encoding various antibiotic resistance mechanisms. © 2018 Society of Chemical Industry.

Safety and Growth Optimization of Lactic Acid Bacteria Isolated From Feedlot Cattle for Probiotic Formula Design

In order to eliminate the widespread use of antibiotics in livestock production, the research for alternatives has increased lately. This study examined the safety of 40 lactic acid bacteria (LAB) isolated from bovine feedlot environment and previously selected as potential probiotics. A high sensitivity prevalence to ampicillin (AMP, 100%), gentamicin (GEN, 96.3%), kanamycin (KAN, 96.3%), clindamycin (CLI, 85.2%), chloramphenicol (CHL, 92.6%) and streptomycin (STR, 88.9%) while moderate and high resistance against erythromycin (ERY, 48%) and tetracycline (TET, 79%) respectively, were determined. Feedlot enterococci and pediococci displayed high resistance to CLI, ERY, GEN and TET (73, 100, 54.5, and 73%, respectively). Among fifteen resistance genes investigated, seven were identified in lactobacilli; their presence not always was correlated with phenotypic resistance. STR resistance genes, aadA and ant(6) were observed in 7.4 and 3.7% of isolates, respectively; genes responsible for aminoglycosides resistance, such as bla (7.4%), and aph(3”)-III (3.7%) were also recognized. In addition, resistance cat and tetS genes (3.7 and 7.4%, respectively) were harbored by feedlot lactobacilli strains. The presence of ermB gene in 22.3% of isolates, including two of the six strains phenotypically resistant to ERY, exhibited the highest prevalence among the assessed antibiotics. None of the feedlot lactobacilli harbored virulence factors genes, while positive PCR amplification for ace, agg, fsrA, and atpA genes was found for enterococci. With the objective of producing large cell biomass for probiotic delivery, growth media without peptone but containing glucose and skim milk powder (Mgl and Mlac) were selected as optimal. Lactobacillus acidophilus CRL2074, L. amylovorus CRL2115, L. mucosae CRL2069, and L. rhamnosus CRL2084 were strains selected as free of antibiotic resistance and virulence determinants, able to reach high cell numbers in non-expensive culture media and being compatible among them.

Characterization and screening of the potential probiotic lactic acid bacteria and Bifidobacterium strains isolated of different biotopes

The use of lactic acid bacteria (LAB) and bifidobacteria species as probiotics may help to reduce antibiotic use for therapeutic, prophylactic and growth promotion in animal husbandry. The choice of the starter cultures has a critical impact on the palatability, processability and nutritional attributes of fermented products. In our research, the aim of this study was to screen and select potent probiotic LAB and Bifidobacterium strains isolated from different niches and to evaluate their characteristic features. A total of fourteen LAB and fifty-four Bifidobacterium were isolated from four fresh cows and camel’s milk, and twenty stool samples of healthy new born infants were identified and characterized by morphology and biochemical tests in order to select most suitable strains according to their technological characteristics including probiotic proprieties, antibiotics resistance and in vitro antagonism against food-poisoning bacteria. When the results of tolerance to both gastric and bile juices are taken together it appears that between fourteen LAB and forty-five, the strain B. longum BHI 07 has significantly the highest ability to survive during gastrointestinal transit (P < 0.05). Therefore, the mixed cultures of Bf. longum strains with LAB strains were more active against pathogenic bacteria than the pure one. These results show that bifidobacteria isolated from infants may be useful for improving probiotic formulae with respect to protection against pathogenic bacteria responsible of infection.

Ceftriaxone promotes the emergence of AmpC-overproducing Enterobacteriaceae in gut microbiota from hospitalized patients

Epidemiological data suggest that ceftriaxone may promote the emergence of commensal AmpC-overproducing Enterobacteriaceae because of a high biliary excretion. We tested this hypothesis in hospitalized patients either treated by ceftriaxone alone or receiving no antibiotics. Hospitalized patients with no previous antibiotics or hospitalization in the last 3 months, treated only with ceftriaxone, were prospectively included. For each ceftriaxone-treated patient, a control patient receiving no antibiotics was included. Clinical data and stools were collected at T0 (before antibiotics) and T1 (at the end of ceftriaxone treatment or at discharge) and T2 (3-6 months after T1) for the ceftriaxone-treated patients and at T0 and T1 for control patients. Third-generation cephalosporin-resistant Enterobacteriaceae were detected, identified by matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF), and characterized genetically. Clonal relatedness was evaluated by random amplified polymorphic DNA-polymerase chain reaction (RAPD-PCR). Fifteen ceftriaxone and 22 control patients were included. Patients' characteristics did not differ. At T0, 2/15 ceftriaxone-treated versus 1/22 control patients carried third-generation cephalosporin-resistant Enterobacteriaceae (p = 0.6). At T1, 4/15 (27%) ceftriaxone-treated patients carried AmpC producers versus 0/22 control patients (p = 0.02). Additionally, two and three subjects carried extended-spectrum β-lactamase (ESBL)-producing Enterobacteriaceae in the ceftriaxone and control groups, respectively (p = 1). At T2, three ceftriaxone-treated patients still carried AmpC-producing Enterobacteriaceae with the same RAPD profile as at T1. In hospitalized subjects with no other selective pressure, treatment by ceftriaxone alone promotes the gut colonization by AmpC-overproducing Enterobacteriaceae in over a quarter of patients, with a persistent carriage after the end of antibiotic exposure. The ecological impact of ceftriaxone should not be underestimated.

Impact of Lactobacillus curvatus 54M16 on microbiota composition and growth of Listeria monocytogenes in fermented sausages

Lactobacillus curvatus 54M16 produced bacteriocins sak X, sak T_α, sak T_β and sak P. The aim of this study was to investigate the anti-listerial activity of the bacteriocins-producing strain against Listeria monocytogenes in vitro co-culture experiments and during the manufacture of fermented sausages. In MRS broth, Lb. curvatus 54M16 was able to inhibit L. monocytogenes to undetectable levels after 48 h at 20 °C or 5 days at 15 °C. Anti-listerial activity was lower during the production of fermented sausages with pathogen inoculation at levels of approximately 4 Log CFU g^-1. However, total inhibition of L. monocytogenes native to the raw ingredients was achieved over the course of the fermentation. Moreover, 16S rRNA-based analysis revealed the ability of Lb. curvatus 54M16 to dominate and affect the bacterial ecosystem, whereas spoilage-associated bacterial genera, such as Brochothrix, Psychrobacter, Pseudomonas and some Enterobacteriaceae, were found until the end of ripening in sausages without Lb. curvatus 54M16. The use of the bacteriocins-producing Lb. curvatus 54M16 in fermented sausages could be an important contribution to product safety, provided that eco-physiological factors and other preservation methods are maintained at levels required for the inhibition of pathogens in controlled conditions.

Ecological impact of ciprofloxacin on commensal enterococci in healthy volunteers

Background

The ecological impact of ciprofloxacin on commensal enterococci is unknown.

Methods

Forty-eight healthy volunteers received ciprofloxacin from day (D) 0 to D14; stools were collected on D7, D14 and D42. Fluoroquinolone-susceptible and -resistant enterococci (FQ-SE and FQ-RE) were detected and quantified by culture, and identified by MALDI-TOF MS. The relative abundance of FQ-RE over FQ-SE was determined. The genetic basis of fluoroquinolone resistance was deciphered by partial sequencing of gyrA and parC genes. Clonal relatedness was determined by random amplification of polymorphic DNA PCR. Clinical trial no.: NCT00190151.

Results

Enterococci were carried by 47/48 (98%) subjects. Total counts were reduced during ciprofloxacin therapy (4.0 and 3.9 log cfu/g on D7 and D14 versus 5.9 log cfu/g before and 6.9 log cfu/g after treatment; P  < 0.05). Twenty-one out of 48 (44%) carried FQ-RE; among them, 21/21 carried Enterococcus faecium , 19 carried Enterococcus faecalis and 11 carried other species. Five out of 48 (10%) harboured FQ-RE (ciprofloxacin MIC >4 mg/L) before treatment (all E. faecium ), 6 on D7 (3 E. faecium and 3 E. faecalis ), 8 on D14 (4 E. faecium and 4 E. faecalis ) and 10 (21%) on D42 (9 E. faecium and 1 E. faecalis ). The relative abundance of FQ-RE increased from 44% on D0 to 73% and 75% on D7 and D14, respectively. No acquisition of fluoroquinolone resistance among endogenous D0 strains was evidenced. All (14/14) distinct Fluoroquinolone-resistant E. faecalis clones were gyrA / parC double mutants with high-level resistance (ciprofloxacin MIC >64 mg/L). In contrast, 34/35 E. faecium exhibited low-level resistance (ciprofloxacin MIC 4-32 mg/L) with no gyrA / parC mutation, but overexpressed the chromosomal Efm qnr gene. As compared with Fluoroquinolone-susceptible strains, Fluoroquinolone-resistant E. faecium were more frequently ampicillin resistant and Fluoroquinolone-resistant E. faecalis were more highly resistant to gentamicin.

Conclusions

Although intrinsically poorly susceptible to fluoroquinolones, gut populations of enterococci are highly impacted both quantitatively and qualitatively by ciprofloxacin.

Probiotic Enterococcus mundtii Isolate Protects the Model Insect Tribolium castaneum against Bacillus thuringiensis

Enterococcus mundtii strains isolated from the larval feces of the Mediterranean flour moth Ephestia kuehniella show antimicrobial activity against a broad spectrum of Gram-positive and Gram-negative bacteria. The in vitro probiotic characterization of one isolate revealed a high auto-aggregation score, a hydrophilic cell surface, tolerance for low pH, no hemolytic activity, and susceptibility to all tested antibiotics. We used the red flour beetle Tribolium castaneum, an established model organism, for the in vivo characterization of one probiotic E. mundtii isolate from E. kuehniella larvae. Tribolium castaneum larvae were fed orally with the probiotic isolate or the corresponding supernatant and then infected with either the entomopathogen Bacillus thuringiensis or Pseudomonas entomophila. Larvae exposed to the isolate or the supernatant showed increased survival following infection with B. thuringiensis but not P. entomophila. Heat treatment or treatment with proteinase K reduced the probiotic effect of the supernatant. However, the increased resistance attracts a fitness penalty manifested as a shorter lifespan and reduced fertility. T. castaneum has, pending on further research, the potential as an alternative model for the pre-screening of probiotics.

The Bacteriophage EF-P29 Efficiently Protects against Lethal Vancomycin-Resistant Enterococcus faecalis and Alleviates Gut Microbiota Imbalance in a Murine Bacteremia Model

Enterococcus faecalis is becoming an increasingly important opportunistic pathogen worldwide, especially because it can cause life-threatening nosocomial infections. Treating E. faecalis infections has become increasingly difficult because of the prevalence of multidrug-resistant E. faecalis strains. Because bacteriophages show specificity for their bacterial hosts, there has been a growth in interest in using phage therapies to combat the rising incidence of multidrug-resistant bacterial infections. In this study, we isolated a new lytic phage, EF-P29, which showed high efficiency and a broad host range against E. faecalis strains, including vancomycin-resistant strains. The EF-P29 genome contains 58,984 bp (39.97% G+C), including 101 open reading frames, and lacks known putative virulence factors, integration-related proteins or antibiotic resistance determinants. In murine experiments, the administration of a single intraperitoneal injection of EF-P29 (4 × 10⁵ PFU) at 1 h after challenge was sufficient to protect all mice against bacteremia caused by infection with a vancomycin-resistant E. faecalis strain (2 × 10⁹ CFU/mouse). E. faecalis colony counts were more quickly eliminated in the blood of EF-P29-protected mice than in unprotected mice. We also found that exogenous E. faecalis challenge resulted in enrichment of members of the genus Enterococcus (family Enterococcaceae) in the guts of the mice, suggesting that it can enter the gut and colonize there. The phage EF-P29 reduced the number of colonies of genus Enterococcus and alleviated the gut microbiota imbalance that was caused by E. faecalis challenge. These data indicate that the phage EF-P29 shows great potential as a therapeutic treatment for systemic VREF infection. Thus, phage therapies that are aimed at treating opportunistic pathogens are also feasible. The dose of phage should be controlled and used at the appropriate level to avoid causing imbalance in the gut microbiota.

Characterization of Enterococcus faecium bacteriophage IME-EFm5 and its endolysin LysEFm5

Due to the worldwide prevalence of antibiotic resistant strains, phages therapy has been revitalized recently. In this study, an Enterococcus faecium phage named IME-EFm5 was isolated from hospital sewage. Whole genomic sequence analysis demonstrated that IME-EFm5 belong to the Siphoviridae family, and has a double-stranded genome of 42,265bp (with a 35.51% G+C content) which contains 70 putative coding sequences. LysEFm5, the endolysin of IME-EFm5, contains an amidase domain in its N-terminal and has a wider bactericidal spectrum than its parental phage IME-EFm5, including 7 strains of vancomycin-resistant E. faecium. The mutagenesis analysis revealed that the zinc ion binding residues (H27, H132, and C140), E90, and T138 are required for the catalysis of LysEFm5. However, the antibacterial activity of LysEFm5 is zinc ion independent, which is inconsistent with most of other amidase members. The phage lysin LysEFm5 might be an alternative treatment strategy for infections caused by multidrug-resistant E. faecium.

Spread of an Enterococcus faecalis sequence type 6 (CC2) clone in patients undergoing selective decontamination of the digestive tract

Enterococcus faecalis (E. faecalis) is a common cause of nosocomial infection in immunocompromised patients. The presence and dissemination of high-risk clonal complexes, such as CC2, is an ongoing problem in hospitals. The aim of this work was to characterize 24 E. faecalis isolates from ICU patients undergoing selective decontamination of the digestive tract (SDD) by phenotypical (antimicrobial susceptibility) and genotypical (presence of virulence genes, RAPD-PCR and MLST) methods. Our results showed high prevalence of the ST6 E. faecalis clone (91.6%), especially adapted to the hospital environment, with a multidrug resistance pattern and a multitude of putative virulence genes. In addition, ST179 (4.2%) and ST191 (4.2%) were detected. By RAPD-PCR analysis, the 22 isolates identified as ST6 showed six different DNA patterns, while the two remaining isolates, ST179 and ST191, showed two additional profiles. CC2 is a known clonal complex with high adaptability to hospital environment and worldwide distribution. The high prevalence of the ST6 clone in the studied population could be related to the presence of gentamicin in the SDD mixture since most strains were gentamicin resistant. Consequently, strict surveillance should be applied for rapid detection and control of this clone to prevent future spread outside the ICU.

Vancomycin-resistance phenotypes, vancomycin-resistance genes, and resistance to antibiotics of enterococci isolated from food of animal origin

In the present study, 500 raw beef, pork, and chicken meat samples and 100 pooled egg samples were analyzed for the presence of vancomycin-resistant enterococci, vancomycin-resistance phenotypes, and resistance genes. Of 141 isolates of enterococci, 88 strains of Enterococcus faecium and 53 strains of E. faecalis were identified. The most prevalent species was E. faecium. Resistance to ampicillin (n = 93, 66%), ciprofloxacin (n = 74, 52.5%), erythromycin (n = 73, 51.8%), penicillin (n = 59, 41.8%) and tetracycline (n = 52, 36.9%) was observed, while 53.2% (n = 75) of the isolates were multiresistant and 15.6% (n = 22) were susceptible to all antibiotics. Resistance to vancomycin was exhibited in 34.1% (n = 30) of the E. faecium isolates (n = 88) and 1.9% (n = 1) of the E. faecalis isolates (n = 53) using the disc-diffusion test and the E-test. All isolates were tested for vanA and vanB using real-time polymerase chain reaction (PCR) and multiplex PCR, and for vanC, vanD, vanE, vanG genes using multiplex PCR only. Among E. faecalis isolates, no resistance genes were identified. Among the E. faecium isolates, 28 carried the vanA gene when tested by multiplex PCR and 29 when tested with real-time PCR. No isolate carrying the vanC, vanD, vanE, or vanG genes was identified. Melting-curve analysis of the positive real-time PCR E. faecium isolates showed that 22 isolates carried the vanA gene only, 2 isolates the vanB2,3 genes only, and seven isolates carried both the vanA and vanB2,3 genes. Enterococci should be considered a significant zoonotic pathogen and a possible reservoir of genes encoding resistance potentially transferred to other bacterial species.

Selection of potential probiotic Enterococcus faecium isolated from Portuguese fermented food

Four Enterococcus faecium strains isolated from fermented products were evaluated for potential use as probiotic strains. In addition to efaAfm gene, commonly found in E. faecium food isolates, none of the isolates possessed virulence genes and none had positive reactions for the production of tyramine, histamine, putrescine and cadaverine in the screening medium used. All of these four isolates proved to be resistant to 65 °C. E. faecium 119 did not show antimicrobial activity against any of the target bacteria investigated. E. faecium 85 and 101 inhibited Listeria innocua and E. faecium DSMZ 13590. The strain E. faecium 120 inhibited seven target bacteria (Listeria monocytogenes 7946, L. monocytogenes 7947, L. innocua 2030c, L. innocua NCTC 11286, E. faecium DSMZ 13590, Enterococcus faecalis ATCC 29212 and Staphylococcus aureus ATCC 29213) and was chosen as the representative to assess the ability to survive gastrointestinal tract passage simulation, as well as the protective role of two food matrices (skim milk and Alheira) during its passage. For both matrices used, no significant differences (p<0.05) were obtained between the types of digestion - quick and slow passage simulation. In the skim milk matrix the isolate was reduced to values below the detection limit of the enumeration technique by the end of the two digestions, in contrast to the Alheira matrix, for which isolate 120 showed a reduction of only ca. 1 log CFU/ml. The E. faecium strain 120 was shown to be a potential candidate for further investigations as a potential probiotic culture.

Wide distribution of virulence genes among Enterococcus faecium and Enterococcus faecalis clinical isolates

Enterococcus, a Gram-positive facultative anaerobic cocci belonging to the lactic acid bacteria of the phylum Firmicutes, is known to be able to resist a wide range of hostile conditions such as different pH levels, high concentration of NaCl (6.5%), and the extended temperatures between 5^°C and 65^°C. Despite being the third most common nosocomial pathogen, our understanding on its virulence factors is still poorly understood. The current study was aimed to determine the prevalence of different virulence genes in Enterococcus faecalis and Enterococcus faecium. For this purpose, 79 clinical isolates of Malaysian enterococci were evaluated for the presence of virulence genes. pilB, fms8, efaAfm, and sgrA genes are prevalent in all clinical isolates. In conclusion, the pathogenicity of E. faecalis and E. faecium could be associated with different virulence factors and these genes are widely distributed among the enterococcal species.

Insusceptibility to disinfectants in bacteria from animals, food and humans-is there a link to antimicrobial resistance?

Enterococcus faecalis (n = 834) and Enterococcus faecium (n = 135) from blood and feces of hospitalized humans, from feces of outpatients and livestock and from food were screened for their susceptibility to a quaternary ammonium compound (didecyldimethylammoniumchloride, DDAC) and to 28 antibiotics by micro-/macrodilution. The maximum DDAC-MIC in our field study was 3.5 mg/l, but after adaptation in the laboratory, MIC values of 21.9 mg/l were observed. Strains for which DDAC had MICs > 1.4 mg/l ("non-wildtype," in total: 46 of 969 isolates/4.7%) were most often found in milk and dairy products (14.6%), while their prevalence in livestock was generally low (0-4%). Of human isolates, 2.9-6.8% had a "non-wildtype" phenotype. An association between reduced susceptibility to DDAC, high-level-aminoglycoside resistance and aminopenicillin resistance was seen in E. faecium (p < 0.05). No indications for a common source of non-wildtype strains were found by RAPD-PCR; however, several non-wildtype E. faecalis shared the same variant of the emeA-gene. In addition, bacteria (n = 42) of different genera were isolated from formic acid based boot bath disinfectant (20 ml of 55% formic acid/l). The MICs of this disinfectant exceeded the wildtype MICs up to 20-fold (staphylococci), but were still one to three orders of magnitude below the used concentration of the disinfectant (i. e., 1.1% formic acid). In conclusion, the bacterial susceptibility to disinfectants still seems to be high. Thus, the proper use of disinfectants in livestock surroundings along with a good hygiene praxis should still be highly encouraged. Hints to a link between antibiotic resistance and reduced susceptibility for disinfectants-as seen for E. faecium-should be substantiated in further studies and might be an additional reason to confine the use of antibiotics.

Role of house flies in the ecology of Enterococcus faecalis from wastewater treatment facilities

Enterococci are important nosocomial pathogens, with Enterococcus faecalis most commonly responsible for human infections. In this study, we used several measures to test the hypothesis that house flies, Musca domestica (L.), acquire and disseminate antibiotic-resistant and potentially virulent E. faecalis from wastewater treatment facilities (WWTF) to the surrounding urban environment. House flies and sludge from four WWTF (1-4) as well as house flies from three urban sites close to WWTF-1 were collected and cultured for enterococci. Enterococci were identified, quantified, screened for antibiotic resistance and virulence traits, and assessed for clonality. Of the 11 antibiotics tested, E. faecalis was most commonly resistant to tetracycline, doxycycline, streptomycin, gentamicin, and erythromycin, and these traits were intra-species horizontally transferrable by in vitro conjugation. Profiles of E. faecalis (prevalence, antibiotic resistance, and virulence traits) from each of WWTF sludge and associated house flies were similar, indicating that flies successfully acquired these bacteria from this substrate. The greatest number of E. faecalis with antibiotic resistance and virulence factors (i.e., gelatinase, cytolysin, enterococcus surface protein, and aggregation substance) originated from WWTF-1 that processed meat waste from a nearby commercial meat-processing plant, suggesting an agricultural rather than human clinical source of these isolates. E. faecalis from house flies collected from three sites 0.7-1.5 km away from WWTF-1 were also similar in their antibiotic resistance profiles; however, antibiotic resistance was significantly less frequent. Clonal diversity assessment using pulsed-field gel electrophoresis revealed the same clones of E. faecalis from sludge and house flies from WWTF-1 but not from the three urban sites close to WWTF-1. This study demonstrates that house flies acquire antibiotic-resistant enterococci from WWTF and potentially disseminate them to the surrounding environment.

Incidence of virulence factors in enterococci from raw and fermented meat and biofilm forming capacity at 25°C and 37°C

Twenty-nine Enterococcus strains from raw and fermented meat products were screened for the presence of virulence genes, including those for aggregation substances (asa1 and asa373), cytolysin activator (cylA), collagen binding protein (ace), endocarditis antigen (efaA), enterococcal surface protein (esp) and gelatinase (gelE). Virulence gene occurrence, expression of gelatinase and pheromone aggregation was greater in Enterococcus faecalis than in Enterococcus faecium strains. All E. faecalis and 54% of E. faecium were positive for at least one or more virulence gene. The only strain of Enterococcus gallinarum tested also contained virulence genes. The effect of different growth temperatures (25 and 37°C) on biofilm formation using polystyrene plates was also assessed. Strong biofilm formation occurred at lower than optimum temperature in all three species of enterococci. Neither esp nor gelE was necessary for biofilm formation and this relationship was species rather than strain specific. This study emphasizes the importance of enterococci as a reservoir of virulence genes and the potential for their genetic transfer to human strains following consumption of uncooked or undercooked contaminated meat.

Antibiotic resistant enterococci-tales of a drug resistance gene trafficker

Enterococci have been recognized as important hospital-acquired pathogens in recent years, and isolates of E. faecalis and E. faecium are the third- to fourth-most prevalent nosocomial pathogen worldwide. Acquired resistances, especially against penicilin/ampicillin, aminoglycosides (high-level) and glycopeptides are therapeutically important and reported in increasing numbers. On the other hand, isolates of E. faecalis and E. faecium are commensals of the intestines of humans, many vertebrate and invertebrate animals and may also constitute an active part of the plant flora. Certain enterococcal isolates are used as starter cultures or supplements in food fermentation and food preservation. Due to their preferred intestinal habitat, their wide occurrence, robustness and ease of cultivation, enterococci are used as indicators for fecal pollution assessing hygiene standards for fresh- and bathing water and they serve as important key indicator bacteria for various veterinary and human resistance surveillance systems. Enterococci are widely prevalent and genetically capable of acquiring, conserving and disseminating genetic traits including resistance determinants among enterococci and related Gram-positive bacteria. In the present review we aimed at summarizing recent advances in the current understanding of the population biology of enterococci, the role mobile genetic elements including plasmids play in shaping the population structure and spreading resistance. We explain how these elements could be classified and discuss mechanisms of plasmid transfer and regulation and the role and cross-talk of enterococcal isolates from food and food animals to humans.

Antimicrobial resistance of Enterococcus species from meat and fermented meat products isolated by a PCR-based rapid screening method

Enterococci are predominantly found in the gastrointestinal tract of humans and animals, but species commonly resident on vegetation are known. Their presence in large numbers in foods may indicate a lapse in sanitation and their ability to serve as a genetic reservoir of transferable antibiotic resistance is of concern. Conventional culture methods for identification of enterococci are slow and sometimes give false results because of the biochemical diversity of the organisms in this genus. This work reports the development of a PCR-based assay to detect enterococci at the genus level by targeting a 16S rRNA sequence. Published 16S rRNA sequences were aligned and used to design genus specific primers (EntF and EntR). The primers were able to amplify a 678 bp target region from Enterococcus faecalis ATCC 7080 and 20 other strains of enterococci from 11 different species, but there was no amplification by 32 species from closely related genera (Pediococcus, Lactobacillus, Streptococcus and Listeria) or species of Escherichia coli and Salmonella. The PCR positive samples were plated, screened by a colony patch technique and their identities were confirmed by API 20 Strep panels and sequencing. When dry fermented sausage and ham as well as fresh meat batter for dry cured sausage manufacture were tested for enterococci by the method, 29 Enterococcus strains (15 E. faecalis, 13 E. faecium, and one E. gallinarum) were identified. When susceptibility of these enterococci to 12 antibiotics was tested, the highest incidence of resistance was to clindamycin (89.6%), followed by tetracycline hydrochloride (65.5%), tylosin (62%), erythromycin (45%), streptomycin and neomycin (17%), chloramphenicol (10.3%), penicillin (10.3%), ciprofloxacin (10.3%) and gentamicin (3.4%). None was resistant to the clinically important drugs vancomycin or ampicillin. Most strains (27/29) were resistant to more than one antibiotic while 17 of 29 strains were resistant to three to 8 antibiotics. The molecular method developed was validated for speciation of enterococci and was useful in assessing uncooked processed meat products as a reservoir for multi-drug resistant Enterococcus species.

Antimicrobial resistance profiles of Enterococcus faecalis and Enterococcus faecium isolated from artisanal food of animal origin in Argentina

Enterococci are part of the indigenous microbiota of human gastrointestinal tract and food of animal origin. Enterococci inhabiting non-human reservoirs play a critical role in the acquisition and dissemination of antimicrobial resistance determinants. The aim of this work was to investigate the antimicrobial resistance in Enterococcus faecalis and Enterococcus faecium strains recovered from artisanal food of animal origin. Samples of goat cheese (n = 42), cow cheese (n = 40), artisanal salami (n = 30), and minced meat for the manufacture of hamburgers (n = 60) were analyzed. Phenotypic and genotypic tests for species-level identification of the recovered isolates were carried out. Minimum inhibitory concentration (MIC) study for in vitro quantitative antimicrobial resistance assessment was performed, and 71 E. faecalis and 22 E. faecium were isolated. The recovered enterococci showed different multi-drug resistance patterns that included tretracycline, erythromycin, ciprofloxacin, linezolid, penicillin, ampicillin, vancomycin, teicoplanin, gentamicin (high-level resistance), and streptomycin (high-level resistance). VanA-type E. faecium were detected. β-lactamase activity was not observed. Artisanal foods of animal origin act as a non-human reservoir of E. faecalis and E. faecuim strains, expressing multi-resistance to antimicrobials. In conclusion, the implementation of a continuous antimicrobial resistance surveillance in enterococci isolated from artisanal food of animal origin is important.

Characterization and risk factors of vancomycin-resistant Enterococci (VRE) among animal-affiliated workers in Malaysia

AIMS

This study determined the risk factors and characteristics of vancomycin-resistant Enterococci (VRE) among individuals working with animals in Malaysia.

METHODS AND RESULTS

Targeted cross-sectional studies accompanied with laboratory analysis for the identification and characterization of resistance and virulence genes and with genotype of VRE were performed. VRE were detected in 9·4% (95% CI: 6·46-13·12) of the sampled populations. Enterococcus faecium, Enterococcus faecalis and Enterococcus gallinarum were isolated, and vanA was detected in 70% of the isolates. Enterococcus faecalis with vanB was obtained from one foreign poultry worker. At least one virulence gene was detected in >50% of Ent. faecium and Ent. faecalis isolates. The esp and gelE genes were common among Ent. faecium (58·3%) and Ent. faecalis (78%), respectively. The VRE species showed diverse RAPD profiles with some clustering of strains based on the individual's background. However, the risk factors found to be significantly associated with the prevalence of VRE were age (OR: 5·39, 95% CI: 1·98-14·61) and previous hospitalization (OR: 4·06, 95% CI: 1·33-12·35).

CONCLUSION

VRE species isolated from individuals in this study have high level of vancomycin resistance, were genetically diverse and possessed the virulence traits. Age of individuals and history of hospitalization rather than occupational background determined VRE colonization.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study provides comprehensive findings on the epidemiological and molecular features of VRE among healthy individuals working with animals.

Enterococci as probiotics and their implications in food safety

Enterococci belong to the lactic acid bacteria (LAB) and they are of importance in foods due to their involvement in food spoilage and fermentations, as well as their utilisation as probiotics in humans and slaughter animals. However, they are also important nosocomial pathogens that cause bacteraemia, endocarditis and other infections. Some strains are resistant to many antibiotics and possess virulence factors such as adhesins, invasins, pili and haemolysin. The role of enterococci in disease has raised questions on their safety for use in foods or as probiotics. Studies on the incidence of virulence traits among enterococcal strains isolated from food showed that some can harbour virulence traits, but it is also thought that virulence is not the result of the presence of specific virulence determinants alone, but is rather a more intricate process. Specific genetic lineages of hospital-adapted strains have emerged, such as E. faecium clonal complex (CC) 17 and E. faecalis CC2, CC9, CC28 and CC40, which are high risk enterococcal clonal complexes. These are characterised by the presence of antibiotic resistance determinants and/or virulence factors, often located on pathogenicity islands or plasmids. Mobile genetic elements thus are considered to play a major role in the establishment of problematic lineages. Although enterococci occur in high numbers in certain types of fermented cheeses and sausages, they are not deliberately added as starter cultures. Some E. faecium and E. faecalis strains are used as probiotics and are ingested in high numbers, generally in the form of pharmaceutical preparations. Such probiotics are administered to treat diarrhoea, antibiotic-associated diarrhoea or irritable bowel syndrome, to lower cholesterol levels or to improve host immunity. In animals, enterococcal probiotics are mainly used to treat or prevent diarrhoea, for immune stimulation or to improve growth. From a food microbiological point of view, the safety of the bacteria used as probiotics must be assured, and data on the major strains in use so far indicate that they are safe. The advantage of use of probiotics in slaughter animals, from a food microbiological point of view, lies in the reduction of zoonotic pathogens in the gastrointestinal tract of animals which prevents the transmission of these pathogens via food. The use of enterococcal probiotics should, in view of the development of problematic lineages and the potential for gene transfer in the gastrointestinal tract of both humans and animals, be carefully monitored, and the advantages of using these and new strains should be considered in a well contemplated risk/benefit analysis.

Species diversity and metabolic impact of the microbiota are low in spontaneously acidified Belgian sausages with an added starter culture of Staphylococcus carnosus

Quality of fermented sausages is affected by acidifying lactic acid bacteria (LAB) and colour- and flavour-promoting coagulase-negative staphylococci (CNS), whether or not used as starter culture. Artisan fermented sausages are often perceived as superior to industrial variants, partially because of the specific microbiota due to spontaneous acidification, which may be considered as an artisan characteristic. Therefore, two kinds of spontaneously acidified Belgian sausages were prepared (Belgian-type salami and Boulogne sausage), but with addition of a Staphylococcus carnosus culture. The Belgian-type salami was made from pork and beef, whereas the Boulogne sausage contained pork and horse meat. In all cases, Lactobacillus sakei was the dominant LAB species present on the raw materials and during fermentation, whereas enterococci remained present in the background. Enterobacteriaceae vanished after fermentation. The CNS species diversity on the raw materials was large and differed between the pork, beef, and horse meat. Nevertheless, this species diversity was annihilated during fermentation by the added S. carnosus culture. The volatiles fraction was mainly composed of aldehydes that originated from lipid oxidation and spices-derived compounds. Aromatic compounds that are typically associated to CNS activity, such as end-products from the metabolism of branched-chain amino acids, were not present in the Belgian-type salami and only marginally present in the Boulogne sausage. In conclusion, spontaneous acidification of Belgian-type fermented sausages leads to dominance of L. sakei and is no guarantee for bacterial contribution to the aroma profile when S. carnosus is added as a starter culture.

Diversity and safety hazards of bacteria involved in meat fermentations

Food safety is a major concern for consumers and a major issue for industry which has become aware of the importance of the starter safety assessment. In the European Union, the Food Safety Authority has introduced the Qualified Presumption of Safety (QPS) approach for safety assessment of microorganisms throughout the food chain. This assessment relies on: taxonomy, familiarity, pathogenicity and end use. Productions of toxins as well as biogenic amines by food isolates are both of major concern as they can lead to food poisoning. The other important criterion is the presence of transmissible antibiotic resistance markers. This review underlined that the main hazard of bacteria involved in food fermentations concerns antibiotic resistance and particularly the presence of transferable genetic determinants that may present a risk for public health. Selection of starter strains should consider this hazard. Following the QPS approach, a list of bacteria has been acknowledged acceptable for consumption.

Volatile profile and microbiological characterization of hollow defect in dry-cured ham

This paper describes the physicochemical and microbiological parameters and volatile profile of the muscles surrounding the coxofemoral joint which are affected with hollow defect when compared to the part of muscles nearby which did not show this defect. Differences of the same parameters between both areas in dry-cured hams without this defect were also analyzed. Gram-positive catalase-positive cocci were the predominant flora in the muscles affected with hollow defect, with the main species being Staphyloccocus equorum, Staphylococcus nepalensis and Staphylococcus xylosus. Lactic acid bacteria, Listeria monocytogenes and Staphylococcus aureus were <2 log CFU g(-1) and Salmonella spp. was not detected. Volatile profile of samples affected with hollow defect had higher amounts of compounds such as esters, pyrazines, sulfurs and furans. There was a positive correlation between the amount of ester compounds and the hollow defect intensity. Moisture content was lower and pH values were higher in affected areas than in unaffected areas.