The pcz1 Gene,which Encodes a Zn(II)2Cys6 Protein,Is Involved in the Control of Growth,Conidiation, and Conidial Germination in the Filamentous Fungus Penicillium roqueforti

Proteins containing Zn(II)₂Cys₆ domains are exclusively found in fungi and yeasts. Genes encoding this class of proteins are broadly distributed in fungi, but few of them have been functionally characterized. In this work, we have characterized a gene from the filamentous fungus Penicillium roqueforti that encodes a Zn(II)₂Cys₆ protein, whose function to date remains unknown. We have named this gene pcz1. We showed that the expression of pcz1 is negatively regulated in a P. roqueforti strain containing a dominant active Gαi protein, suggesting that pcz1 encodes a downstream effector that is negatively controlled by Gαi. More interestingly, the silencing of pcz1 in P. roqueforti using RNAi-silencing technology resulted in decreased apical growth, the promotion of conidial germination (even in the absence of a carbon source), and the strong repression of conidiation, concomitant with the downregulation of the genes of the central conidiation pathway brlA, abaA and wetA. A model for the participation of pcz1 in these physiological processes in P. roqueforti is proposed.     

Insights into Penicillium roqueforti Morphological and Genetic Diversity

Fungi exhibit substantial morphological and genetic diversity, often associated with cryptic species differing in ecological niches. Penicillium roqueforti is used as a starter culture for blue-veined cheeses, being responsible for their flavor and color, but is also a common spoilage organism in various foods. Different types of blue-veined cheeses are manufactured and consumed worldwide, displaying specific organoleptic properties. These features may be due to the different manufacturing methods and/or to the specific P. roqueforti strains used. Substantial morphological diversity exists within P. roqueforti and, although not taxonomically valid, several technological names have been used for strains on different cheeses (e.g., P. gorgonzolae, P. stilton). A worldwide P. roqueforti collection from 120 individual blue-veined cheeses and 21 other substrates was analyzed here to determine (i) whether P. roqueforti is a complex of cryptic species, by applying the Genealogical Concordance Phylogenetic Species Recognition criterion (GC-PSR), (ii) whether the population structure assessed using microsatellite markers correspond to blue cheese types, and (iii) whether the genetic clusters display different morphologies. GC-PSR multi-locus sequence analyses showed no evidence of cryptic species. The population structure analysis using microsatellites revealed the existence of highly differentiated populations, corresponding to blue cheese types and with contrasted morphologies. This suggests that the population structure has been shaped by different cheese-making processes or that different populations were recruited for different cheese types. Cheese-making fungi thus constitute good models for studying fungal diversification under recent selection.     

Viability and ATP content of conidia of sorbic acid-sensitive and-resistant strains of Penicillium roqueforti after exposure to sorbic acid

Summary Conidia from two strains of Penicillium roqueforti, one sensitive and one resistant to inhibition by sorbic acid, were tested to determine how the chemical affected viability and ATP content of the spores. The minimum inhibitory concentration was less than 1,000 ppm for the sensitive strain and 3,000 ppm for the resistant strain. Exposing conidia to 6,000 ppm sorbic acid caused complete loss of viability in 1 day by those of the sensitive strain and in 4 days by those of the resistant strain. Exposure of conidia to sorbate solutions caused a rapid initial decrease in ATP content during the first few hours, followed by a more gradual decrease over the next 48–72 h. The same general trend was observed for both strains, but the resistant strain recovered some of the lost ATP following the rapid initial decrease. Results suggest that increased viability in the resistant strain may result from maintainance of ionic balance and an internal pH high enough to reduce the effectiveness of sorbic acid.     

Overlapping expression patterns and differential transcript levels of phosphate transporter genes in arbuscular mycorrhizal,P<Subscript>i</Subscript>-fertilised and phytohormone-treated <Emphasis Type="Italic">Medicago truncatula</Emphasis> roots

A microarray carrying 5,648 probes of Medicago truncatula root-expressed genes was screened in order to identify those that are specifically regulated by the arbuscular mycorrhizal (AM) fungus Gigaspora rosea, by P_i fertilisation or by the phytohormones abscisic acid and jasmonic acid. Amongst the identified genes, 21% showed a common induction and 31% a common repression between roots fertilised with P_i or inoculated with the AM fungus G. rosea, while there was no obvious overlap in the expression patterns between mycorrhizal and phytohormone-treated roots. Expression patterns were further studied by comparing the results with published data obtained from roots colonised by the AM fungi Glomus mosseae and Glomus intraradices, but only very few genes were identified as being commonly regulated by all three AM fungi. Analysis of P_i concentrations in plants colonised by either of the three AM fungi revealed that this could be due to the higher P_i levels in plants inoculated by G. rosea compared with the other two fungi, explaining that numerous genes are commonly regulated by the interaction with G. rosea and by phosphate. Differential gene expression in roots inoculated with the three AM fungi was further studied by expression analyses of six genes from the phosphate transporter gene family in M. truncatula. While MtPT4 was induced by all three fungi, the other five genes showed different degrees of repression mirroring the functional differences in phosphate nutrition by G. rosea, G. mosseae and G. intraradices. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Impact of sequential exposure of <Emphasis Type="Italic">Beauveria bassiana</Emphasis> and imidacloprid against susceptible and resistant strains of <Emphasis Type="Italic">Musca domestica</Emphasis>

Insecticide resistance in the housefly Musca domestica is hampering pest management. However, entomopathogens, possibly in combination with insecticides, may have control potential against resistant houseflies. This study investigates the combination of the entomopathogenic fungus Beauveria bassiana and the neonicotinoid insecticide, imidacloprid against a susceptible and a resistant housefly strain, respectively under laboratory conditions. The fungus and insecticide were tested alone and in combinations at LC₃₀. Significant and synergistic interactions between B. bassiana and imidacloprid were observed with increased mortality rates of the combined treatment as compared to individual treatment in housefly strains 772a (susceptible) and 766b (resistant). Significant differences in the GST and P450 activities for both strains were found. Female 766b flies caused 15- to 237-fold increases in gene expression of xenobiotic response genes for B. bassiana and 23- to 120-fold changes for imidacloprid. The combination of B. bassiana and imidacloprid caused significant synergistic interaction when applied against two housefly strains irrespective of order of application. The effect was highest when the insecticide was applied first. The resistant housefly strain had elevated detoxification enzymes and higher expression of detoxification genes, but showed the same level of susceptibility to the combined fungus/insecticide treatment as the susceptible strain.     

A mycovirus modulates the endophytic and pathogenic traits of a plant associated fungus

Fungi are generally thought to live in host plants with a single lifestyle, being parasitism, commensalism, or mutualism. The former, known as phytopathogenic fungi, cause various plant diseases that result in significant losses every year; while the latter, such as endophytic fungi, can confer fitness to the host plants. It is unclear whether biological factors can modulate the parasitic and mutualistic traits of a fungus. In this study, we isolated and characterized a mycovirus from an endophytic strain of the fungus Pestalotiopsis theae, a pathogen of tea (Camellia sinensis). Based on molecular analysis, we tentatively designated the mycovirus as Pestalotiopsis theae chrysovirus-1 (PtCV1), a novel member of the family Chrysoviridae, genus Alphachrysovirus. PtCV1 has four double-stranded (ds) RNAs as its genome, ranging from 0.9 to 3.4 kbp in size, encapsidated in isometric particles. PtCV1 significantly reduced the growth rates of its host fungus in vitro (ANOVA; P-value < 0.001) and abolished its virulence in planta (ANOVA; P-value < 0.001), converting its host fungus to a non-pathogenic endophyte on tea leaves, while PtCV1-free isolates were highly virulent. Moreover, the presence of PtCV1 conferred high resistance to the host plants against the virulent P. theae strains. Here we report a mycovirus that modulates endophytic and phytopathogenic fungal traits and provides an alternative approach to biological control of plant diseases caused by fungi.Subject terms: Fungal biology, Applied microbiology, Virus-host interactions     

Characterization of Fosfomycin Resistant Extended-Spectrum β-Lactamase-Producing Escherichia coli Isolates from Human and Pig in Taiwan

To investigate the efficacy of fosfomycin against extended-spectrum β-lactamases (ESBL) producing Escherichia coli in Taiwan and the resistance mechanisms and characterization of human and pig isolates, we analyzed 145 ESBL-producing isolates collected from two hospitals (n = 123) and five farms (n = 22) in Taiwan from February to May, 2013. Antimicrobial susceptibilities were determined. Clonal relatedness was determined by PFGE and multi-locus sequence typing. ESBLs, ampC, and fosfomycin resistant genes were detected by PCR, and their flanking regions were determined by PCR mapping and sequencing. The fosfomycin resistant mechanisms, including modification of the antibiotic target (MurA), functionless transporters (GlpT and UhpT) and their regulating genes such as uhpA, cyaA, and ptsI, and antibiotic inactivation by enzymes (FosA and FosC), were examined. The size and replicon type of plasmids carrying fosfomycin resistant genes were analyzed. Our results revealed the susceptibility rates of fosfomycin were 94% for human ESBL-producing E. coli isolates and 77% for pig isolates. The PFGE analysis revealed 79 pulsotypes. No pulsotype was found existing in both human and pig isolates. Three pulsotypes were distributed among isolates from two hospitals. ISEcp1 carrying bla _{CTX-M-group 9} was the predominant transposable elements of the ESBL genes. Among the thirteen fosfomycin resistant isolates, functionless transporters were identified in 9 isolates. Three isolates contained novel amino acid substitutions (Asn67Ile, Phe151Ser and Trp164Ser, Val146Ala and His159Tyr, respectively) in MurA (the target of fosfomycin). Four isolates had fosfomycin modified enzyme (fosA3) in their plasmids. The fosA3 gene was harboured in an IncN-type plasmid (101 kbp) in the three pig isolates and an IncB/O-type plasmid (113 kbp) in the human isolate. In conclusion, we identified that 6% and 23% of the ESBL-producing E. coli from human and pigs were resistant to fosfomycin, respectively, in Taiwan. No clonal spread was found between human and pig isolates. Functionless transporters were the major cause of fosfomycin resistance, and the fosA3-transferring plasmid between isolates warrants further monitoring.     

The Weak Acid Preservative Sorbic Acid Inhibits Conidial Germination and Mycelial Growth of Aspergillus niger through Intracellular Acidification

The growth of the filamentous fungus Aspergillus niger, a common food spoilage organism, is inhibited by the weak acid preservative sorbic acid (trans-trans-2,4-hexadienoic acid). Conidia inoculated at 10⁵/ml of medium showed a sorbic acid MIC of 4.5 mM at pH 4.0, whereas the MIC for the amount of mycelia at 24 h developed from the same spore inoculum was threefold lower. The MIC for conidia and, to a lesser extent, mycelia was shown to be dependent on the inoculum size. A. niger is capable of degrading sorbic acid, and this ability has consequences for food preservation strategies. The mechanism of action of sorbic acid was investigated using ³¹P nuclear magnetic resonance (NMR) spectroscopy. We show that a rapid decline in cytosolic pH (pH_cyt) by more than 1 pH unit and a depression of vacuolar pH (pH_vac) in A. niger occurs in the presence of sorbic acid. The pH gradient over the vacuole completely collapsed as a result of the decline in pH_cyt. NMR spectra also revealed that sorbic acid (3.0 mM at pH 4.0) caused intracellular ATP pools and levels of sugar-phosphomonoesters and -phosphodiesters of A. niger mycelia to decrease dramatically, and they did not recover. The disruption of pH homeostasis by sorbic acid at concentrations below the MIC could account for the delay in spore germination and retardation of the onset of subsequent mycelial growth.     

Toxigenic fungi isolated from roquefort cheese

To evaluate the potential for mycotoxin production by fungi contaminating blue-veined cheese, as well as by the ripening fungus,Penicillium roqueforti, the fungal flora of six of local and imported brands was determined. A total of 19 fungi were isolated from the six brands tested. Fourteen of the isolates were toxic to chicken embryos. The toxigenic fungi produced the following mycotoxins:Aspergillus fumigatus, kojic acid;A. versicolor, sterigmatocystin;Penicillium roqueforti, penicillic acid and unidentified toxic metabolites.     

The effect of potassium sorbate, NaCl and pH on the growth of food spoilage fungi

In this study, the hurdle technology approach was used to prevent fungal growth of common spoilage fungi in naturally fermented black olives (Alternaria alternata, Aspergillus niger, Fusarium semitectum andPenicillium roqueforti). The factors studied included a combination of different concentrations of potassium sorbate (100 up to 1000 mg/L), a range of pH values (4.5, 5, 5.5, 6, and 6.5) and levels of NaCl (0, 3.5, 5, 7.5, and 10%).Alternaria alternata was the most sensitive fungus whereasP. roqueforti was the most resistant fungi against all hurdle factors. The combination of all hurdles completely inhibitedA. alternata andF. semitectum by lowest inhibitory factors, such as 100 mg/L potassium sorbate with 3.5% NaCl at pH 5. On the other hand, at pH 5, A.niger andP. roqueforti were totally prevented by a combination of 300 mg/L potassium sorbate with 10% NaCl and 400 mg/L potassium sorbate with 7.5% NaCl, respectively. Potassium sorbate and 5–10% NaCl interaction had significant stimulation effect onp. roqueforti andA. niger (p<0.05). This study indicates that potassium sorbate is a suitable preserving agent to inhibit growth of fungi in fermented products of pH near 4.5 regardless levels of NaCl. For products of slightly higher pH, the addition of potassium sorbate is suggested in combination with NaCl.     

Decarboxylation of Sorbic Acid by Spoilage Yeasts Is Associated with the PAD1 Gene

The spoilage yeast Saccharomyces cerevisiae degraded the food preservative sorbic acid (2,4-hexadienoic acid) to a volatile hydrocarbon, identified by gas chromatography mass spectrometry as 1,3-pentadiene. The gene responsible was identified as PAD1, previously associated with the decarboxylation of the aromatic carboxylic acids cinnamic acid, ferulic acid, and coumaric acid to styrene, 4-vinylguaiacol, and 4-vinylphenol, respectively. The loss of PAD1 resulted in the simultaneous loss of decarboxylation activity against both sorbic and cinnamic acids. Pad1p is therefore an unusual decarboxylase capable of accepting both aromatic and aliphatic carboxylic acids as substrates. All members of the Saccharomyces genus (sensu stricto) were found to decarboxylate both sorbic and cinnamic acids. PAD1 homologues and decarboxylation activity were found also in Candida albicans, Candida dubliniensis, Debaryomyces hansenii, and Pichia anomala. The decarboxylation of sorbic acid was assessed as a possible mechanism of resistance in spoilage yeasts. The decarboxylation of either sorbic or cinnamic acid was not detected for Zygosaccharomyces, Kazachstania (Saccharomyces sensu lato), Zygotorulaspora, or Torulaspora, the genera containing the most notorious spoilage yeasts. Scatter plots showed no correlation between the extent of sorbic acid decarboxylation and resistance to sorbic acid in spoilage yeasts. Inhibitory concentrations of sorbic acid were almost identical for S. cerevisiae wild-type and Δpad1 strains. We concluded that Pad1p-mediated sorbic acid decarboxylation did not constitute a significant mechanism of resistance to weak-acid preservatives by spoilage yeasts, even if the decarboxylation contributed to spoilage through the generation of unpleasant odors.     

Molecular characterization of antibiotic resistant Escherichia coli isolates recovered from food samples and outpatient Clinics,KSA

Multidrug-resistant Escherichia coli is one of the most important public health concern worldwide that can be transferred through the food of animal origin to human being causing serious infection. The genetic responsibility of such resistant genes (Plasmids, integrons, and transposons) can be easily transmitted from the resistant strain to another. Therefore, the main objectives of the study is the molecular characterization of the resistant Escherichia coli isolates recovered from food samples and human isolates collected from outpatient clinics, KSA especially the resistance strains against aminoglycoside resistance genes which are responsible for the resistance against gentamicin and the resistance caused β-lactamases genes. Examination of food samples revealed 120 Escherichia coli isolates (22.22%) (30 strains O26: K60, 28 strains O128: K67, 20 strains O111: K58, 18 strains O126: K58, 10 strains O55: K59, 9 strains O86: K61 and 5 strains O157: H7). All the strains were highly resistance to penicillin, amoxicillin-clavulanic and erythromycin with a percentage of 100%, while the resistance to gentamicin, ampicillin, oxytetracycline, chloramphenicol, norfloxacin, trimethoprim, and nalidixic acid were 83%, 75%, 65.3%, 55.8%, 36.5%, 30.7% and 26.9% respectively. On the other hand, 59.6% of tested strains were sensitive to ciprofloxacin. Positive amplification of 896?bp fragments specific for aacC2 genes were observed by PCR designated for the detection of the aminoglycoside resistance genes. Meanwhile, multiplex PCR designed to detect the ampicillin and amoxicillin-clavulanic acid resistant E. coli isolates revealed positive amplification of 516?bp fragments specific for BlaTEM gene with all the resistant strains to ampicillin and amoxicillin-clavulanic acid. Moreover, positive amplification of 392?bp fragments specific for BlaSHV resistant gene were observed with (60.52%) of E. coli isolate. While all the tested strains were negative for amplification of BlaOXA_1.     

The effect of the preservative sorbic acid on the lipid composition of the ascomycete fungus <Emphasis Type="Italic">Penicillium roqueforti</Emphasis> Thom

The mechanism of action of potassium sorbate, a widely used food preservative on the lipid composition of the Ascomycete fungus Penicillium roqueforti, the main contaminant of cheese, was investigated. The inhibition of fungal growth by potassium sorbate was found to be associated with a change in the composition of phospholipids (a decrease in phosphatidylcholine content and an increase in phosphatidylethanolamine and phosphatidic acid content) and of neutral lipids (a decrease in the triacylglycerol and sterol content and an increase in the free fatty acid content). The fatty acid composition of fungal lipids also changed. A drastic decrease in the linoleic acid content occurred both in the total lipid fraction and in the triacylglycerol and total phospholipid fractions, whereas the oleic acid content increased correspondingly. This suggests that sorbic acid (SA) affects Δ12 desaturase activity, which controls the adaptive response of mycelial fungi to deleterious environmental factors.     

Silencing of a second dimethylallyltryptophan synthase of <Emphasis Type="Italic">Penicillium roqueforti</Emphasis> reveals a novel clavine alkaloid gene cluster

Penicillium roqueforti produces several prenylated indole alkaloids, including roquefortine C and clavine alkaloids. The first step in the biosynthesis of roquefortine C is the prenylation of tryptophan-derived dipeptides by a dimethylallyltryptophan synthase, specific for roquefortine biosynthesis (roquefortine prenyltransferase). A second dimethylallyltryptophan synthase, DmaW2, different from the roquefortine prenyltransferase, has been studied in this article. Silencing the gene encoding this second dimethylallyltryptophan synthase, dmaW2, proved that inactivation of this gene does not prevent the production of roquefortine C, but suppresses the formation of other indole alkaloids. Mass spectrometry studies have identified these compounds as isofumigaclavine A, the pathway final product and prenylated intermediates. The silencing does not affect the production of mycophenolic acid and andrastin A. A bioinformatic study of the genome of P. roqueforti revealed that DmaW2 (renamed IfgA) is a prenyltransferase involved in isofumigaclavine A biosynthesis encoded by a gene located in a six genes cluster (cluster A). A second three genes cluster (cluster B) encodes the so-called yellow enzyme and enzymes for the late steps for the conversion of festuclavine to isofumigaclavine A. The yellow enzyme contains a tyrosine-181 at its active center, as occurs in Neosartorya fumigata, but in contrast to the Clavicipitaceae fungi. A complete isofumigaclavines A and B biosynthetic pathway is proposed based on the finding of these studies on the biosynthesis of clavine alkaloids.     

Spreading and mechanisms of antimicrobial resistance in microorganisms,producing beta-lactamases. Molecular mechanisms of resistance to beta-lactam antibiotics of <Emphasis Type="Italic">Klebsiella</Emphasis> spp. strains,isolated in cases of nosocomial infections

Antibiotic sensitivity has been investigated in nosocomial bacterial Klebsiella spp. strains isolated from patients treated in 30 hospitals of 15 Russian regions. Among Klebsiella strains (n = 212) studied the following species were found: Klebsiella pneumoniae ss. pneumoniae—182 (85.8%), Klebsiella pneumoniae ss. ozaenae—1 (0.5%), Klebsiella oxytoca—29 (13.7%) strains. Their sensitivity to antibacterial preparations was estimated by the method of serial dilutions in microvolume (the microdilution method). Carbapenems (imipenem and meropenem) exhibited the highest antibacterial activity against the strains studied. Among third generation cephalosporins the lowest MIC (Minimum inhibitory concentration) were found in the inhibitor protected preparations: ceftazidime/clavulanic acid (MIC₅₀ of 0.25 μg/ml; MIC₉₀ of 64 μg/ml) and cefoperazone/sulbactam (MIC₅₀ of 16 μg/ml; MIC₉₀ of 64 μg/ml). Using the PCR method the detection of class A betalactamases genes (TEM, SHV, CTX) was carried out in 42 strains of Klebsiella pneumoniae ss. pneumoniae. TEM type beta-lactamases were found alone or in various combinations in 16 (38.1%) strains, SHV—in 29 (69%), and CTX—in 27 (64.3%). Combinations of 2 and 3 different resistance determinants were detected in 23.8 and 26.2% of strains, respectively. Screening of carbapenem-resistant Klebsiella strains for production of class B metallo-beta-lactamases did not reveal nosocomial strains with phenotypically documented production of these enzymes.     

Diversity of Multi-Drug Resistant Avian Pathogenic Escherichia coli (APEC) Causing Outbreaks of Colibacillosis in Broilers during 2012 in Spain

Avian pathogenic Escherichia coli (APEC) are the major cause of colibacillosis in poultry production. In this study, a total of 22 E. coli isolated from colibacillosis field cases and 10 avian faecal E. coli (AFEC) were analysed. All strains were characterised phenotypically by susceptibility testing and molecular typing methods such as pulsed-field gel electrophoresis (PFGE) and multi-locus sequence typing (MLST). The presence of 29 virulence genes associated to APEC and human extraintestinal pathogenic E. coli (ExPEC) was also evaluated. For cephalosporin resistant isolates, cephalosporin resistance genes, plasmid location and replicon typing was assessed. Avian isolates belonged to 26 O:H serotypes and 24 sequence types. Out of 22 APEC isolates, 91% contained the virulence genes predictors of APEC; iutA, hlyF, iss, iroN and ompT. Of all strains, 34% were considered ExPEC. PFGE analysis demonstrated a high degree of genetic polymorphism. All strains were multi-resistant, including those isolated from healthy animals. Eleven strains were resistant to cephalosporins; six contained bla _CTX-M-14, two bla _SHV-12, two bla _CMY-2 and one bla _SHV-2. Two strains harboured qnrA, and two qnrA together with aac(6’)-Ib-cr. Additionally, the emergent clone O25b:H4-B2-ST131 was isolated from a healthy animal which harboured bla _CMY-2 and qnrS genes. Cephalosporin resistant genes were mainly associated to the presence of IncK replicons. This study demonstrates a very diverse population of multi-drug resistant E. coli containing a high number of virulent genes. The E. coli population among broilers is a reservoir of resistance and virulence-associated genes that could be transmitted into the community through the food chain. More epidemiological studies are necessary to identify clonal groups and resistance mechanisms with potential relevance to public health.     

Molecular typing, serotyping and cytotoxicity testing of Campylobacter jejuni strains isolated from commercial broilers in Puerto Rico

Aims: Thirty Campylobacter jejuni strains isolated from fecal samples (n = 94; 32%) from 13 positive farms (n = 17; 76%) from commercial broiler chickens in Puerto Rico were analysed by molecular methods. Methods and Results: Isolates were identified with multiplex polymerase chain reaction assays, tested for their antimicrobial susceptibility and characterized with pulsed‐field gel electrophoresis (PFGE), multilocus sequence typing (MLST), serotyping and bacterial cytotoxicity in mammalian cells. Isolates exhibited high resistance to vancomycin (minimum inhibitory concentration, MIC of >256 μg ml^?1) and trimethoprim (MIC of >32 μg ml^?1); few were resistant to clindamycin (MIC₉₀ 4 μg ml^?1), erythromycin (MIC₉₀ 8 μg ml^?1) and tetracycline (MIC₉₀ 8 μg ml^?1); but none was resistant to azithromycin (MIC₉₀ 4 μg ml^?1), ciprofloxacin (MIC₉₀ 1 μg ml^?1) or gentamycin (MIC₉₀ 4 μg ml^?1). Most strains restricted with SmaI, but a combination of SmaI–KpnI digestion was more discriminatory. MLST analysis yielded four sequence types (ST), and ST‐2624 was the predominant one. Phylogenetic analysis revealed a high degree of recombination for glnA and pgm genes. The predominant serotypes were O:3 and O:5. Most strains had lowest cytotoxicity potential with Caco‐2 cells, medium cytotoxicity with INT‐407 and Hep‐2 cells and high cytotoxicity with CHO cells. Conclusion: A low degree of antimicrobial resistance, 13 PFGE profiles, 4 ST and a large variability in cytotoxicity assays were found for these strains. Significance and Impact of the Study: This is the first characterization of C. jejuni strains isolated from broilers in Puerto Rico. The genetic diversity of these strains suggests that several techniques are needed for strain characterization.