Identification of Listeria innocua by PCR targeting a putative transcriptional regulator gene

Prevalence and antimicrobial resistance profile of Listeria spp. isolated from raw fish

BACKGROUND

Listeria spp. contamination in food, particularly antimicrobial-resistant strains, poses an escalating concern for public health. This study investigated the prevalence and antimicrobial resistance profiles of Listeria spp. isolated from raw fish collected from diverse sources in Northern Poland.

METHODS

A total of 750 raw fish samples were collected from standing freshwater tanks, flowing freshwater reservoirs, and a saltwater reservoir. Isolation was performed following the standard protocol, which describes the horizontal method for detecting Listeria spp., including Listeria monocytogenes. The antimicrobial resistance profiles of isolated strains were performed using the disk diffusion method. Antimicrobial resistance genes were identified using PCR, targeting 11 genes associated with resistance to β-lactams, macrolides, glycopeptides, and sulfonamides. Statistical analyses included Phi correlation coefficients, hierarchical clustering, and logistic regression to examine associations between phenotypic resistance patterns and antimicrobial resistance genes.

RESULTS

Listeria spp. was isolated from 13.9% of samples (104 positive samples), comprising L. seeligeri (34.6%), L. welshimeri (28.8%), L. monocytogenes (23.1%), and L. innocua (13.5%). Phenotypic antimicrobial susceptibility testing revealed universal resistance to oxacillin (100%) across all Listeria spp. isolates. High resistance levels were also observed for cefotaxime (97.1%), cefoxitin (92.3%), rifampicin (92.3%), clindamycin (96.2%), and trimethoprim-sulfamethoxazole (91.3%). Alarmingly, 98.1% of all Listeria spp. isolates exhibited multidrug resistance (MDR), reaching 100% MDR among L. monocytogenes isolates. Specifically, L. monocytogenes isolates exhibited complete resistance to meropenem, cefoxitin, cefotaxime, rifampicin, and trimethoprim-sulfamethoxazole, and significant resistance to ciprofloxacin (91.7%), clindamycin (83.3%), tetracycline (75.0%), erythromycin (75.0%), benzylpenicillin (70.8%), and nitrofurantoin (70.8%). Molecular analysis identified blaTEM (100%), ampC (37.5%), and ereB (37.5%) as the most prevalent antimicrobial resistance genes in L. monocytogenes.

CONCLUSIONS

The exceptionally high prevalence of multidrug-resistant Listeria spp., particularly L. monocytogenes, in raw fish underscores a critical public health risk, suggesting the urgent need for ongoing surveillance and robust risk mitigation strategies in aquaculture and seafood processing. The elevated antimicrobial resistance levels may also indicate aquatic environmental contamination, warranting further investigation into the sources and broader ecological implications of antimicrobial resistance in these ecosystems.

Viability and Virulence of Listeria monocytogenes in Poultry

The prevalence of Listeria monocytogenes in 30 samples of poultry was determined using culture-dependent (isolation on OCLA and confirmation by conventional polymerase chain reaction -PCR-, OCLA&PCR) and culture-independent (real-time polymerase chain reaction, q-PCR) methods. L. monocytogenes was detected in 15 samples (50.0%) by OCLA&PCR and in 20 (66.7%) by q-PCR. The concentrations (log10 cfu/g) of L. monocytogenes (q-PCR) ranged from 2.40 to 5.22 (total cells) and from <2.15 to 3.93 (viable cells). The two methods, q-PCR using a viability marker (v-PCR) and OCLA&PCR (gold standard), were compared for their capacity to detect viable cells of L. monocytogenes, with the potential to cause human disease. The values for sensitivity, specificity and efficiency of the v-PCR were 100%, 66.7% and 83.3%, respectively. The agreement between the two methods (kappa coefficient) was 0.67. The presence of nine virulence genes (hlyA, actA, inlB, inlA, inlC, inlJ, prfA, plcA and iap) was studied in 45 L. monocytogenes isolates (three from each positive sample) using PCR. All the strains harbored between six and nine virulence genes. Fifteen isolates (33.3% of the total) did not show the potential to form biofilm on a polystyrene surface, as determined by a crystal violet assay. The remaining strains were classified as weak (23 isolates, 51.1% of the total), moderate (one isolate, 2.2%) or strong (six isolates, 13.3%) biofilm producers. The strains were tested for susceptibility to a panel of 15 antibiotics. An average of 5.11 ± 1.30 resistances per isolate was observed. When the values for resistance and for reduced susceptibility were taken jointly, this figure rose to 6.91 ± 1.59. There was a prevalence of resistance or reduced susceptibility of more than 50.0% for oxacillin, cefoxitin, cefotaxime, cefepime ciprofloxacin, enrofloxacin and nitrofurantoin. For the remaining antibiotics tested, the corresponding values ranged from 0.0% for chloramphenicol to 48.9% for rifampicin. The high prevalence and level of L. monocytogenes with numerous virulence factors in poultry underline how crucial it is to follow correct hygiene procedures during the processing of this foodstuff in order to reduce the risk of human listeriosis.

Prevalence and transmission characteristics of Listeria species from ruminants in farm and slaughtering environments in China

Listeria monocytogenes is an important foodborne pathogen, and is ubiquitously distributed in the natural environment. Cattle and sheep, as natural hosts, can transmit L. monocytogenes to related meat and dairy products. In this study, the prevalence, distribution, and transmission characteristics of Listeria were analysed by investigating 5214 samples of cattle and sheep in farm and slaughtering environments in China. A low contamination incidence of L. monocytogenes (0.5%, 20/4430) was observed in farm environment, but there was a high contamination incidence in slaughtering environment (9.4%, 74/784). The incidence of L. innocua in cattle and sheep farm and slaughtering environments is more common and significantly higher (9.7%, 508/5214) than that of L. monocytogenes (1.8%, 94/5214). The distinct molecular and genetic characteristics of Listeria by PFGE and MLST indicated that L. monocytogenes and L. innocua were gradually transmitted from the farm and slaughtering environments to end products, such as beef and mutton along the slaughtering chain. The ST7, ST9, ST91, and ST155 found in our study were associated with the human listeriosis cases in China. In addition, the findings of virulence markers (inlC, inlJ, LIPI-3, LIPI-4, and ECIII) concerned with the pathogenesis of human listeriosis and antibiotics resistance of L. monocytogenes in this study implies a potential public health risk. This study fills the gap in the epidemiology of beef cattle and sheep that carry Listeria in farm and slaughtering environments in major cattle and sheep producing areas in China.

Molecular approaches to the identification of pathogenic and nonpathogenic listeriae

The genus Listeria consists of a closely related group of Gram-positive bacteria that commonly occur in the environment and demonstrate varied pathogenic potential. Of the 10 species identified to date, L. monocytogenes is a facultative intracellular pathogen of both humans and animals, L. ivanovii mainly infects ungulates (eg., sheep and cattle), while other species (L. innocua, L. seeligeri, L. welshimeri, L. grayi, L. marthii, L. rocourtiae, L. fleischmannii and L. weihenstephanensis) are essentially saprophytes. Within the species of L. monocytogenes, several serovars (e.g., 4b, 1/2a, 1/2b and 1/2c) are highly pathogenic and account for a majority of clinical isolations. Due to their close morphological, biological, biochemical and genetic similarities, laboratory identification of pathogenic and nonpathogenic Listeria organisms is technically challenging. With the development and application of various molecular approaches, accurate and rapid discrimination of pathogenic and nonpathogenic Listeria organisms, as well as pathogenic and nonpathogenic L. monocytogenes strains, has become possible.

Stress survival islet 1 (SSI-1) survey in Listeria monocytogenes reveals an insert common to listeria innocua in sequence type 121 L. monocytogenes strains

Listeria monocytogenes strains (n = 117) were screened for the presence of stress survival islet 1 (SSI-1). SSI-1(+) strains (32.5%) belonged mainly to serotypes 1/2c, 3b, and 3c. All sequence type 121 (ST-121) strains included (n = 7) possessed homologues to Listeria innocua genes lin0464 and lin0465 instead of SSI-1.

Observation of a new pattern in serogroup-related PCR typing of Listeria monocytogenes 4b isolates

Molecular serogroup-related PCR typing has made the determination of serotypes of Listeria monocytogenes isolates easy and rapid. Amplification of selected lineage- and serotype-related genes can produce serotype patterns reflecting the four major serotypes, 1/2a, 1/2b, 1/2c, and 4b. We found that four isolates in our routine testing had a pattern with the four bands lmo0737, ORF2110, ORF2819, and prs positive, a pattern which has not been previously reported in the literature. After testing with a lineage-specific PCR, hybridization, and conventional agglutination serotyping, the isolates with the new pattern were considered to be serotype 4b.

Species-specific diagnostic marker for rapid identification of Staphylococcus aureus

Staphylococcus aureus is a common bacterial pathogen that has emerged as an increasingly important health concern. Following the recent publication of the genome sequences of 9 S. aureus strains (http://www.ncbi.nlm.nih.gov/genomes/lproks.cgi), a gene of S. aureus that relates signal transduction as a target for rapid detection and identification of the pathogen has been investigated. By sequence analysis of S. aureus signal transduction genes from the complete genome of S. aureus ATCC N315 and their comparison with other DNA sequences using GenBank BLAST searches, we identified a unique gene, vicK. Polymerase chain reaction primers (vicK1 and vicK2) derived from this gene allowed amplification of a 289-bp DNA fragment only from S. aureus and not from other Staphylococcus species and other common bacteria tested. Besides offering an additional target for specific confirmation of S. aureus, further analysis of the signal transduction gene vicK and its related protein product may lead to new insights into the molecular mechanisms of S. aureus maintenance and pathogenicity.

Comparison of multiplex PCR with conventional biochemical methods for the identification of Listeria spp. isolates from food and clinical samples in Queensland, Australia

Listeria monocytogenes is an important foodborne pathogen with high mortality. L. monocytogenes and five other Listeria species can frequently be found in the same sample. To identify Listeria isolates found in foods to the species level, two multiplex PCRs were designed. The PCR and conventional biochemical methods were compared for the identification of 456 Listeria isolates collected from routine food quality monitoring schemes between June 2004 and February 2006 and for 62 L. monocytogenes isolates from patients between 1999 and 2005. The results showed that the PCR and biochemical methods had 100% agreement in Listeria identification. The distribution of Listeria species from foods was as follows: L. monocytogenes, 50.4%; L. innocua, 33.8%; L. welshimeri, 14.9%; L. seeligeri, 0.7%; L. grayi, 0.2%; and L. ivanovii, 0.0%. Additional analyses were performed to identify the major serotypes (1/2a, 1/2b, 1/2c, and 4b) and the three lineages of L. monocytogenes isolates from foods and patients, with 1/2a (69.6%) and 1/2b (21.7%) dominating the food isolates and 1/2b (54.8%) and 4b (30.7%) dominating the patient isolates. The lineage results showed that isolates of 1/2a and 1/2c belonged to lineage II and that isolates of 1/2b and 4b belonged to lineage I. The multiplex PCRs for Listeria identification that have been established provide an accurate and rapid method for food quality control. This study has provided the basic knowledge of distribution of Listeria species and L. monocytogenes serotypes in Queensland, Australia, which is useful for epidemiological investigations of listeriosis.

Use of a putative transcriptional regulator gene as target for specific identification of Staphylococcus epidermidis

AIMS

To investigate the use of a Staphylococcus epidermidis transcriptional regulator gene as target for species-specific determination.

METHODS AND RESULTS

Staph. epidermidis genes encoding putative transcriptional regulators were retrieved from GenBank and those showing no homology with other bacterial sequences were selected. Of the four PCR primer sets analysed, the primers Serp0107F/R from serp0107 amplified a specific product of 581 bp from Staph. epidermidis DNA only, and they did not cross-react in PCR with nonepidermidis staphylococci and other common bacteria.

CONCLUSION

Being uniquely present in Staph. epidermidis, putative transcriptional regulator gene serp0107 offers a valuable target for specific identification of Staph. epidermidis.

SIGNIFICANCE AND IMPACT OF THE STUDY

As a member of a specialized gene group, putative transcriptional regulator gene serp0107 may be important to Staph. epidermidis adaptation to its niche environment. Further analysis of serp0107 and its related protein may help reveal new insights on the molecular regulation of Staph. epidermidis survival and virulence.

Identification, subtyping and virulence determination of Listeria monocytogenes, an important foodborne pathogen

Listeria monocytogenes is an opportunistic intracellular pathogen that has become an important cause of human foodborne infections worldwide. Given its close relationship to other Listeria species and its tendency to produce non-specific clinical symptoms, the availability of rapid, sensitive and specific diagnostic tests for the differentiation of L. monocytogenes from other Listeria species is helpful for selecting appropriate treatment regimens. In addition, with L. monocytogenes comprising a diversity of strains of varying pathogenicity, the ability to precisely track the strains involved in listeriosis outbreaks and speedily determine their pathogenic potential is critical for the control and prevention of further occurrences of this deadly disease. Extensive research in recent decades has revealed significant insights regarding the molecular mechanisms of L. monocytogenes infection. This in turn has facilitated the development of laboratory procedures for enhanced detection and identification of L. monocytogenes, and has also contributed to the implementation of improved control and prevention strategies against listeriosis. The purpose of this review is to summarize recent progress in the species-specific identification, subtyping and virulence determination of L. monocytogenes strains, and to discuss future research needs pertaining to these important areas of listeriosis.

Listeria monocytogenes serotype 4b strains belonging to lineages I and III possess distinct molecular features

A collection of Listeria monocytogenes serotype 4b strains belonging to lineages I and III were examined by PCR and Southern blot analysis using species-, virulence-, and serotype-specific primers and probes. Whereas four serotype 4b lineage I strains reacted in PCR with the serotype 4b-, 4d-, and 4e-specific ORF2110 and virulence-specific lmo1134 and lmo2821 primers, all nine serotype 4b lineage III strains were negative by ORF2110 and lmo1134 primers. In addition, the nine serotype 4b lineage III strains formed two separate groups through their reactions in PCR with virulence-specific lmo2821 primers. Southern blot analysis using species-specific lmo0733 and virulence-specific lmo2821 gene probes largely confirmed the PCR results. These findings indicate that L. monocytogenes serotype 4b strains belonging to lineages I and III possess distinct molecular features.

PCR detection of pathogenic Leptospira genomospecies targeting putative transcriptional regulator genes

The genus Leptospira comprises multiple genomospecies that demonstrate varied pathogenic potential. The availability of rapid and precise diagnostic procedures to differentiate pathogenic from nonpathogenic Leptospira spp. is therefore essential to prevent an otherwise easily treatable malaise from developing into a life-threatening disease. In this report, we conducted an investigation on the diagnostic potential of Leptospira genes encoding putative tran scriptional regulators. While PCR primers derived from transcriptional regulator gene la1137 recognized all 24 pathogenic Leptospira strains representing seven species, those from la1937, la3231, la3825, and la4130 detected 19 of the 24 Leptospira strains. However, none of these primers reacted with four nonpathogenic Leptospira species or other common bacteria. The putative transcriptional regulator genes la1137, la1937, la3231, la3825, and la4130 are present in pathogenic Leptospira strains, making them potential targets for diagnostic applications. Further characterization of these genes and their proteins may help elucidate the molecular mechanisms of leptospiral virulence and pathogenicity and pave the way for potential development of novel control strategies against leptospirosis.Key words: Leptospira, pathogenic, transcriptional regulator gene, PCR, identification.

Isolation and PCR amplification of a species-specific oxidoreductase-coding gene region in Listeria grayi

Listeria grayi is a nonpathogenic Gram-positive bacterium that demonstrates considerable similarities to other members in the genus Listeria, including the foodborne human pathogen Listeria monocytogenes and the animal pathogen Listeria ivanovii. A rapid diagnostic test to identify and diagnose listeriosis would be valuable, especially in cases where the presence of L. grayi may complicate diagnosis. This test would be based on a unique gene present in L. grayi. In this study, after comparative screening of a recombinant L. grayi DNA library by dot blot hybridization, an L. grayi specific clone (lgr20-246) with an insert of 722 bp was isolated. By applying PCR primers derived from a distinct region of the clone not shared by other bacteria, a specific band of 420 bp was amplified from the genomic DNA of L. grayi only and not of other Listeria species or common bacteria. These results suggest that the PCR assay employing primers lgr20-246F and lgr20-246R provides an independent and precise means of distinguishing L. grayi from other Listeria species and common bacteria. Therefore, it would be another useful technique for laboratory differentiation of Listeria bacteria.

PCR amplification of a species-specific putative transcriptional regulator gene reveals the identity of Enterococcus faecalis

Enterococcus faecalis, an opportunistic bacterial pathogen, has become prominent in recent decades due to its ability to develop resistance to various antibiotics. The ability to rapidly identify E. faecalis, followed by prompt treatment, is therefore vital for the control of this pathogen. In this report, upon comparative BLAST search of the E. faecalis genome against other bacterial DNA sequences at GenBank, an E. faecalis-specific gene Ef0027, that codes for a putative phosphosugar binding transcriptional regulator, was identified. Using PCR primers derived from this gene (i.e., Ef0027F/R), a specific DNA fragment of 518 bp was detected in E. faecalis strains only, and it was not found in other Enterococcus species and common bacteria. These results suggest that PCR amplification of the putative transcriptional regulator gene Ef0027 provides a useful means of identifying E. faecalis from other bacteria.

Evaluation of PCR primers from putative transcriptional regulator genes for identification of Staphylococcus aureus

AIMS

To examine if PCR primers derived from putative transcriptional regulator genes can be useful for Staphylococcus aureus identification.

METHODS AND RESULTS

Staphylococcus aureus gene sequences that encode transcriptional regulators were retrieved from GenBank and compared with other DNA sequences via BLAST searches. Two uniquely present, putative transcriptional regulator genes (i.e. Sa0836 and Sa0856) were selected as a consequence and PCR primers (Sa0836F/R and Sa0856F/R) were then designed from these genes for evaluation. A total of 84 bacterial strains/isolates including 23 Staph. aureus, 18 nonaureus Staphylococcus and 43 other common bacterial isolates were examined. The results indicated that PCR primers from Sa0836 and Sa0856 recognized genomic DNA from Staph. aureus only, but not from other non-aureus Staphylococcus or common bacteria.

CONCLUSIONS

PCR detection of the putative transcriptional regulator genes Sa0836 and Sa0856 represents a useful means of identifying Staph. aureus from other bacteria.

SIGNIFICANCE AND IMPACT OF THE STUDY

The existence of species-species transcriptional regulator genes may be a common phenomenon in bacteria. Besides their value as novel diagnostic markers, further investigation on the putative transcriptional regulator genes Sa0836 and Sa0856 and their related products may shed light on the molecular mechanisms of Staph. aureus adaptation and virulence.

Rapid identification of Streptococcus pyogenes with PCR primers from a putative transcriptional regulator gene

Streptococcus pyogenes (GAS) is a common bacterial pathogen that has emerged as an increasingly important health concern in many parts of the world. Although GAS may appear harmless in healthy individuals, the ability of this bacterium to take advantage of a weakened or compromised host defense system is extraordinary. Following the recent publication of the genome sequences of several S. pyogenes strains, we undertook an investigation of a specialized gene group in GAS that encodes transcriptional regulators. By screening S. pyogenes transcriptional regulator genes from the complete genome of M1 strain SF370 against other DNA sequences at GenBank by BLAST searches, we identified a gene (i.e., Spy1258) that is uniquely present in the bacterium. Application of PCR primers (spy1258F and spy1258R) derived from this gene facilitated amplification of a 407-bp DNA fragment from S. pyogenes only, but not from other species of the genus Streptococcus and common bacteria. Apart from offering an additional target for specific confirmation of GAS, further analysis of the putative transcriptional regulator gene Spy1258 and its related protein product may lead to new insights into the molecular mechanisms of S. pyogenes maintenance and pathogenicity.

Species-specific PCR determination of Listeria seeligeri

Listeria seeligeri is a non-pathogenic bacterium coming under the genus Listeria. As this bacterium resembles other Listeria species such as L. monocytogenes and L. ivanovii that are pathogenic to man and animals, it is important that rapid and precise identification techniques be available for L. seeligeri in cases where such determination is desirable. A specific molecular test on the basis of a uniquely present gene region in L. seeligeri will be of particular value under the circumstances. In this report, after comparative screening of genomic DNA from six Listeria species by dot blot hybridization, we isolated one L. seeligeri-specific clone (lse24-315) that contains an insert of 1538 bp. Using primers (lse24-315F and lse24-315R) derived from this clone, we showed that a specific PCR product of 375 bp was generated from genomic DNA of L. seeligeri strains only, but not of other Listeria species or common bacteria. Therefore, the PCR employing primers lse24-315F and lse24-315R provides a rapid, sensitive and specific method for distinguishing L. seeligeri from other Listeria and common bacteria.

Specific PCR identification of Pasteurella multocida based on putative transcriptional regulator genes

Pasteurella multocida is an important animal pathogen that may also infect humans through animal bites and scratches. After comparison of transcriptional regulator gene sequences from the P. multocida genome with other DNA sequences at GenBank, we identified two genes (i.e., Pm0762 and Pm1231) uniquely present in P. multocida. By using oligonucleotide primers (Pm0762F/R and Pm1231F/R) designed from these genes in PCR, it was found that specific DNA products of expected sizes were obtained with genomic DNA from P. multocida only, but not from other bacteria. These results indicated that the putative transcriptional regulator genes Pm0762 and Pm1231 are species-specific, and that the PCR methods targeting these genes provide a useful means of rapidly and precisely identifying P. multocida from other bacteria. Further elucidation of the roles and functions of these putative transcriptional regulator genes (Pm0762 and Pm1231) and their protein products may help provide valuable insight into the molecular mechanism of P. multocida virulence and pathogenicity.

PCR detection of a putative N-acetylmuramidase gene from Listeria ivanovii facilitates its rapid identification

Listeria ivanovii is a Gram-positive bacterial pathogen that is capable of causing abortions and stillbirths in farm animals, particularly sheep and cattle. In terms of morphological, biochemical and molecular characteristics, L. ivanovii resembles other Listeria species such as L. monocytogenes, a pathogen of both man and animals. In this study, through comparative analysis of genomic DNA from the six Listeria species, a L. ivanovii specific clone (liv22-228) containing a 946 bp insert was isolated. This clone contained the 5' ends of two divergently transcribed L. ivanovii genes and an intergenic spacer region, similar in organization to homologous regions from the L. innocua and L. monocytogenes genomes. Regions of low homology in the clone were identified by comparing to the L. innocua and L. monocytogenes genomes, and oligonucleotide primers (liv22-228F and liv22-228R) were designed. These primers amplified a 463 bp band from genomic DNA of L. ivanovii strains only, but not from other Listeria species or common bacteria. Thus, PCR employing L. ivanovii specific primers (liv22-228F and liv22-228R) provides a useful and straightforward method for rapid and precise determination of L. ivanovii.

Identification of a gene encoding a putative phosphotransferase system enzyme IIBC in Listeria welshimeri and its application for diagnostic PCR

AIMS

To identify a Listeria welshimeri-specific gene that can be used for identification of this species by PCR.

METHODS AND RESULTS

Through comparative analysis of genomic DNA from Listeria species using dot blot hybridization, an L. welshimeri-specific clone was isolated that contained a gene segment whose translated protein sequence is similar to enzyme IIBC from phosphotransferase systems in other bacteria. Using oligonucleotide primers derived from this L. welshimeri-specific clone, a 608-bp fragment was amplified from L. welshimeri genomic DNA and not from other Listeria species or other Gram-negative and Gram-positive species.

CONCLUSION AND SIGNIFICANCE

The PCR employing L. welshimeri-specific primers shows promise as a useful method for differentiating L. welshimeri from other Listeria species and related bacteria.

Characterization of virulent and avirulent Listeria monocytogenes strains by PCR amplification of putative transcriptional regulator and internalin genes

Listeria monocytogenes is an opportunistic bacterial pathogen that is an important cause of human food-borne illness worldwide. However, L. monocytogenes strains demonstrate considerable variation in pathogenic potential. In this report, virulent and avirulent L. monocytogenes isolates were compared by using a comparative screening strategy. Two clones were identified that contained DNA that was only present in virulent L. monocytogenes strains. PCR primers were designed for three genes from these clones and for five other selected L. monocytogenes genes. All eight primer sets predominantly detected virulent L. monocytogenes isolates, as determined by a mouse virulence assay; one of the putative internalin genes, lmo2821, was detected in all strains that were considered to be virulent. Primers from these eight genes were then tested by PCR against a larger panel of bacterial strains; each of the genes was detected predominantly in clinical or food L. monocytogenes isolates, rather than environmental isolates. The findings from this study suggest that virulent L. monocytogenes strains may possess genes that are not present in avirulent isolates, which could serve as markers for PCR assessment of L. monocytogenes virulence.