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Listeria monocytogenesis a potential hazard for food safety and therefore for public health. The aim of the present study was to determine the prevalence and characteristics of L. monocytogenesin Polish ready-to-eat (RTE) meat products for retail sale. Among the 184,439 food samples collected within the framework of a national official control and monitoring program, only 0.3% were positive for L. monocytogenes. A significant group of products that did not meet the criteria were RTE meat products. This group accounted for 40% of all noncompliant samples. Seventy L. monocytogenesisolates from these RTE meat products (meat, sausages, and delicatessen products with meat) were examined. The majority of the tested isolates (51%) belonged to serogroup 1/2a-3a followed by 1/2c-3c (21%), 1/2b-3b-7 (14%), and 4ab-4b-4d-4e (13%). Serogroup 4a-4c was not present among the tested isolates. All L. monocytogenesisolates harbored the virulence-associated genes inlA, inlC, inlJ,and lmo2672. The llsXmarker was detected in 12 (17%) of the 70 isolates. Ampicillin resistance was the most common resistance phenotype and was identified in 83% of the L. monocytogenesisolates. A low incidence of resistance to amoxicillin–clavulanic acid (6% of isolates) was also detected. All L. monocytogenesisolates were susceptible to chloramphenicol, gentamicin, ciprofloxacin, meropenem, sulfamethoxazole-trimethoprim, tetracycline, and erythromycin. This work provides useful information regarding contamination of RTE meat products with L. monocytogenes,which may have implications for food safety risks.

The prevalence, count and molecular identification of Campylobacterspp. in Polish poultry meat were analysed. 181 samples of meat from chicken (70), turkey (47), duck (54) and goose (10) were studied. Campylobacterspp. was found in 64% of meat samples. The highest prevalence of this pathogen was detected for duck meat. On average 80% of duck samples were contaminated with Campylobacterspp. The counts of Campylobacterspp. in positive samples remained under ten colony forming units per gram of product in 59% of poultry meat. C. jejuniwas more frequently detected in poultry meat than C. coli.

The prevalence, count and molecular identification of Campylobacterspp. in Polish poultry meat were analysed. 181 samples of meat from chicken (70), turkey (47), duck (54) and goose (10) were studied. Campylobacterspp. was found in 64% of meat samples. The highest prevalence of this pathogen was detected for duck meat. On average 80% of duck samples were contaminated with Campylobacterspp. The counts of Campylobacterspp. in positive samples remained under ten colony forming units per gram of product in 59% of poultry meat. C. jejuniwas more frequently detected in poultry meat than C. coli.

AbstractTrimethoprim with sulfamethoxazole is a therapeutic agent combination used to treat infections caused by the facultative intracellular foodborne pathogen Listeria monocytogenes.The aim of this study was to assess the frequency of resistance of L. monocytogenesarising due to exposure to trimethoprim and subsequently investigate the molecular mechanisms of resistance. After exposure of a culture of L. monocytogenesATCC 13932 to trimethoprim at 10-fold the minimal inhibitory concentration spontaneous resistant mutants were recovered, giving a frequency of resistance development of 6.85 ± 0.92 × 10−8. The isolates exhibited a 32–64-fold decrease in susceptibility compared with the parental strain. These results indicate the capacity of L. monocytogenesto develop low-level resistance toward trimethoprim after exposure to the drug. The trimethoprim resistance genes (dhfr) and their promoter regions from all trimethoprim-resistant isolates were amplified and sequenced, leading to the identification of four single amino acid substitutions (Met20-Val, Pro21-Leu, Thr46-Asn, Val95-Leu) and two double substitutions (Met20-Ile+Thr46-Asn and Thr46-Asn+Leu85-Phe) in DHFR. Of the identified mutations, the Thr46-Asn substitution has not been previously reported as the mechanism of resistance to trimethoprim in other bacteria; thus this substitution seems to be unique to L. monocytogenes. The expression of the mutated L. monocytogenes dhfrgenes in Escherichia coliled to decreased susceptibility of the heterological host, therefore proving that the identified point mutations in dhfrserve as the molecular mechanism of acquired resistance of L. monocytogenesto trimethoprim.

AbstractThe aim of this study was to investigate the mechanism of rifampicin resistance in Listeria monocytogenesstrains isolated from different types of food and the impact of specific mutations in the rpoBgene on susceptibility to different antimicrobial agents and on fitness cost. Fifteen spontaneous rifampicin-resistant strains were selected. The DNA regions corresponding to clusters I–II, III, and N-terminal end of the rpoBgene of Escherichia coliwere amplified and sequenced, leading to the identification of 10 different substitutions, nine of which (Ser466Pro, Gln470Lys Asp473Asn, Gly479Asp, His483Tyr/Arg/Asp, Arg486His, and Leu490Pro) were located in cluster I and one (Pro521Leu) in cluster II. From among these mutations, substitutions at positions 466, 470, 486, 490, and 521 have not been described for L. monocytogenes.Only substitutions at positions 470, 479, 483, and 486 lead to resistance to very high concentrations of rifampicin (minimum inhibitory concentration [MIC] ≥256 μg/mL) and rifabutin (MIC 128 μg/mL). Furthermore, mutations at positions 473, 490, and 521 had different effects on susceptibility to rifampicin compared to other bacterial species. A correlation between rifampicin resistance and susceptibility to a wide range of antimicrobials was determined. Substitutions in RpoB did not change the susceptibility of the mutants to different antimicrobials. The fitness of the mutants was assessed by paired competition experiments. Mutations at positions 470 and 479 were not associated with a reduction in fitness level. There was no correlation between the MIC of rifampicin and fitness cost. The risk of transmission of resistant strains through the food chain highlights the need for monitoring resistance, identifying mutant organisms, their genotypes, and their altered phenotypes to understand their dissemination.

The purpose of the present study was to determine the prevalence of thermophilic Campylobacterin poultry, pork, and beef meat at the retail level and to identify the main categories of meat representing the most significant reservoirs of Campylobacter.A monitoring study was conducted throughout Poland from 2009 to 2013. A total of 1,700 fresh meat samples were collected from supermarkets, large retail outlets, and smaller stores. Thermophilic Campylobacterspecies were detected in 690 (49.3%) of 1,400 poultry samples collected from retail trade. Strains were isolated from 50.2 and 41.1% of raw chicken and turkey meat samples, respectively, and from 50.1 and 42.6% of raw chicken and turkey giblets. The incidence of Campylobacterspp. on pork (10.6%) and beef (10.1%) was significantly lower than on poultry. Campylobacter jejuniwas the most prevalent Campylobacterspecies in chicken (46.6%), pork (68.6%), and beef (66.7%), and Campylobacter coliwas the most frequently isolated Campylobacterspecies in turkey meat (71.2%). This study revealed that retail raw meats are often contaminated with Campylobacter; however, the prevalence of these pathogens is markedly different in different meats. Raw retail meats are potential vehicles for transmitting foodborne diseases, and our findings stress the need for increased implementation of hazard analysis critical control point programs and consumer food safety education efforts.

AbstractIn this study, we investigated the molecular mechanisms involved in erythromycin resistance in the first resistant Campylobacterstrains isolated from chicken meat in Poland, and analyzed their genetic relatedness. A total of 297 samples of raw chicken meat and giblets from retail trade in the Warsaw area collected between 2006 and 2009 were examined. Among 211 Campylobacterstrains (52 C. jejuniand 159 C. coli), 10 C. coliisolates (4.7%) were resistant to erythromycin. All the C. jejunistrains were susceptible. Among the high-level macrolide-resistant isolates, two different point mutations within the domain V of the 23S rRNAgene were observed. Eight of the strains had adenine→guanine transitions at position 2075, two other isolates at position 2074. Sequence analysis of ribosomal proteins L4 (rplD) and L22 (rplV) indicated that ribosomal protein modifications did not contribute to macrolide resistance. A mutation in the inverted repeat in the cmeR and cmeABC intergenic region was found in a single resistant strain. The genetic relatedness of Campylobacterisolates showed that two resistant strains obtained from the same production plant in a 2-month interval were genetically identical. The risk of transmission of resistant strains via the food chain highlights the need for constant monitoring of resistance in Campylobacter isolates of human and animal hosts.

In 2007 and 2008, a monitoring study was carried out in Poland to examine the occurrence of thermotolerant Campylobacterspp. in raw and cooked chicken products available on the retail market. A total of 912 samples were tested: 443 samples of raw chicken meat, 146 samples of giblets, and 323 ready-to-eat poultry products (150 samples of spit-roasted chicken, 56 samples of smoked chicken, and 117 samples of Pâté and cold meats). A high level of contamination of raw chicken meat (51.7% of samples) and chicken giblets (47.3% of samples) was detected. However, thermotolerant Campylobacterspp. were found in only 1.2% of the ready-to-eat poultry products.

Campylobacter-associated gastroenteritis remains an important cause of morbidity worldwide, and some evidence suggests that poultry is an important source of this foodborne infection in humans. This study was conducted to analyze the prevalence and genetic background of resistance of 149 Campylobacter jejuniand 54 Campylobacter colistrains isolated from broiler chicken carcasses and from stool samples of infected children in Poland from 2003 through 2005. Nearly all isolates were susceptible to macrolides and aminoglycosides. The highest resistance in both human and chicken strains was observed for ciprofloxacin (more than 40%), followed by ampicillin (13 to 21%), and tetracycline (8 to 29%). Resistance to ampicillin and tetracycline rose significantly between 2003 and 2005. Slight differences in resistance between human and chicken isolates indicate that although chicken meat is not the only source of Campylobacterinfection in our population, it can be involved in the transmission of drug-resistant Campylobacterstrains to humans.

ABSTRACTThe antibiotic susceptibilities and capabilities to induce β-lactamases were studied in multiple Escherichia colimurein (peptidoglycan) hydrolase mutants. E. colimutants lacking either three amidases, three amidases and one lytic transglycosylase, or six lytic transglycosylases showed higher levels of susceptibility to bacitracin, erythromycin, gallidermin, and vancomycin than the wild type. Mutant cells without three amidases lost viability in the presence of vancomycin and gallidermin, whereas the wild type was resistant to both antibiotics. β-Lactamase induction was studied after introduction of a plasmid carrying the ampCand ampRgenes. Upon addition of cefoxitin to the growth medium, the wild type as well as a mutant lacking all known amidases and dd-endopeptidases induced β-lactamase, whereas a mutant lacking all known lytic transglycosylases was unable to induce β-lactamase, showing that lytic transglycosylase activity is essential for β-lactamase induction. Consequently, cells lacking lytic transglycosylase activity lysed in the presence of penicillin, despite the presence of the inducible β-lactamase system. We discuss the potential of murein hydrolase inhibitors for antibiotic therapy.

Three Campylobacter jejuni72Dz/92 genes (cjaA(ompH1), cjaC(hisJ) and cjaD(omp18)) encoding immunodominant proteins are considered to be potential chicken vaccine candidates. The presence and conservation of cjaA, cjaCand cjaDgenes among different Campylobacterclinical isolates were determined. The genes were detected in thirty Campylobacterstrains using hybridization as well as Western blot analysis. However, PCR products of the predicted size were amplified only from ten out of thirty examined strains regardless of the employed primer pair. The nucleotide sequence of the C. jejuni72Dz/92 genes was compared with the nucleotide sequences of their homologs cloned from other Campylobacterstrains as well as with the whole genome sequence of C. jejuniNCTC 11168. The examined sequences revealed 0 to 16% divergence. Strain‐dependent levels of divergence were observed. The polymorphism detected in cjaCwas mainly within the 5′ region of the gene, while the nucleotide substitutions in cjaAand cjaDare distributed uniformly along the whole genes. Most of the observed nucleotide substitutions occurred at the third base of the codons. This observation is consistent with the results of Western blot experiments.

Three Campylobacter jejuni 72Dz/92 genes (cjaA (ompH1), cjaC (hisJ) and cjaD (omp18)) encoding immunodominant proteins are considered to be potential chicken vaccine candidates. The presence and conservation of cjaA, cjaC and cjaD genes among different Campylobacter clinical isolates were determined. The genes were detected in thirty Campylobacter strains using hybridization as well as Western blot analysis. However, PCR products of the predicted size were amplified only from ten out of thirty examined strains regardless of the employed primer pair. The nucleotide sequence of the C. jejuni 72Dz/92 genes was compared with the nucleotide sequences of their homologs cloned from other Campylobacter strains as well as with the whole genome sequence of C. jejuni NCTC 11168. The examined sequences revealed 0 to 16% divergence. Strain-dependent levels of divergence were observed. The polymorphism detected in cjaC was mainly within the 5′ region of the gene, while the nucleotide substitutions in cjaA and cjaD are distributed uniformly along the whole genes. Most of the observed nucleotide substitutions occurred at the third base of the codons. This observation is consistent with the results of Western blot experiments.