Livestock associated methicillin-resistant Staphylococcus aureus (LaMRSA) isolated from lesions of pigs at necropsy in northwest Germany between 2004 and 2007

An increasing number of reported detections of methicillin-resistant Staphylococcus aureus (MRSA) in food animals since 2007 has led to the assumption that there is an emerging zoonotic problem with livestock associated (la)MRSA potentially aggravating the MRSA problem in humans. It was the objective of the study to investigate, whether MRSA was present in clinical specimens of pigs collected at post-mortem since 2004 and to further characterize these isolates. We studied 138 isolates of S. aureus collected between 2004 and 2007 from various pathological lesions of pigs at necropsy. Potential MRSA were identified by growth on selective chromogenic media. Isolates were confirmed as MRSA using multiplex PCR. Confirmed isolates were spa- and SCCmec-typed and were tested for antimicrobial resistance. Overall, 60 (43%) S. aureus isolates were identified as MRSA. The majority (57/60) of the MRSA isolates found in the altered porcine tissues were spa-types associated with MRSA ST398. Three MRSA were ST97 isolates, a type that has not been described as an MRSA in pigs before. Other clonal complexes (ST9, ST30) dominated among the methicillin-sensitive S. aureus. MRSA were found in similar frequency in all 4 years. We assume that MRSA in pigs may have occurred earlier than 2004 and might be not really 'emerging', but rather have been overlooked until recently. The potentially causative role of the MRSA in the lesions warrants further investigation.

High heterogeneity within methicillin-resistant Staphylococcus aureus ST398 isolates, defined by Cfr9I macrorestriction-pulsed-field gel electrophoresis profiles and spa and SCCmec types

During recent years, the animal-associated methicillin-resistant Staphylococcus aureus clone ST398 has extensively been studied. The DNA of these isolates turned out to be refractory to SmaI restriction, and consequently, SmaI is unsuitable for subtyping this clone by standard pulsed-field gel electrophoresis (PFGE). Very recently, ST398 DNA was shown to be digested by Cfr9I, a neoschizomer of SmaI. In the present study, we employed Cfr9I PFGE on 100 German and 5 Dutch ST398 isolates and compared their PFGE profiles, protein A gene variable repeat regions (spa types), and types of the staphylococcal cassette chromosome mec (SCCmec). The isolates (from healthy carrier pigs, clinical samples from pigs, dust from farms, milk, and meat) were assigned to 35 profiles, which were correlated to the SCCmec type. A dendrogram with the Cfr9I patterns assigned all profiles to two clusters. Cluster A grouped nearly all isolates with SCCmec type V, and cluster B comprised all SCCmec type IVa and V* (a type V variant first identified as III) carriers plus one isolate with SCCmec type V. Both clusters also grouped methicillin-susceptible S. aureus isolates. The association of the majority of isolates with SCCmec type V in one large cluster indicated the presence of a successful subclone within the clonal complex CC398 from pigs, which has diversified. In general, the combination of Cfr9I PFGE with spa and SCCmec typing demonstrated the heterogeneity of the series analyzed and can be further used for outbreak investigations and traceability studies of the MRSA ST398 emerging clone.

Prevalence of MRSA types in slaughter pigs in different German abattoirs

To investigate the prevalence of types of meticillin-resistant Staphylococcus aureus (MRSA) in slaughter pigs in German abattoirs, nasal swabs were collected from a total of 1026 pigs in five abattoirs after stunning in the course of two studies, and examined for MRSA. Study 1 included four abattoirs; study 2 was carried out in one large abattoir. Isolates were tested for antimicrobial susceptibility and characterised using spa-typing, multilocus sequence typing (MLST) and typing of the staphylococcal cassette chromosome, SCCmec. Overall, MRSA was isolated from 70.8 per cent of 520 samples in study 1 and from 49.0 per cent of 506 samples in study 2. The proportion of positive samples varied substantially between the abattoirs in study 1. Most isolates belonged to spa-types t011 and t034 and SCCmec types III and V. MLST of selected isolates revealed that they were all MLST ST398. Besides beta-lactams, 100 per cent of the isolates were resistant to tetracycline, 80.5 per cent were resistant to erythromycin and 80.7 per cent were resistant to clindamycin. Less than 5 per cent of the isolates were resistant to other antimicrobials.

Plasmid-mediated quinolone resistance conferred by qnrS1 in Salmonella enterica serovar Virchow isolated from Turkish food of avian origin

OBJECTIVES

To study the molecular characteristics of the quinolone and associated ampicillin resistance mechanisms present in Salmonella enterica serovar Virchow isolated from Turkish foods.

METHODS

Nine epidemiologically unrelated Salmonella Virchow strains isolated from foods (chicken and minced meat) sold in different markets in Ankara were analysed for their susceptibility to 17 antimicrobials. The strains were typed by PFGE and plasmid profiling and investigated by molecular methods (PCR/sequencing) for the presence of several resistance genes, class 1 integrons and mutations in the quinolone resistance-determining regions. Plasmids conferring quinolone resistance were analysed by restriction fragment length polymorphism (RFLP) analysis, DNA hybridization, sequencing, replicon-typing PCR and mating experiments.

RESULTS

All strains showed nalidixic acid resistance (MIC >or= 128 mg/L) together with a decreased susceptibility to ciprofloxacin (three strains with an MIC of 1 mg/L and six with an MIC of 0.25 mg/L), associated with mutations within the gyrA gene (Asp-87 --> Tyr-87). In three strains, qnrS1 genes were detected. Ampicillin resistance encoded by a bla(CTX-M3) gene and/or bla(TEM-1-like) gene was found in four strains. Three of these strains carried an approximately 45 kb conjugative plasmid, designated pRQ2006, harbouring qnrS1 and a Tn3-like transposon. Partial sequencing and RFLP of pRQ2006 indicated its similarity to the qnrS1 plasmid pAH03786 found in a Japanese Shigella flexneri 2b isolate.

CONCLUSIONS

This is the first study describing the presence of qnrS1 genes in bacterial isolates from Turkey. The pRQ2006 plasmid seems to be more related to the S. flexneri 2b qnrS1 plasmid pAH0376 than to the Salmonella qnrS1-carrying plasmids pINF5 and TPqnrS-2.

Characterization of enterocoliticin, a phage tail-like bacteriocin, and its effect on pathogenic Yersinia enterocolitica strains

Yersinia enterocolitica 29930 (biogroup 1A; serogroup O:7,8) produces a bacteriocin, designated enterocoliticin, that shows inhibitory activity against enteropathogenic strains of Y. enterocolitica belonging to serogroups O:3, O:5,27 and O:9. Enterocoliticin was purified, and electron micrographs of enterocoliticin preparations revealed the presence of phage tail-like particles. The particles did not contain nucleic acids and showed contraction upon contact with susceptible bacteria. Enterocoliticin addition to logarithmic-phase cultures of susceptible bacterial strains led to a rapid dose-dependent reduction in CFU. Calorimetric measurements of the heat output of cultures of sensitive bacteria showed a complete loss of cellular metabolic activity immediately upon addition of enterocoliticin. Furthermore, a dose-dependent efflux of K(+) ions into the medium was determined, indicating that enterocoliticin has channel-forming activity.

Isolation of a lysogenic bacteriophage carrying the stx(1(OX3)) gene, which is closely associated with Shiga toxin-producing Escherichia coli strains from sheep and humans

A specific PCR for the detection of a variant of the gene encoding Shiga toxin 1 (stx(1)) called stx(1(OX3)) (GenBank accession no. Z36901) was developed. The PCR was used to investigate 148 Stx(1)-producing Escherichia coli strains from human patients (n = 72), cattle (n = 27), sheep (n = 48), and a goat (n = 1) for the presence of the stx(1(OX3)) gene. The stx(1(OX3)) gene was present in 38 Shiga toxin-producing E. coli (STEC) strains from sheep belonging to serogroups O5, O125, O128, O146, and OX3 but was absent from Stx(1)-positive ovine STEC O91 strains. The stx(1(OX3)) gene was also detected in 22 STEC strains from humans with nonbloody diarrhea and from asymptomatic excreters. Serotypes O146:H21 and O128:H2 were most frequently associated with stx(1(OX3))-carrying STEC from sheep and humans. In contrast, Stx(1)-producing STEC strains from cattle and goats and 50 STEC strains from humans were all negative for the stx(1(OX3)) gene. The stx(1(OX3))-negative strains belonged to 13 serotypes which were different from those of the stx(1(OX3))-positive STEC strains. Moreover, the stx(1(OX3)) gene was not associated with STEC belonging to enterohemorrhagic E. coli (EHEC) serogroups O26, O103, O111, O118, O145, and O157. A bacteriophage carrying the stx(1(OX3)) gene (phage 6220) was isolated from a human STEC O146:H21 strain. The phage was able to lysogenize laboratory E. coli K-12 strain C600. Phage 6220 shared a similar morphology and a high degree of DNA homology with Stx(2)-encoding phage 933W, which originates from EHEC O157. In contrast, few similarities were found between phage 6220 and Stx(1)-encoding bacteriophage H-19B from EHEC O26.

Comparative study of temperate bacteriophages isolated from Yersinia

170 Yersinia strains belonging to various species were investigated for the presence of temperate bacteriophages. By induction with mitomycin C seven phages were isolated from Y. enterocolitica strains and one phage from a Y. frederiksenii strain. The phages were characterized on the basis of their morphology, host range, genome size, DNA homology, and protein composition. They belong to different phage families and reveal narrow to moderate wide host ranges. Some of the isolated phages were able to infect pathogenic as well as nonpathogenic strains of Y. enterocolitica. The genomes of all isolated phages were found to be composed of double stranded DNA ranging from about 40 to 60 kb. In addition to the analysed phages, a number of putative phages were induced in strains of Y. frederiksenii, Y. kristensenii, Y. intermedia, and Y. mollaretii. The putative phages were identified by isolation of phage DNA from cell free lysates but could not be propagated on indicator strains. Southern hybridization experiments revealed relationships between phages belonging to different families. Moreover, DNA homologies were observed between phages isolated from nonpathogenic Yersinia strains and a phage which was isolated from a pathogenic Y. enterocolitica serogroup O:3 strain.

The angiotensinogen gene 235T variant is associated with an increased risk of restenosis after percutaneous transluminal coronary angioplasty

The therapeutic benefit of percutaneous transluminal coronary angioplasty (PTCA) is limited by restenosis in 30-40% of patients. The underlying mechanisms are currently not well understood. Besides clinical and angiographic variables, genetic factors may be involved. In the present study, we investigated the associations between the angiotensinogen T174M and M235T, the angiotensin I-converting enzyme (ACE) I/D and the angiotensin II type 1 receptor A1166C gene polymorphisms and restenosis in 511 patients who had undergone successful PTCA (without stenting) and follow-up angiography. Clinical and angiographic variables were also considered as possible predictors of restenosis. Stenosis severity was estimated by visual inspection of the angiograms. Altogether, 160 patients had restenosis, as defined by a greater than 50% reduction in the diameter of the dilated segment at follow-up angiography compared with the findings immediately following angioplasty. There were significantly more carriers of the angiotensinogen 235T allele and more patients with the ACE DD genotype in the restenosis group than in the no restenosis group, but only the angiotensinogen 235T allele (and not the ACE DD genotype) remained significantly associated with restenosis following multifactorial analyses. No differences between the two groups were found with respect to the other gene polymorphisms. Patients who subsequently developed restenosis had a higher degree of stenosis and more severe lesions before PTCA, as well as less residual stenosis immediately after PTCA. We conclude that the angiotensinogen M235T gene polymorphism may be an independent predictor of restenosis after PTCA.

Is natural genetic transformation a mechanism of horizontal gene transfer in Yersinia?

We investigated the capacity of different Yersinia strains with emphasis to Yersinia enterocolitica to take up and incorporate DNA by natural genetic transformation. Our studies were initiated by the observation of partial homology between the virulence plasmid of a pathogenic Y. enterocolitica strain (O: 3, biovar 4) and plasmids indiginous to different a pathogenic Y. enterocolitica biovar 1A strains revealed by hybridization studies. Furthermore, an observation of natural genetic transformation in a strain of Y. enterocolitica has been published by CALLAHAN and KOROMA (1979). To detect an uptake and incorporation of DNA, we incubated potential recipient strains with naked DNA under varying experimental conditions. The parameters tested were--the recipient strain,--the markers used to detect a DNA transfer,--the condition of the transforming DNA,--the nutrient availability,--the temperature,--the growth phase, and--the influence of stress. In our experiments, we could not identify conditions under which Y. enterocolitica could be naturally transformed. We thus conclude that natural transformation is unlikely to be an important mechanism for horizontal gene transfer in Yersinia.

Generalized transduction of small Yersinia enterocolitica plasmids

To study phage-mediated gene transfer in Yersinia, the ability of Yersinia phages to transduce naturally occurring plasmids was investigated. The transduction experiments were performed with a temperate phage isolated from a pathogenic Yersinia enterocolitica strain and phage mixtures isolated from sewage. Small plasmids (4.3 and 5.8 kb) were transduced at a frequency of 10(-5) to 10(-7)/PFU. However, we could not detect the transduction of any indigenous virulence plasmid (ca. 72 kb) in pathogenic Yersinia strains. Transductants obtained by infection with the temperate phage were lysogenic and harbored the phage genome in their chromosomes.

Purification and characterization of the lytic activity induced by the prolate-headed bacteriophage P001 in Lactococcus lactis

The lytic activity induced by the lactococcal bacteriophage P001 was isolated from phage lysates of Lactococcus lactis by a four-step purification procedure. Two proteins lytic for L. lactis were identified with molecular weights of 28 kDA and 8 kDa, respectively. The N-terminal amino acid sequences of the two proteins were determined and degenerated oligonucleotide probes corresponding to these sequences were synthesized. DNA hybridization experiments with phage P001-DNA and lactococcal DNA revealed that both proteins were apparently encoded by a single lysin gene located on the phage P001 genome. This was confirmed by alignment of the determined N-terminal amino acid sequences with nucleotide sequences which were deduced from cloned Lactococcus bacteriophage lysin genes.

Comparison of plasmids of strains of Yersinia enterocolitica biovar 1A with the virulence plasmid of a pathogenic Y. enterocolitica strain

The plasmid content of apathogenic Y. enterocolitica biovar 1A strains was determined and the plasmids were compared with the virulence plasmid of a pathogenic Y. enterocolitica strain. About 38% of the selected biovar 1A strains contained plasmids of different sizes ranging from 2.7 kb to more than 70 kb. Some of the larger plasmids had a size similar to that of the virulence plasmid of a pathogenic reference strain. The restriction patterns of these plasmids were different from the restriction pattern of the virulence plasmid of the pathogenic reference strain. Differences were also observed in hybridization studies with the virulence plasmid. The plasmids from 15 out of 16 biovar 1A strains showed no homology, whereas the plasmid of one biovar 1A strain partially hybridized to the virulence plasmid.