Comparison of methods for the detection of methicillin resistance in Staphylococcus aureus isolates from food products

AIMS

To compare several methods for detection of methicillin resistance in Staphylococcus aureus isolates from food.

METHODS AND RESULTS

Two hundred S. aureus isolates from food of animal origin were screened for methicillin resistance by a PCR assay specific for the mecA gene, an oxacillin agar screen test and a cefoxitin disk diffusion test. Six out of 200 strains (3%) were found to be methicillin-resistant Staphylococcus aureus (MRSA) by PCR. The oxacillin agar screen test detected only one of the MRSA isolates (sensitivity of 16.7%) and mischaracterized three additional strains as MRSA (specificity of 98.45%). None of the MRSA strains was detected by the cefoxitin test (sensitivity of 0%), while 15 methicillin-susceptible S. aureus (MSSA) strains were misclassified as resistant (specificity of 92.3%). Fifteen MSSA strains displayed a beta-lactamase hyperproducer-like phenotype. The six MRSA (mecA-positive) strains resembled the characteristics of heteroresistant strains.

CONCLUSIONS

As MRSA of animal origin may display atypical phenotypes, PCR appears to be more reliable for detection of methicillin resistance in animal strains.

SIGNIFICANCE AND IMPACT OF THE STUDY

The study stresses the need for implementing the methods of screening S. aureus from food of animal origin for methicillin resistance.

Methicillin-resistant Staphylococcus aureus (MRSA) in foods of animal origin product in Italy

Methicillin-resistant Staphylococcus aureus (MRSA) strains are a global health concern. The present study regarded 160 S. aureus strains that had been isolated from 1634 foodstuff samples of animal origin in a previous survey conducted in Italy during 2003-2005. The strains were characterized by detecting the mecA gene, the production of type A to D staphylococcal enterotoxins (SEs), and studying their resistance properties against several antibiotics; their ecological origin was determined by biotyping. Of the 160 analyzed S. aureus strains six (3.75%) were mecA positive and derived from six different samples; four isolates were from bovine milk and two from dairy products (pecorino cheese and mozzarella cheese). Two strains isolated from milk belonged to the non-host-specific biovar while the others to the ovine biovar. The strain isolated from mozzarella cheese belonged to the non-host-specific biovar and the strain isolated from pecorino cheese to the ovine biovar. All the MRSA strains isolated were enterotoxigenic; two strains synthesized SEA/SED two SED and one SEC. All the strains showed resistance to at least one of the antibiotics tested but none was resistant to glycopeptides.

First detection of canine parvovirus type 2c in pups with haemorrhagic enteritis in Spain

Canine parvovirus type 2 (CPV-2), the aetiological agent of haemorrhagic enteritis in dogs, includes three antigenic variants, types 2a, 2b and 2c. CPV-2c has been detected initially in Italy and subsequently in Vietnam. We report the first identification of this novel antigenic variant in Spain, where it caused an outbreak of fatal enteritis in basset hound pups in association with canine coronavirus type I and type II. We suggest that this new antigenic variant of CPV-2 could spread throughout Europe and that there is a subsequent need to update current CPV vaccines.

Heterogeneity within the hemagglutinin genes of canine distemper virus (CDV) strains detected in Italy

Canine distemper virus (CDV) is a highly contagious viral pathogen causing lethal disease in dogs and other mammalians. A high degree of genetic variation is found between recent CDV strains and the old CDV isolates used in the vaccines and such genetic variation is regarded as a possible cause of the increasing number of CDV-related diseases in dogs. The H gene shows the greatest extent of genetic variation that allows for distinction of various lineages, according to a geographical pattern of distribution and irrespective of the species of identification. In the present study, hemagglutinin (H) genes obtained from field strains detected from clinical specimens of Italian dogs were analyzed genetically. Phylogenetic analysis revealed that a homogeneous group of CDV strains is widespread in Italian dogs, all which are included into the European lineage. Unexpectedly, strains 179/04 and 48/05 clustered along with CDVs of the Arctic lineage, the highest identity being to strain GR88 (98.0 and 98.4%aa, respectively). The full-length sequence of a red fox CDV strain, 207/00 was also determined and analyzed. The H protein of the fox CDV strain was unrelated to strains within the major European lineage. These results suggest that at least three different CDV lineages are present in Italy.

New approaches for the molecular characterization of canine parvovirus type 2 strains

Characterization of the canine parvovirus type 2 (CPV-2) is sometimes ambiguous, frequently requiring more than one technique for definitive prediction of the viral type. Taking into account the single-nucleotide polymorphisms encountered in the VP2-protein gene between types 2a and 2b and between type 2b and Glu-426 mutant (type 2c), two different minor groove binder (MGB) probe assays were developed for rapid identification of the CPV-2 variants. A total of 315 samples collected from dogs with diarrhoea were screened for CPV-2 by a real-time polymerase chain reaction (PCR) assay capable of detecting all CPV-2 types. In order to compare the type-specific assays with the traditional techniques [haemagglutination inhibition with monoclonal antibodies, PCR-restriction fragment-length polymorphism (RFLP), sequence analysis] for prediction of CPV-2 antigen specificity, the 203 samples tested CPV-2 positive were analysed using the different methods. The results showed a 100% concordance between the MGB probe assays and the combined conventional methods, with 116 samples characterized as type 2a, 32 as type 2b and 55 as type 2c. Therefore, the MGB probe assays represent a quick, reliable tool for prediction of CPV-2 antigen specificity, with regard to the more time-consuming assays currently used.