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


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.


CONCLUSIONS
The study stresses the need for implementing the methods of screening S. aureus from food of animal origin for methicillin resistance.
Corrente
M
M
Department of Health and Animal Well-being, Faculty of Veterinary Medicine, University of Bari, Str. prov per Casamassima, km. 3, Valenzano, Bari, Italy. m.corrente@veterinaria.uniba.it
Normanno
G
G
Martella
V
V
Bellacicco
A L
AL
Quaglia
N C
NC
Dambrosio
A
A
Buonavoglia
D
D
D'Abramo
M
M
Buonavoglia
C
C
D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics*; D015373:Bacterial Typing Techniques / Q000379:methods*; D002417:Cattle; D005516:Food Microbiology; D016106:Methicillin Resistance / Q000235:genetics; D046915:Penicillin-Binding Proteins; D016133:Polymerase Chain Reaction; D013202:Staphylococcal Food Poisoning / Q000382:microbiology*; D013211:Staphylococcus aureus / Q000235:genetics / Q000302:isolation & purification*
D001426:Bacterial Proteins; D046915:Penicillin-Binding Proteins; C487789:mecA protein, Staphylococcus aureus