Objectives: to investigate nine antibiotic resistance genes simultaneously in Staphylococcus aureus strains isolated from cows with clinical mastitis. Methods: a total of 21 strains of methicillin-resistant (MRSA) and 29 strains of methicillin-susceptible S. aureus (MSSA) isolated from milk of cows with clinical mastitis and previously identified by PCR as MRSA or MSSA were investigated for nine antibiotic resistance genes of human interest (Strommenger et al., 2003 with a few modifications). The phenotype resistance was evaluated by conventional antibiotic disc diffusion method (Kirby Bauer). Results: among the 21 MRSA, 2 strains had only mecA gene, 2 strains showed 2 resistance genes, 14 had 3 resistance genes and 3 strains had four resistance genes (Table 1). Among the 29 MSSA, 2 strains had tetM gene, 2 had tetK, one had aacA/aphD, one had both ermC and tetK, and one had the three genes aacA/aphD, ermA and tetM. The other 22 MSSA did not show any resistance gene. Genes of resistance to the quinupristin-dalfopristin have not been found in any S. aureus strain. All MRSA having at least two genes of resistance, were phenotypically resistant to methicillin, erythromycin, clindamycin, gentamycin, and oxytetracyclin. Conclusion: the multiplex PCR assay described by Strommenger et al. (2003) is a rapid and suitable method for simultaneously detecting S. aureus and its associated antibiotic resistance genes. The majority of MRSA had more than one gene of antibiotic resistance. MecA, ermA and aacA/aphD were detected in the majority of MRSA, which resulted resistant also by disc diffusion method. Five out of 29 MSSA strains had at least one gene of resistance, demonstrating that multiple resistance is not related only to MRSA strains. The question about the selection of multiple resistant strains must be considered by veterinarians before administering antibiotics to animals. This PCR protocol is quite rapid, takes less than four hours from the bacterial DNA extraction to the PCR results, and is suitable for the surveillance of S. aureus multiple resistant strains cultured from milk. Further studies will be aimed at genotyping the S. aureus strains.

Evaluation of nine antibiotic resistance genes by multiplex polymerase chain reaction (PCR) in methicillin-susceptible and -resistant Staphylococcus aureus isolated from bovine mastitis milk samples

PREZIUSO, Silvia;ATTILI, Annarita;CUTERI, Vincenzo
2013-01-01

Abstract

Objectives: to investigate nine antibiotic resistance genes simultaneously in Staphylococcus aureus strains isolated from cows with clinical mastitis. Methods: a total of 21 strains of methicillin-resistant (MRSA) and 29 strains of methicillin-susceptible S. aureus (MSSA) isolated from milk of cows with clinical mastitis and previously identified by PCR as MRSA or MSSA were investigated for nine antibiotic resistance genes of human interest (Strommenger et al., 2003 with a few modifications). The phenotype resistance was evaluated by conventional antibiotic disc diffusion method (Kirby Bauer). Results: among the 21 MRSA, 2 strains had only mecA gene, 2 strains showed 2 resistance genes, 14 had 3 resistance genes and 3 strains had four resistance genes (Table 1). Among the 29 MSSA, 2 strains had tetM gene, 2 had tetK, one had aacA/aphD, one had both ermC and tetK, and one had the three genes aacA/aphD, ermA and tetM. The other 22 MSSA did not show any resistance gene. Genes of resistance to the quinupristin-dalfopristin have not been found in any S. aureus strain. All MRSA having at least two genes of resistance, were phenotypically resistant to methicillin, erythromycin, clindamycin, gentamycin, and oxytetracyclin. Conclusion: the multiplex PCR assay described by Strommenger et al. (2003) is a rapid and suitable method for simultaneously detecting S. aureus and its associated antibiotic resistance genes. The majority of MRSA had more than one gene of antibiotic resistance. MecA, ermA and aacA/aphD were detected in the majority of MRSA, which resulted resistant also by disc diffusion method. Five out of 29 MSSA strains had at least one gene of resistance, demonstrating that multiple resistance is not related only to MRSA strains. The question about the selection of multiple resistant strains must be considered by veterinarians before administering antibiotics to animals. This PCR protocol is quite rapid, takes less than four hours from the bacterial DNA extraction to the PCR results, and is suitable for the surveillance of S. aureus multiple resistant strains cultured from milk. Further studies will be aimed at genotyping the S. aureus strains.
2013
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11581/319181
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