Cefoxitin screening agar for rapid identification of methicillin-resistant S. aureus in healthcare settings

Abstract

Objective This study was aimed to explore the validity of Cefoxitin-Mueller Hinton broth for detection of MRSA from different pathological
specimens and to explore the susceptibility to β-lactam antibiotics and other selected locally used antimicrobials.
Patients, Materials and Methods The present study was carried out during the period from December 2009 to October 2010. A total of 200
specimens were collected from Baghdad Teaching Hospital and Baquba Teaching Hospital including; 50 specimens from each of hospital
inpatients, medical and paramedical staff, and hospitals environments. several types of clinical specimens comprising (burn, wound,
conjunctival, ear, nasal, and throat swabs, pleural and ascetic fluids, sputum, urine, and urethral discharge, and nasal swabs). Collected
swabs were inoculated in 5 milliliters of Cefoxitin-Mueller-Hinton broth tubes supplemented with 7.5% NaCl (wt. /vol.) and 6μg/ml of
cefoxitin and incubated for 24 hours at 37°C. Positive tubes were subcultured on blood agar and Mannitol-salt agar. Suspected colonies
were identified by biochemical reactions and Staphytect-Plus test (Oxoid, UK). Susceptibility testing was performed by disk diffusion on
Mueller-Hinton agar. Statistical analyses were done using SPSS version 18 computer software (Statistical Package for Social Sciences), and
P values < 0.05 were considered significant.
Results The results revealed that 62(31%) isolates were MRSA. The resistant rate to methicillin was significantly higher (P = 0.004) among
those isolates recovered from inpatients compared to other study groups. All MRSA isolates were found to be multi-drug resistant since,
and that (17.7%), (30.6%) of them were resistant to vancomycin and ciprofloxacin, respectively.
Conclusions About one third of S. aureus isolates were MRSA with multiple antimicrobial resistances. Thus, mandatory MRSA surveillance system
should be implemented in healthcare settings, represented by admission screening of patients using MRSA rapid tests, such as rapid culturing method.