Detection of Oxacillin Resistance in Staphylococcus aureus Isolated from the Neonatal and Pediatric Units of a Brazilian Teaching Hospital.

Clinical medicine. Pediatrics Pub Date : 2009-03-18 Print Date: 2009-01-01 DOI:10.4137/cmped.s2085
Valéria Cataneli Pereira, André Martins, Lígia Maria Suppo de Souza Rugolo, Maria de Lourdes Ribeiro de Souza da Cunha
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引用次数: 25

Abstract

Objective: To determine, by phenotypic and genotypic methods, oxacillin susceptibility in Staphylococcus aureus strains isolated from pediatric and neonatal intensive care unit patients seen at the University Hospital of the Botucatu School of Medicine.

Methods: A total of 100 S. aureus strains isolated from the following materials were studied: 25 blood cultures, 21 secretions, 12 catheters, 3 cannulae and one chest drain from 62 patients in the neonatal unit, and 36 blood cultures, one pleural fluid sample and one peritoneal fluid sample from 38 patients in the pediatric unit. Resistance of the S. aureus isolates to oxacillin was evaluated by the disk diffusion method with oxacillin (1 μg) and cefoxitin (30 μg), agar screening test using Mueller-Hinton agar supplemented with 6 μg/ml oxacillin and 4% NaCl, and detection of the mecA gene by PCR. In addition, the isolates were tested for β-lactamase production using disks impregnated with Nitrocefin and hyperproduction of β-lactamase using amoxicillin (20 μg) and clavulanic acid (10 μg) disks.

Results: Among the 100 S. aureus strains included in the study, 18.0% were resistant to oxacillin, with 16.1% MRSA being detected in the neonatal unit and 21.0% in the pediatric unit. The oxacillin (1 μg) and cefoxitin (30 μg) disk diffusion methods presented 94.4% and 100% sensitivity, respectively, and 98.8% specificity. The screening test showed 100% sensitivity and 98.8% specificity. All isolates produced β-lactamase and one of these strains was considered to be a hyperproducer.

Conclusions: The 30 μg cefoxitin disk diffusion method presented the best result when compared to the 1 μg oxacillin disk. The sensitivity of the agar screening test was similar to that of the cefoxitin disk diffusion method and higher than that of the oxacillin disk diffusion method. We observed variations in the percentage of oxacillin-resistant isolates during the study period, with a decline over the last years which might be related to improved nosocomial infection control and the rational use of antibiotics.

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巴西某教学医院新生儿和儿科分离金黄色葡萄球菌对奥西林的耐药性检测
目的:通过表型和基因型方法确定从博图卡图医学院大学医院儿科和新生儿重症监护病房患者中分离的金黄色葡萄球菌菌株对oxacillin的敏感性。方法:对62例新生儿患者的血培养物25株、分泌物21株、导管12根、套管3根、胸腔引流液1株、儿科38例患者的血培养物36株、胸腔积液1份、腹膜积液1份等材料分离的100株金黄色葡萄球菌进行研究。采用氧苄西林(1 μg)和头孢西丁(30 μg)的盘片扩散法评价金黄色葡萄球菌对氧苄西林的耐药性,采用添加6 μg/ml氧苄西林和4% NaCl的穆勒-辛顿琼脂进行琼脂筛选试验,并采用PCR检测mecA基因。此外,采用硝化甘油浸渍培养皿检测菌株β-内酰胺酶的产量,并用阿莫西林(20 μg)和克拉维酸(10 μg)培养皿检测菌株β-内酰胺酶的高产率。结果:在纳入研究的100株金黄色葡萄球菌中,18.0%的金黄色葡萄球菌对oxacillin耐药,其中新生儿病房的MRSA检出率为16.1%,儿科病房为21.0%。奥西林(1 μg)和头孢西丁(30 μg)圆盘扩散法的灵敏度分别为94.4%和100%,特异度为98.8%。筛选试验的敏感性为100%,特异性为98.8%。所有菌株都产生β-内酰胺酶,其中一株被认为是高产菌株。结论:30 μg头孢西丁纸片扩散法优于1 μg奥西林纸片扩散法。琼脂筛选试验的灵敏度与头孢西丁纸片扩散法相近,高于奥西林纸片扩散法。我们观察到在研究期间耐oxacillin分离株百分比的变化,在过去几年中有所下降,这可能与改善医院感染控制和合理使用抗生素有关。
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