الفهرس 
Introduction
The Genus StaphylococciOnly 14 pages are availabe for public view
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Abstract
This study was carried out for detection of different staphylococcal species causing bacteremia, comparing between results of phenotypic and real time PCR for detection of methicillin and vancomycin resistance in staphylococcal isolates, determination of the antibiogram for the isolated staphylococcal strains and for determination of the possible risk factors for acquiring vancomycin resistance in cases with staphylococcal bacteremia.
This study was carried out on 60 staph isolates collected from positive blood culture bottles (BACTEC 9050 System) of 60 patients with significant bacteremia admitted to 10 different wards and ICUs in Assiut University Hospital. The patients were 35 males and 25 females and their age range from 1 – 70 years. There were 38 ICU patients and 22 non-ICU patients.
Clinical and demographic data of the patients were obtained retrospectively from patients’ medical records following positive signal index of blood culture bottles. Data elements included: age, sex, hospital unit residence, medical history and co-morbidities, recent Vancomycin exposures, recent surgery (within 30 days prior to index blood culture collection), ICU admission prior to blood culture, the presence or absence of intravascular catheters.
All staphylococcal isolates showed both gram positive cocci in clusters and they all were catalase test positive. Identification of staphylococcal species was performed by subculture on MSA and by Microscan system, while antibiotic sensitivity testing was performed by Microscan system, E- test, DD method, ORSAB and by real-time PCR for mec A and van A genes.
On MSA. There were 11.7% of isolates were mannitol fermenting (Yellow colonies), while 88.3% of isolates were non mannitol fermenting (Pink colonies). The same result was obtained from the Microscan system for staph. species identification where 11.7% of isolates were S.aureus, while 88.3% of isolates were CoNS (14 S. epidermidis, 12 S. hominis, 8 S. haemolyticus, 7 S. lugdunensis, 6 S. hyicus, 5 S. auricularis and one S. sciuri isolate).
In this work, real-time PCR for mecA gene which is the gold standard method revealed that about 95% of staphylococcal isolates were resistant to methicillin (the percentage was 85.7 % among S. aureus and 96.2 % among CoNS). Accordingly, sensitivity and specificity of E-test were 96.4 % and 100 % respectively, DD method showed 87.7 % sensitivity and 100 % specificity, ORSAB media showed 92.9 % sensitivity and 100 % specificity while Microscan showed 100.0 % sensitivity and 100.0 % specificity.
Concerning vancomycin resistance, E-test which is the gold standard method detected vancomycin resistance in 10% of staphylococcal isolates. Therefore, the DD method showed 66.7 % sensitivity and 100.0 % specificity while Microscan showed 83.3 % sensitivity and 100.0 % specificity. Real-time PCR detected van A gene in only one staphylococcal isolate (1.7%).
According to Microscan system the most effective antibiotics for staphylococcal isolates were in order: Vancomycin, Linezolid, Synercid, Rifampicin, Chloramphenicol, Gentamycin, Tetracycline, Trimethoprim/Sulphamethoxazole, Clindamycin, Ofloxacin, Ciprofloxacin, Azithromycin and Erythromycin.
This study revealed that 23.3 % of staphylococcal isolates were resistant to linezolid whih is relatively high percentage.
In this study, antibiotic sensitivity tests was also done for all the 60 staph. isolates by DD method using Vancomycin, Linezolid, Teicoplanin and Oxacillin. Vancomycin was the most effective followed by Teicoplanin and Linezolid while Oxacillin was the least effective. In fact, Teicoplanin was as effective as Linezolid against S. aureus isolates but more effective against CoNS isolates. Although Teicoplanin is widely used in Europe, it has not been approved for use in the United States.
In the present study, we compared the demographic and clinical data of patients infected with Vancomycin resistant staphylococcal bacteremia with patients infected with Vancomycin susceptible staphylococcal bacteremia. It was found that infancy and childhood, prior Vancomycin use within 30 days were important risk factors for development of VISA and VRSA bacteremia with a statistically significant difference compared to both VSSA infections and VSCNS infections. We found that Vancomycin resistance was higher among children patients than adults and old patients with a statistically significant difference (P=0.002).
In this study, We found that Vancomycin resistance was higher among patients with prior Vancomycin use within 30 days of index culture collection with a statistically significant difference (P=0.001).
The present study showed no higher Vancomycin staphylococcal resistance in patients according to gender, patients with DM, renal failure, patients with ICU admission, neutropenia, surgery within previous 30 days, resistance to methicillin, use of antibiotics other than vancomycin within 30 days, peripheral I.V catheter and central I.V catheter. However, This study found that hospital mortality was higher among patients with vancomycin resistant staphylococcal bacteremia (P=0.005).