Dissertation > Medicine, health > Clinical > Diagnostics

Analysis on Drug Resistance and Relationship with icaD Genetypes of Clinically Isolated Staphylococcus Epidermidis

Author CaoXiaoGuang
Tutor LiuBao
School Anhui Medical University,
Course Emergency Medicine
Keywords Staphylococcus epidermidis drug resistance PCR mecA icaD
Type Master's thesis
Year 2012
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Preface Gram-Positive Cocci is a kind of common clinical pathogenicbacterium. In the middle of last century, when penicillin appeared, the infection ofGram-Positive Cocci was almost in control, but with the extensive use of penicillin,some strains produced penicillinase, then they expressed as penicillin-resistance. Thusmankind invented meticillin sodium to resist penicillinase. But with its abusiveapplication in1961in the United Kingdom, the first strain of methicillin-resistantStaphylococcus aureus (MRSA) was found, then, infection of MRSA was almost allover the world, covering up to58%of the total number.Staphylococcus epidermidis is a kind of common conditional pathogenic bacterium.In the past, it was regarded as non-pathogenic, weak pathogenic bacteria or the body’snormal flora. However, with the development of medicine, body implants, such as,Peripherally Inserted Central Catheter and single-lumen Central Vein Catheter, etc.,have been widely applied in the ordinary course of medical practice. And in theintensive care unit (ICU), vascular catheter is especially an essential means of disposal.Unfortunately the frequent usage of body implants results in repeated infection ofStaphylococcus epidermidis(which was regarded as non-pathogenic). Besides, theproportion of Staphylococcus epidermidis infection in nosocomial infection increasesyear by year, even being considerable to or over that of Staphylococcus aureus. Withthe wide application of intervention therapy and broad-spectrum antibiotics,immunocompromised patients are easier to get Staphylococcus epidermidis infection,especially the MRSE infection. Timely and effective treatment is the key to control theprevalence and infection of Staphylococcus epidermidis in the hospital.According to some literature, the Staphylococcus epidermidis can express theMECA gene as well as ICA gene. In addition, it can form biomembrane. Once thebiomembrane is formed, the treatment effect will be poor, and doctors have todisconnect the catheter to control infection. Through adhesion colonization--the key way, bacteria poisons infected tissue, which is called virulence function. The resistancemechanism of MRSA to meticillin sodium has been clear, mainly because MRSA canproduce a new type of penicillin-binding protein (PBP2a), encoded and synthesized byspecific mecA gene。But PBP2a’s affinity with β-lactam antibiotics is very low, whenthe connection activity of the two is inhabited, PBP2a can function as synthetizing cellwall, resulting in resistance. But there are still no essential answers on why differentstrains of MRSA have different levels of resistance? And the amount of PBP2aproduced by MRSA has nothing to do with the level of resistance, let alone to explainthe complicated multi-drug resistant (resistance to many types of antimicrobial drugsexcluding β-lactam type) mechanism of MRSA. Besides, the relationship between icagene expression, meca gene expression and multiple drug resistance is unclear. Andeven through there are related reports on biomembrane generation mechanism, no onecan state clearly.METHODSBy biochemical and molecular biological methods according to NCCLS/CLSI,researchers has isolated and identified Staphylococcus epidermidis from clinicalspecimens, then has appraisedd and made contrast of drug resistance of the125strainsof Staphylococcus epidermidis from the humoral of clinical specimens andnon-humoral of nomal people.RESULTS①In two groups, icaD gene expression is correlated withmecA’s(r=0.528,P=0.000;r=0.309,P=0.016).②MecA gene expression in humor ofClinical patients group is significantly higher than that in non-humor of normal people.In statistic aspect, there is significant difference between the two groups (p<0.001),while there exists no distinct difference in bacterial strain of icaD gene expression (p>0.05).③the1two groups’staphylococcus epidermidis were sensitive to rifampicin,nitrofurantoin, linezolid and Vancomycin.④The resistant rates of mecA gene expressionbacterial strain to antibacterial agents have little differences in two groups(p>0.05),butto ampicillin, cefoxitin, bactrim, erythromycin, and chloramphenicol, there are cleardifferences (p<0.05)Conclusion ICU Staphylococcus epidermidis’ resistant rates toantibacterial agents are high,so the ICU Staphylococcus epidermidis must bemonitored more frequently.And doctors must choose rational drug to controlnosocomial infection.ConclusionAmong the patients in ICU, Staphylococcus epidermidis was usuallymulti-antibiotics resistant,so it must be monitored more frequently.Choosing antibioticfor the treatment of Staphylococcus epidermidis infection should be based on the drugsensitive tria1.

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