الفهرس 
Causes of antimicrobial resistance (AMR)Only 14 pages are availabe for public view
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Abstract
The ICU brings together high-risk patients and interventions in a complex environment. The single strongest predictor of an adverse drug event is patient illness severity. Critically ill patients are prescribed twice as many medications as patients outside of the ICU.Antibiotics frequently are empirically prescribed in the ICU and errors have potential implications both for individual patients and populations. Patients are prescribed these medications in an environment that is stressful, complex, changing, under the stewardship of multiple providers, and frequently managing patients in crisis.
Exposure to multiple antibiotic regimens selects and encourages the proliferation of resistant pathogens. Many pathogens can rapidly develop resistance to commonly used antibiotics under the selective pressure of antibiotic exposure. Carbapenems are preferred antibiotics for severe infections of ICU- acquired infections caused by drug- resistant gram-negative bacteria especially for the ESBL producers. The emergence of bacteria resistant to carbapenems is alarming because carbapenems are almost the last resort against end-stage infection, especially against infection with gram-negative bacteria.. Hence, early identification with in vitro testing is of paramount importance to the success of infection control efforts.
The present study aimed to isolate and identify gram-negative bacteria causing infections in ICU patients, to carry out antibiotic susceptibility testing for the isolated organisms, to estimate the percentage of carbapenem resistance among the isolated gram-negative bacteria and to identify the gene coding for carbapenem hydrolyzing in the carbapenem resistant isolates.
The study sample included a total of 327 ICU patients with a mean age of 58 years. The patients were chosen randomly from the ICUs of Alexandria Main University Hospital and a relevant information sheet was filled for every resident.
Clinical samples like urine, sputum, wound swabs, blood, BAL as well as environmental samples (curtains, beds, doors, side tables and machines) were aseptically collected and cultured on MacConkey‟s agar media for isolation of gram-negative bacteria. The isolated colonies were subjected to all microbiological procedures for further identification.
All gram-negative bacterial isolates were subjected to antimicrobial susceptibility testing using the single disc diffusion method described by Bauer and Kirby on the Muller Hinton agar. Inhibition zones were measured and susceptibility to selected antimicrobial agents was differentiated into S, I, R. MHT and CDT were then carried out to confirm the presence of carbapenemase enzymes. Finally, PCR was performed on the carbapenem resistant isolates in order to identify the genes responsible for carbapenemase production.
Summary and Conclusions
95
The results of this study can be summarized as follows:
1. K. pneumoniae was the most frequently encountered gram-negative bacterial isolate accounting for 27.7% of 224 microbial isolates followed by E.coli and A. baumanii both accounting for 25.0% and 24.1% of the isolates respectively.
2. Seventy seven percent (77.2%) of the gram-negative bacterial isolates were obtained from clinical samples and 22.8% were obtained from environmental samples. The most commonly isolated gram-negative bacterial isolate among clinical samples was K. pneumonia (28.9%) and the most commonly isolated gram-negative bacterial isolate among environmental samples was A. baumanii (33.3%).
3. Half (50.0%) of the gram-negative bacterial isolates were carbapenem sensitive and 50.0% were carbapenem resistant.
4. Enterobacteriaceae had resistance rates greater than 45.0% for all antibiotics except for; imipenem, meropenem, ertapenem, polymyxin B, chloramphenicol, amikacin and nitrofurantoin with resistance rates of 35.4%, 37.5%, 36.1%, 43.1%, 34%, 39.6% and 41.7%, respectively.
5. P.aeruginosa showed resistance rates greater than 50.0% for all antibiotics except for; polymyxin B, tetracycline, pipracillin/tazobactam with resistance rates of 22.6%, 48.4% and 35.5%, respectively.
6. A. baumanii showed resistance rates greater than 50.0% for all antibiotics except for; polymyxin B with only 21.8% resistant.
7. Out of the 224 gram-negative bacterial isolates 112 (50.0%) were carbapenemase producers, 99 (44.2%) were ESBL producers and 17 (7.6%) were both carbapenemase and ESBL producers.
8. The majority of the carbapenem resistant isolates were obtained from broncho alveolar lavage (43.8%) followed by urine (27.7%), environmental samples (18.8%), wound (7.1%) and blood samples (2.7%).
9. In Enterobacteriaceae, 35.2%, 37%, 11.1%, 25.9%, 37%, 7.4%, 1.9%, 11.1%, 37.0%, 55.6%, 9.6% and 51.6% of the isolates had VIM, IMP, GIM, SPM, NDM, BIC, DIM, AIM, OXA, KPC, IMI and GES genes, respectively. None of the isolates had SIM or SME genes.
10. In P. aeruginosa, 33.3%, 28.6%, 4.8%, 28.6%, 9.5%, 9.5%, 9.5%, 9.5%, 23.8% and 19.5% of the isolates had VIM, IMP, SIM, SPM, NDM, DIM, AIM, OXA, KPC and GES genes respectively. None of the isolates had GIM, BIC, SME and IMI genes.
11. In A. baumanii, 48.6%, 29.7%, 8.1%, 2.7%, 8.1%, 18.9%, 5.4%, 16.1%, 37.8% and 37.8% of the isolates had VIM, IMP, GIM, SIM, SPM, NDM, BIC, DIM, AIM, OXA, KPC, IMI, GES and SME genes respectively. None of the isolates had DIM, AIM, SME and IMI genes.
12. Among the 112 carbapenem resistant gram-negative bacterial isolates subjected to PCR testing, 73 (65.2%) bacterial isolates had more than one gene, 29 (25.9%) had only one gene and 10 (8.9%) had no genes at all.
13. The sensitivity and specificity of MHT were 79.4% and 80.0%, respectively for all the carbapenem resistant isolates.
14. The sensitivity and specificity of MHT were 92.5% and 100.0 %, respectively for carbapenem resistant Enterobacteriaceae.
15. The sensitivity and specificity of MHT were 29.4% and 100.0%, respectively for carbapenem resistant P. aeruginosa.
Summary and Conclusions
96
16. The sensitivity and specificity of MHT was 84.4% and 60.0 %, respectively for carbapenem resistant A. baumanii.
17. In all carbapenem resistant isolates, MHT had the highest sensitivity of 77.7% with ertapenem disc and the highest specificity of 100.0% with meropenem disc.
18. In the carbapenem resistant Enterobacteriaceae, MHT had both the highest sensitivity and specificity of 90.6% and 100.0%, respectively with ertapenem disc.
19. In the carbapenem resistant P. aeruginosa, MHT had both the highest sensitivity and specificity of 29.41% and 100.0%, respectively with ertapenem disc.
20. In the carbapenem resistant A. baumanii, MHT had the highest sensitivity of 81.8% with ertapenem disc and the highest specificity of 100.0% with meropenem disc.
21. In all carbapenem resistant gram-negative bacterial isolates, the CDT had the best sensitivity and specificity of 90.3% and 85.0%, respectively at a cut off of 5 mm.
22. In the carbapenem resistant Enterobacteriaceae isolates the best sensitivity and specificity of 94.6% and 88.2%, respectively was obtained at a cut off of 5 mm.
23. In the carbapenem resistant P. aeruginosa isolates the best sensitivity and specificity of 69.2% and 87.5%, respectively was obtained at a cut off of 5 mm.
24. In the carbapenem resistant A. baumanii isolates the best sensitivity and specificity of 95.5% and 80.0% was obtained at a cut off of 5 mm.
25. No statistically significant relation was found between previous antibiotic intake and the development of resistance.
It can be concluded from this study that:
1. Gram-negative carbapenem resistant bacteria were isolated from half of the studies samples.
2. K. pneumoniae was the most frequently encountered resistant gram-negative bacilli.
3. Polymyxin B, doxycycline, pipracillin –tazobactam and chloramphenicol are drugs of choice for treatment of carbapenem resistant bacteria.
4. Among the 112 carbapenem resistant bacteria subjected to PCR testing, 73 (65.2%) bacterial isolates had more than one gene, 29 (25.9%) had only one gene and 10 (8.9%) had no genes at all.
5. MHT showed high sensitivity and specificity for detetection of carbapenem resistance in Enterobacteriaceae.
6. Using ertapenem and meropenem discs improved sensitivity and specificity of MHT.
7. CDT detected metallo beta lactmases at a cutoff of 5 mm.