Introduction:
The incidences of nosocomial infections are varied in different studies, and the crude mortality is high, particularly for intensive-care unit (ICU) patients.(1,2) The rates of antimicrobial resistance among pathogens causing health care-associated infections are increasing, and the main mechanisms that must be submitted to surveillance and accurate diagnosis are ESBL, AmpC and carbapenem resistance in gram negative bacilli, and MRSA and VRE in gram positive cocci.(3)
Aim of the work
The aim of this study was to determine the incidence of the gram negative and gram positive resistance among nosocomial pathogens, to assess the abilities of diffusion based methods to detect different resistant patterns in relation to MIC profiles tested by the Sensititre automated system and to guide antimicrobial therapy policy in Benha locality
Material and methods:
The study included total of 205 nosocomial specimens that were cultured and yielded 89 gram negative and 35 gram positive isolates. In our study we only included the nosocomial gram negative isolates resistant to 3rd generation cephalosporins (54) and the gram positive isolates resistant to vancomycin ± methicillin (20) to be tested by Sensititre for identification and susceptibility testing. Diffusion based techniques used for confirmation of resistance of gram negative bacilli included ESBL screening by double disc diffusion test, imipenem (IMP)-EDTA combined disc test and ESBL and AmpC Detection Set (D68C system).
Results:
The incidence of nosocomial MRSA among collected Staphylococcus aureus was 24.4%. According to diffusion based techniques, the rate of resistance to the 3rd generation cephalosporins among the 89 nosocomial gram negative isolates was as follows: for extended spectrum beta-lactamases 50 isolates (56.1%), for AmpC resistance 25 isolates (28.1%), and for carbapenem resistance 11 isolates (12.3%). There was a suitable agreement between the results of Sensititre and diffusion based detection regarding ESBL and carbapenem resistance. However, results of Sensititre showed much higher number of AmpC in comparison with diffusion based detection. The reliance on only cefoxitin resistance by MIC testing is not a guarantee of establishing a diagnosis of AmpC.
Conclusion:
The highest resistance mechanisms were ESBL, followed by AmpC and carbapenem resistance, especially among Klebsiella pneumoniae isolates. Also, from our results, it was highly evident that there was a high endemicity of MRSA and VRE among our Gram positive cocci nosocomial isolates. It's recommended to confirm AmpC resistance by at least on phenotypic method, without complete reliance on the automated MIC results regarding this pattern of resistance.
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