PHENOTYPIC DETECTION OF AMPC β-LACTAMASE ENZYME IN GRAM-NEGATIVE BACILLI

Khanda Abudlateef Anoar a, Sherko Ali Omer a, Bayan Taha Majid aHero Ali Hama Rahim b and Shno Jalal Muhammed c



 Department of Microbiology, College of Medicine, University of Sulaimani. 
b Hewa Teaching Hospital, Sulaimani Directorate of Health. 
c Surgical Teaching Hospital, Sulaimani Directorate of Health.


Submitted: 4/12/2017; Accepted: 6/3/2018; Published 1/8/2018
ABSTRACT


Background 

Bacterial resistance to antimicrobials are achieved by several mechanisms including production of enzymes such as β-lactamases; according to Ambler classification, β-lactamases are classified into four classes, A to D. AmpC β-lactamase production is related to chromosomal or plasmid genes expression in Gram-negative bacteria. 


Objectives 

To determine AmpC β-lactamase production among hospital isolates of Enterobacteriaceae and non-fermener Gram-negative bacilli in Sulaimani providence and to evaluate different phenotypic methods for detection of AmpC β-lactamase.


Materials and Methods

A total of 108 Gram-negative bacilli bacterial isolates collected from different infections in several governmental hospitals in Sulaimani city were assessed for β-lactamase production. The isolates were identified using biochemical methods. Antimicrobial susceptibility test was performed by Bauer-Kirby disk diffusion method using 14 antimicrobial agents including cefoxitin. Cefoxitin-resistant isolates were tested for AmpC production by four phenotypic tests including disk approximation test, disk antagonism test, hodge test, and AmpC disk test.


Results

Among 108 isolates, 47 (43.5%) were Escherichia coli and 35 (32.4%) were Pseudomonas aeruginosa. From the isolates, 98.1% were resistant to ampicillin while 71.3% were sensitive to imipenem and 68 isolates (63%) were resistant to cefoxitin. We found that 59 out of 68 to cefoxitin-resistant isolates (86.8%) produce AmpC by hodge test while other tests detected less AmpC production. In regard to hodge test, specificity of the other three tests reached 100% while sensitivity ranged from 55.93 in disk approximation test to 79.66% from both disk antagonism test and AmpC disk test.


Conclusion

AmpC b-lactamase production was common among Gram-negative bacilli from hospital isolates. Cefoxitin screening followed by hodge test for AmpC production was the best test to find b-lactamase producers. Different AmpC b-lactamase production tests can be used according to the tested bacteria.



KEYWORDS

AmpC β-lactamase detection, Enterobacteriaceae, Gram-negative bacilli, Sulaimani.