Phenotypic Detection of Β-Lactam Antibiotics, Methicillin and Inducible Clindamycin Resistance Among Bacterial Isolates in Patients with Otitis Externa

Otitis is a general terminology used for inflammation or infection of the ear; Staphylococcus aureus and Pseudomonas spp. are the most common causes of otitis externa. The resistance mechanism against the beta-lactams group is due to the production of β-lactamase enzymes by the bacteria; the enzymes in staphylococci are encoded by erm genes that confer inducible Clindamycin resistance.
This study aimed at investigating bacterial resistance by evaluating samples collected from Otitis Externa patients admitted to Ayatollah Roohani Hospital of Babol, Iran.
Ear samples were collected from 72 patients with Otitis Externa referred to Ayatollah Roohani hospital during May 2012 to 2013. At first, the isolated bacteria were identified using appropriate differential and selective media, and then were tested for antimicrobial susceptibility testing following the disk diffusion method. Special diagnostic tests were also performed for the identification of ESBL, iAmpC, pAmpC, metallo beta lactamase producers and inducible resistance to clindamycin and methicillin resistant strains. Data were analyzed by the SPSS 22 statistical software.
Among the 65 isolated bacteria, 24 (36.9%) cases were found to be gram negative and 41 (63.1%) were gram positive; pAmpC beta-lactamase producers were found to have the highest frequency in gram negative bacteria. From 36 (87.8%) isolated CoNS, 18 (50%) bacteria were found to be resistant to the methicillin group and 4 (11.1%) cases had inducible resistance to clindamycin; All isolated S. aureus were sensitive to methicillin and clindamycin.
Considering that some bacteria are concurrently able to produce different types of resistance enzymes, and also the fact that high prevalence rate of resistance belongs to CoNS, it is important and necessary to perform antimicrobial susceptibility testing as per clinical and laboratory standards institute (CLSI) methods in clinical laboratories.