Multi-drug resistant pseudomonas aeruginosa as a cause of chronicity in ear infections

ABSTRACT

Pseudomonas aeruginosa is the most commonly recovered organism from chronic suppurative otitis media [CSOM]. P. aeruginosa has high intrinsic resistance to many antibiotics, and this situation is worsened in infections caused by strains acquiring additional multi-resistance. The aim of this work was to assess the role of P. aeruginosa in the chronicity of ear infection. Routine basic and enriched media [nutrient agar and blood agar] were used as well as P. aeruginosa selective agar [PASA] for isolation. Two pigment enhancer media were used for differentiation Kings A agar and Kings B agar. The anti-microbial resistance patterns of isolated P. aeruginosa were studied with specific regards to new beta-lactamases, including extended spectrum beta-lactamase [ESBL] and metallo-beta-lactamase [MBL]. Seventy six samples were collected from chronic discharging ear, 61 P. aeruginosa isolates were recovered [80.26%] on all media used. Gram positive bacteria were 100% inhibited on PASA, Kings A and Kings B, while Gram negative isolates were 100% inhibited on PASA only and not on other used media. The demarcation of P. aeruginosa colonies was detected in 100% on PASA, 19.67% on Kings A, 36.07% on Kings B, while nutrient and blood agar media could not demarcate colonies at all. ESBL was positive in 54.1%, negative in 24.59%, and indeterminate in 21.31% of pseudomonas isolates. The results of MBL test were 9.84% positive, 65.57% negative, 24.59% indeterminate. This reflects the serious problem of impending resistance of P. aeruginosa to all known sensitive drugs which increases the risk of chronicity of infections caused by these aggressive strains. Careful and experienced interpretation of the routinely done susceptibility testing of P. aeruginosa should be performed so as to predict the production of the new beta lactamases and to correctly formulate the susceptibility results in order not to mislead the clinicians. Special tests for confirmation of such resistance mechanisms are sometimes needed