ABSTRACT
Purpose: Chronic otitis media with effusion (OME) is the leading cause of hearing loss during childhood. In bacterial etiology of OME, the most frequent pathogens responsible are Haemophilus influenzae followed by Streptococcus pneumoniae and Moraxella catarrhalis . This study aimed at evaluating the accuracy of nasopharyngeal (NP) specimens in the identification of pathogens in the middle ear fluid (MEF) in patients with OME. Materials and Methods: In this cross sectional, case-control study, 95 MEFs and 53 NP secretion specimens were obtained from 53 children. As a control group, 102 NP specimens were taken from children having an operation other than an otological disease. Conventional culture methods and multiplex-PCR method have been used to determine the etiology of OME; NP carriage between cases and control groups were compared using conventional culture methods. Pearson Chi-Square and Fisher's Exact tests were used in statistical analysis. Results : Bacteria were isolated by culture in 37.9% of MEF specimens, 14.7% of which belonged to the group H. influenzae , S. pneumoniae and M. catarrhalis. PCR was positive in 30.5% specimens targeting the same pathogens. There was a two-fold increase in carriage rate of S. pneumoniae and H. influenzae in patients than controls for each pathogen. Conclusion: PCR is a more reliable method to detect middle ear pathogens in MEF in comparison with the conventional culture methods. The NP colonization wasn't found to be an indicator of the pathogen in MEF although middle ear pathogens colonize more in nasopharynx of diseased children.
ABSTRACT
PURPOSE: To evaluate three methods for 406 isolates of Staphylococcus aureus and coagulase-negative staphylococci (CNS) for the detection of methicillin resistance (MR) using National Committee for Clinical Laboratory Standards (NCCLS) new interpretive criteria. METHODS: We used polymerase chain reaction (PCR) as a gold standard method to evaluate three methods [disk diffusion with Mueller-Hinton agar (MHA) and mannitol salt agar (MSA) and Sceptor system (Becton Dickinson, USA)] for the detection of mecA gene. The isolates that were methicillin-resistant with any of the three tests were evaluated further for MR by E-test. RESULTS: MHA, MSA and Sceptor showed sensitivities of 100, 100 and 99% for S. aureus and 100, 82.6 and 72.1% for CNS, respectively. The specificities of the same methods were found as 100, 90.1 and 99.3% for S. aureus and 79.2, 95.8 and 97.2% for CNS, respectively. E-test showed 100% sensitivity for both S. aureus and CNS. Forty-eight CNS and 16 S. aureus isolates, which presented discrepancies with the three phenotypic methods (MHA disk diffusion method, MSA disk diffusion method and Sceptor), were correctly classified as resistant/susceptible with the E-test when compared with PCR. Only five CNS isolates, which were mecA-negative with PCR were resistant with E-test. Analysis of 248 S. aureus revealed that MHA is superior to other phenotype-based susceptibility testing methods in detecting MR. When we examined the results of 158 CNS, none of the three methods proved efficient in detecting MR. CONCLUSIONS: We conclude that although the accuracy of the MHA disk diffusion test for the detection of MR approaches the accuracy of PCR for S. aureus isolates, the need for easy and reliable methods of detecting MR in CNS still remains.