Live bacteria in more than 90% of middle ear effusions

By MedWire Reporters

Live bacteria are present in more than 90% of middle ear effusions, research shows.

The present study strongly suggests bacteria and biofilms are important in the pathogenesis of otitis media with effusion (OME), according to Roger Bayston (University of Nottingham, UK) and colleagues.

The findings, published in the International Journal of Pediatric Otorhinolaryngology, could also have clinical implications, say the researchers, as current treatment of OME involves drainage of the effusion and ventilation tube insertion.

This does not address the persistent bacterial infection, and "serves to merely remove the effusion that is the result of a middle ear inflammation," they state.

OME, also known as glue ear, a common cause of deafness in children, is characterized by the absence of symptoms and acute inflammation.

As children with OME do not present with pain, fever, or tympanic membrane inflammation, the role of bacteria in causing OME has been controversial.

Previous studies have identified cultured bacteria in less than half the samples of OME cases. There has also been conflicting evidence between studies showing low rates of culturable bacteria in effusion samples and polymerase chain reaction (PCR) analyses showing bacterial DNA in more than 80% of effusions.

To tackle these discrepancies, Bayston and colleagues performed an extended microbial culture on 62 middle ear effusion samples from 42 patients. In addition, they analyzed the effusions using bacterial viability staining and confocal laser scanning microscopy (CLSM).

The advantage of bacterial viability staining is that it allows for the detection of live bacteria without requiring them to grow on culture. With CLSM, the researchers are able to demonstrate a three-dimensional structure of bacterial communities typical of biofilms.

Of the samples analyzed, 45% were culture positive. Using CLSM, 82% of the samples were positive for bacteria. When the viability staining and CLSM techniques were combined, live bacteria was identified in 92% of the samples.

"The results show that combining culture and confocal microscopy enables demonstration of live bacteria in more than 90% of OME samples, strongly suggesting a role for bacteria in the aetiopathogenesis of OME," state Bayston and colleagues.

Using the laser microscopy, 25 effusions exhibited biofilm morphology while 26 were identified as planktonic bacteria.

Planktonic bacteria would be expected to respond to conventional antibiotic treatment, while bacteria in biofilms might respond to some of the newer antibacterial strategies, such as locally delivered high-dose antibiotics over a prolonged period of time.

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