This study attempted to identify bacterial pathogens and determine their importance in porcine respiratory disease complex in order to identify effective and adequate measures for their control. The study was conducted in three industrial intensive pig farms in different regions of Bulgaria. Nasal swab samples from weaners and fattening pigs affected by respiratory infection were examined, as well as from the lungs of animals that had died or had been emergency slaughtered, with changes characteristic of pneumonia. The results showed that mono-infection was prevalent in the analyzed nasal samples in weaners - 54.2%, and in 70.8% alpha hemolytic Streptococcus was detected. In fattening pigs, associated infections dominated with 54.2%. In a significant part of the samples (62.5%) there were observed alpha hemolytic Streptococcus and S. epidermidis. The results from the microbiological examinations of the lungs showed that the prevailing cases were mono-infections in weaners pigs (70.8%), as well as in fattening pigs (75.0%). A significant proportion of lung specimens were shown to contain E. coli, probably due to coli septicemia potentiated by M. hyopneumoniae.

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