Detection of pathogenic haemolytic bacteria in respiratory tract infections of livestock

Abstract

A study was undertaken to elucidate the role of haemolytic bacteria in respiratory tract infections of livestock. This envisaged the isolation and identification of the haemolytic bacteria, determining their antibiogram patterns and testing the pathogenicity of the isolates in mice. The study also envisaged the detection of Mannheimia haemolytica by polymerase chain reaction, determining the genetic relationship of Staphylococcus aureus isolates from different animal hosts using RAPD-PCR technique and also analysis of plasmid profiles of Escherichia coli isolates. Samples were collected from clinically ill livestock and at random from apparently healthy animals from in an around Thrissur district. A total of 309 samples were taken which consisted of nasal swabs, tracheal swabs, lung samples and blood samples. Samples were cultured on blood agar and on Mannheimia haemolytica selective medium. Mannheimia haemolytica could not be isolated from any of the samples. But pooled nasal swabs when cultured on blood agar gave an isolate with characteristics almost similar to Mannheimia haemolytica, but showed variations for ornithine decarboxylase activity and utilization of sugars like trehalose and salicin. As, no reference strain was available it was not possible to make a comparison and confirm the isolate as Mannheimia haemolytica. From the samples cultured on ordinary blood agar medium a total of 20 haemolytic bacterial isolates could be obtained. The different bacterial isolates were Staphylococcus aureus (40 per cent), Staphylococcus epidermidis (10 per cent), Escherichia coli (30 per cent), Klebsiella pneumoniae (5 per cent), Streptococcus pyogenes (5 per cent), Streptococcus agalactiae (5 per cent) and Arcanobacterium pyogenes (5 per cent). The haemolytic bacteria were identified based on morphology, cultural characteristics and biochemical tests. Antimicrobial sensitivity pattern of the isolates showed that almost all the isolates had high sensitivity to pefloxacin and ampicillin. Antimicrobial resistance was shown maximum to erythromycin. The three Staphylococcus aureus isolates, all the E. coli isolates and Klebsiella isolate caused death of mice. Rest of the five Staphylococcus aureus isolates, Streptococcus pyogenes , Streptococcus agalactiae and Arcanobacterium pyogenes did not cause death of mice but produced internal lesions and could be re-isolated. Staphylococcus epidermidis isolates could neither cause death, nor produce internal lesions and could not be re-isolated. None of the nasal and tracheal swabs, lung samples and blood samples gave a positive result for Mannheimia haemolytica specific PCR. A pooled sample of nasal swabs from cattle with respiratory infection gave a positive result for it. But PCR of the culture could not yield a positive result. Moreover, no reference strain was available to make a comparison and confirm the result. RAPD-PCR of the Staphylococcus aureus isolates showed that there was considerable genetic relationship between Staphylococcus aureus isolates of different species and also there was noticeable genetic diversity of the isolates within the host species. Plasmids could be isolated only from two of the six isolates of Escherichia coli studied. Plasmid profile analysis of the isolates could not ascertain any correlation between the virulence, antibiotic resistance and presence of plasmids.