Isolation and partial characterization of Streptococcus suisfrom clinical cases in cattle

Sixteen isolates of gram-positive, coccoid bacteria were obtained from clinical cases of diverse conditions in cattle and identified as Streptococcus suisusing 16S ribosomal DNA gene sequencing and other bacterial identification methods. None of the isolates could be assigned to any of the known S. suiscapsular types. Virulence-associated gene profiling that targeted muramidase-released protein, extracellular protein factor, suilysin, 89-kb pathogenicity island, and arginine deiminase (arcA) genes were negative except for 1 isolate that was arcApositive. The arcA-positive isolate caused severe widespread lesions, including multiorgan suppurative and hemorrhagic inflammation in the meninges, lung, liver, spleen, lymph nodes, and serosae of heart and intestines. The other isolates were primarily associated with meningitis, bronchopneumonia, and multifocal acute necrotizing hepatitis. The isolates differed from each other by 4–6 fragments when examined by pulsed-field gel electrophoresis, indicating they are possibly related. The isolates were susceptible to ampicillin, penicillin, and tiamulin. Resistance was noted to sulfadimethoxine (93%), oxytetracycline (86%), chlortetracycline (86%), neomycin (67%), tilmicosin (47%), clindamycin (47%), enrofloxacin (33%), gentamicin (13%), florfenicol (7%), trimethoprim–sulfamethoxazole (7%), and spectinomycin (53%). Multi-drug resistance (defined as resistance to at least 1 agent in 3 or more antimicrobial classes) was detected in 67% of the isolates. The pathology observations provide evidence that S. suismay be an important pathogen of bovine calves. S. suisis an agent that clinical bacteriology laboratories should consider when dealing with cases involving cattle.