Pathogenicity and drug resistance of animal streptococci responsible for human infections

Peritonitis-related bacterial infections: a large-scale case-series retrospective study in 160 domestic animals (2009-2022)

Bacterial peritonitis infections comprise a life-threatening clinical condition in domestic animals that commonly lead to sepsis and high mortality. A set of bacterial pathogens have been identified in septic peritonitis in livestock and companion animals. Nonetheless, most descriptions are restricted to case reports or limited to only one domestic species, and a restrict number of comprehensive studies involving this infection has focused on a great number of domestic animals. Here, we retrospectively investigated selected epidemiological data (with an emphasis in outcome), clinical signs, bacteriological culturing, and in vitro antimicrobial susceptibility patterns of microorganisms isolated of peritoneal fluid from 160 domestic animals (2009-2023) compatible with septic peritonitis. Bacteria were isolated from 71.9% (115/160) of the peritoneal fluid from 75 dogs (75/115 = 65.2%), 22 cats (22/115 = 19.1%), 14 horses (14/115 = 12.2%), and 4 cattle (4/115 = 3.5%). Among animals with bacterial isolation, Escherichia coli (34/115 = 29.6%), alfa-hemolytic Streptococcus (12/115 = 10.4%), Staphylococcus aureus (8/115 = 6.9%), beta-hemolytic Streptococcus (7/115 = 6.1%), and Pasteurella multocida (6/115 = 5.2%) were predominant in pure culture, in addition to a miscellaneous of other bacteria isolated in minor frequency, e.g., Pseudomonas sp., Trueperella pyogenes, Klebsiella pneumoniae, and Salmonella sp. In general, in vitro susceptibility tests of isolates revealed that florfenicol, chloramphenicol, and amoxicillin/clavulanic acid showed moderate effectivity (≥ 60%). Conversely, most of isolates exhibited resistance mainly to trimethoprim/sulfamethoxazole, enrofloxacin, and penicillin (> 60%). Additionally, multidrug resistance was found in 42.6% (49/115) of the isolates. Data related to the outcome were available in 37.4% (43/115) of animals that had bacterial isolation and, from these, the mortality rate was 79.1% (34/43), with a significant association (p < 0.036) between mortality and septic peritonitis by gram-negative bacteria. Neoplasia (7/43 = 16.3%), pneumonia/pulmonary abscess (5/43 = 11.6%), hepatitis (5/43 = 11.6%), metritis/pyometra (4/43 = 9.3%), and gall bladder rupture (3/43 = 7%) represented the probable main sources of septic peritonitis. Anorexia (34/115 = 29.6%), emesis (29/115 = 25.2%), lethargy (26/115 = 22.6%), respiratory distress (25/115 = 21.7%), ascites (20/115 = 17.4%), and fever (19/115 = 16.5%) were the most frequent clinical signs among animals with bacterial isolation. A variety of bacteria were isolated in the peritoneal fluid of animals, with a predominance of Enterobacteriaceae, streptococci, and staphylococci, highlighting the opportunistic nature of the pathogens in septic peritonitis. High in vitro multidrug resistance of isolates and high mortality of animals reinforce the need for early diagnosis and therapy based on the in vitro antimicrobial profile of the pathogens involved in septic peritonitis. Our results contribute to the etiological characterization, clinical-epidemiological findings, and vigilance of multidrug-resistant bacteria in septic peritonitis among livestock and companion animals.

Identification and characterization of a novel peptide from rainbow trout (Oncorhynchus mykiss) with antimicrobial activity against Streptococcus iniae

The overuse and misuse of antibiotics has led to the emergence of antibiotic-resistant bacterial species which remain a challenge to treat therapeutically. Novel and efficacious drugs are desperately needed to combat pathogens. One method to facilitate these discoveries is the use of in silico methods. Computational biology has the power to scan large data sets and screen for potential molecules with antibacterial function. In the current study, an in silico approach was used to identify an antimicrobial peptide (AMP) derived from rainbow trout von Willebrand Factor. The AMP was tested against a panel of aquatic bacterial pathogens and was found to possess antibacterial activity against Streptococcus iniae (S. iniae). Since S. iniae is a zoonotic pathogen, this may be useful in other species as well. The peptide was non-hemolytic and non-cytotoxic at the concentrations tested in rainbow trout cells. Pre-treatment of rainbow trout cells with the peptide did not result in an upregulation of immune genes but stimulating the rainbow trout macrophage/monocyte-like cell line, RTS11, with heat-killed S. iniae, did result in a significant upregulation of the tumor necrosis factor alpha (tnfa) gene. In this study, a new AMP has been identified but its expression, synthesis and role in vivo remains unknown. Nevertheless, the findings presented improve our understanding of fish gill and macrophage responses towards this important zoonotic pathogen.