Lactococcus spp. has emerged as a pathogen that is affecting global aquaculture, with L. garvieae, L. petauri, and L. formosensis causing piscine lactococcosis. While antimicrobials are commonly used to treat diseases in aquaculture, reports of antimicrobial resistance in fish isolates are increasing. However, little is known about the susceptibility patterns of Lactococcus spp. strains isolated from native fish species in Brazil. This study aimed to assess the antimicrobial susceptibility of these strains and establish a provisional epidemiological cutoff value for L. garvieae using the normalized resistance interpretation approach. A total of 47 isolates were tested: 17 L. garvieae, 24 L. petauri, and 6 L. formosensis. The isolates were classified as wild-type (WT) or non-wild-type (NWT) based on inhibition zone diameters. Isolates classified as NWT for three or more antimicrobial classes were considered multidrug-resistant, and the multiple antibiotic resistance (MAR) index was calculated. The results revealed heterogeneity in antimicrobial resistance profiles, with higher resistance to trimethoprim/sulfamethoxazole and norfloxacin. Resistance to other antimicrobials, including florfenicol and oxytetracycline (approved for use in Brazil), varied according to the bacterial species. Lactococcus petauri (87.5%) and L. formosensis (66.7%) showed the highest multidrug resistance, compared to L. garvieae (11.7%), along with higher MAR index values. These findings suggest that multidrug-resistant strains could pose future challenges in the production of native species, underscoring the need for ongoing monitoring of antimicrobial resistance and responsible use of antimicrobials in aquaculture.

Lactococcosis has emerged as an economically and ecologically significant disease in aquatic animals worldwide. This study employed multilocus sequence typing (MLST) to investigate the genetic diversity of Lactococcus spp. strains from Brazilian fish species and evaluate their phylogenetic relationships with global isolates to elucidate potential epidemiological connections involving multiple host species and distinct geographic regions. A total of 55 isolates from different laboratories had their DNA extracted, followed by the amplification and sequencing of the internal fragments of seven housekeeping genes (als, atpA, tuf, gapC, gyrB, rpoC and galP). Sequence types (STs) and clonal complexes (CCs) were defined. An unrooted neighbor-joining phylogenetic tree was generated using allele profiles from this study and those previously reported from other aquatic animal species. The isolates comprised 29 STs (11 previously reported, 18 novel ones), which were grouped into species-specific CCs: CC5 (L. formosensis); CC4, CC17, CC62 (L. garvieae); CC24, CC29, CC97 (L. petauri). Considerable genetic divergence was observed, with L. formosensis and L. garvieae forming heterogeneous populations, while L. petauri was more homogeneous. These findings describe the MLST structure of the sampled isolates and should be interpreted as hypothesis-generating rather than population-level estimates of genotype prevalence. Phylogenetics confirmed groupings within the CCs and revealed additional phylogenetic clustering patterns. In conclusion, the Brazilian Lactococcus spp. strains analyzed in this study constitute a genetically diverse population based on their STs. MLST and phylogenetic analysis demonstrated genetic relatedness between the L. garvieae and L. formosensis isolates from this study and those from other aquatic animal species. In contrast, all the STs identified for L. petauri in this study were unrelated to the MLST lineages responsible for outbreaks in Brazilian Nile tilapia (Oreochromis niloticus) and North American rainbow trout (Oncorhynchus mykiss). This suggests that piscine L. petauri populations in the Americas evolved from distinct ancestral origins.

Lactococcus spp. has emerged as a pathogen that is affecting global aquaculture, with L. garvieae, L. petauri, and L. formosensis causing piscine lactococcosis. While antimicrobials are commonly used to treat diseases in aquaculture, reports of antimicrobial resistance in fish isolates are increasing. However, little is known about the susceptibility patterns of Lactococcus spp. strains isolated from native fish species in Brazil. This study aimed to assess the antimicrobial susceptibility of these strains and establish a provisional epidemiological cut-off value for L. garvieae using the normalized resistance interpretation approach. A total of 47 isolates were tested: 17 L. garvieae, 24 L. petauri, and 6 L. formosensis. The isolates were classified as wild-type or non-wild-type (NWT) based on inhibition zone diameters. Isolates classified as NWT for three or more antimicrobial classes were considered multidrug-resistant, and the multiple antibiotic resistance (MAR) index was calculated. The results revealed heterogeneity in antimicrobial resistance profiles, with higher resistance to trimethoprim/sulfamethoxazole and norfloxacin. Resistance to other antimicrobials, including florfenicol and oxytetracycline (approved for use in Brazil), varied according to the bacterial species. Lactococcus petauri (87.5%) and L. formosensis (66.7%) showed the highest multidrug resistance, compared to L. garvieae (11.7%), along with higher MAR index values. These findings suggest that multidrug-resistant strains could pose future challenges in the production of native species, underscoring the need for ongoing monitoring of antimicrobial resistance and responsible use of antimicrobials in aquaculture.

This study evaluated the susceptibility of three Amazonian fish species, Arapaima gigas, Brycon amazonicus and Colossoma macroporum to Lactococcus spp., through experimental infection, and performed a detailed examination of the pathological damage. While lactococcosis-causing bacteria have already been isolated from these fish species, their pathogenic role remains unconfirmed. Lactococcus formosensis, L. garvieae and L. petauri strains were used to intracoelomically infect juvenile Amazonian fish. Following infection, the fish were monitored for 15 days to evaluate clinical signs and mortality. Fish that died or survived until the end of the experiment underwent bacteriological and histopathological examinations. Clinical signs were observed in the L. garvieae-challenged A. gigas, with one fish dying at five days post-infection. The remaining experimental animals, regardless of fish species, did not die. Bacteriological examination confirmed re-isolation of asymptomatic animals in the L. garvieae-challenged A. gigas and L. formosensis-challenged C. macropomum groups. No bacterial growth or histological alterations were observed in the control groups nor in the groups infected with L. petauri. Microscopic examination revealed L. garvieae-induced fibrinoid-necrotic hepatitis, lymphohistiocytic myocarditis and myositis in A. gigas, while L. formosensis caused lymphohistiocytic pericarditis in C. macropomum. These findings demonstrate that A. gigas and C. macropomum are susceptible to L. garvieae and L. formosensis, respectively, and that they can become bacterial carriers. The distinct histopathological profiles—particularly myositis (L. garvieae) and pericarditis (L. formosensis)—highlight species-specific manifestations of piscine lactococcosis in Amazonian fish species.

Introdução: Nos últimos anos, o vírus da dengue consolidou-se como um grave problema de saúde pública, sendo o arbovírus que mais frequentemente afeta os seres humanos. O vírus possui quatro sorotipos conhecidos (DENV-1 a DENV-4) e seu principal vetor é o mosquito Aedes aegypti, um inseto de hábitos diurnos e hematófagos, com preferência por ambientes urbanos e intradomiciliares. Atualmente, o controle do vetor baseia-se no uso de inseticidas químicos; no entanto, o uso contínuo desses produtos tem induzido resistência nas populações de mosquitos, além de causar danos à saúde humana e ao meio ambiente. Portanto, há uma necessidade crescente de buscar alternativas eficazes, ecologicamente corretas e de baixo impacto ambiental. Objetivo: Avaliar o potencial larvicida do óleo essencial de malvarisco (Plectranthus amboinicus (Lour.) Spreng) contra larvas do mosquito Aedes aegypti. Metodologia: O estudo envolveu, inicialmente, a extração do óleo essencial de malvarisco. Para os testes in vitro, utilizaram-se ovos selecionados de Aedes aegypti (fornecidos pelo laboratório de entomologia do INPA). Após a eclosão e o desenvolvimento larval até os estádios L1 a L4, as larvas foram distribuídas em placas de cultura de 6 poços, contendo 10 larvas por poço, em triplicata. O grupo experimental recebeu 5 mL de óleo essencial de malvarisco nas concentrações de 20, 40, 80, 100, 160, 180, 200 e 240 ppm. Água destilada e água com Tween 80 a 0,01% foram utilizadas como grupos controle. Resultados: Os testes confirmaram a eficácia do óleo essencial de malvarisco, que promoveu a mortalidade larval total em um período de até 2 horas. Conclusão: O óleo essencial de malvarisco mostrou-se um produto promissor e uma alternativa viável para o controle de larvas de Aedes aegypti. Apesar da escassez de literatura científica detalhada sobre as propriedades da planta — comumente restritas ao uso medicinal tradicional na Índia e na China para infecções respiratórias —, este trabalho destaca a importância de comprovar cientificamente sua eficácia também como larvicida.

Lactococcosis has emerged as an economically and ecologically significant disease in aquatic animals worldwide. This study employed multilocus sequence typing (MLST) to investigate the genetic diversity of Lactococcus spp. strains from Brazilian fish species and evaluate their phylogenetic relationships with global isolates to elucidate potential epidemiological connections involving multiple host species and distinct geographic regions. A total of 55 isolates had their DNA extracted, followed by the amplification and sequencing of the internal fragments of seven housekeeping genes (als, atpA, tuf, gapC, gyrB, rpoC and galP). Sequence types (STs) and clonal complexes (CCs) were defined. An unrooted neighbor-joining phylogenetic tree was generated using allele profiles from this study and those previously reported from other aquatic animal species. The isolates comprised 29 STs (11 previously reported, 18 novel ones), which were grouped into species-specific CCs: CC5 (L. formosensis); CC4, CC17, CC62 (L. garvieae); CC24, CC29, CC97 (L. petauri). Considerable genetic divergence was observed, with L. formosensis and L. garvieae forming heterogeneous populations, while L. petauri was more homogeneous. Phylogenetics confirmed groupings within the CCs and revealed significant genetic arrangements. In conclusion, the Brazilian Lactococcus spp. strains analyzed in this study constitute a genetically diverse population based on their STs. MLST and phylogenetic analysis demonstrated genetic relatedness between the L. garvieae and L. formosensis isolates from this study and those from other aquatic animal species. In contrast, all the STs identified for L. petauri in this study were unrelated to the MLST lineages responsible for outbreaks in Brazilian Nile tilapia (Oreochromis niloticus) and North American rainbow trout (Oncorhynchus mykiss). This suggests that piscine L. petauri populations in the Americas evolved from distinct ancestral origins.