Acurácia diagnóstica de meio cromogênico para detecção de mastite subclínica causada por Streptococcus agalactiae
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Data
2022-09-02
Autores
Fonseca, Fausto Ribeiro
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Editor
Universidade Estadual Paulista (Unesp)
Resumo
O objetivo deste estudo foi avaliar a acurácia diagnóstica do meio cromogênico Accumast Plus™ para identificação de mastite causada por Streptococcus agalactiae em amostras de leite bovino de quartos mamários e compostas. Cinco rebanhos foram visitados uma única vez para colheita de leite de todos os quartos mamários (N=467) das vacas (N=118) em lactação. As amostras de quarto foram cultivadas simultaneamente em placas Accumast Plus™ e ágar sangue, das quais os isolados foram enviados para identificação por MALDI-TOF MS (padrão ouro). Amostras compostas foram preparadas e cultivadas nas placas Accumast Plus™. Foram adotados dois pontos de corte: I) crescimento de ≥ 1 colônia azul (definição do fabricante) e II) crescimento ≥ 1 colônia azul, branca ou lilás. A prevalência de S. agalactiae nas amostras de quarto foi de 18,44% (83/450). A concordância entre os observadores foi quase perfeita (Kappa = 0,97 e 0,95) para o diagnóstico de S. agalactiae e identificação das cores das colônias. A acurácia da cultura de amostras de quarto na placa Accumast Plus™ (ponto de corte I) foi: sensibilidade (SE) = 60,02%, especificidade (ES) = 97,97%, valor preditivo positivo (VPP) = 85,88% e valor preditivo negativo (VPN) = 92,04%. No ponto de corte II, os parâmetros foram: SE = 73,50%, ES = 97,97%, VPP = 87,89% e VPN = 93,83%. Para as amostras compostas, não houve perdas significantes de acurácia. A SE observada resultou em alta probabilidade de resultados falso negativos (20,00 – 39,98%), o que poderia aumentar o risco de disseminação do agente nos rebanhos.
The objective of this study was to assess the accuracy of Accumast Plus™ to identify mastitis caused by Streptococcus agalactiae in quarter and composite milk samples. Five herds were visited once to collect milk from all mammary quarters (N=467) of the lactating cows (N=118). Quarter samples were cultured simultaneously on Accumast Plus™ and blood agar, from which the isolates were diagnosed by MALDI-TOF MS (gold standard). Composite samples were prepared and plated on Accumast Plus™. Two cut-off points were adopted: I) growth of ≥ 1 blue colony (manufacturer's definition) and II) growth of ≥ 1 blue, white, or purple colony. The quarter-level prevalence of S. agalactiae was 18.44% (83/450). The agreement between observers was almost perfect (Kappa = 0.97 and 0.95) for diagnosis of S. agalactiae (yes or no) and identification of colony colors. The accuracy of culturing quarter milk samples on Accumast Plus™ (cut-off point I) was: sensitivity (SE) = 60.02%, specificity (ES) = 97.97%, positive predictive value (PPV) = 85.88 % and negative predictive value (VPN) = 92.04%. At cut-off point II, the parameters were: SE = 73.50%, ES = 97.97%, PPV = 87.89% and NPV = 93.83%. For the composite samples, there was no significant loss of accuracy. The observed SE resulted in a high probability of false-negative results (20.00 - 39.98%), which could increase the risk of spreading the pathogen within the herd.
The objective of this study was to assess the accuracy of Accumast Plus™ to identify mastitis caused by Streptococcus agalactiae in quarter and composite milk samples. Five herds were visited once to collect milk from all mammary quarters (N=467) of the lactating cows (N=118). Quarter samples were cultured simultaneously on Accumast Plus™ and blood agar, from which the isolates were diagnosed by MALDI-TOF MS (gold standard). Composite samples were prepared and plated on Accumast Plus™. Two cut-off points were adopted: I) growth of ≥ 1 blue colony (manufacturer's definition) and II) growth of ≥ 1 blue, white, or purple colony. The quarter-level prevalence of S. agalactiae was 18.44% (83/450). The agreement between observers was almost perfect (Kappa = 0.97 and 0.95) for diagnosis of S. agalactiae (yes or no) and identification of colony colors. The accuracy of culturing quarter milk samples on Accumast Plus™ (cut-off point I) was: sensitivity (SE) = 60.02%, specificity (ES) = 97.97%, positive predictive value (PPV) = 85.88 % and negative predictive value (VPN) = 92.04%. At cut-off point II, the parameters were: SE = 73.50%, ES = 97.97%, PPV = 87.89% and NPV = 93.83%. For the composite samples, there was no significant loss of accuracy. The observed SE resulted in a high probability of false-negative results (20.00 - 39.98%), which could increase the risk of spreading the pathogen within the herd.
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Palavras-chave
Diagnóstico microbiológico, Streptococcus, Mastite, Mastite bovina, Cultura na fazenda, Accumast Plus™, Estreptococos, Bovine mastitis, On-farm culture, Streptococci