Acurácia diagnóstica de meio cromogênico para detecção de infecção intramamária causada por Streptococcus agalactiae
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Data
2022-12-20
Autores
Juliano, Lára Cristina Bastos
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Editor
Universidade Estadual Paulista (Unesp)
Resumo
O objetivo do presente estudo foi avaliar a acurácia de um meio cromogênico experimental (OnFarm, Piracicaba, SP, Brasil) para a detecção de infecção intramamária (IIM) causada por Streptococcus agalactiae utilizando amostras de leite de quarto e compostas. Quatro rebanhos em MG foram visitados uma única vez para colher amostras de leite de quartos mamários de todas as vacas em lactação (N = 117). Amostras de quarto e compostas (produzidas no laboratório) foram cultivadas no meio cromogênico. Simultaneamente, as amostras de quarto foram semeadas em ágar sangue e os isolados cocos catalase-negativa foram enviados para identificação por Espectrometria de Massas de Tempo de Voo de Ionização/dessorção a laser assistida por matriz (MALDI-TOF MS). Foram utilizados três pontos de corte para estimar os parâmetros de acurácia diagnóstica do meio cromogênico: PC1) isolamento de ≥ 1 colônia rosa, PC2) ≥ 1 colônia rosa ou lilás e PC3) ≥ 1 colônia rosa, lilás ou roxa. Considerando os três pontos de corte estudados, a acurácia diagnóstica utilizando amostras de quarto foi: sensibilidade (SE): 44,35-95,08%; especificidade (ES): 97,81-96,30%; valor preditivo positivo (VPP): 80,68-83,60% e valor preditivo negativo (VPN): 87,62-98,87%. Para as amostras compostas, a acurácia foi: SE: 54,05-89,19%; VPP: 90,90-94,29%; VPN: 82,11-95,12%. A ES (97,50%) se manteve a mesma nos três pontos de corte. O ponto de corte indicado pelo fabricante (PC1) resultou em baixa SE e alta proporção de resultados falso-negativos (FN). No entanto houve melhora da acurácia quando PC2 e PC3 foram utilizados.
The objective was to evaluate the accuracy of an experimental chromogenic medium (OnFarm, Piracicaba, SP, Brazil) for the detection of intramammary infection (IMI) caused by Streptococcus agalactiae using quarter and composite milk samples. Four herds in MG were visited once to collect milk samples from the mammary quarters of all lactating cows (N = 117). Quarter and composite samples (produced in the laboratory) were plated on the chromogenic medium. Simultaneously, quarter samples were plated on blood agar and the catalase-negative cocci isolates were subjected for identification by Matrix-Assisted Laser Desorption Ionization Time of Flight Mass Spectrometry (MALDI-TOF MS). Three thresholds were used to estimate the diagnostic accuracy parameters of the chromogenic medium: T1) growth of ≥ 1 pink colony, T2) ≥ 1 pink or lilac colony, and T3) ≥ 1 pink, lilac, or purple colony. Considering the three thresholds studied, the diagnostic accuracy using quarter samples was: sensitivity (SE): 44.35- 95.08%; specificity (SP): 97.81-96.30%; positive predictive value (PPV): 80.68-83.60% and negative predictive value (NPV): 87.62-98.87%. For composite samples, the accuracy was: SE: 54.05-89.19%; PPV: 90.90-94.29%; NPV: 82.11-95.12%. The SP (97.50%) remained the same at the three thresholds. The threshold indicated by the manufacturer (T1) resulted in a low SE and a high proportion of false-negative (FN) results. However, there was an improvement in accuracy when T2 and T3 were used.
The objective was to evaluate the accuracy of an experimental chromogenic medium (OnFarm, Piracicaba, SP, Brazil) for the detection of intramammary infection (IMI) caused by Streptococcus agalactiae using quarter and composite milk samples. Four herds in MG were visited once to collect milk samples from the mammary quarters of all lactating cows (N = 117). Quarter and composite samples (produced in the laboratory) were plated on the chromogenic medium. Simultaneously, quarter samples were plated on blood agar and the catalase-negative cocci isolates were subjected for identification by Matrix-Assisted Laser Desorption Ionization Time of Flight Mass Spectrometry (MALDI-TOF MS). Three thresholds were used to estimate the diagnostic accuracy parameters of the chromogenic medium: T1) growth of ≥ 1 pink colony, T2) ≥ 1 pink or lilac colony, and T3) ≥ 1 pink, lilac, or purple colony. Considering the three thresholds studied, the diagnostic accuracy using quarter samples was: sensitivity (SE): 44.35- 95.08%; specificity (SP): 97.81-96.30%; positive predictive value (PPV): 80.68-83.60% and negative predictive value (NPV): 87.62-98.87%. For composite samples, the accuracy was: SE: 54.05-89.19%; PPV: 90.90-94.29%; NPV: 82.11-95.12%. The SP (97.50%) remained the same at the three thresholds. The threshold indicated by the manufacturer (T1) resulted in a low SE and a high proportion of false-negative (FN) results. However, there was an improvement in accuracy when T2 and T3 were used.
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Palavras-chave
Mastite contagiosa, Placa cromogênica, Cultura na fazenda, Estreptococos, Epidemiologia, Contagious mastitis, Chromogenic plate, On farm culture, Streptococci, Epidemiology