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The present study was designated to evaluate the antibacterial activities of aqueous and ethanol:water extracts from leaves, roots and stem bark of Psidium guajava L. The antibacterial activities of the extracts against bacteria were tested by using both microdilution assay. The aqueous extracts of P. guajava leaves, roots and stem bark were active against the gram-positive bacteria Staphylococcus aureus (MICs=500, 125 and 250 µg/ml, respectively) and Bacillus subtilis (MICs=500 µg/ml), and virtually inactive against the gram-negative bacteria Escherichia coli and Pseudomonas aeruginosa (MICs >1000 µg/ml). The ethanol:water extracts showed higher antimicrobial activity as compared to aqueous extracts. Based on this finding, the ethanol:water extract of P. guajava leaves was fractionated on silica gel column chromatography in a bioassay-guided fractionation affording flavonoid mixture, triterpenes (α-and β-amyrin) and sterol (β-sitosterol). Flavonoid mixture showed good activity on S. aureus with MIC of 25 µg/ml. β-sitosterol was inactive for all the bacteria tested.

Kasatkina, T.N.; Okhapkina, V.F. Use of Robolact and Linolac dry milk mixtures in the overall therapy of infants with acute intestinal infections. Vopr. Pitan., v. 4, p. 45 -47, 1980. 7 Kubo, M.; Odani, T.; Nakamura S. Pharmacological study on kefir -a fermented milk product in Caucasus. I. On tumor activity. Yakugaku Zsshi, v. 112, n. 7, p. 489 -495, 1992 AbstractExtracts of 13 Brazilian medicinal plants were screened for their antimicrobial activity against bacteria and yeast. Of these, 10 plant extracts showed varied levels of antibacterial activity. Five of the plant extracts presented compounds with Rf values similar to the antibacterial compounds visible on bioautogram. Of these, three plants belong to the Compositae family. This may mean that the same compounds are responsible for the antibacterial activity in these plants. Anticandidal activity was detected in 9 plant extracts. The results might explain the ethnobotanical use of the studied species for the treatment of various infectious diseases.O uso de plantas medicinais especialmente na América do Sul contribui significantemente para os cuidados básicos com a saúde. Para o tratamento de infecções comuns, muitas plantas são utilizadas no Brasil na forma de extrato bruto, infusões ou emplastos, sem nenhuma evidência científica de sua eficácia. Recentemente demonstramos a atividade antibacteriana do óleo essencial e do composto ativo purificado (eugenol) extraído do Ocimum gratissimum, tradicionalmente usado na medicina popular brasileira para o tratamento de várias doenças