Guava, Psidium guajava Linn., is an important medicinal plant in tropical
and sub-tropical regions. Previous studies of the in vitro and in vivo antibacterial
activities of Guava extracts have raised expectations for the potential of
developing medicinal compounds for human use. In addition, with increased
antibiotic-resistant bacteria and drug residues observed in pork, medicinal
plants, such as guava, might serve as an alternative source of medicinal compounds
for veterinary medicine. In the present study, crude extracts from the
leaves of P. guajava were obtained using three different extraction methods.
The extracts were tested for antibacterial activities against pathogenic bacteria
in pigs, namely, Streptococcus suis, Pasteurella multocida, Escherichia coli and
Salmonella typhimurium. The results showed that leaf extracts of P. guajava
in water and methanol potentially inhibited growth of all tested bacteria, while
extraction with acetone exhibited inhibition zones only in colonies of Streptococcus
suis and Pasteurella multocida. The water and methanol extracts of
guava leaves showed the same minimum inhibitory concentration (MIC) values
against Pasteurella multocida (0.156 mg/ml), Escherichia coli (5 mg/ml) and
Salmonella typhimurium (5 mg/ml), while the acetone extract showed the highest
antibacterial activity against Streptococcus suis and Pasteurella multocida
at a MIC of 0.312 mg/ml. In summary, this investigation provides preliminary
information for using guava extracts to control bacterial diseases in pigs. Given
this finding, the crude extracts of guava leaves show promise as an alternative
antibacterial source for use in veterinary medicine.