Antibiogram and conjugative transferability of the resistance determinants of lactic acid bacteria to Escherichia coli

Date of Publication


Document Type

Bachelor's Thesis

Degree Name

Bachelor of Science in Biology

Subject Categories



College of Science




The grounds for granting lactic acid bacteria (LAB) as generally regarded as safe have solely relied on their history of long use. Current knowledge suggests that this group of bacteria, when consumed, usually commits beneficial effects to the host organism, and thus, they are purposely alive added to food products or other supplements. Drug resistant lactic acid bacteria also exist, and are documented to transfer resistance determinants to other bacteria. This in turn is considerably alarming because the addition of lactic acid bacteria in food amplifies the probabilities of the bacterial flora in the gastro-intestinal tract to acquire the antibiotic resistance determinants. The antibiotic resistances and the transferability of the resistance determinants of 13 strains of lactic acid bacteria belonging to the genera Lactobacillus and Enterococcus that were isolated from commercial dairy food and locally produced fermented food products were examined in this study. The study was aimed to determine the susceptibility of the LABs to ampicillin, gentamicin, and, streptomycin. It also aimed to determine the transferability of the resistance through conjugation to Escherichia coli SF800. To achieve this, minimum inhibitory concentrations of the antibiotics for the LABs were determined using the microdilution method. All LABs were resistant to at least one antibiotic tested, with three (RF6, MU8, and MU3) and two (MU7, and MU2) Lactobacillus plantarum isolates being resistant to two (2) and three (3) antibiotic, respectively. In addition, the antibiotic resistant LABs were conjugated with Escherichia coli SF800 on brain heart infusion agar plates. Acquisition of drug resistance was determined by selecting for the transconjugants in Mac Conkey agar plates with antibiotics. Absence of bacterial growth in the selective plates concludes that resistance genes were not conjugatively transferred. It is suggested that further studies should be done on drug resistant LABs because they have a potential to act as vectors of the widening range of antibiotic resistance determinants. It is recommended to implement a rule to govern the quality of the lactic acid bacteria used in food products before they are added into edible products.

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Archives, The Learning Commons, 12F, Henry Sy Sr. Hall


Lactic acid bacteria; Escherichia coli

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