As Godfred A Menezes suggests, you are likely to obtain positive results with garlic extracts, which I have experience of in combination with tetracycline, metronidazole, and amoxicillin for treating the multi species biofilms involved in periodontal disease. It is likely several mechanisms are involved. There are indications that the bacterial organisation of periodontal biofilm is affected by by the presence of gram-negative bacterial quorum sensing inhibitors in garlic extract. This reduces the ability of the biofilm to withstand antibacterial effects, and improves clinical outcomes.  

Hey dear,

I have seen positive results with antimicrobial activity of plant extract conjugated with nanoparticles. So i think they must show an enhance bactericidal effects if combined with antibiotics in comparison to antibiotics only.

Note:- But the condition is plant extract should not  effects the chemical side chains of antibiotics.

@Parth Nayak: Can you give me a copy or a link on this literature/s that suggests what you are telling me? Thank you.

As per what I  have experienced, plant extract has minimal effect on bacteria (whether it is Gram positive or negative).

Plant extracts show very small zone of inhibition against bacteria.

But therapeutically plant extracts could be immuno-modulators.

You have to be optimistic and try the synergistic action with antibiotics. 

Here it is.....

You can refer to these papers.

Do you think archaea  and/or the archaeal cell wall might be resistant to the effects of the silver nano-particles, or would they be likely to be sensitive?

I think it will probably depend on the species. Archaea are highly diverse with multiple types of cell walls. In a brief search I found a salt-loving Archaea that can actually be used to synthesize silver nanoparticles (http://www.ncbi.nlm.nih.gov/pubmed/23884709), as well as indirect evidence that nano silver particle release inhibits methanogenic archaea (http://www.ncbi.nlm.nih.gov/pubmed/22317796). Hope this helps.

Dear Ace,

Yes it is possible. Although it depends on the plant species under study and the Gram -ve bacteria too. You can find ample references for the presence of both Gram +ve and -ve bactericidal activities of various plant extracts (see the links). However, It is hard to learn that you want to use those extracts along with antibiotics! In that case you may deliberately add antibiotics against Gram -ve bacteria and mix plant extract for the desired result! 

I hope this would be of help.

http://www.sciencedirect.com/science/article/pii/037887419290025M

http://www.scielo.br/scielo.php?pid=S0074-02762002000700017&script=sci_arttext&tlng=pt

http://www.ncbi.nlm.nih.gov/pubmed/21208973

http://www.unboundmedicine.com/medline/citation/22568261/In_vitro_and_in_vivo_antibacterial_activity_of_acorn_herbal_extract_against_some_Gram_negative_and_Gram_positive_bacteria_

@Prasun Kumar: I want to test the synergistic effect of Cinnamomum mercadoi extract and antibiotics against S. aureus. Previous studies show that an increase in the level of antimicrobial activity occurred when the cinnamon extracts and antibiotics were combined.. Also, cinnamon oil showed the greatest antimicrobial effect again gram-negative bacteria.

Yes, you would get results if you try.

Convincing way is to demonstrate the decrease in MIC (minimum inhibitory concentration- you could try agar dilution method) when the antibiotic is tested along with the plant extract, such as cinnamon extract or garlic extract.

I agree. You need to test both substances separately in a uniform way and then in combination. This way, you can at least have an idea whether one substance inhibits the other or whether there is a synergistic or additive effect.

Hey S. L. Bräuer

I agree with Jason about the unusual features of Archaea Bacteria. Still according to me archeae bacteria will be sensitive to these plant-silver nanoparticle but at higher concentration of nanoparticles as compare to gram's +ve bacteria or gram's -ve bacteria.

well, it depends on the bacteria u r going to test.

since its not checked for the same against gr -ve bacteria it vl be little tough to answer.

As Godfred A Menezes suggests, you are likely to obtain positive results with garlic extracts, which I have experience of in combination with tetracycline, metronidazole, and amoxicillin for treating the multi species biofilms involved in periodontal disease. It is likely several mechanisms are involved. There are indications that the bacterial organisation of periodontal biofilm is affected by by the presence of gram-negative bacterial quorum sensing inhibitors in garlic extract. This reduces the ability of the biofilm to withstand antibacterial effects, and improves clinical outcomes.  

Azadiracta indica (neem plant) extract has broad antimicrobial activity against a broad range of pathogens include fungi bacteria and protist

Dear Sabia, I hope the below paper will be useful for you

Evidence Based Antibacterial Potentials of Medicinal Plants and Herbs Countering Bacterial Pathogens Especially in the Era of Emerging Drug Resistance: An Integrated Update

Kuldeep Dhama, Ruchi Tiwari, Sandip Chakraborty, Mani Saminathan, Amit Kumar, K. Karthik, Mohd. Yaqoob Wani, Amarpal , Shoor Vir Singh and Anu Rahal

International Journal of Pharmacology Volume 10, Number 1, 1-43, 2014

On can prescribe plant extracts, powders, pure compounds to control bacterial infection in combination to an antibiotic dose. Streptomycin, tetracycline, metronidazole, and amoxicillin  are added to natural product in a known concentration according to the condition.