Tualang honey is readily available in Malaysia, but its quality and floral origin have yet to be determined and standardized. In contrast, manuka honey has been widely researched and its antibacterial potential is renowned worldwide. Honeys with proven antibacterial potency (UMF 10+ and above) have been recommended for wound care preferentially over honeys of low or unknown potency . Therefore, manuka honey with UMF 10+ was chosen as a comparison for this study of the antimicrobial activity of tualang honey.
In this study, we found that tualang honey has variable but broad-spectrum activities against many different species of wound and enteric bacteria. Its activity was comparable to that of manuka honey when tested against certain bacterial species. Lusby et al.  reported that honeys other than the commercially available antibacterial honeys (e.g., manuka honey) can have equivalent antibacterial activity against some bacteria, whereas Basson and Grobler  found no exceptionally high antimicrobial activity of honeys from indigenous wild flowers from South Africa.
We chose the broth dilution method for this study because it generates more quantitative and precise results compared to the agar well diffusion method. Moreover, the MIC values determined by the broth dilution method were lower (indicating higher activity) than those obtained using the agar well diffusion method, as diffusion rates of active constituents in agar may be slower than those in broth .
We also performed spectrophotometric assays using microtiter plates; it is a simple and rapid method, it has a greater sensitivity than the standard well and disc diffusion methods and the results are highly reproducible . Spectrophotometry can detect inhibitory levels below those recorded for well or disc diffusion assays . In our study, visual inspection might not have been accurate because impurities in the honeys (especially in tualang honey) might have caused disturbance and imprecision in the readings. Moreover, a medium containing bacterial growth not detectable by eye would have been described as clear by visual inspection, but the growth would have been detectable spectrophotometrically. These might have caused the wide variation seen in MIC values determined by visual inspection and by spectrophotometric measurement (e.g., our results for S. flexneri). Visual inspection also could not distinguish the percentage of growth in the turbid wells. MIC determination by visual inspection might also vary from person to person depending on the eye of the observer.
Having known that the presence of hydrogen peroxide in honeys contributes to its antibacterial activity, we screened the non-peroxide activity of both tualang and manuka honeys and found that the antibacterial activity persisted after the addition of catalase for both honeys, suggesting the presence of non-peroxide activity.
Analysis of the inhibition of bacterial growth caused by different honey concentrations revealed both differences and similarities in the pattern of inhibition exhibited by the 13 microorganisms tested in this study. Most bacteria showed similar growth inhibition patterns for both honeys tested, but some variations were detected. The observed differences might reflect how each type of bacteria reacts to honey treatment.
Tualang and manuka honeys showed good antimicrobial activity against S. maltophilia; both honeys yielded the lowest visual MIC of 8.75% (w/v) against this microorganism. This organism is an aerobic, non-fermentative, Gram-negative bacterium that causes uncommon but difficult to treat infections in immunocompetent individuals, such as pneumonia, urinary tract infection and blood stream infection. It can lead to nosocomial infections and latent pulmonary infections in immunocompromised patients . S. maltophilia often is difficult to eradicate because it is naturally resistant to many broad-spectrum antibiotics, including all carbapenems; moreover, increasing resistance has been reported for co-trimoxazole and ticarcillin . Thus, the use of tualang honey to treat S. maltophilia infections should be further investigated.
When compared to manuka honey, tualang honey exhibited better antimicrobial activity against A. baumannii. A. baumannii is a pathogenic, aerobic, Gram-negative bacillus and most of its isolates are inherently multi-drug resistant . A. baumannii is an opportunistic pathogen that usually infects immunocompromised individuals through open wounds, catheters and breathing tubes. Multi-drug resistant A. baumannii has emerged as a major cause of nosocomial infection, with resistance against its first line of treatment (i.e., carbapenems such as imipenem) . Therefore, sterilized tualang honey has the potential to be used as an alternative agent for wound infection caused by this bacterium. However, this approach needs to be further studied.
Haffejee and Moosa  discovered that honey is effective in treating bacterial gastroenteritis in infants. Honey was reported to be effective when used as a substitute for glucose in oral rehydration and its antibacterial activity shortened the duration of bacterial diarrhoea. In our study, the growth of bacterial species that cause gastric infections, such as S. typhi, S. flexneri and E. coli, were inhibited by tualang honey at concentrations between 15% and 22.5% (w/v). Previous preliminary study on tualang honey also reported that it has antibacterial activity against E. coli, S. typhi and S. pyogenes . Thus, when taken orally in its pure undiluted form, tualang honey may help speed up recovery from such infections.
The spectrophotometric data obtained in this study revealed that tualang honey had slightly better inhibitory activity than manuka honey against MRSA. This activity may turn out to be quite beneficial, as there has been a discernible increase in difficult-to-treat skin and underlying tissue infections associated with Gram-positive bacteria like MRSA. Thus, more effective treatment is needed to treat MRSA .
The MBC values obtained in this study indicated the minimum concentration of honey needed to kill 99.9% of bacteria. However, the indications for determination of bactericidal activity are rare and are usually meant for serious infections, such as in immunocompromised patients or infections at a site that is difficult to be reached with available antibiotics. In this study, the MBC of tualang honey was remarkable against one Gram-positive bacterium (S. pyogenes) and three Gram-negative bacteria (S. maltophilia, S. typhi and P. aeruginosa).
Most deaths in severely burn-injured patients are due to burn wound sepsis or complications due to inhalation injury. Currently, the emerging antimicrobial resistance trends in burn wound bacterial pathogens are a serious challenge . Thus, honey with effective antimicrobial properties against antibiotic-resistant organisms such as MRSA and multiple-resistant Gram-negative rods such as Pseudomonas aeruginosa, Acinetobacter spp. and members of the family Enterobacteriaceae, which have been associated with infections of burn wounds and sites of major thermal injury and in nosocomial infections, is much anticipated [11, 29].