Sophorolipids: fermentation products of glucose and fatty acids, C18 (unsaturated), glycerol esters with yeast Candida Bombicola, partially hydrolysed

Toxicity to microorganisms

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

activated sludge respiration inhibition testing

Data waiving:

study scientifically not necessary / other information available

Justification for data waiving:

the study does not need to be conducted because the substance is found to be readily biodegradable and the applied test concentrations are in the range of concentrations that can be expected in the influent of a sewage treatment plant

other:

Reason / purpose for cross-reference:

reference to other study

Reference 2

Endpoint:

toxicity to microorganisms, other

Remarks:

antibacterial assays

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

unknown

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Qualifier:

no guideline followed

Principles of method if other than guideline:

Determination of minimal inhibitory concentration (MIC) with the agar dilution method.

GLP compliance:

not specified

Specific details on test material used for the study:

Sophorolipids were produced by fermentation using C. bombicola ATCC 22214 as the producing organism, and glucose + oleic acid as co-substrates.

Analytical monitoring:

no

Vehicle:

yes

Remarks:

Mueller Hinton Agar containing 3 % NaCl

Details on test solutions:

Stock solution: 10 mg/mL dissolved in 70 % ethanol

Test organisms (species):

other: Bacillus licheniformis, Bacillus pumilus, Pseudomonas luteola, Enterococcus faecium, Staphylococcus xylosus, Enterobacter cloacae, Bacillus mycoides, Aerococcus viridans, Staphylococcus cohnii, Enterobacter sakazakii, Staphylococcus equorum

Details on inoculum:

no details given

Test type:

other: agar dilution method

Water media type:

other: not applicable

Total exposure duration:

18 h

Test temperature:

37 °C

Nominal and measured concentrations:

17 different concentrations were tested (10.000 µg/mL, 5000 µg/mL, 2500 µg/mL, 1250 µg/mL, 625 µg/mL, 312.5 µg/mL, 156 µg/mL, 78 µg/mL, 39 µg/mL, 19.5 µg/mL, 9.76 µg/mL, 4.88 µg/mL, 2.44 µg/mL, 1.22 µg/mL, 0.61 µg/mL, 0.30 µg/mL, 0.15 µg/mL, 0.076 µg/mL) in Mueller Hinton Agar containing 3 % NaCl.

Details on test conditions:

Each bacterial suspension of test microorganisms was diluted in 0.85% saline to obtain 1.00E+07 CFU/mL. In addition, the mixed culture of the test isolates was prepared from these bacterial suspensions. Then, the test agent was separately dissolved in 70 % ethanol to a final concentration of 10.000 µg/mL. Series of two-fold dilutions of these test agents, ranging from 10.000 µg/mL to 0.076 µg/mL, were prepared in MHA containing 3 % NaCl.
One mL volumes of 17 different concentrations were separately added to 19 mL volumes of molten MHA. Next, these agar media were mixed thoroughly and poured into sterile petri dishes. One µL (an inoculum of 1.00E+04 CFU/spot) of diluted bacterial suspension of each test isolate and their mixed culture was separately transfered to agar plates containing 17 different concentrations. Control media without test item were used in all experiments.
Later, the plates were incubated at 37 °C for 18 h, and MICs of antibacterial agents against the test bacteria were determined. Inhibitory effects of 70 % ethanol on the test bacteria and mixed culture were also examined on MHA containing the same volume of ethanol concentrations as other agar media containing antimicrobial agents. All test bacteria and the mixed culture grew in the series of ethanol found in MHA. Dilutions of three antimicrobial agents were prepared according
to the method explained in the EUCAST Definitive Document E.Def3.1 (2000).

Reference substance (positive control):

yes

Key result

Duration:

18 h

Dose descriptor:

other: MIC, minimal inhibitory concentration

Effect conc.:

19.5 mg/L

Nominal / measured:

nominal

Conc. based on:

act. ingr.

Basis for effect:

growth inhibition

Remarks on result:

other: all strains except Enterobacter cloacae

Key result

Duration:

18 h

Dose descriptor:

other: MIC, minimal inhibitory concentration

Effect conc.:

9.76 mg/L

Nominal / measured:

nominal

Conc. based on:

act. ingr.

Basis for effect:

growth inhibition

Remarks on result:

other: only Enterobacter cloacae

Details on results:

MICs were determined as the lowest concentration of antibacterial inhibiting the visible growth of each microorganism on the agar media containing 3 % NaCl.
The MIC of the test item against all test bacteria and their mixed culture were found as 19.5 mg/L, except E. cloacae (9.76 mg/L).
The present study affirms that the test item inhibited the growth of Gram-positive endospore-forming bacteria, Gram-positive bacteria, Gram-negative bacteria and their mixed culture on MHA.

Results with reference substance (positive control):

not applicable

Reported statistics and error estimates:

not applicable

Validity criteria fulfilled:

not applicable

Remarks:

non-guideline study

Conclusions:

In this study, minimal inhibitory concentrations (MIC) of the test item against 12 test bacteria and their mixed culture were found as 19.5 mg/L, except E. cloacae (9.76 mg/L).

Executive summary:

In the publication by Solaiman et al. (2016), minimal inhibitory concentrations (MIC) were determined as the lowest concentration of antibacterial inhibiting the visible growth of 12 microorganisms on an agar media containing 3 % NaCl. The study did not follow a specific guideline. The study affirmed that the test item inhibited the growth of Gram-positive endospore-forming bacteria, Gram-positive bacteria, Gram-negative bacteria and their mixed culture on MHA.

The MIC of the test item after 18 h against all test bacteria and their mixed culture were found as 19.5 mg/L, except E. cloacae (9.76 mg/L).

Description of key information

The study does not need to be conducted because in a biodegradation study according to OECD 301F, GLP, reliability 1, no inhibitory effects of the test item were observed in the toxicity control.

According to Guidance R.10, the tested concentration at which toxicity to the inoculum can be ruled out with sufficient reliability can be considered as a NOEC for the toxicity to STP microorganisms. Thus, 100 mg/L are considered as the NOEC.

Key value for chemical safety assessment

EC10 or NOEC for microorganisms:

100 mg/L

Additional information

The study does not need to be conducted because in a biodegradation study according to OECD 301F, GLP, reliability 1, no inhibitory effects of the test item were observed in the toxicity control.

According to Guidance R.10, the tested concentration at which toxicity to the inoculum can be ruled out with sufficient reliability can be considered as a NOEC for the toxicity to STP microorganisms. Thus, 100 mg/L are considered as the NOEC.

In the publication by Solaiman et al. (2016), minimal inhibitory concentrations (MIC) were determined as the lowest concentration of antibacterial inhibiting the visible growth of 12 microorganisms on an agar media containing 3 % NaCl. The study did not follow a specific guideline. The study affirmed that the test item inhibited the growth of Gram-positive endospore-forming bacteria, Gram-positive bacteria, Gram-negative bacteria and their mixed culture on MHA. The MIC of the test item after 18 h against all test bacteria and their mixed culture were found as 19.5 mg/L, except E. cloacae (9.76 mg/L).

Though, test organisms and conditions are not in accordance to OECD guidelines, and the results from this study are thus considered not relevant as compared to the NOEC derived from the OECD 301F guideline study.