Digital Repository for Faculty of Veterinary Medicine

Algal alkaloids are widely used for their pharmacological properties as antimicrobial agents. This study determined the antibacterial activities of algal alkaloid-rich extracts against isolates of multidrug-resistant Staphylococcus aureus and enterohaemorrhagic Escherichia coli (EHEC) O157, as well as the probable mode of action underlying their antibacterial effect. The total alkaloids were extracted from two Libyan brown algae, namely Sargassum hornschuchii and Cystoseira compressa and tested against six different isolates from the bacteria mentioned above using the agar-well diffusion method, and their mode of action on isolates was evaluated by several bacterial physiological indicators, including intracellular potassium ion efflux and nucleotide leakage. Also, the extracts' hemolytic activity was assessed as an indicator of their cytotoxicity on red blood cells. Although not to the same extent, both alkaloid extracts presented antibacterial activities against all tested isolates with no evidence of bacterial regrowth. The alkaloid extract from S. hornschuchii exerted the best effect on bacteria growth with minimum inhibitory concentration values ranging between 125 and 500 mg/mL. The results showed that the alkaloid extracts significantly induced a distinct release of nucleotide and potassium ions out of the cell membrane, indicating that they cause a change in the fluidity or permeability or both of the cell membrane. Moreover, the results revealed that there were very low cytotoxic effects. Therefore, algal alkaloids may contribute to the development of potential antibacterial agents in the future.
Salah M. Azwai(1-2021)

Background and Aim: Foodborne illnesses are a serious challenge to human health and the economic sector. For example, salmonellosis remains a burden in developed and developing nations. Rapid and reliable molecular methods to identify Salmonella strains are essential for minimizing human infection. This study aimed to identify Salmonella spp. in raw milk and dairy products using conventional and molecular techniques and to test the antibiotic susceptibility of the isolated strains. Materials and Methods: One hundred and thirty-one milk and dairy product samples were randomly collected from different localities in Libya. Samples were examined for the presence of Salmonella by conventional culture techniques, including cultivation in Rappaport-Vassiliadis broth and streaking on xylose lysine deoxycholate agar. Identification also used polymerase chain reaction and partial sequencing of 16S rDNA. Twenty-four antibiotics were used for the examination of antimicrobial resistance of Salmonella spp. isolates with the agar disk diffusion method (Kirby–Bauer technique). Multi-antibiotic resistance index and antibiotic resistance index (ARI)for Salmonella enterica isolates were calculated. Results: Twenty-one of 131 samples (16%) were positive for Salmonella spp. recovered from 9 (16%), 2 (11%), 4 (22.2%), and 6 (46%) samples of raw cow milk, fermented raw milk, and fresh locally made soft cheeses, Maasora and Ricotta), respectively. Samples of ice cream, milk powder, and infant formula showed no Salmonella spp. contamination. Only 9 of 21 (42.8%) isolates were confirmed as S. enterica by partial sequence 16S rDNA analysis. All isolates were resistant to amoxycillin, bacitracin, penicillin G, lincomycin, vancomycin, clindamycin,
Salah M. Azwai(5-2022)

The study presents results obtained by examination of cloacal swabs from poultry for the presence of verotoxigenic stains of E.coli O157:H7. Twenty samples (9.2%0 of 216 samples examined were positive for E.coli O157. Out of the twenty E.coli O157, 19 strains were positive for the production of both verotoxins (V1 and V2). However, none of them was positive for the presence of H7 antigen.
Hesham Taher Naas(1-2022)

Abstract This study aimed to evaluate the antibacterial activity of flavonoids extracted from two Libyan brown algae namely Cystoseira compressa and Padina pavonica using microwave-assisted extraction method against pathogenic bacteria isolated from meat, meat products, milk and dairy products (Staphylococcus aureus subsp. aureus (5 isolates), Bacillus cereus (3 isolates), Bacillus pumilus (1 isolate), Salmonella enterica subsp. enteric (4 isolates) and Enterohaemorrhagic Escherichia coli O157 (EHEC O157) (4 isolates)). All of these isolates were muti-drug resistant with high MAR index. The results showed that C. compressa extract exhibited better and stronger antibacterial activities against the seventeen tested isolates with inhibition zones diameter ranged from 14 - 22 mm compared to P. pavonica extract which showed positive effect against 9 isolates with low inhibition zone ranged from 11 - 16.5 mm. Flavonoids extracted from C. compressa also displayed the best spectrum of bactericidal effect with a ratio MBC/MIC ≤ 4 obtained on all susceptible tested bacterial strains. Flavonoids and proanthocyanidins significantly contributed to the antibacterial properties. The mode of action of these active extracts is under investigation.
Hesham Taher Naas(1-2017)

Abstract Background: Whole muscle meat, meat products, and seafood contain different nutrients in adequate quantity providing a better environment for presence and replication of different microorganisms. There are underreported and inaccurate estimations of foodborne diseases due to the lack of effective surveillance systems in Libya. Aim: To determine the extent of microbiological contamination of whole muscle meat, meat products, and seafood. Methods: A total number of 731 samples of retail meat were collected from different stores in four cities in Libya. Samples were analyzed for aerobic plate count and subjected to microbiological enumeration and isolation techniques, followed by molecular identification by PCR and partial sequencing of 16S rDNA. Results: The results showed contamination of samples with enteric and spoilage bacteria. Fifteen genera of spoilage bacteria yielded 149 isolates which were detected and identified by PCR and partial sequencing of 16S rDNA as: Proteus spp., Provedencia spp., Raouttella ornithinolytical, Citrobacter spp., Enterobacter spp., Morganella morgi, Shewanella algea, Rhodobacter capsulatus, Listonella pelagia, Kluyvera spp., Pectobacterium spp., Brenneria spp., Klebsiella spp., Acintobacter radioresistens, and Pantoea spp. While for pathogenic bacteria, 143 isolates distributed among nine genera were identified by PCR and partial sequencing of 16S rDNA as: Bacillus spp., Escherichia spp., Shigella spp., Enterococci spp., Cronobacter spp., Staphylococci spp., Salmonella spp., Aeromonas spp., and Vibrio spp.. Many isolated bacteria are zoonotic bacteria with high importance for public health. Conclusion: Excessive handling and processing of meat and meat products seems to be one of the poorest microbiological qualities. These findings ought to be helpful in risk assessments and quality assurance of meat in order to improve food safety.
Hesham Taher Naas(9-2020)

Aim: The aim of this work was to isolate and molecularly identify enterohemorrhagic Escherichia coli (EHEC) O157 in milk and dairy products in Libya, in addition; to clear the accuracy of cultural and biochemical identification as compared with molecular identification by partial sequencing of 16S rDNA for the existing isolates. Materials and Methods: A total of 108 samples of raw milk (cow, she-camel, and goat) and locally made dairy products (fermented cow’s milk, Maasora, Ricotta and ice cream) were collected from some regions (Janzour, Tripoli, Kremiya, Tajoura and Tobruk) in Libya. Samples were subjected to microbiological analysis for isolation of E. coli that was detected by conventional cultural and molecular method using polymerase chain reaction and partial sequencing of 16S rDNA. Results: Out of 108 samples, only 27 isolates were found to be EHEC O157 based on their cultural characteristics (Tellurite- Cefixime-Sorbitol MacConkey) that include 3 isolates from cow’s milk (11%), 3 isolates from she-camel’s milk (11%), two isolates from goat’s milk (7.4%) and 7 isolates from fermented raw milk samples (26%), isolates from fresh locally made soft cheeses (Maasora and Ricotta) were 9 (33%) and 3 (11%), respectively, while none of the ice cream samples revealed any growth. However, out of these 27 isolates, only 11 were confirmed to be E. coli by partial sequencing of 16S rDNA and E. coli O157 Latex agglutination test. Phylogenetic analysis revealed that majority of local E. coli isolates were related to E. coli O157:H7 FRIK944 strain. Conclusion: These results can be used for further studies on EHEC O157 as an emerging foodborne pathogen and its role in human infection in Libya.
Hesham Taher Naas(11-2016)

Seventy five random samples were collected (25 raw milk, 50 local different made soft cheeses) from different supermarkets in Tripoli- Libya. The Objectives of this study were: (i)- to clear the incidence rate and count of coliforms as an indicator microorganisms for fecal contamination in raw milk and locally made soft cheese samples manufactured by traditional methods and (ii)- to make comparison between the most famous two conventional methods used for counting of such group of microorganisms. Coliforms were recovered from all the raw milk samples using the two methods (most probable number using liquid lauryl sulphate broth and sold plating method using violet red bile agar). The mean count for the former media was 28x106 while for the later one was 15x106 cfu/ml. For cheese samples (locally made Ricotta and Maasora), positive samples were 78% (39 samples) using MPN method, while 76% (38 samples) using sold plating media VRBA. The mean coliform count for positive samples using MPN was 18x107 cfu/g, while for VRBA plates the mean count for positive samples was 21x106 cfu/g. all counts were higher using MPN than VRBA for the same sample in both raw milk and cheese samples, although, clear difference in count between the two methods was recorded in cheese than that in raw milk, conditions that may affect the count in both raw milk and cheese were discussed. Factors that may limit
Hesham Taher Naas(1-2007)

The objective of this study was to evaluate the effect of nisin in combination with different types of packaging on the survival of Listeria monocytogenes in ready-to-eat low-fat turkey bologna. Bologna was inoculated with L. monocytogenes exposed to 1 of 6 treatments: 3 packaging treatments (100% CO2, air, vacuum), each with and without nisin. Bologna was refrigerated and sampled 9 times over 42 d. Nisin reduced initial L. monocytogenes populations by 1.5 to 2 log cycles and 100% CO2 packaging prevented outgrowth throughout 42 d of storage, whereas non-CO2 packaging displayed a 2-log increase in population during storage. Nisin (500 IU/mL) combined with 100% CO2 was effective in reducing Listeria and preventing outgrowth on bologna over 42 d of refrigerated storage.
Hesham Taher Naas(3-2013)