الفهرس 
Introduction and aim of the workOnly 14 pages are availabe for public view
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Abstract
LAB are regarded as a major group of probiotic bacteria. They are used in different medical areas. Antibiotic resistant factors may be transferred from LAB species to other potentially pathogenic species. Available antibiotic therapies to treat infections are compromised by the evolving resistance.
This study was carried out to identify the dominant LAB that occur in
pharmaceutical and dairy products, study of the antibiogram of the isolated
strains against different antimicrobial agents, identify some antibiotic resistance genes and investigate the potential of transfer of these genes from LAB to some pathogenic bacteria.
In the present study, a total of 180 dairy and pharmaceutical samples were collected from different markets and pharmacies in Minia. Out of the 180 samples, 68 were cheese samples, 35 were yogurt samples, 33 were fresh milk samples, 30 were fermented milk samples, 10 were cream samples and 4 were pharmaceutical samples.
Two hundred and forty four LAB strains were recovered from the 180 samples. Out of 244 LAB isolates, 99 strains (40.6%) were cheese isolates, 71 (29.1 %) were yogurt isolates, 31 (12.7%) were fresh milk isolates, 29 (11.9%) were fermented milk isolates, 10 (4.1 %) were cream isolates and 4 (1.6%) were pharmaceutical products isolates.
Biochemical examination of these 244 isolates revealed that Lactobacillus strains represent 152 isolates (62.3 %), Lactococcus strains represent 27 isolates (11.1 %) and Streptococcus strains represent 65 isolates (26.6%) of total LAB.
Genotypic characterization of Lactobacillus isolates by using PCRRbased assay confirmed that Lactobacillus spp. represented 138 isolates instead of 152 isolates previously identified biochemically. The study revealed that
Lactobacillus was the most prevalent genus in dairy samples and the unique genus isolated from pharmaceutical samples.
One hundred and twenty three contaminant strains were recovered from the 180 dairy and pharmaceutical samples. Out of the 123 isolates, 48 were Staphylococcus spp. (39%), 16 were E. coli (13%), 8 were Salmonella spp. (6.5%) and 51 were mould and yeast (41.5%).
One hundred and forty one pathogenic strains were recovered from 120 clinical samples. Out of the 141 isolates, 30 were S. aureus (21.3%), 38 were Enterococcus spp. (27%), 6 were Listeria spp. (4.3%), 46 were E. coli (32.6%) and 21 were Salmonella spp. (14.9%).
The antibiogram of LAB isolates revealed that the isolated Lactobacillus strains showed low resistance to ampiciliin (1.4%), ampiciJIin/sulbactam (0.7%) and amoxycillin/clavulenic acid (2.9%). The LAB isolated showed moderate resistance to gentamicin (15.2%), streptomycin (17.4%), clindamycin and tetracycline (11.6% for each). Relatively high resistance was shown against vancomycin and nalidixic acid (40.6 and 33.3% respectively).
Lactococcus isolates showed relatively high resistance to erythromycin (22.2%) and tetracycline (29.6%), moderate resistance to most cephalosporins (11.1 %), gentamicin and norfloxacin (14.8% for both) and low resistance to amoxycillin (3.7%). They were sensitive to vancomycin and clindamycin. Streptococcus isolates showed moderate resistance to ciprofloxacin (9.2%), gentamicin, and tetracycline (12.3% of both) and low resistance to penicillin G, ampicillin, chloramphenicol (1.5% of each), amoxycillin, erythromycin and clindamycin (3.1 % for each). They were sensitive to vancomycin.
peR assays showed that out of the 36 LAB strains including all tetracycline and/or erythromycin resistant strains only 17 Lactobacillus, 7
was· Enter tetrac antib Lactc resist and a
erm(l paIrs techn
was ( only tet(M
to de phenl was ( extra erm(J mark
For selection of pathogenic recipient and LAB donor strains for mating experiments, susceptibility of the pathogenic isolates to tetracycline and erythromycin, penicillin G, naildixic acid, rifimpicin and streptomycin was tested by the disk diffusion method. Twelve strains (2 S. aureus, 3 Enterococcus spp., 3 Listeria spp., 2 E.coii and 2 Salmonella spp.) sensitive to tetracycline and/or erythromycin and resistant to one or more of the other antibiotics were selected as recipients. Eighteen LAB (11 Lactobacillus, 5 Lactococcus and 2 Streptococcus) strains harbor tet(M) and/or erm(B) resistance genes were selected as donors according to their resistance profiles and antibacterial activity against the selected pathogenic strains.
The ability of the 18 selected LAB strains to transfer tet(M) and/or rm(B) resistance genes to the 12 pathogenic strains representing 174 mating airs was examined through conjugation using plate and broth mating echniques. Of these mating pairs assessed by plate mating method, transfer was confirmed for 56 mating pairs. However, in case of broth mating transfer, nly 50 mating pairs was confirmed. In both mating techniques no transfer of et(M) or enn(B) genes was recorded between the donor LAB strains and S. ureus, E. coli or Salmonella spp. However, one or both genes were transferred
’om LAB to Enterococcus and Listeria spp. Transfer frequency was lower in ase of broth mating when compared with plate mating.
Transconjugants were confirmed by using antibiotic agar dilution test determine MICs. All selected transconjugants displayed the same resistant
henotype of their corresponding donors and recipients. Further confirmation as obtained by detecting tet(M) or erm(B) genes. PCR analysis of the DNA xtracted from transconjugant produced positive signals for the tet(M) and/or rm(B) genes as donor strains. The recipient strains were negative for these arkers.