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The in vitro antibacterial and antifungal activities of five different amino acid Schiff bases derived from the reaction of 2-hydroxy-1-naphthaldehyde with glycine, L-alanine L-phenylalanine, L-histidine, L-tryptophane and the manganese(III) complexes of these bases were investigated. Structures of the Schiff bases were proven by 1H-NMR. In vitro activities against some Gram-positive (Staphylococcus aureus and Bacillus polymyxa) and Gram-negative (Escherichia coli) bacteria and the fungus Candida albicans were determined. The antimicrobial activities tended to decrease with the increasing size of the amino acid residues.

Pseudomonas spp. are aerobic, gram-negative bacteria that are recognized as major food spoilage microorganisms. A total of 32 (22.9%) Pseudomonas spp. from 140 homemade white cheese samples collected from the open-air public bazaar were isolated and characterized. The aim of the present study was to investigate the biochemical characteristics, the production of extracellular enzymes, slime and β-lactamase, and antimicrobial susceptibility of Pseudomonas spp. isolated from cheeses. The identified isolates including Pseudomonas pseudoalcaligenes, Pseudomonas alcaligenes, Pseudomonas aeruginosa, Pseudomonas fluorescens biovar V, and P. pseudoalcaligenes ssp. citrulli were found to produce extracellular enzymes, respectively: protease and lecithinase production (100%), and lipase activity (85.7, 42.9, 100, and 100%, and nonlipolytic, respectively). The isolates did not produce slime and had no detectable β-lactamase activity. The antimicrobial susceptibility of the isolates was tested using the disk diffusion method. Pseudomonas spp. had the highest resistance to penicillin G (100%), then sulphamethoxazole/trimethoprim (28.1%). However, all Pseudomonas spp. isolates were 100% susceptible to ceftazidime, ciprofloxacin, amikacin, gentamicin, and imipenem. Multidrug-resistance patterns were not observed among these isolates. In this study, Pseudomonas spp., exhibiting spoilage features, were isolated mainly from cheeses. Isolation of this organism from processed milk highlights the need to improve the hygienic practices. All of the stages in the milk processing chain during manufacturing have to be under control to achieve the quality and safety of dairy products.

In this study, of 124 samples of ground beef and chicken meat, 101 (81.5%) were positive for Listeria spp. Listeria innocua (35.5%) and Listeria monocytogenes (26.6%) were the most frequently isolated species. All 33 (100%) L. monocytogenes isolates were positive for the virulence genes hlyA, actA, inlA, inlB, inlC, inlJ, prfA, plcA, and iap. Serotype 1/2a, which is one of the listeriosis‐associated serotypes, was the most predominant serotype (57.6%), followed by 1/2c (39.4%) and 3c (3%). In polymerase chain reaction‐restriction fragment length polymorphism (PCR‐RFLP) analysis of inlA for subtyping of the L. monocytogenes strains, the AluI and MluCI enzymes generated two different profiles. Almost all chicken strains were grouped in similar PCR‐RFLP profiles with both restriction enzymes. Most Listeria isolates were resistant to ceftriaxone (79.7%), fusidic acid (63.3%), and clindamycin (47.7%). Resistance to penicillin and ampicillin occurred in 1.6 and 17.9% of the isolates, respectively. The percentage of resistance to three or more agents was 48.1%. Practical application The presence of Listeria spp., especially L. monocytogenes, in foods is inevitable because of the ubiquitous nature of Listeria spp. Illnesses resulting from the consumption of contaminated food severely affect sensitive groups, especially pregnant women, unborn fetuses and newborns as a result of transmission across the placenta or during delivery. Immunosuppressed adults are also sensitive to infection. Listeria grows well at cold temperatures, so storage of contaminated food in the refrigerator can also increase the risk of infections for consumers. In particular, limiting the exposure of pregnant women and immunosuppressed patients to potential sources of Listeria such as raw and undercooked meats is recommended.

In the present study, a total of 225 retail meat products (poultry meat, ground beef, and beef samples) were tested for the prevalence of Salmonella. Of these, 50 (22.2%) were positive for Salmonella. Overall, the pathogen was detected in 22 (29.3%) samples of poultry meat (n = 75), 16 (21.3%) samples of ground beef (n = 75), and 12 (16%) samples of beef (n = 75). The most common isolate was Salmonella enterica serovar Typhimurium (9.8%), followed by S. bongori species (8.9%) and S. enterica subsp. diarizonae (3.5%). The Salmonella strains isolated were also examined for antimicrobial resistance patterns and production of β-lactamase enzyme. The resistance levels of the isolates against 14 different antimicrobial agents were tested by the disk diffusion method. None of the strains exhibited resistance to cefotaxime, ciprofloxacin, norfloxacin, or levofloxacin. However, the highest resistance rates in the meat isolates were 64% each for ampicillin and cephazolin and 56% for amoxicillin-clavulanic acid. A total of 62% of the 50 Salmonella strains were multiresistant to three or more antimicrobial agents. The exhibited multiple resistance to four or more antimicrobial drugs was 32%. Furthermore, none of the isolates had β-lactamase enzyme activity.

A total of 120 samples including 40 freshwaterfish(Oncorhynchus mykiss), 40 seawater fish (Sparus aurata) and 40 ground beef samples were examined for the presence of Staphylococcus aureus. The isolates were identified using biochemical tests and a PCR for the species-specific fragment (Sa442) and thermonuclease gene (nucA). The presence of staphylococcal enterotoxin genes (sea, seb, sec, sed and see), toxin genes (eta, etb, tsst), methicillin resistance gene (mecA) and some phenotypic virulence factors was also tested. Genotypic characterization of the isolates was analyzed by PCR-RFLP of the coa gene. Overall, 36 (30%) meat samples were contaminated with S. aureus. Of the 36 isolates, 3 (8.3%) were found to be positive for enterotoxin genes. Only 1 isolate (5.9%) from ground beef had the sea gene. In addition, 1 (12.5%) of the freshwater fish and 1 (9.1%) of the seawater fish carried both the sea and sed genes. The presence of seb, sec, see, eta, etb and tsst was not detected among the isolates of S. aureus. The amplified coa gene revealed five different clusters. Seven and six distinct RFLP patterns were obtained with AluI and HaeIII digestion, respectively. All isolates were found to be positive for slime, hemolytic and DNase activity while 41.7% of them were beta-lactamase positive. The presence of methicillin resistance was neither detected by PCR nor the disk diffusion method. A total of 94.4% of the isolates were resistant to at least one antimicrobial while 44.4% of them were resistant to at least two or more antimicrobials.

Slime production is considered to be a significant virulence factor for some strains of staphylococci (Christensen et al. 1982, Davenport et al. 1986, Kleeman et al. 1993, Ammendolia et al. 1999, Mack et al. 2000. In coagulase-negative staphylococci (CNS), a loosely bound exopolysaccharides layer (slime) has been found in addition to capsule, and it has been associated with sepsis, including intravenous-catheter-related bacteremia and other prosthetic device infections (Ishak et al. 1985, Diaz-Mitoma et al. 1987, Etienne et al. 1988, Rupp & Archer 1994.Similarly, Staphylococcus aureus strains have bacterial capsules, which are closely associated with the bacterial cell wall. These strains may also have an extracapsular and labile extrapolysaccharidic structure (Caputy & Costerton 1982). Formerly slime production of S. aureus has never been considered as a virulence factor. Recently, some investigators reported that slimeproducing S. aureus strains had a higher colonization capacity than its non-slime-producing variants did. Therefore, S. aureus slime may play a role in the establishment of infection (Baselga et al. 1993, Ammendolia et al. 1999.The importance of the role played by slime is further increased by its frequent association to reduced antibiotic susceptibility (Kloos & Bannerman 1994). The difficulty in eradicating a chronic infection associated with slime formation has been reported, and slime-producing bacteria has been shown to resist higher antibiotic concentrations than non-slime-producing bacteria (Gristina et al. 1987). Moreover, detection of resistance to oxacillin in staphylococci is important to guide the therapy and prevent the patient from being unnecessarily treated with vancomycin, which is an antimicrobial agent that presents therapeutic complications, high costs, and may lead to the selection of resistant mutants (Marshall et al. 1999).In this study, we wanted to evaluate the occurrence of slime production among clinical isolates of both CNS and S. aureus by comparing different methods. To assess the relationship between slime and pathogenicity, we investigated the susceptibility to certain antimicrobial agents, particularly oxacillin. MATERIALS AND METHODSBacterial isolates -One hundred eighty seven staphylococcal isolates, provided by hospital laboratory, were obtained from culture of several specimens; 117 isolated from throat and nasal swabs, 32 from wounds, 21 from urine, 9 from blood, and 8 from catheters. Table I shows distribution of species and clinical samples in the 187 staphylococcal strains. These staphylococcal strains, specifically 115 S. aureus strains, 34 S. epidermidis strains, eight S. chromogenes strains, eight S. hominis strains, three S. saprophyticus strains, one S. lugdunensis strain, one S. capitis strain, one S. haemolyticus strain, one S. warneri strain, one S. cohnii subsp. cohnii strain, isolated from diverse clinical sources were studied. Isolates were characterized at the species level by the API Staph system (Biomerieux, France) according to the instruc...

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