Iranian Journal of Microbiology
Volume:3 Issue: 1, Mar 2011

There is increasing emergence of multidrug resistant Pseudomonas aeruginosa (MDRPA) strains and drug resistance is positively-correlated with biofilm-forming ability. Since about 10% of P. aeruginosa genome is controlled by quorum sensing (QS), alteration in its antibiotic susceptibility by targeting QS was the focus of the present study. One day biofilms of PAO1 and three urinary tract infection MDRPA isolates (PA2, PA8 and PA18) were formed in 96-well microtiter plate. Biofilms were exposed to concentration gradient of ciprofloxacin and gentamicin to obtain Minimum Biofilm Eradication Concentration (MBEC) by direct enumeration method. Susceptibility of 24 h biofilms was evaluated by treatment with ciprofloxacin and gentamicin per se and in combination with lactonase. The effect was also examined on 72 h biofilms by Scanning Electron Microscopy. Lactonase treatment did not have any effect on growth of the selected strains but 73.42, 69.1, 77.34 and 72.5% reduction of biofilm was observed after lactonase (1 unit) treatment, respectively. Antibiotics in combination with lactonase(0.3 units) resulted in an increased susceptibility of the biofilm forms by > 3.3, 4, 5 and 1.5 folds of MBEC, for ciprofloxacin and > 6.67, 12.5, 6 and > 2.5 folds, for gentamicin respectively, which could be due to the disruption of biofilm by lactonasetreatment as shown by scanning electron microscopy. Also there was significant reduction (p < 0.001) in virulence factor production by the strains. Lactonase treatment increased antibiotic susceptibility of the biofilms of MDRPA isolates underscoring the potential of quorum quenching in antimicrobial therapeutics.

Shigella, causative of bacillary dysentery, has two colony forms. The loss of large virulence plasmid from virulent Shigella sonnei form I, during cell storage and subculturing, lead to avirulent form II. Environmental factors, e.g. culture media composition, could affect the conversion of the bacterial forms. In this study, some components, i.e., B-complex vitamins, nicotinic acid and riboflavin, were added to the bacterial culture medium and their influence on colony conversion were examined. The findings revealed that colony conversion is temperature independent and growth on the SS agar did not stabilize the bacterium in form I. Also, the findings showed that colonies on the minimal media supplemented with nicotinic acid and riboflavin, were stable in form I. In addition, according to the findings, the active OxyR has potential binding sites upstream of two genes involved in the replication of large virulence plasmid and expression of O-polysaccharide, i.e., repB and wbgT, respectively. Based on the findings of the present study, it is possible that nicotinic acid and riboflavin activate the transcriptional regulatory protein OxyR via dropping off the intracellular reducing power and in this way stabilize the

Lactobacilli are the well known friendly bacteria for their probiotic activities against pathogens. The inhibitory activity of different strains of lactobacilli either obtained as commercial products or isolated from human feces was investigated against the clinical isolates of Pseudomonas aeruginosa. The isolates were selected as the most resistant strains when challenged with anti-pseudomonal antibiotics already in clinical practice. Both the plate spot test as well as the agar cup method were used for screening of Lactobacillus strains against Pseudomonas aeruginosa. A Lactobacillus acidophilus strain isolated from feces of an Iranian child showed a strong anti-pseudomonal activity (90 percent after 72h incubation) against the multi-drug resistant clinical isolates while a Lactobacillus reuteri strain isolated from a commercial oral product resulted in relatively weak response and a Lactobacillus acidophilus strain isolated from a commercial vaginal product did not show any inhibitory activity. In a kinetic study the lactobacillus sensitive Pseudomonas aeruginosa showed a significant bacteriostatic activity in vitro in the presence of lactobacillus supernatants. Some lactobacilli exhibit significant inhibitory activity against the multidrug resistant clinical isolates of Pseudomonas aeruginosa.

Patients at intensive-care-unit (ICU) are at risk of acquiring nosocomial infections which contributes to higher rates. Approximately 25% of all hospital infections and 90% of outbreaks occur in ICUs. Multi-resistant gram-negative rods are important pathogens in ICUs, causing high rate of mortality. The purpose of this study was to investigate the antimicrobial resistance patterns among common Gram-negative bacilli isolated from patients with nosocomial infection at Army Hospitals. A total of 187 isolates of Gram-negative bacilli were isolated from 904 patients at ICUs of three Army hospitals in Iran during May 2007 to May 2008. All isolates were examined for antimicrobial resistance using disc diffusion method. The most frequent pathogens were E. coli (32.08%) followed by K. pneumoniae (31%), P. aeruginosa (12.8%) and Acinetobacter spp. (9.1%). High rate of resistance to third generation cephalosporines was observed among isolates of E. coli and K. pneumoniae. Production of extended spectrum beta lactamases (ESBLs) was found in 46.6% of isolates of both organisms, but in 38% of all Gram negative bacteria. The prevalence of ESBL producing strains at three Army Hospitals is considerable (38%). However, resistance to imipenem has emerged in these hospitals. Furthermore, studies are required to clarify the situation with multi-drug resistant organisms including the Gram positive bacteria at Army hospitals.

The aim of this study was to investigate the effect of pulsed ultra-violet (UV) irradiation on inactivation of beer spoilage microorganisms. UV irradiation is nowadays cost effective enough to compete with traditional biological, physical, and chemical treatment technologies and has become an alternative to such methods. Photoinactivation effects of pulsed UV laser with the wavelengths of 355 and 266 nm, which inactivate typical prokaryotic (Escherichia coli) and eukaryotic (Saccharomyces cerevisiae) microorganisms, were examined with different doses and exposure times. A dose of 100 J/cm2 of the 355 nm pulsed UV laser was able to reduce about 1 to 2 log (88.75%) of E.coli with the population of 1.6×108 colony-forming units (CFU/ml), and 97% of 3.2×107, 3×106, 5.5×105, and 9×104 CFU/ml. In the case of 266 nm, more than 99% reduction in E. coli serial dilutions was inactivated, using 10 J/cm2 with exception of 7×104 CFU/ml which was not detected any bacterial growth using 5 J/cm2. In addition, 50, 40, and 20 J/cm2 energy were used successfully to inactivate S. cerevisiae at the populations of 5.4×106, 7×105, 5×104 and 4×103 CFU/ml, respectively.As a result, pulsed UV Laser with 266 nm was strong enough to inactivate a high titer of bacterial and yeast indicator standards suspended in non-alcoholic beer in comparison with 355nm doses. Results indicate that pulsed UV technology, in principle, is an attractive alternative to conventional methods for the inactivation of indicator microorganisms and has potential in irradiation of unpasteurized beer.

Due to the extensive use of antibiotics, the spread of drug-resistant bacteria is one of the most worrisome threats to public health. One strategy that can be used to overcome potential shortcomings might be the inactivation of these organisms by photodynamic therapy. In this study, we have investigated whether drug-resistant wound-associated organisms (Staphylococcus aureus, Staphylococcus epidermidis and Escherichia coli) are sensitive to lethal photosensitization using the dye methylene blue coupled with laser light of 660 nm. Effect of photosensitizer concentration (25, 50, 100 μg/ml) and laser light dose (27.3, 54.6 and 109.2 J/cm2) on lethal photosensitization was investigated. All species were susceptible to killing by photodynamic inactivation. The bactericidal effect was not dependent on the concentration of methylene blue but it was dependent on the light dose. Methylene blue photosensitization using red laser light (109.2 J/cm2) was able to achieve reductions of 99.03% and 98.95% in the viable counts of S. aureus and S. epidermidis (using starting concentrations of 104–105 CFU/ml). Eradication of 92.23% were obtained for E. coli (initial concentration 104–105 CFU/ml) photosensitized by the red light (109.2 J/cm2). These findings imply that MB in combination with red light may be an effective means of eradicating drug-resistant bacteria from wounds.

Streptokinase is used clinically as an intravenous thrombolytic agent for the treatment of acute myocardial infarction and is commonly prepared from cultures of Streptococcus equisimilis strain H46A. The objective of the present study was the production of streptokinase from strain H46A and purification by chemical reduction method. The rate of streptokinase production evaluated under the effect of changes on some fermentation factors. Moreover, due to the specific structure of streptokinase, a chemical reduction method employed for the purification of streptokinase from the fermentation broth. The H46A strain of group C streptococcus, was grown in a fermentor. The proper pH adjusted with NaOH under glucose feeding in an optimum temperature. The supernatant of the fermentation product was sterilized by filtration and concentrated by ultrafiltration. The pH of the concentrate was adjusted, cooled, and precipitated by methanol. Protein solution was reduced with dithiothreitol (DTT). Impurities settled down by aldrithiol-2 and the biological activity of supernatant containing streptokinase was determined. In the fed –batch culture, the rate of streptokinase production increased over two times as compared with the batch culture and the impurities were effectively separated from streptokinase by reduction method. Improvements in SK production are due to a decrease in lag phase period and increase in the growth rate of logarithmic phase. The methods of purification often result in unacceptable losses of streptokinase, but the chemical reduction method give high yield of streptokinase and is easy to perform it.

Sodium Dodecyl Sulfate (SDS) is one of the most widely used anionic detergents. The present study deals with isolation and identification of SDS-degrading bacteria from a detergent contaminated pond situated in Varanasi city, India. Employing enrichment technique in minimal medium (PBM), SDS-degrading bacteria were isolated from pond water sample. Rate of degradation of SDS was studied in liquid PBM and also degradation of different concentrations of SDS was also studied to find out maximum concentration of SDS degraded by the potent isolates. Alkyl sulfatase activity (key enzyme in SDS degradation) was estimated in crude cell extracts and multiplicity of alkyl sulfatase was studied by Native PAGE Zymography. The potent isolate was identified by 16S rRNA sequence analysis. Using enrichment technique in minimal medium containing SDS as a sole carbon source, initially three SDS degrading isolates were recovered. However, only one isolate, SP3, was found to be an efficient degrader of SDS. It was observed that this strain could completely metabolize 0.1% SDS in 16 h, 0.2% SDS in 20 h and 0.3% SDS in 24 h of incubation. Specific activity of alkyl sulfatase was 0.087±0.004 μmol SDS/mg protein/min and Native PAGE Zymography showed presence of alkyl sulfatase of Rf value of 0.21. This isolate was identified as Pseudomonas putida strain SP3. This is the report of isolation of SDS-degrading strain of P. putida, which shows high rate of SDS degradation and can degrade up to 0.3% SDS. It appears that this isolate can be exploited for bioremediation of this detergent from water systems.