Gopalkrishna Bhat

Methicillin-resistant Staphylococcus aureus in community-acquired pyoderma

Background  Methicillin‐resistant Staphylococcus aureus (MRSA) is an important nosocomial pathogen. It can also cause community‐acquired infections. Indian reports about MRSA in community‐acquired infections are rare.

Virulence factors and drug resistance in Escherichia coli isolated from extraintestinal infections

PURPOSE To determine the virulence factors produced by Escherichia coli isolated from extraintestinal infections, to study the drug resistance pattern in E. coli with special reference to extended spectrum beta -lactamase (ESBL) and to evaluate screening methods for ESBL. METHODS A total of 152 isolates of E. coli from various extraintestinal infections were screened for virulence factors such as haemolysin, surface hydrophobicity, serum resistance and protease. All the isolates were also studied for antibiotic susceptibility pattern using modified Kirby Bauer disk diffusion method. ESBL production was screened by standard disk diffusion method and confirmed using phenotypic confirmatory method. RESULTS Among 152 isolates, 36 (23.7%) were haemolytic, 42 (27.6%) were hydrophobic, 132 (86.8%) were serum resistant and only four were positive for protease. Multiple virulence factor were observed in 67 (44%) of isolates. Seventy-nine (51.4%) isolates produced ESBL. ESBL producing isolates showed multidrug resistance. There was a significant association ( P E. coli . CONCLUSIONS The present study shows the expression of virulence factors and multidrug resistance in E. coli isolated from various extraintestinal infections. The study also shows that appropriate methods of detecting drug resistance and ESBL production are required for the judicious use of antibiotics in managing these infections.

Factors affecting the nasal carriage of methicillin-resistant Staphylococcus aureus in human immunodeficiency virus-infected patients

Human immunodeficiency virus-infected patients attending skin outpatient department were studied for nasal carriage of methicillin-resistant Staphylococcus aureus (MRSA) and associated factors affecting nasal colonization. Nasal swabs were used for isolation of S. aureus. MRSA were detected by agar screen and agar dilution methods. Careful examination for dermatoses was carried out. Forty-six of the 60 (76.67%) outpatients with HIV infection were colonized with S. aureus in the anterior nares. Significant number of S. aureus carriers were in the 31-40 year age group. Methicillin resistance was found in eight (17.39%) isolates. Of the 46 S. aureus strains, 29 (63%) were resistant to erythromycin, 69.5% to co-trimoxazole and 41.3% to ciprofloxacin. Co-trimoxazole use was found to be a risk factor for S. aureus carriage ( P = 0.0214) but not for methicillin resistance. Hospital stay for more than 10 days was a risk factor for methicillin resistance whereas stay for more than 25 days was found to be a highly significant risk factor. Dermatophytosis and herpes simplex virus infection were other risk factors for nasal carriage of S. aureus.

Significance of MRSA strains in community associated skin and soft tissue infections.

The study was conducted to determine the antibiotic susceptibility profile of community-associated methicillin resistant Staphylococcus aureus (CAMRSA) strains isolated from infections. S. aureus strains were isolated from clinical specimens using the standard procedures. CDC definition was used to classify CAMRSA. Antibiotic susceptibility test was done using Kirby-Bauer disk diffusion method. Double disk diffusion method (D-test) was used to detect inducible macrolide, lincosamide and streptogramin B resistance (inducible MLS B resistance ). A total of 83 CAMRSA were isolated from abscesses and other skin infections in persons without known risk factors for MRSA infection. All CAMRSA were susceptible to vancomycin. Out of 83 CAMRSA, 13 (15.65%) were D-test positive (inducible MLS B positive) and 6 (7.23%) were positive for constitutive MLS B resistance. Eight strains (9.63%) were resistant to tetracycline and 26 (31.32%) strains were resistant to erythromycin. Increased rate of inducible clindamycin resistance among CAMRSA indicates the importance of identification of such strains by D test to avoid treatment failure when clindamycin is used.

Effect of exposure to hydrogen peroxide on the virulence of Escherichia coli.

PURPOSE To eliminate pathogenic bacteria, the host presents conditions that are stressful for bacteria. Oxidative stress arises when the concentration of pro-oxidants like hydrogen peroxide (H2O2 ) and superoxide anion increases to a level over the basal defence capacity of the cell. In the present study, we studied the effect of oxidative stress on the production of certain virulence factors by Escherichia coli . METHODS E. coli was exposed to oxidative stress by growing in the presence of different concentrations of H2O2 . The effect of oxidative stress on the expression of surface hydrophobicity, adherence, haemolysin production, serum resistance and phagocytosis was studied. RESULTS Oxidative stress caused a significant decrease in the expression of all the virulence factors of E. coli . CONCLUSIONS Synthesis of virulence factors can be significantly altered by oxidative stress and such changes may affect the pathogenicity of E. coli.

Biotypes and virulence factors of Gardnerella vaginalis isolated from cases of bacterial vaginosis

The present study was conducted to correlate the biotypes of Gardnerella vaginalis strains isolated from cases of bacterial vaginosis and their virulence factors. Thirty-two strains of G. vaginalis isolated from cases of bacterial vaginosis were biotyped. Adherence to vaginal epithelial cells, biofilm production, surface hydrophobicity, phospholipase C and protease activity were tested on these isolates. Biotype 1 was the most prevalent (8; 25%), followed by biotype 2 (7; 21.9%) and biotypes 5 and 8 (5; 15.6%). We did not find any statistical correlation between G. vaginalis biotypes and its virulence factors. Virulence factors expressed by G. vaginalis were not associated with a single biotype.

Effect of stress on production of heat labile enterotoxin by Escherichia coli.

Enterotoxigenic Escherichia coli (ETEC) is an important pathogen responsible for secretory diarrhoea. The production of heat labile enterotoxin (LT), by ETEC, is largely responsible for the pathogenesis of diarrhoea. In the present study we investigated the effect of stress factors such as temperature, pH, osmotic stress and nutritional limitation on the production of LT by ETEC using in-house GMI-ELISA. Four strains of E. coli consisting, one standard strain MTCC 723 and three clinical isolates were used in the study. Maximum amount of LT (OD 3.285) was produced at 37 0 C followed by 40 0 C (OD 3.305). Growth of E. coli in medium with pH 8.6 resulted in maximum amount of LT production (OD 3.489). LT was not detectable when bacteria were grown in medium with pH < or =7.2 and > or = 9.2. Sodium chloride concentration of 0.2 M stimulated maximum amount of LT production. Maximum amount of LT was produced when the bacteria were grown in medium containing 2.5 g/l of glucose. All the stress factors had a significant effect on the LT production by E. coli , though quantitative differences in the various strains were observed.

Urinary tract infection due to Enterobacter sakazakii

Enterobacter sakazakii is a rare but important cause of necrotizing enterocolitis, bloodstream infection and central nervous system infections in humans, with mortality rates of 40-80%. It has not been reported to cause urinary tract infection. We report a case of urinary tract infection due to E. sakazakii in a 63-year-old lady with chronic renal failure.

Phenotypic switching and its influence on expression of virulence factors by Candida albicans causing candidiasis in human immunodeficiency virus-infected patients

PURPOSE The purpose of the present study was to determine the degree of expression of virulence factors such as adherence, cell surface hydrophobicity (CSH) and production of proteinase by different morphological forms of Candida albicans causing oral candidiasis in human immunodeficiency virus (HIV)-infected individuals. METHODS C. albicans 3153A and two strains isolated from oral thrush in HIV infected individuals were induced to undergo phenotypic switching by exposure to UV light and the degree of expression of virulence factors by the different morphological forms was studied. RESULTS Three different morphological forms of C. albicans were obtained namely, star (S), wrinkled (W) and ring (R) types from the original smooth (O) variety. It was found that proteinase production was greatest with the W type followed by the R type and O type. The S type produced the least proteinase. Expression of cell surface hydrophobicity and adherence was greatest in the O type followed by the R and then the W type and finally the S type. CONCLUSIONS The differential expression of virulence factors occurs with different phenotypic forms of C. albicans and this may provide a particular morphological type with a distinct advantage over other types in causing candidiasis.

Phenotypic expression of methicillin resistance in nosocomial Staphylococcus aureus

Pseudomonas aeruginosa, an important nosocomial pathogen is difÞ cult to treat because of high antimicrobial resistance.[1] The common form of resistance is mediated by lack of drug penetration and / or carbapenem hydrolyzing ß-lactamases.[2] Detection of metallo ß lactamase (MBL)producing P. aeruginosa is crucial for the optimal treatment of patients. The present study was undertaken to study Imipenem resistant P. aeruginosa for MBL production.