Influence on Enterobacter cloacae metabolism, cell-surface hydrophobicity and motility of suprainhibitory concentrations of carbapenems

Some properties of Plesiomonas shigelloides treated with aminoglycosides

The effect of aminoglycoside antibiotics (amikacin, gentamicin, netilmicin and tobramycin) at sublethal concentrations (sub-MICs) on some properties of Plesiomonas shigelloides strains was evaluated. All agents decreased the bacterial surface hydrophobicity. Amikacin (1/4 of the MIC) and netilmicin (1/4 and 1/8 of the MIC) changed the hydrophobic character of P. shigelloides surface to a hydrophilic one. Treatment of the strains with aminoglycosides decreased also motility, netilmicin being the most effective. No significant changes were found in lipolytic activity of antibiotic-treated strains. In the majority of cases aminoglycosides increased sensitivity of bacteria to hydrogen peroxide. The tested antibiotics did not induce production of short-chained N-acylhomoserine lactones signal molecules. Aminoglycosides at sub-MICs affected important activities of P. shigelloides potentially associated with their virulence in dependence on strain, antibiotic and concentration.

Occurrence of extended-spectrum beta-lactamases among Escherichia coli isolates from hospitalized and healthy children

The prevalence of extended-spectrum beta-lactamases (ESBL) was determined among isolates of Escherichia coli (n = 63) isolated from hospitalized (43) and healthy (20) children. Ten isolates (21%) were ESBL-positive for two screening tests, the double disk-synergy test and the Oxoid Combination Disk method. One ESBL-positive isolate came from a healthy child. The transfer frequency of oxyimino-beta-lactam resistance from ESBL-producing isolates to E. coli K12 C600 recipient strain ranged from 10(-8) to 10(-5) per donor cell. Donor strains and transconjugants displayed susceptibility patterns typical of ESBL producers. They were resistant to oxyimino-beta-lactams but susceptible to clavulanic acid and carbapenems. Seven out of the 10 ESBL-positive isolates were found to produce MR/MS fimbria, which may play an important role in the colonization of the human intestinal mucosa.

Toxinogenicity and markers of pathogenicity of Pseudomonas aeruginosa strains isolated from patients with tumor diseases

Potential virulence factors (elastase, proteinase, lipase, phospholipase C, alginate) as well as surface properties (hydrophobicity, motility) were determined in 103 Pseudomonas aeruginosa strains isolated from patients with cancer. Nontypable strains were the dominant group (60%), followed by serotypes O11 (17%), O12 (7%) and O4 (5%). Seventy-one strains (69%) produced high level of elastase (10-60 mg/L), 87% of the strains possessed high activity of proteinase (bacterial) (10-250 mg/L) and 69% of the strains demonstrated higher level of lipase (20-150 U/mL); these elevated levels of enzymes were associated mainly with nontypable strains. On the other hand, 79% of the strains did not produce or produced only a low level of phospholipase C and 60% of isolates did not manifest any or very low production of alginate. Hydrophobicity demonstrated by adherence of the bacteria to xylene was shown by 69% of strains; 94% of strains aggregated with ammonium sulfate. Motility in the range of 31-80 mm was found in 76 strains (74%). The considerable virulence of tested P. aeruginosa strains was confirmed. The nontypable strains manifested the most frequent group with high level of elastase, proteinase, lipase, hydrophobicity and motility.