- Volume 43, Issue 4, 1995

Antimicrobial resistance among 1991 Pseudomonas aeruginosa isolates collected at 24 UK hospitals during late 1993 was surveyed. Three-hundred and seventy-two of the isolates were resistant, or had reduced susceptibility, to some or all of azlocillin, carbenicillin, ceftazidime, imipenem and meropenem, and the mechanisms underlying their behaviour were examined. Only 13 isolates produced secondary β-lactamases: Six possessed PSE-1 or PSE-4 enzymes and seven had novel OXA enzyme types. Those with PSE types were highly resistant to azlocillin and carbenicillin whereas those with OXA enzymes were less resistant to these penicillins. Chromosomal β-lactamase derepression was demonstrated in 54 isolates, most of which were resistant to ceftazidime and azlocillin although susceptible to carbenicillin and carbapenems. β-Lactamase-independent “intrinsic” resistance occurred in 277 isolates and is believed to reflect some combination of impermeability and efflux. Two forms were seen: The classical type, present in 195 isolates, gave carbenicillin resistance (MIC > 128 mg/L) and reduced susceptibility to ciprofloxacin and to all β-lactam agents except imipenem; a novel variant, seen in 82 isolates, affected only azlocillin, ceftazidime and, to a small extent, meropenem. Resistance to imipenem was largely dissociated from that to other β-lactam agents, and probably reflected loss of D2 porin, whereas resistance to meropenem was mostly associated with intrinsic resistance to penicillins and cephalosporins. Comparison of the present results with those of a similar study in 1982 revealed significant increases in the proportions of isolates with intrinsic resistance or stable derepression (p ≪0.01, χ 2 test). Isolates with secondary β-lactamases appeared significantly rarer than in 1982 (p ≪ 0.01, χ 2 test), but this comparison was distorted by outbreak strains.

Two Salmonella typhimurium isolates were studied, one as a representative from a series of neonatal meningitis cases treated at an Istanbul teaching hospital, the other from a gastro-enteritis case seen at a different Istanbul hospital. Both isolates were resistant to extended-spectrum cephalosporins, as well as penicillins, aminoglycosides and chloramphenicol. Cephalosporin resistance depended on production of PER-1 β-lactamase, which is an extended-spectrum class A enzyme that is only distantly related to TEM and SHV enzymes, and which was previously known only from Pseudomonas aeruginosa isolates. The PER-1 gene was carried by an 81-MDa plasmid, which also determined resistance to aminoglycosides and chloramphenicol. Although it was not self-transmissible to Escherichia coli, this element did transfer if mobilised with plasmid pUZ8. The two S. typhimurium isolates gave indistinguishable DNA restriction patterns and, in addition to their 81-MDa plasmid, also contained 52- and 2-8-MDa plasmids, the last of these encoded TEM-1 enzyme. The two isolates were identical in serotype, antibiogram and plasmid-profile but nevertheless differed in phage type, and, therefore, represented distinct strains. The emergence of cefotaxime and ceftriaxone resistance in salmonellae is disturbing, since these agents are preferred therapy for neonatal meningitis caused by members of the genus.

Sera from 20 cystic fibrosis patients, whose lungs were colonised by Pseudomonas aeruginosa, were examined in a 3–5-year prospective study for any relationship between IgG subclass antibody levels to P. aeruginosa a- and b-type flagellins and pulmonary function (FEV1 and radiological score). Patients were divided into two groups according to their pulmonary status: Group 1 comprised 11 patients with poor pulmonary status; group 2 comprised nine patients with relatively good pulmonary status. High concentrations of IgG1, IgG2 and IgG3 antibodies to flagellins, particularly to the b-type, were found in most patients. IgG4 reactivity was observed in only a few patients. Comparison of the two groups of patients showed that those with poor pulmonary status (group 1) had a significantly higher concentration (p ≪ 0.05) of IgG3 for two of the three periods studied and of IgG2 for the last period studied. Moreover, IgG3 and IgG1 reactivities to b-type flagellin and IgG3 to a-type flagellin were also increased significantly (p ≪ 0.05) in group 1 patients between the first and the last period studied. These patients also showed a significant (p ≪ 0.05) time-dependent increase in IgG3 and IgG1 antibody concentrations. These data demonstrate that cystic fibrosis patients with poorer pulmonary status have higher IgG3 levels to flagellin than other cystic fibrosis patients. High concentrations of strong opsonic IgG3 and, to a lesser degree, of IgG1 antibodies may increase pulmonary inflammation and induce heightened pulmonary deterioration.

The effect of bacterial lipopolysaccharide (LPS) on the lymphoid organs in C3H/HeN and C3H/HeJ mice was investigated. In C3H/HeN mice, LPS induced apoptosis, characterised by morphological nuclear condensation and DNA fragmentation resulting in thymic atrophy. Similar but less severe changes were also observed in the spleen and lymph nodes. In C3H/HeJ mice, only a slight depletion of lymphocyte numbers was observed in the lymphoid organs. The plasma endotoxin levels were dependent on the LPS dose regardless of mouse strain. On the other hand, the plasma TNF-a levels were significantly elevated in C3 H/HeN mice 1h post-injection and the time course of plasma corticosterone concentration correlated well with the development of apoptosis. These findings suggest that TNF-a and corticosterone may play an important role in LPS-induced apoptosis of lymphocytes.

A novel aminopeptidase was purified by high performance liquid chromatography from a cytosoluble 100000 g extract of Candida albicans on the basis of its ability to cleave L-arginine 7-amino-4-methylcoumarin. The purification factor was 36 and the yield was 20%. The native enzyme had a mol. wt of 52 kDa as demonstrated by SDS-PAGE in the presence or absence of reducing conditions and exhibited an iso-electric point of 4.3. The aminopeptidase showed optimum activity at pH 7.2, a Michaelis constant of c. 50 μM and a Vmax at 19 mm AMC released/min/mg of protein for L-Arg-AMC. This enzyme was shown to cleave at low affinity L-leucine-7-amino-4-methylcoumarin as demonstrated by the spectrofluorimetric method. The enzyme was strongly inhibited by specific metallo-enzyme inhibitors—EDTA and o-phenanthroline. Furthermore, there is evidence that a similar or identical enzyme occurs in other C. albicans clinical isolates and other Candida spp.