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T L Pitt

Publications and source records attributed to T L Pitt.

At least 37 records · Page 2Linked to original sources
PubMed1999

Isolation of Acinetobacter spp. including A. baumannii from vegetables: implications for hospital-acquired infections.

A. baumannii is rarely recovered from the skin of patients or healthy European subjects as other genospecies predominate, but it isa significant nosocomial pathogen. The natural reservoir of this organism is therefore uncertain. We determined the isolation rates of Acinetobacter spp. from vegetables (as an indicator of the natural environment) using a selective technique and classified the genospecies by amplified ribosomal DNA restriction analysis (ARDRA). Of the 177 samples of vegetables examined, 30 yielded Acinetobacter, with genospecies 2 and 11 being the most common, each with a frequency of 27%. MIC assays showed that strains of genospecies 1, 2, 3, and 13TU (the A. calcoaceticus-A. baumannii complex) were significantly more resistant than other genospecies to ciprofloxacin and gentamicin. Vegetables may therefore be a natural habitat of A. baumannii and provide a route by which these bacteria are introduced into hospitals with obvious implications for infection control.

Acinetobacter↗
PubMed1999

Evaluation of three oligonucleotide primer sets in PCR for the identification of Burkholderia cepacia and their differentiation from Burkholderia gladioli.

AIMS: To evaluate three oligonucleotide primer pairs--two specific for 16S and 23S rRNA sequences of Burkholderia cepacia, and the third specific for internal transcribed spacer region of 16S-23S sequences of B gladioli--for the identification and differentiation of reference and clinical strains of these and other species. METHODS: The three primers sets were applied in polymerase chain reaction (PCR) to a collection of 177 clinical isolates submitted for identification from diagnostic laboratories as presumed B cepacia. RESULTS: At an annealing temperature of 63 degrees C, all eight B cepacia and four B gladioli reference strains reacted with their specific primers. B vandii was the only other species that was positive with both B cepacia primers but five Burkholderia or Ralstonia species reacted with one of these primers. Seventy eight isolates were typical of B cepacia in biochemical tests and 75 of these reacted with specific primers; three, however, were positive with the B gladioli primers. Fifteen asaccharolytic isolates were confirmed as B cepacia by PCR but other non-fermenting Gram negative species were negative with each of the primers. CONCLUSIONS: PCR using 16S rRNA sequences is recommended for identification of B cepacia that give atypical results in biochemical tests.

Burkholderia↗
PubMed1998

Persistence of Pseudomonas aeruginosa strains in respiratory infection in AIDS patients.

OBJECTIVES: To establish the clinical pattern of Pseudomonas aeruginosa respiratory infections in HIV-seropositive patients and to determine whether repeated isolation of the organism represents reinfection or recurrence and to assess whether common source, nosocomial infection occurred. DESIGN AND METHODS: Evaluation of the clinical pattern of P. aeruginosa respiratory infections by case note review and epidemiological characterization of P. aeruginosa by serotype determination and Xbal DNA macrorestriction analysis. Serum sensitivity testing of strains was performed to further define phenotypic characteristics of the isolated organisms. RESULTS: Seventy-three per cent (29 out of 40) of individuals had P. aeruginosa isolated on two or more occasions in the setting of clinical respiratory infection. Overall, 85% had evidence of P. aeruginosa to within 2 months of study completion or death. Epidemiological characterization revealed persistence of unique single strains in 93% of individuals where multiple isolates were available for testing, whereas only two patients harboured a common strain. The serotype distribution of strains was similar to that reported from non-HIV-positive patients. CONCLUSIONS: Once established, eradication of P. aeruginosa from the respiratory tract of HIV-seropositive individuals with advanced immunosuppression is problematic and a chronic infective state appears common. There was no evidence of nosocomial transmission. Serotype loss and development of sensitivity to normal human serum were both observed and were highly correlated. This represents truncation of O-antigenic lipopolysaccharide on the cell surface of P. aeruginosa and may reflect progression to phenotypes commonly associated with chronic infection in other clinical settings such as cystic fibrosis.

Acquired Immunodeficiency Syndrome↗
PubMed1998

Complementation of methionine auxotrophs of Pseudomonas aeruginosa from cystic fibrosis.

Auxotrophic Pseudomonas aeruginosa are exclusive to respiratory infections in cystic fibrosis (CF) and bronchiectatic patients, and isolates require specific amino acids for growth on minimal media, particularly methionine. Since auxotrophic and prototrophic P. aeruginosa from CF are identical by genotyping, we investigated the genetic events leading to methionine auxotrophy (Met-). Most (10/13) Met- strains had the same pattern of growth on methionine precursors and required methionine exclusively for growth. Back mutation to prototrophy was very low (frequencies 10(-8) to <10(-10)). Complementation of the mutations leading to auxotrophy was achieved for five strains with a genomic library of P. aeruginosa PAO1. Strains with different patterns of growth on methionine precursors were complemented by clones with different restriction patterns, while identical clones complemented strains with the same pattern of growth on methionine precursors. Methionine auxotrophy in P. aeruginosa from CF results from stable chromosomal mutations, and the commonest defect is probably in gene(s) encoding enzymes that convert homocysteine to methionine.

Cystic Fibrosis↗
PubMed1998

Regional microbiology of the cystic fibrosis lung: a post-mortem study in adults.

Although the majority of patients with cystic fibrosis (CF) become chronically colonized with Pseudomonas aeruginosa, the mode of acquisition of infection remains unclear. Epidemiological studies using genotyping techniques suggest that person-to-person transmission of this organism may occur. All these studies have utilized sputum or throat swab samples. We have studied the regional microbiological flora of the lungs of five CF patients at post-mortem and genotyped P. aeruginosa strains found therein and in the major airway. We have shown that although in most cases major airway secretions accurately reflect the peripheral lung flora, in cases of multiple strain carriage, major airway cultures may not reflect all strains present in the periphery of the lung. This finding has implications for the interpretation of epidemiological studies that use genotyping of strains from sputum and throat swab samples to assess possible routes of transmission.

Adult↗
PubMed1998

Stability of strain genotypes of Burkholderia pseudomallei from patients with single and recurrent episodes of melioidosis.

The constancy of strain genotypes of multiple isolates of Burkholderia pseudomallei from 13 patients with melioidosis was examined by BamHI ribotyping and pulsed-field gel electrophoresis (PFGE) of XbaI digests of DNA. Seven of 8 patients with single episodes of melioidosis each yielded genetically identical isolates and only one of five patients with recurrent episodes was infected with a new strain clearly distinct from the original primary strain. Variation was observed in PFGE patterns of primary and relapse isolates of another patient but this was insufficient to define genetically distinct strains. We conclude that most patients with single or multiple episodes of melioidosis retain a single strain.

Burkholderia pseudomallei↗
PubMed1998

Epidemiological typing of klebsiellae with extended-spectrum beta-lactamases from European intensive care units.

Extended-spectrum beta-lactamases (ESBLs) are an increasing cause of resistance to oxyimino-aminothiazolyl cephalosporins, especially in klebsiellae. In a recent survey we detected ESBLs in 220 (23%) of 966 consecutive klebsiellae from 35 intensive care units (ICUs) in southern and western Europe. The present study examined the extent to which this distribution reflected epidemic strain spread, as against the distribution of ESBL genes into unrelated strains. All 220 ESBL producers were subjected to capsular serotyping and pulsed-field gel DNA electrophoresis (PFGE). Beta-Lactamases were typed for strains isolated on three or more occasions, with the emphasis on SHV enzymes, as these were commoner than TEM variants. Serotyping and PFGE typing defined 85 distinct strains, from 23 of the 35 participating centres. Of 14 centres that contributed five or more ESBL producers, all sent representatives of more than one strain, and two centres sent members of ten or more different strains in contributions of 17-21 ESBL-producing isolates. Nevertheless, epidemic strains-defined as those represented by three or more isolates-accounted for a majority (61%) of the collection. Fifty-two isolates of the same serotype K25 (occasionally acapsular) strain with SHV-4 beta-lactamase were recovered at two French hospitals and one in Belgium. This strain has been found by others in France, and has become particularly widespread. Another single strain was found in two separate Portuguese centres, and many individual hospitals had one or more epidemic strain(s), as well as a scatter of diverse ESBL producers. Major variation in antibiogram and plasmid profile was apparent within strains, with some intra-strain variation in beta-lactamase type. These data imply a fluid situation, with resistance determinants being gained, modified or lost. The endemicity of ESBL producers is disturbing since it limits the potential for control by blocking strain spread, while the diversity within strains is disturbing because it complicates the design of antibiotic policies even during 'single strain' outbreaks.

Anti-Bacterial Agents↗
PubMed1998

Different O and K serotype distributions among clinical and environmental strains of Serratia marcescens.

Recent revision of the O serotyping scheme for Serratia marcescens has allowed the definitive serological identification of a collection of 511 epidemiologically distinct strains in terms of both lipopolysaccharide (O) antigens and capsular (K) antigens. High levels of typability were achieved, 88% and 91% respectively, with only 2% failing to type with either method. In most cases, non-typability was due to a lack of antigen, i.e., the strains produced only rough LPS or were acapsular, suggesting that typability would be little improved by the discovery of additional serotypes. The distribution of the 58 O:K serotypes was very uneven, with O14:K14 accounting for 30% of the 423 clinical strains in the collection, but only 5% of the 88 non-clinical, environmental strains. Thus, the prevalence of O14:K14 strains in hospitals is not reflected in the environment. Similar conclusions were valid for O27:K14, O21:K3 and O21:K14 strains, as well as those with rough lipopolysaccharide. Conversely, the proportions of O6:K3, O6:K14, O8:K14 or O28:K28 strains were significantly lower among the clinical collection than among their environmental counterparts (12% in total rather than 65%). This suggests that O14:K14 may have a selective advantage in colonising or infecting hospitalised patients and, therefore, that the O14 and K14 polysaccharides themselves may contribute towards the apparent pathogenicity of these serotypes.

Animals↗
PubMed1998

Antibiotic resistance and putative virulence factors of Serratia marcescens with respect to O and K serotypes.

Serratia marcescens serotypes O6:K14, O8:K14 and O28:K28 are common in the natural environment, but rare in hospitals. Serotypes O14:K14 and O27:K14 predominate among clinical strains, but not in the environment, suggesting that the latter serotypes may be more suited for survival in the clinical setting. Consequently, 469 epidemiologically distinct strains of S. marcescens were tested for various putative virulence factors and analysed for associations with serotype. The factors positively associated with serotype O14:K14 were agglutination of five different species of red blood cells and expression of type 1 fimbriae. These were found in 63% and 53% of O14:K14 strains, respectively, compared with 7% and 12% of the three 'environmental serotypes'. Almost a quarter of the collection expressed the mannose-resistant haemagglutinin indicative of type 3 fimbriae, but this was not associated with any serotype. The production of DNAase, haemolysin, lipase, lecithinase, proteases and siderophores was almost universal and showed no serotype correlations. Almost half of the strains (46%) were resistant to serum and serotypes O27:K14 and O6:K14 were strongly associated with this characteristic. Serotype O27:K14 was also associated with higher proportions of antibiotic-resistant strains than other serotypes, but the same was not true of serotype O14:K14. All three 'environmental serotypes' were associated with low frequencies of antibiotic resistance; <12% were resistant to gentamicin, carbenicillin or piperacillin, or any combination of these three, compared with 20-25% of O14:K14 strains and >42-51% of O27:K14 strains. Pigment production was strongly associated with serotype. None of the O14:K14 or O27:K14 strains produced prodigiosin, but frequencies for the three 'environmental serotypes' ranged from 31% of O28:K28 strains to 85% of O6:K14 strains. The results of this study suggest that the adherence capability of S. marcescens strains may play a role in the colonisation of hospital patients, while the production of prodigiosin is a marker of environmental origin.

Animals↗
PubMed1998

Serotyping of Flavobacterium meningosepticum by co-agglutination method.

The purpose of this investigation was to evaluate the usefulness of a co-agglutination procedure for the typing of Flavobacterium meningosepticum. The sensitivity and specificity of the co-agglutination test was compared to the slide agglutination test using reference strains of the bacterial species. Antisera were characterized by both technics to determine their titer and working dilution. The specificity of the sera was assessed by performing tests which include strains of other species and serotypes. A collection of 47 strains of F. meningosepticum isolated from clinical specimens were typed by both co-agglutination and slide agglutination methods. Co-agglutination proved to be markedly more specific than the slide procedure although both methods were similar in sensitivity. It was concluded that co-agglutination proved to be an excellent method for the serotyping of F. meningosepticum.

Agglutination Tests↗
PubMed1997

Epidemiologically related and unrelated strains of Pseudomonas aeruginosa serotype O12 cannot be distinguished by phenotypic and genotypic typing.

A clonal origin for European isolates of antibiotic multi-resistant Pseudomonas aeruginosa serotype O12 has been suggested. This study was designed to assess the value and limitations of several typing methods for the investigation of outbreaks due to this serotype. In Hôpital de Rodez, France, this organism is endemic, and a prospective clinical epidemiological study was undertaken over a 15 month period, encompassing all patients at the hospital from whom P. aeruginosa O12 was isolated. All isolates were examined by auxanogram, antibiogram, phage-typing, electrophoresis of esterases and pulsed-field gel electrophoresis of DNA. The results suggest that (1) the methods used did not clearly differentiate between clinically-related and epidemiologically-unrelated European isolates, (2) in Hôpital de Rodez, while some isolates were likely to have been transmitted from patient-to-patient, most infections or colonizations with this organism were sporadic and their origin is unknown. The limits of typing methods for the investigation of outbreaks of nosocomial infection with multi-resistant P. aeruginosa O12 are emphasized.

Aged↗
PubMed1997

Ribotype differences between clinical and environmental isolates of Burkholderia pseudomallei.

Burkholderia pseudomallei is isolated frequently from the soil in regions where the disease melioidosis occurs. However, recent surveys in Thailand have shown that the frequency of isolation of the organism from soil samples is not directly related to the incidence of melioidosis in an area. To determine whether strain populations of B. pseudomallei prevalent in soil are gentypically related to strains causing clinical disease, rRNA BamHI restriction fragment length polymorphisms (RFLP) of 139 soil environmental isolates and 228 human isolates were compared. Two groups of ribotype patterns were found. Group I comprised 37 different ribotype patterns which were characterised by five to eight hybridisation bands of 2.8- > 23 kb. All of these ribotypes were identified among the clinical isolates, and 18 of them were also found in 59 environmental isolates. Group II was represented by 12 ribotypes found only in environmental strains. These ribotype patterns comprised one to five bands in the size range 9- > 23 kb. All but one of the 73 isolates in this group grew on a minimal medium supplemented with L-arabinose. In contrast, only 3% of the 66 isolates from the environment with group I ribotype patterns could utilise this sugar as their sole energy source. These findings suggest that B. pseudomallei strains that utilise arabinose constitute a population that is genetically distinct from other environmental and clinical strains.

Arabinose↗
PubMed1997

Identification of capsular antigens in Serratia marcescens.

Previous studies with 31 strains of Serratia marcescens, including 28 reference O-serotype strains, have indicated that 19 of them have an acidic polysaccharide which copurifies with lipopolysaccharide during phenol-water extraction. Polysaccharide in crude extracts from 18 of the 19 strains was precipitated with Cetavlon (hexadecyltrimethyl ammonium bromide), and capsules were demonstrated around these 18 strains by Indian ink exclusion zones. Capsule-antibody binding by the Quellung reaction suggested that the acidic polysaccharide formed the capsule around the bacterial cells. Anticapsular (anti-K) antibody was detected in reference O antisera which had been prepared against boiled whole cells. Cross-titration and absorption studies revealed 14 different K antigens among these strains.

O Antigens↗
PubMed1996

Immunochemical characterization of two new O serotypes of Serratia marcescens (O27 and O28).

In an earlier study of the distribution of O-serotypes among clinical isolates of Serratia marcescens, two apparently new serotypes were identified, represented by strains S1254 and S3255. Studies using ELISA, immunoblotting and the Quellung reaction have shown that they qualify for inclusion in the O-antigenic typing scheme on three counts: (1) they possess chemically distinct O-antigenic repeating units, (2) the O-antigens are serologically distinguishable from all others, and (3) they are found in a significant proportion of clinical S. marcescens strains (13% and 6% respectively). S1254, the type strain for serotype O27, is an acapsular strain which expressed a glucorhamnan with a disaccharide repeating unit as its lipopolysaccharide side chain. It cross-reacts with serotype O4, the O antigen of which is an O-acetylated form of the O27 glucorhamnan, but this cross-reaction can be eliminated by reciprocal cross-absorption. S3255, the type strain for serotype O28, has a mannose homopolymer as its O-antigen and is the only S. marcescens serotype with a trimeric repeating-unit structure. However, it cross-reacts with the O5 serotype strain due to similarities in their acidic capsular polysaccharides. Cross-absorption and the production of serum to an acapsular variant of serotype strain O28 produced typing reagents which could differentiate serotypes O5 and O28.

Carbohydrate Sequence↗
PubMed1996

Type characterisation and antibiotic susceptibility of Burkholderia (Pseudomonas) cepacia isolates from patients with cystic fibrosis in the United Kingdom and the Republic of Ireland.

The spread of Burkholderia cepacia among cystic fibrosis (CF) patients in the UK prompted an investigation into whether an epidemic strain was responsible. A total of 366 B. cepacia isolates from 178 CF patients in 17 centres was examined by ribotyping and pulsed-field gel electrophoresis (PFGE). Associations were also sought between antibiotic resistance and strain type. More than 50 ribotype patterns were found but one, termed ribotype 1, was identified from 68 patients in eight centres. One centre had a single patient with this type while, in others, most or all patients harboured this organism. Small clusters of apparent cross-colonisation within centres were also evident for some other ribotypes. PFGE confirmed that ribotype 1 isolates were genetically similar. Ribotype 1 isolates were not markedly more resistant to antimicrobial agents than were other isolates, and the MICs of individual antibiotics were no more tightly clustered for ribotype 1 isolates than for others. Most isolates were resistant to ciprofloxacin, amikacin, gentamicin, tobramycin, carbenicillin, cefuroxime, cefotaxime, imipenem, biapenem, chloramphenicol, tetracycline, trimethoprim and sulphamethoxazole, but > or = 77% were susceptible to ceftazidime, piperacillin, piperacillin/ tazobactam and meropenem. We conclude that numerous strains of B. cepacia colonise CF patients in the UK and Ireland but that one epidemic strain has spread in at least eight centres. Isolates of this strain appear homogenous in total genomic profile but very variable in antibiotic susceptibility.

Bacterial Typing Techniques↗
PubMed1996

The high amino-acid content of sputum from cystic fibrosis patients promotes growth of auxotrophic Pseudomonas aeruginosa.

Many isolates of Pseudomonas aeruginosa from cystic fibrosis (CF) patients are auxotrophic and require amino acids for growth. A quantitative assay was used to determine the total content of free amino acids of sputum sol-phase extracts from CF and non-CF patients to assess the presence of amino acids in the airway. CF patients colonised with auxotrophic P. aeruginosa had a higher sputum amino-acid content (mean 6.77 mg/ml) than those colonised with prototrophs (mean 3.77 mg/ml); overall, CF specimens (mean 5.70 mg/ml) had a higher amino-acid content than non-CF samples (2.52 mg/ml). The amino-acid profile of sputum extracts was assessed by one-dimensional thin layer chromatography (TLC). Several amino acids were identified in the extracts, in particular, leucine, isoleucine, phenylalanine, tyrosine, alanine, serine and methionine or valine or both. All sputum specimens except two (which contained < 1.5 mg of amino acids/ml), promoted the growth, of 34 auxotrophic strains of P. aeruginosa from CF patients in a minimal medium. These results indicate, therefore, that amino acids are plentiful in the sputum of CF patients and are able to supply the requirements of auxotrophic strains. It is suggested that the increased amino-acid content in the airways of CF patients plays a significant role in the selection and maintenance of nutritionally deficient P. aeruginosa.

Amino Acids↗
PubMed1996

Biochemical characteristics of clinical and environmental isolates of Burkholderia pseudomallei.

The biochemical characteristics of 213 isolates of Burkholderia pseudomallei from patients with melioidosis and 140 isolates from the soil in central and northeastern Thailand were compared. Whereas the biochemical profiles of all the clinical isolates were similar, all soil isolates from the central area and 25% of isolates from northeastern Thailand comprised a different phenotype. This was characterised by the ability to assimilate L-arabinose (100%), adonitol (100%), 5-keto-gluconate (90%) and D-xylose (84%), but failure to assimilate dulcitol (0%), erythritol (0%) and trehalose (10%). Compared with clinical isolates, these organisms had similar antibiotic susceptibility profiles and were also recognised by a specific polyclonal antibody against B. pseudomallei. As melioidosis is rare in central Thailand, but common in the northeast, this raises the possibility that this biochemical phenotype may be less virulent, or may even represent a different species.

Anti-Bacterial Agents↗