N.F. Lightfoot

Direct milk excretion of Campylobacter jejuni in a dairy cow causing cases of human enteritis.

Consumption of milk contaminated with Campylobacter jejuni has been described as a cause of human enteritis. Although faecal contamination of milk with the organism has frequently been described, direct milk excretion of Campylobacter jejuni into milk has rarely been linked with cases of human infection. We describe the investigations undertaken following the isolation of Campylobacter jejuni from samples of unpasteurized milk prior to retail. Results of epidemiological investigations including typing of Campylobacter jejuni isolates using pyrolysis mass spectrometry, Penner and Lior serotyping, biotyping, phage typing and restriction fragment length polymorphism analysis provided convincing evidence implicating direct milk excretion of Campylobacter jejuni by one asymptomatic dairy cow as the source of the milk contamination and the cause of local cases of human enteritis.

Rapid inter-strain comparison by pyrolysis mass spectrometry in nosocomial infection with Xanthomonas maltophilia

Seventeen strains of Xanthomonas maltophilia and one strain of Pseudomonas cepacia were examined by pyrolysis mass spectrometry (PYMS). The Xanthomonas strains comprised 11 clinical and environmental isolates from a suspected outbreak of colonization and infection on a heart-lung transplant intensive care unit, two strains from patients elsewhere in the same hospital and four strains from a national reference collection. The single isolate of Pseudomonas cepacia was from a sink in the same affected intensive care unit. A series of discriminant analyses performed on the PYMS-derived data showed that, whereas six strains of Xanthomonas from the respiratory tract, blood and ventilatory equipment of one of the affected patients were indistinguishable, all the other isolates were distinct. The results of PYMS rapid inter-strain comparison were in accord with those of an epidemiological investigation which suggested that the episode was due to unauthorized reuse of disposable nebulizers and not to cross-infection between patients. Pyrolysis mass spectrometry with rapid data analysis is a potentially useful technique for the investigation of nosocomial infections due to organisms such as X. maltophilia.

Analysis of epidemic and sporadic strains of Listeria monocytogenes by pyrolysis mass spectrometry

Twenty‐six cultures of Listeria monocytogenes, serovar 4b, including 10 from a food‐borne outbreak in Switzerland and sporadic patient and food isolates from both Switzerland and the UK, were compared by pyrolysis mass spectrometry (PMS). This clustered all of the Swiss epidemic isolates with four other isolates indistinguishable from the Swiss strain by phage typing, a phage non‐typable isolate from a Swiss patient not known to be part of the epidemic and two strains (both from Switzerland) of a different phage type. The eight strains excluded from the PMS‐derived cluster were all either known to be unrelated to the epidemic, or of a phage type distinct from the epidemic strain, or both.

Inter-strain comparison by pyrolysis mass spectrometry in the investigation of Staphylococcus aureus nosocomial infection

Pyrolysis mass spectrometry (PyMS) was used to examine isolates of Staphylococcus aureus from an outbreak of wound infections on a cardiothoracic surgical unit, some of which were thought to have been related to a point-source in the operating theatre. The PyMS results were compared with the results of phage typing. Both methods suggested that a single strain of S. aureus, of phage pattern 29/52/52A/79/80/81, was responsible for some of the wound infections, but PyMS also identified two patients with phage non-typable isolates. Phage typing indicated four staff members as possible carriers of the epidemic strain, but PyMS indicated only two. Epidemiological enquiry confirmed that one of the two members of staff identified by both methods was likely to have been the source of the theatre-based infection. PyMS is a rapid and relatively inexpensive technique for the investigation of nosocomial S. aureus infection and was more discriminatory than phage typing in this instance.

Strain differentiation of nosocomial isolates of Pseudomonas aeruginosa by pyrolysis mass spectrometry

Pyrolysis mass spectrometry (PyMS) was used for rapid interstrain comparison of Pseudomonas aeruginosa isolates from a small outbreak of sternal wound infections in a cardiothoracic surgical ward. The PyMS results were compared with those obtained by conventional O-serotyping. All the isolates were phage non-typable. Evidence obtained from PyMS of identity/non-identity between isolates correlated completely with that obtained by O-typing and correctly identified those isolates comprising the epidemic strain, in one instance in advance of O-serotyping. The speed and versatility of PyMS make it an attractive technique for the initial screening of isolates from nosocomial outbreaks of infection with P. aeruginosa and other organisms.

Jackdaws and magpies as vectors of milkborne human Campylobacter infection.

In 1990 we reported that milk bottles pecked by jackdaws and magpies were a probable source of human campylobacter infection. During April to June 1990 an extended study of campylobacter infections was carried out in the Gateshead area. Prior to the study a health education programme was undertaken in an attempt to reduce human infection. Fifty-nine cases of human infection were recorded and 52 were interviewed. Thirty were entered into a case control study which demonstrated a very strong association between consumption of pecked milk and human campylobacter infection (chi 2 = 12.6, P less than 0.0004). It was estimated that between 500 and 1000 jackdaws (Corvus monedula) were present in the area where milk bottles were pecked and 63 isolates of campylobacter were made from the bill and cloaca. Target bottles were put out in the early mornings and campylobacters were isolated from 12 of 123 pecked bottles. Typing of the campylobacters revealed a wide distribution of strains amongst birds, pecked milk and human infections. The health education programme had only limited success.

Rapid inter-strain comparison by pyrolysis mass spectrometry of coagulase-negative staphylococci from persistent CAPD peritonitis

Pyrolysis mass spectrometry (PyMS) was used as a method of rapid inter-strain comparison of 19 isolates of coagulase-negative staphylococci from episodes of CAPD peritonitis. Thirteen isolates were from multiple, but distinct, episodes of peritonitis in 6 patients and the remaining 6 isolates were from 6 patients with single episodes. The results, expressed in terms of identity/non-identity of strains, were compared with those obtained using an established typing system comprising an extended antibiogram, determination of biotype and plasmid profile analysis. The PyMS results for inter-strain comparison were in agreement with the reference typing scheme results. PyMS can be used in this setting to rapidly obtain evidence that persistent infection is/is not likely to be due to the same organism, although it cannot be used for formal typing. The results by both methods showed that serial, apparently distinct, episodes of peritonitis over periods as long as 120 days may be due to the same strain of coagulase-negative staphylococcus. Clinically based distinctions between recurrence of infection (same strain) and re-infection (different strains) may not always be supported by the microbiological evidence.

Differentiation between mycobacteria of the Mycobacterium tuberculosis complex by pyrolysis mass spectrometry

32 isolates belonging to the Mycobacterium tuberculosis complex were examined by pyrolysis mass spectrometry (PyMS). This technique demonstrated that recent clinical isolates of M. africanum were indistinguishable from those of M. bovis and together formed a homogeneous group distinct from M. tuberculosis. Isolates of BCG were heterogeneous and more closely related to laboratory-adapted strains of M. tuberculosis than to recent isolates of either M. tuberculosis or M. bovis. PyMS is a simple and inexpensive technique which gives interesting information on the relationships between members of the M. tuberculosis complex and can make the clinically important distinction between strains of M. bovis and M. tuberculosis accurately and much more rapidly than conventional techniques.

Strain differentiation of capsule type 23 penicillin‐resistant Streptococcus pneumoniae from nosocomial infections by pyrolysis mass spectrometry

Sixteen isolates of penicillin‐resistant Streptococcus pneumoniae (penicillin‐resistant pneumococci, PRP) serotype 23 with identical antibiograms were examined by pyrolysis mass spectrometry (PYMS) as a possible method of rapid inter‐strain comparison. Some of the isolates were from well‐documented hospital outbreaks of PRP infection whilst others were sporadic isolates. The results were in good agreement with the epidemiological data and showed that PYMS can distinguish strains within a single serotype of Strep. pneumoniae. Pyrolysis mass spectrometry is an attractive technique for the identification and management of nosocomial infections with penicillin‐resistant strains of Strep. pneumoniae.

Rapid detection of Verocytotoxin production status in Escherichia coli by artificial neural network analysis of pyrolysis-mass spectra

Abstract Verocytotoxin (VT)-producing and VT-non-producing strains of Escherichia coli of four different serogroups were characterised by pyrolysis-mass spectrometry (Py-MS). Py-MS spectral data were used to train artificial neural networks (ANNs) which then accurately assessed the VT-production status of fresh clinical isolates of E. coli of the same serogroups from their Py-MS spectral data. Serogroup-specific ANNs could be trained successfully with Py-MS data from only one exemplar each of VT-producing and VT-non-producing strains and training was accomplished in less than 1 min. Where more than one VT-producing phenotype occurred within a serogroup it was necessary to include an example of each phenotype in the training set. The combination of Py-MS with ANNs may be an important new, powerful and very rapid method for the detection of a particular biological character, such as exotoxin production within strains of single species or sub-species of bacteria.