B. Dwyer

Toxigenic Escherichia coli Associated with Sudden Infant Death Syndrome

The role of Escherichia coli as a cause of sudden infant death syndrome was investigated prospectively. Strains of E. coli producing the heat labile enterotoxin (LT) or the Vero-cell cytotoxin (VT) were isolated from the intestinal contents of 21/46 infants who died from sudden infant death syndrome (SIDS). None were found in the contemporaneously sampled faeces of 24 normal live infants in the same area. Live infants were used as controls in the absence of dead infants who had not died of SIDS. This high incidence of toxigenic E. coli among the SIDS infants versus the low incidence in controls, together with the general rarity of finding such toxigenic E. coli in the community of a temperate developed country, made us conclude that there may be a causal relationship between toxigenic E. coli and SIDS. The O and H serotypes of the toxigenic E. coli associated with SIDS infants tended not to be those normally considered to be toxigenic. The toxigenicity appeared to be relatively labile. It is suggested that SIDS may be associated with the infant either acquiring these unusual types of E. coli or more likely that its normal resident E. coli acquire the plasmids to produce these toxins.

Guillain-Barré syndrome and Campylobacter jejuni/coli.

A close temporal relationship between Guillain-Barre syndrome (GBS) and preceding Campylobacter jejuni or C. coli (CJC) infection has been reported by us’ and in a prospective study in south-east England.’ The acute paralytic symptoms coincide with a serum antibody pattern characteristic of recent infection with CJC. This association suggests a possible immunological cross reaction between the organism and certain hostspecific tissue component(s), hence we undertook to investigate the possible cross-reactivity between CJC and human sciatic nerve (SN) antigens using immunoblotting. For this experiment we used a homogenate of fresh human nerve obtained at lower limb amputation or SN obtained from a sacrificed primate (Rhesus monkey) and a dense suspension of 12 fecal isolates of CJC, none of which had been implicated in a GBS episode. Anti CJC antibodies were produced by immunizing rabbits with twice weekly intravenous injections for a period of 4 wks with a dose increasing weekly from 0.2 mL to 1.0 mL in the fourth week. Many rabbits in our colony are sub-clinically infected with Campylobacter jejuni or Campylobacter coli. and therefore rabbits were selected for immunization if their preimmunization sera showed no or minimal levels of anti CJC antibodies on immunoblotting. Approval for the above experiments was obtained from the hospital’s animal ethics committee. The antisera obtained were then used in a immunoblot setting following our previously published method.’ The neural or CJC peptides were separated by electrophoresis in 12% polyacrylamide gel and then blotted onto a nitrocellulose. The individual nitrocellulose strips containing peptide were then reacted with: (a) pre-bleeds of the immunized rabbits, (b) post-immunization bleeds and (c) postimmunization bleeds which were first absorbed with a dense suspension of CJC. The results of these reactions for the 4 rabbits’ sera are shown in the Figure. As expected and shown on the left side of the

Use of ribosomal RNA gene restriction patterns to investigate two outbreaks of Campylobacter enteritis in Melbourne, Australia.

The analysis of ribosomal RNA (rRNA) gene patterns (ribotyping) has been used to differentiate strains within bacterial species. We used this method to investigate two outbreaks of campylobacter enteritis that occurred recently in Melbourne, Australia. The first outbreak involved seven patients although isolates from only five patients were available for typing. The second outbreak consisted of three patients infected with human immunodeficiency virus (HIV) on the same ward of a hospital. Analysis of the rRNA gene patterns revealed identical patterns for the isolates from five patients in the first outbreak, suggesting that these isolates were from the same source. However, ribotyping of the four isolates from the second outbreak showed three distinct ribotypes indicative of contact with unrelated sources. This study demonstrated that ribotyping is a useful, reliable and convenient typing scheme for epidemiological purposes.

Evaluation of the phadebact ETEC-LT test for the heat-labile enterotoxin of Escherichia coli

The Phadebact ETEC-LT is a rapid method of identifying enterotoxigenic Escherichia coli (ETEC), producing the heat-labile enterotoxin (LT). It uses staphylococcal coagglutination as a means of identifying the LT released from ETEC. In this investigation both known strains of ETEC from a variety of sources as well as strains from patients were tested. Good agreement was found between the Phadebact ETEC-LT test and established tests for LT. The test was found easy to use in the clinical laboratory environment, and revealed that LT producing ETEC may be more common causes of diarrhoea in Australia than had been anticipated.

Comparative evaluation of cryptococcal latex tests.

Summary One hundred and seven specimens (24 CSF and 83 sera) from 90 patients were tested for the presence of Cryptococcus neoformans antigen using the Fairfield Hospital in‐house latex agglutination technique and the IMMY and Meridian commercial latex agglutination kits. Forty one specimens (14 CSF and 27 sera) from 27 patients with culture‐proven cryptococcosis were positive by both the Fairfield and IMMY latex tests. Thirty nine of these specimens were positive by the Meridian latex test. Two were negative. Sixty six specimens (10 CSF and 56 sera) from 63 patients not known to have cryptococcosis were negative by all 3 tests.

Rapid detection and molecular characterization of australian human rickettsial isolates

Australia has a number of unique rickettsial diseases including Queensland Tick Typhus. More recently, Flinders Island Spotted Fever ( FISF ) of presumed rickettsial origin has been described. We have studied Australian human rickettsial disease from 2 perspectives. Firstly, we have detected rickettsial DNA in blood samples of 2 patients with FISF by DNA amplification utilizing the Polymerase Chain Reaction. Confirmation of the rickettsial origin of the amplified DNA was made by hybridization with a rickettsia-specific DNA probe. This probe, made from the genus-common 17 kilodalton antigen of Rickettsia australis has been fully characterised and incorporates non-radioactive detection of target molecules. We aim to develop this method to provide rapid diagnosis of rickettsial disease Secondly, by applying the molecular typing technique of ribosomal DNA hybridization we have investigated the DNA relatedness of Australian human rickettsial isolates from Queensland Tick Typhus and presumptive human rickettsial isolates from FISF. Digestion of purified rickettsial chromosomal DNA from human isolates with the restriction endonuclease Eco R1 revealed specific differences between rickettsial isolates from patients with Queensland Tick Typhus and FISF when probed with ribosomal DNA. Ongoing studies are in progress to establish the relatedness of these isolates.

Mycobacterial Infections: Epidemiological Trends-Australia

Tuberculosis remains an important cause of morbidity in Australia with a significant proportion of new cases aring in immigrant groups. However the most dramatic change in mycobacteria) epidemiology in the last decade has been the accompaniment of AIDS by mycobacterial infections. Tuberculosis occurs as an early manifestation of HIV induced immunodcpletion and has been seen in 11 of 350 AIDS cases at Fairfield Hospital. More frequently encountered have been infections caused by the Mycobacterium avium complex (MAC). Generally these have been due to Mycobacterium avium itself. Infections are seen in 40% of all patients with AIDS and the common sites from which MAC arc recovered include blood, faeces, lymph nodes, bone marrow and skin. Recently a focus of Mycobacterium kansasii infecytioti has been recognised on the Victoria-South Australia border and appears to be linked to the reticulated water supply.

Mycobacterial Infections: New Diagnostic Methods

The prudent microbiologist still relies on the recovery of mycobacteria on solid media for the determination of the presence of infection due to these organisms. In recent years there have been a number of developments which augment the acid fast slain and conventional culture on egg based or defined mycobacterial media. The advent of radiometric culture methodology (Baciec™) and of probes for species or genus specific ribosomal RNA (eg Geneprobe™) offer the opportunity for accelerated detection, speciation and even antibiotic susceptibility. The methods are expensive and may invoke a greater demand on labor than can be spared, especially in laboratories processing fewer than 250() specimens per annum. Newer methods involving the polymerase chain reaction may provide very rapid diagnosis but are likely to be some years away as there are great problems of contamination control yet to be solved. In the meantime ihe new DNA technology requires to be harnessed to studying the epidemiology of these infections as this will lead to new insights into their control