Isolation of Salmonella enterica serotype choleraesuis resistant to ceftriaxone and ciprofloxacin

Salmonella enterica serotype choleraesuis (S choleraesuis) usually causes systemic infections in man that need antimicrobial treatment. We isolated a strain of S choleraesuis that was resistant to ceftriaxone and ciprofloxacin from a patient with sepsis. Ciprofloxacin resistance was associated with mutations in gyrA and parC, whereas the ampC gene (bla(CMY-2)), responsible for ceftriaxone resistance, was carried by a transposon-like mobile element. This element was found inserted into finQ of a potentially transmissible 140 kb plasmid, with an 8 bp direct repeat flanking the junction regions. The appearance of this resistant S choleraesuis is a serious threat to public health, and thus constant surveillance is warranted.

Molecular epidemiology of nalidixic acid-resistant campylobacter isolates from humans and poultry by pulsed-field gel electrophoresis and flagellin gene analysis

To investigate the potential of poultry products as the source of human infections associated with quinolone-resistant campylobacters, 140 human and 75 poultry isolates of nalidixic acid-resistant campylobacters were collected between 1996 and 1998, and analysed by two molecular typing methods. By the analysis of restriction fragment length polymorphism of the flagellin gene, 33 distinct patterns were obtained, with 18 of which shared by both human (89%) and poultry (93%) isolates. By the pulsed-field gel electrophoresis of SmaI-restricted macrofragments, 105 different profiles were obtained, and 11 were found in both human (40%) and poultry (23%) isolates. When the two typing methods were combined, 112 unique genotypes were obtained, 11 of which were shared by both populations, including 53 (38%) human isolates and 14 (19%) poultry isolates. Although domestic poultry products are still important sources of the quinolone-resistant campylobacter infections in humans, there are other factors that might contribute to these increasing infections simultaneously. A more stringent policy in the use of antimicrobial agents in food animals can no longer be ignored.

Secular trends in incidence and antimicrobial resistance among clinical isolates of Salmonella at a university hospital in Taiwan, 1983-1999

The incidence and antimicrobial resistance among clinical isolates of salmonella at a university hospital in Taiwan between 1983 and 1999 are summarized in this report. A total of 7986 isolates were analysed. Serogroup B has been the most prevalent over the years, with an apparently continuous decline after 1995. Concordant decrease was also found among S. choleraesuis and S. typhi isolates in recent years. In contrast, the proportion of serogroup D strains increased significantly after 1996. S. typhi remained relatively susceptible to most of the antimicrobial agents examined. For non-typhoidal isolates, antimicrobial resistance to ampicillin (62%), chloramphenicol (67%), and sulfamethoxazole-trimethoprim (37%) was relatively higher than that reported elsewhere. Newer generation cephalosporins and fluoroquinolones remained effective over the years, although emerging resistance to these drugs has been noticed since 1992. A more prudent selection and use of antimicrobial agents, in both humans and animals, and a continuous surveillance of resistance are essential in the future.

Outbreaks of nosocomial bloodstream infections associated with multiresistant Klebsiella pneumoniae in a pediatric intensive care unit

BACKGROUND

Between June and October 1997, and during April 1998, a cluster of nosocomial bloodstream infections (BSIs) associated with Klebsiella pneumoniae was observed in 8 premature neonates from 1 pediatric intensive care unit (TPICU) in a 4000-bed medical center in northern Taiwan. An investigation was conducted to identify the possible reservoirs and mode of transmission.

METHODS

Epidemiologic surveillance and infection control interventions were executed. The environment was checked by submitting several swab samples for microbiological studies. The antibiograms and results from 2 molecular typing methods (pulsed-field gel electrophoresis and infrequent-restriction site polymerase chain reaction) of all bacteremic and environmental isolates of K. pneumoniae were compared.

RESULTS

Totally 39 K. pneumoniae isolates, including 9 from bacteremia, 26 from the environment, and 4 controls, were analyzed. One major pattern was found in 21 isolates, which included 8 bacteremic isolates with identical antibiograms, a single isolate from rectal swab screening, 2 of 8 isolates from hand cultures of medical staff, and 10 of 17 isolates from swabs of sinks in the TPICU. All 21 isolates illustrated identical antibiograms, while the other 18 isolates shared 4 antibiograms and 15 unique patterns.

CONCLUSIONS

The nosocomial BSIs appeared to be an outbreak induced by 1 multiresistant K. pneumoniae strain. The sinks may have acted as reservoirs for this outbreak strain. During washing, splattered water droplets containing the bacterial particles may have contaminated the hands of medical personnel and were then further transmitted to patients.

Molecular investigation of two clusters of hospital-acquired bacteraemia caused by multi-resistant Klebsiella pneumoniae using pulsed-field gel electrophoresis and in frequent restriction site PCR. Infection Control Group

Two molecular typing methods, DNA macrorestriction analysis with XbaI resolved by pulsed-field gel electrophoresis (PFGE) and infrequent restriction site PCR (IRS-PCR) assay with adapters designed for XbaI and HhaI restriction sites, were used to investigate two clusters of hospital-acquired bacteraemia associated with multi-resistant Klebsiella pneumoniae which occurred in a paediatric intensive care unit (PICU). A total of 56 K. pneumoniae isolates were analysed. These included 10 bacteraemic isolates from eight patients, 26 isolates obtained during an epidemiological survey, and 20 epidemiologically non-related isolates incorporated as controls. One major pattern was demonstrated in 22 of the 56 isolates analysed. These included nine of the 10 bacteraemic isolates, a single rectal isolate, two hand culture isolates and 10 sink isolates. All of these 22 isolates illustrated identical antibiograms, whilst the other 34 isolates shared six antibiograms and 31 unique patterns by either PFGE or IRS-PCR assay. The two clusters of bacteraemia appeared to be outbreaks induced by the same strain of K. pneumoniae which may have utilized sinks as reservoirs and been transmitted through the hands of medical personnel to patients. IRS-PCR demonstrates concordant results with PFGE analysis in studying the genetic relationships among K. pneumoniae isolates, and serves as an excellent epidemiological tool for this bacterium.

DNA polymorphism of Mycobacterium abscessus analyzed by infrequent-restriction-site polymerase chain reaction

BACKGROUND

Mycobacterium abscessus is an important pathogen that has been increasingly associated with many clinical and nosocomial infections. A reliable molecular typing scheme is essential for the epidemiological study of this rapidly growing mycobacterium. Pulsed-field gel electrophoresis (PFGE), considered to be the gold standard among molecular typing methods, has failed to provide satisfactory results in the molecular typing of this bacterium. A newly developed molecular typing method, infrequent-restriction-site polymerase chain reaction (IRS-PCR), was examined in this study to determine its suitability for fingerprinting M. abscessus isolates.

METHODS

Eight clinical isolates of M. abscessus and two reference strains (M. abscessus ATCC 19977 and M. chelonae ATCC 35749) were studied by DNA macrorestriction analysis with XbaI resolved by PFGE, and IRS-PCR assay with adaptors designed for XbaI and HhaI restriction sites.

RESULTS

By PFGE, different banding patterns were found in two clinical isolates of M. abscessus; the other isolates yielded only broken DNA and could not be assessed. By IRS-PCR, unique patterns were noted for the 10 isolates; the 10 appeared to be genetically different.

CONCLUSION

IRS-PCR may be an efficient substitute for PFGE in analyzing the DNA polymorphism and epidemiology of M. abscessus.

Molecular biology of hepatitis D virus: research and potential for application

Superinfection by hepatitis D virus (HDV) leads to acute hepatitis and causes progression to liver cirrhosis in a significant proportion of hepatitis B surface antigen (HBsAg) carriers. Current regimens (interferon) to treat hepatitis D patients has only transient but no lasting effects. New approaches are, therefore, warranted. Recently, several laboratory studies have discovered interesting properties of HDV that may become targets for antiviral chemicals. Viral replication requires the small hepatitis delta antigen (s-HDAg). The s-HDAg is a nuclear phosphoprotein. There is evidence indicating that phosphorylation is important for HDV replication. A second step of replication requires HDV-RNA self-cleavage and self-ligation. Interestingly, one group of antibiotics, the aminoglycosides, exerts strong suppression effects on HDV ribozyme activities. In the following stage of viral assembly, two post-translational modifications, namely isoprenylation of large HDAg and glycosylation of HBsAg are involved. Agents capable of blocking the two modifications should reduce viral production. These four possible targets are reviewed. For prevention, effective vaccines are not yet available. Two novel approaches are discussed. The first demonstrates the immunogenicity of a nucleic acid vaccine in mice. The second approach assembled an empty HDV particle in yeast. Advances on such laboratory investigations may provide new methods for the control of hepatitis D in the future.