Discrimination of SHV beta-lactamase genes by restriction site insertion-PCR

Restriction site insertion-PCR (RSI-PCR) is a simple, rapid technique for detection of point mutations. This technique exploits primers with one to three base mismatches near the 3' end to modulate a restriction site. We have developed this technique to identify described mutations of the bla(SHV) genes for differentiation of SHV variants that cannot be distinguished easily by other techniques. To validate this method, eight standard strains were used, each producing a different SHV beta-lactamase: SHV-1, SHV-2, SHV-3, SHV-4, SHV-5, SHV-6, SHV-8, and SHV-18. Mismatch primers were designed to detect mutations affecting amino acids at positions 8 (SspI), 179 (HinfI), 205 (PstI), 238 (Gly-->Ala) (BsrI), and 240 (NruI) of bla(SHV) genes. All amplimers of the bla(SHV) genes used in this study yielded the predicted restriction endonuclease digestion products. In addition, this study also makes theoretical identification of bla(SHV-6), bla(SHV-8), and 12 novel bla(SHV) variants using the PCR-restriction fragment length polymorphism (RFLP) technique possible. By using a combination of PCR-RFLP and RSI-PCR techniques, up to 27 SHV variants can now be distinguished rapidly and reliably. These simple techniques are readily applied to epidemiological studies of the SHV beta-lactamases and may be extended to the characterisation of other resistance determinants.

Comparison of variable number tandem repeat and IS6110-restriction fragment length polymorphism analyses for discrimination of high- and low-copy-number IS6110 Mycobacterium tuberculosis isolates

The present study was designed to evaluate the use of variable number tandem repeat (VNTR) and IS6110-restriction fragment length polymorphism (RFLP) analyses in combination as a two-step strategy for discrimination (as measured by the Hunter-Gaston Discrimination Index [HGDI]) of both high- and low-copy-number IS6110 Mycobacterium tuberculosis isolates compared to IS6110-RFLP alone with an unselected collection of isolates. Individually, IS6110-RFLP fingerprinting produced six clusters that accounted for 69% of the low-copy-number IS6110 isolates (five clusters) and 5% of the high-copy-number IS6110 isolates (one cluster). A total of 39% of all the isolates were clustered (HGDI = 0.97). VNTR analysis generated a total of 35 different VNTR allele profile sets from 93 isolates (HGDI = 0.938). Combining IS6110-RFLP analysis with VNTR analysis reduced the overall percentage of clustered isolates to 29% (HGDI = 0.988) and discriminated a further 27% of low-copy-number isolates that would have been clustered by IS6110-RFLP alone. The use of VNTR analysis as an initial typing strategy facilitates further analysis by IS6110-RFLP, and more importantly, VNTR analysis subdivides some IS6110-RFLP-defined clusters containing low- and single-copy IS6110 isolates.

Occurrence of a new metallo-beta-lactamase IMP-4 carried on a conjugative plasmid in Citrobacter youngae from the People's Republic of China

During the course of an antimicrobial resistance surveillance programme in Guangzhou, the People's Republic of China, single strains of Citrobacter youngae and Pseudomonas aeruginosa were identified which were resistant to imipenem and found to carry the carbapenemase gene bla(IMP). PCR screening of the citrobacter strain with specific primers for the bla(IMP) type genes gave a 587-bp product which when sequenced gave 100% homology with the bla(IMP-4) sequence reported recently from Acinetobacter spp. The determinant in the C. youngae strain was found to be located on a 156-kb plasmid capable of transfer to Escherichia coli UB1637 by conjugation. Sequencing of the bla(IMP-4) open reading frame in the C. youngae strain and adjacent sequences not only confirmed the presence of bla(IMP-4) but also identified that a conserved core site found within the 59-bp element of integrons was present and the same as the one described in the only other occurrence of bla(IMP-4) in Acinetobacter spp. isolated from an intensive care unit in Hong Kong. This is the second report of transferable carbapenemase genes in Enterobacteriaciae outside of Japan and the first in the People's Republic of China. Under the selective pressure of carbapenems and extended spectrum cephalosporins use we might expect this gene to spread and widespread surveillance should be instituted.

Rapid identification of laboratory contamination with Mycobacterium tuberculosis using variable number tandem repeat analysis

Compared with solid media, broth-based mycobacterial culture systems have increased sensitivity but also have higher false-positive rates due to cross-contamination. Systematic strain typing is rarely undertaken because the techniques are technically demanding and the data are difficult to organize. Variable number tandem repeat (VNTR) analysis by PCR is rapid and reproducible. The digital profile is easily manipulated in a database. We undertook a retrospective study of Mycobacterium tuberculosis isolates collected over an 18-month period following the introduction of the BACTEC MGIT 960 system. VNTR allele profiles were determined with early positive broth cultures and entered into a database with the specimen processing date and other specimen data. We found 36 distinct VNTR profiles in cultures from 144 patients. Three common VNTR profiles accounted for 45% of true-positive cases. By combining VNTR results with specimen data, we identified nine cross-contamination incidents, six of which were previously unsuspected. These nine incidents resulted in 34 false-positive cultures for 29 patients. False-positive cultures were identified for three patients who had previously been culture positive for tuberculosis and were receiving treatment. Identification of cross-contamination incidents requires careful documentation of specimen data and good communication between clinical and laboratory staff. Automated broth culture systems should be supplemented with molecular analysis to identify cross-contamination events. VNTR analysis is reproducible and provides timely results when applied to early positive broth cultures. This method should ensure that patients are not placed on unnecessary tuberculosis therapy or that cases are not falsely identified as treatment failures. In addition, areas where existing procedures may be improved can be identified.

Duodenal microflora in very-low-birth-weight neonates and relation to necrotizing enterocolitis

Necrotizing enterocolitis (NEC) is the most common gastrointestinal emergency in the neonatal period. Small-bowel overgrowth with aerobic gram-negative bacteria has previously been implicated in the development of NEC. This prospective study performed quantitative bacteriology on 422 duodenal aspirates collected from 122 very-low-birth-weight (<1,500-g) newborns, at the time of routine changing of nasogastric tubes. Isolates of Enterobacteriaceae were typed by repetitive extragenic, palindromic PCR and pulsed-field gel electrophoresis. One or more samples from 50% of these infants yielded gram-negative bacteria, predominantly Escherichia coli, Klebsiella spp., and Enterobacter spp., with counts up to 10(8) CFU/g. The proportion of samples with gram-negative bacteria increased with postnatal age, while the percentage of sterile samples declined. Molecular typing revealed marked temporal clustering of indistinguishable strains. All infants had been fed prior to isolation of gram-negative organisms. Antibiotic use had no obvious effect on colonization with Enterobacteriaceae. There were 15 episodes of suspected NEC (stage I) and 8 confirmed cases of NEC (2 stage II and 6 stage III) during the study period. Duodenal aspirates were collected prior to clinical onset in 13 episodes of NEC. Seven of these yielded Enterobacteriaceae, of which five strains were also isolated from infants without NEC. Very-low-birth-weight infants have high levels of duodenal colonization with Enterobacteriaceae, with evidence of considerable cross-colonization with indistinguishable strains. There was no association between duodenal colonization with particular strains of Enterobacteriaceae and development of NEC.

Classification of Proteus vulgaris biogroup 3 with recognition of Proteus hauseri sp. nov., nom. rev. and unnamed Proteus genomospecies 4, 5 and 6

Strains traditionally identified as Proteus vulgaris formed three biogroups. Biogroup 1, characterized by negative reactions for indole production, salicin fermentation and aesculin hydrolysis, is now known as Proteus penneri. Biogroup 2, characterized by positive reactions for indole, salicin and aesculin, was shown by DNA hybridization (hydroxyapatite method) to be a genetic species separate from biogroup 1 and from biogroup 3 which is positive for indole production and negative for salicin and aesculin. In this study, 52 strains were examined, of which 36 strains were Proteus vulgaris biogroup 3, which included the current type strain of the species P. vulgaris (ATCC 29905T), and compared to seven strains of Proteus vulgaris biogroup 2 and nine type strains of other species in the genera Proteus, Providencia and Morganella. By DNA hybridization, these 36 strains were separated into four distinct groups, designated as Proteus genomospecies 3, 4, 5 and 6. DNAs within each separate Proteus genomospecies were 74-99% related to each other in 60 degrees C hybridization reactions with < or = 4.5% divergence between related sequences. Proteus genomospecies 3 contained the former P. vulgaris type strain and one other strain and was negative in reactions for salicin fermentation, aesculin hydrolysis and deoxyribonuclease, unlike the reactions associated with strains considered as typical P. vulgaris which are positive in reactions for salicin, aesculin and DNase. Genomospecies 3 can be distinguished from Proteus genomospecies 4, 5 and 6 because it is negative for Jordan's tartrate. Proteus genomospecies 4, containing five strains, was differentiated from Proteus penneri, genomospecies 3 and 6 and most, but not all, strains of genomospecies 5, by its ability to ferment L-rhamnose. Proteus genomospecies 5 and 6, containing 18 and 11 strains, respectively, could not be separated from each other by traditional biochemical tests, by carbon source utilization tests or SDS-PAGE of whole-cell proteins. In an earlier publication, a request was made to the Judicial Commission that the former type strain of P. vulgaris (ATCC 13315) be replaced by P. vulgaris biogroup 2 strain ATCC 29905T, a strain considered more biochemically typical of P. vulgaris strains. This would have the effect of assigning the name P. vulgaris to P. vulgaris biogroup 2. Since this request has been acceded to, the name Proteus hauseri is herein proposed for Proteus vulgaris genomospecies 3. Its type strain is ATCC 700826T. Proteus genomospecies 4, 5 and 6 will remain unnamed until better phenotypic differentiation can be accomplished. All Proteus genomospecies were similar in their antimicrobial susceptibility patterns. Nineteen strains were isolated from urine, four from faeces, two from wounds, nine from other human sources and two from animals.

Detection of extended-spectrum beta-lactamases in members of the family enterobacteriaceae: comparison of the MAST DD test, the double disc and the Etest ESBL

A technically simple method-the MAST double disc (MDD) test-for the detection of extended-spectrum beta-lactamase (ESBL) production by bacteria is described. A wide range of ESBL, non-ESBL and Class 1 beta-lactamase-producing isolates was examined. The MDD test, which uses discs containing ceftazidime and a complementary disc containing ceftazidime and clavulanate and a second pair containing cefotaxime and cefotaxime and clavulanate was compared with the standard double disc diffusion test and an Etest method. Both the Etest and the MDD correctly identified 93% of ESBL producers. The MDD is an inexpensive alternative to current methods for the detection of ESBL production.

Dynamics of meningococcal long-term carriage among university students and their implications for mass vaccination

In the 1997-98 academic year, we conducted a longitudinal study of meningococcal carriage and acquisition among first-year students at Nottingham University, Nottingham, United Kingdom. We examined the dynamics of long-term meningococcal carriage with detailed characterization of the isolates. Pharyngeal swabs were obtained from 2,453 first-year students at the start of the academic year (October), later on during the autumn term, and again in March. Swabs were immediately cultured on selective media, and meningococci were identified and serologically characterized. Nongroupable strains were genetically grouped using a PCR-based assay. Pulsed-field gel electrophoresis was used to determine the link between sequential isolates. Of the carriers initially identified in October, 44.1% (98 of 222) were still positive later on in the autumn (November or December); 57.1% of these remained persistent carriers at 6 months. Of the index carriers who lost carriage during the autumn, 16% were recolonized at 6 months. Of 344 index noncarriers followed up, 22.1% acquired carriage during the autumn term and another 13.7% acquired carriage by March. Overall, 43.9% (397 of 904) of the isolates were noncapsulated (serologically nongroupable); by PCR-based genogrouping, a quarter of these belonged to the capsular groups B and C. The ratio of capsulated to noncapsulated forms for group B and C strains was 2.9 and 0.95, respectively. Sequential isolates of persistent carriers revealed that individuals may carry the same or entirely different organisms at different times. We identified three strains that clearly switched their capsular expression on and off at different times in vivo. One student developed invasive meningococcal disease after carrying the same organism for over 7 weeks. The study revealed a high rate of turnover of meningococcal carriage among students. Noncapsulated organisms are capable of switching their capsular expression on and off (both ways) in the nasopharynx, and group C strains are more likely to be noncapsulated than group B strains. Carriage of a particular meningococcal strain does not necessarily protect against colonization or invasion by a homologous or heterologous strain.

Characterisation of extended-spectrum beta-lactamases of the SHV family using a combination of PCR-single strand conformational polymorphism (PCR-SSCP) and PCR-restriction fragment length polymorphism (PCR-RFLP)

Polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) has been developed to extend the identification of SHV beta-lactamases previously characterised by PCR-single strand conformational polymorphism (PCR-SSCP) analysis alone. Eight bacteria, each producing a different SHV beta-lactamase, were used in this study. These bacteria harbour bla(SHV-1), bla(SHV-2a), bla(SHV-3), bla(SHV-4), bla(SHV-5) (two strains), bla(SHV-11) and bla(SHV-12). All isolates were characterised by PCR-SSCP and PCR-RFLP with DdeI and NheI digestion. By a combination of these techniques, the genes encoding these beta-lactamases could be differentiated from each other. In addition, the PCR-RFLP technique theoretically can be applied to distinguish the genes encoding SHV-7, SHV-9, SHV-10, SHV-15, SHV-17 and SHV-24 from those encoding other SHV variants. We report a simple PCR-RFLP technique that can be used in epidemiological studies to enable the rapid characterisation of known SHV beta-lactamases in a combination with the previously published PCR-SSCP analysis.

Resistance to ciprofloxacin and the new fluoroquinolones

Resistance to ciprofloxacin has generally remained low in the UK. A low rate of resistance development in vitro has been suggested for the newer fluoroquinolones such as grepafloxacin and trovafloxacin. Levofloxacin is likely to have a pattern of development of resistance similar to that of ofloxacin. Resistance problems with ofloxacin are being reported in the USA, but it is unclear whether similar problems will arise with levofloxacin. Restrained quinolone use, surveillance of pathogen susceptibility and control of cross-infection with resistant clones remain important strategies for managing fluoroquinolone resistance.

Non-pathogenic Escherichia coli versus mesalazine for the treatment of ulcerative colitis: a randomised trial

BACKGROUND

Ulcerative colitis has been suggested to be caused by infection and there is circumstantial evidence linking Escherichia coli with the condition. Our aim was to find out whether the administration of a non-pathogenic strain of E. coli (Nissle 1917) was as effective as mesalazine in preventing relapse of ulcerative colitis. We also examined whether the addition of E. coli to standard medical therapy increased the chance of remission of active ulcerative colitis.

METHODS

This was a single-centre, randomised, double-dummy study in which 120 patients with active ulcerative colitis were invited to take part. 116 patients accepted; 59 were randomised to mesalazine and 57 to E. coli. All patients also received standard medical therapy together with a 1-week course of oral gentamicin. After remission, patients were maintained on either mesalazine or E. coli and followed up for a maximum of 12 months. A two-stage, conditional, intention-to-treat analysis was done.

FINDINGS

44 (75%) patients in the mesalazine group attained remission compared with 39 (68%) in the E. coli group. Mean time to remission was 44 days (median 42) in the mesalazine group and 42 days (median 37) for those treated with E. coli. In the mesalazine group, 32 (73%) patients relapsed compared with 26 (67%) in the E. coli group. Mean duration of remission was 206 days in the mesalazine group (median 175) and 221 days (median 185) in the E. coli group.

INTERPRETATION

Our results suggest that treatment with a non-pathogenic E. coli has an equivalent effect to mesalazine in maintaining remission of ulcerative colitis. The beneficial effect of live E. coli may provide clues to the cause of ulcerative colitis.

Antimicrobial susceptibility testing of Chlamydia trachomatis using a reverse transcriptase PCR-based method

The conventional method for antimicrobial susceptibility testing of Chlamydia trachomatis is subjective and potentially misleading. We have developed a reverse transcriptase PCR (RT-PCR)-based method which is more sensitive and less subjective than the conventional method. Using 16 strains of C. trachomatis in triplicate assays, we found the RT-PCR method consistently more sensitive than the conventional technique for all eight antimicrobials tested, with resultant MICs determined by RT-PCR ranging from 1.6-fold higher (erythromycin) to >/=195-fold higher (amoxicillin).

Evolution and spread of SHV extended-spectrum beta-lactamases in gram-negative bacteria

Resistance to beta-lactam antibiotics has been a problem for as long as these drugs have been used in clinical practice. In clinically significant bacteria the most important mechanism of resistance is the production of one or more beta-lactamases, enzymes that hydrolyse the beta-lactam bond characteristic of this family of antibiotics. Prominent among the beta-lactamases produced by the Enterobacteriaceae is the SHV family. The first reported SHV beta-lactamase had a narrow spectrum of activity. By the accumulation of point mutations at sites that affect the active site of the enzyme, a family of derivatives of SHV-1 has evolved. Derivatives of SHV-1 either have an extended spectrum of activity, capable of inactivating third-generation cephalosporins, or are resistant to beta-lactamase inhibitors. This review describes the evolution and spread of the SHV family of beta-lactamases, introducing the structure-function analysis made possible by DNA sequence analysis. It also reviews the methods used to characterize members of this family of beta-lactamases, indicating some of the difficulties involved.

Non-pathogenic Escherichia coli versus mesalazine for the treatment of ulcerative colitis: a randomised trial

BACKGROUND

Ulcerative colitis has been suggested to be caused by infection and there is circumstantial evidence linking Escherichia coli with the condition. Our aim was to find out whether the administration of a non-pathogenic strain of E. coli (Nissle 1917) was as effective as mesalazine in preventing relapse of ulcerative colitis. We also examined whether the addition of E. coli to standard medical therapy increased the chance of remission of active ulcerative colitis.

METHODS

This was a single-centre, randomised, double-dummy study in which 120 patients with active ulcerative colitis were invited to take part. 116 patients accepted; 59 were randomised to mesalazine and 57 to E. coli. All patients also received standard medical therapy together with a 1-week course of oral gentamicin. After remission, patients were maintained on either mesalazine or E. coli and followed up for a maximum of 12 months. A two-stage, conditional, intention-to-treat analysis was done.

FINDINGS

44 (75%) patients in the mesalazine group attained remission compared with 39 (68%) in the E. coli group. Mean time to remission was 44 days (median 42) in the mesalazine group and 42 days (median 37) for those treated with E. coli. In the mesalazine group, 32 (73%) patients relapsed compared with 26 (67%) in the E. coli group. Mean duration of remission was 206 days in the mesalazine group (median 175) and 221 days (median 185) in the E. coli group.

INTERPRETATION

Our results suggest that treatment with a non-pathogenic E. coli has an equivalent effect to mesalazine in maintaining remission of ulcerative colitis. The beneficial effect of live E. coli may provide clues to the cause of ulcerative colitis.

Pyrolysis mass spectrometry analysis of free-living and symbiotic cyanobacteria

The potential of pyrolysis mass spectrometry to distinguish closely related cyanobacterial strains was assessed by using the technique to compare symbiotic cyanobacteria isolated from the hornwort Phaeoceros laevis and free-living cyanobacterial strains at the same field site. The same strains had previously been compared using polymerase chain reaction-based DNA fingerprinting techniques (West & Adams 1997, Appl. Environ. Microbiol. 63: 4479-4484). Many of the strains were grouped identically by the two techniques, although there were some differences, possibly resulting from the ability of these cyanobacteria to develop a range of specialised cell types having different chemical compositions to the vegetative cells. Although growth conditions were chosen to suppress cellular differentiation, this may not always have been completely successful. With careful control of growth conditions pyrolysis mass spectrometry has considerable potential as an additional tool for the phenetic comparison of cyanobacterial strains. It has the advantage that analysis is directly derived from whole cells, and hence is simpler and cheaper than DNA-based methods, although it does require the growth of axenic strains. The technique may be particularly useful in the study of some of the more cryptic unicellular and non-heterocystous filamentous cyanobacterial groups, in which the lack of cellular differentiation should minimise any variability in the chemical composition of cells.

Correlation between genotype and beta-lactamases of clinical and environmental strains of Stenotrophomonas maltophilia

Heterogeneity of beta-lactamase production by 17 clinical and nine environmental isolates of Stenotrophomonas maltophilia was investigated using MICs of six different beta-lactam antibiotics, isoelectric focusing (IEF) and pulsed field gel electrophoresis. There was no clear correlation between the results of IEF, genotype and MIC determination. Environmental isolates were more susceptible than clinical isolates; eight clinical and none of the environmental isolates expressed high-level resistance to meropenem. Only two isolates expressed high-level resistance to ceftazidime. These results indicate that further studies are required to elucidate the extent of genetic heterogeneity within the L1 and L2 beta-lactamase genes.

Prospective study of the risk of Clostridium difficile diarrhoea in elderly patients following treatment with cefotaxime or piperacillin-tazobactam

BACKGROUND

Rates of Clostridium difficile diarrhoea have recently been rising, with the elderly being at highest risk.

AIM

To compare the incidence of C. difficile colonization and diarrhoea in elderly patients treated for presumed infection with either empirical cefotaxime (CTX) or piperacillin-tazobactam (PT).

METHODS

A prospective, ward-based, crossover study was carried out on two well-matched care of the elderly wards at a UK tertiary care hospital, in patients requiring empirical broad-spectrum antibiotic treatment.

RESULTS

There was a highly significant increased incidence of C. difficile colonization (26/34 vs. 3/14, P=0.001) and diarrhoea (18/34 vs. 1/14, P=0.006) in patients who received CTX as opposed to PT. DNA fingerprinting suggested that most infections arose from strains acquired from the hospital environment.

CONCLUSIONS

Elderly patients are significantly less likely to develop C. difficile diarrhoea after treatment with PT than after CTX. The source of C. difficile appears to be predominantly from the ward environment.

Comparison of ARDRA and recA-RFLP analysis for genomic species identification of Acinetobacter spp

The genus Acinetobacter is subdivided into genospecies on the basis of DNA relatedness of strains. Phenotypic tests are insufficient to identify the genospecies to which an isolate belongs. The effectiveness of two previously described PCR-based methods for genospeciating Acinetobacter spp. was compared using a group of 32 well-characterised strains representing six genospecies. Amplified ribosomal DNA restriction analysis (ARDRA) correctly identified all 32 strains. Using restriction fragment length polymorphism (RFLP) of recA PCR amplimers, only six of the 32 strains were correctly identified. Heterogeneity in the recA gene sequence was demonstrated within five of the genospecies. ARDRA proved to be a reliable method whereas analysis of recA RFLP profiles did not enable the genospecies of most of the isolates of Acinetobacter spp. to be determined.

Exceptional desiccation tolerance of Acinetobacter radioresistens

The taxonomy of the genus Acinetobacter, which includes several important nosocomial pathogens, has been confused due to a lack of discriminatory phenotypic characteristics for identification. Molecular methods such as amplified ribosomal DNA restriction analysis (ARDRA) now enable the accurate identification of species. Ten clinical isolates of Acinetobacter radioresistens had genospecies confirmed by ARDRA but the APJ 20NE system, commonly used in clinical microbiology laboratories, mis-identified them as Acinetobacter lwoffii. Desiccation resistance of Acinetobacter spp. is an important attribute for their survival in the clinical environment. We investigated the ability of A. radioresistens to survive desiccation using an established glass surface model and compared the results to A. lwoffii and Acinetobacter baumannii. The 10 strains of A. radioresistens were extremely resistant to desiccation and survived for an average of 157 days at 31% relative humidity (RH). In contrast, two strains of A. lwoffii and three strains of A. baumannii survived for an average of three and 20 days respectively, at 31% RH, which was used as an approximation to climatic conditions in UK hospitals. A. radioresistens is thus well adapted for survival in the hospital environment and carriage on human skin and yet it is reported less frequently than A. lwoffii amongst clinical isolates. Cases of A. radioresistens infection may be under-reported due to mis-identification as A. lwoffii and further studies that use molecular identification methods are required to elucidate the role of A. radioresistens in human disease.

Survival of Acinetobacter baumannii on dry surfaces: comparison of outbreak and sporadic isolates

Acinetobacter spp. are important nosocomial pathogens reported with increasing frequency in outbreaks of cross-infection during the past 2 decades. The majority of such outbreaks are caused by Acinetobacter baumannii. To investigate whether desiccation tolerance may be involved in the ability of certain strains of A. baumannii to cause hospital outbreaks, a blind study was carried out with 39 epidemiologically well-characterized clinical isolates of A. baumannii for which survival times were determined under simulated hospital conditions. The survival times on glass coverslips of 22 strains isolated from eight well-defined hospital outbreaks in a German metropolitan area were compared with the survival times of 17 sporadic strains not involved in outbreaks but rather isolated from inpatients in the same geographic area. All sporadic isolates have been shown by pulsed-field gel electrophoresis to represent different strain types. There was no statistically significant difference between the survival times of sporadic strains of A. baumannii and outbreak strains (27.2 versus 26.5 days, respectively; P < or = 0.44) by the Wilcoxon-Mann-Whitney test. All investigated A. baumannii strains, irrespective of their areas of endemicity or epidemic occurrence, have the ability to survive for a long time on dry surfaces. Antimicrobial susceptibility testing showed that A. baumannii outbreak strains were significantly more resistant to various broad-spectrum antimicrobial agents than sporadic strains. Both desiccation tolerance and multidrug resistance may contribute to their maintenance in the hospital setting and may explain in part their propensity to cause prolonged outbreaks of nosocomial infection.