Characterization of Burkholderia cepacia complex from environment influenced by human waste

The natural environment is a primary source of infections caused by members of Burkholderia cepacia complex (BCC), but the release of human waste may in return enrich the natural environment with clinically relevant BCC. Seven BCC isolates from environment influenced by human liquid or solid waste across Croatia, and one clinical isolate was characterised. B. multivorans recovered from the soil at illegal dumpsite belonged to sequence type (ST)19; B. ambifaria from the agricultural soil fertilized with swine or poultry manure to ST927 or new ST; B. cenocepacia from creek sediment, river water and wound swab to new STs. Antimicrobial susceptibility of isolates ranged from sensitive to multidrug-resistant. A variety of bla_TEM genes was confirmed in isolates. Isolates expressed the virulence factors and survived in river water during 50 days. The BCC present natural environments influenced by the human waste are of clinical relevance and a potential source of sporadic infections.

Oxacillinases and antimicrobial susceptibility of Ralstonia pickettii from pharmaceutical water systems in Croatia

This study evaluated antibiotic susceptibility and presence of bla_OXA22 and bla_OXA60 genes in 81 isolates of Ralstonia pickettii obtained from different purified and ultra-pure water systems in two different geographical areas of Croatia. E-test and disk diffusion test were performed to determine antibiotic susceptibility. Polymerase Chain Reaction was applied to detect genes encoding OXA-22 and OXA-60, oxacillinases previously identified in R. pickettii. The isolates were genotyped by pulsed-field gel electrophoresis. The results revealed variable susceptibility/resistance profiles. Our isolates exhibited high susceptibility rates to ceftriaxone, cefotaxime, piperacillin-tazobactam, ciprofloxacin, imipenem, cefepime and in lesser extent to ceftazidime. High rates of susceptibility were also observed for sulfamethoxazole-trimethoprim and piperacillin. High resistance rates were noticed for ticarcillin-clavulanate, aztreonam and meropenem, as well as for all aminoglycosides tested. Modified Hodge test was positive in 51,9% strains, indicating production of carbapenemases. bla_OXA22 and bla_OXA60 genes were detected in 37.0% and 80.3% strains, respectively. Pulsed-field gel electrophoresis identified three major clusters containing subclusters. R. pickettii should be taken seriously as a possible cause of nosocomial infections to ensure adequate therapy, to prevent the development of resistant strains and to try to reduce the possibility of R. pickettii surviving in clean and ultra clean water systems.

1200. Molecular Epidemiology of Cephalosporinases and Extended Spectrum β-Lactamases (ESBLs) in Proteus mirabilis Isolates From Croatia: Following the Spread of Resistance Determinants Between Long-Term Care Facilities and the Community

Background

Previous studies on P. mirabilis strains isolated from Croatian healthcare institutions revealed the predominance of TEM-52 extended spectrum β-lactamase (ESBL), as well as the emergence of plasmid AmpC β-lactamases. Our aim was to molecularly characterize cefalosporinases in P. mirabilis isolates from long-term care facilities (LTCFs) and to compare their resistance profile and dynamics with community isolates.

Methods

From a total of 3,321 P. mirabilis isolates collected from two LCTFs and from outpatients between 2015 and 2017, 1.23% of them were resistant to third generation of cephalosporins. Antimicrobial sensitivity was tested by broth microdilution method. ESBLs and plasmid-mediated AmpC β-lactamases were detected with phenotypic inhibitor-based tests and polymerase chain reaction (PCR). Antibiotic resistance dissemination and genetic context of bla genes were interrogated by conjugal mating and PCR mapping, respectively. Plasmids were characterized by conjugation and transformation experiments, as well as PCR-based replicon typing.

Results

High-level of resistance to amoxicillin, co-amoxiclav, first, second and third generation of cephalosporins was found in all isolates. Three isolates tested positive in inhibitor-based test with clavulanic acid, and 38 both in Hodge test and combined disk test with phenylboronic acid, indicating the production of ESBLs and plasmid-mediated AmpC β-lactamases, respectively. Two ESBL-positive organisms yielded amplicons with primers for CTX-M β-lactamase of group 1 and one for TEM. All AmpC-positive organisms were identified by PCR as CMY (with an additional TEM). Insert sequence ISEcp-1 was found upstream of bla_CMYi bla_CTX-M genes. CTX-M positive strains harbored IncK plasmid, whereas AmpC-positive strains were negative for known plasmid types. This is also a first description of P. mirabilis harboring CTX-M-15 β-lactamase in Croatia.

Conclusion

Our study showed the persistence of CMY β-lactamases in one LTCF, but also the dissemination of characteristic resistance determinants to another LTCF and the community. Similar to some other studies, there was a clear trend of cephalosporinase dynamic switch from TEM variants to CMY and CTX-M, with impending consequences for treatment decisions.

Disclosures

All authors: No reported disclosures.

In vitro effect of subminimal inhibitory concentrations of antibiotics on the biofilm formation ability of Acinetobacter baumannii clinical isolates

The ability of A cinetobacter baumannii strains to form biofilm is one of the most important virulence factor which enables bacterial survival in a harsh environment and decreases antibiotic concentration as well. Subminimal inhibitory concentrations (subMICs) of antibiotics may change bacterial ultrastructure or have an influence on some different molecular mechanisms resulting in morphological or physiological changes in bacteria itself. The aim of this study was to determine effects of 1/2, 1/4, 1/8 and 1/16 minimal inhibitory concentrationsof imipenem, ampicillin-sulbactam, azithromycin, rifampicin and colistin on biofilm formation ability of 22 biofilm non-producing and 46 biofilm producing A. baumannii strains (30 weak producing strains and 16 moderate producing strains). Results of this study indicate that 1/2-1/16 MICs of imipenem, azithromycin, and rifampicin can reduce bacterial biofilm formation ability in moderate producing strains (p < 0.05), whereas 1/16 MIC of imipenem and 1/4-1/8 MICs of rifampicin reduce the biofilm formation in weak producing strains (p < 0.05). Statisticaly significant effect was detected among biofilm non-producing strains after their exposure to 1/16 MIC of azithromycin (p = 0.039). SubMICs of ampicillin-sulbactam and colistin did not have any significant effect on biofilm formation among tested A. baumannii strains.

Mechanisms of Carbapenem Resistance in Multidrug-Resistant Clinical Isolates of Pseudomonas aeruginosa from a Croatian Hospital

Pseudomonas aeruginosa is an opportunistic pathogen, one of the leading causes of nosocomial infections such as pneumonia, urinary tract infections, and bacteraemia. The bacterial resistance to structurally unrelated antibiotics and its spread within hospitals limits the efficient antimicrobial options and patients' outcome. Carbapenems are important agents for the therapy of infections due to multidrug-resistant (MDR) P. aeruginosa; hence, the development of carbapenem resistance severely hampers effective therapeutic options. The aim of this investigation was to examine mechanisms of carbapenem resistance and genomic diversity in carbapenem-resistant MDR strains of P. aeruginosa, which caused an outbreak among patients in Clinical Hospital Rijeka. Most of the isolates showed decreased expression of porin that is important for the entry of carbapenems (oprD). Overexpression of MexAB-OprM, MexCD-OprJ, and MexEF-OprN efflux systems was observed in many of the isolates. Production of metallo-β-lactamases was not detected. Typing by pulsed-field gel electrophoresis discriminated the isolates into five clusters. The clonal distribution of the strains was related to the location of hospital departments where the isolates were collected, which implies that most of the infections were caused by spread of the epidemic strains within the hospital.

Antimicrobial susceptibility and beta-lactamase production of selected gram-negative bacilli from two Croatian hospitals: MYSTIC study results

The meropenem yearly Susceptibility Test Information Collection (MYSTIC) programme is a global, longitudinal resistance surveillance network that monitors the activity of meropenem and compares its activity with other broadspectrum antimicrobial agents. We now report the antimicrobial efficacy of meropenem compared to other broad-spectrum agents within the selective Gram-negative pathogen groups from two Croatian Hospitals investigated between 2002-2007. A total of 1510 Gram-negative pathogens were tested and the minimum-inhibitory concentrations (MICs) were determined by broth microdilution method according to CLSI.There was no resistance to either imipenem or meropenem observed for Escherichia coli, Klebsiella pneumoniae and Proteus mirabilis in both medical centers. High resistance rates of K. pneumoniae to ceftazidime (18%), cefepime (17%) and gentamicin (39%) are raising concern. Acinetobacter baumannii turned out to be the most resistant Gram-negative bacteria with 81% resistant to ceftazidime, 73% to cefepime, 69% to gentamicin and 71% to ciprofloxacin. Almost 20% of Pseudomonas aeruginosa strains were resistant to imipenem, 13% to meropenem, 69% to gentamicin and 38% to ciprofloxacin.The prevalence of extended-spectrum beta-lactamases (ESBLs) in E. coli was 10% and in K. pneumoniae 49%. PCR and sequencing of the amplicons revealed the presence of SHV-5 in nine E. coli strains and additional tem-1 beta-lactamase five strains. Five K. pneumoniae strains were positive for bla(SHV-5 )gene. Eight ESBL positive Enterobacter spp. strains were found to produce tem and CtX-m beta-lactamases. Plasmid-mediated AmpC beta-lactamases were not found among K. pneumoniae, E. coli and Enterobacter spp. Three A. baumannii strains from Zagreb University Center were identified by multiplex PCR as OXA-58 like producers. Six A. baumannii strains from Split University Center were found to possess an ISAba1 insertion sequence upstream of bla(OXA-51 )gene. According to our results meropenem remains an appropriate antibiotic for the treatment of severe infections caused by Gram-negative bacteria. These data indicate that despite continued use of meropenem, carbapenem resistance is not increasing among species tested, except for A. Baumannii, in the two study hospitals and suggest that clinicians can still administer carbapenems as a reliable and effective choice in managing serious nosocomial infections.

Clonal spread of CTX-M-15-producing Klebsiella pneumoniae in a Croatian hospital

This study was conducted to detect and analyse the presence of extended-spectrum β-lactamase (ESBL)-producing Klebsiella pneumoniae associated with a nosocomial outbreak at a Croatian hospital. During 2007, 162 K. pneumoniae isolates with reduced susceptibility to third-generation cephalosporins were collected from various hospital units and patient specimens. Most of the strains were isolated from urine (61 %), followed by blood cultures (13 %), wound swabs (13 %), tracheal aspirates (5 %), intra-abdominal abscess aspirates (4 %), intravascular catheters (3 %) and cerebrospinal fluid (1 %). Medical wards were the most important source of the isolates (46 %); 21 % of the isolates originated from surgical intensive-care units. All patients had infections acquired during their stay in hospital. No community-acquired infections were reported. Sixty of these isolates were chosen for further analysis. A double-disc synergy test (DDST) was used to detect ESBLs. MICs were determined by the broth microdilution method according to CLSI guidelines. The transferability of ceftazidime resistance was tested by conjugation (broth mating method). PCR was used to detect alleles encoding ESBL enzymes. Plasmids encoding ESBLs were extracted with the Macherey Nagel Mini kit according to the manufacturer's recommendations. The genotypes of the strains were compared by analysis of banding patterns generated by PFGE of XbaI-digested genomic DNA. ESBLs were found by DDST in all isolates. All strains were resistant to cefuroxime, ceftazidime, cefotaxime, ceftriaxone, aztreonam, piperacillin/tazobactam and ciprofloxacin. There was variable susceptibility/resistance to cefepime and gentamicin. No resistance to ceftazidime/clavulanate and carbapenems was observed. Only six strains transferred resistance to an Escherichia coli recipient strain, with low frequency. All isolates yielded an amplicon of 545 bp with consensus MA primers. Multiplex PCR was positive for group 1 CTX-M β-lactamases. Sequencing of selected amplicons revealed the presence of bla CTX-M-15, with coding regions containing identical nucleotide sequences. Similarly to isolates from India, our isolates contained the ISEcpI insertion sequence located upstream of the bla CTX-M-15 gene, which has recently been demonstrated to mobilize 3′-adjacent genes to transfer between DNA replicons. The isolates contained a large plasmid of approximately 150 kb. The isolates were assigned to five clusters (>85 % similarity), which contained subclusters. The results of this work provided insights into the molecular epidemiology of the spread of ESBLs in K. pneumoniae involved in an outbreak at a Croatian hospital. The hospital antibiotic policy resulted in ceftriaxone being the most heavily prescribed third-generation cephalosporin, which might be expected to select for cefotaximases such as CTX-M-15.

Predominance of SHV-5 β-lactamase in enteric bacteria causing community-acquired urinary tract infections in Bosnia and Herzegovina

The beta-lactamases produced by 14 non-duplicate Klebsiella pneumoniae isolates and five Escherichia coli isolates from urine samples obtained from outpatients were characterised by isoelectric focusing, substrate profile determination, PCR and sequencing of bla(SHV) genes. Three E. coli A15 R(+) transconjugants were identified as isolates that produced SHV-5 beta-lactamase. This report is the first description of SHV-5 beta-lactamase among community isolates. Since the isolates showed distinct pulsed-field gel electrophoresis patterns, it was concluded that there was no clonal spread of bla(TEM) and bla(SHV) genes, and that dissemination of the bla(TEM) and bla(SHV) genes was the result of exchange of plasmids among different clones.

Sensitivity and specificity of various beta-lactam antibiotics and phenotypical methods for detection of TEM, SHV and CTX-M extended-spectrum beta-lactamases

The aim of this study was to compare the sensitivity and specificity of six different beta-lactam antibiotics using five phenotypical tests for detection of extended spectrum beta-lactamases (ESBLs) based on synergism of beta-lactam antibiotics and clavulanate. Experiments were performed on a set of 80 Klebsiella pneumoniae strains and 105 Escherichia coli strains with previously characterized ESBLs (SHV, TEM and CTX-M). ESBLs were detected by five different phenotypical methods: MIC (minimum inhibitory concentration) determination of beta-lactam antibiotics with and without clavulanate, double-disk synergy test (DDST), inhibitor-potentiated disk-diffusion test (IPDDT), CLSI-Clinical and Laboratory Standard Institution (former NCCLS) combined-disk-test, and modified MAST-disk-diffusion test (MAST-DD-test). Seven antibiotics were tested as indicators of ESBL production: ceftazidime, cefotaxime, ceftriaxone, aztreonam, ceftibuten, cefpodoxime and cefepime. Ceftazidime and aztreonam were the best indicators for SHV-5, SHV-12 and TEM beta-lactamases whereas cefotaxime and ceftriaxone were the most sensitive in detection of SHV-2 and CTX-M beta-lactamases in DDST, IPDDT and CLSI test. MIC determination of beta-lactam antibiotics with and without clavulanate was the most sensitive method. DDST was the least sensitive test. Double-disk synergy test, which is the most frequently used test for detection of ESBLs in routine laboratories, was the least sensitive independently of the indicator antibiotic. Since MIC determination is a very laborious and time consuming method, we would recommend the NCCLS combined disk test or IPDD test for detection of ESBLs in routine laboratories with 5 mm zone augmentation breakpoint.

Urinary Bactericidal Activity of Oral Antibiotics against Common Urinary Tract Pathogens in an ex vivo Model

BACKGROUND

In this investigation, the urine samples obtained in a single oral-dose pharmacokinetic study were examined for their bactericidal activity against a range of relevant urinary tract pathogens.

METHODS

Six healthy volunteers received a single oral dose of ten oral antibiotics available in Croatia. Urine samples were taken every 2 h during the whole dosing interval of the particular antibiotic. The urinary bactericidal activity was tested by determination of urinary bactericidal titers.

RESULTS

All antibiotics showed a significant urinary bactericidal activity against non-extended spectrum beta-lactamase Escherichia coli and Proteus mirabilis. Fluoroquinolones displayed high and persisting levels of urinary bactericidal activity against all gram-negative bacteria and Staphylococcus saprophyticus.

CONCLUSIONS

Average urinary bactericidal activity can be predicted from in vitro susceptibility testing, but we expect that there will be patients with a low level of urinary bactericidal activity.

Extended-spectrum-beta-lactamase-producing Enterobacteriaceae in Yaounde, Cameroon

Organisms producing extended-spectrum beta-lactamases (ESBLs) have been reported in many countries, but there is no information on the prevalence of ESBL-producing members of the family Enterobacteriaceae in Cameroon. A total of 259 Enterobacteriaceae strains were isolated between 1995 and 1998 from patients at the Yaounde Central Hospital in Cameroon. Enterobacterial isolates resistant to extended-spectrum cephalosporin and monobactam were screened for ESBL production by the double-disk (DD) synergy test. Thirty-one (12%) of these Enterobacteriaceae strains were shown to be positive by the DD synergy test, suggesting the presence of ESBLs. Resistance to oxyimino-cephalosporins and monobactams of 12 (38.7%) of the 31 strains-i.e., 6 Klebsiella pneumoniae, 4 Escherichia coli, 1 Citrobacter freundii, and 1 Enterobacter cloacae strain-was transferred to E. coli HK-225 by conjugation. Resistance to gentamicin, gentamicin plus trimethoprim-sulfamethoxazole, or trimethoprim-sulfamethoxazole was cotransferred into 6, 2, and 1 of these transconjugants, respectively. All 12 transconjugants were resistant to amoxicillin, piperacillin, all of the cephalosporins, and aztreonam but remained susceptible to cefoxitin and imipenem. Crude extracts of beta-lactamase-producing transconjugants were able to reduce the diameters of inhibition zones around disks containing penicillins, narrow- to expanded-spectrum cephalosporins or monobactams when tested against a fully susceptible E. coli strain but had no effect on such zones around cefoxitin, imipenem, and amoxicillin-clavulanate disks. The beta-lactamases produced by the 12 tranconjugants turned out to be SHV-12 by DNA sequencing. Therefore, the ESBL SHV-12 is described for the first time in Cameroon.

Bactericidal activity of oral β-lactam antibiotics in plasma and urine versus isogenic Escherichia coli strains producing broad- and extended-spectrum β-lactamases

Bacteria harbouring extended-spectrum beta-lactamases (ESBLs), derived by mutation from TEM-1, TEM-2 or SHV-1 beta-lactamases, have been described world-wide. The in vitro activities of these enzymes against beta-lactam antibiotics, including oral cephalosporins, are well recognised. The aim of this investigation was to assess the bactericidal activity of oral beta-lactam antibiotics available in Croatia (amoxicillin/clavulanate, cephalexin, cefuroxime, cefadroxil and ceftibuten), in biological fluids against isogenic Escherichia coli strains producing broad-spectrum (TEM-1, TEM-2 and SHV-1) and extended-spectrum beta-lactamases (SHV-2, SHV-3, SHV-4, SHV-5, SHV-12). Bactericidal activity of oral beta-lactams in plasma and urine was tested in time-kill experiments and by determining bactericidal titres at different time intervals post-dose. The killing rate of antibiotics in urine was slower than in plasma, but faster than in Mueller-Hinton broth. High bactericidal titres in urine were only maintained throughout the whole dosing interval by ceftibuten against strains producing broad-, SHV-2 and SHV-3 beta-lactamases. The older generation cephalosporins can be considered for the therapy of urinary tract infections caused by E. coli harbouring TEM-1, TEM-2 and SHV-1 beta-lactamases but a shorter dosing interval is needed. Ceftibuten can be recommended with caution in ESBL producing E. coli except those producing SHV-4, SHV-5 and SHV-12 that confer resistance to it. If these enzymes are produced, fluoroquinolones or carbapenems could be considered.

Post-exposure effects of cefepime and cefpirome on isogenic Escherichia coli hosts producing SHV-extended-spectrum beta-lactamases

Persistent suppression of bacterial growth after short antimicrobial exposure is called postantibiotic effect (PAE). By definition, there should be no subinhibitory concentrations of antimicrobial agent left when the postantibiotic effect starts. However, if subinhibitory concentrations are maintained after removing the antibiotic, the recovery period of the treated cultures is markedly prolonged. This is defined as postantibiotic-sub-MIC-effect (PA-SME). The aim of this study was to determine the PAE and PA-SME of cefpirome and cefepime on isogenic Escherichia coli strains producing SHV-2, SHV-5, and SHV-12 extended spectrum beta-lactamases (ESBL) compared to a non-ESBL E. coli strain. It was hypothesized that the presence of an ESBL would hydrolyze the cephalosporin molecule before it exerted a toxic effect on the bacterial cell and thus shorten the duration of PA-SME. Cefpirome and cefepime had no PAE against ESBL producing E. coli or it was of a short duration and present only at high antibiotic concentrations, but exposure to subinhibitory concentration of those antibiotics in the PA (postantibiotic) phase resulted in a significant delay of regrowth. The effect was more pronounced with higher concentrations of antibiotics, and uninfluenced by the type of enzyme and the antibiotic. The present study shows that the presence of subinhibitory concentrations of cefepime and cefpirome in the medium after exposure to suprainhibitory concentrations results in a significant delay of regrowth of both ESBL-positive and negative E. coli strains. The production of SHV-2, SHV-5 and SHV-12 ESBLs did not shorten the duration of the PA-SME.

Comparison of five different methods for detection of SHV extended-spectrum beta-lactamases

Five different methods for detection of different types of SHV extended-spectrum beta-lactamases (ESBL) were compared: minimum inhibitory concentration (MIC) determination of beta-lactam with and without clavulanic acid, double-disk synergy test (DDST), inhibitor potentiated disk diffusion test (IPDDT), three-dimensional test (TDT) and PCR/Nhe I test. MIC determination of beta-lactam with and without clavulanic acid was the most sensitive method regardless of the type of beta-lactamase. However the specificity of this method was a little above 90%. IPDDT turned out to be a very sensitive method too but it lacks specificity because 26.9% of ceftazidime sensitive strains (putative ESBL negative), gave a positive result. It is important to put all four disks on the plate because ceftazidime and aztreonam were more sensitive indicators for SHV-5 and SHV-12 beta-lactamase producers while cefotaxime and ceftriaxone were more reliable in detecting SHV-2 beta-lactamase producers. The DDST detected all SHV-5 and SHV-12 beta-lactamase producers and 95.2% of SHV-2, so it was less sensitive than MIC determination but was highly specific, since there were no false negative results observed. The sensitivity of DDST can be improved by using all four disks and placing them at the smaller distance from the central disk (2.5 cm). The TDT was the least sensitive method, particularly for SHV-5 and SHV-12 beta-lactamase producers. The PCR/Nhe I test for detection of ESBL blaSHV genes is a highly sensitive and specific method but it is rather laborious and thus not very practical for use in routine clinical laboratories. Nevertheless it has potential to serve as the gold standard in epidemiological investigations on ESBLs. According to the results of this investigation MIC determination of beta-lactam with and without clavulanic acid, even if only one antibiotic is used and the PCR/Nhe I tests are the most reliable methods for detection of SHV ESBLs.

Extended-spectrum beta-lactamases in clinical isolates of Klebsiella pneumoniae from Zagreb, Croatia

Forty clinical isolates of Klebsiella pneumoniae, from various clinical specimens, with reduced susceptibility to ceftazidime, were tested for extended-spectrum beta-lactamase (ESBL) production. ESBL production was demonstrated by an 8-fold reduction in the minimum inhibitory concentration (MIC) of ceftazidime combined with clavulanate (2 mg/L) compared to ceftazidime alone in all strains. The aim of this investigation was the biochemical and molecular characterization of the ESBL produced by K. pneumoniae strains and their Escherichia coli transconjugants. Transfer of ceftazidime resistance was demonstrated in 23 of 40 strains. Thirteen strains produced an ESBL with the isoelectric point of 8.2 which was encoded by a self-transferable multiresistance plasmid of 150 kb. The substrate profile was similar to that of the SHV-5 isolated initially in Chile. Seven of these 12 strains had an additional TEM beta-lactamase. Six isolates and their transconjugants produced a plasmid-encoded ESBL with an isoelectric point close to 5.4. The remaining 21 strains produced an ESBL with an isoelectric point of 7.6 (thus probably SHV-2) which was encoded on a plasmid transferable to E. coli in 4 strains only. Four of those strains possessed an additional plasmid encoded TEM beta-lactamase with an isoelectric point close to 5.4. The transconjugants harbored a multiresistance plasmid of 150 kb. Thus SHV-2 and SHV-5 enzymes appear to have been the most common ESBLs in K. pneumoniae from Zagreb during 1994-1995.