Presence of genes for beta-lactamases of two different classes on a single plasmid from a clinical isolate of Serratia marcescens

Detection and genetic characterization of extended-spectrum beta-lactamases producers in a tertiary care hospital

BACKGROUND

Extended-spectrum beta-lactamase (ESBL)-producing organisms inactivate extended beta-lactam antibiotics and monobactams and also exhibit coresistance to many other classes of antibiotics. The present study was carried out to assess the prevalence of the ESBLs and to determine the most prevalent genotype in our hospital.

MATERIALS AND METHODS

All clinically significant Gram-negative isolates were identified, and their antimicrobial susceptibility testing was done by Kirby-Bauers' disc diffusion method. ESBL detection was confirmed by minimal inhibitory concentration method using agar dilution technique for those who screened positive by ceftazidime (30 μg) disc. Further, the established ESBL-positive isolates were subjected to genotyping for bla TEM, bla CTX-M, and bla SHV genes by using conventional polymerase chain reaction.

RESULTS

Escherichia coli was the most common (28.84%) Gram-negative bacillus followed by Klebsiella pneumoniae (18.07%), while Pseudomonas spp. (9.61%) was the most commonly identified nonfermenter. ESBL production was detected in 160 (30.8%) isolates. Klebsiella oxytoca (46.7%) followed by E. coli (44%) were the common ESBL producers. Most predominant ESBL gene was bla TEM, found in 122 (76.25%) isolates. Combinations of two genes were seen in 109 (68.1%) isolates, the most common (43.12%) combination being bla_TEM and bla_CTX-M. In this study, 16 (10%) strains had all the three types of genes. Most of the isolated Gram-negative bacilli (GNB) were sensitive to amikacin, imipenem, and colistin.

CONCLUSION

In our study, the 30.8% of GNB were ESBL producers. This is the only study that shows that TEM is the most prevalent ESBL genotypes in our area. Of concern is a good number of isolates showing all three patterns of genes (TEM, SHV, and CTX-M). Amikacin, imipenem, and colistin were the most useful antibiotics in our setup.

Nosocomial blood stream infection in intensive care units at Assiut University Hospitals (Upper Egypt) with special reference to extended spectrum beta-lactamase producing organisms

Aim

This study investigated the nosocomial blood stream infection (BSI) in the adult ICUs in Assiut university hospitals to evaluate the rate of infection in different ICUs, causative microorganisms, antimicrobial resistance, outcome of infection, risk factors, prevalence of extended spectrum B-lactamase producing organisms and molecular typing of Klebsiella pneumoniae strains to highlight the role of environment as a potential source of nosocomial BSI.

Methods

This study was conducted over a period of 12 months from January 2006 to December 2006. All Patients admitted to the different adult ICUs were monitored daily by attending physicians for subsequent development of nosocomial BSI. Blood cultures were collected from suspected patients to detect the causative organisms. After antimicrobial susceptibility testing, detection of ESBLs was conducted among gram negative isolates. Klebsiella pneumoniae isolates were tested by PCR to determine the most common group of B-lactamase genes responsible for resistance. Klebsiella pneumoniae isolates from infected patients and those isolated from the environment were typed by RAPD technique to investigate the role of environment in transmission of infection.

Results

The study included 2095 patients who were admitted to different ICUs at Assiut University Hospitals from January 2006 to December 2006. Blood samples were collected from infected patients for blood cultures. The colonies were identified and antibiotic sensitivities were performed. This study showed that the rate of nosocomial BSI was 75 per 1000 ICU admissions with the highest percentages in Trauma ICU (17%). Out of 159 patients with primary bloodstream infection, 61 patients died representing a crude mortality rate of 38%. Analysis of the organisms causing BSI showed that Gram positive organisms were reported in 69.1% (n = 121); MRSA was the most prevalent (18.9%), followed by methicillin resistant coagulase negative Staphylococci (16%). Gram negative bacilli were reported in 29.1% (n = 51). In this case, Klebsiella pneumoniae was the most common (10.3%) followed E coli (8.6%). Candida spp. was reported only in (1.7%) of isolates. Antibiotics sensitivities of Gram positive organisms showed that these organisms were mostly sensitive to vancomycin (90.1%), while Gram negative organisms were mostly sensitive to imipenem (90.2%). In this study we tested Gram negative isolates for the production of the ESBL enzyme and concluded that 64.7% (33/51) of patients' isolates and 20/135 (14.8%) environmental isolates were confirmed to be ESBL producers. The type of β-lactamase gene was determined by polymerase chain reaction which showed that SHV was the main type. Molecular typing was done for 18 Klebsiella pneumoniae strains that caused nosocomial BSI and for the 36 Klebsiella pneumoniae strains which were isolated from the environmental samples by the RAPD method. The two environmental strains were identical, with one isolated from a patient, which confirms the serious role of the hospital environment in the spread of infections.

Conclusion

Nosocomial BSI represents a current problem in Assiut University Hospitals, Egypt. Problems associated with BSI include infection with multidrug resistant pathogens (especially ESBLs) which are difficult to treat and are associated with increased mortality. Of all available anti-microbial agents, carbapenems are the most active and reliable treatment options for infections caused by ESBL isolates. However, overuse of carbapenems may lead to resistance of other Gram-negative organisms.

Molecular epidemiological analysis of Escherichia coli isolates producing extended-spectrum beta-lactamases for identification of nosocomial outbreaks in Stockholm, Sweden

From June to October of 2002, a cluster of Escherichia coli isolates producing extended-spectrum beta-lactamases (ESBLs) was detected in Stockholm. The isolates were grouped into two clones, one of which had already circulated in the same area before the outbreak. CTX-M-type ESBLs and coresistance to ciprofloxacin were identified in the strains.

A Klebsiella pneumoniae producing three kinds of class A beta-lactamases encoded by one single plasmid isolated from a patient in Huashan Hospital, Shanghai, China

A Klebsiella pneumoniae strain was isolated from a sputum specimen of a patient in the intensive care unit in 1999 in Shanghai Huashan Hospital, China. The isolate was confirmed as an extended-spectrum beta-lactamase (ESBL) producing strain by double-disk synergy test. The results of susceptibility test showed that it was resistant to most beta-lactams (including third generation cephalosporins) and non-beta-lactam antimicrobial agents. Transconjugants were obtained at a frequency of 10(-4). A plasmid of about 60 kb was obtained from the transconjugant by plasmid extraction. Three major nitrocefin-hydrolysing bands with pIs of 5.4, 8.2 and 8.4, were shown in extracts of the transconjugant. Partial gene amplification products of bla(TEM), bla(SHV), and CTX-M-1 group gene were obtained from the isolate as well as its transconjugant. The entire bla(TEM), bla(SHV), and bla(CTX-M) in the transconjugant were amplified by PCR and the PCR products were cloned into a pHSG398 vector. Afterwards, the susceptibility of transformants and activities of beta-lactamases of transformants on antibiotics were tested. The PCR products were directly sequenced, analysed and identified as TEM-1, SHV-12, and CTX-M-3 genes. These results confirm that this strain of Klebsiella pneumoniae produces SHV-12, CTX-M-3 ESBLs and TEM-1 beta-lactamase, encoded by one single plasmid, which is responsible for the resistance of this strain to most beta-lactams.

Investigation of extended-spectrum beta-lactamase in Klebsiellae pneumoniae and Escherichia coli from China

Extended-spectrum beta-lactamases (ESBLs) are an increasing cause of resistance to third-generation cephalosporins in Enterobacteriaceae. However, they have not been well studied in China. We investigated the prevalence, resistance, and probable gene type of ESBLs using MICs testing and polymerase chain reaction in 559 Klebsiellae pneumoniae and 427 Escherichia coli isolates collected from patients in Huashan Hospital from 1 January to 31 December 1999. The incidence of ESBL-producing strains was 51% among Klebsiellae pneumoniae (285/559) and 23.6% among Escherichia coli (101/427), most of which were collected from patients in intensive care unit and neurosurgical ward. PFGE showed that some epidemic ESBL-producing strains were present in the ICU, especially among ESBL-producing Klebsiellae pneumoniae. The major source of ESBL-producing Klebsiellae pneumoniae and Escherichia coli was sputum specimen (63.5%) and urine (64.3%), respectively. These strains were resistant to most beta-lactams (including the third-generation cephalosporins and monobactams) and non-beta-lactams (such as fluoroquinolones, aminoglycosides, tetracycline, and chloramphenicol), all or most ESBL producers were susceptible to imipenem, cefmetazole and beta-lactam/clavulanic acid. TEM was the main type of beta-lactamases and the CTX-M type of ESBLs was common in these isolates. Some ESBL-producing Escherichia coli and most ESBL-producing Klebsiellae pneumoniae produced more than one type of beta-lactamase. These data confirm that ESBL producers are common among hospital strains of Escherichia coli and Klebsiellae pneumoniae in China. It is important to monitor such strains closely and prevent their spread.

Plasmid-encoded metallo-beta-lactamase (IMP-6) conferring resistance to carbapenems, especially meropenem

In 1996, Serratia marcescens KU3838 was isolated from the urine of a patient with a urinary tract infection at a hospital in northern Japan and was found to contain the plasmid pKU501. Previously, we determined that pKU501 carries bla(IMP) and the genes for TEM-1-type beta-lactamases as well as producing both types of beta-lactamases (H. Yano, A. Kuga, K. Irinoda, R. Okamoto, T. Kobayashi, and M. Inoue, J. Antibiot. 52:1135-1139, 1999). pKU502 is a recombinant plasmid that contains a 1.5-kb DNA fragment, including the metallo-beta-lactamase gene, and is obtained by PCR amplification of pKU501. The sequence of the metallo-beta-lactamase gene in pKU502 was determined and revealed that this metallo-beta-lactamase gene differed from the gene encoding IMP-1 by one point mutation, leading to one amino acid substitution: 640-A in the base sequence of the IMP-1 gene was replaced by G, and Ser-196 was replaced by Gly in the mature enzyme. This enzyme was designated IMP-6. The strains that produced IMP-6 were resistant to carbapenems. The MICs of panipenem and especially meropenem were higher than the MIC of imipenem for these strains. The k(cat)/K(m) value of IMP-6 was about sevenfold higher against meropenem than against imipenem, although the MIC of meropenem for KU1917, which produced IMP-1, was lower than that of imipenem, and the MIC of panipenem was equal to that of imipenem. These results support the hypothesis that IMP-6 has extended substrate profiles against carbapenems. However, the activity of IMP-6 was very low against penicillin G and piperacillin. These results suggest that IMP-6 acquired high activity against carbapenems, especially meropenem, via the point mutation but in the process lost activity against penicillins. Although IMP-6 has reduced activity against penicillins due to this point mutation, pKU501 confers resistance to a variety of antimicrobial agents because it also produces TEM-1-type enzyme.