Class I beta-lactamases. Induction and derepression

Pathogen Burden Among ICU Patients in a Tertiary Care Hospital in Hail Saudi Arabia with Particular Reference to β-Lactamases Profile

Purpose

Ventilator-associated pneumonia (VAP) is associated with a higher mortality risk for critical patients in the intensive care unit (ICU). Several strategies, including using β-lactam antibiotics, have been employed to prevent VAP in the ICU. However, the lack of a gold-standard method for VAP diagnosis and a rise in antibiotic-resistant microorganisms have posed challenges in managing VAP. The present study is designed to identify, characterize, and perform antimicrobial susceptibility of the microorganisms from different clinical types of infections in ICU patients with emphasis on VAP patients to understand the frequency of the latter, among others.

Patients and Methods

A 1-year prospective study was carried out on patients in the ICU unit at a tertiary care hospital, Hail, Saudi Arabia.

Results

A total of 591 clinically suspected hospital-acquired infections (HAI) were investigated, and a total of 163 bacterial isolates were obtained from different clinical specimens with a high proportion of bacteria found associated with VAP (70, 43%), followed by CAUTI (39, 24%), CLABSI (25, 15%), and SSI (14, 8.6%). Klebsiella pneumoniae was the most common isolate 39 (24%), followed by Acinetobacter baumannii 35 (21.5%), Pseudomonas aeruginosa 25 (15.3%), and Proteus spp 23 (14%). Among the highly prevalent bacterial isolates, extended-spectrum beta-lactamase was predominant 42 (42.4%).

Conclusion

Proper use of antibiotics, continuous monitoring of drug sensitivity patterns, and taking all precautionary measures to prevent beta-lactamase-producing organisms in clinical settings are crucial and significant factors in fending off life-threatening infections for a better outcome.

Prevalence and Antimicrobial Resistance of Klebsiella Strains Isolated from a County Hospital in Romania

The study evaluated the evolution of the incidence of infections with Klebsiella in the County Clinical Emergency Hospital of Craiova (SCJUC), Romania. Also, we monitored antibiotic resistance over more than two years and detected changes in resistance to various antimicrobial agents. Our study included 2062 patients (823 women and 1239 men) hospitalised in SCJUC during the period 1st of September 2017 to 30 June 2019. In 458 patients (22.21%) from the 2062 total patients, the collected samples (1116) were positive and from those, we isolated 251 strains of Klebsiella spp. We conducted a longitudinal analysis of the prevalence of Klebsiella spp. over calendar months, which showed a prevalence in surgical wards that ranged between 5.25% and 19.49% in June 2018, while in medical wards the variation was much wider, between 5.15% and 17.36% in April 2018. Klebsiella spp. strains showed significant resistance to Amoxicillin/Clavulanate, Aztreonam and Cephalosporins such as Ceftriaxone, Ceftazidime and Cefepime. We examined the possible link with the consumption of antibiotics in the same month by performing a multiple linear regression analysis. The evolution of antibiotic resistance in Klebsiella was correlated with the variation of resistance in other bacteria, which suggests common resistance mechanisms in the hospital environment. By performing the regression for dependency between antibiotic resistance and antibiotic consumption, we observed some correlations between antibiotic consumption and the development of antibiotic resistance after 1, 2 and even 3 months (e.g., resistance to meropenem was influenced by the consumption in the hospital ward of imipenem 1 month and two months before, but only 1 month before by the consumption of meropenem). The clustering of strains showed filiation between multiresistant Klebsiella spp. strains isolated from specific patients from the ICU. The evolution of prevalence and antibiotic resistance in Klebsiella correlated with the resistance in other bacteria, which suggest common resistance mechanisms in the hospital environment, and also with the consumption of antibiotics.

Five-year survey of cefotaxime resistance in Spain

During 1991-1995 a Spain collaborative study group surveyed the resistance to cefotaxime both in community as well as in hospital isolates of bacteria. The isolates tested during the study period of 5 years were 813, 875, 3631, 3184, and 3050 strains, respectively. Antimicrobial activity of cefotaxime was assayed by broth or agar microdilution, in accordance with criteria of the National Committee of Clinical Laboratory Standards (NCCLS). Cefotaxime resistance included 2.5% of all isolates: 2.6% Enterobacteriaceae, 1.7% Streptococcus pneumoniae, 0.5% Haemophilus influenzae, 0.0% Haemophilus spp., and 0.0% Moraxella catarrhalis. The overall incidence of resistance to cefotaxime decreased fro member of Enterobacteriaceae from 3.6% in 1991 to 2.5% in 1995. The incidence of resistance varied with the species and was highest in Enterobacter and in Citrobacter freundii.

Epidemiological study of variations in beta-lactam antibiotic susceptibility of Pseudomonas aeruginosa in two intensive care units

A six-month prospective study was carried out in the medical and surgical intensive care units (ICUs) at Besançon University Hospital to assess the frequency and risk factors for beta-lactam-resistant isolates of Pseudomonas aeruginosa. Clinical samples were screened for P. aeruginosa, and four antibiograms were distinguished using imipenem and ceftazidime, namely: fully susceptible (SS), imipenem-resistant (RS), ceftazidime-resistant (SR), and resistant to both (RR). DraI restriction fragment length polymorphism of isolates from different patients or with different resistance patterns but the same serotype was assessed by pulsed-field gel electrophoresis. One hundred and twenty-one isolates were obtained from 50 of 281 patients, 60.3% were fully susceptible. 19.8% imipenem-resistant, 13.2% ceftazidime-resistant, and 6.6% resistant to both. Antibiotic-resistance was independent of serotype. Twenty-two of 32 imipenem-resistant isolates from six patients were of the same DNA type, and six other isolates from four patients were of a second DNA type. On only one occasion did a clonally defined strain develop imipenem resistance. By contrast ceftazidime-resistant strains had differing DNA types, but had been originally ceftazidime-susceptible in seven of 12 patients. Reversion of imipenem resistant strains to susceptibility occurred in one patient, and of ceftazidime-resistant strains in five patients. Case-control studies identified prior antibiotic therapy as a risk factor in colonization with resistant strains. Resistance to imipenem followed imipenem therapy, and resistance to ceftazidime followed use of weakly anti-pseudomonal beta-lactam antibiotics. The major route of spread of imipenem-resistant strains was cross-colonization. Thus, assuming appropriate isolation, a carbapenem should be preferred to an extended-spectrum cephalosporin to treat pseudomonas infections in ICU patients.

Emergence of resistance to beta-lactam agents in Pseudomonas aeruginosa with group I beta-lactamases in Spain

The contribution of induction and stable derepression of chromosomal class I beta-lactamases to beta-lactam antibiotic resistance was studied in clinical isolates of Pseudomonas aeruginosa collected from patients treated with beta-lactam antibiotics. Multiple isolates from the same patient were characterized by O-serotyping as a primary screen, combined with pyocin typing. Sonicated extracts of cells were assayed for chromosomal and plasmid-mediated beta-lactamases by isoelectric focusing and cloxacillin inhibition studies. The specific beta-lactamase activity, basal and induced, with cefoxitin was determined to differentiate strains with inducible or derepressed production of the enzyme. Beta-lactamase induction was performed in each strain against the beta-lactam agents used in the therapy of each patient. The observations showed that induction against older penicillins such as penicillin, amoxicillin, and amoxicillin/clavulanate resulted in a moderate to strong increase in beta-lactamase activity, whereas the results obtained with first-generation cephalosporins varied with the beta-lactam agent tested. Third-generation cephalosporins were weak inducers of beta-lactamases, and their use as therapy preceded the appearance of strains that produce chromosomal group I beta-lactamases constitutively. These strains showed a remarkable reduction in sensitivity to ureidopenicillins, carboxipenicillins, third-generation cephalosporins, and monobactams, but not to carbapenems.

Imipenem and meropenem induced resistance to beta-lactam antibiotics in Pseudomonas aeruginosa

The ability of imipenem and meropenem in subinhibitory concentrations to influence the results of disk diffusion susceptibility tests was assessed. Selection of stably derepressed mutants resistant to beta-lactam antibiotics other than carbapenems was also investigated. Beta-lactams were shown to be subject to carbapenem-mediated antagonism in the disk diffusion test. On the other hand in vitro selection of stably derepressed mutants resistant to other beta-lactams could not be demonstrated.

The emergence of antibiotic resistance: myths and facts in clinical practice

Selection pressure, caused by the use of antibiotics--especially in hospitals--is the main factor responsible for the emergence of antibiotic-resistant bacteria. Resistance can arise endogenously by mutation (one-step, as found for Mycobacterium tuberculosis to rifampicin, or multi-step, as in gonococci to benzylpenicillin), or exogenously by transfer of R-factors. Mechanisms of resistance may involve a decrease in permeability, chemical modification of the antibiotic, or a change in the affinity of the target site. There are many misconceptions concerning the incidence, nature and spread of antibiotic resistance, and some of the most important of these are discussed. The emergence and spread of resistance can be controlled by adhering to antibiotic policies and by preventing or controlling outbreaks of infection. The importance of resistant organisms can be diminished by the development of new antibiotic agents, preferably containing new chemical entities.