In vitro susceptibility of Citrobacter species to various antimicrobial agents

Comparative Genomic Analysis of Citrobacter and Key Genes Essential for the Pathogenicity of Citrobacter koseri

Citrobacter species are opportunistic bacterial pathogens that have been implicated in both nosocomial and community-acquired infections. Among the genus Citrobacter, Citrobacter koseri is often isolated from clinical material, and has been known to cause meningitis and brain abscess in neonates and immunocompromised individuals. The virulence determinants of Citrobacter, however, remain largely unknown. Based on traditional methods, the genus Citrobacter has been divided into 11 species, but this has been problematic. Here, we determined an improved, detailed, and more accurate phylogeny of the genus Citrobacter based on whole genome sequence (WGS) data from 129 Citrobacter genomes, 31 of which were sequenced in this study. A maximum likelihood (ML) phylogeny constructed with core genome single-nucleotide polymorphisms (SNPs) classified all Citrobacter isolates into 11 distinct groups, with all C. koseri strains clustering into a single group. For comprehensive and systematic comparative genomic analyses, we investigated the distribution of virulence factors, resistance genes, and macromolecular secretion systems among the Citrobacter genus. Moreover, combined with group-specific genes analysis, we identified a key gene cluster for iron transport, which is present in the C. koseri group, but absent in other the groups, suggesting that the high-pathogenicity island (HPI) cluster may be important for the pathogenicity of C. koseri. Animal experiments showed that loss of the HPI cluster significantly decreased C. koseri virulence in mice and rat. Further, we provide evidence to explain why Citrobacter freundii is less susceptible than C. koseri to several antibiotics in silico. Overall, our data reveal novel virulence clusters specific to the predominantly pathogenic C. koseri strains, which form the basis for elucidating the virulence mechanisms underlying these important pathogens.

In vitro susceptibility and resistance phenotypes in contemporary Citrobacter isolates in a University Hospital in Crete, Greece

BACKGROUND

Data on Citrobacter spp. susceptibility are scarce. We sought to study the evolution in the susceptibility of 385 Citrobacter spp. at the University Hospital of Heraklion, Crete, Greece during a six-year period (2010-2015).

METHODS

Non-duplicate strains isolated from inpatients (intensive care unit, oncology, surgery, internal medicine, paediatrics) and outpatients were studied using Vitek 2. Phenotypic confirmatory tests were applied for detection of β-lactamases and aminoglycoside modifying enzymes.

RESULTS

C. freundii (172, 44.7%) and C. koseri (166, 43.1%) were the most commonly isolated species. C. braakii (34), C. amalonaticus (6), C. youngae (6) and C. sedlakii (1) were the remaining isolates. Colistin and fosfomycin were the most active antibiotics (both 99.2%) followed by carbapenems (99%) aminoglycosides (96.6-98.4%), tigecycline (96.1%), cefepime (94.8%), ciprofloxacin (94.3%), tetracycline (92.7%), trimethoprim/sulphamethoxazole (91.4%), chloramphenicol (88.1%), piperacillin/tazobactam (86.5%) and 3rd generation cephalosporins (85.7%). C. freundii were more resistant than C. koseri. Antibiotic resistance did not increase during the study period for most antibiotics. Lower susceptibility to all antibiotics was observed among multi-drug resistant (MDR) strains. AmpC was the most common resistant mechanism (10.9%); carbapenemases (1.3%) and aminoglycoside modifying enzymes (2.9%) were also detected. All AmpC producers were resistant to cephalosporins but not to carbapenems. In all but one isolates aminoglycoside resistance was accompanied by acquired β-lactamases.

CONCLUSIONS

Although Citrobacter species in general were susceptible, antibiotic susceptibility testing is required for the detection of resistant isolates.

Community-Acquired Pneumonia and Empyema Caused by Citrobacter koseri in an Immunocompetent Patient

Citrobacter species, belonging to the family Enterobacteriaceae, are environmental organisms commonly found in soil, water, and the intestinal tracts of animals and humans. Citrobacter koseri is known to be an uncommon but serious cause of both sporadic and epidemic septicemia and meningitis in neonates and young infants. Most cases reported have occurred in immunocompromised hosts. The infections caused by Citrobacter are difficult to treat with usual broad spectrum antibiotics owing to rapid generation of mutants and have been associated with high death rates in the past. We believe this is the first case described in the literature of a community-acquired pneumonia and empyema caused by Citrobacter koseri in an immunocompetent adult patient.

Complete Genome Sequence of Citrobacter freundii Myophage Moon

Citrobacter freundii and other Gram-negative opportunistic pathogens necessitate concern from the public health sector. Bacteriophages that kill such pathogens may be useful in the control and containment of these infections. Here, we describe the genome of a newly isolated T4-like myophage of C. freundii, Moon, and present its features.

Multidrug resistant citrobacter: an unusual cause of liver abscess

Liver abscesses are infectious, space occupying lesions in the liver, the two most common abscesses being pyogenic and amoebic. A pyogenic liver abscess (PLA) is a rare condition with a reported incidence of 20 per 100 000 hospital admissions in the western population. The right lobe of the liver is the most common site in both types of liver abscess. Clinical presentation is elusive with complaints of fever, right upper quadrant pain in the abdomen and hepatomegaly with or without jaundice. The aetiology of PLA has changed in the past few decades and may be of biliary, portal, arterial or traumatic origin, but many cases are still cryptogenic. The most common organisms causing PLA are Gram-negative aerobes, especially Escherichia coli and Klebsiella pneumoniae. Studies have shown a high degree of antimicrobial susceptibility of isolated organism resulting in an overall lower mortality in PLA. Here, we present a case of PLA caused by multidrug-resistant Citrobacter freundii, which is an unusual organism to be isolated.

Citrobacter brain abscesses in neonates: early surgical intervention and review of the literature

PURPOSE

Citrobacter koseri, a facultatively anaerobic, lactose-fermenting, gram-negative bacilli, has a strong propensity to form cerebral abscesses. C. koseri brain abscesses can be a devastating disease of infancy and childhood with more than 30% succumbing to the disease and more than 50% suffering severe neurological deficits.

METHODS

This study represents a retrospective review of two cases of C. koseri brain abscesses along with a review of the literature regarding diagnosis and treatment.

RESULTS

Early aggressive surgical and medical treatment resulted in favorable outcomes for two children with C. koseri brain abscesses, one diagnosed at 6 weeks of age and the other at 2 months of age.

CONCLUSION

C. koseri brain abscesses can be devastating and have been associated historically with significant morbidity and mortality. However, favorable outcomes are possible, and aggressive surgical and medical management should be considered for patients with C. koseri abscesses.

Citrobacter infections in a general hospital: characteristics and outcomes

In this investigation, we sought to investigate the characteristics of Citrobacter spp. infections. A retrospective cohort study in a 700-bed, tertiary care, university hospital was carried out during the period from June 1994 to January 2006. Seventy-eight patients (70 adults) with Citrobacter spp. isolates were identified. C. freundii was more common (71.8%), followed by C. koseri (23.1%) and C. braakii (3.8%). The most common associated clinical syndromes were urinary tract infections (52.6% of cases, including eight cases of asymptomatic bacteriuria), as well as intra-abdominal (14.1%), surgical site (7.7%), skin and soft tissue (6.4%), and respiratory tract infections (6.4%). In 29.5% of patients, Citrobacter spp. isolates were associated to polymicrobial infections, principally at sites other than the urinary tract. Antibiograms of 38 consecutive Citrobacter spp. isolates (29 C. freundii) were available. Most active agents were colistin (100%), fosfomycin (100%), imipenem (97.4%), gentamicin (89.5%), nitrofurantoin (89.5%), ciprofloxacin (80.6%), and cefepime (73.7%). Most patients (82.1%) had at least one underlying illness. Combination antimicrobial therapy was administered in 28.2% of cases. One patient died during hospitalization. The length of hospital stay was longer in patients with polymicrobial compared to monomicrobial infections (23 versus 13 days, respectively, p = 0.02). The isolation of Citrobacter species, although rather infrequent, was clinically relevant in the great majority of cases. Further attention should be paid to these pathogens.

Citrobacter urinary tract infections in children

BACKGROUND

Citrobacter species have been described as the etiologic agents in cases of bacteremia, meningitis, diarrhea and brain abscess, but little is known of their role as a cause of urinary tract infections in children. The purpose of this study was to define the role of Citrobacter species in pediatric urinary tract infections.

METHODS

The project consisted of a retrospective chart review of microbiologic and medical records of patients younger than 18 years of age with urine cultures positive for Citrobacter species during a 3-year period.

RESULTS

Thirty-four patients with 37 infections were included in the review. The average patient age was 6.9 years (range, 1 month to 18 years) and 71% were female. Fifty-six percent of the patients had urinary tract/renal anomalies or neurologic impairment and 26% represented nosocomial infections. Thirty-seven percent of patients were asymptomatic at the time of diagnosis, whereas 63% complained of at least one of the following findings: gastrointestinal symptoms; dysuria; fever; incontinence; penile/vaginal discharge; frequency; flank pain; and hematuria. Twenty-six of the isolates were Citrobacter freundii and 11 were Citrobacter koseri. Blood cultures were obtained in 9 patients and all were negative for Citrobacter isolates.

CONCLUSIONS

Although it is uncommon Citrobacter can cause urinary tract infections in the pediatric population, which occur more frequently in children with underlying medical conditions. It appears that treatment similar to that of other gram-negative enteric organisms is the most prudent approach to these children until more information can be gathered.

Citrobacter meningitis in adults

Citrobacter meningitis is an uncommon infection of neonates and young children. It is rarely seen in adults. We describe a 46-year-old man with a mixed bacterial meningitis caused by C. diversus and Klebsiella oxytoca and a 64-year-old woman with C. freundii meningitis. Review of the English-language literature revealed only 2 adult patients with C. diversus meningitis and another 2, with C. freundii meningitis. The ages of these 6 aforementioned patients ranged from 31 to 84 years. Multiple facial fractures, neurosurgical procedures, alcoholism and diabetes mellitus were predisposing conditions. Among the 5 patients whose outcome was known, antibiotic therapy was successful in 4 but failed in 1. This study emphasizes that almost any of the gram-negative bacilli can cause serious infection of the central nervous system in adults in the proper setting.

Review of Citrobacter bacteremia in cancer patients over a sixteen-year period

A review was conducted of 65 episodes of Citrobacter bacteremia in cancer patients during a 16-year period. Cases of polymicrobial bacteremia were excluded from this analysis. The infection occurred most commonly in patients with acute leukemia. Most patients acquired the infection in the hospital, and 57% had received antibiotic therapy during the preceding ten days. Fever occurred in 98% of cases and shock in 17%. Thirty-eight percent of patients had concomitant pneumonia. Patients with shock, pneumonia or hemorrhage had a substantially poorer prognosis. The response rate was 72% for patients who received appropriate antibiotics. Patients who continued to have positive blood culture results while receiving appropriate antibiotic therapy had a poor prognosis. Beta-lactam antibiotics were more effective than aminoglycosides.

Successful treatment of neonatal Citrobacter freundii meningitis with ceftriaxone

Citrobacter meningitis is an uncommon enteric gram-negative infection that afflicts neonates and young children. Approximately 30 percent of children treated or untreated die from the infection. We report a case of C. freundii meningitis that was resistant to ampicillin and was successfully treated with ceftriaxone, a third-generation cephalosporin. A 13-day-old, full-term baby was admitted to the hospital with a one-day history of fever up to 38.8 degrees C. On admission the infant had a temperature of 39.2 degrees C, pulse of 140 beats/min, and a respiratory rate of 32 breaths/min. Except for a slightly bulging fontanelle, the rest of the physical examination was within normal limits. Complete blood count revealed a white blood cell (WBC) count of 12.5 x 10(9)/L, with 0.66 polymorphonuclear cells, 0.10 bands, 0.18 lymphocytes, and 0.06 monocytes. A stat lumbar puncture showed 10 WBCs per high-power field with gram-negative rods. Empiric therapy with ampicillin 225 mg q12h and gentamicin 11 mg q8h was started. Both antibiotics were discontinued after culture and sensitivity results were positive for C. freundii in the blood and spinal fluid. The patient was successfully treated with nine days of ceftriaxone 250 mg q12h.

Aztreonam in the prevention and treatment of infection in neutropenic cancer patients

The treatment of bacterial infections in neutropenic cancer patients presents a serious challenge to physicians. Although gram-positive infections have become more common in recent years, most infections in this population are caused by gram-negative bacilli. No single regimen has been found to be optimal, and most commonly used regimens are associated with significant disadvantages. Extensive investigation is therefore under way to evaluate the potential of several promising newer antimicrobial agents. Aztreonam, for example, is active against most gram-negative pathogenic bacteria and has been evaluated in several clinical trials in neutropenic patients. As the only agent with gram-negative activity or in combination either with aminoglycosides or with other beta-lactam antibiotics, aztreonam proved useful in the treatment of gram-negative infections in this population. Combination with an aminoglycoside, however, was not found to improve efficacy over aztreonam alone. In fact, since aminoglycosides may potentiate ototoxicity and nephrotoxicity, it may be more appropriate to replace the aminoglycoside component of a combination regimen with aztreonam, as indicated by data from a study of aztreonam plus cefoperazone. Aztreonam selectively inhibits the aerobic gram-negative intestinal flora with only minimal disruption of anaerobic flora, and may be useful for infection prevention, but the importance of anaerobic preservation is not clear. It was concluded that aztreonam appears to be a useful agent for the treatment of febrile neutropenic patients, but further study is recommended.

Netilmicin. A review of its antibacterial activity, pharmacokinetic properties and therapeutic use

Netilmicin is a semisynthetic aminoglycoside derived from sisomicin. It is active against most Gram-negative and some Gram-positive bacteria, including many gentamicin-resistant strains. Netilmicin has proved to be effective in Gram-negative infections of the urinary tract, skin and skin structure, and lower respiratory tract, as well as in intra-abdominal infections, septicaemia and other miscellaneous infections. In some trials, the more easily implemented once daily administration of netilmicin has been as effective as multiple dosing regimens. However, further investigation is required to confirm that efficacy and safety are not compromised with once daily administration. Comparative studies have generally revealed similar clinical and bacteriological efficacies between netilmicin and gentamicin, amikacin or tobramycin. As with other aminoglycosides, the principal adverse effects of netilmicin are nephrotoxicity and ototoxicity. Although animal studies strongly suggest that these are less common with netilmicin than with related drugs, there appears to be no difference in their incidence in clinical use; in clinical trials the incidence of nephrotoxicity and ototoxicity has been low, with the symptoms in many cases being minor and reversible. Netilmicin is, therefore, an effective antibacterial drug for the parenteral treatment of severe infections, offering theoretical advantages in safety which may indicate its use for patients believed to be at risk of adverse effects.

Fluoroquinolone antimicrobial agents

The fluoroquinolones, a new class of potent orally absorbed antimicrobial agents, are reviewed, considering structure, mechanisms of action and resistance, spectrum, variables affecting activity in vitro, pharmacokinetic properties, clinical efficacy, emergence of resistance, and tolerability. The primary bacterial target is the enzyme deoxyribonucleic acid gyrase. Bacterial resistance occurs by chromosomal mutations altering deoxyribonucleic acid gyrase and decreasing drug permeation. The drugs are bactericidal and potent in vitro against members of the family Enterobacteriaceae, Haemophilus spp., and Neisseria spp., have good activity against Pseudomonas aeruginosa and staphylococci, and (with several exceptions) are less potent against streptococci and have fair to poor activity against anaerobic species. Potency in vitro decreases in the presence of low pH, magnesium ions, or urine but is little affected by different media, increased inoculum, or serum. The effects of the drugs in combination with a beta-lactam or aminoglycoside are often additive, occasionally synergistic, and rarely antagonistic. The agents are orally absorbed, require at most twice-daily dosing, and achieve high concentrations in urine, feces, and kidney and good concentrations in lung, bone, prostate, and other tissues. The drugs are efficacious in treatment of a variety of bacterial infections, including uncomplicated and complicated urinary tract infections, bacterial gastroenteritis, and gonorrhea, and show promise for therapy of prostatitis, respiratory tract infections, osteomyelitis, and cutaneous infections, particularly when caused by aerobic gram-negative bacilli. Fluoroquinolones have also proved to be efficacious for prophylaxis against travelers' diarrhea and infection with gram-negative bacilli in neutropenic patients. The drugs are effective in eliminating carriage of Neisseria meningitidis. Patient tolerability appears acceptable, with gastrointestinal or central nervous system toxicities occurring most commonly, but only rarely necessitating discontinuance of therapy. In 17 of 18 prospective, randomized, double-blind comparisons with another agent or placebo, fluoroquinolones were tolerated as well as or better than the comparison regimen. Bacterial resistance has been uncommonly documented but occurs, most notably with P. aeruginosa and Staphylococcus aureus and occasionally other species for which the therapeutic ratio is less favorable. Fluoroquinolones offer an efficacious, well-tolerated, and cost-effective alternative to parenteral therapies of selected infections.

Ciprofloxacin. A review of its antibacterial activity, pharmacokinetic properties and therapeutic use

Ciprofloxacin is one of a new generation of fluorinated quinolones structurally related to nalidixic acid. The primary mechanism of action of ciprofloxacin is inhibition of bacterial DNA gyrase. It is a broad spectrum antibacterial drug to which most Gram-negative bacteria are highly susceptible in vitro and many Gram-positive bacteria are susceptible or moderately susceptible. Unlike most broad spectrum antibacterial drugs, ciprofloxacin is effective after oral or intravenous administration. Ciprofloxacin has been most extensively studied following oral administration. It attains concentrations in most tissues and body fluids which are at least equivalent to the minimum inhibitory concentration designated as the breakpoint for bacterial susceptibility in vitro. The results of clinical trials with orally and intravenously administered ciprofloxacin have confirmed the potential for its use in a wide range of infections, which was suggested by its in vitro antibacterial and pharmacokinetic profiles. It has proven an effective treatment for many types of systemic infections as well as for both acute and chronic infections of the urinary tract. Ciprofloxacin generally appeared to be at least as effective as alternative orally administered antibacterial drugs in the indications in which they were compared, and in some indications, to parenterally administered antibacterial therapy. However, further studies are needed to fully clarify the comparative efficacy of ciprofloxacin and standard antibacterial therapies. Bacterial resistance to ciprofloxacin develops infrequently, both in vitro and clinically, except in the setting of pseudomonal respiratory tract infections in cystic fibrosis patients. The drug is also well tolerated. Thus, as an orally active, broad spectrum and potent antibacterial drug, ciprofloxacin offers a valuable alternative to broad spectrum parenterally administered antibacterial drugs for use in a wide range of clinical infections, including difficult infections due to multiresistant pathogens.