Coagulase-negative staphylococcal sepsis in neonates. Association between antibiotic resistance, biofilm formation and the host inflammatory response

BACKGROUND

Coagulase-negative staphylococci (CoNS) are the most prevalent pathogens causing late onset sepsis in neonates. They are often multiresistant to antibiotics, and the ability to form biofilm is considered their main virulence determinant.

METHODS

During a 12-year period, we identified 150 neonates having 164 suspected septic episodes with growth of CoNS in blood culture. We examined the relationship between antibiotic resistance, phenotypic biofilm production and genetic determinants for biofilm formation in different CoNS species and their correlation with neonatal inflammatory response.

RESULTS

Eighty-five episodes were classified as true sepsis, and 79 episodes of CoNS growth in blood culture were considered contaminations. Sixty-one percent of Staphylococcus epidermidis isolates produced biofilm compared with 26% of CoNS non-epidermidis (P < 0.001). We observed no difference in phenotypic biofilm production or genetic determinants for biofilm formation between invasive isolates and contaminants. C-reactive protein levels as a marker of inflammatory response were higher in CoNS sepsis caused by methicillin and aminoglycoside resistant versus susceptible isolates (P = 0.031). In contrast, there was a significant association between a lower C-reactive protein response and biofilm-positive isolates (P = 0.018). Antibiotic resistance was significantly correlated with biofilm production in S. epidermidis, but not in other CoNS species.

CONCLUSIONS

CoNS sepsis with biofilm-forming strains was associated with a decreased host inflammatory response, potentially limiting the immune system to counteract the infection. The impact of antibiotic resistance and virulence determinants on clinical outcome of neonatal CoNS sepsis warrants additional clinical studies.

Phenotypic and genotypic aminoglycoside resistance in blood culture isolates of coagulase-negative staphylococci from a single neonatal intensive care unit, 1989–2000

OBJECTIVES

To investigate the prevalence of aminoglycoside resistance and genes encoding aminoglycoside-modifying enzymes (AME) in blood culture isolates of coagulase-negative staphylococci (CoNS) from neonates.

MATERIALS AND METHODS

A total of 180 isolates from 148 patients collected in a single neonatal unit over a 12 year period were examined for susceptibility to gentamicin, tobramycin, netilmicin, amikacin and arbekacin by Etest and/or disc diffusion. AME genes were detected by PCR.

RESULTS

The overall non-susceptibility rates to gentamicin, tobramycin, netilmicin, amikacin and arbekacin were 66%, 68%, 52%, 38% and 1%, respectively. Gentamicin non-susceptibility rates were 4% and 91% in methicillin-susceptible and -resistant isolates, respectively. aac(6')-Ie-aph(2'')-Ia, aph(3')-IIIa and/or ant(4')-Ia were encountered in 125 (69%), 1 (0.5%) and 30 (16.6%) isolates, respectively. Forty-six (26%) isolates negative for AME genes were susceptible to all aminoglycosides. In contrast, 115 (92%), 91 (73%) and 66 (53%) of aac(6')-Ie-aph(2'')-Ia positive isolates were non-susceptible to gentamicin, netilmicin and amikacin, respectively. Only one isolate showed arbekacin resistance. However, aac(6')-Ie-aph(2'')-Ia positive isolates and isolates with gentamicin MIC > or =128 mg/L displayed a significant reduction in arbekacin inhibition zones.

CONCLUSIONS

A high prevalence of aminoglycoside resistance was detected and associated with methicillin resistance. Discrepancies between phenotypic and genetic detection of aminoglycoside resistance were discerned. Gentamicin was the preferred substrate for phenotypic detection of aac(6')-Ie-aph(2'')-Ia. Arbekacin showed favourable antibacterial activity even in aac(6')-Ie-aph(2'')-Ia-positive isolates. We suggest including arbekacin in future clinical trials of empirical treatment of late onset neonatal sepsis.

Validation of a simplified netilmicin dosage regimen in infants

The aim of this study was to validate a simplified high-dosage, extended-interval netilmicin dosage regimen for infants. A total of 129 infants receiving 163 treatment courses of netilmicin (6 mg kg every 24 or 36 h depending on gestational age (GA), postnatal age and postmenstrual age) was analysed. Serum netilmicin concentrations were monitored before (Cmin), 30 min (C0.5h) after and 7.5 h (C7.5h) after the third dose. In 110 patients during first week of life mean C0.5h was 10.5 mg/l. Mean C0.5h was significantly lower (9.0 mg/l) in 38 infants older than 1 week of age. 14 of 15 patients with Cmin levels > or = 2 mg/l receiving netilmicin every 36 h were < 28 weeks of gestation. In the first week of life significant correlations between GA and elimination half-life (p < 0.001) and between plasma creatinine and elevated Cmin (p < 0.002) were found, but no correlation between C0.5h and GA. In this high-dosage regimen a dosing interval of 48 h for GA < 29 weeks, 36 h for GA 29-36 weeks and 24 h for full term babies seems appropriate, during first week of life, to avoid the majority of elevated trough levels and still obtain maximal therapeutic efficacy.

[Kingella kingae and osteoarticular infections in children]

BACKGROUND

In septic arthritis and osteomyelitis in children, the infectious agent is frequently not identified because of failure in obtaining bacterial growth from blood culture or osteoarticular aspirations.

MATERIAL AND METHODS

We report a case of septic arthritis caused by Kingella kingae in a two-year-old boy. On the basis of a PubMed literature search, we present an overview of osteoarticular infections with K kingae in childhood.

RESULTS AND INTERPRETATION

Over the last ten years there has been an increasing number of reports on osteoarticular infection in children caused by K kingae. The clinical course is usually benign. Direct inoculation of osteoarticular specimens into blood culture bottles is important in order to enhance isolation of K kingae, as this organism will often fail to grow when plated directly on solid media. Improved culture methods and increased awareness are important in order to identify the organism and thus enable targeted antibiotic therapy.

Rapid detection of the methicillin-resistance gene, mecA, in coagulase-negative Staphylococci

Phenotypical methods are routinely used to detect methicillin resistance in Staphylococci. These methods are time-consuming and there are difficulties in detecting all resistant strains carrying the mecA gene. We detected methicillin-resistant Staphylococci in biological samples by PCR amplification of mecA, without the time-consuming step of identifying a bacterial isolate. Methicillin-resistant Staphylococci isolates were also detected by screening on agar supplemented with oxacillin. The biological samples were collected from the hands of 17 healthcare workers at the Department of Paediatrics at the University Hospital of Tromsø. mecA was amplified in 12 of the 17 samples. The gene was verified by DNA sequencing of the PCR amplicon. Using the phenotypical method, methicillin-resistant Staphylococci were isolated from 6 of the samples. In all 6 of these samples, mecA was amplified by PCR. We conclude that PCR is a sensitive and specific method for detecting methicillin resistance in Staphylococci. The PCR detection of mecA is rapid, fairly simple and can easily be assimilated into the routines of a clinical microbiological laboratory.

Rapid PCR detection of the methicillin resistance gene, mecA, on the hands of medical and non-medical personnel and healthy children and on surfaces in a neonatal intensive care unit

The hands of medical personnel are the chief vectors for transmission of antibiotic-resistant bacteria and probably serve as an important reservoir for antibiotic resistance genes in hospitals. In this survey we examined different reservoirs of the methicillin resistance gene, mecA, using a simplified PCR method. Samples (n = 151) were taken from the hands of medical and non-medical personnel and healthy children and from surfaces in a neonatal intensive care unit (NICU). We also performed sampling from 4 different body sites in 5 of the medical personnel. Fifteen out of 16 nurses (94%) from the ICU carried the mecA gene on their hands, whereas only 35% of the paediatric nurses were mecA-positive. Of all medical personnel, 44% carried the mecA gene on their hands. There was a significant difference (p < 0.015) between medical and non-medical personnel in terms of the carriage rate of mecA. Four samples from surfaces in a NICU--2 ventilators, 1 bench and 1 telephone--were positive for mecA. Our results are comparable with those from previous studies on reservoirs of methicillin-resistant coagulase-negative staphylococci using conventional culture techniques.

[Stickler's syndrome--an underdiagnosed condition?]

BACKGROUND

Stickler's syndrome is an autosomal dominantly inherited connective tissue disorder characterised by ocular, orofacial, skeletal and auditory features. The estimated prevalence is 1:10,000.

MATERIAL AND METHODS

We present a girl with the salient features of Stickler syndrome. Based on a literature search on Medline, we present an overview of this disorder.

RESULTS

The patient presented at birth with Pierre Robin sequence and bilateral exophtalmus. Serial ophthalmological investigations have revealed a non-progressive myopia of high degree and abnormalities of the vitreous gel architecture. From the age of three, she had joint hypermobility and joint pain. Her intelligence is normal, but she requires speech therapy because of problems with articulation.

INTERPRETATION

Recent research has provided a better understanding of the molecular genetic background of this condition. According to mutations in three genes encoding type II- and/or type XI-collagen, Stickler's syndrome can be subclassified into type 1, 2 and 3, but there is a considerable clinical overlap in symptoms. Patients with mild symptoms may be undiagnosed. Once the diagnosis is established, a coordinated multidisciplinary follow-up approach is recommended.

[Latex allergy]

We describe a mother and two children with latex allergy. Their symptoms illustrate the variations in the manifestations of latex allergy. This article reviews currently known aspects of this condition, including diagnosis and treatment. Latex allergy is a hypersensitive response to allergens in natural rubber latex products. It has long been known that latex exposure can cause contact dermatitis. Since 1979 there has been an increasing number of cases of IgE-mediated immediate hypersensitivity reactions, ranging from mild local urticaria to fatal anaphylaxis. The prevalence of latex allergy in the general population is still unknown, but it seems to be less than 1%. Children with spina bifida or urogenital abnormalities, health care workers and workers in the latex industry are known to be high risk groups. Patients belonging to high risk groups or patients with a positive history of latex allergy should be offered testing. High risk patients should be subjected to minimal exposure to latex, and procedures on all patients with a positive history of latex allergy should be performed in a latex-free environment.

[Retroperitoneal chylous cyst]

In pathology, cysts of the retroperitoneum are usually classified together with omental and mesenteric cysts. Because of risk of complications and malignancy these cysts should be extirpated. The frequency of complications and recurrence after surgery is significantly higher for retroperitoneal cysts than for the other types mentioned above. We describe a patient with a retroperitoneal chylous cyst of three litres. Correct diagnosis was made by CT-scan and chemical analysis of cyst fluid prior to surgery. The cyst was removed completely using an intercostal, retroperitoneal approach. The postoperative course was uneventful, and no evidence of recurrence was found after six months.