Colin MacLeod

Limited diversity in the gene pool allows prediction of third-generation cephalosporin and aminoglycoside resistance in Escherichia coli and Klebsiella pneumoniae

Early appropriate antibiotic treatment reduces mortality in severe sepsis, but current methods to identify antibiotic resistance still generally rely on bacterial culture. Modern diagnostics promise rapid gene detection, but the apparent diversity of relevant resistance genes in Enterobacteriaceae is a problem. Local surveys and analysis of publicly available data sets suggested that the resistance gene pool is dominated by a relatively small subset of genes, with a very high positive predictive value for phenotype. In this study, 152 Escherichia coli and 115 Klebsiella pneumoniae consecutive isolates with a cefotaxime, ceftriaxone and/or ceftazidime minimum inhibitory concentration (MIC) of ≥ 2 μg/mL were collected from seven major hospitals in Sydney (Australia) in 2008-2009. Nearly all of those with a MIC in excess of European Committee on Antimicrobial Susceptibility Testing (EUCAST) resistance breakpoints contained one or more representatives of only seven gene types capable of explaining this phenotype, and this included 96% of those with a MIC ≥ 2 μg/mL to any one of these drugs. Similarly, 97% of associated gentamicin-non-susceptibility (MIC ≥ 8 μg/mL) could be explained by three gene types. In a country like Australia, with a background prevalence of resistance to third-generation cephalosporins of 5-10%, this equates to a negative predictive value of >99.5% for non-susceptibility and is therefore suitable for diagnostic application. This is an important proof-of-principle that should be tested in other geographic locations.

Infection of Transjugular Intrahepatic Portosystemic Shunt Devices: Three Cases and a Review of the Literature

During the past decade, transjugular intrahepatic portosystemic shunting (TIPS) has become accepted as an alternative to the surgical shunt procedure for controlling the complications of portal hypertension, yet few data exist regarding infectious complications. The records of all patients who underwent a TIPS procedure during 1992-2000 at a single university teaching hospital were analyzed retrospectively to determine the rate and type of infections that occurred. A search of the English-language literature on the subject was conducted, and the findings were compared with our experience. Three cases of TIPS stent infection were identified out of 180 procedures performed during a 9-year period, resulting in an overall rate of infection of 1.7%. One of the patients was cured, and the other 2 died. A total of 21 cases of TIPS infection were identified from the literature search. A need exists for a standardized case definition for TIPS infection, and one is proposed.

Antibiotic-associated colitis and cystic fibrosis

SummaryThe use of antibiotics in patients with cystic fibrosis is widespread, and fecal carriage ofClostridium difficile occurs in up to 50% of these patients; however, antibiotic-associated colitis appears to be a rare occurrence. The reasons why this is so remain unknown. A case of antibioticassociated colitis occurring in a patient with cystic fibrosis is described. Possible mechanisms for the rarity of antibiotic-associated colitis are reviewed and implications for prompt diagnosis and therapy are discussed.

Improvement in chronic renal impairment following the discontinuation of tenofovir in two HIV-infected patients.

A 50 year old man presented to the clinic with abdominal fullness and dull pain for years. Contrast-enhanced abdominal computed tomography (CT) scan (Fig. 1) disclosed extremely distended pelvis (black arrowheads) and tortuous dilated ureter (black arrows) in addition to the normal functioning lower ureter (white arrows) of the left kidney. The diagnosis of left sided complete duplex kidney with upper moiety giant hydronephrosis and hydroureter was established and further confirmed by heminephroureterectomy, followed by an uneventful postoperative course. Duplex kidney is a common congenital urologic anomaly, but giant hydronephrosis resulting from obstruction of the ureterovesical junction in the complete duplex kidney, as in the current patient, is extraordinarily rare. Partial nephrectomy is recommended for those with complications. Duplex kidneys with hydronephrosis should be taken as one of the differential diagnoses of abdominal cystic lesions.

IMPLICATIONS OF RDNA TECHNOLOGY IN THE MICROBIOLOGY LABORATORY

Summary The present and potential future roles in service and research microbiological laboratories of recombinant DNA (rDNA) techniques (nucleic acid hybridization, nucleic acid amplification, in situ hybridization, pulsed field gel electrophoresis) are described. Applications of rDNA technology include the detection of microorganisms; an approach to the understanding of their role in disease pathogenesis and provision of alternative strategies for studying the epidemiology of infectious diseases.