Neonatal meningitis is most often caused by vertical transmission during labour and delivery.

The most common organisms isolated are S. agalactiae (group B streptococcus), E. coli, other gram negative bacilli, and Listeria monocytogenes.

Citrobacter koseri is intrinsically resistant to cephalothin and virtually always resistant to ampicillin.

Reporting an antimicrobial agent that does not have the ability to adequately pass through the blood-brain barrier and into the CSF is considered unacceptable.

It should be noted that oxidase testing is unreliable when performed directly on colonies growing on TCBS and should not be attempted.

Sensitivity to the vibriostatic compound 0/129 is also useful in identifying members of the genus Vibrio although some strains isolated in India and Bangladesh have been shown to be resistant to the compound

Left untreated, however, cholera can kill quickly following the onset of symptoms.

Only V. cholerae O1 and O139 serotypes have been associated with cholera pandemics.

The CLSI document, M45-A2 “Methods for Antimicrobial Dilution and Disk Susceptibility Testing of Infrequently Isolated or Fastidious Bacteria”1 provides interpretive criteria for susceptibility testing of Erysipelothrix rhusiopathiae.

Molluscs, crustaceans, marine and freshwater fish are also sources of infection as the organism survives and grows on the exterior slime of fish.

Erythromycin was previously included as an alternative for intrapartum prophylaxis in women who were allergic to penicillin however, according to the new CDC guidelines erythromycin is no longer an acceptable alternative for intrapartum GBS prophylaxis for penicillin allergic women at high risk for anaphylaxis.

Resistance to erythromycin and clindamycin among invasive group B streptococcus (GBS) has been increasing over the past 20 years. Resistance rates of 25% to 32% for erythromycin and from 13% to 20% for clindamycin have been reported.

Approximately 10-30% of pregnant women are colonized with GBS in the vagina or rectum.

Corynebacterium urealyticum has been strongly associated with urinary tract infections and should be identified and reported when found to be pure or predominant growth in significant amounts.

Corynebacterium urealyticum is typically resistant to multiple antibiotics. It is normally highly resistant to β-lactams and aminoglycosides, but normally susceptible to vancomycin. Susceptibility to quinolones, erythromycin, rifampicin, and tetracycline varies

Breakdown of urea by a strong urealytic organism like C. urealyticum leads to the formation of ammonium (NH3) which increases pH favoring precipitation of NH4+ with magnesium and phosphate leading to the formation of struvite

Enterococcus faecalis that are vancomycin intermediate should still be notified to Infection Prevention & Control while awaiting for vanA & vanB results so that, where required, appropriate precautions can be taken until final results are available.

Enterococci with intrinsic vancomycin resistance usually have vancomycin MICs of 2 – 32 μg/mL and contain the vanC genes which are not transferable. As these enterococci with vanC genes have not been associated with nosocomial outbreaks, and are not considered true VRE.

Typically, lumbar puncture from patients with cryptococcosis often reveals modestly elevated or normal white cell counts (usually lymphocytes), elevated protein, and low or normal glucose.

MRSA isolates that are extremely hetero-resistant and phenotypically oxacillin-susceptible mecA-positive S. aureus (OS-MRSA) are likely to be missed by the oxacillin/cefoxitin DDT (disk diffusion test) or oxacillin agar screening methods.

Because treatment with a β-lactam antibiotic is likely to be used for infections with MSSA, this could result in treatment failure. Therefore, it is important for these isolates be reported to the clinician as MRSA so that appropriate treatment and isolation precautions can be initiated.

Approximately 1% of MRSA are being misclassified as methicillin-susceptible S. aureus (MSSA) based on routinely used phenotypic tests.

In facilities that do not have specific infection control staff, the laboratory should notify the ward staff about the MRSA isolate and the report should include a comment code indicating isolation precautions are required.

If evidence of more than one morphotype exists, both should be identified so that susceptibilities on each can be performed. In such cases it may occur that one is quite susceptible and the other multi-resistant. Picking the susceptible one only could have significant consequences for treatment, outcome and spread of the organism in hospital.

In most cases the MIC of ertapenem is suggestive of the probable mechanism of carbapenem resistance: low or intermediate level resistance to ertapenem is usually indicative of an altered porin or efflux mechanism where the strain is susceptible using gradient endpoint or broth dilution methods to other carbapenems (imipenem, meropenem, or doripenem). When the MIC to ertapenem is high (> 16 mg/L) there is a greater likelihood that the isolate has a carbapenemase and that imipenem and meropenem will also be resistant.

Resistance to carbapenems can be caused by various mechanisms: production of carbapenemases (carbapenem-specific β-lactamases), efflux pumps, and decreased expression or function of porins and PBPs.

Gram stain of vaginal fluid is an objective method of diagnosis of bacterial vaginosis that correlates well with the clinical criteria described by Amsel and colleagues.

It is important to differentiate women with DSIV from BV because the treatment is different

The reporting of the Gram stain without reference to the presence of RBCs is inaccurate, potentially confusing and misleading because the report will be discordant with the CSF cell count.

Most infectious conjunctivitis are of viral etiology, although bacterial conjunctivitis is more common in children than in adults.

Systemic therapy is the mainstay with Neisseria infections since primary meningococcal conjunctivitis has been known to precede invasive disease

The clinical spectrum of disease caused by group G streptococcus resembles infections caused by group A streptococcus (S. pyogenes). Both group A & G streptococci are associated with upper respiratory tract infections and invasive infections such as necrotizing fasciitis, STSS, bacteremia, and endocarditis.

Morganella are opportunistic pathogens that are found commonly in soil, water and sewage.

Urinary tract infections (UTIs) among elderly are very common and are considered within the context of complicated UTI

Most strains are also resistant to nitrofurantoin but are usually susceptible to aminoglycosides, trimethoprimsulfamethoxazole, quinolones and carbapenems

If the clinician suspects Neisseria infection, a bacterial Gram stain and culture should be obtained immediately. The diagnosis of meningococcal conjunctivitis should be considered when gram-negative diplococci are observed.

Neisseria species, including N. meningitidis, can cause a hyperacute bacterial conjunctivitis that is severe and sight-threatening.

Treatment of conjunctivitis should include systemic therapy in view of the potential for invasiveness of N meningitidis, with topical antibiotics as an adjunct. The risk of invasive disease in those treated initially with topical therapy alone was estimated to be 19 times greater than for those receiving systemic antibiotic.

Chromogenic agars have been developed which allow for detection of sorbitol and non-sorbitol fermenting isolates.

Antimicrobial therapy is not recommended and has been linked to an increased risk of HUS in children.

Bacteremia is rare as STEC are not invasive but they secrete ribosome inactivating toxins which are responsible for the organ damage

Although O157:H7 is the serotype most frequently isolated from humans, a recent CDC surveillance report showed that O157 serotypes comprised 41.1% of all the STEC isolated.

Granulicatella adiacens and other nutritionally variant streptococci (e.g. Abiotrophia defectiva, other Granulicatella species) are infrequent but important isolates from blood cultures. It is important for a laboratory to have the ability to cultivate and recognize a nutritionally variant streptococci.

Their Gram stain appearance varies depending on the culture media. In liquid media containing pyridoxal (e.g. thioglycolate broth), they appear as gram positive cocci in chains, indistinguishable from other streptococci. More commonly, when the Gram stain is performed on colonies from agar plates, especially those poor in pyridoxal, they may appear pleomorphic and even gram variable. Extremely elongated forms may be mistaken for bacilli, and swollen cells may resemble spores, leading to confusion in interpretation of the stain.

From a clinical standpoint, recognition that an isolate belongs to the group of Abiotrophia/Granulicatella spp. is more important than identification to the species level, as there may be ramifications in pathogenicity and antibiotic susceptibilities.

Susceptibility testing methods and interpretation guidelines for Abiotrophia and Granulicatella species have been published by the CLSI in the document M45-A3.

Penicillin resistance is relatively uncommon but still is seen in up to 20% of isolates, but isolates appear to more likely be resistant to ceftriaxone (13 – 60%).13 Macrolide resistance, mediated by mefA and ermB,13 is common: one study reported an azithromycin resistance rate of over 90%.14 Clindamycin resistance has also been observed; however, no vancomycin resistant isolates have been reported

M. chelonae causes sporadic diseases, which include cellulitis, abscess, and disseminated disease; skin trauma may be the primary cause for cutaneous illness

Although C. albicans is the predominant species that causes invasive candidiasis, C. glabrata has emerged as the most common non-albicans Candida in North America