Successful Treatment of Carbapenem-Resistant Acinetobacter baumannii Meningitis with Sulbactam-Durlobactam

BACKGROUND

The treatment of carbapenem-resistant Acinetobacter baumannii/calcoaceticus complex (CRAB) presents significant treatment challenges.

METHODS

We report the case of a 42-year-old woman with CRAB meningitis who experienced persistently positive cerebrospinal fluid (CSF) cultures for 13 days despite treatment with high-dose ampicillin-sulbactam and cefiderocol. On day 13, she was transitioned to sulbactam-durlobactam and meropenem; four subsequent CSF cultures remained negative. After 14 days of sulbactam-durlobactam, she was cured of infection. Whole genome sequencing investigations identified putative mechanisms that contributed to reduced cefiderocol susceptibility observed during cefiderocol therapy. Blood and CSF samples were collected pre-dose and 3-hours post initiation of a sulbactam-durlobactam infusion.

RESULTS

The CRAB isolate belonged to sequence type 2. An acquired blaOXA-23 and an intrinsic blaOXA-51-like (i.e., blaOXA-66) carbapenemase gene were identified. The paradoxical effect (i.e., no growth at lower cefiderocol dilutions but growth at higher dilutions) was observed by broth microdilution after 8 days of cefiderocol exposure but not by disk diffusion. Potential markers of resistance to cefiderocol included mutations in the start codon of piuA and piuC iron transport genes and a A515V substitution in PBP3, the primary target of cefiderocol. Sulbactam and durlobactam were detected in CSF at both timepoints, indicating CSF penetration.

CONCLUSIONS

This case describes successful treatment of refractory CRAB meningitis with the administration of sulbactam-durlobactam and meropenem and highlights the need to be cognizant of the paradoxical effect that can be observed with broth microdilution testing of CRAB isolates with cefiderocol.

Clinical significance of Nosocomiicoccus ampullae isolated from blood cultures

IMPORTANCE

Nosocomiicoccus species are recently described as members of the Staphylococcaceae family. With their inclusion in commercial matrix-assisted laser desorption/ionization-time of flight mass spectrometry databases, Nosocomiicoccus species can now be identified when Gram-positive cocci in clusters are detected in positive blood cultures. However, their clinical significance is not known, making it difficult for the clinical microbiology laboratory to decide the extent of work-up. Based on our study, Nosocomiicoccus species demonstrate low pathogenicity and opportunistic potential. If isolated from a single blood culture set, limited work-up should be performed to an extent similar to other possible blood culture contaminants.

An NDM-Producing Escherichia coli Clinical Isolate Exhibiting Resistance to Cefiderocol and the Combination of Ceftazidime-Avibactam and Aztreonam: Another Step Toward Pan-β-Lactam Resistance

Background

Cefiderocol and ceftazidime-avibactam plus aztreonam (CZA-ATM) are preferred treatment regimens for New Delhi metallo-β-lactamase (NDM)-producing infections.

Methods

We report the case of a US patient who traveled to India to receive a renal transplant. He subsequently experienced pyelonephritis by an NDM-producing Escherichia coli. Broth microdilution and the broth disk elution method indicated resistance to all β-lactams, including cefiderocol and CZA-ATM. Whole-genome sequencing investigations were undertaken to identify resistance mechanisms.

Results

An E. coli isolate belonging to sequence type (ST) 167 containing a bla_NDM-5 gene was identified on a plasmid of the IncFIA/IncFIB/IncFIC replicon groups. When compared with the genome of another ST167 E. coli clinical isolate containing bla_NDM-5 and exhibiting susceptibility to cefiderocol and CZA-ATM, a 12-base pair insertion in ftsI, translating to a 4-amino acid duplication in PBP3, was identified. Moreover, a bla_CMY-59 gene was harbored on an IncI-γ replicon type, and frameshift mutations were identified in the cirA iron transport gene.

Conclusions

This is the first clinical case of a US patient harboring an NDM-producing isolate exhibiting resistance to all available β-lactam agents. The isolate's unexpected resistance to cefiderocol and CZA-ATM was likely due to a combination of (1) a modified PBP3 (increased MICs to both regimens), (2) truncated iron-binding protein (increased cefiderocol MIC), and (3) a bla_CMY gene (reduced CZA-ATM activity). E. coli ST167 clinical isolates harboring bla_NDM-5 genes are a recognized international high-risk clone. When coupled with the additional mechanisms identified in our patient's isolate, which is not uncommon for this high-risk clone, pan-β-lactam resistance may occur.

Evaluation of Piperacillin-Tazobactam Testing against Enterobacterales by the Phoenix, MicroScan, and Vitek2 Tests Using Updated Clinical and Laboratory Standards Institute Breakpoints

In 2022, the Clinical and Laboratory Standards Institute (CLSI) updated piperacillin-tazobactam (TZP) breakpoints for Enterobacterales, based on substantial data suggesting that historical breakpoints did not predict treatment outcomes for TZP. The U.S. Food and Drug Administration (FDA) has not yet adopted these breakpoints, meaning commercial manufacturers of antimicrobial susceptibility testing devices cannot obtain FDA clearance for the revised breakpoints. We evaluated the Phoenix (BD, Sparks, MD), MicroScan (Beckman Coulter, Sacramento, CA), and Vitek2 (bioMérieux, Durham, NC) TZP MICs compared to reference broth microdilution for a collection of 284 Enterobacterales isolates. Phoenix (n = 167 isolates) demonstrated 84.4% categorical agreement (CA), with 4.2% very major errors (VMEs) and 1.8% major errors (MEs) by CLSI breakpoints. In contrast, CA was 85.0% with 4.3% VMEs and 0.8% MEs for the Phoenix with FDA breakpoints. MicroScan (n = 55 isolates) demonstrated 80.0% CA, 36.4% VMEs, and 4.8% MEs by CLSI breakpoints and 81.8% CA, 44.4% VMEs, and 0.0% MEs by FDA breakpoints. Vitek2 (n = 62 isolates) demonstrated 95.2% CA, 6.3% VMEs, and 0.0% MEs by CLSI and 96.8% CA, 0.0% VMEs, and 2.2% MEs by FDA breakpoints. Overall, the performance of the test systems was not substantially different using CLSI breakpoints off-label than using on-label FDA breakpoints. However, limitations were noted with higher-than-desired VME rates (all three systems) and lower-than-desired CA (MicroScan and Phoenix). Laboratories should consider adoption of the revised CLSI breakpoints with automated test systems but be aware that some performance challenges exist for testing TZP on automated systems, regardless of breakpoints applied.

Progressive Development of Cefiderocol Resistance in Escherichia coli During Therapy is Associated With an Increase in blaNDM-5 Copy Number and Gene Expression

BACKGROUND

As cefiderocol is increasingly being prescribed in clinical practice, it is critical that we understand key mechanisms contributing to acquired resistance to this agent.

METHODS

We describe a patient with acute lymphoblastic leukemia and a New Delhi metallo-ß-lactamase (NDM)-5-producing Escherichia coli intra-abdominal infection in whom resistance to cefiderocol evolved approximately 2 weeks after the start of treatment. Through whole-genome sequencing (WGS), messenger RNA expression studies, and ethylenediaminetetraacetic acid inhibition analysis, we investigated the role of increased NDM-5 production and genetic mutations contributing to the development of cefiderocol resistance, using 5 sequential clinical E. coli isolates obtained from the patient.

RESULTS

In all 5 isolates, blaNDM-5 genes were identified. The minimum inhibitory concentrations for cefiderocol were 2, 4, and >32 μg/mL for isolates 1-2, 3, and 4-5, respectively. WGS showed that isolates 1-3 contained a single copy of the blaNDM-5 gene, whereas isolates 4 and 5 had 5 and 10 copies of the blaNDM-5 gene, respectively, on an IncFIA/FIB/IncFII plasmid. These findings were correlated with those of blaNDM-5 messenger RNA expression analysis, in which isolates 4 and 5 expressed blaNDM-5 1.7- and 2.8-fold, respectively, compared to, isolate 1. Synergy testing with the combination of ceftazidime-avibactam and aztreonam demonstrated expansion of the zone of inhibition between the disks for all isolates. The patient was successfully treated with this combination and remained infection free 1 year later.

CONCLUSIONS

The findings in our patient suggest that increased copy numbers of blaNDM genes through translocation events are used by Enterobacterales to evade cefiderocol-mediated cell death. The frequency of increased blaNDM-5 expression in contributing to cefiderocol resistance needs investigation.

Pan-drug resistant Providencia rettgeri contributing to a fatal case of COVID-19

Following prolonged hospitalization that included broad-spectrum antibiotic exposure, a strain of Providencia rettgeri was cultured from the blood of a patient undergoing extracorporeal membrane oxygenation treatment for hypoxic respiratory failure due to COVID-19. The strain was resistant to all antimicrobials tested including the novel siderophore cephalosporin, cefiderocol. Whole genome sequencing detected ten antimicrobial resistance genes, including the metallo-β-lactamase bla _NDM-1, the extended-spectrum β-lactamase bla _PER-1, and the rare 16S methyltransferase rmtB2.

Antibiotic pressure on the acquisition and loss of antibiotic resistance genes in Klebsiella pneumoniae

Objectives

In this study, we characterize a concurrent disseminated infection with a virulent hypermucoviscous (HMV) Klebsiella pneumoniae and an OXA-181-producing XDR K. pneumoniae from a patient with recent hospitalization in India. During exposure to meropenem therapy, the highly susceptible HMV K. pneumoniae became resistant to carbapenems, consistent with the acquisition of blaOXA-181.

Methods

Twelve K. pneumoniae isolates were recovered from the patient and the hospital room environment over a 3 month hospitalization. Phenotypic and molecular studies were completed to characterize the isolates. Oxford Nanopore and Illumina MiSeq WGS were performed to study phylogeny (MLST and SNPs), plasmids and virulence genes and demonstrate changes in the organism's resistome that occurred over time.

Results

WGS revealed that the HMV K. pneumoniae belonged to ST23 and harboured an IncH1B virulence plasmid, while the XDR K. pneumoniae belonged to ST147 and possessed two MDR plasmids (IncR and IncFII), the blaOXA-181-bearing ColKP3 plasmid and chromosomal mutations conferring the XDR phenotype. Sequential isolates demonstrated plasmid diversification (fusion of the IncR and IncFII plasmids), mobilization of resistance elements (ompK35 inactivation by ISEcp1-blaCTX-M-15 mobilization, varying numbers of resistance genes on plasmid scaffolds) and chromosomal mutations (mutations in mgrB) leading to further antibiotic resistance that coincided with antibiotic pressure. Importantly, the HMV strain in this study was unable to preserve the carbapenem-resistant phenotype without the selective pressure of meropenem.

Conclusions

To the best of our knowledge, we are the first to report a carbapenem-resistant HMV K. pneumoniae strain in the USA. Ultimately, this case demonstrates the role of antibiotic pressure in the acquisition and loss of important genetic elements.

Molecular Epidemiology of Ceftriaxone Non-Susceptible Enterobacterales Isolates in an Academic Medical Center in the United States

Background

Knowledge of whether Enterobacterales are not susceptible to ceftriaxone without understanding the underlying resistance mechanisms may not be sufficient to direct appropriate treatment decisions. As an example, extended-spectrum β-lactamase (ESBL)–producing organisms almost uniformly display nonsusceptibility to ceftriaxone. Regardless of susceptibility to piperacillin-tazobactam or cefepime, carbapenem antibiotics are the treatment of choice for invasive infections. No such guidance exists for ceftriaxone-nonsusceptible organisms with mechanisms other than ESBL production. We sought to investigate the molecular epidemiology of ceftriaxone-nonsusceptible Enterobacterales.

Methods

All consecutive Escherichia coli, Klebsiella pneumoniae, Klebsiella oxytoca, or Proteus mirabilis clinical isolates with ceftriaxone minimum inhibitory concentrations (MICs) of ≥2 mcg/mL from unique patients at a United States hospital over an 8-month period were evaluated for β-lactamase genes using a DNA microarray–based assay.

Results

Of 1929 isolates, 482 (25%) had ceftriaxone MICs of ≥2 mcg/mL and were not resistant to any carbapenem antibiotics. Of the 482 isolates, ESBL (bla_CTX-M, bla_SHV, bla_TEM) and/or plasmid-mediated ampC (p-ampC) genes were identified in 376 (78%). ESBL genes were identified in 310 (82.4%), p-ampC genes in 2 (0.5%), and both ESBL and p-ampC genes in 64 (17.0%) of the 376 organisms. There were 211 (56%), 120 (32%), 41 (11%), and 4 (1%) isolates with 1, 2, 3, or ≥4 ESBL or p-ampC genes. The most common ESBL genes were of the bla_CTX-M-1 group (includes bla_CTX-M-15), and the most common p-ampC gene was bla_CMY-2.

Conclusions

There is considerable diversity in the molecular epidemiology of ceftriaxone-nonsusceptible Enterobacterales. An understanding of this diversity can improve antibiotic decision-making.

Face Mask Use and Persistence of Livestock-associated Staphylococcus aureus Nasal Carriage among Industrial Hog Operation Workers and Household Contacts, USA

BACKGROUND

Industrial hog operation (IHO) workers may persistently carry antibiotic-resistant, livestock-associated Staphylococcus aureus in their nasal cavities. It is unclear whether IHO work activities can alter IHO workers' and their household members' exposure to these bacteria.

OBJECTIVE

Our objective was to investigate the relationship of IHO work activities with persistence of antibiotic-resistant, livestock-associated S. aureus nasal carriage among IHO workers and their household members.

METHODS

At biweekly intervals over 4 months, IHO workers and their household members completed questionnaires and provided nasal swabs that were assessed for S. aureus, multidrug-resistant S. aureus (MDRSA), and livestock-associated markers (tetracycline resistance, scn absence, spa type). We examined the association between transient and habitual IHO work activities and S. aureus nasal carriage outcomes.

RESULTS

One hundred one IHO workers and 79 household members completed 1,456 study visits. Face mask use (each 25% increase) was associated with reduced odds of nasal carriage of MDRSA (odds ratio [OR]: 0.65 [95% confidence interval (CI): 0.46, 0.92], tetracycline-resistant S. aureus [OR = 0.74 (95% CI: 0.56, 0.97)], and S. aureus clonal complex (CC) 398/CC9 [OR = 0.77 (95% CI: 0.60, 0.99)]. IHO workers who ever (vs. never) gave pigs injections had higher odds of these outcomes. Among household members, living with an IHO worker who consistently ([Formula: see text] of the time) versus sometimes or never used a face mask was associated with reduced odds of carrying scn-negative S. aureus, tetracycline-resistant S. aureus, and S. aureus CC398/CC9 (OR range: 0.12-0.20, all [Formula: see text]), and consistent IHO worker coveralls use was associated with reduced odds of household member MDRSA carriage only. Living with an IHO worker who habitually had contact with [Formula: see text] hogs (vs. [Formula: see text]) was associated with higher odds of household member livestock-associated S. aureus carriage.

CONCLUSIONS

Consistent face mask use was associated with reduced exposure to antibiotic-resistant, livestock-associated S. aureus among IHO workers and their household members. https://doi.org/10.1289/EHP3453.

Aberrant use and poor quality of trypanocides: a risk for drug resistance in south western Ethiopia

BACKGROUND

Trypanocidal drugs have been used to control African animal trypanosomosis for several decades. In Ethiopia, these drugs are available from both authorized (legal) and unauthorized (illegal) sources but documentation on utilization practices and quality of circulating products is scanty. This study looked at the practices of trypanocidal drug utilization by farmers and the integrity of active ingredient in trypanocides sold in Gurage zone, south western Ethiopia. The surveys were based on a structured questionnaire and drug quality determination of commonly used brands originating from European and Asian companies and sold at both authorized and unauthorized markets. One hundred farmers were interviewed and 50 drug samples were collected in 2013 (Diminazene aceturate = 33 and Isometamidium chloride = 17; 25 from authorized and 25 from unauthorized sources). Samples were tested at the OIE-certified Veterinary Drug Control Laboratory (LACOMEV) in Dakar, Senegal, by using galenic standards and high performance liquid chromatography.

RESULTS

Trypanosomosis was found to be a major threat according to all interviewed livestock keepers in the study area. Diminazene aceturate and isometamidium chloride were preferred by 79% and 21% of the respondents respectively, and 85% of them indicated that an animal receives more than six treatments per year. About 60% of these treatments were reported to be administered by untrained farmers. Trypanocidal drug sources included both unauthorized outlets (56%) and authorized government and private sources (44%). A wide availability and usage of substandard quality drugs was revealed. Twenty eight percent of trypanocidal drugs tested failed to comply with quality requirements. There was no significant difference in the frequency of non-compliance between diminazene-based and isometamidium chloride products (P = 0.87) irrespective of the marketing channel (official and unofficial). However, higher rates of non-compliant trypanocides were detected for drugs originating from Asia than from Europe (P = 0.029).

CONCLUSION

The findings revealed the presence of risk factors for the development of drug resistance, i.e. wide distribution of poor quality drugs as well as substandard administration practices. Therefore, it is strongly recommended to enforce regulatory measures for quality control of veterinary drugs, to expand and strengthen veterinary services and to undertake trypanocidal drug efficacy studies of wider coverage.

Frequency of small-colony variants and antimicrobial susceptibility of methicillin-resistant Staphylococcus aureus in cystic fibrosis patients

BACKGROUND

Small-colony variants (SCVs) are a distinct phenotype of Staphylococcus aureus, known for their role in chronic, difficult to treat infections, including cystic fibrosis (CF) lung disease. The goal of this study was to characterize SCV MRSA infection in an adult and pediatric CF population and to identify antibiotic susceptibility patterns unique to SCV MRSA.

METHODS

We recovered methicillin-resistant S. aureus (MRSA) from respiratory culture samples from CF patients at the Johns Hopkins Hospital during a 6month study period.

RESULTS

Of 1161 samples, 200 isolates (17%) were identified as MRSA, and 37 isolates from 28 patients were identified as SCV MRSA. A higher proportion of MRSA was found among SCV isolates (37/66, 56%) compared to normal colony variant (NCV) isolates (163/417, 39%), p=0.02. All SCV MRSA isolates from individual patients were susceptible to vancomycin and ceftaroline, but they demonstrated higher rates of antibiotic resistance to trimethoprim/sulfamethoxazole, moxifloxacin, and erythromycin, compared to NCV MRSA isolates. Additionally, individuals with SCV MRSA had lower lung function, higher rates of persistent MRSA infection, and higher rates of previous antibiotic use, compared to individuals with NCV MRSA.

CONCLUSIONS

A significant proportion of MRSA isolates recovered from patients with CF have the SCV morphology. Compared to individuals with NCV MRSA, those with SCV MRSA have higher rates of persistent MRSA infection and lower lung function. SCV MRSA isolates were more resistant than NCV, but they are highly susceptible to vancomycin, linezolid and ceftaroline.

Livestock-Associated, Antibiotic-Resistant Staphylococcus aureus Nasal Carriage and Recent Skin and Soft Tissue Infection among Industrial Hog Operation Workers

Swine production work is a risk factor for nasal carriage of livestock-associated (LA-) Staphylococcus aureus and also for skin and soft tissue infection (SSTI). However, whether LA-S. aureus nasal carriage is associated with increased risk of SSTI remains unclear. We aimed to examine S. aureus nasal carriage and recent (≤3 months prior to enrollment) SSTI symptoms among industrial hog operation (IHO) workers and their household contacts. IHO workers and their household contacts provided a nasal swab and responded to a questionnaire assessing self-reported personal and occupational exposures and recent SSTI symptoms. Nasal swabs were analyzed for S. aureus, including methicillin-resistant S. aureus (MRSA), multidrug-resistant-S. aureus (MDRSA), absence of scn (livestock association), and spa type. S. aureus with at least one indicator of LA was observed among 19% of 103 IHO workers and 6% of 80 household members. Prevalence of recent SSTI was 6% among IHO workers and 11% among 54 minor household members (0/26 adult household members reported SSTI). Among IHO workers, nasal carriers of MDRSA and scn-negative S. aureus were 8.8 (95% CI: 1.8, 43.9) and 5.1 (95% CI: 1.2, 22.2) times as likely to report recent SSTI as non-carriers, respectively. In one household, both an IHO worker and child reported recent SSTI and carried the same S. aureus spa type (t4976) intranasally. Prevalence of scn-negative S. aureus (PR: 5.0, 95% CI: 1.2, 21.4) was elevated among IHO workers who reported never versus always wearing a face mask at work. Although few SSTI were reported, this study of IHO workers and their household contacts is the first to characterize a relation between nasal carriage of antibiotic-resistant LA-S. aureus and SSTI. The direction and temporality of this relation and IHO workers' use of face masks to prevent nasal carriage of these bacteria warrant further investigation.

Comparing the Outcomes of Patients With Carbapenemase-Producing and Non-Carbapenemase-Producing Carbapenem-Resistant Enterobacteriaceae Bacteremia

BACKGROUND

Carbapenem-resistant Enterobacteriaceae (CRE) are associated with considerable mortality. As mechanisms of carbapenem resistance are heterogeneous, it is unclear if mortality differs based on resistance mechanisms. We sought to determine whether CRE resistance mechanism determination is prognostically informative.

METHODS

We conducted an observational study comparing 14-day mortality between patients with carbapenemase-producing (CP)-CRE compared with non-CP-CRE bacteremia. Clinical data were collected on all patients. A comprehensive DNA microarray-based assay was performed on all isolates to identify β-lactamase-encoding genes.

RESULTS

There were 83 unique episodes of monomicrobial CRE bacteremia during the study period: 37 (45%) CP-CRE and 46 (55%) non-CP-CRE. The majority of CP-CRE isolates were bla _KPC (92%), followed by bla _NDM (5%) and bla _OXA-48-type (3%). CP-CRE isolates were more likely to have meropenem minimum inhibitory concentrations (MICs) ≥16 µg/mL, while non-CP-CRE isolates were more likely to have meropenem MICs ≤1 µg/mL (P value < .001). A total of 18 (22%) patients died within 14 days, including 12 (32%) in the CP-CRE group and 6 (13%) in the non-CP-CRE group. Adjusting for severity of illness on day 1 of bacteremia, underlying medical conditions, and differences in antibiotic treatment administered, the odds of dying within 14 days were more than 4 times greater for CP-CRE compared with non-CP-CRE bacteremic patients (adjusted odds ratio, 4.92; 95% confidence interval, 1.01-24.81).

CONCLUSION

Our findings suggest that CP-CRE may be more virulent than non-CP-CRE and are associated with poorer outcomes. This underscores the added importance of delineating underlying resistance mechanisms of CRE to direct antibiotic treatment decisions.

High Prevalence of Reduced Chlorhexidine Susceptibility in Organisms Causing Central Line–Associated Bloodstream Infections

In units that bathe patients daily with chlorhexidine gluconate (CHG), organisms causing central line–associated bloodstream infections (CLABSIs) were more likely to have reduced CHG susceptibility than organisms causing CLABSIs in units that do not bathe patients daily with CHG (86% vs 64%; P = .028). Surveillance is needed to detect reduced CHG susceptibility with widespread CHG use.

Infect Control Hosp Epidemiol 2014;35(9):1183-1186

The use of cefepime for treating AmpC β-lactamase-producing Enterobacteriaceae

BACKGROUND

 AmpC β-lactamase-producing organisms are associated with significant morbidity and mortality. Induction of resistance to third-generation cephalosporins after exposure to these agents complicates treatment options and carbapenems are considered optimal therapy. The role of cefepime, however, remains unclear. Our objective was to compare clinical outcomes for patients receiving cefepime compared with meropenem for invasive infections caused by organisms expressing AmpC β-lactamases.

METHODS

 Hospitalized patients with blood, bronchoalveolar lavage, or intra-abdominal fluid cultures growing Enterobacter spp, Serratia spp, or Citrobacter spp were evaluated using the cefotetan-boronic acid disk test and the cefotetan-cloxacillin Etest to identify organisms with AmpC β-lactamase production from February 2010 to January 2011. In patients with organisms hyperproducing AmpC β-lactamases (positive by both methods), clinical outcomes for patients receiving cefepime or meropenem therapy were compared. To minimize the possibility of treatment selection bias, 1:1 nearest neighbor propensity score matching was performed prior to regression analysis.

RESULTS

 Of 399 patients meeting eligibility criteria, 96 (24%) had confirmed infections with AmpC β-lactamase-producing organisms. Propensity score matching of patients infected with AmpC β-lactamase-positive organisms treated with cefepime or meropenem yielded 32 well-balanced patient pairs with no difference in 30-day mortality (odds ratio, 0.63; 95% confidence interval [CI], .23-2.11; P = .36) or length of hospital stay after infection (relative risk, 0.96; 95% CI, .79-1.26; P = .56) between the 2 groups.

CONCLUSIONS

 Cefepime may be a reasonable option for the treatment of invasive infections due to AmpC β-lactamase-producing organisms, particularly when adequate source control is achieved.

Response of four indigenous cattle breeds to natural tsetse and trypanosomosis challenge in the Ghibe valley of Ethiopia

A comparative study on the response of four indigenous cattle breeds of Ethiopia, namely Abigar, Horro, Sheko and Gurage, to natural challenge of trypanosomosis in the Tolley-Gullele area of the Ghibe valley has been undertaken from August 2000 until August 2004. Fifty female yearlings each of Horro, Sheko and Abigar and 31 of the Gurage were purchased from their natural habitats and introduced in to medium to high tsetse-trypanosomosis challenge area of the Ghibe valley. While the natural habitats of first three breeds are naturally infested with tsetse flies and trypanosomosis, that of the Gurage is known to be very minimal, if any, and hence the Gurage breed was used in this study as the known susceptible breed. During the study animal health, production performance and tsetse fly situation were monitored monthly. The Sheko breed has manifested very significantly (p<0.001) high overall average packed cell volume (PCV) values (25%) compared to that of Abigar (24%), Horro (23%) and Gurage (22%). It also had the lowest mean trypanosome prevalence rate of 9% against 23% of Horro, 26% of Abigar and 27% of Gurage, and the least number of Berenil treatments (1.36) compared to Abigar (4.0), Horro (4.6) and Gurage (6.7). While the Abigar manifested high sensitivity and frequent death to PCV depression, the Horro showed strong resilience to PCV depression and better response to Berenil treatment assistance. At this stage the Sheko breed was also found to be equal to the other breeds in its reproductive performance. These results need to be substantiated with further in-depth investigation including immune response, animal behavior and environmental influences.

Failure of Clindamycin Treatment of Methicillin-Resistant Staphylococcus aureus Expressing Inducible Clindamycin Resistance In Vitro

We report a case of a surgical site infection caused by clindamycin-susceptible, erythromycin-resistant methicillin-resistant Staphylococcus aureus (MRSA) that did not respond to treatment with clindamycin. The MRSA isolate obtained after treatment was resistant to clindamycin but was found to be identical by pulsed-field gel electrophoresis to the clindamycin-susceptible isolate obtained before treatment. A post hoc erythromycin-induction test (D test) confirmed the presence of in vitro inducible macrolide-lincosamide-streptogramin B resistance (iMLS) in the pretreatment isolate. Erythromycin induction testing confirmed in vitro iMLS in 90 (56%) of 161 erythromycin-resistant, clindamycin-susceptible clinical S. aureus isolates overall and in a significantly higher proportion (78%) of methicillin-susceptible S. aureus isolates from pediatric patients. Our clinical laboratory currently tests all S. aureus isolates for iMLS before reporting clindamycin susceptibility.